Mike 1833
Content
Mike1833 (Mechanical) (OP)
2 Jan 13 16:26
Currently Currently I am in the point of design where I must determine the outside air !entilation re"uirements re"uirements for a #uilding #y using the 62$1 2%1% &!entilation rate procedure$& procedure$& I am a #it confused a#out the two terms &!entilation& and &outside air&that are #eing thrown around and would appreciate any guidance$ 'tandard 62$1 lists a method called &!entilation rate procedure$& his method calculates the re"uired re"uired outside air needed #ased on a one*s occupancy and s"uare footage$ (I thought !entilation was +ust replacing air in a !olume regardless regardless if it is outside air or return return air) I thought there would #e another set of re"uirements re"uirements aimed speci,cally towards !entilation- independent of outside air$ I would thin. !entilation would simply #e the amount of air changes per hour that your supply air (return air plus outside air) can achie!e on a space$ I was anticipating a ta#le that would pro!ide such !alues- #ut all I see is an outdoor air re"uirement re"uirement method that I descri#ed a#o!e$ /ow to me- ,nding the re"uired outdoor air amount to #e used in a #uilding does not really tell me Im getting proper !entilation (air changes per hour) into my ones #ecause the supply air rate is what really does the air changing- and I can only #ase this supply air on my cooling load since I ha!e no other standard to loo. at here$ his is the only method I see- and I am s.eptical that there should #e more info stating how m uch supply air is re"uired to each one to reach an accepta#le air change per hour$ I am new at this so I may #e missing a .ey point$ 0our thoughts are appreciated$ han.s$ DRWeig (lectrical)
2 Jan 13 1:3
4i Mi.e5elcome to engtips$ In my e7perience- !entilation !entilation is always outside air- which is dictated #y occupancy and s"uare footage in each space$ 'upply air C8M is a function of the heating andor cooling load in the space$ o my .nowledge- there is no standard for supply air per s"uare foot (or per person) that is independent of outside air$ 9entilation outside air$ /ote: I*m a controls and energysimulation energysimulation guy- my e7perience e7perience is in ma.ing the !entilation wor. right and analying what some#ody else designed to compute energy use$ I*m not a designer$ 4ang around- there are some !ery e7perienced Ms in this forum$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: now: Forum Policies
oeag (Mechanical)
I*m with =@5eig$ I*m still pretty new to this 49AC stuB myself- #ut as far as I .now- there is no other standard that dictates supply air other than the outside air speci,ed in A'4@A$
2 Jan 13 1?:%%
I*!e #een wor.ing on a couple pro+ects- and "uic.ly loo.ing o!er our calculations and assumptions e!erything is wholesomely #ased on your re"uired re"uired cooling and heating loads$ urgross (Mechanical)
3 Jan 13 :D6
I thin. you would need to consider speci,c applications$ applications$ A wet la# may ta.e 1% air changes per hour- #ut the 1% AC4 doesn*t need to #e outside air$ 4ealth care facilities ha!e EA and total AC4 well spelled out$ Fharmacies and clean rooms will ha!e AC4 typically #ased on I'E le!el$ 8ederal agencies typically ha!e their own re"uirements for EA and total AC4$ 5hile I .now of no onesie ,ts all- air#orne odor control would #e a typical area where EA is not a re"uirementG re"uirementG pu#lic #athrooms would #e an e7ample$ Eutside air is not n ot always re"uired- return air under the door can #e used$ ( Mechanical) cd!!13" (M
3 Jan 13 ?:D
a.e a.e another loo. at 622%1%$ he he 9entilation 9entilation @ate @ate Frocedure Frocedure uses uses a#le a#le 61 gi!es Feople EH=EE@ Air @ate and Area EH=EE@ Air @ate$ @ate$ If that amount of air doesnt meet your cooling or heating load (as stated #y drweig)- or AC4 rate re"uirements re"uirements (as stated #y urgros)- then increase the supply cfm (usually with return air)- to get the supply air needed$ I suggest you reread 62*s ,ne print when you want to fall asleep at night$ .nowledge is power
Mike1833 (Mechanical) (OP)
3 Jan 13 12:%2
han.s e!eryone e!eryone for your help$ help$ HgrossHgross- are these these AC4 re"uirem re"uirements ents in 62$1> hese hese are the the .ind of re"uirements Im spea.ing of$ han.s$ 5hen ta.ing 49AC design classes (some time ago)- there were three possi#le constraints that determined your supply air$ air$ he ,rst was to ,gure out your cooling load on the one$ his would #e #e the minnimum supply air rate rate ( ne!er should should it go under under the cooling load supply rate)$ he second constraint was occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement re"uirement (for school- not in the standard) #ased on supply air- not outside airand that*s why I was surprised to not see it in the standard 62$1)$ he third constraint was ma.eup air from e7haust$ he supply air would ha!e to increase if your #lowing out more than whats re"uired #y the cooling load or cfmperson (this constaint is a #it oB topic since e7haust is independent of this discussion)$ discussion)$ 'o in summary- Im loo.ing for supply air constraints #ased on occupancy (li.e Hrgross Hrgross pointed out)- #ut also a cfmpeople supply air constraint$ Consider this scenario$$$ I ha!e a speci,c room that re"uires 1%%%C8M of outside air (found #y following the &!entilation re"uirements&)$ re"uirements&)$ If my air conditioning unit ser!ices 1% diBerent rooms- each room ha!ing a diBerent outside air re"uirement- how can this re"uirement #e met for e!ery room> he supply air rates to each room can #e controlled with actuated dampers- #ut the outside air is +ust going to #e a ,7ed percentage percentage of the supply air regardlessregardless- right> 'o when a speci,c room re"uires !entilation- I would thin. to loo. for a supply air constraint$ 0our 0our thoughts are are greatly appreciatedK appreciatedK urgross (Mechanical)
3 Jan 13 13:21
I*!e #een wor.ing on a couple pro+ects- and "uic.ly loo.ing o!er our calculations and assumptions e!erything is wholesomely #ased on your re"uired re"uired cooling and heating loads$ urgross (Mechanical)
3 Jan 13 :D6
I thin. you would need to consider speci,c applications$ applications$ A wet la# may ta.e 1% air changes per hour- #ut the 1% AC4 doesn*t need to #e outside air$ 4ealth care facilities ha!e EA and total AC4 well spelled out$ Fharmacies and clean rooms will ha!e AC4 typically #ased on I'E le!el$ 8ederal agencies typically ha!e their own re"uirements for EA and total AC4$ 5hile I .now of no onesie ,ts all- air#orne odor control would #e a typical area where EA is not a re"uirementG re"uirementG pu#lic #athrooms would #e an e7ample$ Eutside air is not n ot always re"uired- return air under the door can #e used$ ( Mechanical) cd!!13" (M
3 Jan 13 ?:D
a.e a.e another loo. at 622%1%$ he he 9entilation 9entilation @ate @ate Frocedure Frocedure uses uses a#le a#le 61 gi!es Feople EH=EE@ Air @ate and Area EH=EE@ Air @ate$ @ate$ If that amount of air doesnt meet your cooling or heating load (as stated #y drweig)- or AC4 rate re"uirements re"uirements (as stated #y urgros)- then increase the supply cfm (usually with return air)- to get the supply air needed$ I suggest you reread 62*s ,ne print when you want to fall asleep at night$ .nowledge is power
Mike1833 (Mechanical) (OP)
3 Jan 13 12:%2
han.s e!eryone e!eryone for your help$ help$ HgrossHgross- are these these AC4 re"uirem re"uirements ents in 62$1> hese hese are the the .ind of re"uirements Im spea.ing of$ han.s$ 5hen ta.ing 49AC design classes (some time ago)- there were three possi#le constraints that determined your supply air$ air$ he ,rst was to ,gure out your cooling load on the one$ his would #e #e the minnimum supply air rate rate ( ne!er should should it go under under the cooling load supply rate)$ he second constraint was occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement re"uirement (for school- not in the standard) #ased on supply air- not outside airand that*s why I was surprised to not see it in the standard 62$1)$ he third constraint was ma.eup air from e7haust$ he supply air would ha!e to increase if your #lowing out more than whats re"uired #y the cooling load or cfmperson (this constaint is a #it oB topic since e7haust is independent of this discussion)$ discussion)$ 'o in summary- Im loo.ing for supply air constraints #ased on occupancy (li.e Hrgross Hrgross pointed out)- #ut also a cfmpeople supply air constraint$ Consider this scenario$$$ I ha!e a speci,c room that re"uires 1%%%C8M of outside air (found #y following the &!entilation re"uirements&)$ re"uirements&)$ If my air conditioning unit ser!ices 1% diBerent rooms- each room ha!ing a diBerent outside air re"uirement- how can this re"uirement #e met for e!ery room> he supply air rates to each room can #e controlled with actuated dampers- #ut the outside air is +ust going to #e a ,7ed percentage percentage of the supply air regardlessregardless- right> 'o when a speci,c room re"uires !entilation- I would thin. to loo. for a supply air constraint$ 0our 0our thoughts are are greatly appreciatedK appreciatedK urgross (Mechanical)
3 Jan 13 13:21
/o- the AC4 re"uirements are not in 62$1$ I don*t thin. there is a onesie,ts all$ Criteria is usually #ased on a speci,c function or occupancy$ 4ospitals would #e a prime e7ample$ @efer @efer to A'4@A 1% and you will get recommended recommended AC4 for most areas of a hospital$ !en with that- additional criteria goes into speci,c areas- such as pharmacy$ @oom AC4 might go up to D% for to7ic compounding #ased on I'E le!el re"uirements$ re"uirements$ 'ome areas the AC4 and EA are spelled out #ased upon the 49AC system #eing used$ As an e7ample- nursing homes re"uire 6 AC4 per A'4@A and 2 EA AC4$ If using a Dpipe fan coil for en!elope load- the total AC4 can #e reduced to D$ he EA fraction fraction calculationsalso calculationsalso change with with system con,guration$ con,guration$ /o o!erall o!erall guidance is .nown- you ha!e to loo. at the occupancy and the proposed system$ DRWeig (lectrical)
3 Jan 13 2%:1
his portion of your "uestion confuses confuses me: #uote (Mike1833)
he second constraint was occupancy occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement (for school- not in the standard) #ased on supply air- not outside air- and that* s why I was surprised to not see it i n the standard 62$1)
Are you saying that your space had a re"uirement re"uirement of 1 C8M supply air per person- not 1 C8M of outside air per person> If so- what sort of space was it> I*m curious- #ecause 1 C8M per person was the standard outside air "uantity for a lot of ordinary occupancies #ac. when all we had were ta#les in the standards$ 5hat e!eryone is getting at is this: 8or special areas (see urgross*s replies)- there will often #e set air changes that must #e met$ 8or nonspecial areasareas- such as an oLce or classroomthere is no standard re"uirement$ here here is only a standard for !entilation (outside air)$ As for apportioning outside air amongst your ones- you*ll ha!e to control the outside air fraction of the A4H to meet the worst case one*s needs$ a.e a.e a loo. through this thread for some discussion discussion of one way to !ary !entilation in a 9A9 9A9 system: $ttp%&&eng'tipscom&ie*t$readcfm+,id-3./03
;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: now: Forum Policies
Mike1833 (Mechanical) (OP)
D Jan 13 11:1D
#uote (DRWeig)
Are you saying that your space had a re"uirement of 1 C8M supply air per person- not 1 C8M of outside air per person> If so- what sort of space was it> I*m curious- #ecause 1 C8M per person was the standard outside air "uantity for a lot of ordinary occupancies #ac. when all we had were ta#les in the standards$
@ight$ At least that is the way it was formatted in my class$ It was a standard oLce space$
!en when analying standard classrooms or oLces we used a certain C8M per person of supply air to ma.e sure it was not higher than t he re"uired load$ I am going to contact my old professor to clarify this$ I may ha!e interpreted it wrong$ I .new it was gi!en as a supply air constraint #ut it really ne!er did go o!er the cooling load re"uirement anyways$ If it did- perhaps I would ha!e had to increase the supply air re"uirement for that one- not to 1 cfmperson- #ut to a higher supply air amount that had the correct percentage of outside air of 1cfmperson$ #uote (DRWeig)
As for apportioning outside air amongst your ones- you*ll ha!e to control the outside air fraction of the A4H to meet the worst case one*s needs$
<reat point$ In lieu of this topic- what if the cooling load supply re"uirement was lower than the amount of outside air needed (+ust out of curiosity since I!*e ne!er encountered this)> I would thin. I would ,rst ha!e to predetermine an outside air percentage- then raise the supply air re"uirement for that one to a C8M that contains that outside air needed$ ;ut how can I predetermine an outside air percentage without .nowledge of the new supply air re"uirement> It seems li.e this may #e an iterati!e process$ DRWeig (lectrical)
D Jan 13 12:D6
If it*s a constant!olume air handler- no pro#lem$ he minimum outside air for the A4H was set at commissioning time- and the supply air to the space remains constant$ husoutdoor air is ,ne at all times as long as the fan is running$ he cooling coil simply cycles (d7) or modulates (chw) to meet the load with the constant air ow- and if the supply air ow is greater than what is needed e!en with supply air temperature reset- the reheat system comes into play$ If it*s a 9A9 air handler- it can #e done in se!eral diBerent ways$ he one in the thread I lin.ed a#o!e is my fa!orite$ 5ithout demand control for !entilation- the controller needs to .now the air ow to the space and the percent of osa in the air from the air handler$ It will maintain air ow to meet the minimum !entilation rate- no matter the load$ Air ow monitoring at each 9A9 #o7 is not totally necessary to accomplish this$ 5ith a .nown duct pressure and 9A9 #o7 damper position- the percent of ma7imum supply air ow to the space can #e estimated$ In #oth cases- if the re"uired osa cfm e7ceeds the supply cfm for a space- the osa ow rate is maintained and the supply air is either reheated to maintain comfort or else the supply air temperature is modulated (within limits)$ 0ou might #ene,t from loo.ing into se"uences of operation for A4H and 9A9 systems that ha!e already #een done$ 7amples are usually a!aila#le online from pu#lic uni!ersities the specs for +o#s to #e #id are pu#lic$ here might #e some #uilding automation tutorials a!aila#le that co!er the topic as well$ 5hat you*re as.ing is more of a controls issue than an e"uipment design issue$ Again- my hum#le opinion only$ I teach a couple of classes that co!er !entilation control with #uilding automation- so I*m used to co!ering it from that standpoint$ ;est to you<oo#er =a!e
4a!en*t see the forum policies> =o so now: Forum Policies
Dra2en (Mechanical)
D Jan 13 1D:D%
mi.e- i #elie!e there is nothing confusing a#out that- #ut you need to study #asic .nowledge ,rstly- than you will not ha!e to waste your energy in rein!enting the wheel$ !entilation rate is rate of replacement of room air with outside air$ period$ supply air has nothing to do with that$ relation #etween supply air and outdoor air does aBect all your design concepts- decisions on system and e"uipment- #ut you calculate fresh air and supply air re"uirements independently- one per 62$1 or other applica#le standard- the other per thermal load calculations$ =rweig- i opened one post some time ago- a#out how to ensure minimum outdoor air in diBerent !a! setups- #ut did not reach &one #ullet .ills all& answer- which is not surprising as that is not fully co!ered anywhere$ if you sie your !a! system to ensure minimum outdoor air rate at minimum supply ow situation- you are still not sure that each and e!ery one will recei!e minimum- for simple reason that not all ones ha!e the same supply airoutdoor air ratios- and that is what system fan can deli!er$ if you sie your system #ased on one with lowest outdoorsupply air ratio- than your other ones will #e o!er!entilated- which poses energy eLciency "uestions$ i #elie!e !a! concept itself ne!er sol!ed that pro#lem fully- and it is only dc! concept that can ma.e more sense in such setups- in future (until something new would #e in!ented)$ Dra2en (Mechanical)
oops- i did not realied that you lin.ed to that !ery post
D Jan 13 1D:D2 $$$
urgross (Mechanical)
D Jan 13 1:2D
=raen hat sounds li.a a real good argument for =EA' and delin.ing !entilation air from thermal loading$ DRWeig (lectrical)
D Jan 13 16:2%
0ou*re on the money as usual- =raen$ A minimum outside air in+ection fan helps- #ut it*s not perfect either$ I lo!e =EA'- urgrossK Apparently- though- only the military and the I@' can aBord it$ ;est to you<oo#er =a!e
pa#lo2D1% (Mechanical) (EF)
1 Apr %6 :D
4ello- INm new in this forum and ha!e a "uestion$ I need to calculate de cooling load of an area that demands 1%%O outside air- and to #e honest- I donNt Pnow how to do it$ here are some "uestions that comes to my mind: 5hat should #e the lea!ing air temperature> he loads produce #y peoplelights- walls- etc that we estimate in a recirculating system- should #e calculated in this .ind of system too>$ I really apreciate some help$ (INm from =ominican @epu#licso e7cuse my english)$
han.s$
willard3 (Mechanical)
1 Apr %6 1D:3
8or the outside air:
'ensi#le cooling CH 8MI/ 7 1$% Q outside AI@ =RA t ;H4@ '/'I;R
Ratent cooling: fu ftmin 7 %$66 7 (delta moisture in grainsl# from psychometric chart) #tuhr latent
'ensi#le load S latent load total cooling load for outside air
In general- cold air is deli!ered at 8 dry #ul# and wet #ul# (ie- saturated)
;uilding solar loads- lights- e"uipment and people loading should #e included in your calculations$
0ou should pro#a#ly hire a Mechanical ngineer to do this as he is familiar with it and you aren*t$
waross (lectrical)
1 Apr %6 1:3%
4ello willard3 I ha!e met some intelligent dedicated engineers in the third world$ Hnfortunatelythe training and educational systems there are not up to ,rst world standards$ pa#lo2D1% has recognied that he doesn*t ha!e the information that he needs to sol!e his pro#lem and has wisely gone loo.ing for good ad!ice$ I than. you on #ehalf of pa#lo2D1% for your .ind help- #ut I wish to gently point out that your last suggestion may not #e feasi#le$ pa#lo2D1% is "uite possi#ly the #est mechanical engineer a!aila#le$ 0ou may ,nd it rewarding- willard3 to mentor pa#lo2D1% and help him to #ecome a #etter engineer$ 8rom the tone of his post I #elie!e he is intelligent and dedicated$ 4e recognies shortcomings in his education and is trying to impro!e himself$
0ou ha!e already gi!en pa#lo2D1% the #asics- go a little farther and help him through his calculations and you may ,nd that you en+oy it$ respectfully
MintJulep (Mechanical)
2 Apr %6 1:33
pa#lo-
a.e a loo. at this site:
http:www$engineeringtool#o7$comh!acsystemstT23$html
"uar. (Mechanical)
2 Apr %6 23:13
Fa#lo-
he room lea!ing air condition should always #e the room condition$
Calculate heat load as per the general rules$ Flot the room condition and am#ient condition state points on the psychro chart$ =raw a line with a slope of '4@ from the room condition to the saturated cur!e$ his is your dew point condition$ Join the am#ient condition state point to the dew point$ he total load on the coil will #e the mass ow rate of air times the enthalpy diBerence #etween the am#ient condition
and the dew point condition$ In some cases- the '4@ line #ecomes an asymptote to the saturation cur!e$ In this case- assume some ar#itrary dew point and add reheat into the process$
he lin. #elow gi!es you description and details of many psychrometric processes$ 4a!e a loo. into it$
http:www$coolit$co$apsychart
5aross-
/ice thin.ing and I feel that is the whole idea #ehind these forums$
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 :2
han. you all of you for your help
4ere comes another "uestion- how can i calculate mass ow- i mean- i .now the !olume of air in the room- #ut how do i .now how many times do i ha!e to recirculate it
R'A (Mechanical)
3 Apr %6 12:11
correct me if I am wrong #ut I am assumming you meant 9olume ow instead of mass ow$
;elow is something I gra##ed oB a we#site descr#ing what I thin. will #e of help to you$
Ene air change occurs in a room when a "uantity of air e"ual to the !olume of the room is supplied andor e7hausted$ Air change rates are units of !entilation that compare the amount of air mo!ing through a space to the !olume of the space$ Air change rates are calculated to determine how well a space is !entilated compared to pu#lished standards- codesor recommendations$ Air changes per hour (AC4) is the most common unit used$ his is the !olume of air (usually e7pressed in cu#ic feet) e7hausted or supplied e!ery hour di!ided #y the room !olume (also usually e7pressed in cu#ic feet)$
Airow is usually measured in cu#ic feet per minute (C8M)$ his is multiplied #y 6% minutes to determine the !olume of air deli!ered per hour (in cu#ic feet)$
AC4 (C8M Q 6% minutes)(room !olume in cu#ic feet)
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 12:33
5hat i want to .now is how can i determine the C8M needed for the area$
willard3 (Mechanical)
3 Apr %6 12:3?
Fa#lo: he sensi#le heat ratio and cooling load will dictate the air changeshour and is the solution to the pro#lem$ p ro#lem$ ry ry not to confuse the cause for the eBect$
In my climate- ie- D2 deg latitude and 3 deg longitude- in a frame#uilt- insulated #uilding with appro7 2%O glass and * ceilings- cfm !aries from 1 cfms"uare foot to 3 cfms"uare foot of oor depending upon internal loading- ie- num#er of peoplelighting- e"uipment loads and !entilation loads$
;H load !aries from 3%% #tucu foot e7clusi!e of internal loadings$
5e ha!e #uilding codes in /ew 0or. 0or. that ma.e the range of these num#ers pretty small$
0our 0our latitude is 1 deg and longitude is 6? deg- so solar loading and air temperatures will #e !ery diBerent than /ew 0or.$ 0or.$ I am also sure that you construction materials and methods are diBerent than ours so #uilding mass and etc will #e diBerent
0ou 0ou should get a copy of A'4@A 8undamentals 8undamentals 9olume(American 9olume(American 'ociety of 4eating- @efrigeration and Air Conditioning ngineers)G it contains answers to all the "uestions you are as.ing$ 0ou ha!e access to the we#- so &<oogle& A'4@A$ A' 4@A$
0ou 0ou can also use rane rane software to calculate calculate heatingcooling loads- #ut you need ,rst to understand the input$ A'4@A will #e a #ig help with the input$
willard3 (Mechanical)
3 Apr %6 12:D2
5rong data:
;H load !aries from 3%% #tucu foot e7clusi!e of internal loadings$
@ight data:
;H load !aries from 3 #tucu foot e7clusi!e of internal loadings$
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 13:1D
E.- (willard3) the ,rst formula you ga!e- me was a !ariation of the ,rst law of thermodinamics- another way to put it is using the mass ow times the enthalpy diBerence #etween am#ient condition and dew point condition- #ut in #oth cases i need a ow of air in terms of mass or !olume- and there is my confusion$ he other "uestion is : do i need a U8 lea!ing air temperature in a system using 1%%O outside air>$ I ma.e this "uestion #ecause i assume that in this .ind of systemthere is no mi7 #etween the air in the room and the air from outside to achi!e a medium temperature- #ecause e!entually the total !olume of air in the room will #e e7hauted and replace for a new !olume from the outside- so i was thin.ing that the lea!ing air temperature should #e the temperature of the conditions i want in the room- letNs say 3U$
R'A (Mechanical)
3 Apr %6 1:%3
I am going to ta.e a sta# at this$
=esign condition: Eutside air temp (=;5;) ?2868 (%$O mean summer temp Ros Angeles) 'upply air temp 8
Assumptions: =imension of space 6%*(R)76%*(5)71*(4) 2% people 7 2% #tuhr %%% #tuhr 2$ wattssf lighting ?%%% #tuhr Assume -%%% ;Hhr e7terior loads
AC4 (Air change per hour) 1% therefore C8M AC4 7 9olume 6% (1% 7 D-%%% cu ft)6% ?-%%% cfm
'o ?-%%% cfm is re"uired to e7haust the room 1% times per hour$
/ow to determine the load on the cooling coil: Cooling coil load 1$1 7 C8M 7 (1 2) 1$1 7 ?-%%% 7 (?2) 366-3%% ;Hhr
'umming all the loads: 366-3%% #tuhr S %%% #tuhr S ?%%% #tuhr S -%%% #tuhr 3-3%% #tuhr or 32 tons$
'o to select a unit to suit all the a#o!e loads- I will select a 3 ton unit$
his is +ust a generic e7ample$ here are many other loads that I am not incorporating$ 4opefully this can get you in the right direction$
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 1:D1
E.- so far- all the things that had #een told here- i already .new it$I thin. i-m not as.ing the right "uestion- so here i go- how can i determine the total cfm that is re"uired to pass trough a cooling coil in a system that re"uires 1%%O outside air- or how do i .now how many changes of air do i need$
R'A (Mechanical)
3 Apr %6 1:%1
he C8M re"uired is calculated #y the engineer$ ypically for a la#oratory the AC4 is 61 AC4$ A restroom is D AC4$ (these are recommended num#ers we use in our oLce$ hese are not a standard$)
=oes that help>
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 1:3
o.- here is the pro#lem
a loc.er room Area 3% s"ft height 1%ft 3 persons in the room what will #e the diference in my load calculation if the system is 1%%O recirculate air or 1%%O outside air$
R'A (Mechanical)
3 Apr %6 2%:D
Air change method Assumptions: 'ummer design condition ?28638 Indoor design condition 28 Interior location therefore no e7ternal load Roc.er @oom AC4 1 (again- this is our oLce standard) 9olume: 3% sf 7 1%* 3-%% Feople load sensi#le 2% #tuhperson (1-2%% #tuh) (+ust got done wor.ing out) Feople load latentperson 1% #tuh (3 #tuh) Righting load 1$ wattssf (32 #tuh)
C8M 1 7 3-%% 6% - cfm (lets say ?%%% for simplicity)
1$ 8or 1%%O outside air: Cooling coil load 366-3%% #tuh otal sensi#le load 366-3%% S 32 S 1-2%% 3?-2 #tuh or 32$ tons$
2$ he diBerence will #e su#stantial #ut Roc.er rooms are ne!er 1%%O recirculated$ here will always #e some amount fresh air #rought into the space$
he air change method is a simple method of getting an appro7imate idea of what sie unit is re"uired$ In loc.er room applications many times they are heated and !entilated only$ And Ma.eup air is usually always re"uired to achie!e proper air #alance$
4ope that clears up some "uestions you may ha!e$ <R
cme (Mechanical)
Apr %6 16:D1
a rule of thum# $$$$$ 1% cfmton for a preliminary siing load
,nal psych chart analysis on =;mean5; per ashrae geographic data
don*t forget fan heat gain
62hog (Mechanical)
2D Apr %6 12:2%
Ene other thing must #e ta.en into account$ If you are planning on using a pac.aged system (ie$- rooftop unit)- you must consult with the manufacturer$ As a general rule- (at least according to my local reps) a pac.aged unit is only capa#le of accepting appro7imately 23%O of the total airow in the form of unconditioned outside air$
Any system you use should #e discussed with you local rep$ 0ou should also re"uire them to also pro!ide you with any documentation for information that may diBer from you &sound engineering +udgement$&
80I- A'4@A list the design condtions for =ominican @epu#lic cooling- in the %$DO range- as ?1% d8 d#w#$
lilliput1 (Mechanical)
2D Apr %6 12:D?
62hog is right$ Chilled water systems are recommended for 1%%O EA applications$ 4owe!er it is also possi#le to use multistage pac.age =Q AC units #y recirculating a portion of the supply direct to the return and supplying to the room only the C8M e"ui!alent of the EA handled$ 8or e7ample- if the load for say D%%% C8M 1%%O EA is 2% tons$ Hse a 2% ton unit say nominal %%% C8M- #ut use D%%% C8M EA- %%% C8M
total 'A- D%%% C8M recirc direct #ac. to A4H and D%%% C8M supply to the room$ 'ol!e for the mi7ed air conditions of the EA and recirc air to get cooling coil entering air condition$ Interpolate performance from ta#ulated date$ 'ol!e for cooling coil lea!ing air temperature$ =etermine fan and duct heat gains and deduct from ta#ulated capacity to get net capacity$
thoot (Mechanical)
3% Apr %6 23:2
8irst you need to compute the total heat load $li.e num#er of window- sie of doors what materials used in the #uilding 5all$ 0ou may ,nd the !alue of each material in Ashrae hand#oo. or Mechanical hand#oo.$0ou may also use Manual J method- a software for load computation$ his wil guide you step #y step method$
sloyal (Mechanical)
1 Jun %6 1:%2
4ere*s my 2 cents$$$
;H4 D$ 7 cfm 7 =elta 4 4psych chart enthalpy McVuay W rane as well as others ha!e downloada#le Charts that should gi!e nthalpy conditionsI prefer the straight edge on a paper graph (calcs for the ,les)
My design conditions are ?d#3w# nthalpy 36$ indoor cond$ d8 %O 4umidity nthalpy 2
%$ or %d8 %O 4umidity nthalpy 26$3 8or ease of use I call it a d4 of 1%
;tuh cfm 7 D$ 7 1%
If I ,nd I need a 2% on system- I*ll #e !ery careful to select a coil on face !elocity- to a!oid freee upas well as Ratent W sensi#le capacities$ Interlaced coils with multiple stages (more is #etter) wor. #est$
I a!oid conditioning the space with this system as it would re"uire a larger system$ I prefer deli!ering room temp air W ha!ing a seperate recirculating system for space loads$ I may e!en deli!er a portion of the &tempered outdoor air& into the return of the space conditioning system- Fossi#ly 1%%O if the cfm matches- with a return setup for independent operation$
My winter design is 2%d8 so any outdoor air is heated W it*s usually done with a direct ,re MAH$ he products of com#ustion in this air has recently #ecome an issue- especially on units recirculating any inside air$
5ith these design conditions- I would loo. at incorporating a 4eat @eco!ery 9entilator$ 'omething li.e a @enewAire with latent W sensi#le e7change can sa!e a #oatload on the aforementioned <as MHA w2%ton coil$ 7h air conditions (i$e$ dust- oil- etc$$$) might prohi#it a heat e7changer altogether$
good luc. sl+
0or.man (Mechanical)
1 Jun %6 1?:3
Ene thing not to o!erloo. is that the latent load is going to #e rather high- gi!en that this is a loc.er room with showers$ A recirculated system*s latent loads at the coil could #e higher than the E'A senario$ I would loo. up latent load and air change recommendations in the A'4@A 8undamentals 4and#oo.$ It may ma.e more economical sense to go with 1%%O E$'$A$ and .eep my discharge air at say 6% 6 degrees afterall it is a loc.er room$ 4ey I ha!e enough pro#lem with shrin.age$ GX) <ood luc.- with this much ad!ise how could you go wrong> I*m not a real engineer- #ut I play one on $9$ A$J$ <est- 0or. Int$
Coreech%1 (Mechanical)
D Jun %6 13:D
VuoteTTTTTTTTTTTTTTTT o.- here is the pro#lem
a loc.er room Area 3% s"ft height 1%ft 3 persons in the room what will #e the diference in my load calculation if the system is 1%%O recirculate air or 1%%O outside air$ TTTTTTTTTTTTTTTTTTTTT
he diBerence in your load calculation is 4H<$
Fost a little more information li.e whatYs your design room temp> 8or pu#lic loc.er rooms I design around a =eg$ Indoor temp year round$
A few things you need to .now ,rst a#out loc.er rooms$
Roc.er rooms should always #e .ept slightly negati!e$ he loc.er room area should #e completely sealed /E plenum returns /o mi7ing of air with other systems$ 0ou are allowed to recirculate air pro!iding it is the air from the loc.er room area$ 0ou must ha!e e7haust fans$ 0ou donYt always need 1%%O Eutside air +ust enough to pro!ide proper !entilation to match your e7haust$
I ha!e use $@$9Ys in loc.er rooms to reco!er as much energy as possi#le to lower the load$
In your case if you use 1%%O outside air you will need to e7haust 11%O of that air (to .eep the space slightly negati!e) hatYs a 4H< load to cool and then to e7haust if you li!e in a warm climate$
Core ssn/1 (Mechanical) (OP)
31 Jul 12 1?:16
I am designing the 49AC system of a storagewarehouse in laredo- 7- which is supposed to #e .ept at % degrees 8 year round$ I ha!e #een told #y the #uilding contractor that there are no people in this place$ Am I still supposed to implement outside air into the design to con,rm with A'4@A re"uirements> he second part of my "uestion is that I ha!e ran the load calculation using rane race and not sure if the system sie is large enough$ his storage is 1%% s"$ft$ 2%* ceiling- no load e7cept lighting- which is a#out total
of D%% 5atts$ @ !alue of walls is 1?- and ceiling is 3%$ Road calculation result is 2$1 tons116D cfm$ his is a#out 6% s"$ft$ton- which seems a #it too high of s"$ft$ton I am used to seeing$ cd!!13" (Mechanical)
1 Aug 12 11:33
A'4@A 62 (if that is your code re"uirement) still has an Area Eutdoor @ate for wharehouses- so yes- you still need EA$ 'ee a#le 61 =ont ha!e e7perrience with wharehouses- #ut I thin. the s"ftton @ule of hum# you are used to seeing is pro#a#ly for oLce space etc (closer to D%%>- +ust a hunch)$ 'o without windows and EA- the @E may clim# to close to what your seeing$ /ow dont forget to ad the EA .nowledge is power
ssn/1 (Mechanical) (OP)
1 Aug 12 16:D6
han.s for the reply cd77$ I did some google search And found the following lin.s$ I am not sure if these are really legit or not since I ran across them online$ If these douments are correct- then I #elie!e there is no need for outside air in an unoccupied storage$ 8rom what I ha!e #een told #y the #uilder- this space is +ust for purpose of storage$ $ttp%&&***as$raeorg&File.45i6rary&doc5i6&Pu6lic
And $ttp%&&***as$raeorg&File.45i6rary&doc5i6&Pu6lic ssn/1 (Mechanical) (OP)
1 Aug 12 1:%2
I searched the A4@A we#site for the douments I posted in my pre!ious post and they are on the we#site$ 'o they appear to #e legit$ cd!!13" (Mechanical)
1 Aug 12 1?:11
<ood one$ he interpretations are legit$ Vuestions is are they related> he intent of 62 is safety$ 'o if the material you store does not produce oB gassing etc$ And for.lifts etc are not used in the space- then may#e$ Again- I ha!e ne!er designed a wharehouse- (#ut ha!e fought a#out the intent of 62 with R= interpreters)$ ;uilders want cheap- your +o# to design right$ 'end the #uilder an email- with the wording you descri#e and as. if that is what the #uilding*s intended use is- when he answers you #y email- at least you ha!e something to C0A$ .nowledge is power
ssn/1 (Mechanical) (OP)
1 Aug 12 2%:D1
han.s again cd7$ In the past I ha!e seen engineers as. for EA inlet to #e a motoried damper- which closes shut when unit is not operating$ =o you .now if that is a code
re"uirement or a design preference> cd!!13" (Mechanical)
1 Aug 12 2%:D?
/ot !ery de,niti!e answer #ut may#e youll get a wharehousee7perienced engineer response as well$ My energy code (2%%? ICC) re"uires low lea.age dampers- #ut allows gra!ity dampers for #uildigns less than 3 stories$ <ood Ruc. .nowledge is power
DrR7 (Mechanical)
Aug 12 1:11
I ha!e completed numerous conditioned self storage faculties$ 0ou may not #e oB in the %%ft2ton trust your load calculations$ he ,rst few I did- I could not #elie!e the results I got Z o!er 1%%ft2 per ton$ Indoor lighting is on motion sensors and will run %$2 wft2 or less$ 0ou will need to account for outside air #ased upon IMC or 62$ 4umidity and design temperature setpoint and minimum C8Mft2 ha!e a large impact on the loads$ 4ere in the Midwest I ha!e had issues with moisture in ,rst year if itYs a precast #uilding- condensate on outside walls in the winter due to pac.ing stored materials tight to outside wall and smo.e remo!al systems$ 5hy %8> 'eems !ery low for a thin en!elope$ 9$as:ean1 (Mechanical)
12 Aug 12 3:%%
=o you ha!e any e7haust> If so- the minimum ma.eup air you #ring in should always #e a#out 1%O more than the e7haust !olume$$$ 4ello all wo ones AW; ha!e the same occupancy- let say 1% persons each- the load calculation told us that one A needs 6%% cfm- [one ; needs D%% cfm fore e7ample- and #oth of them need 1% cfm of fresh air each for !entilation$ /ow total cfm is 1%%% cfm- fresh air is 3%% cfm which means 3%O$ 'o- 3%O of D%% cfm is less than 1% and 3%O of 6%% is more than 1%$ Am I right> DRWeig (lectrical)
? Ect 11 16:3%
0es$ If you want to distri#ute the outdoor air in a proportion that is diBerent from the proportion of supply air- you can*t +ust mi7 them and send them down the duct$ A separate tempered outdoorair system is needed$ If not- you must increase the outside air so that the worst case room is !entilated to minimum re"uired #y code$ In your case- 3O total outdoor air will gi!e you +ust o!er 1% C8M to one ;$ [one A will #e o!er!entilated (22 C8M)$ <ood on ya-
<oo#er =a!e ms,uared;8 ('tructural)
? Ect 11 1?:D
=a!e: If [one A is a #athroom- o!er!entilation is a good thing$ Mi.e McCann MMC ngineering
DrR7 (Mechanical)
1% Ect 11 :%
0es and no$ If the system is C9- then one ; is your &critical& one and it will dri!e your O EA$ his is the dilution O$ If the system is 9A9 and has the a#ility to !ary minimum ow to each one- then total EA could #e as your calculation$ his may re"uire EA ow measurement- CE2 sensors- reheat or ==C controls$ I suggest you read A'4@A 62 documents$ A properly completed !entilation schedule will re!eal the critical space- EA ow and damper min$ position$ Pruger has a few white papers on this topic and an 62 spreadsheet to run thru the math$ $ttp%&&***krueger'$accom&lit&*$itepaperasp Ma.e sure you .now which code standard your are designing to Z the num#ers !ary$ Most load programs ha!e the a#ility to specify which code you are designing to and will de!elop the !entilation schedule$ CE2 reset will help with high O EA$ *alkes (Mechanical)
1% Ect 11 :%
Also- if one A is a #athroom- you would li.ely use transfer air to ma.e up the e7haust$ 3104/" (Mechanical) (OP)
11 Ect 11 21:16
han. you for your reply- #ut I ha!e points regardless to the control system for now$ 1 for C9 systemsit is o. that we need 3O EA in order to ha!e 1% cfm of EA in one ;$ I guees this is the ratio of 1%D%%$ /ow- If I went with %$3 as 3%%1%%% that mean on unit le!el I am o. with the code #ut at one le!el I am not$ 2 for 9A9 systems- here is the pro#lem one ; at D%% cfm- and one A at 6%% cfm- the EA Ois %$3O$ what if the one ; #o7 modulate to 2% cfm while one A #o7 still at 6%% cfm>$ =oes that mean the one ; #o7 has to has a ,7ed position at D%% cfm alwayes and one A minimum cfm is D%% cfm or more in order to .eep %$3O of EA$> 5eftyr (Mechanical)
12 Ect 11 ?:31
I guess you are ha!ing a pro#lem #ecause you will #e using an A4H system$ 5hich force you to mi7 your fresh air and return air in the unit #efore supplying to your two ones$ I suggest you use 8CH system were you ha!e to duct your fresh air to your diBerent one in a re"uired proportioin$ hat is my two cent worth opinion$ *alkes (Mechanical)
12 Ect 11 13:3D
[one ; may then #e your critical one that will determine the percentage of EA re"uired
for the unit$ 6%O assuming that the space is still occupied at that point$ If the #o7 is throttling #ac. #ecause there is no load then there may not #e anyone in the space$ tys"4 (Mechanical)
12 Ect 11 16:D3
=r@H hit on some of the points if you are under A'4@A 62$1 for your !entilation code$ It*s a little more complicated than you are descri#ing$ 0ou need to follow the method outlined to calculate the system outdoor air ow for multione systems$ It will actually end up somewhere #etween 3%O and 3O for the constant !olume system$ In the !aria#le !olume case you ha!e to account for the minimum airow settings$ It will increase your system outdoor air the lower your minimums are$ DrR7 (Mechanical)
12 Ect 11 1:2
@un thru the num#ers$ 8irst we need to assume you ha!e run the loads correctly for the systems #eing applied and ha!e correctly applied the re"uired !entilation code$ Roads will change #ased upon system selection$ 8or a C9 design Z [one ; is the critical space$ his one will determine the outside air minimum damper position$ 1%D%% 3$O$ his will pro!ide 1% cfm of EA$ [one A 6%% cfm at 3$ O 22 cfm of EA$ 0ou will o!er !entilate this one #ut since you ha!e a C9 system you cannot easily alter EA ow unless you apply additional controls$
otal system 1%%% cfm at 3$O EA$ 8or a 9A9 design Z [one ; will still #e the critical space$ [one ; ma7imum terminal ow D%% cfm and minimum ow of 1% cfm (3$O of ma7) from the central A4H$ [one A ma7imum terminal ow of 6%% cfm and a minimum ow of 1% cfm (2O of ma7) from central A4H$ otal system 1%%% cfm at 2O EA$ /e7t you need to ma.e sure the 9A9 system will pro!ide correct 'A dilution o!er the A4H ow range$ Controls can #e applied such as =C9 (CE2 sensors) or ow sensors (rane ra" dampers) to ensure proper EA to each one at all times$ 3104/" (Mechanical) (OP)
12 Ect 11 23:%D
you said &Roads will change #ased upon system selection$& could you please e7plain this point alittle more$ how can #e sure that my load calculation is correct if I used the code !alue (3%% cfm in our e7ample) and then interduced 2O more than that(3%3%%)-what a#out unit capacity in this case> in 9A9 system you said&[one ; ma7imum terminal ow D%% cfm and minimum ow of 1% cfm (3$O of ma7)& if the one ; minimum is 1%cfm how can #e sure this 1% cfm has 1% cfm of EA-> if we use the same C9 e"uation then the EA O would #e 1%%O- and this is right if all ones are in minimum postion at the same time then the unit will pro!ide 1%%O EA$ #ut what if one ; is in minimum and one A is not> also if one A minimum is 1% cfm same "uestion a#o!e> when one or #oth ones are in mimimum the total will #e less than 1%%%cfm$ when load droped down that does not mean for sure some people left- it could #e north
one and west one$ tys"4 (Mechanical)
13 Ect 11 1%:D2
E.ay- there still seems to #e some confusion$ I used the calculator on the Prueger we#site to simulate your pro#lem$ I assumed cooling mode only (1$%)$ 4ere are the results: Constant 9olume 'ystem: 32 C8M of EA re"uired 9aria#le 9olume 'ystem: 3?? C8M of EA re"uired Ri.e I said- it*s not as simple as +ust summing your EA airows if you are re"uired to use A'4@A 62$1$ he !entilation eBecti!eness in each scenario is diBerent #ecause you ha!e to use your minimum ow for [one ;$ Can I ha!e a constant speed =EA' system ser!ing 1% air handlers that ha!e !aria#le fre"uency dri!es> 5ill the outdoor airow rate remain the same throughout all operating points of the air handler fan> I*m assuming it won*t since the pressure in the mi7ing #o7 will change and I would need some sort of 98= on the =EA' unit$ If I do need a 98=- what is the se"uence of operation and what controls the =EA' fan speed$ han.s in ad!ance$ <McD (Mechanical)
3 /o! 11 %:1?
If your =EA' system is sied to pro!ide the minimum !entilation air to satisfy A'4@A 62then lea!e it at constant !olume$ he !aria#le !olume A4H*s will +ust use less return air in the mi7ing section and you*ll still #e deli!ering the minumum re"uired !entilation air to the spaces- as well as ma.eup air for constant e7haust systems (washrooms- general e7haustetc$)$ hat*s assuming the 9A9 A4H*s are sied and !arying the supply air ow for cooling (or heating) demand to their spacesones during a normally occupied period$ =>?" (Mechanical)
3 /o! 11 1:
here are two ways to go a#out this: 1$Constant !olume =EA' deli!ering constant !olume to each A4H irrespecti!e of what speed they are running at$E#!iously when the A4Hs ramp down on the 9'=-the mi7ing #o7 static pressure will drop resulting in less fresh air #eing drawn$0ou need to open the fresh air air damper on the mi7ing #o7 more to .eep the air ow constant$Ene way of doing this is to hold the diBerential pressure across the damper constant no matter what the static pressure in the mi7ing #o7 is$ 2$A !aria#le !olume =EA' responding to change in fresh air re"uirement from each A4H$he fresh air damper in each A4H will modulate in response to a CE2 monitor in each of the ones$he =EA' A4H will ha!e a duct static pressure sensor tuned for the ma7imum air ow$Any =EA' ow reduction will cause the static pressure to rise and will slow the unit down$ Eption 2 is more comple7 and is re"uired only if the occupant load is li.ely to !ary signic,cantly ie lecture theatres-auditorium-restaurant etc s*oos$10. (Mechanical) (OP)
3 /o! 11 1:
hese are pretty small air handlers- no more than 2-%%% cfm each$ I am not sure that the outside air will drop much when the ahu speed ramps down- #ut I do ha!e to su#mit for R= 'il!er and I want to ma.e sure it is correct$ 5hat do you thin. a#out ha!ing a pressure independent 9A9 #o7 on the EA duct to each air handler> cry.. (Mechanical)
/o! 11 12:2?
'moosh 0ou ha!e to gi!e all data when as.ing a "uestion$ his data of 2%%% C8M ma7 for A4H is important in your pro#lem and should ha!e #een stated$ second- you need to state amount of EA and total =EA' unit sie for people to ma.e a sound +udgment third- you need to mention the R= aspect and what part of R= are you pursuing> are you implementing a =C9 control strategy> using CE2 sensors> if you do- you need means to control the reduction of EA into the #uilding$ 8rom what you state- you system is no more than a 8CH with =EA'- you +ust call them A4H$ we*re tal.ing a#out 1%O EA> (2%% C8M for each unit> total =EA'2%%% C8M- or 2%% C8M>) if so- then your system is fairly small- and #oth your =EA' and A4H ha!e fans 4F are so small that 98=*s do not ma.e sense any way$ It appears that C9 =EA'- C9 A4H*s with manual #alancing is the way to go$ If you get tangled into that air ow measuremnt- =C9 control etc- you*ll #e spending a fortune for minimal gain$ /o way in hell you can ha!e a pay #ac. on such small systems$ I*d go C9 all the way- A4H*s and =EA' unit as for 98=*s for such small systems- it is as they say in ;roo.lyn &8oggeta#outit& =>?" (Mechanical)
6 /o! 11 16:36
I fully second cry22 *s !iews$ s*oos$10. (Mechanical) (OP)
/o! 11 :3
han.s Cry and 'AP$ I ran the energy model and I was only getting a 2O sa!ings with the 98=s so it is not worth it$ I was surprised to see that I was also #rea.ing e!en on the energy wheel tonnage sa!ings !s what it costs to run the erw motor$ he EA is only 1%% cfm as cry guessed- so I guess energy reco!ery is also not worth it$ cry.. (Mechanical)
/o! 11 :%
'moosh here is no 'il!er ;ullet in sustaina#ility$ 0ou ha!e to throw a lot of darts at a prro+ect to sa!e energy$ hey do ha!e to ma.e sense though$ I*d say @5 total enthalpy wheel is worth loo.ing at (again another data you did not indicate in your pro#lem statement your Rocality weather data) the harsher the climatethe more opportunities to sa!e$ It is not +ust tonnage- it is also ;oiler sie (then again- are you in a heated climnate>) I would pay attention to that @5 load- if the load comes down say from to % ton for e7ample- then it may ma.e sense #ecause you*d #e going from a larger @H or aircooled chiller to a low end (!erify actual P5 of e"uipment) from 6% to % ton- your %ton will #e rightly sied w@5- while your 6%ton will #e o!ersied wo @5$ he following are some of the ma+or things you should consider upfront when doing a 'ustaina#le design 1$ @5 total nthalpy wheels 2$ Row <lass 3$ Righting Min A'4@A ?%$1 1 5'8 or e!en #etter R= lighting D$ =C9 using CE2 sensors for large occupancy spaces to pro!ide di!ersity$ $ &@ight'iing& of e"uipment- actually H/=@'iing is <EE=- especially for residential$ this can*t #e stressed enough- we*!e seen people pro!ide a 2%ton AC unit for an ele!ator
machine room when a ton will do$ Chec. tose calcs$ 6$ Airside econimier when climate permits$ $ 98=*s on 8ans W pumps etc of 1% 4F motor and larger$ $ <ood control se"uence of operation H@/E88 e"uipment when you can- nothing #eats E88$ ?$ 'ystem choice for the right occupancy$ 1%$ some rules of thum#s: using points 1 thru D a#o!e- you should get around %%'8ton for cooling and 12% ;H4'8 of heating in a moderate climate such as the H' mid atlantic$ Rast #ut not least- watch out that sensi#le load going down so much that you ha!e under %$ C8M'8 of cooling- you need to mo!e some air- I li.e to see no less than %$ C8M'8 (especially for 9A9 systems)- then again watch that dehumidi,cation pro#lem resulting from high 'A temp$ (?) when mo!ing more air purposely$ 0ou ha!e to ,nd a #alance of things that ma.e sense and apply them- that*s why we are hired as engineers- to ,nd all the solutions for each speci,c pro#lem$ 4icould any one e7plain - for a Constant !olume system what is Cooling coil supply air temperature reset pro!ided normally$is the @eset =elta is calculated #ased on the ma7imum and the minimum cooling load or is there any thum# rule han.s and @egards !ignesh$ Dra2en (Mechanical)
8e# 12 12:%%
Pnowing a#out such formal re"uirement- I do not .now how it actually wor.s in practice$ In theory- temperature reset should refer to one with highest cooling load- raising supply temperature as much as possi#le during part load- which should reduce reheat energy needs for the whole system$ In my opinion that would ma.e sense if '4@ is constant in all load conditions- which- of course- is not the case- and therefore such reset can directly reduce dehumidi,cation eBecti!eness- and the only mean to cope with that is to plot chart of part loads- ma.e graph of reset temperatures accordingly- and than apply it to control logic (similarly to outside temperature dictated supply temperature reset in hydronic systems)$ I did not hear a#out that in practice- howe!er$ Mec$@ngA9P@ (Mechanical)
8e# 12 16:2
'ay you ha!e a la# with constant !olume wreheat$ /ormally the discharge temp would #e degrees and then reheated to maintain space temp setpoint$ If humidity monitoring is in place- you may increase the supply air discharge setpoint until the space rh raises a#o!e setpoint (say %O)- then the chilled water control !al!e modulates or compressors stage up to get the @4 down #elow setpoint$ It is a way to sa!e energy throughout the yearespecially if you ha!e a 1%%O EA system$ =>?" (Mechanical)
1% 8e# 12 23:22
he usual reset #and is 13\1C$@eset may #e done #ased on either return air temperauture or outside air temperature or a com#ination of #oth$0ou need to #e mindful
of internal humidity re"uirements and e7ternal humidity ranges #efore employing supply air reset$It is not recommended for humid climate such as across asia or the middle east$ Dra2en (Mechanical)
13 8e# 12 13:1D
'AP?At ,rst glance things loo. !ery simple if you ta.e latent load out of analysis$ he #ig "uestion is- howe!er- what are you sa!ing than$ My understanding is that temperature reset is done to sa!e on reheat energy- #ut if you do not ha!e controlled dehumidi,cation !ia cooling coil- that you do not ha!e reheat at all$ Rower lea!ing air temperature will reduce load co!ered #y space cooling and your sa!ings are coming to eroK Mechng/CF he e7ample you mentioned is one that I could imagine- though it seems to #e limited to one one systems$ Etherwise- I am wandering how to decide on referent internal dry #ul# temperature- when each one may ha!e diBerent latent load patterns$ At design stage you are already aware that your ones will not ha!e the same relati!e humidity- #ut will rather #e within accepta#le (as wide as possi#le) range- #ut when you #egin playing with supply air temperature things #ecome complicated$ $ouseman.4 (Mechanical)
13 8e# 12 16:
@ecommend that any constant !olume system #e re!iewed for compliance with A'4@A ?%$ especially section 6$$2 'imultaneous 4eating and Cooling Rimitation$ here are limits on how much reheating is allowed$ here are also e7ceptions to the rule$ his is a prescripti!e section- you may need to document the path for energy code compliance$ =>?" (Mechanical)
13 8e# 12 21:31
=raenApart from the reduction in reheat re"uirements-there is a sa!ing due to compressor ha!ing to do less wor. at higher e!aporator pressures in a =Q system$here is scope for chilled water temperature to #e reset up in C45 systems with a reduction in energy consumption$ 21 'ep % 1:D3 I am in the process of trou#leshooting an EA duct distri#uting air to four A4Hs$ he most remote A4H is modulating the return air dampers to gi!e a constant ?%%C8M of outside air$ =ue to the return air damper modulating down the total air is low$ I am getting a !aring consensus of opinion among my cowor.ers and the A; on this- from #ringing in a separate EA duct- to adding a fan in line for the speci,c unit- to adding a fan on the main duct(a#out 2%% C8M total EA demand)with #ac.draft dampers in the EA duct near each unit$ I would li.e to sol!e this #y adding an inline EA fan at the speci,c A4H with #ac.draft dampers at the other units #ut I am not shure how to calculate the fan sie or if this will wor. at all$ :ronBr>ur (Mechanical)
21 'ep % 1:%1
Is the EA ductwor. sied to handle the EA re"uirements of all A4H*s$ 'ounds li.e they are
,ghting each other for the air$ Clippo/ (Mechanical) (OP)
21 'ep % 1?:3
/o- I don*t thin. they are ,ghting for air$ his unit is the most remote- longest distance from the Rou!er$ Mintulep (Mechanical)
21 'ep % 21:D
5hat is the actual pro#lem that you need to sol!e> It is not clear in your original post$ I*ll guess that the pro#lem is that &the total air (supply>) is low (from the most remote A4H)&$ If that is it- I would guess that mo!ing ?%% cfm through the EA duct has used up most of the a!aila#le static pressure from the A4H*s fan$ he simplest way to to sol!e this would #e to simply increase the A4H fan speed- pro!ided that the motor has suLcient unused capacity$ he lowest cost (life cycle wise) would #e a separate EA duct- sied for low pressure drop$ Adding a #ooster fan means you need to pay to run the fan fore!er$ Adding dampers at the other A4H*s increases the pressure drop at each- ma.ing their fans costlier to operate$ Clippo/ (Mechanical) (OP)
22 'ep % 2%:D
Agree$ 5hen the A; opened the return air damper manually to 1%%O the total air increased to near design$ he EA decreased #elow design$ 5e do ha!e some margin in the motor to increase the fan @FM #ut this thing is already outside of the fan cur!e en!elope$ he static pressure is #elow where the fan cur!e would ha!e it at the lower C8M when I replotted it$ I thin. the reducting of the EA is the only realistic- cost eBecti!e solution$ 5e ha!e some restrictions on where the EA lou!er can #e placed to complecate things$ tras$canman (Mechanical)
2D 'ep % :1
Increasing the speed of the A4H will also directly increase the A4Hs cfm$ 5ill this #e a pro#lem> Also 4F increases as cu#e of speed$ 5hy not consider a separate EA fan for each A4H> hat fan could #e interloc.ed with its respecti!e A4H$ 0es- you will face operating e7pense of the EA fan- #ut it will wor.$ ,uark (Mechanical)
2D 'ep % :D
I agree with MintJulep$ he reduction in total owrate is not due to the control of return damper #ut #ecause the outside air is consuming the fan static$ Chec. the fan total static when the return damper is fully open (as this gi!es you the design owrate)$ =isconnect the EA duct- control the return damper to get the re"uired owrate of EA and again chec. the total static pressure of fan$ If the diBerence in static pressures is positi!e then design your duct as per the a!aila#le static$ If the diBerence is negati!e- then select the fan for the new ducted EA system S the diBerence$ >66yAormal (Mechanical)
26 'ep % 1:12
It is always tough I thin.- when you ha!e a 98= and you want to try and ha!e return air
dampers close oB and outside air dampers to open up- to try and .eep the outside air contant under lower airows when the supply #lower is ramped down$ May#e get an inline fan with a pressure independent 9A9 #o7 to contol the amount of outside air you want$ >D>< (Mechanical) (OP)
2 Apr % 1%:%
I am wor.ing on the design of a Constant !olume- =Q ac system (cooling only)for a <o!ernment ELce$ 8or the cooling load calculation I am including a !entilation load of 1 C8Mperson in occupied oLce areas$ /ow in this same #uilding I also ha!e a cafeteria room- to #e used only #y the oLce staB (around 2% people)$ If I now again include a !entilation load of 1 C8Mperson for these same people when in the cafeteria- I will #e dou#ling the re"uired !entilation air and introducing dou#le the air I actually need (and o!ersiing my e"uipment)$ If I donYt- I will run short on the supply air for the cafeteria$ 5hat is the criteria to follow> Ferhaps the #est would #e to ha!e an independent system for the cafeteria- #ut what if this is not possi#le> Another issue on !entilation: Considering the local construction standards I .now I will #e ha!ing some in,ltration- this howe!er is hardly "uanti,a#le$ 'hould I reduce my system !entilation re"uirements (i$e$ 1C8Mperson to 1% C8M person) to compensate for the in,ltration !entilation> han. you-
*illiams<> (Mechanical)
2 Apr % 11:3
0ou need follow the A'4@A 62 guidelines$ It is no longer as simple as 1 cfmperson$ 0ou will need to ta.e into account the airow percentage that is deli!ered to each space- and what portion of that is EA$ 'ince it is a constant !olume system this is an easy calculation$ Also- A'4@A 62 now re"uires EA for space contaminates- this is a EAsf num#er- and EA occupants$ 26 Jun % 1%:% I am wor.ing on a reno!ation pro+ect- the #uilding is #uilt in 1?D- I assume 1?1 ;ECA mechanical code is used at that time$ =oes anyone .now what is the outside air and !entilation re"uirements for oLce and conference rooms in 1?1 ;ECA Mechanical code> MarauderE (Mechanical)
26 Jun % 12:2D
I would imagine that you won*t #e a#le to design to the *1 code for current permits$ ***ander*eilcom
ap$ou (Mechanical) (OP)
26 Jun % 1D:3D
he outside air re"uirements for #uilding #uilt in 1?D is cfmperson and $33 cfmperson in conference room$ It is almost impossi#le to upgrade the outside air to the current code re"uirements$ he local #uilding code authority agree us to follow the !entilation code #ased on the year the #uilding was #uilt$ It ma.e sense- #ecause if one oor is #eing reno!ated in a high rise #uilding- it is unfair to as. the tenant or owner to upgrade the oa re"uirements for the
entire #uilding$ MarauderE (Mechanical)
26 Jun % 1:%2
It may ma.e sense- #ut it doesn*t ma.e for a good #uilding$ I wouldn*t want to li!e or wor. in the +urisdiction you are under- as e!ery #uilding would comply only with the year it was #uilt$ Almost impossi#le means that it can #e done$ I should hope that you ma.e the #est engineering decision when designing those oLce and conference spaces$
***ander*eilcom
7>Diep (Mechanical)
2 Jun % 1:D1
&It may ma.e sense- #ut it doesn*t ma.e for a good #uilding$ I wouldn*t want to li!e or wor. in the +urisdiction you are under- as e!ery #uilding would comply only with the year it was #uilt$ Almost impossi#le means that it can #e done$ I should hope that you ma.e the #est engineering decision when designing those oLce and conference spaces$ & he #est engineeing decision is to #ring the #uilding up to code$ hat is a no#rainer$ 4owe!er- #oth you and I .now that doings thing the proper engineering way e"uals money$ In this case- alot of money$ he house system is not setup for the additional outside air needed to #ring the space up to code$ Also- since this is located in a high rise$$$the units are most li.ely central units that ser!e multiple oors$ As engineers- we should inform the #uilding owner of the situation and that we recommend they upgrade the units to allow for the current E'A re"uirement$ If they say- &we do not ha!e the money and the local +urisdiction appro!es of gradfathering in the pre!ious code$& At least you performed your due diligence$ And thats all we can do$ A green thought$$$&5e don*t inherit the earth from our ancestors- we #orrow it from our children$& (un.nown)
*illard3 (Mechanical)
2 Jun % ?:21
If the Ewner doesn*t want to spend any money on the new space- he surely doesn*t need an ngineer$ ngineers are responsi#le for #est practice and cfmperson in a conference room is not #est practice$ mike0";1 (Mechanical)
2 Jun % 13:%6
5hat a#out 7tra ,ltration of the return air and H9 or ;iFolar Ioniation treatment of the supply airstream> According to their salesmen it can #ring the outside air re"uirements #ac. down to the cfm le!el$ hey wouldn*t lie to us- would they> 4onestly I ha!en*t tried it$ ;ut Its something I*d thin. a#out- if forced into a corner$
Mi.e A9Design (Mechanical)
2 Jun % 1:3
mi.e6D1 W the EF A'4@A 62$12%%D section 6$3 allows for an Indoor Air Vuality approach- so there is !alidity to what the salesmen is trying to sell$ ;ut- there are se!eral issues$ Ene is if your +urisdiction will go for it$ A lot of codes don*t reference 62$1 as a !ia#le way to pro!ide outside air per code$ In the case of the International Mechanical Code and se!eral state*s deri!ati!es- they ha!e ta.en 'ection 6$2- 9entilation @ate Frocedure- from 62$1 1??? (I thin. thats the right year) and made it part of the code$ /ot #y reference #ut #y directly placing that section in the code$ his stin.s #ecause in my opinion they are re"uiring way to much outside air and don*t gi!e you !ery much e7i#ility$ he second is actually #eing a#le to meet that approach if the +urisdiction allows it$ It ta.es a lot more wor. to approach it from that direction$ 0ou ha!e to identify and "uantify contaminants and then pro!e that the system you are pro!iding will ta.e care of all those$ !en after you ha!e dotted all your i*s and crossed all your t*s you are still left hanging #y section 6$3$1$3 which says: #uote (/313)%
he criteria to achie!e the design le!el of accepta#ility shall #e speci,ed in terms of the percentage of #uilding occupants andor !isitors e7pressing satisfaction with perceived indoor air "uality
hat perception part is enough to scare most people away e!en if they can get it through the A4J$ /othing li.e ha!ing to go #ac. and redo your design #ecause the client andor A4J +ust doesn*t thin. the air is clean enough$ In my opinion your safety net +ust isn*t there li.e it is if you follow the !entilation rate procedure$ atlas4/ (Mechanical)
2 Jul % :D2
=ynamic Air ,lters claims the same air "uality approach to reduce outside air "uatities$ he latest IMC 2%%6 D%3$2 7ception allows an &engineered !entilation system& outside of rates stated in section D%3$3$ I #elie!e this re!ision to the code is there to allow the engineer to follow A'4@A 62$1 instead of the more stringent IMC rates$ >66yAormal (Mechanical)
3 Jul % 11:31
A climate where you can run a constant positi!e or negati!e it is no pro#lem$ 0ou can neglect in,ltration load and +ust worry a#out !entilation$ /A'A can recycle urine into pota#le water- I would rather drin. the fresh stuB myself$ a.e the &9& out of 49AC and you are left with a 4AC(.) +o#$
Ross>:# (Mechanical)
Jul % 21:D2
here is li.ely to #e an initial pro#lem with that low of a !entilation rate- if the pro+ect includes repainting and new carpets (seems li.ely)$ It will ta.e wee.s to get rid of the oB gassing products$ An approach may #e to specify that only carpet and paints with low !olatiles #e used- and ha!e the contractor de!elop and use an IAV plan (similar to those in <reen ;uilding guidelines)$ Ence the reno!ated areas ha!e &aged&- the occupants will +ust ha!e their own ;E and farts to deal with$$$ 1 Apr %3 1%:%% I*m designing an air conditioning system for 1%%O outside air$ he area is a small la# room appro7imately ?% ft3$ My heating loads are 66%% ;tuh sensi#le and 1%% ;tuh latent$ I trying to design the cfm re"uired$ I*m wor.ing in a dry climate so I*!e neglected the latent$
'ome people suggest that I should: 66%%(1$%](?)) where ? is the outside air re"uirements and is the lea!ing temperature oB the coil$ his deli!ers a#out 12 cfm$ he reason I*!e #een gi!en is #ecause that temperature of the air I want to deli!er and am ma.ing up for the 66%% heat gain$ his gi!es me a#out 1% Air Changes4our Ether people suggest that I should use: 66%%(1$%]()) where is the temperature inside the room$ his deli!ers a#out 3% cfm$ I will sie the coil from this formula: 1$%](?)]3%$ I ha!e also #een told if I use this method that I will freee up the coil #ecause the air ow is too great$ 5hich method is right> Can I #uy this system as a pac.aged unit> Also where can I ,nd a psychometric chart for D%% feet ele!ation> han.s F9:=@ (Mechanical)
1 Apr %3 1D:
4a!e you consider 9entilation =isplacement system yet> 9$ipFuller (Mechanical) (OP)
1 Apr %3 22:%?
5hat*s a !entilation desplacement system> c$icopee (Mechanical)
1? Apr %3 21:3%
your reasoning escapes me$ Is the sensi#le heat of 66%% #tuh generated #y la# e"uipmentlighting and the 1% or less air changes and heat transfer thru walls- ceiling and oor> 9$as:ean1 (Mechanical)
2% Apr %3 %:31
Chip 4ere*s how I see this$ I wouldn*t go #y either option you*!e shown$ I would analye this from load to source- and there is a latent gain at the load$ I would therefore use: VD$]cfm]d4 in lieu of V1$%]cfm]d otal space load is latent S sensi#le- which is -1%% ;Hhr$ o o#tain cooling airow needed- use the VD$]cfm]d4 e"uation- which sol!es for total load (sensi#le and latent) #ased on enthalpy$ 5ith a saturated ^8 supply air stream- and to maintain the ^8 space temperature at %O relati!e humidity- the load (room) would re"uire 36D cfm$ 36D cfm is the !olumetric ow rate that the central A4H would need to cool from ?^8 to ^8$ Hsing V1$%]cfm]d- as you note that this is a dry area- the A4H coil would need to #e sied for this reduction in temperature at this ow$ his e"uates to an A4H cooling capacity of 16-%% ;Hhr$ /ote that I*m s.eptical of the lac. of need for the A4H to remo!e moisture #ecause this is a &dry climate$& =ry is a relati!e term$ ?^8 and 2D$6O humidity would produce saturated ^8 air$ If the humidity were higher than 2D$6O- the coil would also need to remo!e moisture$ I*m open to re#uttal on this ha!en*t gone #ac. to thermo49AC #oo.s- #ut this way seems
to ma.e sense to me$ As a side note- #e careful of siing =Q units$ he load conditions stated will #e rare so you need a unit that will perform well at partial load$ ;est of luc.$ C; ,uark (Mechanical)
2% Apr %3 23:?
I !ote for C;$ 4owe!er if you want to go your way you should consider to deg$8 #ecause at no time you want to increase the room temperature a#o!e deg$8$ If you consider a = of ? to for a load of 66%% ;tu4r then when this heat load adds up from the room the lea!ing temperature will #e higher than deg$8$ 0ou #etter follow C;*s comments$ anandGH>9 (Mechanical)
2 Apr %3 3:31
I am sorry- Ferhaps not agree with all a#o!e e7planation$ My answer to C4IF8HRR@*s "uestion is as follows$ I will start with #asics$ If you refer to carrier hand#oo. or any other engineering #oo. on Airconditioning$ 0ou will ,nd that the grand total heat- in your case it is 1%%#tuhr i$e %$6 tons- is used to calculate the tonnage re"uirement$his means that your coil should #e capa#le to gi!e you an output of %$6$ /ow the "uestion is how much air is needed to achie!e this$his can not #e decided with a#o!e two e"uations$0ou will ha!e to do the iterations$8irst assume some fresh air i$e 1 airchangehr and calculate the dehumidi,ed air "uantity re"uied$@epeat this procedure till you #alances your fresh air with dehumidi,ed air$his will gi!e you the "uantity of air re"uired to maintain the desired inside conditions$ Answer to your second "uestion regarding pyschometric chart for diBerent ele!ation$H will note that all the standard psychometric charts are designed at atmospheric pressure of 6%mm of 4g$8or pressure other than 6%mm of 4g- you will ha!e to physically draw it$ Frocedure on how to draw psychometric chart is a!aila#le in any air conditioning #oo.$ H can refer to that$ I hope all a#o!e e7planation clari,ed all your "ueries$ In case of any "uery pls$ let me .now$ 9$as:ean1 (Mechanical)
2 Apr %3 13:%
Anand- could you clarify the iteration> 5hat do you get for an answer> han.s- C; 6riand. (Mechanical)
2 Apr %3 1:
Chas;ean1*s response of 2%th April 2%%3 is a#solutely perfect$ I*!e sied countless air conditioning systems o!er the years- and I*!e ne!er had to carry out some &iteration& to get the cooling re"uirement$ Anand49AC: I too would #e really interested to see why an iterati!e process should #e necessary on this occasion (I might #e e7perienced- #ut I ne!er miss the opportunity to learnKK)$ @egards;rian coolingunit (Automoti!e)
26 Apr %3
6:%D anand49AC: 0our e7planation is e7cellent$ I would li.e to .now the iterati!e procedure of calculating the fresh air re"uirement$ anandGH>9 (Mechanical)
2 Apr %3 1:3%
&Iteration& means trial and error method$ =uring heatload calculation you will ha!e to assume some fresh air "uantity to calculte dehudi,ed C8M re"uirement$ 0ou will ha!e to reiterate this procedure #y !arying fresh air "uantity till it #alances with dehumidi,ed C8M$ Hnless this #oth "uantity matches you will not satisfy the condition of 1%%O fresh air$ It is imposi#le for me to e7plain the method of calculation !ia mail$ 4owe!er- u can refer to carrier hand#oo. for more information$ In case of any "ueriescmments do let me .now$ I will try my #est to address it$ c6i6er (Mechanical)
2 Apr %3 12:D
I ha!e found se!eral psychrometric charts online for ele!ations other than sea le!el$ 8or e7ample <oogle found this one for me using the search terms &psychrometric chart altitude&: $ttp%&&***$eatcraft$eattransfercom&pdfs&Aormal444PDF It*s for %%% feet- not D%%- #ut it*s close enough to get you started$ ;i#er hermal =esign ***6i6ert$ermalcom ,uark (Mechanical)
2? Apr %3 %:D
=r$ [e.yl says- it is always #etter if you ha!e time to practically design a system$ (supplying air "uantity to remo!e heat load and moisture load and incrementing it to reach #alance) Mr$ 4yde says- well if you want to increase comple7ity of a simple solution go ahead$ /one of carrier*s people nor any other engineer o#+ects you$he fundamental is to chec. the total enthalpy of fresh air and the conditions you wanted at the room$ ;asically theair e7iting the room should ha!e same properties of re"uired condition otherwise room conditions cannot #e maintained$ /ow #y the simple calculation gi!en #y C; and used widely e!erywhere- calculate the cfm$ his is enough cfm that will carry heat and moisture out of the room$ his is more simpler than recirculation system #ecause you need not further remo!e the moisture from the e7iting air stream$ Just you are throwing it away$ 'till- if you lo!e math iterations- higher order diBerential e"uations and pro#a#ility will always help you$ ;est of Ruc.$ (;ahK am I #eing too dramatic>) 9$as:ean1 (Mechanical)
2? Apr %3 12:3
his could #e a good e7ercise #ecause we might #e tal.ing apples and apples here$ Anand-
did the reiterati!e process produce a result> energy0 (Mechanical)
1% May %3 1:%
Rets .eep it simple- your application is not roc.et science 1st- your C8M re"uired is dictated #y your total sensi#le load and the temp you want to maintain in the room at the supplly air temp you plan to pro!ide$ it is simply found as @m C8M @oom ;4H V' 1$% ( rm sa ) 2nd- #eause you specify 1%%O E'A ( I will not as. why 1%%O )your coils will ne!er see this load$ Coil Capacity will need to #e #ased on the air ow design a#o!e at ( E'A A d# w# 'A (RA) d#w# ) good luc. lilliput1 (Mechanical)
12 May %3 13:1
he cooling coil will need to cool 1%%OEA to the condition such that when this coil lea!ing air is discharged into the room$ it will pic. up heat and moisture W air is then e7hausted$ he condition of the air e7hausted typically matches the room inside conditions$ If the cooling coil cools the air to % deg 8 W the room design condition is 2 def 8 then the air "uantity re"uired @m Road in ;H per hr(1$1 7 (2%))$ /ow you must also satisfy the latent loads$ he Coil must dehumidify the same "uantity of air to the humidity such that when discharged into the room it will a#sor# the latent load W it*s @4 will #e within the design range$ 0ou may ha!e to reheat to maintain the re"uired space humidity$ lilliput1 (Mechanical)
13 May %3 12:2?
Ra#s typically re"uire 1%%O outdoor air$ Ma.e sure you ha!e enough for e7haust hood ma.eup$ 'implest control is constant !olume reheat$ 0ou can also ha!e (2) position occupiedunoccupied or !aria#le !olume- all with reheat$ Hsually humidity is cirtical so humidi,cation is also re"uired$ Chilled water system is #est$ If =Q you will ,nd out that when you sie the it for the load w 1%%O EA- the unit C8M (typically 3% C8Mton) would #e more than you need to do the room sensi#le load$5hat I ha!e done is recirculate #ac. some of the air$ his unit should only ser!e a la# not a group of la#s to a!oid cross contamination$ Fart of the fan discharge is ducted direct #ac. to the return$ 0ou ha!e to recalculate W do trial W error of the coil entering air condition (mi7 of EA W recirculated air at coil discharge condition plus fan heat$ he AC unit should ha!e hot gas controls$ A humidistat in addition to a thermostat should #e used to #ring on cooling$ 8inal space temperature should #e controlled #y the reheat coil$ greenaire (Mechanical)
2 Jun %3 D:DD
Could you see &the dedicated units& from the news letter of ***tranecom> 9$as:ean1 (Mechanical)
2 Jun %3 21:D6
/o I couldn*t$ Rin. is to trane$com main page$ Chec.ed under &/ews& and didn*t see &dedicated units$& ried a search for &dedicated units& and no luc.$ Could you #e more
speci,c> tmprider (Mechanical)
3 Jun %3 ?:16
ry using an @9 sied for the 1%%O fresh air load$ Rocate it in the ceiling space of the la# for ease of maintenance and cleaning$ his will most li.ley decrease the sie of the unit that you go with- and will allow you to ta.e ad!antage of &free cooling&$ E!erall- your energy consumption will #e less due to the lower delta at your coils$ =4 H==riram (Mechanical)
12 Jul %3 13:3D
his seems to #e an interesting heat load which I used to do manually at the start of my career$ 1%%O outside air application cooling load calculations are normally done #y iteration$ 8irst assume a particular outside air "uantity and do the load calculations- ,nd out what the dehumidifed air "uantity is$ If it matches the assumed outside air "uantity- then the initial assumption is right$ Etherwise- do another load calculation a#sed on the dehumidi,ed air "uantity o#tained and .eep doing this (iteration KKK) till you get the same ,gure$ Alternati!ely- if you ha!e a software li.e 2%II of Carrier- you can +ust input all the rele!ant data and put 1%%O outside air and the program gi!es an output which will #e 1%%O outside air$ greenaire (Mechanical)
12 Jul %3 22:23
4i 4ere is we# address for mentioned article and complete article name$ If you still can not get it- gi!e my your email address$ hen send it to u #y email$ My email: naymoIgreenairecomsg &$ttp%&&***tranecom&commercial&li6rary&arc$iedJne*slettersaspKG =esign tips for eBecti!e- eLcient dedicated !entilation systems #y =ennis 'tan.e- 2%%1!olume 3%3$ F=8 or 4MR genieconseil (Mechanical) (OP)
1% 8e# %6 21:D6
I*m a small mechelect consulting ,rm me #eing the only engineer I specialie in #uilding engineering in #oth disciplines and recognied #y the order of engineers of Vue#ec$ I*!e #een practicing since 1? and in all that time i ha!e ne!er had to do any energy analysis where the degree days or the #in method had to #e used$ My situation is the following- my client has a commercial #uilding in Montreal _1%%-%%% s"$ ft$ and is de!ided in 2 locals$ one tenant is using 2 ga ,red fresh air units of 2-%%% cfm (gas ,red 2-%%-%%% #tuhr) W 16-%%% cfm (gas ,red 2-%%%-%%% #tuhr)he only has one main meter and conce"uently one in!oice for the whole #uilding$ he has as.ed me to e!aluate precisely the percentage of natural ga consumed for the year for those two unit only so he can in!oice the tenant fairly$ I*m a little em#arassed to as. for help- I realise that the #in method would #e the appropiate method to use considering the fact that the units only pro!ide fresh air 1% hrs a day and re"uires heating from octo#er to mid may$ I ha!e ne!er used this method and cant seem to ,nd any good e7amples for me to follow$ Can someone help me direct me with my pro#lem>
han. you in ad!ance <enieconseil 2eos (Mechanical)
11 8e# %6 :2
genieconseil his pu#lication gi!es some #in calculation e7amples in the appendi7$ $ttp%&&***energyroc$esteredu&eLciency&optimalJ6oilerJsi2epdfsearc$ *#in O2%methodO2%andO2%heating* Mintulep (Mechanical)
11 8e# %6 12:23
0ou will need to use actual temperature data for the period of time in "uestion$ Fu#lished ;I/ data is &a!erage& o!er some ar#itrarilly long past time$ I dou#t that in!oicing a tennant #ased on calculation is legal$ 2das4; (Mechanical)
11 8e# %6 13:D1
Any method that is consistent with the contract is &legal&$ As far as that goes- it would #e legal to charge each of them the full gas #ill if the contract will allow it$ It sounds li.e the landlord is trying to #end o!er #ac.wards to #e fair$ 'ince no method is going to #e &accurate& (e7cept to install another meter which is an unreasona#le e7pense)I would opt for simple$ 5hat I*d propose is an allocation #ased on heated area times cfm$ 'ay the one with the larger unit has 6%O of the heated space then I*d allocate him: (6%-%%%ft]2%% cfm)(6%%%%ft]2%%cfmSD%%%%ft]16%%cfm)%O his isn*t &right&- #ut it will come as close as a much more comple7 calculation with historical a!erages$ 0ou could do the same thing with heat capacity- #ut you*d get to around the same num#er (6O instead of %O)$ At today*s industrial gas prices you are tal.ing a#out splitting a#out `22$% H'day (assuming `1MM;H- hoursday run time) getting it &wrong& is not a huge deal and most tenants will accept a logical- consistent- and hopefully fair allocation$ 0ou can easily spend more in #illa#le hours than this could e!er #e worth$ =a!id Mintulep (Mechanical)
11 8e# %6 2%:1
@ight- #ut if you were the tennant would you ha!e signed a lease with a term along the lines of: he landlord will in!oice the tennant for gas usage #ased on an un.nown method of calculation and performed #y someone not familiar with performing energy calculations$ 2das4; (Mechanical)
12 8e# %6 :%
Cute- #ut a good point$ he contract has some language a#out utilities$ hat is the only reasona#le place to start$ My point is that you should use the simplest reasona#le allocation method consistent with contract language$ I*!e successfully used &simplistic& allocation routines on pro+ects that were a lot more money than we*re tal.ing a#out hereand I was successful #ecause they were percei!ed #y the parties as fair enough$
he &#in& calculation is a collection of a!erages of a!erages of standard conditions (whate!er they might #e) that is comple7 enough to dri!e an e7perienced engineer to start this thread$ It is no more &accurate& than allocating #ased on heated area or num#er of employees- +ust harder$ =a!id 2eos (Mechanical)
12 8e# %6 :1
MintJulep- das%D: I thin. you are #oth right$ In!oicing your tenants for gas supplied #y the utility may #e considered an infringement on the utilityYs franchise rights$ If you want your tenants to pay for their energy consumption- you would ha!e the utility meter each tenant separately such that the tenant #ecomes a customer of the utility$ Randlords usually get around this #y including in the monthly rent an amount t hat would co!er the a!erage monthly utility e7pense$ It is then appropriate to estimate the energy usage of each rental unit and #ase the rental rate accordingly$ daeCt2 (Mechanical)
12 8e# %6 16:%
;eing that it is a commercial #uilding- there is a good chance that one or #oth tenants ha!e amny operatiing periods with the doors open or high fresha air input- which would gorssly s.ew the accuracy of a calcualtion that assumes the doors and !ents are closed$ 8or the sie heaters in!ol!ed- why not install 2 custody meters> Er retro,t the heaters with gas cosnumption meters that are recognied #y the pro!incial authority> genieconseil (Mechanical) (OP)
13 8e# %6 1%:%?
han.s- I*m glad and greatfull to see such response to my pro#lem$ ;ut ,rst of all to clear things the 2 air ma.e up units are for the same tenant (the larger area)$ If you read my "uestion carefully you will see that it is stated as such$ I realise that many factors are implicated in the solution(eB of heater- modulation of #urner proportional to the demands.edual- inside temp re"uirements- scheduals- and I lea!e alot more factors out that inuences the calc) #ut since oLcially the #in method is recognied and #reay descri#ed in A'4@A then science #ecomes the lead hand and may#e some logic in court$ @<A'/< than.s for the lin. to an e7ample it is usefull #ut some !alues calculated are not clearly identi,ed$ I*m #lo.ed in my calc$ =o you ha!e more resourses$ han.s a lot for your response It si !ery appreciated <enieconseil P$ilrock (Mechanical)
13 8e# %6 13:2%
Commercial heating and cooling loads are typically diLcult to predict accurately$ If your client truly wants to #e fair to the tenants- he must meter their consumption separately$ !en if there is an administrati!e pro#lem with the utility company doing this- there should #e commercially a!aila#le meters which could #e installed downstream of the utility meters- which could #e used to determine tenant usage$ If you ha!e faith in the accuracy of #oth the utility meters and the downstream meters- you could get away with metering only one of the tenants separately- and assume the other tenant is using the #alance of the energy$
genieconseil (Mechanical) (OP)
13 8e# %6 1:1
I totally agree with measuring seperately and that was my ,rst comment to my client #ut it is not the case at the moment and #efore he can accurately diBerentiate he will ha!e to measure for a year- this is o#!ious$ ;ut he needs to get a good appro7imation now and only two methods e7ist which are the degree days method and the #in method$ My pro#lem is that I dont ha!e good e7amples of how to use them$ 8orget metering for now I need to calculate$ than.s <enieconseil 2eos (Mechanical)
1D 8e# %6 :32
genieconseilChec. out Appendi7 ;: @A@R<B 9OA=MP7OA >AD 9O=7 >A>5B== in the attached lin.$ $ttp%&&interscope.doastatencus&<uidelines&lcca&599>.4Manualdoc mic$aelr0;" (Mechanical)
3 Mar %6 D:D1
<enieconseil;in method is #ased on temperature groups and typically includes all hours annually of data for a gi!en city$ 0ou need to #rea. out the temperature #ins #ased on the operating hours$ ;in Ma.er (type &;in Ma.er Fro& into <oogle) pro!ides this capa#ility$ /e7t thing how are the units controlled> Are they 1%%O EA> Are they constant !olume> 5hat is the discharge air temperature setpoint during heating> Is there a 4= reset se"uence> All of these factors will impact how you perform your calculations$ 0ou can calculate sensi#le energy using the following e"uation 1$% ] C8M ] (emp I/ emp EH)$ C8M- of course- is the air ow through the unit$ emp I/ is the temperature of the air #efore the heating coil and temperature EH is the temperature of the air after the coil$ 0ou can see now how .nowing the operating conditions of you system$ If your unit is 1%%O EA and constant !olume with a discharge temperature setpoint of say %8- then the calc is easy$ 0ou get your #in ta#le setup from ;in Ma.er and set up a calculation in 7cel as follows: 1$% ] 2-%%% ] (%8 #in temp) 1$% ] 16-%%% ] (%8 #in temp) hen pull down the calc through the range of temperatures during Eutside Air conditions where heating is #eing pro!ided$ he e"uation will pro!ide you with !alues in ;tuhr$ 0ou will then need to multiply these !alues in each #in #y the hours in each #in to get ;tus and then con!ert into appropriate heating energy units$ Also- don*t forget the eLciency of the heating system$ he calcs you will ha!e performed is the energy to heat the air$ 4ow much /< is re"uired to heat that air$ 0ou will re"uire appro7imately 2O more /<- assuming %O eLciency$ /ow- if you ha!e minimum EA and are mi7ing with return air you will need to modify your calcs$ Also- if it is a 9A9 system$$$ another le!el of comple7ity$ Another thing to loo. at is utility #ills$ If these units are the only source of heating other
than domestic heating loo. at a couple of years of gas data$ 'hould loo. li.e a nice #ell shaped cur!e if you graph it #y month with a pea. in the 5inter and minimum use in the 'ummer$ a.e the a!erage of the cooling months (assuming that no heating is performed during the cooling months) and multiply #y twel!e$ his should #e a good estimate of the domestic hot water load$ If the only remaining load is heating then su#tract the calculated domestic heating load from the total utility (.eep your units straight) and that will gi!e you your heating load$ If the two units are the only other sources of /< use and the units are controlled in the same manner- then +ust pro!ide a proportionality constant for each unit 61O and 3?O$ his will pro!ide for a "uic. and dirty calc andor a sanity chec. against your #in calcs$ <ood Ruc.Michael @osen#erg 3 Jun % ?:%6 4i and greetings to all of 0ou$ As e new one I ha!e a serious pro#lem: 1$ I ha!e 2 systems to compare: he one is 1%%O fresh air (input)- with #uild in coil reco!ery energy loop on e7it side$ he second is a system with 2%O of fresh air with no energy reco!ery de!ice on it$ 4ow to ma.e a decision which one is a #etter (this 49AC system are two diBerent solutions for our pharmaceutical factory with class 1%%$%%%)$ I*!e searched thru this forum- and ,nd something- #ut as a new- i did not understand your units (american !s euro)- and the way you calculate the diBerence #etween this systems$ he only thing I ha!e to do is to calculate (formulas and suggestions)energy needed for heating (cooling) input air- to ma.e a constant temperature of app$ 22 degrees centigrades- and @4 of %O$ Ma7imum summer and winter temperatures are 2% and SD% degrees centigrades$ Also I*!e =R F'0C4@EM@IC A/AR0[@- and tried to calculate it- #ut it do not include the energy of energy loop$ I ha!e to mention that this is only for this time and no need for further comparement than this one$ Any help is a !ery #ig help to me$ han7 in ad!ance$ set$uM@ (Mechanical)
3 Jun % 11:26
hi i dont thin. that 1%%O fresh air is needed for the class 1%%%%% area$#ecause going for 1%%O will increase your cooling load$ 9$ris9onley (Mechanical)
3 Jun % 13:1D
@egardless of how you deli!er outside air- the system will re"uire the same amount of energy to cool and heat the air$ he only way to decrease this energy is to use heat reco!ery$ If your space re"uires 1%%% cfm (cu#ic feet per minute) of outdoor air then it will ta.e ?-2%% ;tuhr to heat that air from 2% to % 8$ If you mi7 1%%% cfm of EA with ?%%% cfm of
return air- it will still ta.e 1%-%%% ;tuhr of additional energy to heat the air #ac. to % 8$ 5hich system is #etter> ell us more a#out what you are trying to do- use whate!er units you feel comforta#le withG we can con!ert$ 4ow much air or air changes are you trying to do$ Are you heating or cooling with the air- or is this +ust for !entilation$ GH>9/8 (Mechanical)
D Jun % %:%
5hy are you trying to use a 1%%O fresh air and then using a heat reco!ery system > Is 1%%O fresh air a process re"uirement > As ChrisConley has said- units are not a pro#lem we can con!ert$ 49AC6 friartuck (Mechanical)
Jun % :16
he amount of fresh air will depend on the occupancy and the process$ generally you can recirc a lot of the air to reduce the energy costs$ his is much more eBecti!eeLcient than ha!ing a heat reco!ery loop and 1%%O fresh air$ En a lot of clean room pro+ects we ha!e seen- the fresh air is only a#out 1%O to 1O$ I*m not sure how ChrisConley wor.s out that the f resh air component does not aBect the energy use$ If you recirc 1%%O- then the load is simply the heat gain from the space$ If you #ring fresh air in- you ha!e to add this component- which could #e far greater than the room load$ (hence recirc air is a good method of reducing the o!erall load)
8riar uc. of 'herwood G@9 (Mechanical)
Jun % 1?:3
Another thing to consider in this is ,lter loadings$ Although only trying to maintain Class 1%%-%%% standard- ,ltration of return air may #e cleaner- than ,ltration of outside air$ Ef course this depands upon the process in the room$ =usty processes wouold #e #etter with once through$ nergy usage will #e a large part of the design choice- howe!er also consider other aspects of the operation such as ,lters- replacement or cleaning- o!erall facility air ow re"uirements and pressure gradients- etc- etc$ @egards Gutton;engIpickno*lcomau Mar. 4utton
akaodr2 (Industrial) (OP)
6 Jun % 1:%
8irst at all$ ha7 for e!eryone for a "uic. answer$ 'econd: 1$Chris Conley: I don*t thin. that it is the same colingheating energy that we are using for
the #oth systems$5hy> ;ecause I thin. energy needed for 1%%O fresh air is not the same as the one for 2%O$ 2$EP- let*s say ( E ARR): I need 1%% metercu#icminute for all rooms$ emperature for rooms is 2 degrees C- with %O @4$ a$ he 1%%O fresh air system: I need a load of 1%% metercu#icminute for all rooms$ 5hat is needed energy (in .5) to ma.e needed air- if we suppose that outdoor air is with 1 degrees C- thru winter > And needed energy in summer- with outdoor air of S36 degrees C > Also a use of coil type of energy reco!er is included in a system of e7saust air from the factory$ #$ he system with 2%O income and %O recirculating air$ he same calculations are !alid (1%% mccminute for rooms- 1C in winter and S36C in summer)$ I need +ust fact (formulas) how can we calculate it #ut fast$ Just ha!e to mention that this is a need for deciding what type of system to use in our new pharmaceutical factory- and the ,rst criteria is economic side of energy used for #oth systems- and the second the maintenance of the system$ he factory is class 1%%%%%$ Also- results using Fsychrom program from Mc"uay shows me that needed energy isn*t same$ ;ut this is +ust for a dry#ul# type$ 5ith energy reco!er I do not .now the results$ <reetings$ 9$ris9onley (Mechanical)
6 Jun % 21:2D
8riartuc.I didn*t say that the fresh air component didn*t ma.e a diBerence$ 5hat I said was that regardless on how you deli!er 1%%% cfm you ha!e to heatcool it the same amount$ If we are mo!ing air to pro!ide a le!el of ,ltration- or course it will #e less e7pensi!e to pro!ide 2%O outdoor air$ I*m comparing a =EA' (=edicated Eutdoor Air 'ystem) with heat reco!ery to a recirc system with the same fresh air re"uirements$ ,uark (Mechanical)
Jun % 2:%
he #est heat reco!ery systems operate at an eLciency of ?%O$ 'o- you ha!e to cough up 1%O more energy cost$ 8urther- for room pressuriation and fresh air re"uirement- you ha!e to #leed oB re"uired "uantity from rooms either if you go with recirculatory system or fresh air system$ 8or a conser!ati!e comparision you ha!e to deduct this energy component also(i$e appro7imately 1%O !olume rate of air is not a!aila#le for energy reco!ery)$ @egards-
akaodr2 (Industrial) (OP)
Jun % 2:12
E: ChrisConley Ret*s do this pro#lem together: as you .now- 2 system are in !aluation$ he pro#lem why I*m as.ing a formula (a simple one)- to calculate input energy is that &some#ody& is telling me that using 1%%O fresh air is cheaper than using 2%%O
com#ination$ he 1%%O system ha!e in a)input side:inta.e section- ,lter 8- @un around system reco!ery (heating) with eB$ of 3%$DO- Centrifugal fan #elt dri!en- diBusor- ,lter 413 and sound attenuator$ #)output side: sound attenuator- ,lter 8- run around system reco!ery (cooling)- and outlet section with centrifugal fan #elt dri!en$ I was told- that- if I*m using this type of 49AC solution- with com#ination of cooling plant with air compressors !entilation (dry)Correct me a#out my e7planation of cooling plantbmy energy sa!ings will #e #ig- according to <MF re"uirements we are loo.ing for$ he controlled !alues are temperature- humidity and pressure$ According to - and @4 of the output- also including outside conditions- the system needs (do not needs) some additional air preparations of inta.e air$ he out ta.e air is not needed any more- #ut for colleting of waste energy$ he point is- comparing to recirc system- where additional preparation of out ta.e air is a must (,ltration- dehumidi,cation- heating- cooling)- the control points are much more then the other- I will sa!e money in start and the pay#ac. is much shorter$ Rower energy costs > In a future there is a chance to upgrade do class 1%%%% with only adding terminal 4FA ,lters and nothing more> o help 0ou- the conditions of the placement of the plant is on around D23 m (13?1 ft- with appro7imate 6O of sunny days- and temperature !ariations from 2% to SD% C$ han7I*m +ust confused$ ,uark (Mechanical)
Jun % 2:1
=idn*t get what you mean #y cooling plant with air compressor !entilation$ /e!ertheless*some#ody* is playing wrong$ akaodr2 (Industrial) (OP)
Jun % 2:32
o: Vuar. E.- I .now that the #est heat reco!ery systems wor. at ?%O eB$- #ut the eB$ of included reco!ery system is around 3%O (technical factory written info)$ It*s ,lled with ethylen- with med$ow of 3$2 ls- medium in 1D$D6C- med$out 1$D2C$ Air in 1%C- air out %$3DC (this is for heating side)- with 111 Fa pressure drop$ capacity 233$2 .5$ Medium press drop D$3D .Fa$ he cooling side is: air in 3C- D%O 4um$- out 16$%1 with O hum- air pressure drop 16 Fa- capacity 66 .5 '4@$ Medium ethylen- ow 33$2? ls- med$in C- med$out 1%Cmedium press drop 32$? .Fa$ VHE=: &8urther- for room pressuriation and fresh air re"uirement- you ha!e to #leed oB re"uired "uantity from rooms either if you go with recirculatory system or fresh air system$ 8or a conser!ati!e comparision you ha!e to deduct this energy component also(i$e appro7imately 1%O !olume rate of air is not a!aila#le for energy reco!ery)$& I do not understand well this: 0ou mean that the "uantity of air ta.en from rooms in #oth situations is the same- #ut additional processing of recirc air is a must in system 2%%O$ It is EP- I .now that- #ut still the "uestion is : how much energy will #e used in #oth
situations e7pressed in .5 (let*s say for 1%%%% m3h) in #oth ways: with 1%%O fresh airand with 2%%O recirc air system> han7$ ,uark (Mechanical)
Jun % 3:%
I will try to simplify the things$ 8irst- for room pressuriation- say- you may re"uire 1%O of air owrate$ 'o this will #e directly e7hausted from the rooms and you won*t get it #ac. in the A4Hs$ his is compensated #y fresh air inta.e in the second cycle$ 5hen we consider 1%%O fresh air system- you will ha!e only ?%O appearing at t he heat reco!ery unit$ Considering 3%O eLciency of the heat reco!ery system- you need not cool or heat 3%O of ?%O of total air ow(or 2O of total air ow)$ 5hen you use a recirculatory system with 1%O fresh air- you should coolheat 1%O !olume rate from am#ient conditions to coil A=F and ?%O from room condition to A=F$ 5ith a heat reco!ery unit- it is (1%%2) 3O !olume rate from am#ient condition to coil A=F$ 'o- compare 63O(i$e3O1%O) owrate with am#ient condition to A=F !s ?%O owrate with room condition to coil A=F$ @egards akaodr2 (Industrial) (OP)
Jun % 3:1D
E: "HA@P Cooling plant (Cold water 1%C) from Carrier8rance type 3%<Q %23 or 3%4QC %% 3$ Air cooled li"uid chiller capacity 271%%%.5$ he coorect name is: 'crew compressor watercooled Ri"uid Chillers and aircooled li"uid chillers$ his is what a meant of cooling plant$ greets akaodr2 (Industrial) (OP)
Jun % 3:D2
o: Vuar. E.- I*ll "uote your message and do it step #y step: &8irst- for room pressuriation- say- you may re"uire 1%O of air owrate$ 'o this will #e directly e7hausted from the rooms and you won*t get it #ac. in the A4Hs$ his is compensated #y fresh air inta.e in the second cycle$& 8irst: his is for recirculating system or it is for #oth systems> Ret*s say: 1%%%m3h 1%O ?%% m3h- right > &5hen we consider 1%%O fresh air system- you will ha!e only ?%O appearing at the heat reco!ery unit$ Considering 3%O eLciency of the heat reco!ery system- you need not cool or heat 3%O of ?%O of total air ow(or 2O of total air ow)$ &
E.- if we suppose that a#o!e is corect and for #oth systems: ?%% m3h 3%O 2% m3h of total input ow to heat with reco!ery unit- right > he other 3% (or 63%) m3h ha!e to #e heated with heatingcooling unit- o. > 2% m3h reco!ery unit 3%(63%) m3h heating cooling unit &5hen you use a recirculatory system with 1%O fresh air- you should coolheat 1%O !olume rate from am#ient conditions to coil A=F and ?%O from room condition to A=F$& In this case I need 1%% m3h to heat from outdoor air- and another ?%% m3h to heatcold from room air > 5hat is A=F > &5ith a heat reco!ery unit- it is (1%%2) 3O !olume rate from am#ient condition to coil A=F$ 'o- compare 63O(i$e3O1%O) owrate with am#ient condition to A=F !s ?%O owrate with room condition to coil A=F$& I*m stuc. here at the last point :) 4elp$ 0ou mean: 2% m3h heated with reco!ery coil and 3% m3h heated with heater in h!ac- and for secure reason it is lowered to 63O of outdoor air> 0ou mean to compare 63O outdoor air to ta.e heated and ?%O of recirculated air to ta.e heated > If I misunderstood correct me$ <reets akaodr2 (Industrial) (OP)
Jun % D:%3
I*m stuc.$ Can some#ody +ust say: 0ou*ll need this and this formula- or this program (free if possi#le :) )- and no fear$ Jo# is done in a minute$ greets akaodr2 (Industrial) (OP)
Jun % :%
Er +ust using informations a#o!e for my pro#lem (23 messages a#o!e this)- and help me for right solutions$ he &catch& is in the price of #oth systems- which one to #uy- and in my opinion is that in the system with 1%%O fresh air- must #e something that I*m missing- which inuence of the lower costs of whole 49AC solution$ hat*s why I*m as.ing for help- to do a fast calc of energy used in #oth system- for same "uantity of air- for cooling and for heating$ In fact- this #ecame so confusing- that I do not .now where to start and where to end$ I*!e tried lot of programs (freewareshareware-demo #ut no use) to ,nd out the right one- where I can enter needed air in m3h- to choose one- then the other system- and to read out and compare the gi!en results (usage of energy in .5- for cooling and for heating)$ 'o- if some#ody ha!e this type of program (it is doesn*t matter whene!er I .now it or not)let +ust enter needed info which can #e ,nd in messages a#o!e- and gi!e me a simple answer: In 1st system you*ll need $$$.5 of energy for heating and cooling- and in 2nd system you*ll need $$$.5 of energy$ I*m not as.ing nothing more and nothing less$ Just to mention that this is my ,rst contact with 49AC pro#lem- solutions (may#e constructions) and simply I can*t manage as good as you can here- e7periensed engineers$
I hope 0ou*ll understand in what .ind of trou#le I am :) <reets,uark (Mechanical)
Jun % :12
'ay- you ha!e 1%%%cmh re"uirement$ 5ith fresh air 8irst cool 1%%%cmh from am#ient condition to coil condition(or Apparatus =ew Foint)$ 1%O is wasted in #oth cases- i$e 1%%cmh$ 'o ?%% cmh is present for reco!ery$ Eut of this you can a!ail 3%O of heat- which is a#out 2%cmh$ his is as if you need not condition this much owrate from am#ient to coil condition$ 'o what you ha!e to treat is 1%%%2% 3%cmh$ (1) 5ith recirculation 1%%cmh air is at am#ient condition and ?%%cmh is at room condition$ 'o you ha!e to cool 1%%cmh from am#ient condition to coil condition and ?%%cmh f rom room condition to coil condition (2) 8or your comparison 1%%cmh fresh air treatment is common$ 'o deduct this from #oth options$ 'o- the fresh air option #ecomes treating (3%1%%)63%cmh from am#ient condition to coil condition and recirculatory system option #ecomes treating ?%%cmh from room condition to coil condition$ he formulae 41 is am#ient air enthalpy in #tul# 42 is room air enthalpy in #tul# and 43 is enthalpy of air at coil e7it in #tul# 'o- fresh air energy(for comparision) is D$7(4143)73%$cfm(i$e 63%cmh) (3) @ecirculation air energy is D$7(4243)72?$2cfm(i$e ?%%cmh) (D) he lower !alue of (3) and (D) is your ultimate choice$ 4ope I cleared the issue$ @egards,uark (Mechanical)
Jun % :2?
En a second reading- you seem to ha!e grasped what I said perfectly e7cept 63%cmh thing- which I cleared in my third post$ @egards akaodr2 (Industrial) (OP)
Jun % 6:16
Eh- than. 0ou Vuar.- !ery much$ his is a real thing$ 7cept for one thing ("uoted): &41 is am#ient air enthalpy in #tul#
42 is room air enthalpy in #tul# and 43 is enthalpy of air at coil e7it in #tul# 'o- fresh air energy(for comparision) is D$7(4143)73%$cfm(i$e 63%cmh) (3) @ecirculation air energy is D$7(4243)72?$2cfm(i$e ?%%cmh) (D) & he !alues for 41- 42 and 43 where can #e get > specially in #tul#$ Also- isn*t any changes if in formulae are used diBerent !aluses of units (e7$ #tul# and cmh) > <reets-
akaodr2 (Industrial) (OP)
Jun % 6:?
o Vuar.: EP- I did some calc: he !alues of 414243 are ta.en from Fsychrometric analyer- for altitude of D23 m$ (If they are wrong- correct me)$ Input: 41: D%C%O@4- e"ual of 1%D$%%D .J.g 42: 2C%O@4- e"ual of 1$631 .J.g 43: 22CD%O@4- e"ual of 3?$66D .J.g 1%%O fresh air: D$7(1%D$%%D3?$6D)763%123$1 (.J]m3)(.g]h) ?%O recirc air: D$7(1$6313?$66D)7?%%DD1?-3 (.J]m3)(.g]h) Is is the correct !alue a#o!e > 5hat gi!es (.J]m3)(.g]h)precisely > he 2nd: 5hat happens if I*m heating the air > I got negati!e !alue for 1%%O fresh air: Eutdoor temperature is: 1%C3O@4 D$7($6%%3?$66D)763%1366%$1 (or may#e I ha!e to to opposite process to su#stract from 3?$66D !alue of $6%%)> Anyway- I still can*t ,nd the &catch& in solution of 1%%O fresh air$ simply- .nowing people that are wor.ing on their solution- there must #e some tric. in their solution of 49AC$ <reets-
,uark (Mechanical)
Jun % 1:%3
he other !alues seem to #e o. #ut not the 43- for the coil outlet condition should essentially #e saturated(or near to saturation)$ hat means the @4 should #e nearer to 1%%$ 'econdly- 22C coil outlet temperature is "uite high e!en for comforta#le cooling application$ If your area deals with any of li"uid in+ecta#les- granulation- coating or capsulation areas- the moisture load will #e a #it high$ My e"uations can*t #e used with metric units$ 4owe!er- you can download an e7cellent unit con!ersion program *Hconeer* written #y Patmar- a fellow mem#er of engtips- from the following lin.$ $ttp%&&***katmarsoft*arecom&uconeer$tm
0u should also consider heat gain in return ducting when you deal with recirculatory system$ ;ut as far as the primary comparision is concerned- the procedure is o.$ he whole idea is to show that fresh air systems always pro!e you costly$ @egards akaodr2 (Industrial) (OP)
Jun % 2:2% 1 Apr %6 :D
4ello- INm new in this forum and ha!e a "uestion$ I need to calculate de cooling load of an area that demands 1%%O outside air- and to #e honest- I donNt Pnow how to do it$ here are some "uestions that comes to my mind: 5hat should #e the lea!ing air temperature> he loads produce #y people- lights- wallsetc that we estimate in a recirculating system- should #e calculated in this .ind of system too>$ I really apreciate some help$ (INm from =ominican @epu#lic- so e7cuse my english)$ han.s$ *illard3 (Mechanical)
1 Apr %6 1D:3
8or the outside air: 'ensi#le cooling CH 8MI/ 7 1$% Q outside AI@ =RA t ;H4@ '/'I;R Ratent cooling: fu ftmin 7 %$66 7 (delta moisture in grainsl# from psychometric chart) #tuhr latent 'ensi#le load S latent load total cooling load for outside air In general- cold air is deli!ered at 8 dry #ul# and wet #ul# (ie- saturated) ;uilding solar loads- lights- e"uipment and people loading should #e included in your calculations$ 0ou should pro#a#ly hire a Mechanical ngineer to do this as he is familiar with it and you aren*t$ *aross (lectrical)
1 Apr %6
1:3% 4ello willard3 I ha!e met some intelligent dedicated engineers in the third world$ Hnfortunately- the training and educational systems there are not up to ,rst world standards$ pa#lo2D1% has recognied that he doesn*t ha!e the information that he needs to sol!e his pro#lem and has wisely gone loo.ing for good ad!ice$ I than. you on #ehalf of pa#lo2D1% for your .ind help- #ut I wish to gently point out that your last suggestion may not #e feasi#le$ pa#lo2D1% is "uite possi#ly the #est mechanical engineer a!aila#le$ 0ou may ,nd it rewarding- willard3 to mentor pa#lo2D1% and help him to #ecome a #etter engineer$ 8rom the tone of his post I #elie!e he is intelligent and dedicated$ 4e recognies shortcomings in his education and is trying to impro!e himself$ 0ou ha!e already gi!en pa#lo2D1% the #asics- go a little farther and help him through his calculations and you may ,nd that you en+oy it$ respectfully Mintulep (Mechanical)
2 Apr %6 1:33
pa#lo a.e a loo. at this site: $ttp%&&***engineeringtool6o!com&$ac'systems'tJ.3$tml ,uark (Mechanical)
2 Apr %6 23:13
Fa#lo he room lea!ing air condition should always #e the room condition$ Calculate heat load as per the general rules$ Flot the room condition and am#ient condition state points on the psychro chart$ =raw a line with a slope of '4@ from the room condition to the saturated cur!e$ his is your dew point condition$ Join the am#ient condition state point to the dew point$ he total load on the coil will #e the mass ow rate of air times the enthalpy diBerence #etween the am#ient condition and the dew point condition$ In some cases- the '4@ line #ecomes an asymptote to the saturation cur!e$ In this case- assume some ar#itrary dew point and add reheat into the process$ he lin. #elow gi!es you description and details of many psychrometric processes$ 4a!e a loo. into it$ $ttp%&&***coolitco2a&psyc$art&
5aross/ice thin.ing and I feel that is the whole idea #ehind these forums$ pa6lo.;14 (Mechanical) (OP)
3 Apr %6 :2
han. you all of you for your help 4ere comes another "uestion- how can i calculate mass ow- i mean- i .now the !olume of air in the room- #ut how do i .now how many times do i ha!e to recirculate it
5=> (Mechanical)
3 Apr %6 12:11
correct me if I am wrong #ut I am assumming you meant 9olume ow instead of mass ow$ ;elow is something I gra##ed oB a we#site descr#ing what I thin. will #e of help to you$ Ene air change occurs in a room when a "uantity of air e"ual to the !olume of the room is supplied andor e7hausted$ Air change rates are units of !entilation that compare the amount of air mo!ing through a space to the !olume of the space$ Air change rates are calculated to determine how well a space is !entilated compared to pu#lished standards- codes- or recommendations$ Air changes per hour (AC4) is the most common unit used$ his is the !olume of air (usually e7pressed in cu#ic feet) e7hausted or supplied e!ery hour di!ided #y the room !olume (also usually e7pressed in cu#ic feet)$ Airow is usually measured in cu#ic feet per minute (C8M)$ his is multiplied #y 6% minutes to determine the !olume of air deli!ered per hour (in cu#ic feet)$ AC4 (C8M Q 6% minutes)(room !olume in cu#ic feet) pa6lo.;14 (Mechanical) (OP)
3 Apr %6 12:33
5hat i want to .now is how can i determine the C8M needed for the area$ *illard3 (Mechanical)
3 Apr %6 12:3?
Fa#lo: he sensi#le heat ratio and cooling load will dictate the air changeshour and is the solution to the pro#lem$ ry not to confuse the cause for the eBect$ In my climate- ie- D2 deg latitude and 3 deg longitude- in a frame#uilt- insulated #uilding with appro7 2%O glass and * ceilings- cfm !aries from 1 cfms"uare foot to 3 cfms"uare foot of oor depending upon internal loading- ie- num#er of people- lightinge"uipment loads and !entilation loads$ ;H load !aries from 3%% #tucu foot e7clusi!e of internal loadings$ 5e ha!e #uilding codes in /ew 0or. that ma.e the range of these num#ers pretty small$ 0our latitude is 1 deg and longitude is 6? deg- so solar loading and air temperatures will #e !ery diBerent than /ew 0or.$ I am also sure that you construction materials and methods are diBerent than ours so #uilding mass and etc will #e diBerent 0ou should get a copy of A'4@A 8undamentals 9olume(American 'ociety of 4eating@efrigeration and Air Conditioning ngineers)G it contains answers to all the "uestions you are as.ing$ 0ou ha!e access to the we#- so &<oogle& A'4@A$ 0ou can also use rane software to calculate heatingcooling loads- #ut you need ,rst to understand the input$ A'4@A will #e a #ig help with the input$ *illard3 (Mechanical)
5rong data:
3 Apr %6 12:D2
;H load !aries from 3%% #tucu foot e7clusi!e of internal loadings$ @ight data: ;H load !aries from 3 #tucu foot e7clusi!e of internal loadings$ pa6lo.;14 (Mechanical) (OP)
3 Apr %6 13:1D
E.- (willard3) the ,rst formula you ga!e- me was a !ariation of the ,rst law of thermodinamics- another way to put it is using the mass ow times the enthalpy diBerence #etween am#ient condition and dew point condition- #ut in #oth cases i need a ow of air in terms of mass or !olume- and there is my confusion$ he other "uestion is : do i need a U8 lea!ing air temperature in a system using 1%%O outside air>$ I ma.e this "uestion #ecause i assume that in this .ind of system- there is no mi7 #etween the air in the room and the air from outside to achi!e a medium temperature- #ecause e!entually the total !olume of air in the room will #e e7hauted and replace for a new !olume from the outside- so i was thin.ing that the lea!ing air temperature should #e the temperature of the conditions i want in the room- letNs say 3U$ 5=> (Mechanical)
3 Apr %6 1:%3
I am going to ta.e a sta# at this$ =esign condition: Eutside air temp (=;5;) ?2868 (%$O mean summer temp Ros Angeles) 'upply air temp 8 Assumptions: =imension of space 6%*(R)76%*(5)71*(4) 2% people 7 2% #tuhr %%% #tuhr 2$ wattssf lighting ?%%% #tuhr Assume -%%% ;Hhr e7terior loads AC4 (Air change per hour) 1% therefore C8M AC4 7 9olume 6% (1% 7 D-%%% cu ft)6% ?-%%% cfm 'o ?-%%% cfm is re"uired to e7haust the room 1% times per hour$ /ow to determine the load on the cooling coil: Cooling coil load 1$1 7 C8M 7 (1 2) 1$1 7 ?-%%% 7 (?2) 366-3%% ;Hhr 'umming all the loads: 366-3%% #tuhr S %%% #tuhr S ?%%% #tuhr S -%%% #tuhr 3-3%% #tuhr or 32 tons$ 'o to select a unit to suit all the a#o!e loads- I will select a 3 ton unit$ his is +ust a generic e7ample$ here are many other loads that I am not incorporating$ 4opefully this can get you in the right direction$
pa6lo.;14 (Mechanical) (OP)
3 Apr %6
1:D1 E.- so far- all the things that had #een told here- i already .new it$I thin. i-m not as.ing the right "uestion- so here i go- how can i determine the total cfm that is re"uired to pass trough a cooling coil in a system that re"uires 1%%O outside air- or how do i .now how many changes of air do i need$ 5=> (Mechanical)
3 Apr %6 1:%1
he C8M re"uired is calculated #y the engineer$ ypically for a la#oratory the AC4 is 61 AC4$ A restroom is D AC4$ (these are recommended num#ers we use in our oLce$ hese are not a standard$) =oes that help>
pa6lo.;14 (Mechanical) (OP)
3 Apr %6 1:3
o.- here is the pro#lem a loc.er room Area 3% s"ft height 1%ft 3 persons in the room what will #e the diference in my load calculation if the system is 1%%O recirculate air or 1%%O outside air$ 5=> (Mechanical)
3 Apr %6 2%:D
Air change method Assumptions: 'ummer design condition ?28638 Indoor design condition 28 Interior location therefore no e7ternal load Roc.er @oom AC4 1 (again- this is our oLce standard) 9olume: 3% sf 7 1%* 3-%% Feople load sensi#le 2% #tuhperson (1-2%% #tuh) (+ust got done wor.ing out) Feople load latentperson 1% #tuh (3 #tuh) Righting load 1$ wattssf (32 #tuh) C8M 1 7 3-%% 6% - cfm (lets say ?%%% for simplicity) 1$ 8or 1%%O outside air: Cooling coil load 366-3%% #tuh otal sensi#le load 366-3%% S 32 S 1-2%% 3?-2 #tuh or 32$ tons$ 2$ he diBerence will #e su#stantial #ut Roc.er rooms are ne!er 1%%O recirculated$ here will always #e some amount fresh air #rought into the space$ he air change method is a simple method of getting an appro7imate idea of what sie unit is re"uired$ In loc.er room applications many times they are heated and !entilated only$ And Ma.eup air is usually always re"uired to achie!e proper air #alance$ 4ope that clears up some "uestions you may ha!e$ <R cme (Mechanical)
Apr %6 16:D1
a rule of thum# $$$$$ 1% cfmton for a preliminary siing load ,nal psych chart analysis on =;mean5; per ashrae geographic data don*t forget fan heat gain /.$og (Mechanical)
2D Apr %6 12:2%
Ene other thing must #e ta.en into account$ If you are planning on using a pac.aged system (ie$- rooftop unit)- you must consult with the manufacturer$ As a general rule- (at least according to my local reps) a pac.aged unit is only capa#le of accepting appro7imately 23%O of the total airow in the form of unconditioned outside air$ Any system you use should #e discussed with you local rep$ 0ou should also re"uire them to also pro!ide you with any documentation for information that may diBer from you &sound engineering +udgement$& 80I- A'4@A list the design condtions for =ominican @epu#lic cooling- in the %$DO rangeas ?1% d8 d#w#$ lilliput1 (Mechanical)
2D Apr %6 12:D?
62hog is right$ Chilled water systems are recommended for 1%%O EA applications$ 4owe!er it is also possi#le to use multistage pac.age =Q AC units #y recirculating a portion of the supply direct to the return and supplying to the room only the C8M
e"ui!alent of the EA handled$ 8or e7ample- if the load for say D%%% C8M 1%%O EA is 2% tons$ Hse a 2% ton unit say nominal %%% C8M- #ut use D%%% C8M EA- %%% C8M total 'AD%%% C8M recirc direct #ac. to A4H and D%%% C8M supply to the room$ 'ol!e for the mi7ed air conditions of the EA and recirc air to get cooling coil entering air condition$ Interpolate performance from ta#ulated date$ 'ol!e for cooling coil lea!ing air temperature$ =etermine fan and duct heat gains and deduct from ta#ulated capacity to get net capacity$ t$oot2 (Mechanical)
3% Apr %6 23:2
8irst you need to compute the total heat load $li.e num#er of window- sie of doors what materials used in the #uilding 5all$ 0ou may ,nd the !alue of each material in Ashrae hand#oo. or Mechanical hand#oo.$0ou may also use Manual J method- a software for load computation$ his wil guide you step #y step method$ sloyal (Mechanical)
1 Jun %6 1:%2
4ere*s my 2 cents$$$ ;H4 D$ 7 cfm 7 =elta 4 4psych chart enthalpy McVuay W rane as well as others ha!e downloada#le Charts that should gi!e nthalpy conditionsI prefer the straight edge on a paper graph (calcs for the ,les) My design conditions are ?d#3w# nthalpy 36$ indoor cond$ d8 %O 4umidity nthalpy 2$% or %d8 %O 4umidity nthalpy 26$3 8or ease of use I call it a d4 of 1% ;tuh cfm 7 D$ 7 1% If I ,nd I need a 2% on system- I*ll #e !ery careful to select a coil on face !elocity- to a!oid freee upas well as Ratent W sensi#le capacities$ Interlaced coils with multiple stages (more is #etter) wor. #est$ I a!oid conditioning the space with this system as it would re"uire a larger system$ I prefer deli!ering room temp air W ha!ing a seperate recirculating system for space loads$ I may e!en deli!er a portion of the &tempered outdoor air& into the return of the space conditioning system- Fossi#ly 1%%O if the cfm matches- with a return setup for independent operation$ My winter design is 2%d8 so any outdoor air is heated W it*s usually done with a direct ,re MAH$ he products of com#ustion in this air has recently #ecome an issue- especially on units recirculating any inside air$ 5ith these design conditions- I would loo. at incorporating a 4eat @eco!ery 9entilator$ 'omething li.e a @enewAire with latent W sensi#le e7change can sa!e a #oatload on the aforementioned <as MHA w2%ton coil$ 7h air conditions (i$e$ dust- oil- etc$$$) might prohi#it a heat e7changer altogether$ good luc. sl+
Borkman (Mechanical)
1 Jun %6 1?:3
Ene thing not to o!erloo. is that the latent load is going to #e rather high- gi!en that this is a loc.er room with showers$ A recirculated system*s latent loads at the coil could #e higher than the E'A senario$ I would loo. up latent load and air change recommendations in the A'4@A 8undamentals 4and#oo.$ It may ma.e more economical sense to go with 1%%O E$'$A$ and .eep my discharge air at say 6% 6 degrees afterall it is a loc.er room$ 4ey I ha!e enough pro#lem with shrin.age$ GX) <ood luc.- with this much ad!ise how could you go wrong> I*m not a real engineer- #ut I play one on $9$ A$J$ <est- 0or. Int$ 9ore7ec$41 (Mechanical)
D Jun %6 13:D
VuoteTTTTTTTTTTTTTTTT o.- here is the pro#lem a loc.er room Area 3% s"ft height 1%ft 3 persons in the room what will #e the diference in my load calculation if the system is 1%%O recirculate air or 1%%O outside air$ TTTTTTTTTTTTTTTTTTTTT he diBerence in your load calculation is 4H<$ Fost a little more information li.e whatYs your design room temp> 8or pu#lic loc.er rooms I design around a =eg$ Indoor temp year round$ A few things you need to .now ,rst a#out loc.er rooms$ Roc.er rooms should always #e .ept slightly negati!e$ he loc.er room area should #e completely sealed /E plenum returns /o mi7ing of air with other systems$ 0ou are allowed to recirculate air pro!iding it is the air from the loc.er room area$ 0ou must ha!e e7haust fans$ 0ou donYt always need 1%%O Eutside air +ust enough to pro!ide proper !entilation to match your e7haust$ I ha!e use $@$9Ys in loc.er rooms to reco!er as much energy as possi#le to lower the load$ In your case if you use 1%%O outside air you will need to e7haust 11%O of that air (to .eep the space slightly negati!e) hatYs a 4H< load to cool and then to e7haust if you li!e in a warm climate$ 2 Jan 12 11:1? 4i I am designing a MAH for the ,rst time I am trying to understand how to determine the amount of return air to supply a mi7ing
#o7 #efore the heater$ he outside winter design conditions are 1f at %O humidity$ inside design is f at %O humidity$ I need to supply 1%-%%%cfm of fresh air which is need to meet my air change rate per hour $ he room needs 1%%% cfm to maintain the pressure needed$ I would li.e to mi7 some return air with the outside air to sa!e some energy$ ;ut want minimie the sie of my supply fan$ 4ow do I determine the amount of return air to use$ Attach is a general free #ody diagram$ $ $ouseman.4 (Mechanical)
2 Jan 12 1D:21
Eutside air and &air change rate& are not usually the same$ Minimum fresh air is calculated per A'4@A 62$1 or code and is often a function of oor area and occupancy$ 'ince this aBects sie of heating signi,cantly- you should minimie the outside air as much as you can$ Air change is usually a summer cooling re"uirement and is e"ual to supply air ow$ Also- #y de,nition a ma.e up air unit doesn*t recirculate air$ ?i*iMace (Mechanical)
2 Jan 12 1:%2
'tudent $enegg (Mechanical) (OP)
2 Jan 12 1:3
than.s for the info$ the air change per hour AC4-in this case is dictated #y the purpose of this room- not the occupancy of the room$ he ach re"uirement is larger than the heat loss so I am using the AC4 for this design$ so if I need to use 1%%O fresh air(,nished food product area) to meet my AC4 how would one determine how much return air to use$ I tried using 2O of t he mass ow rate of the fresh supply air$ #ut at 1f fresh air 12%%l#min and f return air D%%l#min( the rates are appro7imate)- the mi7ed air is at the left of the saturation line$ I assume this is not a good situation$ Flease straighten me out$ where $ouseman.4 (Mechanical)
5ith EA1%-%%%cfm lea.age1-%%%cfm Q 'A @A Rea.age
2 Jan 12 16:D1
@A S EA 'A 2 e"uations- 3 un.nowns if you want to minimie 'A- set @A% Q ?-%%% cfm 'A 1%-%%% cfm @ecirculating air won*t sa!e heating energy- so there is no mi7ing pro#lem$ $enegg (Mechanical) (OP)
2 Jan 12 21:3?
han.s that helps 9$as:ean1 (Mechanical)
2? Jan 12 %:13
0ou need 1-%%% cfm supply and 1%-%%% cfm of outdoor air$ <o with ?-%%% cfm return$$$ @eturn air "uantity is not something you design around$ 0ou +ust ma7imie it when conditions permit (!ery hot or !ery cold out)$ 8or help- you might need to clarify your pro#lem$ lma1 (Mechanical)
D 8e# 12 1?:D1
As Chas;ean1 (Mechanical) suggested- you need to clearly de,ne your pro#lem$ he following might help: 1$ I understood that you need to supply 1%-%%% C8M EA to the room$ And this is #ased on your AC4 rate re"uired> 2$ 0ou need also 1-%%% C8M 'A to pressurie the room> 3$ Is the 1-%%% C8M the lea.age air as houseman2% (Mechanical) suggested> D$ I*!e trou#le with the statement &he ach re"uirement is larger than the heat loss so I am using the AC4 for this design$& AC4 gi!es you an idea of what !entilation air (fresh air) is re"uired$ 4eat loss or gain determines the heating or cooling (airconditioning) supply air ('A) re"uired$ I thin. you mean the AC4 criterion re"uires more air than that #ased on the heating or cooling calculation and you therefore #ased the supply air on 1%-%%% 'A which is re"uired #y the AC4 estimate> $ 'ince 'A EA S @A W your 'A EA- @A must #e %> 0ou lose 1-%%% C8M thru lea.age and another ?-%%% thru other e7haust opening(s)$ 'o 'A 1%-%%% C8M A (1-%%% S ?-%%%) C8M$ 6$ /o @A is needed or desired in your case as houseman2% (Mechanical) demonstrated if we understand what you*!e #een as.ing$ 1 Apr %3 1%:%% I*m designing an air conditioning system for 1%%O outside air$ he area is a small la# room appro7imately ?% ft3$ My heating loads are 66%% ;tuh sensi#le and 1%% ;tuh latent$ I trying to design the cfm re"uired$ I*m wor.ing in a dry climate so I*!e neglected the latent$ 'ome people suggest that I should: 66%%(1$%](?)) where ? is the outside air re"uirements and is the lea!ing temperature oB the coil$ his deli!ers a#out 12 cfm$ he reason I*!e #een gi!en is #ecause that temperature of the air I want to deli!er and am ma.ing up for the 66%% heat gain$ his gi!es me a#out 1% Air Changes4our Ether people suggest that I should use:
66%%(1$%]()) where is the temperature inside the room$ his deli!ers a#out 3% cfm$ I will sie the coil from this formula: 1$%](?)]3%$ I ha!e also #een told if I use this method that I will freee up the coil #ecause the air ow is too great$ 5hich method is right> Can I #uy this system as a pac.aged unit> Also where can I ,nd a psychometric chart for D%% feet ele!ation> han.s F9:=@ (Mechanical)
1 Apr %3 1D:
4a!e you consider 9entilation =isplacement system yet> 9$ipFuller (Mechanical) (OP)
1 Apr %3 22:%?
5hat*s a !entilation desplacement system> c$icopee (Mechanical)
1? Apr %3 21:3%
your reasoning escapes me$ Is the sensi#le heat of 66%% #tuh generated #y la# e"uipmentlighting and the 1% or less air changes and heat transfer thru walls- ceiling and oor> 9$as:ean1 (Mechanical)
2% Apr %3 %:31
Chip 4ere*s how I see this$ I wouldn*t go #y either option you*!e shown$ I would analye this from load to source- and there is a latent gain at the load$ I would therefore use: VD$]cfm]d4 in lieu of V1$%]cfm]d otal space load is latent S sensi#le- which is -1%% ;Hhr$ o o#tain cooling airow needed- use the VD$]cfm]d4 e"uation- which sol!es for total load (sensi#le and latent) #ased on enthalpy$ 5ith a saturated ^8 supply air stream- and to maintain the ^8 space temperature at %O relati!e humidity- the load (room) would re"uire 36D cfm$ 36D cfm is the !olumetric ow rate that the central A4H would need to cool from ?^8 to ^8$ Hsing V1$%]cfm]d- as you note that this is a dry area- the A4H coil would need to #e sied for this reduction in temperature at this ow$ his e"uates to an A4H cooling capacity of 16-%% ;Hhr$ /ote that I*m s.eptical of the lac. of need for the A4H to remo!e moisture #ecause this is a &dry climate$& =ry is a relati!e term$ ?^8 and 2D$6O humidity would produce saturated ^8 air$ If the humidity were higher than 2D$6O- the coil would also need to remo!e moisture$ I*m open to re#uttal on this ha!en*t gone #ac. to thermo49AC #oo.s- #ut this way seems to ma.e sense to me$ As a side note- #e careful of siing =Q units$ he load conditions stated will #e rare so you need a unit that will perform well at partial load$ ;est of luc.$ C; ,uark (Mechanical)
2% Apr %3
23:? I !ote for C;$ 4owe!er if you want to go your way you should consider to deg$8 #ecause at no time you want to increase the room temperature a#o!e deg$8$ If you consider a = of ? to for a load of 66%% ;tu4r then when this heat load adds up from the room the lea!ing temperature will #e higher than deg$8$ 0ou #etter follow C;*s comments$ anandGH>9 (Mechanical)
2 Apr %3 3:31
I am sorry- Ferhaps not agree with all a#o!e e7planation$ My answer to C4IF8HRR@*s "uestion is as follows$ I will start with #asics$ If you refer to carrier hand#oo. or any other engineering #oo. on Airconditioning$ 0ou will ,nd that the grand total heat- in your case it is 1%%#tuhr i$e %$6 tons- is used to calculate the tonnage re"uirement$his means that your coil should #e capa#le to gi!e you an output of %$6$ /ow the "uestion is how much air is needed to achie!e this$his can not #e decided with a#o!e two e"uations$0ou will ha!e to do the iterations$8irst assume some fresh air i$e 1 airchangehr and calculate the dehumidi,ed air "uantity re"uied$@epeat this procedure till you #alances your fresh air with dehumidi,ed air$his will gi!e you the "uantity of air re"uired to maintain the desired inside conditions$ Answer to your second "uestion regarding pyschometric chart for diBerent ele!ation$H will note that all the standard psychometric charts are designed at atmospheric pressure of 6%mm of 4g$8or pressure other than 6%mm of 4g- you will ha!e to physically draw it$ Frocedure on how to draw psychometric chart is a!aila#le in any air conditioning #oo.$ H can refer to that$ I hope all a#o!e e7planation clari,ed all your "ueries$ In case of any "uery pls$ let me .now$ 9$as:ean1 (Mechanical)
2 Apr %3 13:%
Anand- could you clarify the iteration> 5hat do you get for an answer> han.s- C; 6riand. (Mechanical)
2 Apr %3 1:
Chas;ean1*s response of 2%th April 2%%3 is a#solutely perfect$ I*!e sied countless air conditioning systems o!er the years- and I*!e ne!er had to carry out some &iteration& to get the cooling re"uirement$ Anand49AC: I too would #e really interested to see why an iterati!e process should #e necessary on this occasion (I might #e e7perienced- #ut I ne!er miss the opportunity to learnKK)$ @egards;rian coolingunit (Automoti!e)
26 Apr %3 6:%D
anand49AC: 0our e7planation is e7cellent$ I would li.e to .now the iterati!e procedure of calculating the fresh air re"uirement$ anandGH>9 (Mechanical)
2 Apr %3 1:3%
&Iteration& means trial and error method$ =uring heatload calculation you will ha!e to assume some fresh air "uantity to calculte dehudi,ed C8M re"uirement$ 0ou will ha!e to reiterate this procedure #y !arying fresh air "uantity till it #alances with dehumidi,ed C8M$ Hnless this #oth "uantity matches you will not satisfy the condition of 1%%O fresh air$ It is imposi#le for me to e7plain the method of calculation !ia mail$ 4owe!er- u can refer to carrier hand#oo. for more information$ In case of any "ueriescmments do let me .now$ I will try my #est to address it$ c6i6er (Mechanical)
2 Apr %3 12:D
I ha!e found se!eral psychrometric charts online for ele!ations other than sea le!el$ 8or e7ample <oogle found this one for me using the search terms &psychrometric chart altitude&: $ttp%&&***$eatcraft$eattransfercom&pdfs&Aormal444PDF It*s for %%% feet- not D%%- #ut it*s close enough to get you started$ ;i#er hermal =esign ***6i6ert$ermalcom ,uark (Mechanical)
2? Apr %3 %:D
=r$ [e.yl says- it is always #etter if you ha!e time to practically design a system$ (supplying air "uantity to remo!e heat load and moisture load and incrementing it to reach #alance) Mr$ 4yde says- well if you want to increase comple7ity of a simple solution go ahead$ /one of carrier*s people nor any other engineer o#+ects you$he fundamental is to chec. the total enthalpy of fresh air and the conditions you wanted at the room$ ;asically theair e7iting the room should ha!e same properties of re"uired condition otherwise room conditions cannot #e maintained$ /ow #y the simple calculation gi!en #y C; and used widely e!erywhere- calculate the cfm$ his is enough cfm that will carry heat and moisture out of the room$ his is more simpler than recirculation system #ecause you need not further remo!e the moisture from the e7iting air stream$ Just you are throwing it away$ 'till- if you lo!e math iterations- higher order diBerential e"uations and pro#a#ility will always help you$ ;est of Ruc.$ (;ahK am I #eing too dramatic>) 9$as:ean1 (Mechanical)
2? Apr %3 12:3
his could #e a good e7ercise #ecause we might #e tal.ing apples and apples here$ Ananddid the reiterati!e process produce a result> energy0 (Mechanical)
1% May %3 1:%
Rets .eep it simple- your application is not roc.et science 1st- your C8M re"uired is dictated #y your total sensi#le load and the temp you want to
maintain in the room at the supplly air temp you plan to pro!ide$ it is simply found as @m C8M @oom ;4H V' 1$% ( rm sa ) 2nd- #eause you specify 1%%O E'A ( I will not as. why 1%%O )your coils will ne!er see this load$ Coil Capacity will need to #e #ased on the air ow design a#o!e at ( E'A A d# w# 'A (RA) d#w# ) good luc. lilliput1 (Mechanical)
12 May %3 13:1
he cooling coil will need to cool 1%%OEA to the condition such that when this coil lea!ing air is discharged into the room$ it will pic. up heat and moisture W air is then e7hausted$ he condition of the air e7hausted typically matches the room inside conditions$ If the cooling coil cools the air to % deg 8 W the room design condition is 2 def 8 then the air "uantity re"uired @m Road in ;H per hr(1$1 7 (2%))$ /ow you must also satisfy the latent loads$ he Coil must dehumidify the same "uantity of air to the humidity such that when discharged into the room it will a#sor# the latent load W it*s @4 will #e within the design range$ 0ou may ha!e to reheat to maintain the re"uired space humidity$ lilliput1 (Mechanical)
13 May %3 12:2?
Ra#s typically re"uire 1%%O outdoor air$ Ma.e sure you ha!e enough for e7haust hood ma.eup$ 'implest control is constant !olume reheat$ 0ou can also ha!e (2) position occupiedunoccupied or !aria#le !olume- all with reheat$ Hsually humidity is cirtical so humidi,cation is also re"uired$ Chilled water system is #est$ If =Q you will ,nd out that when you sie the it for the load w 1%%O EA- the unit C8M (typically 3% C8Mton) would #e more than you need to do the room sensi#le load$5hat I ha!e done is recirculate #ac. some of the air$ his unit should only ser!e a la# not a group of la#s to a!oid cross contamination$ Fart of the fan discharge is ducted direct #ac. to the return$ 0ou ha!e to recalculate W do trial W error of the coil entering air condition (mi7 of EA W recirculated air at coil discharge condition plus fan heat$ he AC unit should ha!e hot gas controls$ A humidistat in addition to a thermostat should #e used to #ring on cooling$ 8inal space temperature should #e controlled #y the reheat coil$ greenaire (Mechanical)
2 Jun %3 D:DD
Could you see &the dedicated units& from the news letter of ***tranecom> 9$as:ean1 (Mechanical)
2 Jun %3 21:D6
/o I couldn*t$ Rin. is to trane$com main page$ Chec.ed under &/ews& and didn*t see &dedicated units$& ried a search for &dedicated units& and no luc.$ Could you #e more speci,c> tmprider (Mechanical)
3 Jun %3 ?:16
ry using an @9 sied for the 1%%O fresh air load$ Rocate it in the ceiling space of the la# for ease of maintenance and cleaning$ his will most li.ley decrease the sie of the unit that you go with- and will allow you to ta.e ad!antage of &free cooling&$ E!erall- your energy consumption will #e less due to the lower delta at your coils$
=4 H==riram (Mechanical)
12 Jul %3 13:3D
his seems to #e an interesting heat load which I used to do manually at the start of my career$ 1%%O outside air application cooling load calculations are normally done #y iteration$ 8irst assume a particular outside air "uantity and do the load calculations- ,nd out what the dehumidifed air "uantity is$ If it matches the assumed outside air "uantity- then the initial assumption is right$ Etherwise- do another load calculation a#sed on the dehumidi,ed air "uantity o#tained and .eep doing this (iteration KKK) till you get the same ,gure$ Alternati!ely- if you ha!e a software li.e 2%II of Carrier- you can +ust input all the rele!ant data and put 1%%O outside air and the program gi!es an output which will #e 1%%O outside air$ greenaire (Mechanical)
12 Jul %3 22:23
4i 4ere is we# address for mentioned article and complete article name$ If you still can not get it- gi!e my your email address$ hen send it to u #y email$ My email: naymoIgreenairecomsg &$ttp%&&***tranecom&commercial&li6rary&arc$iedJne*slettersaspKG 1? May 13 %:3 Achie!ing the =esired @eturn Air "uantities from occupied spaces$ he 49AC 'ystem consists of roof mounted Air 4andling units for a single storey #uilding that has many rooms$ he system is designed for 2%O fresh air and %O return air that is achie!ed in the mi7ing #o7 of the air handler$ he return air from the ceiling diBusers #ac. to the Air 4andler is not ducted$ A short piece of duct with a #ell mouth is e7tended from the A4H on the roof to the space a#o!e the acoustic tile false ceiling to draw air from all the rooms and corridors in the #uilding$ he 'upply air in each room is D%% C8M- #ut the return air "uantity measured from the return air diBusers is coming to only 1%% C8M$ 5e could not detect any in,ltration of air from the light ,7tures or the crac.s and cre!ices in the false ceiling$ he measurements from such light ,7tures and edges of the false ceiling panels is registering ero on the measuring 4ood$ he total return air measured at the #ell mouthed duct to the A4H or at the straight piece of duct at the roof #efore its connection to the machine is as per design "uantity$ 'o the A4H is drawing air from somewhere$ 5hile we are in the process of chec.ing the point of in,ltration- the "uestions are: 1) 5hat is the accepta#le tolerance of return air "uantities from the rooms whose type of occupancy is oLces> G 2) Is this achie!a#le in non ducted return air systems> *illard3 (Mechanical)
1? May 13 :3?
0ou will ne!er #alance a plenum air return properly$ If you need to #alance accurately- you need return ducts$ solidspaces (Mechanical) (OP)
1? May 13 ?:D?
I agree willard3- #ut there must #e the practice of the trade or Ashrae'macna guidelines a#out accepta#le performance$ Is 1%O de!iation E. or is e!en 2%O e7cusa#le$ here has to #e a minimum accepta#le performance in such cases$ <etting only 2O return air compared to supply air appears way too far$ DRWeig (lectrical)
1? May 13 13:3%
As long as the plenum is at a negati!e pressure relati!e to the space- there should #e no pro#lem> Is there a comfort or odor pro#lem you are trying to sol!e> 0ou can*t specify a tolerance for return air ow if there is no means to ad+ust it- so there won*t #e any sort of standard in my opinion$ I*m agreeing with 5illard3 here- #ut going a #it farther$
;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
solidspaces (Mechanical) (OP)
1? May 13 1:32
he #uilding is not occupied yet$ 5ith so little return- an odor pro#lem would most li.ely arise$ If the plenum is at a negati!e pressure compared to the space #ut the return air "uantity that is showing up on the hood is !ery little- that might mean that the rooms will !ery soon face hea!y air$ Is it #eing implied that we need not do air #alancing of the return air> 'econdly if there is no pro#lem- then we can always omit a ducted return (if we can aBord a little cooling load increase)$ Dra2en (Mechanical)
2% May 13 :D1
why would you not open return diBusers to the ma7imum and measure "uantity- as a ,rst step$ open the one closest to ahu- measure- than close it and open the farthest one$ DRWeig (lectrical)
2% May 13 ?:11
I was assuming that you do not ha!e ad+usta#le return diBusers$ I ha!e ne!er seen ad+usta#le return diBusers in a plenumreturn system$ Aren*t they something li.e eggcrate panels> If so- you cannot possi#ly #alance return ows$ 4ow can you #alance the airow through se!eral holes that don*t ha!e dampers> I don*t understand your comment- &$$$that might mean that the rooms will !ery soon face hea!y air$& If you ha!e D%% C8M going into a room- you also ha!e D%% C8M lea!ing the room$ If it*s not going up the return grille- it*s going into the hallway$ Many places ha!e no return grille at all in the rooms- #ut a single common return in a corridor that is ducted #ac. to the rooftop unit$ Close all the oLce doors$ Right up a cigarette (or spend some money on a smo.e candle)$ 'tand in a room farthest away from the rooftop unit$ 5ith D%% C8M supply and 1%% C8M return 8ollow your smo.e until it ma.es it to a return grille$ It will pro#a#ly #e in the few oLces !ery close to the rooftop unit$
0ou mentioned 2% percent outside air$ 4ow does the relief air e7it the #uilding> ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
solidspaces (Mechanical) (OP)
2% May 13 1%:11
=@5eig: 'ince D%% C8M are coming in- the same "uantity is de,nitely lea!ing #ut not from the return grille and this is the issue$ If the door is closed this might e!en pressurie the room forcing the supply air to go to ad+acent rooms$ I feel this will somehow desta#ilie the system and would cause odors in rooms that a re not ha!ing the same C8M lea!ing the room$ It would also cause a nuisance when the room occupied #y a smo.er is not getting the smo.e pulled out from the ceiling diBuser and it is instead going to the hallway$ he 2%O ma.e up of fresh air is due to the 2%O #eing e7tracted #y e7haust fans from the toilets$ DRWeig (lectrical)
2% May 13 11:3%
hat*s great- solidspaces$ 0ou are right- odors will go from oLce to corridor to the other oLces$ 4owe!er- this will happen whether the door is open or closed- unless the door is gas.eted and sealed well at the oor$ he point is you cannot change it unless you install return dampers in each room and #alance them$ ry my e7periment$ Close all the doors$ hen start at the last oLce on the end of the supply duct run$ Ma.e some smo.e and follow it$ 'ee where it goes$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
Gerr?a5eun (Mechanical)
2% May 13 12:2D
not sure I fully understand- #ut did you account for all the air that goes &through& the acoustical ceiling and not through the return grill> An acoustical ceiling with laidin tiles ,7tures etc$ is li.e a sie!e and the air goes path of least resistance$ In addition at such low ow rates your measuring hood isn*t accurate$ Just measuring adds resistance- di!erting more air &through& the ceiling$ E#!iously as much air as comes in will lea!e the room- same for the A4H$ If the plenum doesn*t ha!e lea.s to the outside or restrictions- it pro#a#ly will #e ,ne unless you e7perience actual pro#lems$ solidspaces (Mechanical) (OP)
2% May 13 16:%
I am grateful to all who responded$ he net result of this discussion is that matching the return air "uantities with supply is not as critical as I thought *illard3 (Mechanical)
21 May 13 :2?
0ou will ,nd out- after the #uilding occupants complain a#out humidity- odors and draftsthat there should #e return air ducts and the air !olumes should #e #alanced$ solidspaces (Mechanical) (OP)
21 May 13 11:D
5illard3: I thought the consensus was that it is EP e!en if the "uantities of supply and return do not e"ual$ =iBerent arguments and e7planations poured in a#out this disparity from the sensiti!ity of measuring hood to the crac.s and cre!ices of the false ceiling panels to the positi!e and negati!e pressures to the argument that the air that is coming in must #e e7iting also- etc$ 0our eye opener response goes against all the a#o!e consensus and has re!i!ed my concerns$ 'o more responses are re"uested a#out the ,nal action that is needed in this matter$ DRWeig (lectrical)
21 May 13 13:%%
5illard3 is not going against the consensus- he is adding information to it$ I +ust ,nished wor.ing 1 years in a #uilding with plenum return$ Complaints were few and far #etween$ here is no way to tell until 1% occupants all get together for a #ean #urrito lunch on the same day that another occupant #urns popcorn in the microwa!e and another occupant heats up chic.en ti..a masala on a hot plate in his oLce$ hat happened in our oLce may#e twice a year$ =ucted return would swoop that stuB #ac. to the A4H to #e mi7ed with E'A #efore returning to the spaces$ It*s a chance you ta.e$ ry my suggestion$ Ret some smo.e loose in a room farthest from the @H$ 8ollow it$ 5hen it lea!es the hallway and starts entering other oLces- imagine that it is &#ioeuent gas& instead of +ust smo.e$ he point is: It*s EP to ha!e supply not e"ual return with a plenum system because you can't do anything about it $ It occurs in all systems in which the owner doesn*t want to spring for ducted return$ here is nothing you can do to #alance the return air- so ignore it$ E@- duct the return$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
3104/" (Mechanical)
design conditions: D%% cfmroom- 32%cfm of return$ % cfm of fresh air$ actual conditions: D%% cfmroom- 1%% cfm of return- 3%% cfm of fresh air$ did you chec. supply air condition>
22 May 13 12:D
what if you close the fresh air inlet then chec. return ow again> solidspaces (Mechanical) (OP)
23 May 13 1%:2
31%6?: 0es we did chec. the supply air "uantities$ hey are as per design$ 5e could do the e7periment that you ha!e suggested of #lan.ing oB the supply and chec. out the return "uantities$ I am curious a#out your e7pectations or predictions a#out the eBect of doing soK =>?" (Mechanical)
23 May 13 1:D
Flenum return is ,ne if you ha!e air tight ceiling !oid as in oLce towers with concrete oors$ Flenum return is not to #e used in #uildings with metal dec. or similar roof structure that are unli.ely to #e air tight$ ;y measuring room conditions and the return conditions at A4H inlet- you can esta#lish if there is outside air lea.ing into the !oid$ An easy way to chec. if return is all right is to see if the doors are easy to open$ solidspaces (Mechanical) (OP)
2 May 13 1:?
'AP? All that you say ma.es sense$ I am recei!ing the Air ;alancing wor. from a su#contractor$ I +ust need to .now if supply is D%% C8M and return is coming at only 1%% C8M- can the su#contractor #e paid> 5ill these num#ers #e appro!ed #y the consultant> Er will the company ha!e to do it all o!er again> /o o#+ection was raised a#out the non ducted return at the time of accepting the Air ;alancing Jo#- so can anyone #ac. trac. and start raising hue and cry now- that it is not ducted> 3104/" (Mechanical)
2 May 13 11:D%
I didn*t mean air "uantities- (3%% cfm fresh airS1%% cfm return air)is a diBerent than (3%% cfm return air S1%% cfm fresh air) for the same A4H or @H- may #e you ha!e to hire an air #alance contractor to #alance your system$ 3104/" (Mechanical)
2 May 13 13:%?
ooops you already ha!e a contractor$ 6erks$ire (Aeronautics)
2 May 13 1D:33
he total return air measured at the #ell mouthed duct to the A4H or at the straight piece of duct at the roof #efore its connection to the machine is as per design "uantity $ 'o the disconnect if you can say that- is that the space a#o!e the ceiling is pro!iding air from somewhere other than the rooms to the air handler$ 4as any#ody loo.ed at the point where the dec. meets the e7terior walls- to see if foam seals are installed> DRWeig (lectrical)
2 May 13 22:13
#uote (solidspaces)
I +ust need to .now if supply is D%% C8M and return is coming at only 1%% C8M- can the su#contractor
#e paid>
here is no control for return air in a nonducted system$ he contractor cannot ma.e it any diBerent than it is right now$ If they #alanced the supply air to D%% C8M- they are done$ Mission accomplished$ he #alancing ,rm did its +o#$ If you are supplying D%% to the space- suc.ing % of it out the toilet e7haust- measuring design return air ow at the unit inta.e- and design outdoor air at the unit inta.e- you ha!e done all that you can do$ here is no more that can #e done$ I would not #other measuring return air in indi!idual rooms$ It cannot #e #alanced in any way- shape- or form$ 'orry for the dead horse a#o!e- feel free to red ag it$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
=>?" (Mechanical)
2 May 13 :%2
0ou ha!e not told us whether the A4H inlet conditions were close to design$If it is high there may #e outside air lea.ing into the system$As a matter of due diligence you should highlight it to your consultant$ solidspaces (Mechanical) (OP)
2? May 13 16:
'AP?: he supply- return and fresh air "uantities measured at or near the machine all add up$ he only pro#lem is that the return air "uantities are a fraction of what they should #e when measured #y the hood at the ceiling return diBusers$ =>?" (Mechanical)
2? May 13 2%:2
hen it loo.s li.e most of the return is through light ,ttings(!ented>)and through the gap #etween lay in tiles and the frame$he hood may not register any air ow when held against the light ,tting as it will #e well #elow its measuring range$ry a smo.e test if you need to put your mind at rest$ 6erks$ire (Aeronautics)
3% May 13 1:%
'AP? his thing is getting circular- I #elie!e =@5eig suggested this in his second reply$ And at the ris. of him #eating me- with the stic. instead of the horse$ 'uspended ceiling tile are notorious for this #eha!ior$ ;$$ *illard3 (Mechanical)
3% May 13 ?:D6
his is +ust recursi!e and some#ody should .ill this thread$$$$$it*s going nowhere$$$$$ DRWeig (lectrical)
0ou*re right 'AP? and #er.shire- no #eatings in the oLng$
3% May 13 1%:3
As for the last post #y solidspaces#uote (solidspaces)
he only pro#lem is that the return air "uantities are a fraction of what they should #e$$$
I will again- #ut more gently- state that there &what they should #e& is what they areunless you ha!e ducted return with #alancing dampers$ 0our return "uantities measured at the return diBuser in each room are QACR0 what they should #e$ ;est to you<oo#er =a!e
Cneartsnyc (Mechanical) (OP)
12 Aug 13 1%:2
4i all- IYm wor.ing on 49AC system for lu7ury residential #uilding$ Hnit 1 two oors$ 8our #athrooms cfm e7haust each$ otal e7haust is 3%% cfm$ Hnit 2 one oor$ wo #athrooms cfm e7haust each$ otal e7haust is 1% cfm Hnit3 one oor$ wo #athrooms cfm e7haust each$ otal e7haust is 1% cfm HnitD two oors$ 8our #athroom s cfm e7haust each$ otal e7haust is 3%% cfm$ he e7haust fan will #e controlled #y local #athroom light switch$ IYm planning to #ring a fresh air to each air handler unit e"ual to the amount e7hausted from the toilet$ hru a common duct to the roof with a goosenec.- each air handler fresh air ta.esoB from the main fresh air duct$ My Vuestion is$ 4ow do I treat the outside air to protect the coil from freeing> 'hould I install electric duct heater slip in type with a #ooster fan> If so- how the control would wor.$ Flease ad!ice$ han.sKK 3104/" (Mechanical)
12 Aug 13 11:D?
Rea!e toilet e7haust alone- it doesn*t wor. all the time$ 0ou can use an 4@9 for each air handler sprinkler1444 (Mechanical)
12 Aug 13 11:%
It depends on the system you are installing and the minimum outside air temperature e7pected$ 0ou may ha!e not only a coil freeing pro#lem #ut a heating load higher than the unit can handle$ If your option is a 9@8 system they ha!e indoor units to treat outside air or e!en 4eat @eco!ery Hnits to e7change heat with e7haust$ Cneartsnyc (Mechanical) (OP)
12 Aug 13 11:?
in fact I*m using 9@8 system (Mitsu#ishi system) $ ? =;- D 5; summer condition and 1 8 winter emp$
2% cfmperson Q 1%% cfm min$ outside air$ Cneartsnyc (Mechanical) (OP)
12 Aug 13 12:13
since the toilet e7haust fan is not continuously we cant use @9$ Also its only 1%% cfm EA re"uired$ sprinkler1444 (Mechanical)
12 Aug 13 2%:3?
Chec. with Mitsu#ishi$ I am more familiar with =ai.in- #ut they should also ha!e a dedicated outside air unit$ he 1^8 may #e a little low- #ut it will wor. most of the year$ Cneartsnyc (Mechanical) (OP)
12 Aug 13 23:D%
i don*t li.e the idea of using a dedicated outside air unit for +ust 1%% cfm$ is there any other solution> sprinkler1444 (Mechanical)
13 Aug 13 :
he idea was that you supply the total amount of fresh air (?%% cfm) with the outside air unit$ I thought you had a common duct$ Cneartsnyc (Mechanical) (OP)
13 Aug 13 :16
han.s$ /o we can*t use a common h!ac unit howe!er the ductwor. can #e shared$ 5e ha!e to use a separate unit since the unit owner has to pay the electric #ills and maintenance$ Waramanga (Mechanical)
1 Aug 13 :%?
what is your mi7ed air temp onto the coil> <i!e the mitsu#ishi engineers your parameters and see what they come #ac. with- your lu7ury units are not li.ely to ha!e small 8CHs so I thin. you will #e EP$ Etherwise it is heat reco!ery- there are "uite a few small ones a!aia#le now$ Cneartsnyc (Mechanical) (OP)
16 Aug 13 11:2
han.s 5aramanga- since the toilet e7haust fan is not continuously we cant use @9$ Also the 1%%O outside air unit from Mitsu#ishi is 12%% cfm- therefore I cant use it$ I*m thin.ing of using a small electric duct heater with inline fan to maintain the duct heater !elocity in each fresh air ta.eoB to the air handler$ (he #uilding will share a common fresh air duct wor. #ut the electric coil and fan has to #e operated- maintained and ser!iced #y the apartment owner from the ta.eoB) ProcessGH>9 (Mechanical)
16 Aug 13 1:%
&IYm planning to #ring a fresh air to each air handler unit e"ual to the amount e7hausted from the toilet& this is ?%% C8M not 1%% C8M EA as you said after- !ery confusing$$$ c$icopee (Mechanical)
1? Aug 13 21:%
If this residential structure is a condominium with annual maintenance fees- I would ha!e a
duct or a chase- dedicated for all the toilets- with a roof mounted e7haust fan whose cost for replacement and electricity would #e included in the annual fees$ Cneartsnyc (Mechanical) (OP)
1? Aug 13 21:32
Initially the design was to e"ual the fresh air inta.e and toilet e7haust- since the toilet e7haust fan energie #y light switch therefore the fresh air reduced to 16% cfm 8AI to each duple7 condominium and 1%% cfm 8AI for the single unit$ yes the owner concern a#out the condominium maintenance fees$ each unit will ha!e own e7haust system and fresh air inta.e$ I came up with an idea to use a small inline fanelectric duct heater with temperature sensor for each unit$ 22 Ect 1D :1? oday I got into some discussion with a colleague regarding Air Changes and 8resh Air 9olume and I would li.e to get a &referee& to sol!e this$ Imagine the following situation for the sa.e of argument: @oom 9olume: 1%% m3 AC4 (Air Change per 4our): My position is that the AC4 ,gures tells me how many times in a hour I ha!e to replace the air- so #asically I would need to put in the room %% m3 of fresh air My colleagueNs position is that AC4 means that we will ha!e to circulate the air through the 49AC system in an e"ui!alent !olume of times the roomNs !olume (%%m3) and that fresh air should #e around 12 ls per person which gi!e much lower fresh air needs$ I see !alidity on my colleaguesNapproach and may#e I am #eing put oB #y the semanticsin which for #e air changes per hour #asically means that I ha!e to replace air inside the room times$ 5hich approach is the correct one> han.s a lot for your help$
Mintulep (Mechanical)
22 Ect 1D :2D
0ou are right$ Medicine@ng (Industrial) (OP)
22 Ect 1D :D
MintJulep: han.s a lot for your feed#ac.$ /e!ertheless- and since meanwhile I also found some minimum fresh air ta#les that de,ne a diferent approach for instance Fart 8 HP #uilding regulations 2%1% calls for a 1%ls per person of fresh air$ =oes thi smeans that if no Air changes are de,ned- we apply this !alue- if AC4 is de,nedthen it will o!erule the minimum fresh air re"uirements- correct>
DRWeig (lectrical)
22 Ect 1D :D
0ou can meet the higher AC4 !alue and include the lower 1% ls per person$ It*s a matter of mi7ing return and fresh air (and controlling same)$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
sprinkler1444 (Mechanical)
22 Ect 1D :D
0ou ha!e to chec. what are the code re"uirements$ A'4@A clearly states &Air changes per hour of outdoor air& which is diBerent from &Air changes per hour supplied to room&$ he latter refers to air mo!ement$ urgross (Mechanical)
22 Ect 1D ?:12
0ou*re friend is correct in my opinion$ As an e7ample- an E@ room needs- under A'4@A 1%- to ha!e 2% AC4 and D AC4 of outside air$ /e7t point is that the AC4 are measured o+n the supply side if space is relati!e posit!e diBerential pressure and oB the e7huastretrun if needed to #e relati!e neg pressure$ ProcessGH>9 (Mechanical)
22 Ect 1D ?:2%
It goes down to code de,nition$ 8or instance /8FA 2% de,nes AC4 as per your de,nition (i$e$ 1%%O E$A) #ut as mentioned in other standards- it could mean fan*s C8M$ Medicine@ng (Industrial) (OP)
22 Ect 1D ?:?
han.s e!ery#ody for yout answers$ I guess that we can call it a draw then$ he two approaches are correct- depending on the go!erning code$ *illard3 (Mechanical)
23 Ect 1D :D
0ou are arguing semantics and not physics$ Medicine@ng (Industrial) (OP)
23 Ect 1D 1%:3?
willard3: In a sense you are right- #ut as someone pointed out a#o!e- diBerent standards also ha!e diBerent understandings of the word$ 8urther to our discussion- today my colleague came with a portion of a 49AC tender that stated: & Air ;alance Fressure 12 literssec per person& and he claims that this is related with our discussion of the air changes per hour$ I ha!e a feeling that it doesnNt #ut I also couldnNt e7plain why$ Can any#ody gi!e a hint on what does this parameter relates with AC4>
han.s a lot$ Medicine@ng (Industrial) (OP)
2D Ect 1D 12:%3
I noticed now that I missed one line in my pre!ious post: he paper that my my colleague showed showed me was written li.e li.e this: & ($$$) Area Air @e"uirements: AC4 Air ;alance Fressure: 12 ltssecperson$ ($$$) & 'o thatNs why he is claiming that the AC4 ,gure is referring to recirculating air- while the air #alance pressure is the fresh air$ Any thoughts on teh line of reasoning> han.s a lot 2 Ect 13 1:DD 4elloI*m a #eginner in rane race %%- and I*m ha!ing a pro#lem I can*t ,gure out$ I*m doing load calculations for a #uilding$ I ran the calcs and e!erything came out EP$ he procedure for me now is to go through the EA calculations using A'4A@ 62$1 e7cel sheet (the company ad!ises us not to use race !entilation method)$ /ow that I h!e the new EA num#ers- I*d li.e to add them to the rooms- #ut I also want to speci,y the design airow for the room so I don*t ha!e to go through a new set of EA calcs when race outputs a new design C8M$ I attempted to set the &Main 'upply& airow in the airow ta# for the rooms- #ut the airow was still oB #y around 1%O$ I can*t ,gure out why- #ut the designspace C8M is not coming out to what I speci,ed$ =oes anyone .now what the pro#lem might #e> Gerr?a5eun (Mechanical)
3 Ect 13 :2
I*m not sure if you mi7 up EA and design aiow$ 0our company is right to re"uire separate EA calculation$ 0ou 0ou should call rane rane support ( it is free free with your nandatory su#scription)$ su#scription)$ ( Mechanical) Dra2en (M
3 Ect 13 16:?
do you swear that you ha!e read manual in detail> if you don*t do that- you will ne!er reach accepta#le le!el le!el of .nowledge and tips will not help you$ i don*t use trace- #ut common fault in such setups is when concepts of supply air and outside air are mi7ed$ most of load calcs software pro!ides supply air calculation- and fresh air setup stands somewhere #esides that$ Moe@ng (Mechanical) (OP)
3 Ect 13 1:%
;y design airow I mean the 'A C8M- not the EA$ I contact rane support as 4errPaReun suggested and they were a#le to help me out (not at once- #ut they got #ac. to me)$ o o
who*s interested- the answer is #elow$ o o speci,y the desired design 'A C8M- the #loc. cooling cooling airow must must not #e ,lled ,lled out for the system$ hat*s the only way to specify the 'A C8M$ Ef course- that means that for a single system- you*d need to specify all of the one 'A C8M*s so that you get to your #loc. cooling airow (from the A4H)$ (Mechanical) cry.. (M
3 Ect 13 1:21
you may ha!e loc.ed the supply air temperature oB the coil$ lea!e it #lan. and it will gi!e you a diBerent C8M ;H- watch out if you get a too high 'A temperature- you*ll end with dehumidi,cation pro#lems$ suggest that you gi!e your ,le a generic name and post a A8 ,le for others to see$ 0ou 0ou .now how to ma.e ma.e a A8 A8 ,le- don*t you> If not- close the ,le- go to ,learchi!e pro+ect- clic. on the @C ,le and an archi!ed A8 ,le will #e generated- post that ,le and we can chec. it out for you$ Moe@ng (Mechanical) (OP)
D Ect 13 :D
I do ha!e the 'A temperatures loc.edloc.ed- and I*d li.e to .eep them that way so I don*t ha!e to critically loo. at e!ery one in this #uilding e!ery time I ad+ust the race ,le$ I do ha!e another pro#lem I*m trying to ,gure out- howe!er$ 8or the outside air calculations- we design #ased on the pea. design C8M for the 9A9 (in our case 9A9 with hot water @4)$ I got the EA num#ers I needed to satisfy A'4@A 62$1and I inputted that into race as a C8M !alue$ I set the 'A C8M to the pea. design of the 9A9 #o7$ 4owe!er- I*m designing the system #ased on the ;loc. C8M- not the pea.$ @egardless of which C8M I*m designing to- the C8Mton comes out to around 22% which isn*t easy to get fromn an oBtheshelf A4H$ 5hen I got selections- the C8M for the A4H was 6O o!er the design C8M speci,ed #y race- in order to meet the cooling load re"uirements$ 5hat would #e the procedure now> 'hould I #ump up all of the 9A9 9A9 C8M*s in order to get a total C8M that matches the A4H- redo the EA calculations- and reinput the !alues in race> race> Er is is there a standard method method for ad+usting the EA and load calculations #ased on the selected A4H> As Cry22 mentioned- the 'A temp should change since the cooling load is relati!ely the same- #ut the C8M is a lot higher$ 4owe!er- the num#ers in race stil ha!e the speci,ed 'A temperatures- so I*m ha!ing trou#le ,guring this out$ Any help would #e greatly appreciated$ appreciated$ Moe@ng (Mechanical) (OP)
D Ect 13 :D?
I can archi!e it later today and post it if it*ll help$ Gerr?a5eun (Mechanical)
D Ect 13 13:2%
rane rane support also also can ta.e your archi!ed archi!ed ,le and re!iew re!iew it if needed$ hat can can ta.e them them a day or two- though$ Moe@ng (Mechanical) (OP)
D Ect 13 13:
5ell the "uestion I ha!e now isn*t necessarily a race "uestion$ It*s what the standard procedure procedure for matching your load C8M from your load calculations and your C8M from your selected A4H$
( Mechanical) Dra2en (M
6 Ect 13 1%:22
i am "uite impressed on how complicated your posts are$ can we go step #y step- for instance if you would re!eal how trace*s supply air calculations are tied to your change of oa settings- we could possi#ly go forward$$$ Gerr?a5eun (Mechanical)
6 Ect 13 13:%1
In my e7perience it is easier to calcaulte EA re"uirement and minimum ow rates separately in 7cel (and you also need to meet local code- since that may diBer from A'4@A)$ A'4@A)$ and then +ust dump that t hat amount of air into the A4H (in rane system settings you +ust don*t do all the fancy A'4@A A'4@A stuB)$ his is easier easier to understandunderstand- less error errorprone$ prone$ Also easeir to show to A4J what you did$ I once did a full A'4@A calcaultion in 7cel and race and ne!er really had 1%%O the same num#ers- they always were a #it diBerent whne you include all the A'4@A A'4@A loopholes$ And this didn*t e!en wor. well with e7haust$ 4ere in 5I code for !entialtion is diBerent from IMCA'4@A$ 'o what i do is calculate EA for code- EA for A'4@A and pic. the higher num#er$ In addition we ha!e often huge e7haust re"uirements- that supersede the EA re"uirements$ In tha tcase the EA is o!erdesigned anyway$ his is not easily doen in rane- if possi#le at all$ rane rane is really really really really good$ #ut if if you don*t understand understand something 1%%O you easily do it it wrong and get totally wrong num#ers$ Moe@ng (Mechanical) (OP)
Ect 13 :32
I*m not sure how to simplify what I*m saying I ha!e the re"uired EA calcs from an 7cel sheet$ I inputted those !alues in race and I*m getting the cirrect cirrect EA outputs$ /ow- I too. the #loc. capcacity- the 'A C8M- and got selections for an A4H$ he C8Mton #ased on the t he race race ,le was around 22%- which is too low to get a good match from an oBtheshelf A4H$ he selection selection I got from from the sales rep rep had a 6O higher higher 'A C8M than than the one race race said I should ha!e$ he "uestion is- what now> F'$ 4errPaReun- yea race is funny li.e that$ 5e*re actually supposed to do energy modeling with race in a later phase of the pro+ect$ I*!e ne!er done it #efore and wonder how accurate the results will #e$ I heard somewhere somewhere around S 2%OK Dra2en (M ( Mechanical)
Ect 13 12:2?
o.- from the new post it loo.s li.e there there is no direct lin. #etween your oa inputs and trace load output though it loo.ed so in ,rst posts$$$ i ha!e to guess and say that #loc. load and a nd !entilation load are summed up to reach reference data for your ahu> on the other hand- i also ha!e to guess that you ha!e no any other choice #ut to ta.e some pac.aged rooftop with ,7ed toncfm capacity$ ,rst you should do is to chec. whether calculated minimum cfm can #e reached #y
controls with your pic.ed ahu at all$ if not- you simply ha!e to change ahu selection concept- gi!e up loc.ing supply temperature or similar$ changing supply air temperature should reduce collision$ it is also interesting to see how much #loc. load diBers from pea. loads sum> if you are limited with ahu choices- there could #e- for instance- possi#ility to split into two completely separate systems where two separate ahu*s could ,t$ no tool i use is a magic tool$ #est of them ha!e most of useful options- #ut we always ha!e to #e aware that each of them ha!e their own limitations$ Gerr?a5eun (Mechanical)
Ect 13 12:DD
Mong: race is pro#a#ly the most accurate energy simulation since it actually has all the 49AC options$ ;ut since it is more detailed- the user can ma.e more mista.es$ If you use race for load anyway- it is natural to use it for energy simulation$ ;ut you should .now what you are doing$ Moe@ng (Mechanical) (OP)
Ect 13 12:?
=raen: 0ou guessed right in that I ha!e no choice #ut to ta.e some pac.ed rooftop with a ,7ed toncfm capacity$ I*ll try redoing the calculations to get a #etter ,t$ he pea. loads and #loc. loads are pretty closeG a diBerence of a#out 1%1O ma7$ ;ut that*s a good way of !alidating ones$ <otta .eep that one in mindK han.s for the help$ 4errPaReun: Eh yea- I can*t wait til I ha!e to redo the energy model 1% times to ,gure out what I inputted wrong haha$ Gerr?a5eun (Mechanical)
Ect 13 1D:%
Moeng: there are so many A4H options (=EA'- where you add EA etc$)$ supply temp$$$ and ran can simulate almost e!erything$ +ust for giggles change ducted to plenum return and you see a diBerence$ 0ou also can insert the actual e"uipment unload and am#ient relief cur!es etc$ Many energy simulations are not detailed with 49AC options$ 'o the user can*t do much wrong$ If you enter e!erything right- race will #e accurate$ Ene issue with all energy simulations: they simulate the assumed occupancy and usage and also assume the system was properly commissioned and wor.s as designed$ In reality this isn*t the case$ Moe@ng (Mechanical) (OP)
Ect 13 1D:16
0ea that*s true$ I did read something that mentioned that some pro+ects needed some sort of testing of the facility 1 year after #uilding &openup& to !alidate the energy model$ I thin. the term was called cali#rating$ Gerr?a5eun (Mechanical)
Ect 13 1:D
I thin. you mean the &!alidation and !eri,cation& re"uirement$ Hnless the energy simulation was wrong- this isn*t to cali#rate the energy simulation$ this is more to !erify if
the system was installed and commissioned as designed$ the energy simulation- in my opinion- is to decide on what system is to #e chosen$ the owner can use upfront cost- maintaina#ility- energy consumption etc$ to ma.e a decision$ it isn*t to predict e7act consumption$ +ust for the fact that the energy simulation uses M03 or some other weather data (which are an a!erage design year) will ma.e it impossi#le to compare one year to the simulation$ Moe@ng (Mechanical) (OP)
Ect 13 16:%1
Eh I see$ As far as using energy modeling to ma.e #etter design decisions- it*s a pri!elage I don*t see here !ery often$ 8rom what I*!e o#ser!ed at many companies in the /0/J areaenergy modeling is usually used to ful,l some sort of pro+ect re"uirement such as R=and it comes so far into the design phase that it ma.es it almost impossi#le to redesign in time for the deadline*s$ I*m hoping one day we can get a pro+ect where the client cares more a#out eLciency and longterm returns than initial cost and deadlines$ Gerr?a5eun (Mechanical)
Ect 13 2%:%3
Is it possi#le that your 22% cfmton num#er is caused #y including EA treatment> yes for recirculated air rule of thum# is D%% cfm ton$ ;ut for EA this num#er is lower depending on your climate$ Just an idea$$$ 2 =ec 11 %:2 4i <uys8or one of the pro+ect that i am wor.ing on we ha! calculated the #uilding load and ha!e suggested fan coil units for most of the rooms in the #ldg- the total fresh air re"uirement for the #uilding is 2%%% ls- indoor condition 2223 C %O @4 and the outdoor condition is =; D C and w# 32$ 4ow do i calculate the load in P5 for selecting the 8A4H>> han. 0ou$ sspeare (Mechanical)
2 =ec 11 11:31
8irst- you need to demonstrate to the forum that you understand certain thermodynamic fundamentals for e7ample: 1) =o you .now the de,nition of sensi#le load> 2) =o you .now the de,nition of latent load> 3) =o you .now what enthalpy is> D) 4a!e you used a psychrometric chart> $e!gala!y (Mechanical) (OP)
2 =ec 11 12:%
4iya 'speare8rom my understanding sensi#le load in terms of h!ac is head load ina space that is gained #y !arious factors such as direct e7posure of sun- heat radiated #y people- lights and e"uipment as such- in terms of thermodynamics it is the heat re"uired to raise the temp of a #odyelement or may # water .eepings its state constantlatent load is essentially the humidity load with in the space or heat a#sor#ed #y a #ody while .eeping its temperature constant while its phase changes$
nthalpy is sum of all internal energies in a system$ and yes i ha! used a psychrometric chart$ regards than. you Dra2en (Mechanical)
2 =ec 11 13:26
than draw your outside air and indoor design conditions in psychro chart and enthalpy diBerence will ma.e your cooling capacity needed in the simplest scenario$ cry.. (Mechanical)
1 =ec 11 1:%D
V D$ 7 C8M 7 =elta 4 $ttp%&&***engineeringtool6o!com&cooling'$eating'e,uations'dJ0;0$tml
3% 'ep %? 16:3D I am the 49AC designer for my engineering ,rm- and we fre"uently come across 9A9 systems in medical oLce #uildings that pose a uni"ue pro#lem$ ;ased on heat loads and standard practices- we supply enough owrate to each room to cool the space using the D%% C8M per ton rule of thum#$ 4owe!er- #ased on A'4@A standards- oLce spaces re"uire a minimum of D air changes per hour$ 5hen we are dealing with a 9A9 system that is only capa#le of supplying degree %O humidity air- how does one design for the correct amount of air changes without o!er cooling the space> Also- how do you handle the outside air re"uirements gi!en you can only pro!ide air from the main loop$ I' it a safe assumption to e7haust the amount of E$A$ you need and ma.e sure the A4H for the entire oor is pulling in enough E$A$ to co!er the diBerence> han.s for the helpK Chris 5$ operatingeng (Mechanical)
3% 'ep %? 21:3D
!ery 9A9 system I*!e come across seems to ha!e the same aw$ ;ecause of the minimum damper postion in the 9A9 #o7 certain areas will always #e o!ercooled$ ELce #uildings mo!e people around all the time- so areas that were designed for ten people may h a!e only two which +ust compounds the pro#lem$ I*m only an operating engineer- #ut e!ery 9A9 air handler i*!e come across seems to ha!e the minimum EA damper sied #ased on the total amount of air that unit mo!es$ tys"4 (Mechanical)
1 Ect %? 1%:D
5here do you get the D AC4 for oLces num#er from> According to A'4@A 62$12%% an oLce room is C8Mperson plus %$%6 cfms"$ ft$ o not o!er cool spaces you pro!ide hot water or electric reheat on your 9A9 #o7es to #ring space temperature up in the e!ent of an o!er cool$ Er you can use fan powered #o7es to mi7 return air with primary air to achie!e a higher discharge air temperature$ here are e7amples of control se"uences around on the internet$ hird- you set your minimum EA #ased on your A'4@A calcs or in the case of a medical oLce #uilding we use AIA guidelines$ 0ou ha!e to watch your e7haust rates- if you are starting to #ecome neutral or negati!e it*s time to increase your EA and do energy reco!ery on the e7haust side$
Rastly- unless your are in an early design phase we ne!er use rules of thum# for cooling loads$ Always do proper load calculations$ 1 Ect %? 12:1
(.) mauricestoker (Mechanical)
he D AC4 would #e typical for oLce function and is diBerent than EA re"uirement$ A standard procedure for doing this is gi!en #y 62$12%%$ EA should #e estimated for normal (ma7 9A9) and lowest ow$ Rowest ow (if you ha!e reheat) is limited #y A'4@A ?%$1$ A'4@A has a guideline speci,cally for outside air inta.e$ Hse of a dedicated minimum EA inta.e- with static set at minimum ow- would #e one way of assuring minimum EA$ Hsing an IAV outside air damper would #e another$ Eperatingeng hit the nail on the headG one day a room will #e a house.eeping closet- the ne7t day it will #e an oLce$ Conference rooms always seem to #ecome a large oLce for whome!er has clout$ srid$ar131. (Mechanical)
11 /o! %? :11
@oom Air changes within room in an air conditioned space is in the range of 13 to 1 $ 8resh air change shall #e cfm person and %$%6 cfm per s"uare feet or as per A'4@A standard depending on the usage of the a rea$ 5here!er 9A9 is used it is recommended to ta.e care of the additional load due to occupancy e"uipment etc which may !ary through the 9A9 and #ase fa#ric load separately to a!oid any distur#ed conditions mauricestoker (Mechanical)
12 /o! %? :3
I ha!e to say that I*!e ne!er seen 131 AC4 for oLce space$ Flease let me .now the #asis for that- it*s a new one to me$ If you are supplying air at ]8 without reheat and only one or two rooms are getting o!ercooled- then you are luc.y$ I*d recommend !erifying what criteria you are designing for$ I thin. you*ll see a large diBerence #etween A'4@A 4and#oo.- A'4@A =esign Manual for 4ospitals and ClinicsA'4@A 1%- AIA- 62$1- and go!ernmental (=o=- 9A) standards- and which edition #y year$ If you don*t want to own the IAV re"uirements- I*d recommend a reheat$ 7OMec$@ng (Mechanical)
22 =ec %? 23:D
As others ha!e noted the #est way to pre!ent o!ercooling a space is to use some form of reheat$ he issue is o#!iously that you may #e cooling air only to ha!e to heat it up againwhich is not so good for energy eLciency$ A way to reduce the amount of reheat re"uired is to use a supply air temperature reset #ased on outdoor air temperature(or EA 5; if you monitor it)$ he issue of ensuring that you are maintaining your outdoor air rate when the 9A9 system is at minimum ow is a tric.y one$ =epending on your system it may #e possi#le to !ary your outdoor air damper #ased on the fan speed so that you pro!ide an increased O of EA
at min ow to maintain re"uirements$ Another way is to seperate your !entilation and coolingheating system so that the re"uired !entilation is accurately controlled$ =>?" (Mechanical)
23 =ec %? 2:13
Choose your supply air temperature such that you are a#le to achie!e the re"uired air change rates in the space$Also #ear in mind your dehumidi,cation needs$ *illard3 (Mechanical)
2D =ec %? 11:D
An e7cellent method of getting a .nown "uantity of EA in a 9A9 system is to install a constant !olume fan that #lows into the A4H @A plenum$ A =EA' will also o#!iate the pro#lem with pressure changes in a 9A9 system$ srid$ar131. (Mechanical)
2 =ec %? 6:2
mauricesto.er (Mechanical) @oom air changes will #e 13 to 1 for any normal air conditioned space$ his will increase as we go for Class 1%%%%- class 1%%% class 1%% etc$ 8resh air change shall #e #ased on A'4@A cfm per person and %$%6 cfm per s"uare feet of the area- if it is designed for green #uilding we do ta.e additional 3%O o#n the 8resh air with damper with actuator to wor. #ased o n CE2 sensor in the return air or room air accordingly fresh air is ta.en as per re"uirement$ As far as air "uantity for a 9A9 system it is #etter to cater to the pea. air "uantity and minimum air "uantity(min opening of damper in 9A9) shall #e set for minimum load which may occur$ In many +o#s we normally ta.e 1$ times the normal air distri#ution in that area$ 'till the @4 pro#lem may #e there depending on the !ariation of fresh air$ mauricestoker (Mechanical)
2 =ec %? ?:32
sridharI*!e ne!er designed an oLce to clean room standards$ Ross>:# (Mechanical)
2 =ec %? ?:
I thin. the term &room air changes& is #eing confused with recirculation rate$ &Changes& is used in cleanroom wor. to #e the recirculation rate- #ut in oLce 49AC it is often the !entilation (fresh air) rate$ mauricestoker (Mechanical)
2 =ec %? 13:32
I*m wor.ing on se!eral 49AC pro+ects for medical en!ironment now$ EA and AC4 are re"uired for oLces$ 8or clean rooms- I thin. it may depend on whether personnel protection is needed- or product- or #oth$ 4ospitals include clean rooms under H'F ?$ 8or to7ic compounding- AC4 and EA are the same$ 8or nonto7ic- recirc is allowed$ EA re"uirement and EA damperducting depend greatly on unit con,guration$ 8or 9A9 with air side economier- EA duct and damper would #e sied for total air ow- unless (my preference)a separate minimum EA and economier inta.es are included$ I thin. reference to A'4@A <uideline 16 would #e the point of the EF$
8or oLce 49AC- corrected EA calculations should #e made- unless it is a single one system$ If the air path is not considered- which is #oth EA and @A- then calculations per 62$12%% are not #eing done$ 'ome areas will always recei!e too much cooling or not enough- which is why ?%$12%% addresses reheat limitations on 9A9$ he Ad!anced 9A9 =esign <uide from FI@ is a real good source for understanding and designing 9A9 for energy eLceincy and IAV$ Rin. is #elow: $ttp%&&***energydesignresourcescom&Resources&Pu6lications&Design<uideline sasp!
2 Jan 13 16:26 Currently I am in the point of design where I must determine the outside air !entilation re"uirements for a #uilding #y using the 62$1 2%1% &!entilation rate procedure$& I am a #it confused a#out the two terms &!entilation& and &outside air&that are #eing thrown around and would appreciate any guidance$ 'tandard 62$1 lists a method called &!entilation rate procedure$& his method calculates the re"uired outside air needed #ased on a one*s occupancy and s"uare footage$ (I thought !entilation was +ust replacing air in a !olume regardless if it is outside air or return air) I thought there would #e another set of re"uirements aimed speci,cally towards !entilation- independent of outside air$ I would thin. !entilation would simply #e the amount of air changes per hour that your supply air (return air plus outside air) can achie!e on a space$ I was anticipating a ta#le that would pro!ide such !alues- #ut all I see is an outdoor air re"uirement method that I descri#ed a#o!e$ /ow to me- ,nding the re"uired outdoor air amount to #e used in a #uilding does not really tell me Im getting proper !entilation (air changes per hour) into my ones #ecause the supply air rate is what really does the air changing- and I can only #ase this supply air on my cooling load since I ha!e no other standard to loo. at here$ his is the only method I see- and I am s.eptical that there should #e more info stating how much supply air is re"uired to each one to reach an accepta#le air change per hour$ I am new at this so I may #e missing a .ey point$ 0our thoughts are appreciated$ han.s$ DRWeig (lectrical)
2 Jan 13 1:3
4i Mi.e5elcome to engtips$ In my e7perience- !entilation is always outside air- which is dictated #y occupancy and s"uare footage in each space$ 'upply air C8M is a function of the heating andor cooling load in the space$ o my .nowledge- there is no standard for supply air per s"uare foot (or per person) that is independent of outside air$ 9entilation outside air$ /ote: I*m a controls and energysimulation guy- my e7perience is in ma.ing the !entilation wor. right and analying what some#ody else designed to compute energy use$ I*m not a designer$ 4ang around- there are some !ery e7perienced Ms in this forum$
;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
oeag (Mechanical)
2 Jan 13 1?:%%
I*m with =@5eig$ I*m still pretty new to this 49AC stuB myself- #ut as far as I .now- there is no other standard that dictates supply air other than the outside air speci,ed in A'4@A$ I*!e #een wor.ing on a couple pro+ects- and "uic.ly loo.ing o!er our calculations and assumptions e!erything is wholesomely #ased on your re"uired cooling and heating loads$ urgross (Mechanical)
3 Jan 13 :D6
I thin. you would need to consider speci,c applications$ A wet la# may ta.e 1% air changes per hour- #ut the 1% AC4 doesn*t need to #e outside air$ 4ealth care facilities ha!e EA and total AC4 well spelled out$ Fharmacies and clean rooms will ha!e AC4 typically #ased on I'E le!el$ 8ederal agencies typically ha!e their own re"uirements for EA and total AC4$ 5hile I .now of no onesie ,ts all- air#orne odor control would #e a typical area where EA is not a re"uirementG pu#lic #athrooms would #e an e7ample$ Eutside air is not always re"uired- return air under the door can #e used$ cd!!13" (Mechanical)
3 Jan 13 ?:D
a.e another loo. at 622%1%$ he 9entilation @ate Frocedure uses a#le 61 gi!es Feople EH=EE@ Air @ate and Area EH=EE@ Air @ate$ If that amount of air doesnt meet your cooling or heating load (as stated #y drweig)- or AC4 rate re"uirements (as stated #y urgros)- then increase the supply cfm (usually with return air)- to get the supply air needed$ I suggest you reread 62*s ,ne print when you want to fall asleep at night$ .nowledge is power
Mike1833 (Mechanical) (OP)
3 Jan 13 12:%2
han.s e!eryone for your help$ Hgross- are these AC4 re"uirements in 62$1> hese are the .ind of re"uirements Im spea.ing of$ han.s$ 5hen ta.ing 49AC design classes (some time ago)- there were three possi#le constraints that determined your supply air$ he ,rst was to ,gure out your cooling load on the one$ his would #e the minnimum supply air rate ( ne!er should it go under the cooling load supply rate)$ he second constraint was occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement (for school- not in the standard) #ased on supply air- not outside air- and that*s why I was surprised to not see it in the standard 62$1)$ he third constraint was ma.eup air from e7haust$ he supply air would ha!e to increase if your #lowing out more than whats re"uired #y the cooling load or cfmperson (this constaint is a #it oB
topic since e7haust is independent of this discussion)$ 'o in summary- Im loo.ing for supply air constraints #ased on occupancy (li.e Hrgross pointed out)- #ut also a cfmpeople supply air constraint$ Consider this scenario$$$ I ha!e a speci,c room that re"uires 1%%%C8M of outside air (found #y following the &!entilation re"uirements&)$ If my air conditioning unit ser!ices 1% diBerent rooms- each room ha!ing a diBerent outside air re"uirement- how can this re"uirement #e met for e!ery room> he supply air rates to each room can #e controlled with actuated dampers- #ut the outside air is +ust going to #e a ,7ed percentage of the supply air regardless- right> 'o when a speci,c room re"uires !entilation- I would thin. to loo. for a supply air constraint$ 0our thoughts are greatly appreciatedK urgross (Mechanical)
3 Jan 13 13:21
/o- the AC4 re"uirements are not in 62$1$ I don*t thin. there is a onesie,ts all$ Criteria is usually #ased on a speci,c function or occupancy$ 4ospitals would #e a prime e7ample$ @efer to A'4@A 1% and you will get recommended AC4 for most areas of a hospital$ !en with that- additional criteria goes into speci,c areas- such as pharmacy$ @oom AC4 might go up to D% for to7ic compounding #ased on I'E le!el re"uirements$ 'ome areas the AC4 and EA are spelled out #ased upon the 49AC system #eing used$ As an e7amplenursing homes re"uire 6 AC4 per A'4@A and 2 EA AC4$ If using a Dpipe fan coil for en!elope load- the total AC4 can #e reduced to D$ he EA fraction calculationsalso change with system con,guration$ /o o!erall guidance is .nown- you ha!e to loo. at the occupancy and the proposed system$ DRWeig (lectrical)
3 Jan 13 2%:1
his portion of your "uestion confuses me: #uote (Mike1833)
he second constraint was occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement (for school- not in the standard) #ased on supply air- not outside air - and that*s why I was surprised to not see it in the standard 62$1)
Are you saying that your space had a re"uirement of 1 C8M supply air per person- not 1 C8M of outside air per person> If so- what sort of space was it> I*m curious- #ecause 1 C8M per person was the standard outside air "uantity for a lot of ordinary occupancies #ac. when all we had were ta#les in the standards$ 5hat e!eryone is getting at is this: 8or special areas (see urgross*s replies)- there will often #e set air changes that must #e met$ 8or nonspecial areas- such as an oLce or classroom- there is no standard re"uirement$ here is only a standard for !entilation (outside air)$ As for apportioning outside air amongst your ones- you*ll ha!e to control the outside air fraction of the A4H to meet the worst case one*s needs$ a.e a loo. through this thread for some discussion of one way to !ary !entilation in a 9A9 system: $ttp%&&eng'tipscom&ie*t$readcfm+,id-3./03
;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
Mike1833 (Mechanical) (OP)
D Jan 13 11:1D
#uote (DRWeig)
Are you saying that your space had a re"uirement of 1 C8M supply air per person- not 1 C8M of outside air per person> If so- what sort of space was it> I*m curious- #ecause 1 C8M per person w as the standard outside air "uantity for a l ot of ordinary occupancies #ac. when all we had were ta#les in the standards$
@ight$ At least that is the way it was formatted in my class$ It was a standard oLce space$ !en when analying standard classrooms or oLces we used a certain C8M per person of supply air to ma.e sure it was not higher than the re"uired load$ I am going to contact my old professor to clarify this$ I may ha!e interpreted it wrong$ I .new it was gi!en as a supply air constraint #ut it really ne!er did go o!er the cooling load re"uirement anyways$ If it did- perhaps I would ha!e had to increase the supply air re"uirement for that onenot to 1 cfmperson- #ut to a higher supply air amount that had the correct percentage of outside air of 1cfmperson$ #uote (DRWeig)
As for apportioning outside air amongst your ones- you*ll ha!e to control the outside air fraction of the A4H to meet the worst case one*s needs$
<reat point$ In lieu of this topic- what if the cooling load supply re"uirement was lower than the amount of outside air needed (+ust out of curiosity since I!*e ne!er encountered this)> I would thin. I would ,rst ha!e to predetermine an outside air percentage- then raise the supply air re"uirement for that one to a C8M that contains that outside air needed$ ;ut how can I predetermine an outside air percentage without .nowledge of the new supply air re"uirement> It seems li.e this may #e an iterati!e process$ DRWeig (lectrical)
D Jan 13 12:D6
If it*s a constant!olume air handler- no pro#lem$ he minimum outside air for the A4H was set at commissioning time- and the supply air to the space remains constant$ husoutdoor air is ,ne at all times as long as the fan is running$ he cooling coil simply cycles (d7) or modulates (chw) to meet the load with the constant air ow- and if the supply air ow is greater than what is needed e!en with supply air temperature reset- the reheat system comes into play$ If it*s a 9A9 air handler- it can #e done in se!eral diBerent ways$ he one in the thread I lin.ed a#o!e is my fa!orite$ 5ithout demand control for !entilation- the controller needs to .now the air ow to the space and the percent of osa in the air from the air handler$ It will maintain air ow to meet the minimum !entilation rate- no matter the load$ Air ow monitoring at each 9A9 #o7 is not totally necessary to accomplish this$ 5ith a .nown duct pressure and 9A9 #o7 damper position- the percent of ma7imum supply air ow to the space can #e estimated$ In #oth cases- if the re"uired osa cfm e7ceeds the supply cfm for a space- the osa ow rate is maintained and the supply air is either reheated to maintain comfort or else the
supply air temperature is modulated (within limits)$ 0ou might #ene,t from loo.ing into se"uences of operation for A4H and 9A9 systems that ha!e already #een done$ 7amples are usually a!aila#le online from pu#lic uni!ersities the specs for +o#s to #e #id are pu#lic$ here might #e some #uilding automation tutorials a!aila#le that co!er the topic as well$ 5hat you*re as.ing is more of a controls issue than an e"uipment design issue$ Again- my hum#le opinion only$ I teach a couple of classes that co!er !entilation control with #uilding automation- so I*m used to co!ering it from that standpoint$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
Dra2en (Mechanical)
D Jan 13 1D:D%
mi.e- i #elie!e there is nothing confusing a#out that- #ut you need to study #asic .nowledge ,rstly- than you will not ha!e to waste your energy in rein!enting the wheel$ !entilation rate is rate of replacement of room air with outside air$ period$ supply air has nothing to do with that$ relation #etween supply air and outdoor air does aBect all your design concepts- decisions on system and e"uipment- #ut you calculate fresh air and supply air re"uirements independently- one per 62$1 or other applica#le standard- the other per thermal load calculations$ =rweig- i opened one post some time ago- a#out how to ensure minimum outdoor air in diBerent !a! setups- #ut did not reach &one #ullet .ills all& answer- which is not surprising as that is not fully co!ered anywhere$ if you sie your !a! system to ensure minimum outdoor air rate at minimum supply ow situation- you are still not sure that each and e!ery one will recei!e minimum- for simple reason that not all ones ha!e the same supply airoutdoor air ratios- and that is what system fan can deli!er$ if you sie your system #ased on one with lowest outdoorsupply air ratio- than your other ones will #e o!er!entilated- which poses energy eLciency "uestions$ i #elie!e !a! concept itself ne!er sol!ed that pro#lem fully- and it is only dc! concept that can ma.e more sense in such setups- in future (until something new would #e in!ented)$ Dra2en (Mechanical)
oops- i did not realied that you lin.ed to that !ery post urgross (Mechanical)
D Jan 13 1D:D2 $$$ D Jan 13 1:2D
=raen hat sounds li.a a real good argument for =EA' and delin.ing !entilation air from thermal loading$ DRWeig (lectrical)
D Jan 13 16:2%
0ou*re on the money as usual- =raen$ A minimum outside air in+ection fan helps- #ut it*s not perfect either$
I lo!e =EA'- urgrossK Apparently- though- only the military and the I@' can aBord it$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum
it$ayapun (Mechanical)
3% =ec %? 1D:1
I ha!e yet to read through e!eryone else*s reply so what I type might either agree or conict$ ;ut in 9A9 systems the #o7 can #e e"uipped with a hot water or electric heating coil to heat #ac. up the air that has essentially #een *o!ercooled* due to air changes$ As far as the outside air rate$$$,rst you will ha!e to ,nd out what the outside air percentage is that the unit is pro!iding$ 7$ D%% cfm return air mi7ed with 1%% cfm outside air$ so you ha!e 2%O outside air$ hen you need to determine if the room re"uires an outside air change rate (e7 patient rooms re"uire 2 outside air changes) 7ample: 7am room 9olume: 1%%% ft3 air change re"uired: 6 air changes per hour outside air change re"uired: 2 air changes per hour A4H outside air O 2%O total heat gain % #tuh A re"uired room temp so you will need AI@ C4A/< @A (1%%% ft3 ] 6 AC4)6% 1%% C8M EH'I= AI@ C4A/< @A (1%%% 83 ] 2) ( $2 ] 6%) 166 C8M in this case you would need to supply 166 cfm of air to achie!e the outside air re"uirements (which also satis,es the air change rate re"uirement)$ you would need to heat 166 cfm from your 8 to - which is roughly 362 #tuh$ ;ut since the room already gi!es oB % #tu- you need a coil that would #e a#le to do 2%2 #tu$ 26 May 13 3:32 4iI +ust want your thought a#out an issue we are facing now in our design drawing$ we are now in the e7ecution stage that*s why this issue is raised$ Issue is: 1$ we ha!e 9A9 #o7es without thermostat in the drawings$ I insisted to contractor that each 9A9 #o7 should ha!e its own thermostat to control it$am i right> 2$ we ha!e multiple 9A9 #o7es( 3 units) in 1 @oom- our design drawing states only 1 thermostat$ 4owe!er- I insisted to ha!e thermostat in each one of the 9A9 #o7es$is it right>
3$ we ha!e also CA9 #o7es in the return ducts which do not ha!e thermostat$ I assume that there should also #e thermostat e!en in return ducts$is it right> I would appreciate your replies$than.s$ *illard3 (Mechanical)
26 May 13 ?:1D
hermostats are not re"uired for e!ery 9A9 unit is they all ser!e the same thermal one$ 0ou should tal. to the original ngineer who designed this system rather than guessing$ DRWeig (lectrical)
26 May 13 11:3
=o what 5illard3 said$ hen- while you*re tal.ing to the original ngineer- as. him to e7plain the purpose of the CA9 #o7es in the return ducts$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
:ronBr>ur (Mechanical)
1 Jul 13 1:%6
du7I am +ust now seeing your post$ =id you get it resol!ed> I agree with 5illard3 that you only need 1 thermostat per thermal one- especially if it*s an enclosed room$ If you had multiple thermostats- they would #e set at the same temperature anyway in an enclosed room$ 5hat happened with the CA9 #o7es on the return> I ha!e ne!er seen such a thing other than on a la#oratory or some other critical space where the supply and return must #e closely and constantly maintained$ It doesn*t ma.e sense in my mind to ha!e !aria#le supply and constant return$ please let us .now what happened$ tras$canman (Mechanical)
16 Jul 13 13:3
4ow do you ha!e constant return air !olume if the supply air !olume !aries>>> 21 May %D 22:33 As mentioned in another thread- I too need the &Idiot*s <uide to 49AC& as this is not my discipline$ I am an instrumentation and controls engineer trying to understand the impact of a client changee on wor. #y those in!o!ed 49AC$ I am at a fa#rication yard where nglish is not the ,rst language so "uestions here are poorly discussed$ I am #eginning with the changes that aBect controls$ 'ome re"uire more dampers to permit lea!ing the airhandler operating while isolating areas$ 'o- let me start with "uestions speci,c to dampers$ /on return dampers appear to wor. li.e a chec. !al!e$ 5ith the fan running- the !elocity lifts the lou!ers #ut they close #y gra!ity when the fan stops$ 5hat signi,cant details should I .now a#out other type dampers$ 5e ha!e the following types: 8ire damper and com#ination shutoB shutoB pressure control constant !olume #alancing
non return wathertight shutoB weather tight shutoB han.s in ad!ance$ John imok. (Mechanical)
22 May %D 2%:%%
4ere are some types of dampers =ampersAutomatic or Manual: Ad+usta#le metal plates installed inside of a duct to restrict- control !olume- #alance- or #y pass air- as re"uired in an air conditioning system$ 8ire =ampers A normally open damper installed in an air distri#ution system- designed to close automatically upon the detection of heat- to interrupt migratory air ow- and to restrict the passage of ame$ he de!ice has #een tested in accordance with a standard for safety #y a recognied testing la#oratory and is identi,ed #y a la#el- aLda!it or listing accepta#le to the authority ha!ing +urisdiction$ (Hnless the conditions of appro!al indicate so they are not rated for closing against mo!ing air streams or for withstanding pressure diBerentials$) A com#ination of ,re and smo.e damper must meet the re"uirements of #oth$ A smo.e damper is a de!ice to resist the passage of smo.e which: a$ Is arranged to operate automatically and #$ Is controlled #y a smo.e detector- and c$ May #e #ut is not necessarily re"uired to #e positioned manually from a remote command station$ A smo.e damper may #e a ,re damper or a damper ser!ing other functions- if its location lends itself to the multiple functions$ A com#ination ,re and smo.e damper shall meet the re"uirements of #oth$ Ceiling =ampers A specialied form of a heat stop installed in the air distri#ution portion of a ,rerated oor ceiling or roof ceiling assem#lyG the sole purpose of which is to help maintain the ,re endurance rating of the assem#ly$ =amper- lou!er A damper madeup of se!eral !anes operated #y gra!ity or motor control$ his type of damper is generally used to control !olume of outside air inta.e or e7haust to the atmosphere$ =amper- 'plitter A damper used to change air ow from one duct to another$ Mi7ing =ampers =ampers used to mi7 #oth heating and cooling supply air at point of dischargeG as in a room friartuck (Mechanical)
D Jun %D 1:33
8rom a control perspecti!e there are two type of damper- parallel #laded and Epposed #laded$
2 Jan 13 16:26
Currently Currently I am in the point of design where I must determine the outside air !entilation re"uirements re"uirements for a #uilding #y using the 62$1 2%1% &!entilation rate procedure$& procedure$& I am a #it confused a#out the two terms &!entilation& and &outside air&that are #eing thrown around and would appreciate any guidance$ 'tandard 62$1 lists a method called &!entilation rate procedure$& his method calculates the re"uired re"uired outside air needed #ased on a one*s occupancy and s"uare footage$ (I thought !entilation was +ust replacing air in a !olume regardless regardless if it is outside air or return return air) I thought there would #e another set of re"uirements re"uirements aimed speci,cally towards !entilation- independent of outside air$ I would thin. !entilation would simply #e the amount of air changes per hour that your supply air (return air plus outside air) can achie!e on a space$ I was anticipating a ta#le that would pro!ide such !alues- #ut all I see is an outdoor air re"uirement re"uirement method that I descri#ed a#o!e$ /ow to me- ,nding the re"uired outdoor air amount to #e used in a #uilding does not really tell me Im getting proper !entilation (air changes per hour) into my ones #ecause the supply air rate is what really does the air changing- and I can only #ase this supply air on my cooling load since I ha!e no other standard to loo. at here$ his is the only method I see- and I am s.eptical that there should #e more info stating how m uch supply air is re"uired to each one to reach an accepta#le air change per hour$ I am new at this so I may #e missing a .ey point$ 0our thoughts are appreciated$ han.s$ DRWeig (lectrical)
2 Jan 13 1:3
4i Mi.e5elcome to engtips$ In my e7perience- !entilation !entilation is always outside air- which is dictated #y occupancy and s"uare footage in each space$ 'upply air C8M is a function of the heating andor cooling load in the space$ o my .nowledge- there is no standard for supply air per s"uare foot (or per person) that is independent of outside air$ 9entilation outside air$ /ote: I*m a controls and energysimulation energysimulation guy- my e7perience e7perience is in ma.ing the !entilation wor. right and analying what some#ody else designed to compute energy use$ I*m not a designer$ 4ang around- there are some !ery e7perienced Ms in this forum$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: now: Forum Policies
oeag (Mechanical)
I*m with =@5eig$ I*m still pretty new to this 49AC stuB myself- #ut as far as I .now- there is no other standard that dictates supply air other than the outside air speci,ed in A'4@A$
2 Jan 13 1?:%%
I*!e #een wor.ing on a couple pro+ects- and "uic.ly loo.ing o!er our calculations and assumptions e!erything is wholesomely #ased on your re"uired re"uired cooling and heating loads$ urgross (Mechanical)
3 Jan 13 :D6
I thin. you would need to consider speci,c applications$ applications$ A wet la# may ta.e 1% air changes per hour- #ut the 1% AC4 doesn*t need to #e outside air$ 4ealth care facilities ha!e EA and total AC4 well spelled out$ Fharmacies and clean rooms will ha!e AC4 typically #ased on I'E le!el$ 8ederal agencies typically ha!e their own re"uirements for EA and total AC4$ 5hile I .now of no onesie ,ts all- air#orne odor control would #e a typical area where EA is not a re"uirementG re"uirementG pu#lic #athrooms would #e an e7ample$ Eutside air is not n ot always re"uired- return air under the door can #e used$ ( Mechanical) cd!!13" (M
3 Jan 13 ?:D
a.e a.e another loo. at 622%1%$ he he 9entilation 9entilation @ate @ate Frocedure Frocedure uses uses a#le a#le 61 gi!es Feople EH=EE@ Air @ate and Area EH=EE@ Air @ate$ @ate$ If that amount of air doesnt meet your cooling or heating load (as stated #y drweig)- or AC4 rate re"uirements re"uirements (as stated #y urgros)- then increase the supply cfm (usually with return air)- to get the supply air needed$ I suggest you reread 62*s ,ne print when you want to fall asleep at night$ .nowledge is power
Mike1833 (Mechanical) (OP)
3 Jan 13 12:%2
han.s e!eryone e!eryone for your help$ help$ HgrossHgross- are these these AC4 re"uirem re"uirements ents in 62$1> hese hese are the the .ind of re"uirements Im spea.ing of$ han.s$ 5hen ta.ing 49AC design classes (some time ago)- there were three possi#le constraints that determined your supply air$ air$ he ,rst was to ,gure out your cooling load on the one$ his would #e #e the minnimum supply air rate rate ( ne!er should should it go under under the cooling load supply rate)$ he second constraint was occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement re"uirement (for school- not in the standard) #ased on supply air- not outside airand that*s why I was surprised to not see it in the standard 62$1)$ he third constraint was ma.eup air from e7haust$ he supply air would ha!e to increase if your #lowing out more than whats re"uired #y the cooling load or cfmperson (this constaint is a #it oB topic since e7haust is independent of this discussion)$ discussion)$ 'o in summary- Im loo.ing for supply air constraints #ased on occupancy (li.e Hrgross Hrgross pointed out)- #ut also a cfmpeople supply air constraint$ Consider this scenario$$$ I ha!e a speci,c room that re"uires 1%%%C8M of outside air (found #y following the &!entilation re"uirements&)$ re"uirements&)$ If my air conditioning unit ser!ices 1% diBerent rooms- each room ha!ing a diBerent outside air re"uirement- how can this re"uirement #e met for e!ery room> he supply air rates to each room can #e controlled with actuated dampers- #ut the outside air is +ust going to #e a ,7ed percentage percentage of the supply air regardlessregardless- right> 'o when a speci,c room re"uires !entilation- I would thin. to loo. for a supply air constraint$ 0our 0our thoughts are are greatly appreciatedK appreciatedK urgross (Mechanical)
3 Jan 13 13:21
I*!e #een wor.ing on a couple pro+ects- and "uic.ly loo.ing o!er our calculations and assumptions e!erything is wholesomely #ased on your re"uired re"uired cooling and heating loads$ urgross (Mechanical)
3 Jan 13 :D6
I thin. you would need to consider speci,c applications$ applications$ A wet la# may ta.e 1% air changes per hour- #ut the 1% AC4 doesn*t need to #e outside air$ 4ealth care facilities ha!e EA and total AC4 well spelled out$ Fharmacies and clean rooms will ha!e AC4 typically #ased on I'E le!el$ 8ederal agencies typically ha!e their own re"uirements for EA and total AC4$ 5hile I .now of no onesie ,ts all- air#orne odor control would #e a typical area where EA is not a re"uirementG re"uirementG pu#lic #athrooms would #e an e7ample$ Eutside air is not n ot always re"uired- return air under the door can #e used$ ( Mechanical) cd!!13" (M
3 Jan 13 ?:D
a.e a.e another loo. at 622%1%$ he he 9entilation 9entilation @ate @ate Frocedure Frocedure uses uses a#le a#le 61 gi!es Feople EH=EE@ Air @ate and Area EH=EE@ Air @ate$ @ate$ If that amount of air doesnt meet your cooling or heating load (as stated #y drweig)- or AC4 rate re"uirements re"uirements (as stated #y urgros)- then increase the supply cfm (usually with return air)- to get the supply air needed$ I suggest you reread 62*s ,ne print when you want to fall asleep at night$ .nowledge is power
Mike1833 (Mechanical) (OP)
3 Jan 13 12:%2
han.s e!eryone e!eryone for your help$ help$ HgrossHgross- are these these AC4 re"uirem re"uirements ents in 62$1> hese hese are the the .ind of re"uirements Im spea.ing of$ han.s$ 5hen ta.ing 49AC design classes (some time ago)- there were three possi#le constraints that determined your supply air$ air$ he ,rst was to ,gure out your cooling load on the one$ his would #e #e the minnimum supply air rate rate ( ne!er should should it go under under the cooling load supply rate)$ he second constraint was occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement re"uirement (for school- not in the standard) #ased on supply air- not outside airand that*s why I was surprised to not see it in the standard 62$1)$ he third constraint was ma.eup air from e7haust$ he supply air would ha!e to increase if your #lowing out more than whats re"uired #y the cooling load or cfmperson (this constaint is a #it oB topic since e7haust is independent of this discussion)$ discussion)$ 'o in summary- Im loo.ing for supply air constraints #ased on occupancy (li.e Hrgross Hrgross pointed out)- #ut also a cfmpeople supply air constraint$ Consider this scenario$$$ I ha!e a speci,c room that re"uires 1%%%C8M of outside air (found #y following the &!entilation re"uirements&)$ re"uirements&)$ If my air conditioning unit ser!ices 1% diBerent rooms- each room ha!ing a diBerent outside air re"uirement- how can this re"uirement #e met for e!ery room> he supply air rates to each room can #e controlled with actuated dampers- #ut the outside air is +ust going to #e a ,7ed percentage percentage of the supply air regardlessregardless- right> 'o when a speci,c room re"uires !entilation- I would thin. to loo. for a supply air constraint$ 0our 0our thoughts are are greatly appreciatedK appreciatedK urgross (Mechanical)
3 Jan 13 13:21
/o- the AC4 re"uirements are not in 62$1$ I don*t thin. there is a onesie,ts all$ Criteria is usually #ased on a speci,c function or occupancy$ 4ospitals would #e a prime e7ample$ @efer @efer to A'4@A 1% and you will get recommended recommended AC4 for most areas of a hospital$ !en with that- additional criteria goes into speci,c areas- such as pharmacy$ @oom AC4 might go up to D% for to7ic compounding #ased on I'E le!el re"uirements$ re"uirements$ 'ome areas the AC4 and EA are spelled out #ased upon the 49AC system #eing used$ As an e7ample- nursing homes re"uire 6 AC4 per A'4@A and 2 EA AC4$ If using a Dpipe fan coil for en!elope load- the total AC4 can #e reduced to D$ he EA fraction fraction calculationsalso calculationsalso change with with system con,guration$ con,guration$ /o o!erall o!erall guidance is .nown- you ha!e to loo. at the occupancy and the proposed system$ DRWeig (lectrical)
3 Jan 13 2%:1
his portion of your "uestion confuses confuses me: #uote (Mike1833)
he second constraint was occupancy occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement (for school- not in the standard) #ased on supply air- not outside air- and that* s why I was surprised to not see it i n the standard 62$1)
Are you saying that your space had a re"uirement re"uirement of 1 C8M supply air per person- not 1 C8M of outside air per person> If so- what sort of space was it> I*m curious- #ecause 1 C8M per person was the standard outside air "uantity for a lot of ordinary occupancies #ac. when all we had were ta#les in the standards$ 5hat e!eryone is getting at is this: 8or special areas (see urgross*s replies)- there will often #e set air changes that must #e met$ 8or nonspecial areasareas- such as an oLce or classroomthere is no standard re"uirement$ here here is only a standard for !entilation (outside air)$ As for apportioning outside air amongst your ones- you*ll ha!e to control the outside air fraction of the A4H to meet the worst case one*s needs$ a.e a.e a loo. through this thread for some discussion discussion of one way to !ary !entilation in a 9A9 9A9 system: $ttp%&&eng'tipscom&ie*t$readcfm+,id-3./03
;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: now: Forum Policies
Mike1833 (Mechanical) (OP)
D Jan 13 11:1D
#uote (DRWeig)
Are you saying that your space had a re"uirement of 1 C8M supply air per person- not 1 C8M of outside air per person> If so- what sort of space was it> I*m curious- #ecause 1 C8M per person was the standard outside air "uantity for a lot of ordinary occupancies #ac. when all we had were ta#les in the standards$
@ight$ At least that is the way it was formatted in my class$ It was a standard oLce space$
!en when analying standard classrooms or oLces we used a certain C8M per person of supply air to ma.e sure it was not higher than t he re"uired load$ I am going to contact my old professor to clarify this$ I may ha!e interpreted it wrong$ I .new it was gi!en as a supply air constraint #ut it really ne!er did go o!er the cooling load re"uirement anyways$ If it did- perhaps I would ha!e had to increase the supply air re"uirement for that one- not to 1 cfmperson- #ut to a higher supply air amount that had the correct percentage of outside air of 1cfmperson$ #uote (DRWeig)
As for apportioning outside air amongst your ones- you*ll ha!e to control the outside air fraction of the A4H to meet the worst case one*s needs$
<reat point$ In lieu of this topic- what if the cooling load supply re"uirement was lower than the amount of outside air needed (+ust out of curiosity since I!*e ne!er encountered this)> I would thin. I would ,rst ha!e to predetermine an outside air percentage- then raise the supply air re"uirement for that one to a C8M that contains that outside air needed$ ;ut how can I predetermine an outside air percentage without .nowledge of the new supply air re"uirement> It seems li.e this may #e an iterati!e process$ DRWeig (lectrical)
D Jan 13 12:D6
If it*s a constant!olume air handler- no pro#lem$ he minimum outside air for the A4H was set at commissioning time- and the supply air to the space remains constant$ husoutdoor air is ,ne at all times as long as the fan is running$ he cooling coil simply cycles (d7) or modulates (chw) to meet the load with the constant air ow- and if the supply air ow is greater than what is needed e!en with supply air temperature reset- the reheat system comes into play$ If it*s a 9A9 air handler- it can #e done in se!eral diBerent ways$ he one in the thread I lin.ed a#o!e is my fa!orite$ 5ithout demand control for !entilation- the controller needs to .now the air ow to the space and the percent of osa in the air from the air handler$ It will maintain air ow to meet the minimum !entilation rate- no matter the load$ Air ow monitoring at each 9A9 #o7 is not totally necessary to accomplish this$ 5ith a .nown duct pressure and 9A9 #o7 damper position- the percent of ma7imum supply air ow to the space can #e estimated$ In #oth cases- if the re"uired osa cfm e7ceeds the supply cfm for a space- the osa ow rate is maintained and the supply air is either reheated to maintain comfort or else the supply air temperature is modulated (within limits)$ 0ou might #ene,t from loo.ing into se"uences of operation for A4H and 9A9 systems that ha!e already #een done$ 7amples are usually a!aila#le online from pu#lic uni!ersities the specs for +o#s to #e #id are pu#lic$ here might #e some #uilding automation tutorials a!aila#le that co!er the topic as well$ 5hat you*re as.ing is more of a controls issue than an e"uipment design issue$ Again- my hum#le opinion only$ I teach a couple of classes that co!er !entilation control with #uilding automation- so I*m used to co!ering it from that standpoint$ ;est to you<oo#er =a!e
4a!en*t see the forum policies> =o so now: Forum Policies
Dra2en (Mechanical)
D Jan 13 1D:D%
mi.e- i #elie!e there is nothing confusing a#out that- #ut you need to study #asic .nowledge ,rstly- than you will not ha!e to waste your energy in rein!enting the wheel$ !entilation rate is rate of replacement of room air with outside air$ period$ supply air has nothing to do with that$ relation #etween supply air and outdoor air does aBect all your design concepts- decisions on system and e"uipment- #ut you calculate fresh air and supply air re"uirements independently- one per 62$1 or other applica#le standard- the other per thermal load calculations$ =rweig- i opened one post some time ago- a#out how to ensure minimum outdoor air in diBerent !a! setups- #ut did not reach &one #ullet .ills all& answer- which is not surprising as that is not fully co!ered anywhere$ if you sie your !a! system to ensure minimum outdoor air rate at minimum supply ow situation- you are still not sure that each and e!ery one will recei!e minimum- for simple reason that not all ones ha!e the same supply airoutdoor air ratios- and that is what system fan can deli!er$ if you sie your system #ased on one with lowest outdoorsupply air ratio- than your other ones will #e o!er!entilated- which poses energy eLciency "uestions$ i #elie!e !a! concept itself ne!er sol!ed that pro#lem fully- and it is only dc! concept that can ma.e more sense in such setups- in future (until something new would #e in!ented)$ Dra2en (Mechanical)
oops- i did not realied that you lin.ed to that !ery post
D Jan 13 1D:D2 $$$
urgross (Mechanical)
D Jan 13 1:2D
=raen hat sounds li.a a real good argument for =EA' and delin.ing !entilation air from thermal loading$ DRWeig (lectrical)
D Jan 13 16:2%
0ou*re on the money as usual- =raen$ A minimum outside air in+ection fan helps- #ut it*s not perfect either$ I lo!e =EA'- urgrossK Apparently- though- only the military and the I@' can aBord it$ ;est to you<oo#er =a!e
pa#lo2D1% (Mechanical) (EF)
1 Apr %6 :D
4ello- INm new in this forum and ha!e a "uestion$ I need to calculate de cooling load of an area that demands 1%%O outside air- and to #e honest- I donNt Pnow how to do it$ here are some "uestions that comes to my mind: 5hat should #e the lea!ing air temperature> he loads produce #y peoplelights- walls- etc that we estimate in a recirculating system- should #e calculated in this .ind of system too>$ I really apreciate some help$ (INm from =ominican @epu#licso e7cuse my english)$
han.s$
willard3 (Mechanical)
1 Apr %6 1D:3
8or the outside air:
'ensi#le cooling CH 8MI/ 7 1$% Q outside AI@ =RA t ;H4@ '/'I;R
Ratent cooling: fu ftmin 7 %$66 7 (delta moisture in grainsl# from psychometric chart) #tuhr latent
'ensi#le load S latent load total cooling load for outside air
In general- cold air is deli!ered at 8 dry #ul# and wet #ul# (ie- saturated)
;uilding solar loads- lights- e"uipment and people loading should #e included in your calculations$
0ou should pro#a#ly hire a Mechanical ngineer to do this as he is familiar with it and you aren*t$
waross (lectrical)
1 Apr %6 1:3%
4ello willard3 I ha!e met some intelligent dedicated engineers in the third world$ Hnfortunatelythe training and educational systems there are not up to ,rst world standards$ pa#lo2D1% has recognied that he doesn*t ha!e the information that he needs to sol!e his pro#lem and has wisely gone loo.ing for good ad!ice$ I than. you on #ehalf of pa#lo2D1% for your .ind help- #ut I wish to gently point out that your last suggestion may not #e feasi#le$ pa#lo2D1% is "uite possi#ly the #est mechanical engineer a!aila#le$ 0ou may ,nd it rewarding- willard3 to mentor pa#lo2D1% and help him to #ecome a #etter engineer$ 8rom the tone of his post I #elie!e he is intelligent and dedicated$ 4e recognies shortcomings in his education and is trying to impro!e himself$
0ou ha!e already gi!en pa#lo2D1% the #asics- go a little farther and help him through his calculations and you may ,nd that you en+oy it$ respectfully
MintJulep (Mechanical)
2 Apr %6 1:33
pa#lo-
a.e a loo. at this site:
http:www$engineeringtool#o7$comh!acsystemstT23$html
"uar. (Mechanical)
2 Apr %6 23:13
Fa#lo-
he room lea!ing air condition should always #e the room condition$
Calculate heat load as per the general rules$ Flot the room condition and am#ient condition state points on the psychro chart$ =raw a line with a slope of '4@ from the room condition to the saturated cur!e$ his is your dew point condition$ Join the am#ient condition state point to the dew point$ he total load on the coil will #e the mass ow rate of air times the enthalpy diBerence #etween the am#ient condition
and the dew point condition$ In some cases- the '4@ line #ecomes an asymptote to the saturation cur!e$ In this case- assume some ar#itrary dew point and add reheat into the process$
he lin. #elow gi!es you description and details of many psychrometric processes$ 4a!e a loo. into it$
http:www$coolit$co$apsychart
5aross-
/ice thin.ing and I feel that is the whole idea #ehind these forums$
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 :2
han. you all of you for your help
4ere comes another "uestion- how can i calculate mass ow- i mean- i .now the !olume of air in the room- #ut how do i .now how many times do i ha!e to recirculate it
R'A (Mechanical)
3 Apr %6 12:11
correct me if I am wrong #ut I am assumming you meant 9olume ow instead of mass ow$
;elow is something I gra##ed oB a we#site descr#ing what I thin. will #e of help to you$
Ene air change occurs in a room when a "uantity of air e"ual to the !olume of the room is supplied andor e7hausted$ Air change rates are units of !entilation that compare the amount of air mo!ing through a space to the !olume of the space$ Air change rates are calculated to determine how well a space is !entilated compared to pu#lished standards- codesor recommendations$ Air changes per hour (AC4) is the most common unit used$ his is the !olume of air (usually e7pressed in cu#ic feet) e7hausted or supplied e!ery hour di!ided #y the room !olume (also usually e7pressed in cu#ic feet)$
Airow is usually measured in cu#ic feet per minute (C8M)$ his is multiplied #y 6% minutes to determine the !olume of air deli!ered per hour (in cu#ic feet)$
AC4 (C8M Q 6% minutes)(room !olume in cu#ic feet)
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 12:33
5hat i want to .now is how can i determine the C8M needed for the area$
willard3 (Mechanical)
3 Apr %6 12:3?
Fa#lo: he sensi#le heat ratio and cooling load will dictate the air changeshour and is the solution to the pro#lem$ p ro#lem$ ry ry not to confuse the cause for the eBect$
In my climate- ie- D2 deg latitude and 3 deg longitude- in a frame#uilt- insulated #uilding with appro7 2%O glass and * ceilings- cfm !aries from 1 cfms"uare foot to 3 cfms"uare foot of oor depending upon internal loading- ie- num#er of peoplelighting- e"uipment loads and !entilation loads$
;H load !aries from 3%% #tucu foot e7clusi!e of internal loadings$
5e ha!e #uilding codes in /ew 0or. 0or. that ma.e the range of these num#ers pretty small$
0our 0our latitude is 1 deg and longitude is 6? deg- so solar loading and air temperatures will #e !ery diBerent than /ew 0or.$ 0or.$ I am also sure that you construction materials and methods are diBerent than ours so #uilding mass and etc will #e diBerent
0ou 0ou should get a copy of A'4@A 8undamentals 8undamentals 9olume(American 9olume(American 'ociety of 4eating- @efrigeration and Air Conditioning ngineers)G it contains answers to all the "uestions you are as.ing$ 0ou ha!e access to the we#- so &<oogle& A'4@A$ A' 4@A$
0ou 0ou can also use rane rane software to calculate calculate heatingcooling loads- #ut you need ,rst to understand the input$ A'4@A will #e a #ig help with the input$
willard3 (Mechanical)
3 Apr %6 12:D2
5rong data:
;H load !aries from 3%% #tucu foot e7clusi!e of internal loadings$
@ight data:
;H load !aries from 3 #tucu foot e7clusi!e of internal loadings$
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 13:1D
E.- (willard3) the ,rst formula you ga!e- me was a !ariation of the ,rst law of thermodinamics- another way to put it is using the mass ow times the enthalpy diBerence #etween am#ient condition and dew point condition- #ut in #oth cases i need a ow of air in terms of mass or !olume- and there is my confusion$ he other "uestion is : do i need a U8 lea!ing air temperature in a system using 1%%O outside air>$ I ma.e this "uestion #ecause i assume that in this .ind of systemthere is no mi7 #etween the air in the room and the air from outside to achi!e a medium temperature- #ecause e!entually the total !olume of air in the room will #e e7hauted and replace for a new !olume from the outside- so i was thin.ing that the lea!ing air temperature should #e the temperature of the conditions i want in the room- letNs say 3U$
R'A (Mechanical)
3 Apr %6 1:%3
I am going to ta.e a sta# at this$
=esign condition: Eutside air temp (=;5;) ?2868 (%$O mean summer temp Ros Angeles) 'upply air temp 8
Assumptions: =imension of space 6%*(R)76%*(5)71*(4) 2% people 7 2% #tuhr %%% #tuhr 2$ wattssf lighting ?%%% #tuhr Assume -%%% ;Hhr e7terior loads
AC4 (Air change per hour) 1% therefore C8M AC4 7 9olume 6% (1% 7 D-%%% cu ft)6% ?-%%% cfm
'o ?-%%% cfm is re"uired to e7haust the room 1% times per hour$
/ow to determine the load on the cooling coil: Cooling coil load 1$1 7 C8M 7 (1 2) 1$1 7 ?-%%% 7 (?2) 366-3%% ;Hhr
'umming all the loads: 366-3%% #tuhr S %%% #tuhr S ?%%% #tuhr S -%%% #tuhr 3-3%% #tuhr or 32 tons$
'o to select a unit to suit all the a#o!e loads- I will select a 3 ton unit$
his is +ust a generic e7ample$ here are many other loads that I am not incorporating$ 4opefully this can get you in the right direction$
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 1:D1
E.- so far- all the things that had #een told here- i already .new it$I thin. i-m not as.ing the right "uestion- so here i go- how can i determine the total cfm that is re"uired to pass trough a cooling coil in a system that re"uires 1%%O outside air- or how do i .now how many changes of air do i need$
R'A (Mechanical)
3 Apr %6 1:%1
he C8M re"uired is calculated #y the engineer$ ypically for a la#oratory the AC4 is 61 AC4$ A restroom is D AC4$ (these are recommended num#ers we use in our oLce$ hese are not a standard$)
=oes that help>
pa#lo2D1% (Mechanical) (EF)
3 Apr %6 1:3
o.- here is the pro#lem
a loc.er room Area 3% s"ft height 1%ft 3 persons in the room what will #e the diference in my load calculation if the system is 1%%O recirculate air or 1%%O outside air$
R'A (Mechanical)
3 Apr %6 2%:D
Air change method Assumptions: 'ummer design condition ?28638 Indoor design condition 28 Interior location therefore no e7ternal load Roc.er @oom AC4 1 (again- this is our oLce standard) 9olume: 3% sf 7 1%* 3-%% Feople load sensi#le 2% #tuhperson (1-2%% #tuh) (+ust got done wor.ing out) Feople load latentperson 1% #tuh (3 #tuh) Righting load 1$ wattssf (32 #tuh)
C8M 1 7 3-%% 6% - cfm (lets say ?%%% for simplicity)
1$ 8or 1%%O outside air: Cooling coil load 366-3%% #tuh otal sensi#le load 366-3%% S 32 S 1-2%% 3?-2 #tuh or 32$ tons$
2$ he diBerence will #e su#stantial #ut Roc.er rooms are ne!er 1%%O recirculated$ here will always #e some amount fresh air #rought into the space$
he air change method is a simple method of getting an appro7imate idea of what sie unit is re"uired$ In loc.er room applications many times they are heated and !entilated only$ And Ma.eup air is usually always re"uired to achie!e proper air #alance$
4ope that clears up some "uestions you may ha!e$ <R
cme (Mechanical)
Apr %6 16:D1
a rule of thum# $$$$$ 1% cfmton for a preliminary siing load
,nal psych chart analysis on =;mean5; per ashrae geographic data
don*t forget fan heat gain
62hog (Mechanical)
2D Apr %6 12:2%
Ene other thing must #e ta.en into account$ If you are planning on using a pac.aged system (ie$- rooftop unit)- you must consult with the manufacturer$ As a general rule- (at least according to my local reps) a pac.aged unit is only capa#le of accepting appro7imately 23%O of the total airow in the form of unconditioned outside air$
Any system you use should #e discussed with you local rep$ 0ou should also re"uire them to also pro!ide you with any documentation for information that may diBer from you &sound engineering +udgement$&
80I- A'4@A list the design condtions for =ominican @epu#lic cooling- in the %$DO range- as ?1% d8 d#w#$
lilliput1 (Mechanical)
2D Apr %6 12:D?
62hog is right$ Chilled water systems are recommended for 1%%O EA applications$ 4owe!er it is also possi#le to use multistage pac.age =Q AC units #y recirculating a portion of the supply direct to the return and supplying to the room only the C8M e"ui!alent of the EA handled$ 8or e7ample- if the load for say D%%% C8M 1%%O EA is 2% tons$ Hse a 2% ton unit say nominal %%% C8M- #ut use D%%% C8M EA- %%% C8M
total 'A- D%%% C8M recirc direct #ac. to A4H and D%%% C8M supply to the room$ 'ol!e for the mi7ed air conditions of the EA and recirc air to get cooling coil entering air condition$ Interpolate performance from ta#ulated date$ 'ol!e for cooling coil lea!ing air temperature$ =etermine fan and duct heat gains and deduct from ta#ulated capacity to get net capacity$
thoot (Mechanical)
3% Apr %6 23:2
8irst you need to compute the total heat load $li.e num#er of window- sie of doors what materials used in the #uilding 5all$ 0ou may ,nd the !alue of each material in Ashrae hand#oo. or Mechanical hand#oo.$0ou may also use Manual J method- a software for load computation$ his wil guide you step #y step method$
sloyal (Mechanical)
1 Jun %6 1:%2
4ere*s my 2 cents$$$
;H4 D$ 7 cfm 7 =elta 4 4psych chart enthalpy McVuay W rane as well as others ha!e downloada#le Charts that should gi!e nthalpy conditionsI prefer the straight edge on a paper graph (calcs for the ,les)
My design conditions are ?d#3w# nthalpy 36$ indoor cond$ d8 %O 4umidity nthalpy 2
%$ or %d8 %O 4umidity nthalpy 26$3 8or ease of use I call it a d4 of 1%
;tuh cfm 7 D$ 7 1%
If I ,nd I need a 2% on system- I*ll #e !ery careful to select a coil on face !elocity- to a!oid freee upas well as Ratent W sensi#le capacities$ Interlaced coils with multiple stages (more is #etter) wor. #est$
I a!oid conditioning the space with this system as it would re"uire a larger system$ I prefer deli!ering room temp air W ha!ing a seperate recirculating system for space loads$ I may e!en deli!er a portion of the &tempered outdoor air& into the return of the space conditioning system- Fossi#ly 1%%O if the cfm matches- with a return setup for independent operation$
My winter design is 2%d8 so any outdoor air is heated W it*s usually done with a direct ,re MAH$ he products of com#ustion in this air has recently #ecome an issue- especially on units recirculating any inside air$
5ith these design conditions- I would loo. at incorporating a 4eat @eco!ery 9entilator$ 'omething li.e a @enewAire with latent W sensi#le e7change can sa!e a #oatload on the aforementioned <as MHA w2%ton coil$ 7h air conditions (i$e$ dust- oil- etc$$$) might prohi#it a heat e7changer altogether$
good luc. sl+
0or.man (Mechanical)
1 Jun %6 1?:3
Ene thing not to o!erloo. is that the latent load is going to #e rather high- gi!en that this is a loc.er room with showers$ A recirculated system*s latent loads at the coil could #e higher than the E'A senario$ I would loo. up latent load and air change recommendations in the A'4@A 8undamentals 4and#oo.$ It may ma.e more economical sense to go with 1%%O E$'$A$ and .eep my discharge air at say 6% 6 degrees afterall it is a loc.er room$ 4ey I ha!e enough pro#lem with shrin.age$ GX) <ood luc.- with this much ad!ise how could you go wrong> I*m not a real engineer- #ut I play one on $9$ A$J$ <est- 0or. Int$
Coreech%1 (Mechanical)
D Jun %6 13:D
VuoteTTTTTTTTTTTTTTTT o.- here is the pro#lem
a loc.er room Area 3% s"ft height 1%ft 3 persons in the room what will #e the diference in my load calculation if the system is 1%%O recirculate air or 1%%O outside air$ TTTTTTTTTTTTTTTTTTTTT
he diBerence in your load calculation is 4H<$
Fost a little more information li.e whatYs your design room temp> 8or pu#lic loc.er rooms I design around a =eg$ Indoor temp year round$
A few things you need to .now ,rst a#out loc.er rooms$
Roc.er rooms should always #e .ept slightly negati!e$ he loc.er room area should #e completely sealed /E plenum returns /o mi7ing of air with other systems$ 0ou are allowed to recirculate air pro!iding it is the air from the loc.er room area$ 0ou must ha!e e7haust fans$ 0ou donYt always need 1%%O Eutside air +ust enough to pro!ide proper !entilation to match your e7haust$
I ha!e use $@$9Ys in loc.er rooms to reco!er as much energy as possi#le to lower the load$
In your case if you use 1%%O outside air you will need to e7haust 11%O of that air (to .eep the space slightly negati!e) hatYs a 4H< load to cool and then to e7haust if you li!e in a warm climate$
Core ssn/1 (Mechanical) (OP)
31 Jul 12 1?:16
I am designing the 49AC system of a storagewarehouse in laredo- 7- which is supposed to #e .ept at % degrees 8 year round$ I ha!e #een told #y the #uilding contractor that there are no people in this place$ Am I still supposed to implement outside air into the design to con,rm with A'4@A re"uirements> he second part of my "uestion is that I ha!e ran the load calculation using rane race and not sure if the system sie is large enough$ his storage is 1%% s"$ft$ 2%* ceiling- no load e7cept lighting- which is a#out total
of D%% 5atts$ @ !alue of walls is 1?- and ceiling is 3%$ Road calculation result is 2$1 tons116D cfm$ his is a#out 6% s"$ft$ton- which seems a #it too high of s"$ft$ton I am used to seeing$ cd!!13" (Mechanical)
1 Aug 12 11:33
A'4@A 62 (if that is your code re"uirement) still has an Area Eutdoor @ate for wharehouses- so yes- you still need EA$ 'ee a#le 61 =ont ha!e e7perrience with wharehouses- #ut I thin. the s"ftton @ule of hum# you are used to seeing is pro#a#ly for oLce space etc (closer to D%%>- +ust a hunch)$ 'o without windows and EA- the @E may clim# to close to what your seeing$ /ow dont forget to ad the EA .nowledge is power
ssn/1 (Mechanical) (OP)
1 Aug 12 16:D6
han.s for the reply cd77$ I did some google search And found the following lin.s$ I am not sure if these are really legit or not since I ran across them online$ If these douments are correct- then I #elie!e there is no need for outside air in an unoccupied storage$ 8rom what I ha!e #een told #y the #uilder- this space is +ust for purpose of storage$ $ttp%&&***as$raeorg&File.45i6rary&doc5i6&Pu6lic
And $ttp%&&***as$raeorg&File.45i6rary&doc5i6&Pu6lic ssn/1 (Mechanical) (OP)
1 Aug 12 1:%2
I searched the A4@A we#site for the douments I posted in my pre!ious post and they are on the we#site$ 'o they appear to #e legit$ cd!!13" (Mechanical)
1 Aug 12 1?:11
<ood one$ he interpretations are legit$ Vuestions is are they related> he intent of 62 is safety$ 'o if the material you store does not produce oB gassing etc$ And for.lifts etc are not used in the space- then may#e$ Again- I ha!e ne!er designed a wharehouse- (#ut ha!e fought a#out the intent of 62 with R= interpreters)$ ;uilders want cheap- your +o# to design right$ 'end the #uilder an email- with the wording you descri#e and as. if that is what the #uilding*s intended use is- when he answers you #y email- at least you ha!e something to C0A$ .nowledge is power
ssn/1 (Mechanical) (OP)
1 Aug 12 2%:D1
han.s again cd7$ In the past I ha!e seen engineers as. for EA inlet to #e a motoried damper- which closes shut when unit is not operating$ =o you .now if that is a code
re"uirement or a design preference> cd!!13" (Mechanical)
1 Aug 12 2%:D?
/ot !ery de,niti!e answer #ut may#e youll get a wharehousee7perienced engineer response as well$ My energy code (2%%? ICC) re"uires low lea.age dampers- #ut allows gra!ity dampers for #uildigns less than 3 stories$ <ood Ruc. .nowledge is power
DrR7 (Mechanical)
Aug 12 1:11
I ha!e completed numerous conditioned self storage faculties$ 0ou may not #e oB in the %%ft2ton trust your load calculations$ he ,rst few I did- I could not #elie!e the results I got Z o!er 1%%ft2 per ton$ Indoor lighting is on motion sensors and will run %$2 wft2 or less$ 0ou will need to account for outside air #ased upon IMC or 62$ 4umidity and design temperature setpoint and minimum C8Mft2 ha!e a large impact on the loads$ 4ere in the Midwest I ha!e had issues with moisture in ,rst year if itYs a precast #uilding- condensate on outside walls in the winter due to pac.ing stored materials tight to outside wall and smo.e remo!al systems$ 5hy %8> 'eems !ery low for a thin en!elope$ 9$as:ean1 (Mechanical)
12 Aug 12 3:%%
=o you ha!e any e7haust> If so- the minimum ma.eup air you #ring in should always #e a#out 1%O more than the e7haust !olume$$$ 4ello all wo ones AW; ha!e the same occupancy- let say 1% persons each- the load calculation told us that one A needs 6%% cfm- [one ; needs D%% cfm fore e7ample- and #oth of them need 1% cfm of fresh air each for !entilation$ /ow total cfm is 1%%% cfm- fresh air is 3%% cfm which means 3%O$ 'o- 3%O of D%% cfm is less than 1% and 3%O of 6%% is more than 1%$ Am I right> DRWeig (lectrical)
? Ect 11 16:3%
0es$ If you want to distri#ute the outdoor air in a proportion that is diBerent from the proportion of supply air- you can*t +ust mi7 them and send them down the duct$ A separate tempered outdoorair system is needed$ If not- you must increase the outside air so that the worst case room is !entilated to minimum re"uired #y code$ In your case- 3O total outdoor air will gi!e you +ust o!er 1% C8M to one ;$ [one A will #e o!er!entilated (22 C8M)$ <ood on ya-
<oo#er =a!e ms,uared;8 ('tructural)
? Ect 11 1?:D
=a!e: If [one A is a #athroom- o!er!entilation is a good thing$ Mi.e McCann MMC ngineering
DrR7 (Mechanical)
1% Ect 11 :%
0es and no$ If the system is C9- then one ; is your &critical& one and it will dri!e your O EA$ his is the dilution O$ If the system is 9A9 and has the a#ility to !ary minimum ow to each one- then total EA could #e as your calculation$ his may re"uire EA ow measurement- CE2 sensors- reheat or ==C controls$ I suggest you read A'4@A 62 documents$ A properly completed !entilation schedule will re!eal the critical space- EA ow and damper min$ position$ Pruger has a few white papers on this topic and an 62 spreadsheet to run thru the math$ $ttp%&&***krueger'$accom&lit&*$itepaperasp Ma.e sure you .now which code standard your are designing to Z the num#ers !ary$ Most load programs ha!e the a#ility to specify which code you are designing to and will de!elop the !entilation schedule$ CE2 reset will help with high O EA$ *alkes (Mechanical)
1% Ect 11 :%
Also- if one A is a #athroom- you would li.ely use transfer air to ma.e up the e7haust$ 3104/" (Mechanical) (OP)
11 Ect 11 21:16
han. you for your reply- #ut I ha!e points regardless to the control system for now$ 1 for C9 systemsit is o. that we need 3O EA in order to ha!e 1% cfm of EA in one ;$ I guees this is the ratio of 1%D%%$ /ow- If I went with %$3 as 3%%1%%% that mean on unit le!el I am o. with the code #ut at one le!el I am not$ 2 for 9A9 systems- here is the pro#lem one ; at D%% cfm- and one A at 6%% cfm- the EA Ois %$3O$ what if the one ; #o7 modulate to 2% cfm while one A #o7 still at 6%% cfm>$ =oes that mean the one ; #o7 has to has a ,7ed position at D%% cfm alwayes and one A minimum cfm is D%% cfm or more in order to .eep %$3O of EA$> 5eftyr (Mechanical)
12 Ect 11 ?:31
I guess you are ha!ing a pro#lem #ecause you will #e using an A4H system$ 5hich force you to mi7 your fresh air and return air in the unit #efore supplying to your two ones$ I suggest you use 8CH system were you ha!e to duct your fresh air to your diBerent one in a re"uired proportioin$ hat is my two cent worth opinion$ *alkes (Mechanical)
12 Ect 11 13:3D
[one ; may then #e your critical one that will determine the percentage of EA re"uired
for the unit$ 6%O assuming that the space is still occupied at that point$ If the #o7 is throttling #ac. #ecause there is no load then there may not #e anyone in the space$ tys"4 (Mechanical)
12 Ect 11 16:D3
=r@H hit on some of the points if you are under A'4@A 62$1 for your !entilation code$ It*s a little more complicated than you are descri#ing$ 0ou need to follow the method outlined to calculate the system outdoor air ow for multione systems$ It will actually end up somewhere #etween 3%O and 3O for the constant !olume system$ In the !aria#le !olume case you ha!e to account for the minimum airow settings$ It will increase your system outdoor air the lower your minimums are$ DrR7 (Mechanical)
12 Ect 11 1:2
@un thru the num#ers$ 8irst we need to assume you ha!e run the loads correctly for the systems #eing applied and ha!e correctly applied the re"uired !entilation code$ Roads will change #ased upon system selection$ 8or a C9 design Z [one ; is the critical space$ his one will determine the outside air minimum damper position$ 1%D%% 3$O$ his will pro!ide 1% cfm of EA$ [one A 6%% cfm at 3$ O 22 cfm of EA$ 0ou will o!er !entilate this one #ut since you ha!e a C9 system you cannot easily alter EA ow unless you apply additional controls$
otal system 1%%% cfm at 3$O EA$ 8or a 9A9 design Z [one ; will still #e the critical space$ [one ; ma7imum terminal ow D%% cfm and minimum ow of 1% cfm (3$O of ma7) from the central A4H$ [one A ma7imum terminal ow of 6%% cfm and a minimum ow of 1% cfm (2O of ma7) from central A4H$ otal system 1%%% cfm at 2O EA$ /e7t you need to ma.e sure the 9A9 system will pro!ide correct 'A dilution o!er the A4H ow range$ Controls can #e applied such as =C9 (CE2 sensors) or ow sensors (rane ra" dampers) to ensure proper EA to each one at all times$ 3104/" (Mechanical) (OP)
12 Ect 11 23:%D
you said &Roads will change #ased upon system selection$& could you please e7plain this point alittle more$ how can #e sure that my load calculation is correct if I used the code !alue (3%% cfm in our e7ample) and then interduced 2O more than that(3%3%%)-what a#out unit capacity in this case> in 9A9 system you said&[one ; ma7imum terminal ow D%% cfm and minimum ow of 1% cfm (3$O of ma7)& if the one ; minimum is 1%cfm how can #e sure this 1% cfm has 1% cfm of EA-> if we use the same C9 e"uation then the EA O would #e 1%%O- and this is right if all ones are in minimum postion at the same time then the unit will pro!ide 1%%O EA$ #ut what if one ; is in minimum and one A is not> also if one A minimum is 1% cfm same "uestion a#o!e> when one or #oth ones are in mimimum the total will #e less than 1%%%cfm$ when load droped down that does not mean for sure some people left- it could #e north
one and west one$ tys"4 (Mechanical)
13 Ect 11 1%:D2
E.ay- there still seems to #e some confusion$ I used the calculator on the Prueger we#site to simulate your pro#lem$ I assumed cooling mode only (1$%)$ 4ere are the results: Constant 9olume 'ystem: 32 C8M of EA re"uired 9aria#le 9olume 'ystem: 3?? C8M of EA re"uired Ri.e I said- it*s not as simple as +ust summing your EA airows if you are re"uired to use A'4@A 62$1$ he !entilation eBecti!eness in each scenario is diBerent #ecause you ha!e to use your minimum ow for [one ;$ Can I ha!e a constant speed =EA' system ser!ing 1% air handlers that ha!e !aria#le fre"uency dri!es> 5ill the outdoor airow rate remain the same throughout all operating points of the air handler fan> I*m assuming it won*t since the pressure in the mi7ing #o7 will change and I would need some sort of 98= on the =EA' unit$ If I do need a 98=- what is the se"uence of operation and what controls the =EA' fan speed$ han.s in ad!ance$ <McD (Mechanical)
3 /o! 11 %:1?
If your =EA' system is sied to pro!ide the minimum !entilation air to satisfy A'4@A 62then lea!e it at constant !olume$ he !aria#le !olume A4H*s will +ust use less return air in the mi7ing section and you*ll still #e deli!ering the minumum re"uired !entilation air to the spaces- as well as ma.eup air for constant e7haust systems (washrooms- general e7haustetc$)$ hat*s assuming the 9A9 A4H*s are sied and !arying the supply air ow for cooling (or heating) demand to their spacesones during a normally occupied period$ =>?" (Mechanical)
3 /o! 11 1:
here are two ways to go a#out this: 1$Constant !olume =EA' deli!ering constant !olume to each A4H irrespecti!e of what speed they are running at$E#!iously when the A4Hs ramp down on the 9'=-the mi7ing #o7 static pressure will drop resulting in less fresh air #eing drawn$0ou need to open the fresh air air damper on the mi7ing #o7 more to .eep the air ow constant$Ene way of doing this is to hold the diBerential pressure across the damper constant no matter what the static pressure in the mi7ing #o7 is$ 2$A !aria#le !olume =EA' responding to change in fresh air re"uirement from each A4H$he fresh air damper in each A4H will modulate in response to a CE2 monitor in each of the ones$he =EA' A4H will ha!e a duct static pressure sensor tuned for the ma7imum air ow$Any =EA' ow reduction will cause the static pressure to rise and will slow the unit down$ Eption 2 is more comple7 and is re"uired only if the occupant load is li.ely to !ary signic,cantly ie lecture theatres-auditorium-restaurant etc s*oos$10. (Mechanical) (OP)
3 /o! 11 1:
hese are pretty small air handlers- no more than 2-%%% cfm each$ I am not sure that the outside air will drop much when the ahu speed ramps down- #ut I do ha!e to su#mit for R= 'il!er and I want to ma.e sure it is correct$ 5hat do you thin. a#out ha!ing a pressure independent 9A9 #o7 on the EA duct to each air handler> cry.. (Mechanical)
/o! 11 12:2?
'moosh 0ou ha!e to gi!e all data when as.ing a "uestion$ his data of 2%%% C8M ma7 for A4H is important in your pro#lem and should ha!e #een stated$ second- you need to state amount of EA and total =EA' unit sie for people to ma.e a sound +udgment third- you need to mention the R= aspect and what part of R= are you pursuing> are you implementing a =C9 control strategy> using CE2 sensors> if you do- you need means to control the reduction of EA into the #uilding$ 8rom what you state- you system is no more than a 8CH with =EA'- you +ust call them A4H$ we*re tal.ing a#out 1%O EA> (2%% C8M for each unit> total =EA'2%%% C8M- or 2%% C8M>) if so- then your system is fairly small- and #oth your =EA' and A4H ha!e fans 4F are so small that 98=*s do not ma.e sense any way$ It appears that C9 =EA'- C9 A4H*s with manual #alancing is the way to go$ If you get tangled into that air ow measuremnt- =C9 control etc- you*ll #e spending a fortune for minimal gain$ /o way in hell you can ha!e a pay #ac. on such small systems$ I*d go C9 all the way- A4H*s and =EA' unit as for 98=*s for such small systems- it is as they say in ;roo.lyn &8oggeta#outit& =>?" (Mechanical)
6 /o! 11 16:36
I fully second cry22 *s !iews$ s*oos$10. (Mechanical) (OP)
/o! 11 :3
han.s Cry and 'AP$ I ran the energy model and I was only getting a 2O sa!ings with the 98=s so it is not worth it$ I was surprised to see that I was also #rea.ing e!en on the energy wheel tonnage sa!ings !s what it costs to run the erw motor$ he EA is only 1%% cfm as cry guessed- so I guess energy reco!ery is also not worth it$ cry.. (Mechanical)
/o! 11 :%
'moosh here is no 'il!er ;ullet in sustaina#ility$ 0ou ha!e to throw a lot of darts at a prro+ect to sa!e energy$ hey do ha!e to ma.e sense though$ I*d say @5 total enthalpy wheel is worth loo.ing at (again another data you did not indicate in your pro#lem statement your Rocality weather data) the harsher the climatethe more opportunities to sa!e$ It is not +ust tonnage- it is also ;oiler sie (then again- are you in a heated climnate>) I would pay attention to that @5 load- if the load comes down say from to % ton for e7ample- then it may ma.e sense #ecause you*d #e going from a larger @H or aircooled chiller to a low end (!erify actual P5 of e"uipment) from 6% to % ton- your %ton will #e rightly sied w@5- while your 6%ton will #e o!ersied wo @5$ he following are some of the ma+or things you should consider upfront when doing a 'ustaina#le design 1$ @5 total nthalpy wheels 2$ Row <lass 3$ Righting Min A'4@A ?%$1 1 5'8 or e!en #etter R= lighting D$ =C9 using CE2 sensors for large occupancy spaces to pro!ide di!ersity$ $ &@ight'iing& of e"uipment- actually H/=@'iing is <EE=- especially for residential$ this can*t #e stressed enough- we*!e seen people pro!ide a 2%ton AC unit for an ele!ator
machine room when a ton will do$ Chec. tose calcs$ 6$ Airside econimier when climate permits$ $ 98=*s on 8ans W pumps etc of 1% 4F motor and larger$ $ <ood control se"uence of operation H@/E88 e"uipment when you can- nothing #eats E88$ ?$ 'ystem choice for the right occupancy$ 1%$ some rules of thum#s: using points 1 thru D a#o!e- you should get around %%'8ton for cooling and 12% ;H4'8 of heating in a moderate climate such as the H' mid atlantic$ Rast #ut not least- watch out that sensi#le load going down so much that you ha!e under %$ C8M'8 of cooling- you need to mo!e some air- I li.e to see no less than %$ C8M'8 (especially for 9A9 systems)- then again watch that dehumidi,cation pro#lem resulting from high 'A temp$ (?) when mo!ing more air purposely$ 0ou ha!e to ,nd a #alance of things that ma.e sense and apply them- that*s why we are hired as engineers- to ,nd all the solutions for each speci,c pro#lem$ 4icould any one e7plain - for a Constant !olume system what is Cooling coil supply air temperature reset pro!ided normally$is the @eset =elta is calculated #ased on the ma7imum and the minimum cooling load or is there any thum# rule han.s and @egards !ignesh$ Dra2en (Mechanical)
8e# 12 12:%%
Pnowing a#out such formal re"uirement- I do not .now how it actually wor.s in practice$ In theory- temperature reset should refer to one with highest cooling load- raising supply temperature as much as possi#le during part load- which should reduce reheat energy needs for the whole system$ In my opinion that would ma.e sense if '4@ is constant in all load conditions- which- of course- is not the case- and therefore such reset can directly reduce dehumidi,cation eBecti!eness- and the only mean to cope with that is to plot chart of part loads- ma.e graph of reset temperatures accordingly- and than apply it to control logic (similarly to outside temperature dictated supply temperature reset in hydronic systems)$ I did not hear a#out that in practice- howe!er$ Mec$@ngA9P@ (Mechanical)
8e# 12 16:2
'ay you ha!e a la# with constant !olume wreheat$ /ormally the discharge temp would #e degrees and then reheated to maintain space temp setpoint$ If humidity monitoring is in place- you may increase the supply air discharge setpoint until the space rh raises a#o!e setpoint (say %O)- then the chilled water control !al!e modulates or compressors stage up to get the @4 down #elow setpoint$ It is a way to sa!e energy throughout the yearespecially if you ha!e a 1%%O EA system$ =>?" (Mechanical)
1% 8e# 12 23:22
he usual reset #and is 13\1C$@eset may #e done #ased on either return air temperauture or outside air temperature or a com#ination of #oth$0ou need to #e mindful
of internal humidity re"uirements and e7ternal humidity ranges #efore employing supply air reset$It is not recommended for humid climate such as across asia or the middle east$ Dra2en (Mechanical)
13 8e# 12 13:1D
'AP?At ,rst glance things loo. !ery simple if you ta.e latent load out of analysis$ he #ig "uestion is- howe!er- what are you sa!ing than$ My understanding is that temperature reset is done to sa!e on reheat energy- #ut if you do not ha!e controlled dehumidi,cation !ia cooling coil- that you do not ha!e reheat at all$ Rower lea!ing air temperature will reduce load co!ered #y space cooling and your sa!ings are coming to eroK Mechng/CF he e7ample you mentioned is one that I could imagine- though it seems to #e limited to one one systems$ Etherwise- I am wandering how to decide on referent internal dry #ul# temperature- when each one may ha!e diBerent latent load patterns$ At design stage you are already aware that your ones will not ha!e the same relati!e humidity- #ut will rather #e within accepta#le (as wide as possi#le) range- #ut when you #egin playing with supply air temperature things #ecome complicated$ $ouseman.4 (Mechanical)
13 8e# 12 16:
@ecommend that any constant !olume system #e re!iewed for compliance with A'4@A ?%$ especially section 6$$2 'imultaneous 4eating and Cooling Rimitation$ here are limits on how much reheating is allowed$ here are also e7ceptions to the rule$ his is a prescripti!e section- you may need to document the path for energy code compliance$ =>?" (Mechanical)
13 8e# 12 21:31
=raenApart from the reduction in reheat re"uirements-there is a sa!ing due to compressor ha!ing to do less wor. at higher e!aporator pressures in a =Q system$here is scope for chilled water temperature to #e reset up in C45 systems with a reduction in energy consumption$ 21 'ep % 1:D3 I am in the process of trou#leshooting an EA duct distri#uting air to four A4Hs$ he most remote A4H is modulating the return air dampers to gi!e a constant ?%%C8M of outside air$ =ue to the return air damper modulating down the total air is low$ I am getting a !aring consensus of opinion among my cowor.ers and the A; on this- from #ringing in a separate EA duct- to adding a fan in line for the speci,c unit- to adding a fan on the main duct(a#out 2%% C8M total EA demand)with #ac.draft dampers in the EA duct near each unit$ I would li.e to sol!e this #y adding an inline EA fan at the speci,c A4H with #ac.draft dampers at the other units #ut I am not shure how to calculate the fan sie or if this will wor. at all$ :ronBr>ur (Mechanical)
21 'ep % 1:%1
Is the EA ductwor. sied to handle the EA re"uirements of all A4H*s$ 'ounds li.e they are
,ghting each other for the air$ Clippo/ (Mechanical) (OP)
21 'ep % 1?:3
/o- I don*t thin. they are ,ghting for air$ his unit is the most remote- longest distance from the Rou!er$ Mintulep (Mechanical)
21 'ep % 21:D
5hat is the actual pro#lem that you need to sol!e> It is not clear in your original post$ I*ll guess that the pro#lem is that &the total air (supply>) is low (from the most remote A4H)&$ If that is it- I would guess that mo!ing ?%% cfm through the EA duct has used up most of the a!aila#le static pressure from the A4H*s fan$ he simplest way to to sol!e this would #e to simply increase the A4H fan speed- pro!ided that the motor has suLcient unused capacity$ he lowest cost (life cycle wise) would #e a separate EA duct- sied for low pressure drop$ Adding a #ooster fan means you need to pay to run the fan fore!er$ Adding dampers at the other A4H*s increases the pressure drop at each- ma.ing their fans costlier to operate$ Clippo/ (Mechanical) (OP)
22 'ep % 2%:D
Agree$ 5hen the A; opened the return air damper manually to 1%%O the total air increased to near design$ he EA decreased #elow design$ 5e do ha!e some margin in the motor to increase the fan @FM #ut this thing is already outside of the fan cur!e en!elope$ he static pressure is #elow where the fan cur!e would ha!e it at the lower C8M when I replotted it$ I thin. the reducting of the EA is the only realistic- cost eBecti!e solution$ 5e ha!e some restrictions on where the EA lou!er can #e placed to complecate things$ tras$canman (Mechanical)
2D 'ep % :1
Increasing the speed of the A4H will also directly increase the A4Hs cfm$ 5ill this #e a pro#lem> Also 4F increases as cu#e of speed$ 5hy not consider a separate EA fan for each A4H> hat fan could #e interloc.ed with its respecti!e A4H$ 0es- you will face operating e7pense of the EA fan- #ut it will wor.$ ,uark (Mechanical)
2D 'ep % :D
I agree with MintJulep$ he reduction in total owrate is not due to the control of return damper #ut #ecause the outside air is consuming the fan static$ Chec. the fan total static when the return damper is fully open (as this gi!es you the design owrate)$ =isconnect the EA duct- control the return damper to get the re"uired owrate of EA and again chec. the total static pressure of fan$ If the diBerence in static pressures is positi!e then design your duct as per the a!aila#le static$ If the diBerence is negati!e- then select the fan for the new ducted EA system S the diBerence$ >66yAormal (Mechanical)
26 'ep % 1:12
It is always tough I thin.- when you ha!e a 98= and you want to try and ha!e return air
dampers close oB and outside air dampers to open up- to try and .eep the outside air contant under lower airows when the supply #lower is ramped down$ May#e get an inline fan with a pressure independent 9A9 #o7 to contol the amount of outside air you want$ >D>< (Mechanical) (OP)
2 Apr % 1%:%
I am wor.ing on the design of a Constant !olume- =Q ac system (cooling only)for a <o!ernment ELce$ 8or the cooling load calculation I am including a !entilation load of 1 C8Mperson in occupied oLce areas$ /ow in this same #uilding I also ha!e a cafeteria room- to #e used only #y the oLce staB (around 2% people)$ If I now again include a !entilation load of 1 C8Mperson for these same people when in the cafeteria- I will #e dou#ling the re"uired !entilation air and introducing dou#le the air I actually need (and o!ersiing my e"uipment)$ If I donYt- I will run short on the supply air for the cafeteria$ 5hat is the criteria to follow> Ferhaps the #est would #e to ha!e an independent system for the cafeteria- #ut what if this is not possi#le> Another issue on !entilation: Considering the local construction standards I .now I will #e ha!ing some in,ltration- this howe!er is hardly "uanti,a#le$ 'hould I reduce my system !entilation re"uirements (i$e$ 1C8Mperson to 1% C8M person) to compensate for the in,ltration !entilation> han. you-
*illiams<> (Mechanical)
2 Apr % 11:3
0ou need follow the A'4@A 62 guidelines$ It is no longer as simple as 1 cfmperson$ 0ou will need to ta.e into account the airow percentage that is deli!ered to each space- and what portion of that is EA$ 'ince it is a constant !olume system this is an easy calculation$ Also- A'4@A 62 now re"uires EA for space contaminates- this is a EAsf num#er- and EA occupants$ 26 Jun % 1%:% I am wor.ing on a reno!ation pro+ect- the #uilding is #uilt in 1?D- I assume 1?1 ;ECA mechanical code is used at that time$ =oes anyone .now what is the outside air and !entilation re"uirements for oLce and conference rooms in 1?1 ;ECA Mechanical code> MarauderE (Mechanical)
26 Jun % 12:2D
I would imagine that you won*t #e a#le to design to the *1 code for current permits$ ***ander*eilcom
ap$ou (Mechanical) (OP)
26 Jun % 1D:3D
he outside air re"uirements for #uilding #uilt in 1?D is cfmperson and $33 cfmperson in conference room$ It is almost impossi#le to upgrade the outside air to the current code re"uirements$ he local #uilding code authority agree us to follow the !entilation code #ased on the year the #uilding was #uilt$ It ma.e sense- #ecause if one oor is #eing reno!ated in a high rise #uilding- it is unfair to as. the tenant or owner to upgrade the oa re"uirements for the
entire #uilding$ MarauderE (Mechanical)
26 Jun % 1:%2
It may ma.e sense- #ut it doesn*t ma.e for a good #uilding$ I wouldn*t want to li!e or wor. in the +urisdiction you are under- as e!ery #uilding would comply only with the year it was #uilt$ Almost impossi#le means that it can #e done$ I should hope that you ma.e the #est engineering decision when designing those oLce and conference spaces$
***ander*eilcom
7>Diep (Mechanical)
2 Jun % 1:D1
&It may ma.e sense- #ut it doesn*t ma.e for a good #uilding$ I wouldn*t want to li!e or wor. in the +urisdiction you are under- as e!ery #uilding would comply only with the year it was #uilt$ Almost impossi#le means that it can #e done$ I should hope that you ma.e the #est engineering decision when designing those oLce and conference spaces$ & he #est engineeing decision is to #ring the #uilding up to code$ hat is a no#rainer$ 4owe!er- #oth you and I .now that doings thing the proper engineering way e"uals money$ In this case- alot of money$ he house system is not setup for the additional outside air needed to #ring the space up to code$ Also- since this is located in a high rise$$$the units are most li.ely central units that ser!e multiple oors$ As engineers- we should inform the #uilding owner of the situation and that we recommend they upgrade the units to allow for the current E'A re"uirement$ If they say- &we do not ha!e the money and the local +urisdiction appro!es of gradfathering in the pre!ious code$& At least you performed your due diligence$ And thats all we can do$ A green thought$$$&5e don*t inherit the earth from our ancestors- we #orrow it from our children$& (un.nown)
*illard3 (Mechanical)
2 Jun % ?:21
If the Ewner doesn*t want to spend any money on the new space- he surely doesn*t need an ngineer$ ngineers are responsi#le for #est practice and cfmperson in a conference room is not #est practice$ mike0";1 (Mechanical)
2 Jun % 13:%6
5hat a#out 7tra ,ltration of the return air and H9 or ;iFolar Ioniation treatment of the supply airstream> According to their salesmen it can #ring the outside air re"uirements #ac. down to the cfm le!el$ hey wouldn*t lie to us- would they> 4onestly I ha!en*t tried it$ ;ut Its something I*d thin. a#out- if forced into a corner$
Mi.e A9Design (Mechanical)
2 Jun % 1:3
mi.e6D1 W the EF A'4@A 62$12%%D section 6$3 allows for an Indoor Air Vuality approach- so there is !alidity to what the salesmen is trying to sell$ ;ut- there are se!eral issues$ Ene is if your +urisdiction will go for it$ A lot of codes don*t reference 62$1 as a !ia#le way to pro!ide outside air per code$ In the case of the International Mechanical Code and se!eral state*s deri!ati!es- they ha!e ta.en 'ection 6$2- 9entilation @ate Frocedure- from 62$1 1??? (I thin. thats the right year) and made it part of the code$ /ot #y reference #ut #y directly placing that section in the code$ his stin.s #ecause in my opinion they are re"uiring way to much outside air and don*t gi!e you !ery much e7i#ility$ he second is actually #eing a#le to meet that approach if the +urisdiction allows it$ It ta.es a lot more wor. to approach it from that direction$ 0ou ha!e to identify and "uantify contaminants and then pro!e that the system you are pro!iding will ta.e care of all those$ !en after you ha!e dotted all your i*s and crossed all your t*s you are still left hanging #y section 6$3$1$3 which says: #uote (/313)%
he criteria to achie!e the design le!el of accepta#ility shall #e speci,ed in terms of the percentage of #uilding occupants andor !isitors e7pressing satisfaction with perceived indoor air "uality
hat perception part is enough to scare most people away e!en if they can get it through the A4J$ /othing li.e ha!ing to go #ac. and redo your design #ecause the client andor A4J +ust doesn*t thin. the air is clean enough$ In my opinion your safety net +ust isn*t there li.e it is if you follow the !entilation rate procedure$ atlas4/ (Mechanical)
2 Jul % :D2
=ynamic Air ,lters claims the same air "uality approach to reduce outside air "uatities$ he latest IMC 2%%6 D%3$2 7ception allows an &engineered !entilation system& outside of rates stated in section D%3$3$ I #elie!e this re!ision to the code is there to allow the engineer to follow A'4@A 62$1 instead of the more stringent IMC rates$ >66yAormal (Mechanical)
3 Jul % 11:31
A climate where you can run a constant positi!e or negati!e it is no pro#lem$ 0ou can neglect in,ltration load and +ust worry a#out !entilation$ /A'A can recycle urine into pota#le water- I would rather drin. the fresh stuB myself$ a.e the &9& out of 49AC and you are left with a 4AC(.) +o#$
Ross>:# (Mechanical)
Jul % 21:D2
here is li.ely to #e an initial pro#lem with that low of a !entilation rate- if the pro+ect includes repainting and new carpets (seems li.ely)$ It will ta.e wee.s to get rid of the oB gassing products$ An approach may #e to specify that only carpet and paints with low !olatiles #e used- and ha!e the contractor de!elop and use an IAV plan (similar to those in <reen ;uilding guidelines)$ Ence the reno!ated areas ha!e &aged&- the occupants will +ust ha!e their own ;E and farts to deal with$$$ 1 Apr %3 1%:%% I*m designing an air conditioning system for 1%%O outside air$ he area is a small la# room appro7imately ?% ft3$ My heating loads are 66%% ;tuh sensi#le and 1%% ;tuh latent$ I trying to design the cfm re"uired$ I*m wor.ing in a dry climate so I*!e neglected the latent$
'ome people suggest that I should: 66%%(1$%](?)) where ? is the outside air re"uirements and is the lea!ing temperature oB the coil$ his deli!ers a#out 12 cfm$ he reason I*!e #een gi!en is #ecause that temperature of the air I want to deli!er and am ma.ing up for the 66%% heat gain$ his gi!es me a#out 1% Air Changes4our Ether people suggest that I should use: 66%%(1$%]()) where is the temperature inside the room$ his deli!ers a#out 3% cfm$ I will sie the coil from this formula: 1$%](?)]3%$ I ha!e also #een told if I use this method that I will freee up the coil #ecause the air ow is too great$ 5hich method is right> Can I #uy this system as a pac.aged unit> Also where can I ,nd a psychometric chart for D%% feet ele!ation> han.s F9:=@ (Mechanical)
1 Apr %3 1D:
4a!e you consider 9entilation =isplacement system yet> 9$ipFuller (Mechanical) (OP)
1 Apr %3 22:%?
5hat*s a !entilation desplacement system> c$icopee (Mechanical)
1? Apr %3 21:3%
your reasoning escapes me$ Is the sensi#le heat of 66%% #tuh generated #y la# e"uipmentlighting and the 1% or less air changes and heat transfer thru walls- ceiling and oor> 9$as:ean1 (Mechanical)
2% Apr %3 %:31
Chip 4ere*s how I see this$ I wouldn*t go #y either option you*!e shown$ I would analye this from load to source- and there is a latent gain at the load$ I would therefore use: VD$]cfm]d4 in lieu of V1$%]cfm]d otal space load is latent S sensi#le- which is -1%% ;Hhr$ o o#tain cooling airow needed- use the VD$]cfm]d4 e"uation- which sol!es for total load (sensi#le and latent) #ased on enthalpy$ 5ith a saturated ^8 supply air stream- and to maintain the ^8 space temperature at %O relati!e humidity- the load (room) would re"uire 36D cfm$ 36D cfm is the !olumetric ow rate that the central A4H would need to cool from ?^8 to ^8$ Hsing V1$%]cfm]d- as you note that this is a dry area- the A4H coil would need to #e sied for this reduction in temperature at this ow$ his e"uates to an A4H cooling capacity of 16-%% ;Hhr$ /ote that I*m s.eptical of the lac. of need for the A4H to remo!e moisture #ecause this is a &dry climate$& =ry is a relati!e term$ ?^8 and 2D$6O humidity would produce saturated ^8 air$ If the humidity were higher than 2D$6O- the coil would also need to remo!e moisture$ I*m open to re#uttal on this ha!en*t gone #ac. to thermo49AC #oo.s- #ut this way seems
to ma.e sense to me$ As a side note- #e careful of siing =Q units$ he load conditions stated will #e rare so you need a unit that will perform well at partial load$ ;est of luc.$ C; ,uark (Mechanical)
2% Apr %3 23:?
I !ote for C;$ 4owe!er if you want to go your way you should consider to deg$8 #ecause at no time you want to increase the room temperature a#o!e deg$8$ If you consider a = of ? to for a load of 66%% ;tu4r then when this heat load adds up from the room the lea!ing temperature will #e higher than deg$8$ 0ou #etter follow C;*s comments$ anandGH>9 (Mechanical)
2 Apr %3 3:31
I am sorry- Ferhaps not agree with all a#o!e e7planation$ My answer to C4IF8HRR@*s "uestion is as follows$ I will start with #asics$ If you refer to carrier hand#oo. or any other engineering #oo. on Airconditioning$ 0ou will ,nd that the grand total heat- in your case it is 1%%#tuhr i$e %$6 tons- is used to calculate the tonnage re"uirement$his means that your coil should #e capa#le to gi!e you an output of %$6$ /ow the "uestion is how much air is needed to achie!e this$his can not #e decided with a#o!e two e"uations$0ou will ha!e to do the iterations$8irst assume some fresh air i$e 1 airchangehr and calculate the dehumidi,ed air "uantity re"uied$@epeat this procedure till you #alances your fresh air with dehumidi,ed air$his will gi!e you the "uantity of air re"uired to maintain the desired inside conditions$ Answer to your second "uestion regarding pyschometric chart for diBerent ele!ation$H will note that all the standard psychometric charts are designed at atmospheric pressure of 6%mm of 4g$8or pressure other than 6%mm of 4g- you will ha!e to physically draw it$ Frocedure on how to draw psychometric chart is a!aila#le in any air conditioning #oo.$ H can refer to that$ I hope all a#o!e e7planation clari,ed all your "ueries$ In case of any "uery pls$ let me .now$ 9$as:ean1 (Mechanical)
2 Apr %3 13:%
Anand- could you clarify the iteration> 5hat do you get for an answer> han.s- C; 6riand. (Mechanical)
2 Apr %3 1:
Chas;ean1*s response of 2%th April 2%%3 is a#solutely perfect$ I*!e sied countless air conditioning systems o!er the years- and I*!e ne!er had to carry out some &iteration& to get the cooling re"uirement$ Anand49AC: I too would #e really interested to see why an iterati!e process should #e necessary on this occasion (I might #e e7perienced- #ut I ne!er miss the opportunity to learnKK)$ @egards;rian coolingunit (Automoti!e)
26 Apr %3
6:%D anand49AC: 0our e7planation is e7cellent$ I would li.e to .now the iterati!e procedure of calculating the fresh air re"uirement$ anandGH>9 (Mechanical)
2 Apr %3 1:3%
&Iteration& means trial and error method$ =uring heatload calculation you will ha!e to assume some fresh air "uantity to calculte dehudi,ed C8M re"uirement$ 0ou will ha!e to reiterate this procedure #y !arying fresh air "uantity till it #alances with dehumidi,ed C8M$ Hnless this #oth "uantity matches you will not satisfy the condition of 1%%O fresh air$ It is imposi#le for me to e7plain the method of calculation !ia mail$ 4owe!er- u can refer to carrier hand#oo. for more information$ In case of any "ueriescmments do let me .now$ I will try my #est to address it$ c6i6er (Mechanical)
2 Apr %3 12:D
I ha!e found se!eral psychrometric charts online for ele!ations other than sea le!el$ 8or e7ample <oogle found this one for me using the search terms &psychrometric chart altitude&: $ttp%&&***$eatcraft$eattransfercom&pdfs&Aormal444PDF It*s for %%% feet- not D%%- #ut it*s close enough to get you started$ ;i#er hermal =esign ***6i6ert$ermalcom ,uark (Mechanical)
2? Apr %3 %:D
=r$ [e.yl says- it is always #etter if you ha!e time to practically design a system$ (supplying air "uantity to remo!e heat load and moisture load and incrementing it to reach #alance) Mr$ 4yde says- well if you want to increase comple7ity of a simple solution go ahead$ /one of carrier*s people nor any other engineer o#+ects you$he fundamental is to chec. the total enthalpy of fresh air and the conditions you wanted at the room$ ;asically theair e7iting the room should ha!e same properties of re"uired condition otherwise room conditions cannot #e maintained$ /ow #y the simple calculation gi!en #y C; and used widely e!erywhere- calculate the cfm$ his is enough cfm that will carry heat and moisture out of the room$ his is more simpler than recirculation system #ecause you need not further remo!e the moisture from the e7iting air stream$ Just you are throwing it away$ 'till- if you lo!e math iterations- higher order diBerential e"uations and pro#a#ility will always help you$ ;est of Ruc.$ (;ahK am I #eing too dramatic>) 9$as:ean1 (Mechanical)
2? Apr %3 12:3
his could #e a good e7ercise #ecause we might #e tal.ing apples and apples here$ Anand-
did the reiterati!e process produce a result> energy0 (Mechanical)
1% May %3 1:%
Rets .eep it simple- your application is not roc.et science 1st- your C8M re"uired is dictated #y your total sensi#le load and the temp you want to maintain in the room at the supplly air temp you plan to pro!ide$ it is simply found as @m C8M @oom ;4H V' 1$% ( rm sa ) 2nd- #eause you specify 1%%O E'A ( I will not as. why 1%%O )your coils will ne!er see this load$ Coil Capacity will need to #e #ased on the air ow design a#o!e at ( E'A A d# w# 'A (RA) d#w# ) good luc. lilliput1 (Mechanical)
12 May %3 13:1
he cooling coil will need to cool 1%%OEA to the condition such that when this coil lea!ing air is discharged into the room$ it will pic. up heat and moisture W air is then e7hausted$ he condition of the air e7hausted typically matches the room inside conditions$ If the cooling coil cools the air to % deg 8 W the room design condition is 2 def 8 then the air "uantity re"uired @m Road in ;H per hr(1$1 7 (2%))$ /ow you must also satisfy the latent loads$ he Coil must dehumidify the same "uantity of air to the humidity such that when discharged into the room it will a#sor# the latent load W it*s @4 will #e within the design range$ 0ou may ha!e to reheat to maintain the re"uired space humidity$ lilliput1 (Mechanical)
13 May %3 12:2?
Ra#s typically re"uire 1%%O outdoor air$ Ma.e sure you ha!e enough for e7haust hood ma.eup$ 'implest control is constant !olume reheat$ 0ou can also ha!e (2) position occupiedunoccupied or !aria#le !olume- all with reheat$ Hsually humidity is cirtical so humidi,cation is also re"uired$ Chilled water system is #est$ If =Q you will ,nd out that when you sie the it for the load w 1%%O EA- the unit C8M (typically 3% C8Mton) would #e more than you need to do the room sensi#le load$5hat I ha!e done is recirculate #ac. some of the air$ his unit should only ser!e a la# not a group of la#s to a!oid cross contamination$ Fart of the fan discharge is ducted direct #ac. to the return$ 0ou ha!e to recalculate W do trial W error of the coil entering air condition (mi7 of EA W recirculated air at coil discharge condition plus fan heat$ he AC unit should ha!e hot gas controls$ A humidistat in addition to a thermostat should #e used to #ring on cooling$ 8inal space temperature should #e controlled #y the reheat coil$ greenaire (Mechanical)
2 Jun %3 D:DD
Could you see &the dedicated units& from the news letter of ***tranecom> 9$as:ean1 (Mechanical)
2 Jun %3 21:D6
/o I couldn*t$ Rin. is to trane$com main page$ Chec.ed under &/ews& and didn*t see &dedicated units$& ried a search for &dedicated units& and no luc.$ Could you #e more
speci,c> tmprider (Mechanical)
3 Jun %3 ?:16
ry using an @9 sied for the 1%%O fresh air load$ Rocate it in the ceiling space of the la# for ease of maintenance and cleaning$ his will most li.ley decrease the sie of the unit that you go with- and will allow you to ta.e ad!antage of &free cooling&$ E!erall- your energy consumption will #e less due to the lower delta at your coils$ =4 H==riram (Mechanical)
12 Jul %3 13:3D
his seems to #e an interesting heat load which I used to do manually at the start of my career$ 1%%O outside air application cooling load calculations are normally done #y iteration$ 8irst assume a particular outside air "uantity and do the load calculations- ,nd out what the dehumidifed air "uantity is$ If it matches the assumed outside air "uantity- then the initial assumption is right$ Etherwise- do another load calculation a#sed on the dehumidi,ed air "uantity o#tained and .eep doing this (iteration KKK) till you get the same ,gure$ Alternati!ely- if you ha!e a software li.e 2%II of Carrier- you can +ust input all the rele!ant data and put 1%%O outside air and the program gi!es an output which will #e 1%%O outside air$ greenaire (Mechanical)
12 Jul %3 22:23
4i 4ere is we# address for mentioned article and complete article name$ If you still can not get it- gi!e my your email address$ hen send it to u #y email$ My email: naymoIgreenairecomsg &$ttp%&&***tranecom&commercial&li6rary&arc$iedJne*slettersaspKG =esign tips for eBecti!e- eLcient dedicated !entilation systems #y =ennis 'tan.e- 2%%1!olume 3%3$ F=8 or 4MR genieconseil (Mechanical) (OP)
1% 8e# %6 21:D6
I*m a small mechelect consulting ,rm me #eing the only engineer I specialie in #uilding engineering in #oth disciplines and recognied #y the order of engineers of Vue#ec$ I*!e #een practicing since 1? and in all that time i ha!e ne!er had to do any energy analysis where the degree days or the #in method had to #e used$ My situation is the following- my client has a commercial #uilding in Montreal _1%%-%%% s"$ ft$ and is de!ided in 2 locals$ one tenant is using 2 ga ,red fresh air units of 2-%%% cfm (gas ,red 2-%%-%%% #tuhr) W 16-%%% cfm (gas ,red 2-%%%-%%% #tuhr)he only has one main meter and conce"uently one in!oice for the whole #uilding$ he has as.ed me to e!aluate precisely the percentage of natural ga consumed for the year for those two unit only so he can in!oice the tenant fairly$ I*m a little em#arassed to as. for help- I realise that the #in method would #e the appropiate method to use considering the fact that the units only pro!ide fresh air 1% hrs a day and re"uires heating from octo#er to mid may$ I ha!e ne!er used this method and cant seem to ,nd any good e7amples for me to follow$ Can someone help me direct me with my pro#lem>
han. you in ad!ance <enieconseil 2eos (Mechanical)
11 8e# %6 :2
genieconseil his pu#lication gi!es some #in calculation e7amples in the appendi7$ $ttp%&&***energyroc$esteredu&eLciency&optimalJ6oilerJsi2epdfsearc$ *#in O2%methodO2%andO2%heating* Mintulep (Mechanical)
11 8e# %6 12:23
0ou will need to use actual temperature data for the period of time in "uestion$ Fu#lished ;I/ data is &a!erage& o!er some ar#itrarilly long past time$ I dou#t that in!oicing a tennant #ased on calculation is legal$ 2das4; (Mechanical)
11 8e# %6 13:D1
Any method that is consistent with the contract is &legal&$ As far as that goes- it would #e legal to charge each of them the full gas #ill if the contract will allow it$ It sounds li.e the landlord is trying to #end o!er #ac.wards to #e fair$ 'ince no method is going to #e &accurate& (e7cept to install another meter which is an unreasona#le e7pense)I would opt for simple$ 5hat I*d propose is an allocation #ased on heated area times cfm$ 'ay the one with the larger unit has 6%O of the heated space then I*d allocate him: (6%-%%%ft]2%% cfm)(6%%%%ft]2%%cfmSD%%%%ft]16%%cfm)%O his isn*t &right&- #ut it will come as close as a much more comple7 calculation with historical a!erages$ 0ou could do the same thing with heat capacity- #ut you*d get to around the same num#er (6O instead of %O)$ At today*s industrial gas prices you are tal.ing a#out splitting a#out `22$% H'day (assuming `1MM;H- hoursday run time) getting it &wrong& is not a huge deal and most tenants will accept a logical- consistent- and hopefully fair allocation$ 0ou can easily spend more in #illa#le hours than this could e!er #e worth$ =a!id Mintulep (Mechanical)
11 8e# %6 2%:1
@ight- #ut if you were the tennant would you ha!e signed a lease with a term along the lines of: he landlord will in!oice the tennant for gas usage #ased on an un.nown method of calculation and performed #y someone not familiar with performing energy calculations$ 2das4; (Mechanical)
12 8e# %6 :%
Cute- #ut a good point$ he contract has some language a#out utilities$ hat is the only reasona#le place to start$ My point is that you should use the simplest reasona#le allocation method consistent with contract language$ I*!e successfully used &simplistic& allocation routines on pro+ects that were a lot more money than we*re tal.ing a#out hereand I was successful #ecause they were percei!ed #y the parties as fair enough$
he &#in& calculation is a collection of a!erages of a!erages of standard conditions (whate!er they might #e) that is comple7 enough to dri!e an e7perienced engineer to start this thread$ It is no more &accurate& than allocating #ased on heated area or num#er of employees- +ust harder$ =a!id 2eos (Mechanical)
12 8e# %6 :1
MintJulep- das%D: I thin. you are #oth right$ In!oicing your tenants for gas supplied #y the utility may #e considered an infringement on the utilityYs franchise rights$ If you want your tenants to pay for their energy consumption- you would ha!e the utility meter each tenant separately such that the tenant #ecomes a customer of the utility$ Randlords usually get around this #y including in the monthly rent an amount t hat would co!er the a!erage monthly utility e7pense$ It is then appropriate to estimate the energy usage of each rental unit and #ase the rental rate accordingly$ daeCt2 (Mechanical)
12 8e# %6 16:%
;eing that it is a commercial #uilding- there is a good chance that one or #oth tenants ha!e amny operatiing periods with the doors open or high fresha air input- which would gorssly s.ew the accuracy of a calcualtion that assumes the doors and !ents are closed$ 8or the sie heaters in!ol!ed- why not install 2 custody meters> Er retro,t the heaters with gas cosnumption meters that are recognied #y the pro!incial authority> genieconseil (Mechanical) (OP)
13 8e# %6 1%:%?
han.s- I*m glad and greatfull to see such response to my pro#lem$ ;ut ,rst of all to clear things the 2 air ma.e up units are for the same tenant (the larger area)$ If you read my "uestion carefully you will see that it is stated as such$ I realise that many factors are implicated in the solution(eB of heater- modulation of #urner proportional to the demands.edual- inside temp re"uirements- scheduals- and I lea!e alot more factors out that inuences the calc) #ut since oLcially the #in method is recognied and #reay descri#ed in A'4@A then science #ecomes the lead hand and may#e some logic in court$ @<A'/< than.s for the lin. to an e7ample it is usefull #ut some !alues calculated are not clearly identi,ed$ I*m #lo.ed in my calc$ =o you ha!e more resourses$ han.s a lot for your response It si !ery appreciated <enieconseil P$ilrock (Mechanical)
13 8e# %6 13:2%
Commercial heating and cooling loads are typically diLcult to predict accurately$ If your client truly wants to #e fair to the tenants- he must meter their consumption separately$ !en if there is an administrati!e pro#lem with the utility company doing this- there should #e commercially a!aila#le meters which could #e installed downstream of the utility meters- which could #e used to determine tenant usage$ If you ha!e faith in the accuracy of #oth the utility meters and the downstream meters- you could get away with metering only one of the tenants separately- and assume the other tenant is using the #alance of the energy$
genieconseil (Mechanical) (OP)
13 8e# %6 1:1
I totally agree with measuring seperately and that was my ,rst comment to my client #ut it is not the case at the moment and #efore he can accurately diBerentiate he will ha!e to measure for a year- this is o#!ious$ ;ut he needs to get a good appro7imation now and only two methods e7ist which are the degree days method and the #in method$ My pro#lem is that I dont ha!e good e7amples of how to use them$ 8orget metering for now I need to calculate$ than.s <enieconseil 2eos (Mechanical)
1D 8e# %6 :32
genieconseilChec. out Appendi7 ;: @A@R<B 9OA=MP7OA >AD 9O=7 >A>5B== in the attached lin.$ $ttp%&&interscope.doastatencus&<uidelines&lcca&599>.4Manualdoc mic$aelr0;" (Mechanical)
3 Mar %6 D:D1
<enieconseil;in method is #ased on temperature groups and typically includes all hours annually of data for a gi!en city$ 0ou need to #rea. out the temperature #ins #ased on the operating hours$ ;in Ma.er (type &;in Ma.er Fro& into <oogle) pro!ides this capa#ility$ /e7t thing how are the units controlled> Are they 1%%O EA> Are they constant !olume> 5hat is the discharge air temperature setpoint during heating> Is there a 4= reset se"uence> All of these factors will impact how you perform your calculations$ 0ou can calculate sensi#le energy using the following e"uation 1$% ] C8M ] (emp I/ emp EH)$ C8M- of course- is the air ow through the unit$ emp I/ is the temperature of the air #efore the heating coil and temperature EH is the temperature of the air after the coil$ 0ou can see now how .nowing the operating conditions of you system$ If your unit is 1%%O EA and constant !olume with a discharge temperature setpoint of say %8- then the calc is easy$ 0ou get your #in ta#le setup from ;in Ma.er and set up a calculation in 7cel as follows: 1$% ] 2-%%% ] (%8 #in temp) 1$% ] 16-%%% ] (%8 #in temp) hen pull down the calc through the range of temperatures during Eutside Air conditions where heating is #eing pro!ided$ he e"uation will pro!ide you with !alues in ;tuhr$ 0ou will then need to multiply these !alues in each #in #y the hours in each #in to get ;tus and then con!ert into appropriate heating energy units$ Also- don*t forget the eLciency of the heating system$ he calcs you will ha!e performed is the energy to heat the air$ 4ow much /< is re"uired to heat that air$ 0ou will re"uire appro7imately 2O more /<- assuming %O eLciency$ /ow- if you ha!e minimum EA and are mi7ing with return air you will need to modify your calcs$ Also- if it is a 9A9 system$$$ another le!el of comple7ity$ Another thing to loo. at is utility #ills$ If these units are the only source of heating other
than domestic heating loo. at a couple of years of gas data$ 'hould loo. li.e a nice #ell shaped cur!e if you graph it #y month with a pea. in the 5inter and minimum use in the 'ummer$ a.e the a!erage of the cooling months (assuming that no heating is performed during the cooling months) and multiply #y twel!e$ his should #e a good estimate of the domestic hot water load$ If the only remaining load is heating then su#tract the calculated domestic heating load from the total utility (.eep your units straight) and that will gi!e you your heating load$ If the two units are the only other sources of /< use and the units are controlled in the same manner- then +ust pro!ide a proportionality constant for each unit 61O and 3?O$ his will pro!ide for a "uic. and dirty calc andor a sanity chec. against your #in calcs$ <ood Ruc.Michael @osen#erg 3 Jun % ?:%6 4i and greetings to all of 0ou$ As e new one I ha!e a serious pro#lem: 1$ I ha!e 2 systems to compare: he one is 1%%O fresh air (input)- with #uild in coil reco!ery energy loop on e7it side$ he second is a system with 2%O of fresh air with no energy reco!ery de!ice on it$ 4ow to ma.e a decision which one is a #etter (this 49AC system are two diBerent solutions for our pharmaceutical factory with class 1%%$%%%)$ I*!e searched thru this forum- and ,nd something- #ut as a new- i did not understand your units (american !s euro)- and the way you calculate the diBerence #etween this systems$ he only thing I ha!e to do is to calculate (formulas and suggestions)energy needed for heating (cooling) input air- to ma.e a constant temperature of app$ 22 degrees centigrades- and @4 of %O$ Ma7imum summer and winter temperatures are 2% and SD% degrees centigrades$ Also I*!e =R F'0C4@EM@IC A/AR0[@- and tried to calculate it- #ut it do not include the energy of energy loop$ I ha!e to mention that this is only for this time and no need for further comparement than this one$ Any help is a !ery #ig help to me$ han7 in ad!ance$ set$uM@ (Mechanical)
3 Jun % 11:26
hi i dont thin. that 1%%O fresh air is needed for the class 1%%%%% area$#ecause going for 1%%O will increase your cooling load$ 9$ris9onley (Mechanical)
3 Jun % 13:1D
@egardless of how you deli!er outside air- the system will re"uire the same amount of energy to cool and heat the air$ he only way to decrease this energy is to use heat reco!ery$ If your space re"uires 1%%% cfm (cu#ic feet per minute) of outdoor air then it will ta.e ?-2%% ;tuhr to heat that air from 2% to % 8$ If you mi7 1%%% cfm of EA with ?%%% cfm of
return air- it will still ta.e 1%-%%% ;tuhr of additional energy to heat the air #ac. to % 8$ 5hich system is #etter> ell us more a#out what you are trying to do- use whate!er units you feel comforta#le withG we can con!ert$ 4ow much air or air changes are you trying to do$ Are you heating or cooling with the air- or is this +ust for !entilation$ GH>9/8 (Mechanical)
D Jun % %:%
5hy are you trying to use a 1%%O fresh air and then using a heat reco!ery system > Is 1%%O fresh air a process re"uirement > As ChrisConley has said- units are not a pro#lem we can con!ert$ 49AC6 friartuck (Mechanical)
Jun % :16
he amount of fresh air will depend on the occupancy and the process$ generally you can recirc a lot of the air to reduce the energy costs$ his is much more eBecti!eeLcient than ha!ing a heat reco!ery loop and 1%%O fresh air$ En a lot of clean room pro+ects we ha!e seen- the fresh air is only a#out 1%O to 1O$ I*m not sure how ChrisConley wor.s out that the f resh air component does not aBect the energy use$ If you recirc 1%%O- then the load is simply the heat gain from the space$ If you #ring fresh air in- you ha!e to add this component- which could #e far greater than the room load$ (hence recirc air is a good method of reducing the o!erall load)
8riar uc. of 'herwood G@9 (Mechanical)
Jun % 1?:3
Another thing to consider in this is ,lter loadings$ Although only trying to maintain Class 1%%-%%% standard- ,ltration of return air may #e cleaner- than ,ltration of outside air$ Ef course this depands upon the process in the room$ =usty processes wouold #e #etter with once through$ nergy usage will #e a large part of the design choice- howe!er also consider other aspects of the operation such as ,lters- replacement or cleaning- o!erall facility air ow re"uirements and pressure gradients- etc- etc$ @egards Gutton;engIpickno*lcomau Mar. 4utton
akaodr2 (Industrial) (OP)
6 Jun % 1:%
8irst at all$ ha7 for e!eryone for a "uic. answer$ 'econd: 1$Chris Conley: I don*t thin. that it is the same colingheating energy that we are using for
the #oth systems$5hy> ;ecause I thin. energy needed for 1%%O fresh air is not the same as the one for 2%O$ 2$EP- let*s say ( E ARR): I need 1%% metercu#icminute for all rooms$ emperature for rooms is 2 degrees C- with %O @4$ a$ he 1%%O fresh air system: I need a load of 1%% metercu#icminute for all rooms$ 5hat is needed energy (in .5) to ma.e needed air- if we suppose that outdoor air is with 1 degrees C- thru winter > And needed energy in summer- with outdoor air of S36 degrees C > Also a use of coil type of energy reco!er is included in a system of e7saust air from the factory$ #$ he system with 2%O income and %O recirculating air$ he same calculations are !alid (1%% mccminute for rooms- 1C in winter and S36C in summer)$ I need +ust fact (formulas) how can we calculate it #ut fast$ Just ha!e to mention that this is a need for deciding what type of system to use in our new pharmaceutical factory- and the ,rst criteria is economic side of energy used for #oth systems- and the second the maintenance of the system$ he factory is class 1%%%%%$ Also- results using Fsychrom program from Mc"uay shows me that needed energy isn*t same$ ;ut this is +ust for a dry#ul# type$ 5ith energy reco!er I do not .now the results$ <reetings$ 9$ris9onley (Mechanical)
6 Jun % 21:2D
8riartuc.I didn*t say that the fresh air component didn*t ma.e a diBerence$ 5hat I said was that regardless on how you deli!er 1%%% cfm you ha!e to heatcool it the same amount$ If we are mo!ing air to pro!ide a le!el of ,ltration- or course it will #e less e7pensi!e to pro!ide 2%O outdoor air$ I*m comparing a =EA' (=edicated Eutdoor Air 'ystem) with heat reco!ery to a recirc system with the same fresh air re"uirements$ ,uark (Mechanical)
Jun % 2:%
he #est heat reco!ery systems operate at an eLciency of ?%O$ 'o- you ha!e to cough up 1%O more energy cost$ 8urther- for room pressuriation and fresh air re"uirement- you ha!e to #leed oB re"uired "uantity from rooms either if you go with recirculatory system or fresh air system$ 8or a conser!ati!e comparision you ha!e to deduct this energy component also(i$e appro7imately 1%O !olume rate of air is not a!aila#le for energy reco!ery)$ @egards-
akaodr2 (Industrial) (OP)
Jun % 2:12
E: ChrisConley Ret*s do this pro#lem together: as you .now- 2 system are in !aluation$ he pro#lem why I*m as.ing a formula (a simple one)- to calculate input energy is that &some#ody& is telling me that using 1%%O fresh air is cheaper than using 2%%O
com#ination$ he 1%%O system ha!e in a)input side:inta.e section- ,lter 8- @un around system reco!ery (heating) with eB$ of 3%$DO- Centrifugal fan #elt dri!en- diBusor- ,lter 413 and sound attenuator$ #)output side: sound attenuator- ,lter 8- run around system reco!ery (cooling)- and outlet section with centrifugal fan #elt dri!en$ I was told- that- if I*m using this type of 49AC solution- with com#ination of cooling plant with air compressors !entilation (dry)Correct me a#out my e7planation of cooling plantbmy energy sa!ings will #e #ig- according to <MF re"uirements we are loo.ing for$ he controlled !alues are temperature- humidity and pressure$ According to - and @4 of the output- also including outside conditions- the system needs (do not needs) some additional air preparations of inta.e air$ he out ta.e air is not needed any more- #ut for colleting of waste energy$ he point is- comparing to recirc system- where additional preparation of out ta.e air is a must (,ltration- dehumidi,cation- heating- cooling)- the control points are much more then the other- I will sa!e money in start and the pay#ac. is much shorter$ Rower energy costs > In a future there is a chance to upgrade do class 1%%%% with only adding terminal 4FA ,lters and nothing more> o help 0ou- the conditions of the placement of the plant is on around D23 m (13?1 ft- with appro7imate 6O of sunny days- and temperature !ariations from 2% to SD% C$ han7I*m +ust confused$ ,uark (Mechanical)
Jun % 2:1
=idn*t get what you mean #y cooling plant with air compressor !entilation$ /e!ertheless*some#ody* is playing wrong$ akaodr2 (Industrial) (OP)
Jun % 2:32
o: Vuar. E.- I .now that the #est heat reco!ery systems wor. at ?%O eB$- #ut the eB$ of included reco!ery system is around 3%O (technical factory written info)$ It*s ,lled with ethylen- with med$ow of 3$2 ls- medium in 1D$D6C- med$out 1$D2C$ Air in 1%C- air out %$3DC (this is for heating side)- with 111 Fa pressure drop$ capacity 233$2 .5$ Medium press drop D$3D .Fa$ he cooling side is: air in 3C- D%O 4um$- out 16$%1 with O hum- air pressure drop 16 Fa- capacity 66 .5 '4@$ Medium ethylen- ow 33$2? ls- med$in C- med$out 1%Cmedium press drop 32$? .Fa$ VHE=: &8urther- for room pressuriation and fresh air re"uirement- you ha!e to #leed oB re"uired "uantity from rooms either if you go with recirculatory system or fresh air system$ 8or a conser!ati!e comparision you ha!e to deduct this energy component also(i$e appro7imately 1%O !olume rate of air is not a!aila#le for energy reco!ery)$& I do not understand well this: 0ou mean that the "uantity of air ta.en from rooms in #oth situations is the same- #ut additional processing of recirc air is a must in system 2%%O$ It is EP- I .now that- #ut still the "uestion is : how much energy will #e used in #oth
situations e7pressed in .5 (let*s say for 1%%%% m3h) in #oth ways: with 1%%O fresh airand with 2%%O recirc air system> han7$ ,uark (Mechanical)
Jun % 3:%
I will try to simplify the things$ 8irst- for room pressuriation- say- you may re"uire 1%O of air owrate$ 'o this will #e directly e7hausted from the rooms and you won*t get it #ac. in the A4Hs$ his is compensated #y fresh air inta.e in the second cycle$ 5hen we consider 1%%O fresh air system- you will ha!e only ?%O appearing at t he heat reco!ery unit$ Considering 3%O eLciency of the heat reco!ery system- you need not cool or heat 3%O of ?%O of total air ow(or 2O of total air ow)$ 5hen you use a recirculatory system with 1%O fresh air- you should coolheat 1%O !olume rate from am#ient conditions to coil A=F and ?%O from room condition to A=F$ 5ith a heat reco!ery unit- it is (1%%2) 3O !olume rate from am#ient condition to coil A=F$ 'o- compare 63O(i$e3O1%O) owrate with am#ient condition to A=F !s ?%O owrate with room condition to coil A=F$ @egards akaodr2 (Industrial) (OP)
Jun % 3:1D
E: "HA@P Cooling plant (Cold water 1%C) from Carrier8rance type 3%<Q %23 or 3%4QC %% 3$ Air cooled li"uid chiller capacity 271%%%.5$ he coorect name is: 'crew compressor watercooled Ri"uid Chillers and aircooled li"uid chillers$ his is what a meant of cooling plant$ greets akaodr2 (Industrial) (OP)
Jun % 3:D2
o: Vuar. E.- I*ll "uote your message and do it step #y step: &8irst- for room pressuriation- say- you may re"uire 1%O of air owrate$ 'o this will #e directly e7hausted from the rooms and you won*t get it #ac. in the A4Hs$ his is compensated #y fresh air inta.e in the second cycle$& 8irst: his is for recirculating system or it is for #oth systems> Ret*s say: 1%%%m3h 1%O ?%% m3h- right > &5hen we consider 1%%O fresh air system- you will ha!e only ?%O appearing at the heat reco!ery unit$ Considering 3%O eLciency of the heat reco!ery system- you need not cool or heat 3%O of ?%O of total air ow(or 2O of total air ow)$ &
E.- if we suppose that a#o!e is corect and for #oth systems: ?%% m3h 3%O 2% m3h of total input ow to heat with reco!ery unit- right > he other 3% (or 63%) m3h ha!e to #e heated with heatingcooling unit- o. > 2% m3h reco!ery unit 3%(63%) m3h heating cooling unit &5hen you use a recirculatory system with 1%O fresh air- you should coolheat 1%O !olume rate from am#ient conditions to coil A=F and ?%O from room condition to A=F$& In this case I need 1%% m3h to heat from outdoor air- and another ?%% m3h to heatcold from room air > 5hat is A=F > &5ith a heat reco!ery unit- it is (1%%2) 3O !olume rate from am#ient condition to coil A=F$ 'o- compare 63O(i$e3O1%O) owrate with am#ient condition to A=F !s ?%O owrate with room condition to coil A=F$& I*m stuc. here at the last point :) 4elp$ 0ou mean: 2% m3h heated with reco!ery coil and 3% m3h heated with heater in h!ac- and for secure reason it is lowered to 63O of outdoor air> 0ou mean to compare 63O outdoor air to ta.e heated and ?%O of recirculated air to ta.e heated > If I misunderstood correct me$ <reets akaodr2 (Industrial) (OP)
Jun % D:%3
I*m stuc.$ Can some#ody +ust say: 0ou*ll need this and this formula- or this program (free if possi#le :) )- and no fear$ Jo# is done in a minute$ greets akaodr2 (Industrial) (OP)
Jun % :%
Er +ust using informations a#o!e for my pro#lem (23 messages a#o!e this)- and help me for right solutions$ he &catch& is in the price of #oth systems- which one to #uy- and in my opinion is that in the system with 1%%O fresh air- must #e something that I*m missing- which inuence of the lower costs of whole 49AC solution$ hat*s why I*m as.ing for help- to do a fast calc of energy used in #oth system- for same "uantity of air- for cooling and for heating$ In fact- this #ecame so confusing- that I do not .now where to start and where to end$ I*!e tried lot of programs (freewareshareware-demo #ut no use) to ,nd out the right one- where I can enter needed air in m3h- to choose one- then the other system- and to read out and compare the gi!en results (usage of energy in .5- for cooling and for heating)$ 'o- if some#ody ha!e this type of program (it is doesn*t matter whene!er I .now it or not)let +ust enter needed info which can #e ,nd in messages a#o!e- and gi!e me a simple answer: In 1st system you*ll need $$$.5 of energy for heating and cooling- and in 2nd system you*ll need $$$.5 of energy$ I*m not as.ing nothing more and nothing less$ Just to mention that this is my ,rst contact with 49AC pro#lem- solutions (may#e constructions) and simply I can*t manage as good as you can here- e7periensed engineers$
I hope 0ou*ll understand in what .ind of trou#le I am :) <reets,uark (Mechanical)
Jun % :12
'ay- you ha!e 1%%%cmh re"uirement$ 5ith fresh air 8irst cool 1%%%cmh from am#ient condition to coil condition(or Apparatus =ew Foint)$ 1%O is wasted in #oth cases- i$e 1%%cmh$ 'o ?%% cmh is present for reco!ery$ Eut of this you can a!ail 3%O of heat- which is a#out 2%cmh$ his is as if you need not condition this much owrate from am#ient to coil condition$ 'o what you ha!e to treat is 1%%%2% 3%cmh$ (1) 5ith recirculation 1%%cmh air is at am#ient condition and ?%%cmh is at room condition$ 'o you ha!e to cool 1%%cmh from am#ient condition to coil condition and ?%%cmh f rom room condition to coil condition (2) 8or your comparison 1%%cmh fresh air treatment is common$ 'o deduct this from #oth options$ 'o- the fresh air option #ecomes treating (3%1%%)63%cmh from am#ient condition to coil condition and recirculatory system option #ecomes treating ?%%cmh from room condition to coil condition$ he formulae 41 is am#ient air enthalpy in #tul# 42 is room air enthalpy in #tul# and 43 is enthalpy of air at coil e7it in #tul# 'o- fresh air energy(for comparision) is D$7(4143)73%$cfm(i$e 63%cmh) (3) @ecirculation air energy is D$7(4243)72?$2cfm(i$e ?%%cmh) (D) he lower !alue of (3) and (D) is your ultimate choice$ 4ope I cleared the issue$ @egards,uark (Mechanical)
Jun % :2?
En a second reading- you seem to ha!e grasped what I said perfectly e7cept 63%cmh thing- which I cleared in my third post$ @egards akaodr2 (Industrial) (OP)
Jun % 6:16
Eh- than. 0ou Vuar.- !ery much$ his is a real thing$ 7cept for one thing ("uoted): &41 is am#ient air enthalpy in #tul#
42 is room air enthalpy in #tul# and 43 is enthalpy of air at coil e7it in #tul# 'o- fresh air energy(for comparision) is D$7(4143)73%$cfm(i$e 63%cmh) (3) @ecirculation air energy is D$7(4243)72?$2cfm(i$e ?%%cmh) (D) & he !alues for 41- 42 and 43 where can #e get > specially in #tul#$ Also- isn*t any changes if in formulae are used diBerent !aluses of units (e7$ #tul# and cmh) > <reets-
akaodr2 (Industrial) (OP)
Jun % 6:?
o Vuar.: EP- I did some calc: he !alues of 414243 are ta.en from Fsychrometric analyer- for altitude of D23 m$ (If they are wrong- correct me)$ Input: 41: D%C%O@4- e"ual of 1%D$%%D .J.g 42: 2C%O@4- e"ual of 1$631 .J.g 43: 22CD%O@4- e"ual of 3?$66D .J.g 1%%O fresh air: D$7(1%D$%%D3?$6D)763%123$1 (.J]m3)(.g]h) ?%O recirc air: D$7(1$6313?$66D)7?%%DD1?-3 (.J]m3)(.g]h) Is is the correct !alue a#o!e > 5hat gi!es (.J]m3)(.g]h)precisely > he 2nd: 5hat happens if I*m heating the air > I got negati!e !alue for 1%%O fresh air: Eutdoor temperature is: 1%C3O@4 D$7($6%%3?$66D)763%1366%$1 (or may#e I ha!e to to opposite process to su#stract from 3?$66D !alue of $6%%)> Anyway- I still can*t ,nd the &catch& in solution of 1%%O fresh air$ simply- .nowing people that are wor.ing on their solution- there must #e some tric. in their solution of 49AC$ <reets-
,uark (Mechanical)
Jun % 1:%3
he other !alues seem to #e o. #ut not the 43- for the coil outlet condition should essentially #e saturated(or near to saturation)$ hat means the @4 should #e nearer to 1%%$ 'econdly- 22C coil outlet temperature is "uite high e!en for comforta#le cooling application$ If your area deals with any of li"uid in+ecta#les- granulation- coating or capsulation areas- the moisture load will #e a #it high$ My e"uations can*t #e used with metric units$ 4owe!er- you can download an e7cellent unit con!ersion program *Hconeer* written #y Patmar- a fellow mem#er of engtips- from the following lin.$ $ttp%&&***katmarsoft*arecom&uconeer$tm
0u should also consider heat gain in return ducting when you deal with recirculatory system$ ;ut as far as the primary comparision is concerned- the procedure is o.$ he whole idea is to show that fresh air systems always pro!e you costly$ @egards akaodr2 (Industrial) (OP)
Jun % 2:2% 1 Apr %6 :D
4ello- INm new in this forum and ha!e a "uestion$ I need to calculate de cooling load of an area that demands 1%%O outside air- and to #e honest- I donNt Pnow how to do it$ here are some "uestions that comes to my mind: 5hat should #e the lea!ing air temperature> he loads produce #y people- lights- wallsetc that we estimate in a recirculating system- should #e calculated in this .ind of system too>$ I really apreciate some help$ (INm from =ominican @epu#lic- so e7cuse my english)$ han.s$ *illard3 (Mechanical)
1 Apr %6 1D:3
8or the outside air: 'ensi#le cooling CH 8MI/ 7 1$% Q outside AI@ =RA t ;H4@ '/'I;R Ratent cooling: fu ftmin 7 %$66 7 (delta moisture in grainsl# from psychometric chart) #tuhr latent 'ensi#le load S latent load total cooling load for outside air In general- cold air is deli!ered at 8 dry #ul# and wet #ul# (ie- saturated) ;uilding solar loads- lights- e"uipment and people loading should #e included in your calculations$ 0ou should pro#a#ly hire a Mechanical ngineer to do this as he is familiar with it and you aren*t$ *aross (lectrical)
1 Apr %6
1:3% 4ello willard3 I ha!e met some intelligent dedicated engineers in the third world$ Hnfortunately- the training and educational systems there are not up to ,rst world standards$ pa#lo2D1% has recognied that he doesn*t ha!e the information that he needs to sol!e his pro#lem and has wisely gone loo.ing for good ad!ice$ I than. you on #ehalf of pa#lo2D1% for your .ind help- #ut I wish to gently point out that your last suggestion may not #e feasi#le$ pa#lo2D1% is "uite possi#ly the #est mechanical engineer a!aila#le$ 0ou may ,nd it rewarding- willard3 to mentor pa#lo2D1% and help him to #ecome a #etter engineer$ 8rom the tone of his post I #elie!e he is intelligent and dedicated$ 4e recognies shortcomings in his education and is trying to impro!e himself$ 0ou ha!e already gi!en pa#lo2D1% the #asics- go a little farther and help him through his calculations and you may ,nd that you en+oy it$ respectfully Mintulep (Mechanical)
2 Apr %6 1:33
pa#lo a.e a loo. at this site: $ttp%&&***engineeringtool6o!com&$ac'systems'tJ.3$tml ,uark (Mechanical)
2 Apr %6 23:13
Fa#lo he room lea!ing air condition should always #e the room condition$ Calculate heat load as per the general rules$ Flot the room condition and am#ient condition state points on the psychro chart$ =raw a line with a slope of '4@ from the room condition to the saturated cur!e$ his is your dew point condition$ Join the am#ient condition state point to the dew point$ he total load on the coil will #e the mass ow rate of air times the enthalpy diBerence #etween the am#ient condition and the dew point condition$ In some cases- the '4@ line #ecomes an asymptote to the saturation cur!e$ In this case- assume some ar#itrary dew point and add reheat into the process$ he lin. #elow gi!es you description and details of many psychrometric processes$ 4a!e a loo. into it$ $ttp%&&***coolitco2a&psyc$art&
5aross/ice thin.ing and I feel that is the whole idea #ehind these forums$ pa6lo.;14 (Mechanical) (OP)
3 Apr %6 :2
han. you all of you for your help 4ere comes another "uestion- how can i calculate mass ow- i mean- i .now the !olume of air in the room- #ut how do i .now how many times do i ha!e to recirculate it
5=> (Mechanical)
3 Apr %6 12:11
correct me if I am wrong #ut I am assumming you meant 9olume ow instead of mass ow$ ;elow is something I gra##ed oB a we#site descr#ing what I thin. will #e of help to you$ Ene air change occurs in a room when a "uantity of air e"ual to the !olume of the room is supplied andor e7hausted$ Air change rates are units of !entilation that compare the amount of air mo!ing through a space to the !olume of the space$ Air change rates are calculated to determine how well a space is !entilated compared to pu#lished standards- codes- or recommendations$ Air changes per hour (AC4) is the most common unit used$ his is the !olume of air (usually e7pressed in cu#ic feet) e7hausted or supplied e!ery hour di!ided #y the room !olume (also usually e7pressed in cu#ic feet)$ Airow is usually measured in cu#ic feet per minute (C8M)$ his is multiplied #y 6% minutes to determine the !olume of air deli!ered per hour (in cu#ic feet)$ AC4 (C8M Q 6% minutes)(room !olume in cu#ic feet) pa6lo.;14 (Mechanical) (OP)
3 Apr %6 12:33
5hat i want to .now is how can i determine the C8M needed for the area$ *illard3 (Mechanical)
3 Apr %6 12:3?
Fa#lo: he sensi#le heat ratio and cooling load will dictate the air changeshour and is the solution to the pro#lem$ ry not to confuse the cause for the eBect$ In my climate- ie- D2 deg latitude and 3 deg longitude- in a frame#uilt- insulated #uilding with appro7 2%O glass and * ceilings- cfm !aries from 1 cfms"uare foot to 3 cfms"uare foot of oor depending upon internal loading- ie- num#er of people- lightinge"uipment loads and !entilation loads$ ;H load !aries from 3%% #tucu foot e7clusi!e of internal loadings$ 5e ha!e #uilding codes in /ew 0or. that ma.e the range of these num#ers pretty small$ 0our latitude is 1 deg and longitude is 6? deg- so solar loading and air temperatures will #e !ery diBerent than /ew 0or.$ I am also sure that you construction materials and methods are diBerent than ours so #uilding mass and etc will #e diBerent 0ou should get a copy of A'4@A 8undamentals 9olume(American 'ociety of 4eating@efrigeration and Air Conditioning ngineers)G it contains answers to all the "uestions you are as.ing$ 0ou ha!e access to the we#- so &<oogle& A'4@A$ 0ou can also use rane software to calculate heatingcooling loads- #ut you need ,rst to understand the input$ A'4@A will #e a #ig help with the input$ *illard3 (Mechanical)
5rong data:
3 Apr %6 12:D2
;H load !aries from 3%% #tucu foot e7clusi!e of internal loadings$ @ight data: ;H load !aries from 3 #tucu foot e7clusi!e of internal loadings$ pa6lo.;14 (Mechanical) (OP)
3 Apr %6 13:1D
E.- (willard3) the ,rst formula you ga!e- me was a !ariation of the ,rst law of thermodinamics- another way to put it is using the mass ow times the enthalpy diBerence #etween am#ient condition and dew point condition- #ut in #oth cases i need a ow of air in terms of mass or !olume- and there is my confusion$ he other "uestion is : do i need a U8 lea!ing air temperature in a system using 1%%O outside air>$ I ma.e this "uestion #ecause i assume that in this .ind of system- there is no mi7 #etween the air in the room and the air from outside to achi!e a medium temperature- #ecause e!entually the total !olume of air in the room will #e e7hauted and replace for a new !olume from the outside- so i was thin.ing that the lea!ing air temperature should #e the temperature of the conditions i want in the room- letNs say 3U$ 5=> (Mechanical)
3 Apr %6 1:%3
I am going to ta.e a sta# at this$ =esign condition: Eutside air temp (=;5;) ?2868 (%$O mean summer temp Ros Angeles) 'upply air temp 8 Assumptions: =imension of space 6%*(R)76%*(5)71*(4) 2% people 7 2% #tuhr %%% #tuhr 2$ wattssf lighting ?%%% #tuhr Assume -%%% ;Hhr e7terior loads AC4 (Air change per hour) 1% therefore C8M AC4 7 9olume 6% (1% 7 D-%%% cu ft)6% ?-%%% cfm 'o ?-%%% cfm is re"uired to e7haust the room 1% times per hour$ /ow to determine the load on the cooling coil: Cooling coil load 1$1 7 C8M 7 (1 2) 1$1 7 ?-%%% 7 (?2) 366-3%% ;Hhr 'umming all the loads: 366-3%% #tuhr S %%% #tuhr S ?%%% #tuhr S -%%% #tuhr 3-3%% #tuhr or 32 tons$ 'o to select a unit to suit all the a#o!e loads- I will select a 3 ton unit$ his is +ust a generic e7ample$ here are many other loads that I am not incorporating$ 4opefully this can get you in the right direction$
pa6lo.;14 (Mechanical) (OP)
3 Apr %6
1:D1 E.- so far- all the things that had #een told here- i already .new it$I thin. i-m not as.ing the right "uestion- so here i go- how can i determine the total cfm that is re"uired to pass trough a cooling coil in a system that re"uires 1%%O outside air- or how do i .now how many changes of air do i need$ 5=> (Mechanical)
3 Apr %6 1:%1
he C8M re"uired is calculated #y the engineer$ ypically for a la#oratory the AC4 is 61 AC4$ A restroom is D AC4$ (these are recommended num#ers we use in our oLce$ hese are not a standard$) =oes that help>
pa6lo.;14 (Mechanical) (OP)
3 Apr %6 1:3
o.- here is the pro#lem a loc.er room Area 3% s"ft height 1%ft 3 persons in the room what will #e the diference in my load calculation if the system is 1%%O recirculate air or 1%%O outside air$ 5=> (Mechanical)
3 Apr %6 2%:D
Air change method Assumptions: 'ummer design condition ?28638 Indoor design condition 28 Interior location therefore no e7ternal load Roc.er @oom AC4 1 (again- this is our oLce standard) 9olume: 3% sf 7 1%* 3-%% Feople load sensi#le 2% #tuhperson (1-2%% #tuh) (+ust got done wor.ing out) Feople load latentperson 1% #tuh (3 #tuh) Righting load 1$ wattssf (32 #tuh) C8M 1 7 3-%% 6% - cfm (lets say ?%%% for simplicity) 1$ 8or 1%%O outside air: Cooling coil load 366-3%% #tuh otal sensi#le load 366-3%% S 32 S 1-2%% 3?-2 #tuh or 32$ tons$ 2$ he diBerence will #e su#stantial #ut Roc.er rooms are ne!er 1%%O recirculated$ here will always #e some amount fresh air #rought into the space$ he air change method is a simple method of getting an appro7imate idea of what sie unit is re"uired$ In loc.er room applications many times they are heated and !entilated only$ And Ma.eup air is usually always re"uired to achie!e proper air #alance$ 4ope that clears up some "uestions you may ha!e$ <R cme (Mechanical)
Apr %6 16:D1
a rule of thum# $$$$$ 1% cfmton for a preliminary siing load ,nal psych chart analysis on =;mean5; per ashrae geographic data don*t forget fan heat gain /.$og (Mechanical)
2D Apr %6 12:2%
Ene other thing must #e ta.en into account$ If you are planning on using a pac.aged system (ie$- rooftop unit)- you must consult with the manufacturer$ As a general rule- (at least according to my local reps) a pac.aged unit is only capa#le of accepting appro7imately 23%O of the total airow in the form of unconditioned outside air$ Any system you use should #e discussed with you local rep$ 0ou should also re"uire them to also pro!ide you with any documentation for information that may diBer from you &sound engineering +udgement$& 80I- A'4@A list the design condtions for =ominican @epu#lic cooling- in the %$DO rangeas ?1% d8 d#w#$ lilliput1 (Mechanical)
2D Apr %6 12:D?
62hog is right$ Chilled water systems are recommended for 1%%O EA applications$ 4owe!er it is also possi#le to use multistage pac.age =Q AC units #y recirculating a portion of the supply direct to the return and supplying to the room only the C8M
e"ui!alent of the EA handled$ 8or e7ample- if the load for say D%%% C8M 1%%O EA is 2% tons$ Hse a 2% ton unit say nominal %%% C8M- #ut use D%%% C8M EA- %%% C8M total 'AD%%% C8M recirc direct #ac. to A4H and D%%% C8M supply to the room$ 'ol!e for the mi7ed air conditions of the EA and recirc air to get cooling coil entering air condition$ Interpolate performance from ta#ulated date$ 'ol!e for cooling coil lea!ing air temperature$ =etermine fan and duct heat gains and deduct from ta#ulated capacity to get net capacity$ t$oot2 (Mechanical)
3% Apr %6 23:2
8irst you need to compute the total heat load $li.e num#er of window- sie of doors what materials used in the #uilding 5all$ 0ou may ,nd the !alue of each material in Ashrae hand#oo. or Mechanical hand#oo.$0ou may also use Manual J method- a software for load computation$ his wil guide you step #y step method$ sloyal (Mechanical)
1 Jun %6 1:%2
4ere*s my 2 cents$$$ ;H4 D$ 7 cfm 7 =elta 4 4psych chart enthalpy McVuay W rane as well as others ha!e downloada#le Charts that should gi!e nthalpy conditionsI prefer the straight edge on a paper graph (calcs for the ,les) My design conditions are ?d#3w# nthalpy 36$ indoor cond$ d8 %O 4umidity nthalpy 2$% or %d8 %O 4umidity nthalpy 26$3 8or ease of use I call it a d4 of 1% ;tuh cfm 7 D$ 7 1% If I ,nd I need a 2% on system- I*ll #e !ery careful to select a coil on face !elocity- to a!oid freee upas well as Ratent W sensi#le capacities$ Interlaced coils with multiple stages (more is #etter) wor. #est$ I a!oid conditioning the space with this system as it would re"uire a larger system$ I prefer deli!ering room temp air W ha!ing a seperate recirculating system for space loads$ I may e!en deli!er a portion of the &tempered outdoor air& into the return of the space conditioning system- Fossi#ly 1%%O if the cfm matches- with a return setup for independent operation$ My winter design is 2%d8 so any outdoor air is heated W it*s usually done with a direct ,re MAH$ he products of com#ustion in this air has recently #ecome an issue- especially on units recirculating any inside air$ 5ith these design conditions- I would loo. at incorporating a 4eat @eco!ery 9entilator$ 'omething li.e a @enewAire with latent W sensi#le e7change can sa!e a #oatload on the aforementioned <as MHA w2%ton coil$ 7h air conditions (i$e$ dust- oil- etc$$$) might prohi#it a heat e7changer altogether$ good luc. sl+
Borkman (Mechanical)
1 Jun %6 1?:3
Ene thing not to o!erloo. is that the latent load is going to #e rather high- gi!en that this is a loc.er room with showers$ A recirculated system*s latent loads at the coil could #e higher than the E'A senario$ I would loo. up latent load and air change recommendations in the A'4@A 8undamentals 4and#oo.$ It may ma.e more economical sense to go with 1%%O E$'$A$ and .eep my discharge air at say 6% 6 degrees afterall it is a loc.er room$ 4ey I ha!e enough pro#lem with shrin.age$ GX) <ood luc.- with this much ad!ise how could you go wrong> I*m not a real engineer- #ut I play one on $9$ A$J$ <est- 0or. Int$ 9ore7ec$41 (Mechanical)
D Jun %6 13:D
VuoteTTTTTTTTTTTTTTTT o.- here is the pro#lem a loc.er room Area 3% s"ft height 1%ft 3 persons in the room what will #e the diference in my load calculation if the system is 1%%O recirculate air or 1%%O outside air$ TTTTTTTTTTTTTTTTTTTTT he diBerence in your load calculation is 4H<$ Fost a little more information li.e whatYs your design room temp> 8or pu#lic loc.er rooms I design around a =eg$ Indoor temp year round$ A few things you need to .now ,rst a#out loc.er rooms$ Roc.er rooms should always #e .ept slightly negati!e$ he loc.er room area should #e completely sealed /E plenum returns /o mi7ing of air with other systems$ 0ou are allowed to recirculate air pro!iding it is the air from the loc.er room area$ 0ou must ha!e e7haust fans$ 0ou donYt always need 1%%O Eutside air +ust enough to pro!ide proper !entilation to match your e7haust$ I ha!e use $@$9Ys in loc.er rooms to reco!er as much energy as possi#le to lower the load$ In your case if you use 1%%O outside air you will need to e7haust 11%O of that air (to .eep the space slightly negati!e) hatYs a 4H< load to cool and then to e7haust if you li!e in a warm climate$ 2 Jan 12 11:1? 4i I am designing a MAH for the ,rst time I am trying to understand how to determine the amount of return air to supply a mi7ing
#o7 #efore the heater$ he outside winter design conditions are 1f at %O humidity$ inside design is f at %O humidity$ I need to supply 1%-%%%cfm of fresh air which is need to meet my air change rate per hour $ he room needs 1%%% cfm to maintain the pressure needed$ I would li.e to mi7 some return air with the outside air to sa!e some energy$ ;ut want minimie the sie of my supply fan$ 4ow do I determine the amount of return air to use$ Attach is a general free #ody diagram$ $ $ouseman.4 (Mechanical)
2 Jan 12 1D:21
Eutside air and &air change rate& are not usually the same$ Minimum fresh air is calculated per A'4@A 62$1 or code and is often a function of oor area and occupancy$ 'ince this aBects sie of heating signi,cantly- you should minimie the outside air as much as you can$ Air change is usually a summer cooling re"uirement and is e"ual to supply air ow$ Also- #y de,nition a ma.e up air unit doesn*t recirculate air$ ?i*iMace (Mechanical)
2 Jan 12 1:%2
'tudent $enegg (Mechanical) (OP)
2 Jan 12 1:3
than.s for the info$ the air change per hour AC4-in this case is dictated #y the purpose of this room- not the occupancy of the room$ he ach re"uirement is larger than the heat loss so I am using the AC4 for this design$ so if I need to use 1%%O fresh air(,nished food product area) to meet my AC4 how would one determine how much return air to use$ I tried using 2O of t he mass ow rate of the fresh supply air$ #ut at 1f fresh air 12%%l#min and f return air D%%l#min( the rates are appro7imate)- the mi7ed air is at the left of the saturation line$ I assume this is not a good situation$ Flease straighten me out$ where $ouseman.4 (Mechanical)
5ith EA1%-%%%cfm lea.age1-%%%cfm Q 'A @A Rea.age
2 Jan 12 16:D1
@A S EA 'A 2 e"uations- 3 un.nowns if you want to minimie 'A- set @A% Q ?-%%% cfm 'A 1%-%%% cfm @ecirculating air won*t sa!e heating energy- so there is no mi7ing pro#lem$ $enegg (Mechanical) (OP)
2 Jan 12 21:3?
han.s that helps 9$as:ean1 (Mechanical)
2? Jan 12 %:13
0ou need 1-%%% cfm supply and 1%-%%% cfm of outdoor air$ <o with ?-%%% cfm return$$$ @eturn air "uantity is not something you design around$ 0ou +ust ma7imie it when conditions permit (!ery hot or !ery cold out)$ 8or help- you might need to clarify your pro#lem$ lma1 (Mechanical)
D 8e# 12 1?:D1
As Chas;ean1 (Mechanical) suggested- you need to clearly de,ne your pro#lem$ he following might help: 1$ I understood that you need to supply 1%-%%% C8M EA to the room$ And this is #ased on your AC4 rate re"uired> 2$ 0ou need also 1-%%% C8M 'A to pressurie the room> 3$ Is the 1-%%% C8M the lea.age air as houseman2% (Mechanical) suggested> D$ I*!e trou#le with the statement &he ach re"uirement is larger than the heat loss so I am using the AC4 for this design$& AC4 gi!es you an idea of what !entilation air (fresh air) is re"uired$ 4eat loss or gain determines the heating or cooling (airconditioning) supply air ('A) re"uired$ I thin. you mean the AC4 criterion re"uires more air than that #ased on the heating or cooling calculation and you therefore #ased the supply air on 1%-%%% 'A which is re"uired #y the AC4 estimate> $ 'ince 'A EA S @A W your 'A EA- @A must #e %> 0ou lose 1-%%% C8M thru lea.age and another ?-%%% thru other e7haust opening(s)$ 'o 'A 1%-%%% C8M A (1-%%% S ?-%%%) C8M$ 6$ /o @A is needed or desired in your case as houseman2% (Mechanical) demonstrated if we understand what you*!e #een as.ing$ 1 Apr %3 1%:%% I*m designing an air conditioning system for 1%%O outside air$ he area is a small la# room appro7imately ?% ft3$ My heating loads are 66%% ;tuh sensi#le and 1%% ;tuh latent$ I trying to design the cfm re"uired$ I*m wor.ing in a dry climate so I*!e neglected the latent$ 'ome people suggest that I should: 66%%(1$%](?)) where ? is the outside air re"uirements and is the lea!ing temperature oB the coil$ his deli!ers a#out 12 cfm$ he reason I*!e #een gi!en is #ecause that temperature of the air I want to deli!er and am ma.ing up for the 66%% heat gain$ his gi!es me a#out 1% Air Changes4our Ether people suggest that I should use:
66%%(1$%]()) where is the temperature inside the room$ his deli!ers a#out 3% cfm$ I will sie the coil from this formula: 1$%](?)]3%$ I ha!e also #een told if I use this method that I will freee up the coil #ecause the air ow is too great$ 5hich method is right> Can I #uy this system as a pac.aged unit> Also where can I ,nd a psychometric chart for D%% feet ele!ation> han.s F9:=@ (Mechanical)
1 Apr %3 1D:
4a!e you consider 9entilation =isplacement system yet> 9$ipFuller (Mechanical) (OP)
1 Apr %3 22:%?
5hat*s a !entilation desplacement system> c$icopee (Mechanical)
1? Apr %3 21:3%
your reasoning escapes me$ Is the sensi#le heat of 66%% #tuh generated #y la# e"uipmentlighting and the 1% or less air changes and heat transfer thru walls- ceiling and oor> 9$as:ean1 (Mechanical)
2% Apr %3 %:31
Chip 4ere*s how I see this$ I wouldn*t go #y either option you*!e shown$ I would analye this from load to source- and there is a latent gain at the load$ I would therefore use: VD$]cfm]d4 in lieu of V1$%]cfm]d otal space load is latent S sensi#le- which is -1%% ;Hhr$ o o#tain cooling airow needed- use the VD$]cfm]d4 e"uation- which sol!es for total load (sensi#le and latent) #ased on enthalpy$ 5ith a saturated ^8 supply air stream- and to maintain the ^8 space temperature at %O relati!e humidity- the load (room) would re"uire 36D cfm$ 36D cfm is the !olumetric ow rate that the central A4H would need to cool from ?^8 to ^8$ Hsing V1$%]cfm]d- as you note that this is a dry area- the A4H coil would need to #e sied for this reduction in temperature at this ow$ his e"uates to an A4H cooling capacity of 16-%% ;Hhr$ /ote that I*m s.eptical of the lac. of need for the A4H to remo!e moisture #ecause this is a &dry climate$& =ry is a relati!e term$ ?^8 and 2D$6O humidity would produce saturated ^8 air$ If the humidity were higher than 2D$6O- the coil would also need to remo!e moisture$ I*m open to re#uttal on this ha!en*t gone #ac. to thermo49AC #oo.s- #ut this way seems to ma.e sense to me$ As a side note- #e careful of siing =Q units$ he load conditions stated will #e rare so you need a unit that will perform well at partial load$ ;est of luc.$ C; ,uark (Mechanical)
2% Apr %3
23:? I !ote for C;$ 4owe!er if you want to go your way you should consider to deg$8 #ecause at no time you want to increase the room temperature a#o!e deg$8$ If you consider a = of ? to for a load of 66%% ;tu4r then when this heat load adds up from the room the lea!ing temperature will #e higher than deg$8$ 0ou #etter follow C;*s comments$ anandGH>9 (Mechanical)
2 Apr %3 3:31
I am sorry- Ferhaps not agree with all a#o!e e7planation$ My answer to C4IF8HRR@*s "uestion is as follows$ I will start with #asics$ If you refer to carrier hand#oo. or any other engineering #oo. on Airconditioning$ 0ou will ,nd that the grand total heat- in your case it is 1%%#tuhr i$e %$6 tons- is used to calculate the tonnage re"uirement$his means that your coil should #e capa#le to gi!e you an output of %$6$ /ow the "uestion is how much air is needed to achie!e this$his can not #e decided with a#o!e two e"uations$0ou will ha!e to do the iterations$8irst assume some fresh air i$e 1 airchangehr and calculate the dehumidi,ed air "uantity re"uied$@epeat this procedure till you #alances your fresh air with dehumidi,ed air$his will gi!e you the "uantity of air re"uired to maintain the desired inside conditions$ Answer to your second "uestion regarding pyschometric chart for diBerent ele!ation$H will note that all the standard psychometric charts are designed at atmospheric pressure of 6%mm of 4g$8or pressure other than 6%mm of 4g- you will ha!e to physically draw it$ Frocedure on how to draw psychometric chart is a!aila#le in any air conditioning #oo.$ H can refer to that$ I hope all a#o!e e7planation clari,ed all your "ueries$ In case of any "uery pls$ let me .now$ 9$as:ean1 (Mechanical)
2 Apr %3 13:%
Anand- could you clarify the iteration> 5hat do you get for an answer> han.s- C; 6riand. (Mechanical)
2 Apr %3 1:
Chas;ean1*s response of 2%th April 2%%3 is a#solutely perfect$ I*!e sied countless air conditioning systems o!er the years- and I*!e ne!er had to carry out some &iteration& to get the cooling re"uirement$ Anand49AC: I too would #e really interested to see why an iterati!e process should #e necessary on this occasion (I might #e e7perienced- #ut I ne!er miss the opportunity to learnKK)$ @egards;rian coolingunit (Automoti!e)
26 Apr %3 6:%D
anand49AC: 0our e7planation is e7cellent$ I would li.e to .now the iterati!e procedure of calculating the fresh air re"uirement$ anandGH>9 (Mechanical)
2 Apr %3 1:3%
&Iteration& means trial and error method$ =uring heatload calculation you will ha!e to assume some fresh air "uantity to calculte dehudi,ed C8M re"uirement$ 0ou will ha!e to reiterate this procedure #y !arying fresh air "uantity till it #alances with dehumidi,ed C8M$ Hnless this #oth "uantity matches you will not satisfy the condition of 1%%O fresh air$ It is imposi#le for me to e7plain the method of calculation !ia mail$ 4owe!er- u can refer to carrier hand#oo. for more information$ In case of any "ueriescmments do let me .now$ I will try my #est to address it$ c6i6er (Mechanical)
2 Apr %3 12:D
I ha!e found se!eral psychrometric charts online for ele!ations other than sea le!el$ 8or e7ample <oogle found this one for me using the search terms &psychrometric chart altitude&: $ttp%&&***$eatcraft$eattransfercom&pdfs&Aormal444PDF It*s for %%% feet- not D%%- #ut it*s close enough to get you started$ ;i#er hermal =esign ***6i6ert$ermalcom ,uark (Mechanical)
2? Apr %3 %:D
=r$ [e.yl says- it is always #etter if you ha!e time to practically design a system$ (supplying air "uantity to remo!e heat load and moisture load and incrementing it to reach #alance) Mr$ 4yde says- well if you want to increase comple7ity of a simple solution go ahead$ /one of carrier*s people nor any other engineer o#+ects you$he fundamental is to chec. the total enthalpy of fresh air and the conditions you wanted at the room$ ;asically theair e7iting the room should ha!e same properties of re"uired condition otherwise room conditions cannot #e maintained$ /ow #y the simple calculation gi!en #y C; and used widely e!erywhere- calculate the cfm$ his is enough cfm that will carry heat and moisture out of the room$ his is more simpler than recirculation system #ecause you need not further remo!e the moisture from the e7iting air stream$ Just you are throwing it away$ 'till- if you lo!e math iterations- higher order diBerential e"uations and pro#a#ility will always help you$ ;est of Ruc.$ (;ahK am I #eing too dramatic>) 9$as:ean1 (Mechanical)
2? Apr %3 12:3
his could #e a good e7ercise #ecause we might #e tal.ing apples and apples here$ Ananddid the reiterati!e process produce a result> energy0 (Mechanical)
1% May %3 1:%
Rets .eep it simple- your application is not roc.et science 1st- your C8M re"uired is dictated #y your total sensi#le load and the temp you want to
maintain in the room at the supplly air temp you plan to pro!ide$ it is simply found as @m C8M @oom ;4H V' 1$% ( rm sa ) 2nd- #eause you specify 1%%O E'A ( I will not as. why 1%%O )your coils will ne!er see this load$ Coil Capacity will need to #e #ased on the air ow design a#o!e at ( E'A A d# w# 'A (RA) d#w# ) good luc. lilliput1 (Mechanical)
12 May %3 13:1
he cooling coil will need to cool 1%%OEA to the condition such that when this coil lea!ing air is discharged into the room$ it will pic. up heat and moisture W air is then e7hausted$ he condition of the air e7hausted typically matches the room inside conditions$ If the cooling coil cools the air to % deg 8 W the room design condition is 2 def 8 then the air "uantity re"uired @m Road in ;H per hr(1$1 7 (2%))$ /ow you must also satisfy the latent loads$ he Coil must dehumidify the same "uantity of air to the humidity such that when discharged into the room it will a#sor# the latent load W it*s @4 will #e within the design range$ 0ou may ha!e to reheat to maintain the re"uired space humidity$ lilliput1 (Mechanical)
13 May %3 12:2?
Ra#s typically re"uire 1%%O outdoor air$ Ma.e sure you ha!e enough for e7haust hood ma.eup$ 'implest control is constant !olume reheat$ 0ou can also ha!e (2) position occupiedunoccupied or !aria#le !olume- all with reheat$ Hsually humidity is cirtical so humidi,cation is also re"uired$ Chilled water system is #est$ If =Q you will ,nd out that when you sie the it for the load w 1%%O EA- the unit C8M (typically 3% C8Mton) would #e more than you need to do the room sensi#le load$5hat I ha!e done is recirculate #ac. some of the air$ his unit should only ser!e a la# not a group of la#s to a!oid cross contamination$ Fart of the fan discharge is ducted direct #ac. to the return$ 0ou ha!e to recalculate W do trial W error of the coil entering air condition (mi7 of EA W recirculated air at coil discharge condition plus fan heat$ he AC unit should ha!e hot gas controls$ A humidistat in addition to a thermostat should #e used to #ring on cooling$ 8inal space temperature should #e controlled #y the reheat coil$ greenaire (Mechanical)
2 Jun %3 D:DD
Could you see &the dedicated units& from the news letter of ***tranecom> 9$as:ean1 (Mechanical)
2 Jun %3 21:D6
/o I couldn*t$ Rin. is to trane$com main page$ Chec.ed under &/ews& and didn*t see &dedicated units$& ried a search for &dedicated units& and no luc.$ Could you #e more speci,c> tmprider (Mechanical)
3 Jun %3 ?:16
ry using an @9 sied for the 1%%O fresh air load$ Rocate it in the ceiling space of the la# for ease of maintenance and cleaning$ his will most li.ley decrease the sie of the unit that you go with- and will allow you to ta.e ad!antage of &free cooling&$ E!erall- your energy consumption will #e less due to the lower delta at your coils$
=4 H==riram (Mechanical)
12 Jul %3 13:3D
his seems to #e an interesting heat load which I used to do manually at the start of my career$ 1%%O outside air application cooling load calculations are normally done #y iteration$ 8irst assume a particular outside air "uantity and do the load calculations- ,nd out what the dehumidifed air "uantity is$ If it matches the assumed outside air "uantity- then the initial assumption is right$ Etherwise- do another load calculation a#sed on the dehumidi,ed air "uantity o#tained and .eep doing this (iteration KKK) till you get the same ,gure$ Alternati!ely- if you ha!e a software li.e 2%II of Carrier- you can +ust input all the rele!ant data and put 1%%O outside air and the program gi!es an output which will #e 1%%O outside air$ greenaire (Mechanical)
12 Jul %3 22:23
4i 4ere is we# address for mentioned article and complete article name$ If you still can not get it- gi!e my your email address$ hen send it to u #y email$ My email: naymoIgreenairecomsg &$ttp%&&***tranecom&commercial&li6rary&arc$iedJne*slettersaspKG 1? May 13 %:3 Achie!ing the =esired @eturn Air "uantities from occupied spaces$ he 49AC 'ystem consists of roof mounted Air 4andling units for a single storey #uilding that has many rooms$ he system is designed for 2%O fresh air and %O return air that is achie!ed in the mi7ing #o7 of the air handler$ he return air from the ceiling diBusers #ac. to the Air 4andler is not ducted$ A short piece of duct with a #ell mouth is e7tended from the A4H on the roof to the space a#o!e the acoustic tile false ceiling to draw air from all the rooms and corridors in the #uilding$ he 'upply air in each room is D%% C8M- #ut the return air "uantity measured from the return air diBusers is coming to only 1%% C8M$ 5e could not detect any in,ltration of air from the light ,7tures or the crac.s and cre!ices in the false ceiling$ he measurements from such light ,7tures and edges of the false ceiling panels is registering ero on the measuring 4ood$ he total return air measured at the #ell mouthed duct to the A4H or at the straight piece of duct at the roof #efore its connection to the machine is as per design "uantity$ 'o the A4H is drawing air from somewhere$ 5hile we are in the process of chec.ing the point of in,ltration- the "uestions are: 1) 5hat is the accepta#le tolerance of return air "uantities from the rooms whose type of occupancy is oLces> G 2) Is this achie!a#le in non ducted return air systems> *illard3 (Mechanical)
1? May 13 :3?
0ou will ne!er #alance a plenum air return properly$ If you need to #alance accurately- you need return ducts$ solidspaces (Mechanical) (OP)
1? May 13 ?:D?
I agree willard3- #ut there must #e the practice of the trade or Ashrae'macna guidelines a#out accepta#le performance$ Is 1%O de!iation E. or is e!en 2%O e7cusa#le$ here has to #e a minimum accepta#le performance in such cases$ <etting only 2O return air compared to supply air appears way too far$ DRWeig (lectrical)
1? May 13 13:3%
As long as the plenum is at a negati!e pressure relati!e to the space- there should #e no pro#lem> Is there a comfort or odor pro#lem you are trying to sol!e> 0ou can*t specify a tolerance for return air ow if there is no means to ad+ust it- so there won*t #e any sort of standard in my opinion$ I*m agreeing with 5illard3 here- #ut going a #it farther$
;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
solidspaces (Mechanical) (OP)
1? May 13 1:32
he #uilding is not occupied yet$ 5ith so little return- an odor pro#lem would most li.ely arise$ If the plenum is at a negati!e pressure compared to the space #ut the return air "uantity that is showing up on the hood is !ery little- that might mean that the rooms will !ery soon face hea!y air$ Is it #eing implied that we need not do air #alancing of the return air> 'econdly if there is no pro#lem- then we can always omit a ducted return (if we can aBord a little cooling load increase)$ Dra2en (Mechanical)
2% May 13 :D1
why would you not open return diBusers to the ma7imum and measure "uantity- as a ,rst step$ open the one closest to ahu- measure- than close it and open the farthest one$ DRWeig (lectrical)
2% May 13 ?:11
I was assuming that you do not ha!e ad+usta#le return diBusers$ I ha!e ne!er seen ad+usta#le return diBusers in a plenumreturn system$ Aren*t they something li.e eggcrate panels> If so- you cannot possi#ly #alance return ows$ 4ow can you #alance the airow through se!eral holes that don*t ha!e dampers> I don*t understand your comment- &$$$that might mean that the rooms will !ery soon face hea!y air$& If you ha!e D%% C8M going into a room- you also ha!e D%% C8M lea!ing the room$ If it*s not going up the return grille- it*s going into the hallway$ Many places ha!e no return grille at all in the rooms- #ut a single common return in a corridor that is ducted #ac. to the rooftop unit$ Close all the oLce doors$ Right up a cigarette (or spend some money on a smo.e candle)$ 'tand in a room farthest away from the rooftop unit$ 5ith D%% C8M supply and 1%% C8M return 8ollow your smo.e until it ma.es it to a return grille$ It will pro#a#ly #e in the few oLces !ery close to the rooftop unit$
0ou mentioned 2% percent outside air$ 4ow does the relief air e7it the #uilding> ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
solidspaces (Mechanical) (OP)
2% May 13 1%:11
=@5eig: 'ince D%% C8M are coming in- the same "uantity is de,nitely lea!ing #ut not from the return grille and this is the issue$ If the door is closed this might e!en pressurie the room forcing the supply air to go to ad+acent rooms$ I feel this will somehow desta#ilie the system and would cause odors in rooms that a re not ha!ing the same C8M lea!ing the room$ It would also cause a nuisance when the room occupied #y a smo.er is not getting the smo.e pulled out from the ceiling diBuser and it is instead going to the hallway$ he 2%O ma.e up of fresh air is due to the 2%O #eing e7tracted #y e7haust fans from the toilets$ DRWeig (lectrical)
2% May 13 11:3%
hat*s great- solidspaces$ 0ou are right- odors will go from oLce to corridor to the other oLces$ 4owe!er- this will happen whether the door is open or closed- unless the door is gas.eted and sealed well at the oor$ he point is you cannot change it unless you install return dampers in each room and #alance them$ ry my e7periment$ Close all the doors$ hen start at the last oLce on the end of the supply duct run$ Ma.e some smo.e and follow it$ 'ee where it goes$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
Gerr?a5eun (Mechanical)
2% May 13 12:2D
not sure I fully understand- #ut did you account for all the air that goes &through& the acoustical ceiling and not through the return grill> An acoustical ceiling with laidin tiles ,7tures etc$ is li.e a sie!e and the air goes path of least resistance$ In addition at such low ow rates your measuring hood isn*t accurate$ Just measuring adds resistance- di!erting more air &through& the ceiling$ E#!iously as much air as comes in will lea!e the room- same for the A4H$ If the plenum doesn*t ha!e lea.s to the outside or restrictions- it pro#a#ly will #e ,ne unless you e7perience actual pro#lems$ solidspaces (Mechanical) (OP)
2% May 13 16:%
I am grateful to all who responded$ he net result of this discussion is that matching the return air "uantities with supply is not as critical as I thought *illard3 (Mechanical)
21 May 13 :2?
0ou will ,nd out- after the #uilding occupants complain a#out humidity- odors and draftsthat there should #e return air ducts and the air !olumes should #e #alanced$ solidspaces (Mechanical) (OP)
21 May 13 11:D
5illard3: I thought the consensus was that it is EP e!en if the "uantities of supply and return do not e"ual$ =iBerent arguments and e7planations poured in a#out this disparity from the sensiti!ity of measuring hood to the crac.s and cre!ices of the false ceiling panels to the positi!e and negati!e pressures to the argument that the air that is coming in must #e e7iting also- etc$ 0our eye opener response goes against all the a#o!e consensus and has re!i!ed my concerns$ 'o more responses are re"uested a#out the ,nal action that is needed in this matter$ DRWeig (lectrical)
21 May 13 13:%%
5illard3 is not going against the consensus- he is adding information to it$ I +ust ,nished wor.ing 1 years in a #uilding with plenum return$ Complaints were few and far #etween$ here is no way to tell until 1% occupants all get together for a #ean #urrito lunch on the same day that another occupant #urns popcorn in the microwa!e and another occupant heats up chic.en ti..a masala on a hot plate in his oLce$ hat happened in our oLce may#e twice a year$ =ucted return would swoop that stuB #ac. to the A4H to #e mi7ed with E'A #efore returning to the spaces$ It*s a chance you ta.e$ ry my suggestion$ Ret some smo.e loose in a room farthest from the @H$ 8ollow it$ 5hen it lea!es the hallway and starts entering other oLces- imagine that it is &#ioeuent gas& instead of +ust smo.e$ he point is: It*s EP to ha!e supply not e"ual return with a plenum system because you can't do anything about it $ It occurs in all systems in which the owner doesn*t want to spring for ducted return$ here is nothing you can do to #alance the return air- so ignore it$ E@- duct the return$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
3104/" (Mechanical)
design conditions: D%% cfmroom- 32%cfm of return$ % cfm of fresh air$ actual conditions: D%% cfmroom- 1%% cfm of return- 3%% cfm of fresh air$ did you chec. supply air condition>
22 May 13 12:D
what if you close the fresh air inlet then chec. return ow again> solidspaces (Mechanical) (OP)
23 May 13 1%:2
31%6?: 0es we did chec. the supply air "uantities$ hey are as per design$ 5e could do the e7periment that you ha!e suggested of #lan.ing oB the supply and chec. out the return "uantities$ I am curious a#out your e7pectations or predictions a#out the eBect of doing soK =>?" (Mechanical)
23 May 13 1:D
Flenum return is ,ne if you ha!e air tight ceiling !oid as in oLce towers with concrete oors$ Flenum return is not to #e used in #uildings with metal dec. or similar roof structure that are unli.ely to #e air tight$ ;y measuring room conditions and the return conditions at A4H inlet- you can esta#lish if there is outside air lea.ing into the !oid$ An easy way to chec. if return is all right is to see if the doors are easy to open$ solidspaces (Mechanical) (OP)
2 May 13 1:?
'AP? All that you say ma.es sense$ I am recei!ing the Air ;alancing wor. from a su#contractor$ I +ust need to .now if supply is D%% C8M and return is coming at only 1%% C8M- can the su#contractor #e paid> 5ill these num#ers #e appro!ed #y the consultant> Er will the company ha!e to do it all o!er again> /o o#+ection was raised a#out the non ducted return at the time of accepting the Air ;alancing Jo#- so can anyone #ac. trac. and start raising hue and cry now- that it is not ducted> 3104/" (Mechanical)
2 May 13 11:D%
I didn*t mean air "uantities- (3%% cfm fresh airS1%% cfm return air)is a diBerent than (3%% cfm return air S1%% cfm fresh air) for the same A4H or @H- may #e you ha!e to hire an air #alance contractor to #alance your system$ 3104/" (Mechanical)
2 May 13 13:%?
ooops you already ha!e a contractor$ 6erks$ire (Aeronautics)
2 May 13 1D:33
he total return air measured at the #ell mouthed duct to the A4H or at the straight piece of duct at the roof #efore its connection to the machine is as per design "uantity $ 'o the disconnect if you can say that- is that the space a#o!e the ceiling is pro!iding air from somewhere other than the rooms to the air handler$ 4as any#ody loo.ed at the point where the dec. meets the e7terior walls- to see if foam seals are installed> DRWeig (lectrical)
2 May 13 22:13
#uote (solidspaces)
I +ust need to .now if supply is D%% C8M and return is coming at only 1%% C8M- can the su#contractor
#e paid>
here is no control for return air in a nonducted system$ he contractor cannot ma.e it any diBerent than it is right now$ If they #alanced the supply air to D%% C8M- they are done$ Mission accomplished$ he #alancing ,rm did its +o#$ If you are supplying D%% to the space- suc.ing % of it out the toilet e7haust- measuring design return air ow at the unit inta.e- and design outdoor air at the unit inta.e- you ha!e done all that you can do$ here is no more that can #e done$ I would not #other measuring return air in indi!idual rooms$ It cannot #e #alanced in any way- shape- or form$ 'orry for the dead horse a#o!e- feel free to red ag it$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
=>?" (Mechanical)
2 May 13 :%2
0ou ha!e not told us whether the A4H inlet conditions were close to design$If it is high there may #e outside air lea.ing into the system$As a matter of due diligence you should highlight it to your consultant$ solidspaces (Mechanical) (OP)
2? May 13 16:
'AP?: he supply- return and fresh air "uantities measured at or near the machine all add up$ he only pro#lem is that the return air "uantities are a fraction of what they should #e when measured #y the hood at the ceiling return diBusers$ =>?" (Mechanical)
2? May 13 2%:2
hen it loo.s li.e most of the return is through light ,ttings(!ented>)and through the gap #etween lay in tiles and the frame$he hood may not register any air ow when held against the light ,tting as it will #e well #elow its measuring range$ry a smo.e test if you need to put your mind at rest$ 6erks$ire (Aeronautics)
3% May 13 1:%
'AP? his thing is getting circular- I #elie!e =@5eig suggested this in his second reply$ And at the ris. of him #eating me- with the stic. instead of the horse$ 'uspended ceiling tile are notorious for this #eha!ior$ ;$$ *illard3 (Mechanical)
3% May 13 ?:D6
his is +ust recursi!e and some#ody should .ill this thread$$$$$it*s going nowhere$$$$$ DRWeig (lectrical)
0ou*re right 'AP? and #er.shire- no #eatings in the oLng$
3% May 13 1%:3
As for the last post #y solidspaces#uote (solidspaces)
he only pro#lem is that the return air "uantities are a fraction of what they should #e$$$
I will again- #ut more gently- state that there &what they should #e& is what they areunless you ha!e ducted return with #alancing dampers$ 0our return "uantities measured at the return diBuser in each room are QACR0 what they should #e$ ;est to you<oo#er =a!e
Cneartsnyc (Mechanical) (OP)
12 Aug 13 1%:2
4i all- IYm wor.ing on 49AC system for lu7ury residential #uilding$ Hnit 1 two oors$ 8our #athrooms cfm e7haust each$ otal e7haust is 3%% cfm$ Hnit 2 one oor$ wo #athrooms cfm e7haust each$ otal e7haust is 1% cfm Hnit3 one oor$ wo #athrooms cfm e7haust each$ otal e7haust is 1% cfm HnitD two oors$ 8our #athroom s cfm e7haust each$ otal e7haust is 3%% cfm$ he e7haust fan will #e controlled #y local #athroom light switch$ IYm planning to #ring a fresh air to each air handler unit e"ual to the amount e7hausted from the toilet$ hru a common duct to the roof with a goosenec.- each air handler fresh air ta.esoB from the main fresh air duct$ My Vuestion is$ 4ow do I treat the outside air to protect the coil from freeing> 'hould I install electric duct heater slip in type with a #ooster fan> If so- how the control would wor.$ Flease ad!ice$ han.sKK 3104/" (Mechanical)
12 Aug 13 11:D?
Rea!e toilet e7haust alone- it doesn*t wor. all the time$ 0ou can use an 4@9 for each air handler sprinkler1444 (Mechanical)
12 Aug 13 11:%
It depends on the system you are installing and the minimum outside air temperature e7pected$ 0ou may ha!e not only a coil freeing pro#lem #ut a heating load higher than the unit can handle$ If your option is a 9@8 system they ha!e indoor units to treat outside air or e!en 4eat @eco!ery Hnits to e7change heat with e7haust$ Cneartsnyc (Mechanical) (OP)
12 Aug 13 11:?
in fact I*m using 9@8 system (Mitsu#ishi system) $ ? =;- D 5; summer condition and 1 8 winter emp$
2% cfmperson Q 1%% cfm min$ outside air$ Cneartsnyc (Mechanical) (OP)
12 Aug 13 12:13
since the toilet e7haust fan is not continuously we cant use @9$ Also its only 1%% cfm EA re"uired$ sprinkler1444 (Mechanical)
12 Aug 13 2%:3?
Chec. with Mitsu#ishi$ I am more familiar with =ai.in- #ut they should also ha!e a dedicated outside air unit$ he 1^8 may #e a little low- #ut it will wor. most of the year$ Cneartsnyc (Mechanical) (OP)
12 Aug 13 23:D%
i don*t li.e the idea of using a dedicated outside air unit for +ust 1%% cfm$ is there any other solution> sprinkler1444 (Mechanical)
13 Aug 13 :
he idea was that you supply the total amount of fresh air (?%% cfm) with the outside air unit$ I thought you had a common duct$ Cneartsnyc (Mechanical) (OP)
13 Aug 13 :16
han.s$ /o we can*t use a common h!ac unit howe!er the ductwor. can #e shared$ 5e ha!e to use a separate unit since the unit owner has to pay the electric #ills and maintenance$ Waramanga (Mechanical)
1 Aug 13 :%?
what is your mi7ed air temp onto the coil> <i!e the mitsu#ishi engineers your parameters and see what they come #ac. with- your lu7ury units are not li.ely to ha!e small 8CHs so I thin. you will #e EP$ Etherwise it is heat reco!ery- there are "uite a few small ones a!aia#le now$ Cneartsnyc (Mechanical) (OP)
16 Aug 13 11:2
han.s 5aramanga- since the toilet e7haust fan is not continuously we cant use @9$ Also the 1%%O outside air unit from Mitsu#ishi is 12%% cfm- therefore I cant use it$ I*m thin.ing of using a small electric duct heater with inline fan to maintain the duct heater !elocity in each fresh air ta.eoB to the air handler$ (he #uilding will share a common fresh air duct wor. #ut the electric coil and fan has to #e operated- maintained and ser!iced #y the apartment owner from the ta.eoB) ProcessGH>9 (Mechanical)
16 Aug 13 1:%
&IYm planning to #ring a fresh air to each air handler unit e"ual to the amount e7hausted from the toilet& this is ?%% C8M not 1%% C8M EA as you said after- !ery confusing$$$ c$icopee (Mechanical)
1? Aug 13 21:%
If this residential structure is a condominium with annual maintenance fees- I would ha!e a
duct or a chase- dedicated for all the toilets- with a roof mounted e7haust fan whose cost for replacement and electricity would #e included in the annual fees$ Cneartsnyc (Mechanical) (OP)
1? Aug 13 21:32
Initially the design was to e"ual the fresh air inta.e and toilet e7haust- since the toilet e7haust fan energie #y light switch therefore the fresh air reduced to 16% cfm 8AI to each duple7 condominium and 1%% cfm 8AI for the single unit$ yes the owner concern a#out the condominium maintenance fees$ each unit will ha!e own e7haust system and fresh air inta.e$ I came up with an idea to use a small inline fanelectric duct heater with temperature sensor for each unit$ 22 Ect 1D :1? oday I got into some discussion with a colleague regarding Air Changes and 8resh Air 9olume and I would li.e to get a &referee& to sol!e this$ Imagine the following situation for the sa.e of argument: @oom 9olume: 1%% m3 AC4 (Air Change per 4our): My position is that the AC4 ,gures tells me how many times in a hour I ha!e to replace the air- so #asically I would need to put in the room %% m3 of fresh air My colleagueNs position is that AC4 means that we will ha!e to circulate the air through the 49AC system in an e"ui!alent !olume of times the roomNs !olume (%%m3) and that fresh air should #e around 12 ls per person which gi!e much lower fresh air needs$ I see !alidity on my colleaguesNapproach and may#e I am #eing put oB #y the semanticsin which for #e air changes per hour #asically means that I ha!e to replace air inside the room times$ 5hich approach is the correct one> han.s a lot for your help$
Mintulep (Mechanical)
22 Ect 1D :2D
0ou are right$ Medicine@ng (Industrial) (OP)
22 Ect 1D :D
MintJulep: han.s a lot for your feed#ac.$ /e!ertheless- and since meanwhile I also found some minimum fresh air ta#les that de,ne a diferent approach for instance Fart 8 HP #uilding regulations 2%1% calls for a 1%ls per person of fresh air$ =oes thi smeans that if no Air changes are de,ned- we apply this !alue- if AC4 is de,nedthen it will o!erule the minimum fresh air re"uirements- correct>
DRWeig (lectrical)
22 Ect 1D :D
0ou can meet the higher AC4 !alue and include the lower 1% ls per person$ It*s a matter of mi7ing return and fresh air (and controlling same)$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
sprinkler1444 (Mechanical)
22 Ect 1D :D
0ou ha!e to chec. what are the code re"uirements$ A'4@A clearly states &Air changes per hour of outdoor air& which is diBerent from &Air changes per hour supplied to room&$ he latter refers to air mo!ement$ urgross (Mechanical)
22 Ect 1D ?:12
0ou*re friend is correct in my opinion$ As an e7ample- an E@ room needs- under A'4@A 1%- to ha!e 2% AC4 and D AC4 of outside air$ /e7t point is that the AC4 are measured o+n the supply side if space is relati!e posit!e diBerential pressure and oB the e7huastretrun if needed to #e relati!e neg pressure$ ProcessGH>9 (Mechanical)
22 Ect 1D ?:2%
It goes down to code de,nition$ 8or instance /8FA 2% de,nes AC4 as per your de,nition (i$e$ 1%%O E$A) #ut as mentioned in other standards- it could mean fan*s C8M$ Medicine@ng (Industrial) (OP)
22 Ect 1D ?:?
han.s e!ery#ody for yout answers$ I guess that we can call it a draw then$ he two approaches are correct- depending on the go!erning code$ *illard3 (Mechanical)
23 Ect 1D :D
0ou are arguing semantics and not physics$ Medicine@ng (Industrial) (OP)
23 Ect 1D 1%:3?
willard3: In a sense you are right- #ut as someone pointed out a#o!e- diBerent standards also ha!e diBerent understandings of the word$ 8urther to our discussion- today my colleague came with a portion of a 49AC tender that stated: & Air ;alance Fressure 12 literssec per person& and he claims that this is related with our discussion of the air changes per hour$ I ha!e a feeling that it doesnNt #ut I also couldnNt e7plain why$ Can any#ody gi!e a hint on what does this parameter relates with AC4>
han.s a lot$ Medicine@ng (Industrial) (OP)
2D Ect 1D 12:%3
I noticed now that I missed one line in my pre!ious post: he paper that my my colleague showed showed me was written li.e li.e this: & ($$$) Area Air @e"uirements: AC4 Air ;alance Fressure: 12 ltssecperson$ ($$$) & 'o thatNs why he is claiming that the AC4 ,gure is referring to recirculating air- while the air #alance pressure is the fresh air$ Any thoughts on teh line of reasoning> han.s a lot 2 Ect 13 1:DD 4elloI*m a #eginner in rane race %%- and I*m ha!ing a pro#lem I can*t ,gure out$ I*m doing load calculations for a #uilding$ I ran the calcs and e!erything came out EP$ he procedure for me now is to go through the EA calculations using A'4A@ 62$1 e7cel sheet (the company ad!ises us not to use race !entilation method)$ /ow that I h!e the new EA num#ers- I*d li.e to add them to the rooms- #ut I also want to speci,y the design airow for the room so I don*t ha!e to go through a new set of EA calcs when race outputs a new design C8M$ I attempted to set the &Main 'upply& airow in the airow ta# for the rooms- #ut the airow was still oB #y around 1%O$ I can*t ,gure out why- #ut the designspace C8M is not coming out to what I speci,ed$ =oes anyone .now what the pro#lem might #e> Gerr?a5eun (Mechanical)
3 Ect 13 :2
I*m not sure if you mi7 up EA and design aiow$ 0our company is right to re"uire separate EA calculation$ 0ou 0ou should call rane rane support ( it is free free with your nandatory su#scription)$ su#scription)$ ( Mechanical) Dra2en (M
3 Ect 13 16:?
do you swear that you ha!e read manual in detail> if you don*t do that- you will ne!er reach accepta#le le!el le!el of .nowledge and tips will not help you$ i don*t use trace- #ut common fault in such setups is when concepts of supply air and outside air are mi7ed$ most of load calcs software pro!ides supply air calculation- and fresh air setup stands somewhere #esides that$ Moe@ng (Mechanical) (OP)
3 Ect 13 1:%
;y design airow I mean the 'A C8M- not the EA$ I contact rane support as 4errPaReun suggested and they were a#le to help me out (not at once- #ut they got #ac. to me)$ o o
who*s interested- the answer is #elow$ o o speci,y the desired design 'A C8M- the #loc. cooling cooling airow must must not #e ,lled ,lled out for the system$ hat*s the only way to specify the 'A C8M$ Ef course- that means that for a single system- you*d need to specify all of the one 'A C8M*s so that you get to your #loc. cooling airow (from the A4H)$ (Mechanical) cry.. (M
3 Ect 13 1:21
you may ha!e loc.ed the supply air temperature oB the coil$ lea!e it #lan. and it will gi!e you a diBerent C8M ;H- watch out if you get a too high 'A temperature- you*ll end with dehumidi,cation pro#lems$ suggest that you gi!e your ,le a generic name and post a A8 ,le for others to see$ 0ou 0ou .now how to ma.e ma.e a A8 A8 ,le- don*t you> If not- close the ,le- go to ,learchi!e pro+ect- clic. on the @C ,le and an archi!ed A8 ,le will #e generated- post that ,le and we can chec. it out for you$ Moe@ng (Mechanical) (OP)
D Ect 13 :D
I do ha!e the 'A temperatures loc.edloc.ed- and I*d li.e to .eep them that way so I don*t ha!e to critically loo. at e!ery one in this #uilding e!ery time I ad+ust the race ,le$ I do ha!e another pro#lem I*m trying to ,gure out- howe!er$ 8or the outside air calculations- we design #ased on the pea. design C8M for the 9A9 (in our case 9A9 with hot water @4)$ I got the EA num#ers I needed to satisfy A'4@A 62$1and I inputted that into race as a C8M !alue$ I set the 'A C8M to the pea. design of the 9A9 #o7$ 4owe!er- I*m designing the system #ased on the ;loc. C8M- not the pea.$ @egardless of which C8M I*m designing to- the C8Mton comes out to around 22% which isn*t easy to get fromn an oBtheshelf A4H$ 5hen I got selections- the C8M for the A4H was 6O o!er the design C8M speci,ed #y race- in order to meet the cooling load re"uirements$ 5hat would #e the procedure now> 'hould I #ump up all of the 9A9 9A9 C8M*s in order to get a total C8M that matches the A4H- redo the EA calculations- and reinput the !alues in race> race> Er is is there a standard method method for ad+usting the EA and load calculations #ased on the selected A4H> As Cry22 mentioned- the 'A temp should change since the cooling load is relati!ely the same- #ut the C8M is a lot higher$ 4owe!er- the num#ers in race stil ha!e the speci,ed 'A temperatures- so I*m ha!ing trou#le ,guring this out$ Any help would #e greatly appreciated$ appreciated$ Moe@ng (Mechanical) (OP)
D Ect 13 :D?
I can archi!e it later today and post it if it*ll help$ Gerr?a5eun (Mechanical)
D Ect 13 13:2%
rane rane support also also can ta.e your archi!ed archi!ed ,le and re!iew re!iew it if needed$ hat can can ta.e them them a day or two- though$ Moe@ng (Mechanical) (OP)
D Ect 13 13:
5ell the "uestion I ha!e now isn*t necessarily a race "uestion$ It*s what the standard procedure procedure for matching your load C8M from your load calculations and your C8M from your selected A4H$
( Mechanical) Dra2en (M
6 Ect 13 1%:22
i am "uite impressed on how complicated your posts are$ can we go step #y step- for instance if you would re!eal how trace*s supply air calculations are tied to your change of oa settings- we could possi#ly go forward$$$ Gerr?a5eun (Mechanical)
6 Ect 13 13:%1
In my e7perience it is easier to calcaulte EA re"uirement and minimum ow rates separately in 7cel (and you also need to meet local code- since that may diBer from A'4@A)$ A'4@A)$ and then +ust dump that t hat amount of air into the A4H (in rane system settings you +ust don*t do all the fancy A'4@A A'4@A stuB)$ his is easier easier to understandunderstand- less error errorprone$ prone$ Also easeir to show to A4J what you did$ I once did a full A'4@A calcaultion in 7cel and race and ne!er really had 1%%O the same num#ers- they always were a #it diBerent whne you include all the A'4@A A'4@A loopholes$ And this didn*t e!en wor. well with e7haust$ 4ere in 5I code for !entialtion is diBerent from IMCA'4@A$ 'o what i do is calculate EA for code- EA for A'4@A and pic. the higher num#er$ In addition we ha!e often huge e7haust re"uirements- that supersede the EA re"uirements$ In tha tcase the EA is o!erdesigned anyway$ his is not easily doen in rane- if possi#le at all$ rane rane is really really really really good$ #ut if if you don*t understand understand something 1%%O you easily do it it wrong and get totally wrong num#ers$ Moe@ng (Mechanical) (OP)
Ect 13 :32
I*m not sure how to simplify what I*m saying I ha!e the re"uired EA calcs from an 7cel sheet$ I inputted those !alues in race and I*m getting the cirrect cirrect EA outputs$ /ow- I too. the #loc. capcacity- the 'A C8M- and got selections for an A4H$ he C8Mton #ased on the t he race race ,le was around 22%- which is too low to get a good match from an oBtheshelf A4H$ he selection selection I got from from the sales rep rep had a 6O higher higher 'A C8M than than the one race race said I should ha!e$ he "uestion is- what now> F'$ 4errPaReun- yea race is funny li.e that$ 5e*re actually supposed to do energy modeling with race in a later phase of the pro+ect$ I*!e ne!er done it #efore and wonder how accurate the results will #e$ I heard somewhere somewhere around S 2%OK Dra2en (M ( Mechanical)
Ect 13 12:2?
o.- from the new post it loo.s li.e there there is no direct lin. #etween your oa inputs and trace load output though it loo.ed so in ,rst posts$$$ i ha!e to guess and say that #loc. load and a nd !entilation load are summed up to reach reference data for your ahu> on the other hand- i also ha!e to guess that you ha!e no any other choice #ut to ta.e some pac.aged rooftop with ,7ed toncfm capacity$ ,rst you should do is to chec. whether calculated minimum cfm can #e reached #y
controls with your pic.ed ahu at all$ if not- you simply ha!e to change ahu selection concept- gi!e up loc.ing supply temperature or similar$ changing supply air temperature should reduce collision$ it is also interesting to see how much #loc. load diBers from pea. loads sum> if you are limited with ahu choices- there could #e- for instance- possi#ility to split into two completely separate systems where two separate ahu*s could ,t$ no tool i use is a magic tool$ #est of them ha!e most of useful options- #ut we always ha!e to #e aware that each of them ha!e their own limitations$ Gerr?a5eun (Mechanical)
Ect 13 12:DD
Mong: race is pro#a#ly the most accurate energy simulation since it actually has all the 49AC options$ ;ut since it is more detailed- the user can ma.e more mista.es$ If you use race for load anyway- it is natural to use it for energy simulation$ ;ut you should .now what you are doing$ Moe@ng (Mechanical) (OP)
Ect 13 12:?
=raen: 0ou guessed right in that I ha!e no choice #ut to ta.e some pac.ed rooftop with a ,7ed toncfm capacity$ I*ll try redoing the calculations to get a #etter ,t$ he pea. loads and #loc. loads are pretty closeG a diBerence of a#out 1%1O ma7$ ;ut that*s a good way of !alidating ones$ <otta .eep that one in mindK han.s for the help$ 4errPaReun: Eh yea- I can*t wait til I ha!e to redo the energy model 1% times to ,gure out what I inputted wrong haha$ Gerr?a5eun (Mechanical)
Ect 13 1D:%
Moeng: there are so many A4H options (=EA'- where you add EA etc$)$ supply temp$$$ and ran can simulate almost e!erything$ +ust for giggles change ducted to plenum return and you see a diBerence$ 0ou also can insert the actual e"uipment unload and am#ient relief cur!es etc$ Many energy simulations are not detailed with 49AC options$ 'o the user can*t do much wrong$ If you enter e!erything right- race will #e accurate$ Ene issue with all energy simulations: they simulate the assumed occupancy and usage and also assume the system was properly commissioned and wor.s as designed$ In reality this isn*t the case$ Moe@ng (Mechanical) (OP)
Ect 13 1D:16
0ea that*s true$ I did read something that mentioned that some pro+ects needed some sort of testing of the facility 1 year after #uilding &openup& to !alidate the energy model$ I thin. the term was called cali#rating$ Gerr?a5eun (Mechanical)
Ect 13 1:D
I thin. you mean the &!alidation and !eri,cation& re"uirement$ Hnless the energy simulation was wrong- this isn*t to cali#rate the energy simulation$ this is more to !erify if
the system was installed and commissioned as designed$ the energy simulation- in my opinion- is to decide on what system is to #e chosen$ the owner can use upfront cost- maintaina#ility- energy consumption etc$ to ma.e a decision$ it isn*t to predict e7act consumption$ +ust for the fact that the energy simulation uses M03 or some other weather data (which are an a!erage design year) will ma.e it impossi#le to compare one year to the simulation$ Moe@ng (Mechanical) (OP)
Ect 13 16:%1
Eh I see$ As far as using energy modeling to ma.e #etter design decisions- it*s a pri!elage I don*t see here !ery often$ 8rom what I*!e o#ser!ed at many companies in the /0/J areaenergy modeling is usually used to ful,l some sort of pro+ect re"uirement such as R=and it comes so far into the design phase that it ma.es it almost impossi#le to redesign in time for the deadline*s$ I*m hoping one day we can get a pro+ect where the client cares more a#out eLciency and longterm returns than initial cost and deadlines$ Gerr?a5eun (Mechanical)
Ect 13 2%:%3
Is it possi#le that your 22% cfmton num#er is caused #y including EA treatment> yes for recirculated air rule of thum# is D%% cfm ton$ ;ut for EA this num#er is lower depending on your climate$ Just an idea$$$ 2 =ec 11 %:2 4i <uys8or one of the pro+ect that i am wor.ing on we ha! calculated the #uilding load and ha!e suggested fan coil units for most of the rooms in the #ldg- the total fresh air re"uirement for the #uilding is 2%%% ls- indoor condition 2223 C %O @4 and the outdoor condition is =; D C and w# 32$ 4ow do i calculate the load in P5 for selecting the 8A4H>> han. 0ou$ sspeare (Mechanical)
2 =ec 11 11:31
8irst- you need to demonstrate to the forum that you understand certain thermodynamic fundamentals for e7ample: 1) =o you .now the de,nition of sensi#le load> 2) =o you .now the de,nition of latent load> 3) =o you .now what enthalpy is> D) 4a!e you used a psychrometric chart> $e!gala!y (Mechanical) (OP)
2 =ec 11 12:%
4iya 'speare8rom my understanding sensi#le load in terms of h!ac is head load ina space that is gained #y !arious factors such as direct e7posure of sun- heat radiated #y people- lights and e"uipment as such- in terms of thermodynamics it is the heat re"uired to raise the temp of a #odyelement or may # water .eepings its state constantlatent load is essentially the humidity load with in the space or heat a#sor#ed #y a #ody while .eeping its temperature constant while its phase changes$
nthalpy is sum of all internal energies in a system$ and yes i ha! used a psychrometric chart$ regards than. you Dra2en (Mechanical)
2 =ec 11 13:26
than draw your outside air and indoor design conditions in psychro chart and enthalpy diBerence will ma.e your cooling capacity needed in the simplest scenario$ cry.. (Mechanical)
1 =ec 11 1:%D
V D$ 7 C8M 7 =elta 4 $ttp%&&***engineeringtool6o!com&cooling'$eating'e,uations'dJ0;0$tml
3% 'ep %? 16:3D I am the 49AC designer for my engineering ,rm- and we fre"uently come across 9A9 systems in medical oLce #uildings that pose a uni"ue pro#lem$ ;ased on heat loads and standard practices- we supply enough owrate to each room to cool the space using the D%% C8M per ton rule of thum#$ 4owe!er- #ased on A'4@A standards- oLce spaces re"uire a minimum of D air changes per hour$ 5hen we are dealing with a 9A9 system that is only capa#le of supplying degree %O humidity air- how does one design for the correct amount of air changes without o!er cooling the space> Also- how do you handle the outside air re"uirements gi!en you can only pro!ide air from the main loop$ I' it a safe assumption to e7haust the amount of E$A$ you need and ma.e sure the A4H for the entire oor is pulling in enough E$A$ to co!er the diBerence> han.s for the helpK Chris 5$ operatingeng (Mechanical)
3% 'ep %? 21:3D
!ery 9A9 system I*!e come across seems to ha!e the same aw$ ;ecause of the minimum damper postion in the 9A9 #o7 certain areas will always #e o!ercooled$ ELce #uildings mo!e people around all the time- so areas that were designed for ten people may h a!e only two which +ust compounds the pro#lem$ I*m only an operating engineer- #ut e!ery 9A9 air handler i*!e come across seems to ha!e the minimum EA damper sied #ased on the total amount of air that unit mo!es$ tys"4 (Mechanical)
1 Ect %? 1%:D
5here do you get the D AC4 for oLces num#er from> According to A'4@A 62$12%% an oLce room is C8Mperson plus %$%6 cfms"$ ft$ o not o!er cool spaces you pro!ide hot water or electric reheat on your 9A9 #o7es to #ring space temperature up in the e!ent of an o!er cool$ Er you can use fan powered #o7es to mi7 return air with primary air to achie!e a higher discharge air temperature$ here are e7amples of control se"uences around on the internet$ hird- you set your minimum EA #ased on your A'4@A calcs or in the case of a medical oLce #uilding we use AIA guidelines$ 0ou ha!e to watch your e7haust rates- if you are starting to #ecome neutral or negati!e it*s time to increase your EA and do energy reco!ery on the e7haust side$
Rastly- unless your are in an early design phase we ne!er use rules of thum# for cooling loads$ Always do proper load calculations$ 1 Ect %? 12:1
(.) mauricestoker (Mechanical)
he D AC4 would #e typical for oLce function and is diBerent than EA re"uirement$ A standard procedure for doing this is gi!en #y 62$12%%$ EA should #e estimated for normal (ma7 9A9) and lowest ow$ Rowest ow (if you ha!e reheat) is limited #y A'4@A ?%$1$ A'4@A has a guideline speci,cally for outside air inta.e$ Hse of a dedicated minimum EA inta.e- with static set at minimum ow- would #e one way of assuring minimum EA$ Hsing an IAV outside air damper would #e another$ Eperatingeng hit the nail on the headG one day a room will #e a house.eeping closet- the ne7t day it will #e an oLce$ Conference rooms always seem to #ecome a large oLce for whome!er has clout$ srid$ar131. (Mechanical)
11 /o! %? :11
@oom Air changes within room in an air conditioned space is in the range of 13 to 1 $ 8resh air change shall #e cfm person and %$%6 cfm per s"uare feet or as per A'4@A standard depending on the usage of the a rea$ 5here!er 9A9 is used it is recommended to ta.e care of the additional load due to occupancy e"uipment etc which may !ary through the 9A9 and #ase fa#ric load separately to a!oid any distur#ed conditions mauricestoker (Mechanical)
12 /o! %? :3
I ha!e to say that I*!e ne!er seen 131 AC4 for oLce space$ Flease let me .now the #asis for that- it*s a new one to me$ If you are supplying air at ]8 without reheat and only one or two rooms are getting o!ercooled- then you are luc.y$ I*d recommend !erifying what criteria you are designing for$ I thin. you*ll see a large diBerence #etween A'4@A 4and#oo.- A'4@A =esign Manual for 4ospitals and ClinicsA'4@A 1%- AIA- 62$1- and go!ernmental (=o=- 9A) standards- and which edition #y year$ If you don*t want to own the IAV re"uirements- I*d recommend a reheat$ 7OMec$@ng (Mechanical)
22 =ec %? 23:D
As others ha!e noted the #est way to pre!ent o!ercooling a space is to use some form of reheat$ he issue is o#!iously that you may #e cooling air only to ha!e to heat it up againwhich is not so good for energy eLciency$ A way to reduce the amount of reheat re"uired is to use a supply air temperature reset #ased on outdoor air temperature(or EA 5; if you monitor it)$ he issue of ensuring that you are maintaining your outdoor air rate when the 9A9 system is at minimum ow is a tric.y one$ =epending on your system it may #e possi#le to !ary your outdoor air damper #ased on the fan speed so that you pro!ide an increased O of EA
at min ow to maintain re"uirements$ Another way is to seperate your !entilation and coolingheating system so that the re"uired !entilation is accurately controlled$ =>?" (Mechanical)
23 =ec %? 2:13
Choose your supply air temperature such that you are a#le to achie!e the re"uired air change rates in the space$Also #ear in mind your dehumidi,cation needs$ *illard3 (Mechanical)
2D =ec %? 11:D
An e7cellent method of getting a .nown "uantity of EA in a 9A9 system is to install a constant !olume fan that #lows into the A4H @A plenum$ A =EA' will also o#!iate the pro#lem with pressure changes in a 9A9 system$ srid$ar131. (Mechanical)
2 =ec %? 6:2
mauricesto.er (Mechanical) @oom air changes will #e 13 to 1 for any normal air conditioned space$ his will increase as we go for Class 1%%%%- class 1%%% class 1%% etc$ 8resh air change shall #e #ased on A'4@A cfm per person and %$%6 cfm per s"uare feet of the area- if it is designed for green #uilding we do ta.e additional 3%O o#n the 8resh air with damper with actuator to wor. #ased o n CE2 sensor in the return air or room air accordingly fresh air is ta.en as per re"uirement$ As far as air "uantity for a 9A9 system it is #etter to cater to the pea. air "uantity and minimum air "uantity(min opening of damper in 9A9) shall #e set for minimum load which may occur$ In many +o#s we normally ta.e 1$ times the normal air distri#ution in that area$ 'till the @4 pro#lem may #e there depending on the !ariation of fresh air$ mauricestoker (Mechanical)
2 =ec %? ?:32
sridharI*!e ne!er designed an oLce to clean room standards$ Ross>:# (Mechanical)
2 =ec %? ?:
I thin. the term &room air changes& is #eing confused with recirculation rate$ &Changes& is used in cleanroom wor. to #e the recirculation rate- #ut in oLce 49AC it is often the !entilation (fresh air) rate$ mauricestoker (Mechanical)
2 =ec %? 13:32
I*m wor.ing on se!eral 49AC pro+ects for medical en!ironment now$ EA and AC4 are re"uired for oLces$ 8or clean rooms- I thin. it may depend on whether personnel protection is needed- or product- or #oth$ 4ospitals include clean rooms under H'F ?$ 8or to7ic compounding- AC4 and EA are the same$ 8or nonto7ic- recirc is allowed$ EA re"uirement and EA damperducting depend greatly on unit con,guration$ 8or 9A9 with air side economier- EA duct and damper would #e sied for total air ow- unless (my preference)a separate minimum EA and economier inta.es are included$ I thin. reference to A'4@A <uideline 16 would #e the point of the EF$
8or oLce 49AC- corrected EA calculations should #e made- unless it is a single one system$ If the air path is not considered- which is #oth EA and @A- then calculations per 62$12%% are not #eing done$ 'ome areas will always recei!e too much cooling or not enough- which is why ?%$12%% addresses reheat limitations on 9A9$ he Ad!anced 9A9 =esign <uide from FI@ is a real good source for understanding and designing 9A9 for energy eLceincy and IAV$ Rin. is #elow: $ttp%&&***energydesignresourcescom&Resources&Pu6lications&Design<uideline sasp!
2 Jan 13 16:26 Currently I am in the point of design where I must determine the outside air !entilation re"uirements for a #uilding #y using the 62$1 2%1% &!entilation rate procedure$& I am a #it confused a#out the two terms &!entilation& and &outside air&that are #eing thrown around and would appreciate any guidance$ 'tandard 62$1 lists a method called &!entilation rate procedure$& his method calculates the re"uired outside air needed #ased on a one*s occupancy and s"uare footage$ (I thought !entilation was +ust replacing air in a !olume regardless if it is outside air or return air) I thought there would #e another set of re"uirements aimed speci,cally towards !entilation- independent of outside air$ I would thin. !entilation would simply #e the amount of air changes per hour that your supply air (return air plus outside air) can achie!e on a space$ I was anticipating a ta#le that would pro!ide such !alues- #ut all I see is an outdoor air re"uirement method that I descri#ed a#o!e$ /ow to me- ,nding the re"uired outdoor air amount to #e used in a #uilding does not really tell me Im getting proper !entilation (air changes per hour) into my ones #ecause the supply air rate is what really does the air changing- and I can only #ase this supply air on my cooling load since I ha!e no other standard to loo. at here$ his is the only method I see- and I am s.eptical that there should #e more info stating how much supply air is re"uired to each one to reach an accepta#le air change per hour$ I am new at this so I may #e missing a .ey point$ 0our thoughts are appreciated$ han.s$ DRWeig (lectrical)
2 Jan 13 1:3
4i Mi.e5elcome to engtips$ In my e7perience- !entilation is always outside air- which is dictated #y occupancy and s"uare footage in each space$ 'upply air C8M is a function of the heating andor cooling load in the space$ o my .nowledge- there is no standard for supply air per s"uare foot (or per person) that is independent of outside air$ 9entilation outside air$ /ote: I*m a controls and energysimulation guy- my e7perience is in ma.ing the !entilation wor. right and analying what some#ody else designed to compute energy use$ I*m not a designer$ 4ang around- there are some !ery e7perienced Ms in this forum$
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oeag (Mechanical)
2 Jan 13 1?:%%
I*m with =@5eig$ I*m still pretty new to this 49AC stuB myself- #ut as far as I .now- there is no other standard that dictates supply air other than the outside air speci,ed in A'4@A$ I*!e #een wor.ing on a couple pro+ects- and "uic.ly loo.ing o!er our calculations and assumptions e!erything is wholesomely #ased on your re"uired cooling and heating loads$ urgross (Mechanical)
3 Jan 13 :D6
I thin. you would need to consider speci,c applications$ A wet la# may ta.e 1% air changes per hour- #ut the 1% AC4 doesn*t need to #e outside air$ 4ealth care facilities ha!e EA and total AC4 well spelled out$ Fharmacies and clean rooms will ha!e AC4 typically #ased on I'E le!el$ 8ederal agencies typically ha!e their own re"uirements for EA and total AC4$ 5hile I .now of no onesie ,ts all- air#orne odor control would #e a typical area where EA is not a re"uirementG pu#lic #athrooms would #e an e7ample$ Eutside air is not always re"uired- return air under the door can #e used$ cd!!13" (Mechanical)
3 Jan 13 ?:D
a.e another loo. at 622%1%$ he 9entilation @ate Frocedure uses a#le 61 gi!es Feople EH=EE@ Air @ate and Area EH=EE@ Air @ate$ If that amount of air doesnt meet your cooling or heating load (as stated #y drweig)- or AC4 rate re"uirements (as stated #y urgros)- then increase the supply cfm (usually with return air)- to get the supply air needed$ I suggest you reread 62*s ,ne print when you want to fall asleep at night$ .nowledge is power
Mike1833 (Mechanical) (OP)
3 Jan 13 12:%2
han.s e!eryone for your help$ Hgross- are these AC4 re"uirements in 62$1> hese are the .ind of re"uirements Im spea.ing of$ han.s$ 5hen ta.ing 49AC design classes (some time ago)- there were three possi#le constraints that determined your supply air$ he ,rst was to ,gure out your cooling load on the one$ his would #e the minnimum supply air rate ( ne!er should it go under the cooling load supply rate)$ he second constraint was occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement (for school- not in the standard) #ased on supply air- not outside air- and that*s why I was surprised to not see it in the standard 62$1)$ he third constraint was ma.eup air from e7haust$ he supply air would ha!e to increase if your #lowing out more than whats re"uired #y the cooling load or cfmperson (this constaint is a #it oB
topic since e7haust is independent of this discussion)$ 'o in summary- Im loo.ing for supply air constraints #ased on occupancy (li.e Hrgross pointed out)- #ut also a cfmpeople supply air constraint$ Consider this scenario$$$ I ha!e a speci,c room that re"uires 1%%%C8M of outside air (found #y following the &!entilation re"uirements&)$ If my air conditioning unit ser!ices 1% diBerent rooms- each room ha!ing a diBerent outside air re"uirement- how can this re"uirement #e met for e!ery room> he supply air rates to each room can #e controlled with actuated dampers- #ut the outside air is +ust going to #e a ,7ed percentage of the supply air regardless- right> 'o when a speci,c room re"uires !entilation- I would thin. to loo. for a supply air constraint$ 0our thoughts are greatly appreciatedK urgross (Mechanical)
3 Jan 13 13:21
/o- the AC4 re"uirements are not in 62$1$ I don*t thin. there is a onesie,ts all$ Criteria is usually #ased on a speci,c function or occupancy$ 4ospitals would #e a prime e7ample$ @efer to A'4@A 1% and you will get recommended AC4 for most areas of a hospital$ !en with that- additional criteria goes into speci,c areas- such as pharmacy$ @oom AC4 might go up to D% for to7ic compounding #ased on I'E le!el re"uirements$ 'ome areas the AC4 and EA are spelled out #ased upon the 49AC system #eing used$ As an e7amplenursing homes re"uire 6 AC4 per A'4@A and 2 EA AC4$ If using a Dpipe fan coil for en!elope load- the total AC4 can #e reduced to D$ he EA fraction calculationsalso change with system con,guration$ /o o!erall guidance is .nown- you ha!e to loo. at the occupancy and the proposed system$ DRWeig (lectrical)
3 Jan 13 2%:1
his portion of your "uestion confuses me: #uote (Mike1833)
he second constraint was occupancy (say 1 cfm of supply air per person)$ If this &supply air& re"uirement was greatest- than it was to #e used for the supply air rate instead of the cooling load supply air rate$(this is generally where Im trou#led #ecause this was a re"uirement (for school- not in the standard) #ased on supply air- not outside air - and that*s why I was surprised to not see it in the standard 62$1)
Are you saying that your space had a re"uirement of 1 C8M supply air per person- not 1 C8M of outside air per person> If so- what sort of space was it> I*m curious- #ecause 1 C8M per person was the standard outside air "uantity for a lot of ordinary occupancies #ac. when all we had were ta#les in the standards$ 5hat e!eryone is getting at is this: 8or special areas (see urgross*s replies)- there will often #e set air changes that must #e met$ 8or nonspecial areas- such as an oLce or classroom- there is no standard re"uirement$ here is only a standard for !entilation (outside air)$ As for apportioning outside air amongst your ones- you*ll ha!e to control the outside air fraction of the A4H to meet the worst case one*s needs$ a.e a loo. through this thread for some discussion of one way to !ary !entilation in a 9A9 system: $ttp%&&eng'tipscom&ie*t$readcfm+,id-3./03
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Mike1833 (Mechanical) (OP)
D Jan 13 11:1D
#uote (DRWeig)
Are you saying that your space had a re"uirement of 1 C8M supply air per person- not 1 C8M of outside air per person> If so- what sort of space was it> I*m curious- #ecause 1 C8M per person w as the standard outside air "uantity for a l ot of ordinary occupancies #ac. when all we had were ta#les in the standards$
@ight$ At least that is the way it was formatted in my class$ It was a standard oLce space$ !en when analying standard classrooms or oLces we used a certain C8M per person of supply air to ma.e sure it was not higher than the re"uired load$ I am going to contact my old professor to clarify this$ I may ha!e interpreted it wrong$ I .new it was gi!en as a supply air constraint #ut it really ne!er did go o!er the cooling load re"uirement anyways$ If it did- perhaps I would ha!e had to increase the supply air re"uirement for that onenot to 1 cfmperson- #ut to a higher supply air amount that had the correct percentage of outside air of 1cfmperson$ #uote (DRWeig)
As for apportioning outside air amongst your ones- you*ll ha!e to control the outside air fraction of the A4H to meet the worst case one*s needs$
<reat point$ In lieu of this topic- what if the cooling load supply re"uirement was lower than the amount of outside air needed (+ust out of curiosity since I!*e ne!er encountered this)> I would thin. I would ,rst ha!e to predetermine an outside air percentage- then raise the supply air re"uirement for that one to a C8M that contains that outside air needed$ ;ut how can I predetermine an outside air percentage without .nowledge of the new supply air re"uirement> It seems li.e this may #e an iterati!e process$ DRWeig (lectrical)
D Jan 13 12:D6
If it*s a constant!olume air handler- no pro#lem$ he minimum outside air for the A4H was set at commissioning time- and the supply air to the space remains constant$ husoutdoor air is ,ne at all times as long as the fan is running$ he cooling coil simply cycles (d7) or modulates (chw) to meet the load with the constant air ow- and if the supply air ow is greater than what is needed e!en with supply air temperature reset- the reheat system comes into play$ If it*s a 9A9 air handler- it can #e done in se!eral diBerent ways$ he one in the thread I lin.ed a#o!e is my fa!orite$ 5ithout demand control for !entilation- the controller needs to .now the air ow to the space and the percent of osa in the air from the air handler$ It will maintain air ow to meet the minimum !entilation rate- no matter the load$ Air ow monitoring at each 9A9 #o7 is not totally necessary to accomplish this$ 5ith a .nown duct pressure and 9A9 #o7 damper position- the percent of ma7imum supply air ow to the space can #e estimated$ In #oth cases- if the re"uired osa cfm e7ceeds the supply cfm for a space- the osa ow rate is maintained and the supply air is either reheated to maintain comfort or else the
supply air temperature is modulated (within limits)$ 0ou might #ene,t from loo.ing into se"uences of operation for A4H and 9A9 systems that ha!e already #een done$ 7amples are usually a!aila#le online from pu#lic uni!ersities the specs for +o#s to #e #id are pu#lic$ here might #e some #uilding automation tutorials a!aila#le that co!er the topic as well$ 5hat you*re as.ing is more of a controls issue than an e"uipment design issue$ Again- my hum#le opinion only$ I teach a couple of classes that co!er !entilation control with #uilding automation- so I*m used to co!ering it from that standpoint$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
Dra2en (Mechanical)
D Jan 13 1D:D%
mi.e- i #elie!e there is nothing confusing a#out that- #ut you need to study #asic .nowledge ,rstly- than you will not ha!e to waste your energy in rein!enting the wheel$ !entilation rate is rate of replacement of room air with outside air$ period$ supply air has nothing to do with that$ relation #etween supply air and outdoor air does aBect all your design concepts- decisions on system and e"uipment- #ut you calculate fresh air and supply air re"uirements independently- one per 62$1 or other applica#le standard- the other per thermal load calculations$ =rweig- i opened one post some time ago- a#out how to ensure minimum outdoor air in diBerent !a! setups- #ut did not reach &one #ullet .ills all& answer- which is not surprising as that is not fully co!ered anywhere$ if you sie your !a! system to ensure minimum outdoor air rate at minimum supply ow situation- you are still not sure that each and e!ery one will recei!e minimum- for simple reason that not all ones ha!e the same supply airoutdoor air ratios- and that is what system fan can deli!er$ if you sie your system #ased on one with lowest outdoorsupply air ratio- than your other ones will #e o!er!entilated- which poses energy eLciency "uestions$ i #elie!e !a! concept itself ne!er sol!ed that pro#lem fully- and it is only dc! concept that can ma.e more sense in such setups- in future (until something new would #e in!ented)$ Dra2en (Mechanical)
oops- i did not realied that you lin.ed to that !ery post urgross (Mechanical)
D Jan 13 1D:D2 $$$ D Jan 13 1:2D
=raen hat sounds li.a a real good argument for =EA' and delin.ing !entilation air from thermal loading$ DRWeig (lectrical)
D Jan 13 16:2%
0ou*re on the money as usual- =raen$ A minimum outside air in+ection fan helps- #ut it*s not perfect either$
I lo!e =EA'- urgrossK Apparently- though- only the military and the I@' can aBord it$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum
it$ayapun (Mechanical)
3% =ec %? 1D:1
I ha!e yet to read through e!eryone else*s reply so what I type might either agree or conict$ ;ut in 9A9 systems the #o7 can #e e"uipped with a hot water or electric heating coil to heat #ac. up the air that has essentially #een *o!ercooled* due to air changes$ As far as the outside air rate$$$,rst you will ha!e to ,nd out what the outside air percentage is that the unit is pro!iding$ 7$ D%% cfm return air mi7ed with 1%% cfm outside air$ so you ha!e 2%O outside air$ hen you need to determine if the room re"uires an outside air change rate (e7 patient rooms re"uire 2 outside air changes) 7ample: 7am room 9olume: 1%%% ft3 air change re"uired: 6 air changes per hour outside air change re"uired: 2 air changes per hour A4H outside air O 2%O total heat gain % #tuh A re"uired room temp so you will need AI@ C4A/< @A (1%%% ft3 ] 6 AC4)6% 1%% C8M EH'I= AI@ C4A/< @A (1%%% 83 ] 2) ( $2 ] 6%) 166 C8M in this case you would need to supply 166 cfm of air to achie!e the outside air re"uirements (which also satis,es the air change rate re"uirement)$ you would need to heat 166 cfm from your 8 to - which is roughly 362 #tuh$ ;ut since the room already gi!es oB % #tu- you need a coil that would #e a#le to do 2%2 #tu$ 26 May 13 3:32 4iI +ust want your thought a#out an issue we are facing now in our design drawing$ we are now in the e7ecution stage that*s why this issue is raised$ Issue is: 1$ we ha!e 9A9 #o7es without thermostat in the drawings$ I insisted to contractor that each 9A9 #o7 should ha!e its own thermostat to control it$am i right> 2$ we ha!e multiple 9A9 #o7es( 3 units) in 1 @oom- our design drawing states only 1 thermostat$ 4owe!er- I insisted to ha!e thermostat in each one of the 9A9 #o7es$is it right>
3$ we ha!e also CA9 #o7es in the return ducts which do not ha!e thermostat$ I assume that there should also #e thermostat e!en in return ducts$is it right> I would appreciate your replies$than.s$ *illard3 (Mechanical)
26 May 13 ?:1D
hermostats are not re"uired for e!ery 9A9 unit is they all ser!e the same thermal one$ 0ou should tal. to the original ngineer who designed this system rather than guessing$ DRWeig (lectrical)
26 May 13 11:3
=o what 5illard3 said$ hen- while you*re tal.ing to the original ngineer- as. him to e7plain the purpose of the CA9 #o7es in the return ducts$ ;est to you<oo#er =a!e 4a!en*t see the forum policies> =o so now: Forum Policies
:ronBr>ur (Mechanical)
1 Jul 13 1:%6
du7I am +ust now seeing your post$ =id you get it resol!ed> I agree with 5illard3 that you only need 1 thermostat per thermal one- especially if it*s an enclosed room$ If you had multiple thermostats- they would #e set at the same temperature anyway in an enclosed room$ 5hat happened with the CA9 #o7es on the return> I ha!e ne!er seen such a thing other than on a la#oratory or some other critical space where the supply and return must #e closely and constantly maintained$ It doesn*t ma.e sense in my mind to ha!e !aria#le supply and constant return$ please let us .now what happened$ tras$canman (Mechanical)
16 Jul 13 13:3
4ow do you ha!e constant return air !olume if the supply air !olume !aries>>> 21 May %D 22:33 As mentioned in another thread- I too need the &Idiot*s <uide to 49AC& as this is not my discipline$ I am an instrumentation and controls engineer trying to understand the impact of a client changee on wor. #y those in!o!ed 49AC$ I am at a fa#rication yard where nglish is not the ,rst language so "uestions here are poorly discussed$ I am #eginning with the changes that aBect controls$ 'ome re"uire more dampers to permit lea!ing the airhandler operating while isolating areas$ 'o- let me start with "uestions speci,c to dampers$ /on return dampers appear to wor. li.e a chec. !al!e$ 5ith the fan running- the !elocity lifts the lou!ers #ut they close #y gra!ity when the fan stops$ 5hat signi,cant details should I .now a#out other type dampers$ 5e ha!e the following types: 8ire damper and com#ination shutoB shutoB pressure control constant !olume #alancing
non return wathertight shutoB weather tight shutoB han.s in ad!ance$ John imok. (Mechanical)
22 May %D 2%:%%
4ere are some types of dampers =ampersAutomatic or Manual: Ad+usta#le metal plates installed inside of a duct to restrict- control !olume- #alance- or #y pass air- as re"uired in an air conditioning system$ 8ire =ampers A normally open damper installed in an air distri#ution system- designed to close automatically upon the detection of heat- to interrupt migratory air ow- and to restrict the passage of ame$ he de!ice has #een tested in accordance with a standard for safety #y a recognied testing la#oratory and is identi,ed #y a la#el- aLda!it or listing accepta#le to the authority ha!ing +urisdiction$ (Hnless the conditions of appro!al indicate so they are not rated for closing against mo!ing air streams or for withstanding pressure diBerentials$) A com#ination of ,re and smo.e damper must meet the re"uirements of #oth$ A smo.e damper is a de!ice to resist the passage of smo.e which: a$ Is arranged to operate automatically and #$ Is controlled #y a smo.e detector- and c$ May #e #ut is not necessarily re"uired to #e positioned manually from a remote command station$ A smo.e damper may #e a ,re damper or a damper ser!ing other functions- if its location lends itself to the multiple functions$ A com#ination ,re and smo.e damper shall meet the re"uirements of #oth$ Ceiling =ampers A specialied form of a heat stop installed in the air distri#ution portion of a ,rerated oor ceiling or roof ceiling assem#lyG the sole purpose of which is to help maintain the ,re endurance rating of the assem#ly$ =amper- lou!er A damper madeup of se!eral !anes operated #y gra!ity or motor control$ his type of damper is generally used to control !olume of outside air inta.e or e7haust to the atmosphere$ =amper- 'plitter A damper used to change air ow from one duct to another$ Mi7ing =ampers =ampers used to mi7 #oth heating and cooling supply air at point of dischargeG as in a room friartuck (Mechanical)
D Jun %D 1:33
8rom a control perspecti!e there are two type of damper- parallel #laded and Epposed #laded$
