The Residential HVAC Design Process

The Residential HVAC
Design Process Design Process
To comply with the IRC
[email protected]
J ac k Bar t el l
Director, Service & Training Director, Service & Training
VIRGINIA AIR DISTRIBUTORS
I nt r oduc t i on
• Purpose: • Purpose:
– Provides the
reasons behind reasons behind
the reality
• Reference:
B b’ H – Bob’s House
– ACCA
Handouts Handouts
I nt r oduc t i on
Pl an Ex ami ner s For m
• Developed by ACCA
C d C itt Codes Committee
• Permit application process
C C • Completed by the HVAC
contractor
S ft i d d t • Software independent
• Simple over-arching view
of the design process of the design process
I nt r oduc t i on
• Required • Required
(M1401.3 and M1601.1)
• Applicable
• Fast
• Expandable
I nt r oduc t i on
• Keep It SIMPLE
• Skimming
• Digging gg g
Manual J : Load
Cal c ul at i ons Cal c ul at i ons
Manual J8
Manual J8AE
For additional information
on ACCA, click on the logo
Over si zi ng Equi pment Over si zi ng Equi pment
R d ffi i • Reduces efficiency
• Increases operating costs
• Reduces control over the space
– Rises likelihood of mold and mildew
• Optimum efficiency occurs when the
equipment operates under full load equipment operates under full load.
– This only happens for several hours per
year. year.
Under si zi ng Equi pment
• Slightly undersizing equipment will
provide comfort and efficiency most of provide comfort and efficiency most of
the time
S diti ill d ift h t i – Space conditions will drift when extremes in
weather occur.
P f bl t i i th i t • Preferable to oversizing the equipment.
The result is increased energy efficiency
ith i l f f t with a minor loss of comfort.
• This must be explained to the owner.
What ar e t he benef i t s of a det ai l ed
and ac c ur at e l oad c al c ul at i on?
May Not
or or
Will Not
What ar e t he pi t f al l s and c onsequenc es p q
of an i nac c ur at e l oad c al c ul at i on?
Si x I ngr edi ent s of For c ed Ai r
Comf or t Comf or t
1. Even temperature
2. Filtration
3. Noise
4. Outdoor air
5 Humidity control 5. Humidity control
6. Air circulation
A Properly Designed Comfort System “ Simultaneously controls
the temperature, humidity, air quality and air movement in a
manner that is not noticeable to the occupants”
Manual J 8
t h
Edi t i on
– Infiltration Load
• Accounts for wind velocity • Accounts for wind velocity
• Accounts for air in-take needed for people and
equipment
– Solar Gains
• Variation of solar gain through the day
• The impact of reflection on solar gains
• The loads for skylight including the curbs
– Adds Loads for the affect of equipment,
piping, and humidification
Choosing Procedures
One procedure – Average Load for Winter Conditions
Average or Peak Procedure for Summer Conditions
• Average Load Procedure
– When t here is a const ant
• Peak Load Procedure
– When t here is a spik e in
t h li l d
load t hrough t he day
– Or ef f ect of solar gain s isn’t
signif icant ly dif f erent f rom
t he cooling load
– When t he ef f ect of t he
solar gain causes
signif icant ly dif f erent f rom
hour t o hour wit hin a room
or space
solar gain causes
dif f erences f rom hour t o
hour
Di er si t
Lack of
AED
Adequate
E
Di ver si t y
E
Exposure
Diversity
N S
E
W
N S
Condo A Condo B Condo C
W
Peak Load
Conditions
An excursion adjustment is added
to the average fenestration gain to the average fenestration gain
when the application does not
have AED.
Adequat e Ex posur e Di ver si t y
Ex c ur si on Adj ust ment Requi r ed
Need to use manual
MJ8 & software MJ8 & software
Adequat e Ex posur e Di ver si t y
• For MJ8ae a dwelling is assumed to
q p y
Appendi x 3
For MJ8ae a dwelling is assumed to
have AED if:
– The total area of the windows glass doors and The total area of the windows, glass doors and
skylight assemblies does not exceed 15 percent of
the associated floor area.
– The dwelling has four exposures.
– Each exposure is equipped with a representative
amount of glass area amount of glass area.
How do I decide which road to take: How do I decide which road to take:
Limitations and Guidelines
Fi g. 3-5 Heat Loss & Gai n Tabl es
Cont ent Compar i son p
Component Heat Loss
Cal c ul at i ons Cal c ul at i ons
Component Heat Loss p
Cal c ul at i ons
• Heat loss calculations.
Fenestration heat loss • Fenestration heat loss.
• Opaque panel heat loss.
f • Radiant floor.
• Block infiltration load for heating.
• Room infiltration load for heating.
Component Heat Loss
• Duct load for heating
p
Cal c ul at i ons
Duct load for heating.
• Engineered ventilation load for heating.
Wi t h idifi ti l d • Winter humidification load.
• Hydronic piping loss.
• Equipment sizing.
Component Heat Gai n
Cal c ul at i ons Cal c ul at i ons
Component Heat Gai n Cal c ul at i ons Component Heat Gai n Cal c ul at i ons
• Heat gain calculations
Fenestration heat gain • Fenestration heat gain
• Opaque panel heat gain
• Block infiltration load for cooling
• Room infiltration load for cooling Room infiltration load for cooling
• Internal gain
Component Heat Gai n
D t l d f li
Cal c ul at i ons
• Duct load for cooling
• Engineered ventilation load for cooling
• Blower heat
• Moisture migration Moisture migration
• Total cooling load
E i t i i • Equipment sizing
Physi c al Pr i nc i pl es & Mat hemat i c s
Units of meas rement and Units of measurement and
measurements protocols.
Measured dimensions – Measured dimensions.
– Areas of building
components components.
– Perimeters and
volumes volumes.
Pr epar at i on of For ms and Wor k sheet s
• Order of procession for block load estimate • Order of procession for block load estimate
– Worksheet A: design conditions
– Worksheet B – C: window, glass doors & sky light loads , g y g
– Worksheet D: opaque surface loads
– Worksheet E: infiltration loads
W k h t F i t l l d – Worksheet F: internal loads
– Worksheet G: duct loads
– Worksheet H: ventilation loads Worksheet H: ventilation loads
– Form J1ae: room load estimates
Manual J do’s
(mandat or y r equi r ement s)
Use outdoor design conditions recommended g
by table 1 manual J.
Use the default indoor design conditions
recommended by manual J.
Consider orientation of the structure on the site.
Verify all construction details prior to calculating
loads.
Take full credit for all internal shading devices
and external overhangs.
Manual J do’s
(mandat or y r equi r ement s)
Use internal shading devices that are compatible Use internal shading devices that are compatible
with the type of room.
Take credit for insect screens when installed or Take credit for insect screens when installed or
specified.
Take full credit for rated performance of
construction materials, insulation and construction
features.
Take full credit for tightness of of the envelope Take full credit for tightness of of the envelope
construction.
Follow the manual J procedures for infiltration and Follow the manual J procedures for infiltration and
ventilation.
Manual J do’s
( d t i t ) (mandat or y r equi r ement s)
Take full credit for duct system sealing and Take full credit for duct system sealing and
insulation.
Match location as close as possible when p
selecting a duct load table.
Match duct supply and return system geometry.
Use the correct R-values for duct wall
insulation.
Add blower heat to the sensible gain if Add blower heat to the sensible gain if
equipment performance data is not adjusted for
blower heat.
What i s t he def i ni t i on of a BTU? What i s t he def i ni t i on of a BTU?
Br i t i sh Ther mal Uni t Br i t i sh Ther mal Uni t
The amount of heat needed
to raise the temperature of to raise the temperature of
1 pound of water 1º F p
Whi c h has mor e heat ,
a pound of w at er at 212ºF or
a pound of st eam at 212ºF? p
Sensible heat
• Heat which when added to a material raises its • Heat, which when added to a material, raises its
temperature. Expressed as dry bulb temperature.
Latent heat Latent heat
• Heat, which when added to a material, changes its
state but not its temperature Expressed in Btu per state but not its temperature. Expressed in Btu per
pound of material.
I
144
32°
WATER
Ice
32°
BTU/LB
Latent heat
WATER
180
32°
212°
180
BTH/LB
SENSIBLE HEAT
WATER
WATER
970
BTU/LB
Latent heat
212°
STEAM
212°
WATER
Latent heat
Heat moves i n t hr ee w ays:
c onvec t i on c onvec t i on
c onduc t i on
r adi at i on r adi at i on
The Sensi bl e Heat Equat i on
• Q = 1.08 x CFM x TD
– Q = Sensible heat in Btuh
– 1.08 = is a constant (Properties of air at sea level)
– CFM = Cubic Feet per minute of Air
– TD = is the change (temperature difference) in air
temperature in ºF. Referred to as the Delta T.
– .076 (pounds of air in a cubic foot) X
– .24 (specific heat of standard air at sea level) X
– 60 (number of minutes in an hour)
The Sensi bl e Heat Equat i on The Sensi bl e Heat Equat i on
By knowing any two variables we can find By knowing any two variables we can find
the remaining by algebraic re-arrangement
of the equation. q
• BTUH = CFM x TD x 1.1 BTUH CFM x TD x 1.1
• CFM = BTUH/(1.1 x TD)
• TD = BTUH/(1 1 x CFM)
CFM =
Load
1.08 X TD
• TD = BTUH/(1.1 x CFM)
Manual J : Load Cal c ul at i ons
Resul t s of Over -Si zi ng
• Results of Oversizing
– More consumer expense
• Equipment
• Materials
• Labor Labor
– More starts and stops
• Wear and tear on
equipment
Hi h
$
• Higher energy usage
– Poor comfort
• Less humidity control
• Stagnant air pockets
$
g p
• Stratified air
temperatures
– Marginalized part-load
capacity capacity
What f ac t or s det er mi ne
t he heat i ng and c ool i ng
r equi r ement s of a r equi r ement s of a
home?
Manual J : Load Cal c ul at i ons
Desi gn Condi t i ons Desi gn Condi t i ons
Heat Gain
Heat Loss
Heat Gain
Manual J : Load Cal c ul at i ons Manual J : Load Cal c ul at i ons
• What factors determine a
house’s heating and cooling
requirements:
Location – Location
• Orientation
• Latitude
• Ventilation
Heat Loss
Ventilation
– Building components
• Windows
• Insulation
Heat Gain
Heat Loss
– Occupants and Plants
– Appliances
– Infiltration Infiltration
– Etc…
Manual J : Load Cal c ul at i ons
• Factors that determine a house’s
Loc at i on Fac t or s
• Factors that determine a house s
heating and cooling load calculation:
Design Conditions – Design Conditions
• Indoor Conditions
• Winter Design Temp.
• Summer Design Temp.
• Moisture Difference
– Latitude Latitude
– Altitude
– Orientation
Heat Gain
Heat Loss
Manual J : Load Cal c ul at i ons
Loc at i on Fac t or s
• Factors that determine a house’s
Loc at i on Fac t or s
heating and cooling load calculation:
– Design Conditions g
• Indoor Conditions
Manual J8 Section A5-3 Manual J8, Section A5 3,
“Use of this set of conditions
is mandatory, unless
Heat Loss
75°F
y
superceded by a code,
regulation, or documented
h lth i t ”
Heat Gain 70°F
75 F
health requirement.”
Manual J : Load Cal c ul at i ons
Desi gn Condi t i ons
Design Conditions
• Winter: Winter:
– Indoor: 70°F
• Summer:
70
Summer:
– Indoor: 75°F 75
Manual J : Load Cal c ul at i ons
• Factors that determine a house’s
Loc at i on Fac t or s
• Factors that determine a house s
heating and cooling load calculation:
Design Conditions – Design Conditions
• Indoor Conditions
• Winter Design Temp.
• Summer Design Temp.
• Moisture Difference
– Latitude Latitude
– Altitude
– Orientation
Heat Gain
Heat Loss
Manual J : Load Cal c ul at i ons
Desi gn Condi t i ons
Manual J : Load Cal c ul at i ons
Desi gn Condi t i ons
• Design Conditions
– Winter Design Temp.
– Summer Design
Temp.
Moisture Difference – Moisture Difference
Manual J : Load Cal c ul at i ons
Desi gn Condi t i ons (Chi c ago) Desi gn Condi t i ons (Chi c ago)
Design Conditions
• Winter: Winter:
– Outdoor: 2°F
• Summer:
70
2
Summer:
– Outdoor: 91°F
– OD Grains: 37∆ Gr
75
91
37
75
50
Manual J : Load Cal c ul at i ons
Desi gn Condi t i ons (Mi nneapol i s) Desi gn Condi t i ons (Mi nneapol i s)
Design Conditions
• Winter: Winter:
– Outdoor: -11°F
• Summer:
70
-11
Summer:
– Outdoor: 88°F
– OD Grains: 24∆ Gr
75
88
24
75
50
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
Manual J : Load Cal c ul at i ons
Chicago
1,299 Btu/h
g
1,578 Btu/h
Manual J : Load Cal c ul at i ons
• Factors that determine a house’s
Loc at i on Fac t or s
• Factors that determine a house s
heating and cooling load calculation:
Design Conditions – Design Conditions
• Indoor Conditions
• Winter Design Temp.
• Summer Design Temp.
• Moisture Difference
– Orientation Orientation
– Latitude
– Altitude
Heat Gain
Heat Loss
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
Orientation
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
Orientation
Sout h
Fr ont Door
Manual J8 requires sketches based on a plan take-off or field Manual J8 requires sketches based on a plan take-off or field
observation with an arrow or directional rosette that points
north.
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
Bedrooms
South
1
3
2
3
2
3
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
O t
South
Occupants
Manual J8: Occupants
3
1800
a ua J8 Occupa s
produce sensible and
latent loads. The
number of occupants
shall equal the number q
of bedrooms plus one.
Manual J : Load Cal c ul at i ons
Oc c upant s
• Factors that determine a house’s Factors that determine a house s
heating and cooling
l d l l ti load calculation:
– Occupants
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
O t
South
Occupants
Manual J8: Occupants
3
1800
a ua J8 Occupa s
produce sensible and
latent loads. The
1
number of occupants
shall equal the number
3 +1 = 4
q
of bedrooms plus one.
2
3
2
3
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
Envelope Tightness Envelope Tightness
South
Manual J8: §3.10 (Page 14)
3
1800
4
§
Infiltration load estimates
shall be based on one of
the tightness categories
(tight, semi-tight, average,
semi loose and loose) semi-loose, and loose)
provided by Table 5A and
5 B (well defined on page 174) 5 B. (well defined on page 174)
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
Envelope Tightness
South
•Ceilings
3
1800
4
Ceilings
•Walls
•Windows and Doors Windows and Doors
•Engineered Openings
•Exhaust systems
Average
y
•Duct systems
•Overall
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
Design Design
Ventilation
South South
Manual J8: §3.13 (Page 19)
• Ventilation Requirement
N t kit h / b th h t
3
1800
4
3
1800
4
• Not kitchen / bath exhaust
• ERV and HRV
• Special Kitchen exhaust
Average
0
Special Kitchen exhaust
• Fireplace/stove operation
Manual J : Load Cal c ul at i ons
Fenest r at i on Fenest r at i on
(Wi ndow s, Sk yl i ght s, Fr enc h door s, et c )
• Factors that determine a house’s
heating and cooling
load calculation: load calculation:
– Building components
• Windows
– Rough opening
– Orientation
– Overhang
S th?
North?
Overhang
– Internal shading
– Bug screen (or not)
– Skylights (or not)
Southwest?
South?
Skylights (or not)
Manual J : Load Cal c ul at i ons
Fenest r at i on Fenest r at i on
(Wi ndow s, Sk yl i ght s, Fr enc h door s, et c )
• Factors that determine a house’s Factors that determine a house s
heating and cooling
load calc lation load calculation:
– Windows
L tit d
Boston
Phoenix
• Latitude
Miami Miami
Manual J : Load Cal c ul at i ons
Fenest r at i on Fenest r at i on
(Wi ndow s, Sk yl i ght s, Fr enc h door s, et c )
• Factors that determine a house’s
heating and cooling
load calculation: load calculation:
– Building components
• Windows
– Rough opening
– Orientation
– Overhang
S th?
North?
Overhang
– Internal shading
– Bug screen (or not)
– Skylights (or not)
Southwest?
South?
Skylights (or not)
Manual J : Load Cal c ul at i ons
Bui l di ng Component s
Windows
No overhang
Windows
South South
No overhang
Manual J8: §3.13 (Page 19)
• Eave overhang
I t l h d
3
1800
4
3
1800
4
• Internal shade
• Skylights
• Optional: Latitude
Avg
0
N
(26°) Optional: Latitude
None
Drapes, Light ½ Closed
None
(26 )
None
Manual J : Load Cal c ul at i ons
Ot her f ac t or s
• What other factors determine a What other factors determine a
houses heating and cooling
i t requirements:
– Appliances
– Duct Loads
– AED - Zoning
House A
House B
Manual J : Load Cal c ul at i ons
2
70
South
3
1,800
91
4
Average
0
75
37 None
D Li ht ½ Cl d Drapes, Light, ½ Closed
None
Manual J : Load Cal c ul at i ons
Manual J : Load Cal c ul at i ons
2
70
South
3
1,800
91
4
Average
0
51,838
75
37 None
D Li ht ½ Cl d 21 23 Drapes, Light, ½ Closed
None
21,423
4,684
26,107 26,107
Manual J : Load Cal c ul at i ons
Questions Questions
Br eak Br eak
15:00 14:00 13:00 12:00 11:00 10:00 9:00 7:00 8:00 5:00 4:00 3:00 6:00 2:00 1:00 0:30 0:15 0:00
Manual S: Equi pment Sel ec t i on Manual S: Equi pment Sel ec t i on
Manual S: Equi pment Sel ec t i on Manual S: Equi pment Sel ec t i on
• Heatingg
– Load
– Output Capacity
– Target Airflow
– Design airflow
– Altitude adjustments Altitude adjustments
• Cooling
– Load
– Sensible / Latent Capacity
– Target airflow
D i i fl – Design airflow
– Altitude adjustments
Manual S: Equi pment Sel ec t i on
• Heating
– Load
56,000 Btu/h
= 51 838 Btu/h
103°F - 133°F
– Load
– Output Capacity
– Target Airflow = 51,838 Btu/h
= 51,838 Btu/h
Output capacity
∆T°=
56,000
∆T°=
56,000
52°=
g
– Design airflow
– Altitude adjustments
,
68°F
p p y
CFM × 1.08 × ACF
∆T =
,
1,000 × 1.08 × ACF
∆T =
1000 × 1.08 × ACF
52 =
ABC CompanyFU60-036
60,000 Btu/h
ABC Company FU60-036
Air Delivery – CFM (With Filter)
Unit Size Speed
External Static Pressure (inches water column)
0.1 0.2 0.3 0.4 0.5 0.6 0.7
High 1075 1040 995 945 895 840 760
Med– Hi 950 925 895 845 795 740 660
FU60 - 024
Med Hi 950 925 895 845 795 740 660
Med – Lo 850 825 780 740 685 635 560
Low 740 700 650 620 565 515 455
FU60 - 036
High 1470 1415 1400 1285 1215 1120 995
Med – Hi 1315 1280 1235 1298 1115 1035 930
Med – Lo 1125 1110 1085 1045 1000 915 830
Low 930 9256 910 850 830 770 705
FU60 - 048
High 1700 1685 1640 1580 1545 1450 1380
Med – Hi 1500 1465 1435 1385 1255 1300 1250
Med – Lo 1325 1295 1265 1230 1190 1150 1105
Low 1205 1170 1145 1110 1080 1035 990
Manual S: Equi pment Sel ec t i on
• Cooling
– Load
= 26,107 Btu/h
Manual S: Equi pment Sel ec t i on
• Cooling
– Sensible / Latent Capacity
= 26,107 Btu/h
Total Heat = Sensible + Latent
26, 107 Btu/h = Sensible + Latent 26,107 Btu/h = 21,423 Btu/h + 4,686 Btu/h
Total Heat Sensible Latent
26, 107 Btu/h Sensible Latent 26,107 Btu/h 21,423 Btu/h 4,686 Btu/h
Manual S: Equi pment Sel ec t i on
• Cooling
Total Load – Total Load
– Sensible Load
– Latent Load
= 26,107 Btu/h (Total)
+ 4,684 Btu/h (Latent)
21,423 Btu/h (Sensible)
– Target airflow
– Design airflow
26,107 Btu/h (Total)
21,423 Btu/h (Sensible)
Sensible Heat Ratio = 0 82 =
21,423 Btu/h (Sensible) Sensible Btu/h
Sensible Heat Ratio
V ∆T
26,107 Btu/h (Total)
Sensible Heat Ratio = 0.82 =
Airflow (CFM) = 1,044 CFM =
1.08 x (∆T from SHR Table) x ACF
21,423 Btu/h (Sensible)
1.08 x ∆T x ACF
Sensible Btu/h
Versus ∆T
Manual S page 3-4
SHR ∆T
Belo 0 80 21
1.08 x 19°F x ACF
Below 0.80 21
0.80 – 0.85 19
Above 0.85 17
Manual S: Equi pment Sel ec t i on
• Cooling
Total Load
26,107 Btu/h
21, 423 Btu/h
= 26 107 Btu/h (Total)
21,423 Btu/h (Sensible)
+ 4,684 Btu/h (Latent)
– Total Load
– Sensible Load
– Latent Load
4,684 Btu/h
21, 423 Btu/h
21,423 Btu/h (Sensible)
0 82 =
= 26,107 Btu/h (Total)
– Target airflow
– Design airflow
Sensible Heat Ratio
V ∆T
26,107 Btu/h (Total)
0.82 =
21 423 Btu/h
Versus ∆T
Manual S page 3-4
SHR ∆T
Belo 0 80 21
21,423 Btu/h
1.08 x 19°F x ACF
1,044 CFM
Below 0.80 21
0.80 – 0.85 19
Above 0.85 17
Manual S: Equi pment Sel ec t i on
AHRI data AHRI data
vs.
Regional Design data Regional Design data
Manual S: Equi pment Sel ec t i on
C li • Cooling
– Total Load 26,107 Btu/h
– Sensible Load 21,423 Btu/h
– Latent Load 4,684 Btu/h
– Target airflow 1,044 CFM
Manual S: Equi pment Sel ec t i on
Summer OD
91°F 91 F
Target
airflow
1,044 CFM ,
EWB
63°F
Total Load
26,107 Btu/h
Sensible Load
21,423 Btu/h
Latent Load
4,684 Btu/h
Manual S: Equi pment Sel ec t i on
Summer OD
91°F
T t l L d
EWB
63°F
Total Load
26,107 Btu/h
Sensible Load
21 423 Btu/h 21,423 Btu/h
Latent Load
4,684 Btu/h
Target airflow
1,044 CFM
Manual S: Equi pment Sel ec t i on Manual S: Equi pment Sel ec t i on
+ 3 073
+ 3 425
+ 3,073
- 63
3 136
+ 3,425
+ 5,401
2 976
+ 3,136
- 2,976
Manual S: Equi pment Sel ec t i on Manual S: Equi pment Sel ec t i on
ABCCompanyFU60 036 ABC Company FU60-036
Air Delivery – CFM (With Filter)
Unit Size Speed
External Static Pressure (inches water column)
0.1 0.2 0.3 0.4 0.5 0.6 0.7
Target
airflow
FU60 - 024
High 1075 1040 995 945 895 840 760
Med – Hi 950 925 895 845 795 740 660
Med – Lo 850 825 780 740 685 635 560
L 740 700 650 620 565 515 455
1,044
CFM
Low 740 700 650 620 565 515 455
FU60 - 036
High 1470 1415 1400 1285 1215 1120 995
Med – Hi 1315 1280 1235 1298 1115 1035 930
Med – Lo 1125 1110 1085 1045 1000 915 830
Low 930 9256 910 850 830 770 705
FU60 - 048
High 1700 1685 1640 1580 1545 1450 1380
Med – Hi 1500 1465 1435 1385 1255 1300 1250
Med – Lo 1325 1295 1265 1230 1190 1150 1105
Low 1205 1170 1145 1110 1080 1035 990
Manual S: Equi pment Sel ec t i on Manual S: Equi pment Sel ec t i on
ABC System Capacity
995 CFM, 91°F ODT, 63°F EWB and 75°F EDB
ABC
Manual J
Load
Heating Cooling
Heating Btu/h 51,838 56,000 g , ,
Cooling Btu/h 26,107 29,180
Sensible Btu/h
21,423 21,360
Latent Btu/h
4,684 7,820
Manual D: Duc t Di st r i but i on Syst em Manual D: Duc t Di st r i but i on Syst em
Basi c Resi dent i al Duc t Syst ems Basi c Resi dent i al Duc t Syst ems
• The following slides will describe some of The following slides will describe some of
the various styles of residential duct
systems systems.
• Following each slide will be listed some of
the Pros and Cons of each type of system the Pros and Cons of each type of system.
Ex t ended Pl enum Syst em Desi gn Ex t ended Pl enum Syst em Desi gn
Ex t ended Pl enum Syst em
Desi gn
Pros
• The most common residential duct system
• Easy to fabricate and install.
Pros
y
F b l bl b ll
Cons
For best results blower must be centrally
located.
Long duct runs make it difficult to turn air
into branch runs near the fan.
Reduc i ng Pl enum Syst em
Desi gn
Reduc i ng Pl enum Syst em
Desi gn
f
Pros
• Improves performance over end mounted
blower, extended plenum systems.
• Usually less expensive for small systems
Pros
• Usually less expensive for small systems.
Con
Historically, duct design manuals arbitrarily
assignedthereductionpoint at 24’ fromthe
Con
s
assigned the reduction point at 24 from the
blower, resulting in less that maximum
performance performance.
Reduc i ng Tr unk Syst em Desi gn Reduc i ng Tr unk Syst em Desi gn
Reduc i ng Tr unk Syst em Desi gn Reduc i ng Tr unk Syst em Desi gn
Pros
• Less material used to fabricate duct
system.
Pros
• Good air distribution if designed properly.
R i k f b i di ll
Cons
Requires more work to fabricate and install
because each takeoff requires its own
i section.
Each section is a different size and requires
a transition to reach the next size.
Radi al or Oc t opus Syst em
Desi gn
Radi al or Oc t opus Syst em
Desi gn Desi gn
• One of the most cost effective systems
t i t ll
Pros
to install.
• Easy to fabricate and install.
Pros
F b l bl b ll
Cons
For best results blower must be centrally
located.
Installers tend to use long flex duct runs
resulting poor performance due to high
resistance.
Per i met er Loop Syst em Desi gn Per i met er Loop Syst em Desi gn
Per i met er Loop Syst em Desi gn Per i met er Loop Syst em Desi gn
Pros
• Effective in cold climates with slab floor
construction.
Pros
• Maintains comfort at the floor level in heating
season.
Diffi lt t d i
Cons
Difficult to design.
Expensive to install.
What c an be c onsi der ed t he best
use of Duc t Tape?
Manual D: Duc t Di st r i but i on Syst em y
Equi pment & Ai r Si de Devi c es Equi pment & Ai r -Si de Devi c es
• The design of the house the selection of The design of the house, the selection of
the HVAC equipment and peripheral
devices determines the duct system devices determines the duct system
requirements.
• Fan performance governs the static • Fan performance governs the static
pressure limitations of the duct system.
Equi pment & Ai r Si de Devi c es Equi pment & Ai r -Si de Devi c es
Air-sidedevicesareusedtocontrol airflow
• Supply outlets introduce supply air into the
Air side devices are used to control airflow.
• Supply outlets introduce supply air into the
room.
R t i l t t th t i • Return inlets capture the return air.
• Dampers and junction boxes control air
volume in the duct system.
Equi pment & Ai r Si de Devi c es Equi pment & Ai r -Si de Devi c es
Air-sidedevicesareusedtocontrol airflow
• Diffusers typically introduce supply air
into the room from the ceiling
Air side devices are used to control airflow.
into the room from the ceiling.
• Supply Registers and Grilles typically
introduce supply air into the room from introduce supply air into the room from
the wall. Registers are grilles that have
dampers dampers.
• Return Registers and grilles are the
same as above but used on the return same as above but used on the return
side.
OCCUPIED ZONE
The occupied zone consists of the space between the
fl d 6 f t b th fl i th ti l di ti d floor and 6 feet above the floor in the vertical direction and
the space that is more than 2 feet from the wall in the
horizontal direction.
It is within the occupied zone that comfort
conditions must be maintained.
Therefore, do not distribute conditioned
air into the occupied zone
Ter mi nal vel oc i t y (f pm) Ter mi nal vel oc i t y (f pm)
• When the velocity of total air drops to 50 When the velocity of total air drops to 50
or 75 fpm, depending on the particular
application, it reaches terminal velocity. pp y
• Terminal velocity can be said to be the Terminal velocity can be said to be the
velocity of the air stream at the end of the
throw.
Thr ow (f t ) Thr ow (f t .)
Throw
(20’)
Terminal velocity
(50 fpm) (50 fpm)
The horizontal distance that an air stream travels after leaving a
horizontal sidewall outlet before maximum velocity is reduced to
terminal velocity.
Dr op (f t ) Dr op (f t .)
• The distance that the bottom edge of a horizontally projected air • The distance that the bottom edge of a horizontally projected air
stream falls by the time the air reaches the end of its throw.
Spr ead (f t ) Spr ead (f t .)
The maximumwidth of the total air streamat The maximum width of the total air stream at
the point of terminal velocity.
Induction (Aspiration) The process of drawing room air into the
projected air stream due to the velocity of the projected air stream.
Secondary air
Primary air Primary air The supply air The supply air
Primary air
Primary air Primary air The supply air The supply air
from the outlet. from the outlet.
Secondary air Secondary air The induced The induced
Secondary air
Secondary air Secondary air The induced The induced
room air (can be 10 to 20 times room air (can be 10 to 20 times
greater than the primary air greater than the primary air
quantity). quantity). q y) q y)
Ceiling or Wall Effect The tendency of an air stream moving along a
ceiling or wall to remain in contact with that surface ceiling or wall to remain in contact with that surface.
Ter ms used i n Duc t
Desi gn Desi gn
• IWC - Inches of Water Column - A unit used to
measure pressure p
• CFM - Cubic Feet per Minute - A unit used to
measure air flow
• ESP - External Static Pressure - A unit used to
measure resistance outside of the fan
• ASP – Available Static Pressure of a blower
after deducting all component loses g p
• Pressure Drop - is equal to the pressure loss
that occurs between any two points in a duct y p
system
Ter ms used i n Duc t
Desi gn Desi gn
• Friction Rate - is equal to the pressure loss
that occurs between any two points in a duct that occurs between any two points in a duct
system that are separated by a specific
distance (usually 100 feet) distance. (usually 100 feet)
• Equivalent Length - A term used to describe
l th h fitti pressure loss through a fitting.
• TEL - Total Effective Length - A term used to
describe the friction losses through a duct and
all of its fittings and air-side devices.
VELOCITY is measured in feet per minute (fpm)
V = CFM CFM = A x V
A
The area of the duct (A) must always be stated in
square feet Therefore divide the duct square feet. Therefore, divide the duct
dimensions (w x h) by 144.
1200 CFM in a 24” x 8” duct has a velocity of: 1200 CFM in a 24 x 8 duct has a velocity of:
V = CFM 1200 1200 = 900 fpm
A 24x8/144 1.33
Pr essur e
Measured in inches of water column (“ w.c.)
1 psig = 27.72” w.c.
Velocity pressure is movement, dynamic pressure.
Static pressure is a bursting pressure. It lacks
movement.
Total pressure is static pressure plus velocity
pressure pressure.
Ex t er nal St at i c Pr essur e Ex t er nal St at i c Pr essur e
Item Static pressure
drop in “ w.c.
Supply duct 10 Supply duct
system
.10
Return duct
system
.10
Evaporator .20
Furnace
Evaporator
(Coil)
.20
Air cleaner .20
Supply registers .03
R ill 03 Return grilles .03
Volume
dampers
.03
Total external
static pressure
.69
Furnace blower must be able to deliver the required volume of air
(CFM) against an external static pressure of .69” water column.
static pressure
Tot al St at i c Pr essur e
Whi c h t w o poi nt s w i l l measur e Whi c h t w o poi nt s w i l l measur e
Tot al St at i c pr essur e on t he f ur nac e?
D
Furnace
B
C
A
Manual D: Duc t Di st r i but i on Syst em
• Duct system design and overview
–Calc each rooms CFM
–Sketch on the blue print
• Notes with approx lengths
• Show CFM for each supply and return
Sho CFM for each tr nk • Show CFM for each trunk
• ID fittings
Gather OEM performance data –Gather OEM performance data
–Use EL calc sheet
Manual D: Duc t Di st r i but i on Syst em
• Calculate
each
room’s
airflow airflow
Manual D: Duc t Di st r i but i on Syst em
Sketch duct geometry
Manual D: Duc t Di st r i but i on Syst em
Assign CFM
Manual D: Duc t Di st r i but i on Syst em y
Determine the duct run with the
longest Total Effective Length
Manual D: Duc t Di st r i but i on Syst em y
Assign CFM
4I=10EL
4I=10EL
4I=10EL
9’
4I 10EL
= 35 EL
9
15’
5J=15EL 6L=20 EL
8’
15
15’
1P=20EL
2Q=10 EL 15’
Manual D: Duc t Di st r i but i on Syst em y
Determine the duct run with the
longest Total Effective Length
10 5 10 15 5
35
20
20
10
20
10
20
10
5
20
50
60 40 40 40 40
125 90 80 100 120
Manual D: Duc t Di st r i but i on Syst em y
0 50
1,000
Determine the
0.50
1,000
0.16
Friction Rate
0.10
-0.05
0.03
0.30
0.03
0.03
0.50 0.30 0.20
Manual D: Duc t Di st r i but i on Syst em y
Determine the
0 50 0 30
0 20
Friction Rate
0.50 0.30
0.20
120
125 225
FR = (ASP × 100 ) ÷ TEL
FR = (0.20 × 100 ) ÷ 225
FR = 20 ÷ 225 = .0888 ≈ 0.09
Manual D: Duc t Di st r i but i on Syst em y
0.50
0.30
0.20
Determine the
120
125 225
0.09
Friction Rate
0.5 1000
0.16
-0.05
0.10
0.03
0.03
0.03
0.20
0.3 0.2
120 125 225
0.5
0.9
120 125 225
Manual D : Duc t Di st r i but i on Syst em
0.5 1000
0.16
1,000 0.50 0.50 1,000
0.16
0 05
0.50
0.30
0.20
-0.05
0.10
0.03
0.03
0.03
0 30
120 125
225
0 09
0 30
0.10
-0.05
0.03
0.03
0.03
120 125
225
0 09
0.20
0.3 0.2
120 125 225
0.5
0.30
0.20
0.09
0.50 0.30
0.30
0.20
0.09
0.9
120 125 225
Manual D : Duc t Di st r i but i on Syst em
1,000
0.50
120
0.30
0.20
125
225
0.09
Sheetmetal, Flex
Manual J : Load Cal c ul at i ons
2
South
3
70
91
1,800
4
Average
0
51,838
75
37
None
Drapes, Light, ½ Closed 21,423
50
None
4,684
26,107
1 000 1,000
0.50
0.30
0 20
120
125
225
0.20
225
0.09
Sheetmetal, Flex
Resi dent i al HVAC Syst em Desi gn y g
Resi dent i al HVAC Syst em Desi gn y g
• Conclusion • Conclusion
• Questions???