IN+ Center for Innovation, Technology and Policy Research,
Instituto Superior Técnico, Universidade Técnica de Lisboa
October 2005
1. Introduction.
The goal of this work was to practice the COSMOS FloWorks (SolidWorks add-in). It’s a
promising tool to support the design process. It’s simple and intuitive, but offers some problems
on the object preparation for the simulation. It was time consuming because it was the first time
that I used this application. To deliver this report on time I needed to simplify the model to
overcome the difficulties I found without compromising the goals.
This experiment was pleasant. In the future it will be useful for my projects and career – I work
on the thermo fluids scholarship.
2. Work Description
The ACADS solar concept is explained to contextualize the model simulations. Next the solar
collector was removed from the auditory room model and simplified. This action was essential
to reduce complexity and to increase the computing capacity during the simulations.
Two models designed on SolidWorks software are presented: Real Model; Simplified Model.
This indicates that later simplifications were made, because software errors were not solved.
But the goals for this work were guaranteed.
The FloWorks is an application that simulates flows inside or outside de solids. Also it can
simulate the turbulent or laminar flows, on a time-dependent form of the Navier - Stokes
equations. It can also be applied for steady or unsteady problems. On this particular case a
steady flow problem was considered. COSMOSFloworks starts the calculation from initial
conditions defined by the user. The solver iterates on the variables until there is no appreciable
change, i.e. the solution converges. The input-data was then introduced with the help of
tutorials. This software has advanced features, to be explored by the student on other
opportunities.
The most important results were the temperature distributions along the air flow movement
through out the chambers. After data analysis some conclusions were made, resulting in a
redesign of the concept.
3. ACADS Solar Concept
The ACADS system can be used on the classic spaces or in a new kind of spaces as purposed
here. Some of the classic rooms can also be modified to retrieve more of the new features. The
full concept is presented on append A. The air conditioning system is a hybrid between the
mechanical system and a solar energy battery.
This space normally functions better with 100 % fresh air supply, to match the 8 L/s/person
requirement (see append B). The disadvantage is the increased energy consumption to head
the winter cold air. The solution is the air heat permutation between exhaust and inlet air. The
efficiency permutation is about 50 %. The exhaust air carries heat from the people metabolism
and solar energy retrieved by a solar collector placed behind the film projection screen. Also
the collector is placed on the plenum that carries the air from the room to the building exterior.
The hybrid solution is also an organic one, because the two acclimatization systems work and
complement themselves. Two extreme cases are:
- Solar energy not disposable: In this case, in a cloudy day it’s impossible to retrieve solar
energy to heat the room. The mechanical heating system functions at full;
- Low room occupancy: The solar energy contribution to heat the air increases. The
utilization of heat from the mechanical system decreases.
The space is well insulated to match the noise level requirement and the heat transmission
thought the space is minimal – adiabatic - (see append B). Also the energy gains trough the
electric equipment is low. Basically, the whole heat gained by the space, is supplied from the
spectators. This is an opportunity to use an air localized distribution system, based on the
occupation distribution information, gathered from the ticket management system.
The advantage of this solution is to carry the air only to the zones that need acclimatization,
reducing the energy waste during the transportation and delivery operations, mainly for the
solar case.
Other important observation is the good matching between the Auditory and Solar Heat Gain
schedules (see Append D). When the solar energy is stronger, the auditory occupation is low,
given an optimal match between zone heat requirement and solar energy, complemented by
an air localized distributed system.
This concept needs more refinement. One of the tools to see more constraints that will improve
de product by the redesign process is the flow simulation. The geometric model of the building
was initially proposed to the simulation, but was complex and consumed resources and time. A
new approach consisted on the model simplification and the establishment of new
assumptions. The model was restricted to the solar collector, and the rest of the building
considered adiabatic. Some limitations were also due to the lack of the student knowledge.
The software used to model the solar collector was the SolidWorks and the flow simulations
were made with the FloWorks.
4. SolidWorks Model
4.1. Real Model
The concept model is presented on the append E. The spaces between the structural
pillars are used to heat the air. Each space has nervures that increase the exposed
collector area, hence increasing the efficiency of the heat transmission mechanisms –
radiation, conduction, convection. The room exhaust air enters at the top of the wall, and in
contact with the spaces is reheated (first was heated on the room). After this process the
air exits from the wall and enters on the return chamber. Two air handling units that
operate on this chamber, have a device that exchanges the heat from the rejected air to
the fresh air. The overall dimensions are not far away from the real. Only the nervure,
inlet/outlet openings and glass windows parameters have to be refined.
4.2. Simplified Model
Problems occurred during FloWorks configuration and preparation for the simulation,
manly on the nervures case. The model has to be simplified. The assumption was that the
entire solar energy incident on the windows was effectively transmitted to the air flow. This
is an ideal goal, but serves as a driver for subsequent design process. Remember that
increasing efforts were made to obtain more results on the last few years leading, on the
material research and products referred here.
5. FloWorks Input Data
5.1. Computational domain
The computational domain is a rectangular prism that encloses the model (see append F),
for the 3D analysis. The computational domain’s boundary planes envelop the entire
model, because the options Internal Flows and Heat Transfer in Solids were selected.
5.2. Boundary Conditions
Two kinds of boundary conditions were selected (see append G):
o Inlet volume flow boundary condition, applied on the Inlet Lids. In this case the
volume flow was calculated for a room with low occupancy (20 persons) each with a
requirement of 8 L/s/person. The temperature selected was 293.K (20 ºC) and the
volume air flow for each inlet lid is about 0,0533 m
3
/s.
o Pressure boundary condition, applied on the outlet lids: the pressure value
selected is the same as the pressure at the chamber entrance, because pressure
losses were discarded.
5.3. Heat Sources
The volume source boundary condition type was considered to simulate the solar energy
that enters the chambers (see append H). The heat generation rates were retrieved from
the design day maximum solar heat gains (see append D), for a window orientation to
South and on a typical day on January. The value selected was 375 W/m
2
. But due a
multiplier factor (cloud clearance) of 0.47, the final result was 176 W/m
2
(without the
compensation due to the direct radiation incident angle). The total heat power delivered to
the air is:
Total Heat Power [W] = 10384 = 3520 + 3344 + 3520
If the heat permutation has an efficiency of 50 % then the heat power transferred to the
fresh air is 10384 * 0,5 = 5,2 kW. This is a good result since the heat power required at 12
PM is 5.3 KW and decreases to 16 PM. Then a match between the solar source power
and the room power requirements exists:
o 12:00 PM (5.3 kW);
o 13:00 PM (4.2 kW);
o 14:00 PM (3.4 kW);
o 15:00 PM (3.0 kW);
o 16:00 PM (3.2 kW).
See append D for a better understanding of the hourly air system results for a typical
Saturday, January 1.
5.4. Material Conditions
The material selected for the walls and windows were: insulation and glass.
5.5. Goals
The software initially considers any steady flow problem as a time-dependent problem.
The solver module iterates on an internally determined time step to seek a steady state
flow field, so it is necessary to have a criterion of determining that a steady state flow field
is obtained, in order to stop the calculations. The criteria to stop the calculation are named
Goals. These goals are the physical parameters of interest in the project. Then the Goals
convergence is one of the conditions for finishing the calculation. The Goals used on this
project are:
o GG Average Pressure: Static Pressure goal type; Average value calculation;
o GG Av Fluid Temperature: Temperature of fluid; Average value calculation;
o AVInletPressure: Static Pressure goal type; Average value calculation;
o OutletMassflowRate: Mass Flow Rate goal type;
o TempMinimaColector: Temperature of solid; Maximum Value calculation.
6. Results
The results are presented on the append I. On figures nº 12 & 13, the air temperature varies
293 K (20º C) to 387 K (114º C). In some chamber places, the temperature rises to 450 K (177º
C). The exit temperature is high and can damage de air handling units and conduits that
operate on the under floor plenum. This happen for a low air volume flow (low room occupancy,
see the schedules), because the air moves slowly and is exposed to the chamber heat more
time than for increased air flows (increased occupancy levels). This case can be considered
the worst for a variable air volume system with a solar energy collector.
The temperature distribution on the heat source can be seen on figure nº 14. This distribution
does not correspond to the real distribution of the window glass, because the radiation energy
that passes through the windows is the main energy that reaches the chamber. The rest of the
energy – real energy on the window - is absorbed, irradiated and conducted to the air. But the
goal was to see the air flow distribution. But in the figure the decrease of temperature on the
window as the air temperature increases can be seen. This is a numerical validation of the heat
transfer mechanism between the heat source and the air.
The flow trajectories are presented on figure nº 15 (Inlet Lid).
On figures nº 16 to 19, are presented the behavior of the calculation process – convergence of
goal parameters vs. iterations. On the table it can be seen the final results for the goal
parameters.
7. Conclusion
Some redesign has to be made. Two constrains are:
- The extreme air temperature generated by the collector, and delivered to the under floor
plenum, can damage the equipment and materials and induce hazards like fire;
- The collector is useful only for the winter. On the summer it’s usefulness. So heat gains due
the solar radiation on the summer need to be eliminated.
8. Redesign
To solve the constraints, the alterations made on the collector are:
- Registers installation at the bottom of the air chambers, to mix the exhaust air with fresh air
to reduce the air temperature, mainly, for the low occupancies. The register sizing will be
made to satisfy noise, pressure losses constrains. It will be motorized and controlled by the
DDC system. In case of failure the register opens automatically – spring return. Two or
more Safety Thermostats will also be installed;
- Installation of an overhang to externally shade the windows. Shade dimensions are used
together with the solar position data in HAP – Hourly Analysis Software – load calculations
to determine the fraction of the window surface shaded by the overhang. The intent of the
shading geometry is to eliminate the solar heat gain and solar load for the windows on the
summer (on the summer the solar direct radiation angle relatively to the windows is higher
than on the winter).
If this passive solution solves partially the problem, then a hybrid solution must be used. A
second exhaust air system must be installed to bypass the air flow to the collector
chambers. At the same time the bottom register is opened to supply fresh air to the under
floor plenum and to the collector chamber, to remove the heat.
- The material selection for the collector must correspond to the insulation and black body
constraints;
- The windows characteristics for the collector are the same used on the commercial solar
collectors (utilization of the best practices).
Appends
A ACADS Solar Concept
B Auditory Data
C Schedules
D Design Weather Parameters & Hourly Simulation Results
E SolidWorks Model
F Computational Domain
G Boundary Conditions
H Heat Sources
I Results
J Design Alterations
Append A – ACADS Solar Concept
Figure nº 1 – ACADS Solar Concept
Figure nº2 – Air Entrance of the Solar Collector
Figure nº 3 – Solar Collector
Append B – Auditory Data
Auditory
1. General Details:
Floor Area ................................................ 266.0 m²
Avg. Ceiling Height ....................................... 6.0 m
Building Weight ........................................ 634.7 kg/m²
1.1. OA Ventilation Requirements:
Space Usage ............. THEATERS: Auditorium
OA Requirement 1 ........................................ 8.0 L/s/person
OA Requirement 2 ...................................... 0.00 L/(s-m²)
2.4. People:
Occupancy .................................................. 308 People
Activity Level ............................. Seated at Rest
Sensible ..................................................... 67.4 W/person
Latent ......................................................... 35.2 W/person
Schedule .............................. People – Auditory
2.5. Miscellaneous Loads:
Sensible .......................................................... 0 W
Schedule ................................................... None
Latent .............................................................. 0 W
Schedule ................................................... None
3. Walls, Windows, Doors:
Exp. Wall Gross Area (m²) Window 1 Qty. Window 2 Qty. Door 1 Qty.
S 98.0 0 0 0
3.1. Construction Types for Exposure S
4. Roofs, Skylights:
(No Roof or Skylight data).
5. Infiltration:
Design Cooling ........................................... 0.00 L/s
Design Heating ........................................... 0.00 L/s
Energy Analysis ......................................... 0.00 L/s
Infiltration occurs only when the fan is off.
6. Floors:
Type ................................ Slab Floor On Grade
Floor Area ................................................ 266.0 m²
Total Floor U-Value .................................. 0.550 W/(m²-°K)
Exposed Perimeter ..................................... 66.0 m
Edge Insulation R-Value ............................. 1.82 (m²-°K)/W
Door Details:
Gross Area ................................................... 2.3 m²
Door U-Value ........................................... 2.300 W/(m²-°K)
Glass Details:
Glass Area ................................................... 0.0 m²
Glass U-Value .......................................... 3.293 W/(m²-°K)
Glass Shade Coefficient ........................... 0.880
Glass Shaded All Day? ................................. No
Append C - Schedules
Light - Auditory (Fractional)
Hourly Profiles:
1:Termostato
Hour 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Value O O O U U U U U U U U U U U O O O O O O O O O O
2:Profile Two
Hour 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Value O O O O O O O O O O O O O O O O O O O O O O O O
3:Profile Three
Hour 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Value O O O O O O O O O O O O O O O O O O O O O O O O
4:Profile Four
Hour 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Value O O O O O O O O O O O O O O O O O O O O O O O O
City Name ................................................................................. Lisbon
Location ................................................................................. Portugal
Latitude ......................................................................................... 38.4 Deg.
Longitude ........................................................................................ 9.1 Deg.
Elevation ....................................................................................... 10.0 m
Summer Design Dry-Bulb ............................................................. 32.0 °C
Summer Coincident Wet-Bulb ....................................................... 20.8 °C
Summer Daily Range .................................................................... 10.5 °K
Winter Design Dry-Bulb ................................................................... 3.5 °C
Winter Design Wet-Bulb .................................................................. 2.3 °C
Atmospheric Clearness Number ................................................... 1.00
Average Ground Reflectance ........................................................ 0.20
Soil Conductivity ......................................................................... 1.385 W/(m-°K)
Local Time Zone (GMT +/- N hours) ................................................ 0.0 hours
Consider Daylight Savings Time ..................................................... No
Simulation Weather Data ............................................... Lisbon (TRY)
Current Data is .............................................................. User Modified
Design Cooling Months .................................... January to December
Design Day Maximum Solar Heat Gains:
(The MSHG values are expressed in W/m² )
Month N NNE NE ENE E ESE SE SSE S
January 30.1 30.1 30.1 127.4 234.9 309.6 362.1 376.6 375.0
February 36.5 36.5 85.0 184.1 289.7 348.5 370.5 361.6 350.6
March 43.6 43.6 149.8 256.1 319.7 356.6 344.2 313.5 296.9
April 53.8 116.0 220.5 305.9 354.2 348.5 315.4 259.7 231.3
May 62.5 174.2 277.1 338.0 368.6 343.9 285.6 210.8 174.8
June 90.6 219.6 326.1 387.3 409.5 370.7 297.1 206.1 165.9
July 96.5 265.0 406.1 508.4 546.2 502.2 419.8 307.2 255.2
August 87.0 177.4 323.4 458.8 525.2 518.2 467.8 385.1 343.8
September 64.6 64.6 189.4 343.2 438.7 480.5 475.3 434.4 411.9
October 45.9 45.9 87.0 230.5 329.9 407.3 430.7 423.6 414.2
November 30.7 30.7 30.7 121.3 229.7 309.4 354.2 367.3 370.3
December 27.4 27.4 27.4 97.7 209.6 288.3 350.4 372.9 376.7
Month SSW SW WSW W WNW NW NNW HOR Mult
January 373.9 356.6 316.3 228.4 130.5 30.1 30.1 209.3 0.47
February 362.1 370.9 343.8 290.1 195.8 76.8 36.5 276.6 0.47
March 316.6 348.6 353.7 326.7 249.2 153.1 43.6 338.7 0.47
April 260.7 315.6 352.0 353.3 300.9 225.2 112.9 403.7 0.50
May 211.1 285.3 344.9 367.3 340.3 278.2 172.2 448.0 0.53
June 206.9 295.6 373.2 405.0 392.3 328.2 213.7 510.3 0.60
July 309.3 418.0 509.8 538.9 509.7 414.6 254.0 667.1 0.80
August 388.0 469.1 523.0 524.7 447.8 337.0 172.0 609.9 0.77
September 433.7 474.4 481.9 437.2 343.8 192.4 64.6 467.9 0.67
October 423.3 431.8 408.7 334.1 222.5 97.8 45.9 331.1 0.57
November 369.9 356.2 303.5 231.9 119.1 30.7 30.7 209.4 0.47
December 371.5 350.2 290.3 210.3 90.1 27.4 27.4 181.1 0.47
Figure nº 5 – Chambers of the Solar Collector – Exterior Wall
Figure nº 6 - Chambers of the Solar Collector – Interior Wall
Figure nº 7 – Collector Chamber
Append F – Computational Domain
Fig 8 - Computational Domain
Append G – Boundary Conditions
Fig 9 - Outlet Lids
Pressure boundary condition Settings
Static Pressure 101325 Pa
Temperature 291 K
Fig 10 - Inlet Lids
Inlet volume flow
boundary condition
Settings
Volume flow rate normal to face 0.0533 m
3
/s
Flow vectors direction Normal to Face
Inlet Profile Uniform
Approximate pressure 101325 Pa
Temperature 293.2 K
Append H – Heat Sources
Fig 11 - Heat Sources
Volume source
boundary condition
Settings
Heat Generation Rate 3520 W
Volume source
boundary condition
Settings
Heat Generation Rate 3344 W
Volume source
boundary condition
Settings
Heat Generation Rate 3520 W
Append I – Results
Fig 12 – Air Flow Temperature Distribution- Rear View
Fig 13 - Air Flow Temperature Distribution – Front View
Fig 14 – Window Temperature Distribution – Front View
Fig 15 – Air Flow Trajectories
Colector3.SLDASM [ColectorSolar]
-200
0
200
400
600
800
1000
0 50 100 150 200 250 300 350 400
Iterations
T
e
m
p
e
r
a
t
u
r
e
o
f
S
o
l
i
d
[
K
]
TempMinimaColector
Fig 16 – Collector Temperature Convergence
Colector3.SLDASM [ColectorSolar]
-0.25
-0.2
-0.15
-0.1
-0.05
0
0 50 100 150 200 250 300 350 400
Iterations
M
a
s
s
F
l
o
w
R
a
t
e
[
k
g
/
s
]
OutletMassflowRate
Fig 17 – Mass Flow Rate Convergence
Colector3.SLDASM [ColectorSolar]
-50
0
50
100
150
200
250
300
350
400
0 50 100 150 200 250 300 350 400
Iterations
T
e
m
p
e
r
a
t
u
r
e
o
f
F
l
u
i
d
[
K
]
GG Av Fluid Temperature
Fig 18 – Air Flow Temperature convergence
Colector3.SLDASM [ColectorSolar]
101324.95
101325
101325.05
101325.1
101325.15
101325.2
101325.25
0 50 100 150 200 250 300 350 400
Iterations
S
t
a
t
i
c
P
r
e
s
s
u
r
e
[
P
a
]
GG Average Pressure
AVInletPressure
Fig 19 – Static Pressure convergence
Colector3.SLDASM [ColectorSolar]
Goal Name Unit Value
Averaged
Value
Minimum
Value
Maximum
Value
Progress
[%] Use In Convergence Delta Criteria
GG Average Pressure [Pa] 101325.0033 101325 101325 101325 100 Yes 1.43E-06 0.00506625
AVInletPressure [Pa] 101325.0056 101325 101325 101325 100 Yes 1.49E-06 0.00506625
GG Av Fluid Temperature [K] 357.501783 357.497 357.458 357.542 100 Yes 1.09E-02 16.7925202
OutletMassflowRate