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Air Flow Modeling Study: Central Gallery of the National Museum of the Marine Corps Analysis by: Galen Burrell Fred Porter Architectural Energy Corporation.

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Presentation on theme: "Air Flow Modeling Study: Central Gallery of the National Museum of the Marine Corps Analysis by: Galen Burrell Fred Porter Architectural Energy Corporation."— Presentation transcript:

1 Air Flow Modeling Study: Central Gallery of the National Museum of the Marine Corps Analysis by: Galen Burrell Fred Porter Architectural Energy Corporation

2 Background Standard HVAC sizing and modeling based on mixed air in space (uniform temperature) If space is stratified, these methods overpredict air flow needs CFD provides more accurate design information (350,000 nodes instead of one!)

3 Assumptions & Simplifications Steady-state analysis Solar gains calculated for floor, walls, and glass (accounts for shading by skylight structure) No wind effects on glazing heat transfer No internal flow resistance due to suspended planes and exhibit objects Thermal lag due to mass is assumed to be minimal Walls of adjacent exhibit spaces modeled as adiabatic No airflow assumed through wall openings between Central Gallery and adjacent exhibit spaces Airlock main entry assumed

4 Exterior Glass Properties Glass “Walls” –VE8-2M –Visible transmittance = 0.52 –Shading coefficient = 0.31 –Index of refraction = 1.5 –C.O.G. U-factor = 0.29 Glass “Roof” –VE8-40 –Visible transmittance = 0.27 –Shading coefficient = 0.22 –Index of refraction = 1.5 –C.O.G. U-factor = 0.29 Influence of skylight glazing framing system is accounted for in the total solar heat gain, which has been apportioned to the floor, walls and glazing.

5 Solar Load Calculation Radiance model of Central Gallery used to calculate incident solar radiation on interior surfaces, including all influences of skylight structure and framing system Incident solar radiation values translated into an effective shading coefficient Effective shading coefficient used in DOE-2 modeling of skylight glazing system to accurately calculate solar heat gain into the Central Gallery DOE-2 calculates net flux on building surfaces and glazing Net flux is incorporated into the Airpak model to account for solar heat gain, including the shading effects of the structure July 21, 2:00 PM Dec 21, 12:00 PM

6 Cooling Load Comparison LOADTRACE MODELAIRPAK MODEL Lighting Power Density3.3 W/ft21.5 W/ft2 Occupancy1,000 persons500 persons Solar Heat Gain1,500,000 Btu/hr1,600,000 Btu/hr Total Sensible Loads1,950,000 Btu/hr1,850,000 Btu/hr Total Internal Gains450,000 Btu/hr250,000 Btu/hr

7 Conservative Inputs No conduction of floor heat load into ground Floor absorbs 100% of transmitted solar (perfect absorber) No delay of heat load by thermal mass Suspended planes do not decrease solar load to occupied zone Lighting load modeled at floor level

8 Initial Airpak Model Geometry 10 Upper band supply diffusers (Titus DL) 27 Lower band supply diffusers (Seiho PK). Effective area is equivalent to proposed design of 80 diffusers Second Floor Walkway North Exhaust Fan Continuous floor-level return air grilles

9 Initial Design Scenarios Summer –90,000 CFM Supply, 30,000 CFM Exhaust (suggested by mixed zone analyses) –60,000 CFM Supply, 30,000 CFM Exhaust –40,000 CFM Supply, 15,000 CFM Exhaust All with 90 °F Outside Temperature Sun position: July 21, 2:00 PM Winter –60,000 CFM Supply, No exhaust from top Night time, 14 °F Outside Temperature Worst case condensation scenario –30,000 CFM Supply, No exhaust from top Cloudy Morning, 30 °F Outside Temperature –10,000 CFM Supply, No exhaust from top Cloudy Morning, 30 °F Outside Temperature

10 Predicted Mean Vote (PMV) Based on: –Clothing –Activity level –Air velocity –Temperature –Radiant Temperature –Humidity hot warm slightly neutral slightly cool cold warm cool User input Calculated by Airpak * Does not include radiation from direct sun

11 Summer: 90k CFM 55 °F 30k CFM Exhaust Conditions: 2:00 pm / July 21 / Outside Temp = 90 F Occupied zone average temperature: 67 °F Top zone average temperature: 80 °F Maximum zone temperature: 115 °F Excess cooling capacity exists because air is stratified Predicted Mean Vote Comfort Calculation Accounts for air temperature, humidity, velocity and radiation temperature. Scale ranges from - 3 (too cold) to 3 (too hot) Average PMV in occupied zone: -1.5 Assumes short sleeve shirt and light trousers

12 Summer: 60k CFM 55 °F 30k CFM Exhaust Conditions: 2:00 pm / July 21 / Outside Temp = 90 F Occupied zone average temperature: 71 °F Top zone average temperature: 92 °F Maximum zone temperature: 110 °F Modeled cooling capacity is adequate Predicted Mean Vote Comfort Calculation Average PMV in occupied zone: 0 (comfortable) Assumes short sleeve shirt and light trousers

13 Summer: 40k CFM 55 °F 15k CFM Exhaust Conditions: 2:00 pm / July 21 / Outside Temp = 90 F Does not meet the cooling load adequately Insufficient venting of top space causes extreme temperatures near the glazing Occupied zone average temperature: 80 °F Top zone average temperature: 100 °F Maximum zone temperature: 120 °F

14 Summer Summary 90k supply / 30k exhaust –Occupied space and above are overcooled –Average Predicted Mean Vote in occupied zone is -1.5 (cold) 60k supply / 30k exhaust –Maintains comfort in occupied zone –Average temperature: 71 °F –Air velocities are lower in occupied zones relative to 90k CFM scenario 40k supply / 15k exhaust –Does not supply adequate temperatures in occupied zone –120 °F air accumulates in top of skylight

15 Winter: 60k CFM 82 °F Conditions: Night time / Outside Temp = 14 F Outside air temperature: 14 °F Banquet conditions –500 People –500 Btu/hr per person –Humidity: 0.24 lb/hr per person No recirculation of air from top of skylight Represents worst case condensation scenario Temperature adjacent to glass averages in the high 60 °F range Relative humidity adjacent to glass averages in the mid 60% range No cold pockets exist that would lead to condensation on center of glass panels THERM required for detailed analysis of frame and edge effects Temperature Relative Humidity

16 Winter: 60k CFM 82 °F Conditions: Night time / Outside Temp = 14 F No recirculation of air from top of skylight Little stratification of air temperature Occupied zone average temperature: 72 °F Top zone average temperature : 72 °F Occupied zone average velocity: 100 fpm Temperature Relative Humidity Little stratification of humidity Average relative humidity: 60%

17 Winter: 60k CFM 82 F Airflow distribution from upper and lower diffusers

18 Winter: Partly Cloudy Morning 30k CFM 90 °F Conditions: Partly Cloudy / Outside Temp = 30 F Occupied zone average temperature: 75 °F Actual supply air volume could be reduced if supply temperature is increased Top zone average temperature: 76 °F Temperature is well-mixed throughout the space Predicted Mean Vote Comfort Calculation Average PMV in occupied zone: 0.4 (slightly warm) Assumes long sleeve shirt and trousers

19 Winter: Partly Cloudy Morning 10k CFM 110 °F Conditions: Partly Cloudy / Outside Temp = 30 F / All air discharged from lower diffusers Temperature is well-mixed throughout the space Occupied zone average temperature: 68 °F Top zone average temperature: 69 °F Lower airflow with higher temperature achieves comfort conditions and adequate mixing Predicted Mean Vote Comfort Calculation Average PMV in occupied zone: (slightly cool) Assumes long sleeve shirt and trousers

20 Winter Summary 60,000 CFM 82 °F –No cold pockets exist that would lead to condensation on center of glass panels –THERM analysis will determine edge and frame effects –Air temperature is well-mixed throughout the space 30,000 CFM 90 °F –Air temperature is well-mixed throughout the space –Average occupied zone temperature: 75 °F 10,000 CFM 110 °F –Comfort conditions are achieved –Average occupied zone temperature: 68 °F

21 Initial Conclusions Lower cooling supply air flow rate will satisfy the design cooling load Lower heating supply air flow rate will satisfy the design heating load Air exhaust from the top of the Central Gallery during the summer is required to control temperatures and radiant heat transfer In the summer, Central Gallery air temperatures will stratify between 20 and 45 degrees from the top of the “drum” to the top of the skylight, depending on exhaust flow rate Heating system can provide adequate heat along the skylight glazing to control surface temperatures and condensation potential Little stratification occurs in the winter heating modes studied in this analysis

22 Interim Design Direction Size cooling supply air flow rate at 60,000 CFM Size exhaust air flow rate at 15,000 CFM Heating supply air flow rate at 42,000 CFM Eliminate radiation/convection heating elements at base of skylight glazing Further analysis is required to determine if central mast is used to exhaust/recirculate air from the top of the skylight to the Central Gallery air-handling unit

23 Scenarios: Round 2 Summer, 60,000 CFM –55 °F supply, 15k CFM top exhaust –52 °F supply, 15k CFM top exhaust Winter, 42,000 CFM – Night time – 86 °F supply

24 Changes from Previous Model Eliminated upper band supply diffusers Changed diffuser height to 18’-0” Added balcony above main entrance to Central Gallery Eliminated diffusers below the balconies Added return air through lobby

25 New Airpak Model Geometry 38 supply diffusers (Seiho PK). Effective area and throw is equivalent to proposed design Second floor balcony Exhaust Fan Continuous floor-level return air grilles Second floor balcony Lobby return air (modeled as exhaust fans)

26 Summer Design Conditions Full cooling load conditions 92 °F outside Internal loads applied to floor as a constant heat flux 500 People Solar Lights 250 Btu/hr/person 1,600,000 Btu/hr 1.5 W/ft 2 DescriptionSensible Load Total 1,850,000 Btu/hr

27 Summer: 60k 55 °F Occupied zone average temperature: 76 ° F Top zone stratified temperature: 80 to 115 ° F Conservative estimate of internal heat gains at floor level Predicted Mean Vote Comfort Calculation Average PMV in occupied zone: 0.5 (slightly warm) Assumes short sleeve shirt and trousers (0.5 clo)

28 Summer: 60k 55 °F Temperature contour at 6’-0” AFF Temperature is uniform across the plane (76 °F average) Higher temperatures near back walls are due to solar flux

29 Summer: 60k 55 °F Air velocity contours at 6’-0” and 18’-0” AFF 6’-0” Plane 18’-0” Plane

30 Summer: 60k 55 °F Vertical velocity contour Air is relatively still under west balcony due to lack of diffusers Maximum speed of air in center of gallery approaches 125 fpm

31 Summer: 60k 55 °F Side velocity plane cut Induction effects are present near diffusers

32 Summer: 60k 52 °F Temperature contour at 6’-0” AFF Temperature is uniform across the plane (73 °F average) Temperatures are approximately 3 °F lower than 55 °F supply case throughout the space

33 Winter Design Conditions Night time, 14 F outside Banquet conditions 500 people 500 hot meals 30’ steam table 250 Btu/hr/person 38 Btu/hr/meal 36,000 Btu/hr 250 Btu/hr/person 12 Btu/hr/meal 18,000 Btu/hr LoadSensibleLatent Total 150,000 Btu/hr180,000 Btu/hr

34 Winter: 42k CFM 86 °F Occupied zone average temperature: 70 ° F Actual supply air volume or temperature could be reduced Top zone average temperature: 71 ° F Temperature is well-mixed throughout the space Predicted Mean Vote Comfort Calculation Average PMV in occupied zone: -0.5 (slightly cool) Assumes long sleeve shirt and trousers (0.68 clo)

35 Winter: 42k CFM 86 °F Conditions: Night time / Outside Temp = 14 °F Outside air temperature: 14 ° F Banquet conditions –500 people –500 hot meals –30’ steam table No recirculation of air from top of skylight Represents worst case condensation scenario Temperature adjacent to glass Average: 62 ° F Relative humidity adjacent to glass Average: 40% THERM required for detailed analysis of frame and edge effects Temperature Relative Humidity

36 Winter: 42k CFM 86 °F Velocity vector cut showing downward draft from skylight

37 Winter: 42k CFM 86 °F Velocity contour cut showing downward draft from skylight

38 Winter: 42k CFM 86 °F Temperature cut at 6’-0” AFF showing uniform temperature (70 °F average)

39 THERM Analysis Based on 14 °F outside temperature, 60 °F inside (adjacent to glass) Dew point temperature: 37 °F Worst case temperature: 42 °F Condensation will not occur under these conditions Inside (60 °F) Outside (14 °F)

40 Winter: 42k CFM 70 °F (Neutral air case) Occupied zone average temperature: 65 ° F Actual supply air volume or temperature could be reduced Top zone average temperature: 63 ° F Temperature is well-mixed throughout the space Predicted Mean Vote Comfort Calculation Average PMV in occupied zone: -2.5 (too cold) Assumes long sleeve shirt and trousers (0.68 clo)

41 Conclusions CFD analysis shows that the Central Gallery temperatures stratify during summer design conditions Proposed design (60,000 CFM) maintains comfort during peak summer design conditions in the occupied zone Mast return/exhaust air (15,000 CFM minimum) is needed to eliminate risk of overheating in the skylight Air velocities in the occupied zone are acceptable

42 Conclusions The proposed design maintains comfort during winter design conditions At 70% air flow (42,000 CFM) the Central Gallery is well-mixed Air flow can be modulated using the VSD to maintain comfort under less severe conditions Condensation will not occur under modeled conditions


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