“Atrium Design Strategies for Daylighting and Natural … Nov. 2003 USGBC : International Conference Atrium Cooling Strategies The following strategies were investigated Natural

Pittsburgh, Nov. 2003

USGBC : International Conference

GreenBuild: International Conference & Expo

S. Faruq Ahmed, PE [email protected]

P. Richard Rittelmann, [email protected]

Jayesh [email protected]

“Atrium Design Strategies for Daylighting and Natural Ventilation”

Pittsburgh, PennsylvaniaNovember 12 – 14, 2003

Burt Hill Kosar Rittelmann Associates101 East Diamond Street

Butler, PA 16001714-285-4761

www.burthill.com



Introduction§ The study examines the daylighting and thermal

performance of an atrium§ The atrium is a three-story space § The building is located in Troy, New York

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Introduction (Cont’d)§ Investigations were conducted to examine the natural

cooling/ventilation strategies for the atriumV

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Building Description§ The building is

a laboratory building, “Biotechnology and Interdisciplinary Building”, at Rensselaer Polytechnics Institute

§ Total area: 220,000 SF

§ Building functions are:§ Biotechnology and

Interdisciplinary Labs§ Offices§ Computational Labs

Add building plan



Building Description (Cont’d)§ Building massing study (animation)



Glass Properties

100.280.240.291638Lower

300.240.210.31330Middle

500.20.180.31023Top

Frit.%

Shading Coeff.

Solar Heat Gain Coeff.SHGC

Summer “U”Btu/(sq.ft-hr.F)

SolarTrans.%

Light Trans.%

Glass Location

§Double Glass assemblyOuter Glass ¼”Air gap ½”Inner glass, safety glass ¼ + ¼”



Glass Properties§ Glass fritting patterns



Daylighting§ Efficient daylighting with little heat gain

East Atrium South Atrium



Daylighting§ Daylighting animation, August 1, 7:30 am to 7:30 pm

East Atrium South Atrium



Atrium Thermal Performance Study§ Investigate the use of natural cooling

§ Quantify the expected temperature regime in the atrium during the year

§ CFD analysis and TRNSYS were used as complementary methodologies§ CFD analysis was used for studying temperature

profiles and surface temperatures

§ TRNSYS was used to quantify average space temperature throughout the year (hourly simulation)



Software Used§ CFD Analysis§ Flovent by Flomerics

§ TRNSYS – Transient Simulation System from University of Wisconsin§ Development started in 1975

§ Modular software

§ No fixed component configuration

§ Flexible modeling approach

§ Single node lumped capacitance model was used



Atrium Cooling Strategies§ The following strategies were investigated§ Natural ventilation, using CFD analysis

§ Forced ventilation using CFD analysis

§ Hourly simulation on non-vented atrium using TRNSYS

§ Hourly simulation of forced ventilation using TRNSYS

§ Hourly simulation of forced ventilation of atrium, air leakage from conditioned space and night pre-cooling of atrium



CFD Analysis - Assumptions§ In the south atrium, 20% of the air from offices is relieved into

the atrium

§ Relief air temperature is 73F

§ Outside heat transfer coefficient, 1.76 Btu/(hr-sq. ft.-F)

§ Solar angles at 2pm solar time were used

§ Number of louvers for air inlet§ 24 in south atrium§ 12 in east atrium



CFD Analysis – Assumptions (Cont’d)§ Five smoke exhaust fans, total 150,000 CFM Max, used

at 50% capacity

§ Outlet louvers§ 27 in South Atrium§ 18 in East atrium

§ Solar radiation, 900, 600, and 400 Watts/meter sq.

§ CFD analysis done for following times:§ Natural ventilation: Spring and Fall§ Forced Ventilation: Summer



Results of CFD Analysis

§ CFD-1: Natural ventilation, March, 2 pm§ Maximum 33,000 CFM flow was observed

South Atrium East Atrium



Results of CFD Analysis (Cont’d)

§ CFD-2: Fall/Spring Forced Ventilation, 2 pm, solar radiation 900 W/m-sq




Results of CFD Analysis (Cont’d)§ CFD-2 (Cont’d): Summer Forced Ventilation, 2 pm, solar

radiation 900 W/m-sq




Results of CFD Analysis (Cont’d)§ CFD-3: Summer Forced Ventilation, 2 pm, solar radiation

600 W/m-sq




Results of CFD Analysis (Cont’d)§ CFD-3 (Cont’d): Temperature profile though stairs,

summer Forced Ventilation, 2 pm, solar radiation 600 W/m-sq

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Results of CFD Analysis (Cont’d)

§ CFD-3 (cont’d): Summer Forced Ventilation, 2 pm, solar radiation 400 W/m-sq




Results of CFD Analysis (Cont’d)§ Temperature profile though stairs, summer Forced

Ventilation, 2 pm, solar radiation 400 W/m-sq

Sou

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CFD Analysis - Observations

§ The software assumed no internal reflections from white atrium walls

§ The slopped glazing was modeled as stepped glass

§ Double glass was not modeled, instead single glass was used with “corrections” to simulate the temperature of glass surfaces

§ Solar modeling capabilities of the software seemed limited, the air flow was accurately modeled



Results of TRNSYS Analysis

§ TMY2 weather data for Albany, NY was used.

§ Analysis was performed to quantify the behavior of atrium temperature during the year.

§ Frequency of occurrence of the atrium temperature in various ranges is used to examine various cases (alternatives).



Results of TRNSYS Analysis - Cases Studied

§ Case CT-1: Base case, no atrium ventilation

§ Case CT-2: Forced ventilation with smoke exhaust fans.

§ Case CT-3: Forced ventilation (Case CT-2) and lab support relief air.

§ Case CT-4: Same as Case CT-3 and night cooling of the space.

§ Case CT-5: Same as Case CT-4 with uninsulatedatrium interior walls and air leakage from door opening



Results of TRNSYS Analysis – Yearly Performance, SOUTH ATRIUM



Results of TRNSYS Analysis – Yearly Performance, EAST ATRIUM



Result for Selected Strategy – Case CT-5Detailed Performance



Observations – TRNSYS Analysis

§ The analysis was useful in quantifying the behavior of the space throughout the year

§ The high quality glass allows adequate amount of light transmission but reduces the heat gain to the space

§ Increasing the quantity of forced ventilation does not necessarily help – limitation of resource (ambient air temperature)



Recommendations

§ Natural ventilation alone is not a very effective strategy

§ Limited amount of of available opening for ventilation

§ Large temperature gradient along the height of the atrium

§ Forced ventilation with smoke control fans using variable frequency drives, provides acceptable comfort conditions



Recommendations (Cont’d)

§ The air leakage from the computer labs support and the heat conduction through uninsulated interior walls helps

§ The strategy in Case CT-5 allows the elimination of 250 tons of cooling which would have been used for very few hours during the years




§ During the study a parametric analysis was performed using various quantities of forced ventilation air quantity. The result shows:

§ Increasing the ventilation beyond 50,000 CFM does not help much

§ At certain times, depending on the outdoor conditions, only 10% of the air flow may be enough




§ The building is using the strategies listed in Case CT-5 with fans controlled by an algorithm so that the fan capacity as a function of outdoor air temperature and atrium temperature:

§ Building control system will control the fans and VFD

§ The Building is under construction



Overall Observations

§ CFD analysis is an excellent tool for such studies

§ Modeling of solar radiation through the glazing must be evaluated carefully

§ Scattering of solar radiation from inside surfaces must be carefully considered

§ The analyst must have good appreciation of solar systems



Overall Observations (Cont’d)

§ TRNSYS is an excellent tool which is:

§ Very flexible (configuration is not fixed)

§ Well documented

§ However it is not easy to use

§ Ideally CFD analysis should be used for all hours of the year, however this activity is resource intensive and almost impractical at this time



Thank youS. Faruq Ahmed, [email protected]

P. Richard Rittelmann, [email protected]

Jayesh [email protected]

Documents

“Atrium Design Strategies for Daylighting and Natural … Nov. 2003 USGBC : International Conference Atrium Cooling Strategies The following strategies were investigated Natural