External Shading Devices in Commercial Buildings

Transcription

1 External Shading Devices in Commercial Buildings The Impact on Energy Use, Peak Demand and Glare Control John Carmody and Kerry Haglund Center for Sustainable Building Research University of Minnesota The Alcoa Building in Pittsburgh, PA uses exterior shading devices. Architect: The Design Alliance Architects; Photo: Courtesy of Viracon Sponsored by Air Movement and Control Association International 30 West University Drive Arlington Heights, IL

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3 External Shading Devices in Commercial Buildings The Impact on Energy Use, Peak Demand and Glare Control John Carmody and Kerry Haglund Center for Sustainable Building Reserach, University of Minnesota Contents Acknowledgements...2 Introduction...3 Minneapolis, Minnesota East Orientation Moderate Window Area...6 East Orientation Large Window Area...7 South Orientation Moderate Window Area...8 South Orientation Large Window Area...9 West Orientation Moderate Window Area...10 West Orientation Large Window Area...11 Houston, Texas East Orientation Moderate Window Area...24 East Orientation Large Window Area...25 South Orientation Moderate Window Area...26 South Orientation Large Window Area...27 West Orientation Moderate Window Area...28 West Orientation Large Window Area...29 Chicago, Illinois East Orientation Moderate Window Area...12 East Orientation Large Window Area...13 South Orientation Moderate Window Area...14 South Orientation Large Window Area...15 West Orientation Moderate Window Area...16 West Orientation Large Window Area...17 Phoenix, Arizona East Orientation Moderate Window Area...30 East Orientation Large Window Area...31 South Orientation Moderate Window Area...32 South Orientation Large Window Area...33 West Orientation Moderate Window Area...34 West Orientation Large Window Area...35 Washington, DC East Orientation Moderate Window Area...18 East Orientation Large Window Area...19 South Orientation Moderate Window Area...20 South Orientation Large Window Area...21 West Orientation Moderate Window Area...22 West Orientation Large Window Area...23 Los Angeles, California East Orientation Moderate Window Area...36 East Orientation Large Window Area...37 South Orientation Moderate Window Area...38 South Orientation Large Window Area...39 West Orientation Moderate Window Area...40 West Orientation Large Window Area...41 Appendix...42 Air Movement and Control Association International ( Page 1

4 Acknowledgments The material in this report was prepared by John Carmody and Kerry Haglund from the Center for Sustainable Building Research at the University of Minnesota. The information in this publication is based on computer simulations done at Lawrence Berkeley National Laboratory for the U.S Department of Energy Windows and Glazing Program. The source of some of the text and data in this publication is the book, Window Systems for High Performance Commercial Buildings by John Carmody, Steve Selkowitz, Eleanor S. Lee, Dariush Arasteh and Todd Willmert (Norton, 2004). More extensive results are available in the book, Window Systems for High Performance Buildings, and at the web site umn.edu. The roster of AMCA Committee members who guided the development include the Committee Chair Roger Lichtenwald, American Warming & Ventilating; Randall Geedey, The Airolite Company; Vince Kreglewicz, Arrow United Industries; Steve Lynch, Construction Specialties, Inc.; Mike Watz, Greenheck Fan Corp.; Jo Reinhardt, Industrial Louvers, Inc.; Michael McGill, M.W. McGill & Associates Ltd., Dane Carey, NCA Manufacturing; Mike Almaguer, Pottorff; James Livingston, Ruskin Company, and Timothy Orris, AMCA International, Inc. For further information, contact: Air Movement and Control Association International 30 West University Drive Arlington Heights, IL Copyright 2006 Regents of the University of Minnesota, Twin Cities Campus, College of Design. All rights reserved. Page 2 Air Movement and Control Association International (

5 Introduction Benefits of External Shading Devices Exterior shading devices such as overhangs and vertical have a number of advantages that contribute to a more sustainable building. First, exterior shading devices result in energy savings by reducing direct solar gain through windows. By using exterior shading devices with less expensive glazings, it is sometimes possible to obtain performance equivalent to unshaded higher performance glazings. A second benefit is that peak electricity demand is also reduced by exterior shading devices resulting in lower peak demand charges from utilities and reduced mechanical equipment costs. ally, exterior shading devices have the ability to reduce glare in an interior space without the need to lower shades or close blinds. This means that daylight and view are not diminished by dark tinted glazings or blocked by interior shades. With exterior shading devices, glare control does not depend on user operation. Using This Publication This publication shows the impact of external shading devices on the energy use, peak demand, and glare conditions in commercial office buildings. This publication is intended to help the designer quickly narrow the range of possibilities and understand the approximate impacts in commercial office buildings in order to provide general guidance during early stages of design. If there is more time and budget, this can be followed by a more detailed computer simulation of the specific building and the design conditions. In the following sections, results are presented for six cities with differing climates: Minneapolis, Chicago, Washington DC, Houston, Phoenix and Los Angeles. Within each climate, results are shown for east, south, and westfacing orientations. The north orientation is not shown since the impacts of external shading devices are small. Within each orientation, there are results for both moderate (WWR=0.30) and a large (WWR=0.60) window areas (WWR is the windowtowall ratio). For each set of conditions, there are six window types and five shading conditions. As shown in Figure 1, the five shading conditions include: (), vertical (), (), deep overhang (), and with (f). For each location, orientation and window area, there is a table summarizing the impacts of external shading devices. An example of one of these tables is shown in Table 1 for a perimeter office zone in Houston, Texas with a south facing orientation and large glazing area. For a given glass type, there are five lines of data one for each shading condition. The Energy column shows the actual energy use for each shading condition and the Energy % Save shows the percent savings compared to the unshaded case (). Similarly, the Peak column shows actual peak demand and the Peak % Save shows the percent savings compared to the unshaded case (). The Glare column shows the weighted glare index for each shading condition and the Glare % Red. shows the percent glare reduction compared to the unshaded case (). In comparing different sections of the publication, it is clear that the impacts of external shading devices are different depending on the building location, the window orientation, and window size. In addition, as shown in Table 1, the type of glazing and shading device used also impact the results. FIGURE 1 Air Movement and Control Association International ( Page 3

6 Energy Use Impacts and shading condition, Table 1 the percent savings compared to the Regarding energy use, the percent savings resulting from using a varies from 25.6% when applied to a clear double glazed window compared to 11.3% when applied to a triple glazed lowe window. The actual energy savings from the deep overhang in the two cases ranges from 52 kbtu per square foot when applied to a clear double glazed window to 15 kbtu per square foot when applied to a triple glazed lowe window. They key to this difference is that clear double glazing has a Solar Heat Gain Coefficient (SHGC) of 0.60 meaning that 60% of the solar heat gain is transmitted through the glass while 40% is blocked, while triple glazed lowe glazing has an SHGC of 0.22 meaning only 22% of the solar heat gain is transmitted and 78% is blocked by the glass. In effect, the higher performance glazing is already diminishing the solar gain quite a bit before the external shading device is applied. The overhang still makes a substantial difference in both cases but the value and payback varies depending on the conditions. Figure 2 illustrates this pattern for all the glazings and shading devices in Table 1. As the SHGC of the glazing improves, the absolute value of savings from the external shading device is smaller. This situation also presents an interesting design alternative it is possible to obtain equivalent performance to a low solar heat gain glazing with device by using external shading devices with glazings that have higher solar heat gain characteristics. Peak Demand Impacts The impact of external shading devices on peak demand follows a similar pattern to the impact on energy use. Table 1 shows that the percent savings resulting from using a varies from 44.1% when applied to a clear double glazed window compared to 18.8% when applied to a triple glazed lowe window. The actual peak demand reduction from the in the two cases ranges from 5.03 kw per square foot when applied to a clear double glazed window to 1.19 kw per square foot when applied to a triple glazed lowe window. As with energy use, the overhang still makes a substantial difference on peak demand in both cases but the value and payback varies depending on the conditions. Figure 3 illustrates this pattern for all the glazings and shading devices in Table 1. TABLE 1 IMPACT OF EXTERIOR SHADING HOUSTON, TX South Orientation Large Window Area (WWR=0.60) Note: All cases are southfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical 3.36 Page 4 Air Movement and Control Association International (

7 FIGURE 2 FIGURE 3 25 ANNUAL ENERGY USE HOUSTON, TX South Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND HOUSTON, TX South Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Glare Impacts The impact of exterior shading devices on glare in interior spaces is also illustrated by Table 1. The glare index is calculated at a point five feet from the window for a person facing the side wall. A lower index is better. A glare index of 10 is considered just perceptible, an index of 16 is just acceptable and an index of 22 is just uncomfortable. Unlike energy use and peak demand, glare reduction appears to be similar in percentage and amount for all glazing types. The greatest glare reduction occurs with a combination of a with vertical. The percent savings in glare index resulting from using a with is 35.1% when applied to a clear double glazed window compared to 40.8% when applied to a triple glazed lowe window. The glare index is reduced from 15 to 10 when the with are applied to a clear double glazed window. The glare index is reduced from 14 to 8 when applied to a triple glazed lowe window. A key advantage of external shading devices is that they can provide glare reduction without the need to lower shades or close blinds. This means that daylight and view are not diminished by dark tinted glazings or blocked by interior shades. With exterior shading devices, glare control does not depend on user operation. External shading devices can play an important role in creating more sustainable buildings with less energy use and peak demand as well as improved glare conditions for the building occupants. The AMCA publication and other resources are now available to assist designers in optimizing façade design. References Carmody, John, External Shading Devices in Commercial Buildings: The Impact on Energy Use, Peak Demand and Glare Control. Published by Air Movement and Control Association International (AMCA), 30 West University Drive, Arlington Heights, Illinois Phone: Web: Carmody, J., E. Lee, S. Selkowitz, D. Arasteh, and T. Willmert, Window Systems for High Performance Buildings, W.W. Norton & Company, Commercial Windows Web Site: Air Movement and Control Association International ( Page 5

8 Minneapolis, Minnesota East Orientation Moderate Window Area page show the impact of external shading devices on an eastfacing facade with moderate window area in a commercial office building in Minneapolis, Minnesota. device used. Six typical commercial heat gain coefficients are analyzed. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING MINNEAPOLIS, MN East Orientation Moderate Window Area (WWR=0.30) Note: All cases are eastfacing with a 0.30 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE MINNEAPOLIS, MN East Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND MINNEAPOLIS, MN East Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 6 Air Movement and Control Association International (

9 Minneapolis, Minnesota East Orientation Large Window Area shading devices on an eastfacing facade with a large window area Minneapolis, Minnesota. device used. Six typical commercial heat gain coefficients are analyzed. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING MINNEAPOLIS, MN East Orientation Large Window Area (WWR=0.60) Note: All cases are eastfacing with a 0.60 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE MINNEAPOLIS, MN East Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND MINNEAPOLIS, MN East Orientation Large Window Area (WWR=0.60) 20 1 kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 7

10 Minneapolis, Minnesota South Orientation Moderate Window Area shading devices on an southfacing facade with moderate window area Minneapolis, Minnesota. device used. Six typical commercial heat gain coefficients are analyzed. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING MINNEAPOLIS, MN South Orientation Moderate Window Area (WWR=0.30) Note: All cases are southfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE MINNEAPOLIS, MN South Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND MINNEAPOLIS, MN South Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 8 Air Movement and Control Association International (

11 Minneapolis, Minnesota South Orientation Large Window Area shading devices on an southfacing facade with a large window area Minneapolis, Minnesota. device used. Six typical commercial heat gain coefficients are analyzed. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING MINNEAPOLIS, MN South Orientation Large Window Area (WWR=0.60) Note: All cases are southfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE MINNEAPOLIS, MN South Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND MINNEAPOLIS, MN South Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 9

12 Minneapolis, Minnesota West Orientation Moderate Window Area shading devices on an westfacing facade with moderate window area Minneapolis, Minnesota. device used. Six typical commercial heat gain coefficients are analyzed. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING MINNEAPOLIS, MN West Orientation Moderate Window Area (WWR=0.30) Note: All cases are westfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE MINNEAPOLIS, MN West Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND MINNEAPOLIS, MN West Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 10 Air Movement and Control Association International (

13 Minneapolis, Minnesota West Orientation Large Window Area shading devices on an westfacing facade with a large window area Minneapolis, Minnesota. device used. Six typical commercial heat gain coefficients are analyzed. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING MINNEAPOLIS, MN West Orientation Large Window Area (WWR=0.60) Note: All cases are westfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE MINNEAPOLIS, MN West Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND MINNEAPOLIS, MN West Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 11

14 Chicago, Illinois East Orientation Moderate Window Area shading devices on an eastfacing facade with moderate window area Chicago, Illinois. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING CHICAGO, IL East Orientation Moderate Window Area (WWR=0.30) Note: All cases are eastfacing with a 0.30 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE CHICAGO, IL East Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND CHICAGO, IL East Orientation Moderate Window Area (WWR=0.30) kbtu/sfyear B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 12 Air Movement and Control Association International (

15 Chicago, Illinois East Orientation Large Window Area page show the impact of external shading devices on an eastfacing facade with large window area in a commercial office building in Chicago, Illinois. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING CHICAGO, IL East Orientation Large Window Area (WWR=0.60) Note: All cases are eastfacing with a 0.60 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE CHICAGO, IL East Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND CHICAGO, IL East Orientation Large Window Area (WWR=0.60) kbtu/sfyear B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 13

16 Chicago, Illinois South Orientation Moderate Window Area shading devices on an southfacing facade with moderate window area Chicago, Illinois. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING CHICAGO, IL South Orientation Moderate Window Area (WWR=0.30) Note: All cases are southfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE CHICAGO, IL South Orientation Moderate Window Area (WWR=0.30) PEAK ELECTRICITY DEMAND CHICAGO, IL South Orientation Moderate Window Area (WWR=0.30) kbtu/sfyear B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 14 Air Movement and Control Association International (

17 Chicago, Illinois South Orientation Large Window Area shading devices on an southfacing facade with a large window area Chicago, Illinois. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING CHICAGO, IL South Orientation Large Window Area (WWR=0.60) Note: All cases are southfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE CHICAGO, IL South Orientation Large Window Area (WWR=0.60) 1 1 PEAK ELECTRICITY DEMAND CHICAGO, IL South Orientation Large Window Area (WWR=0.60) kbtu/sfyear B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 15

18 Chicago, Illinois West Orientation Moderate Window Area shading devices on an westfacing facade with moderate window area Chicago, Illinois. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING CHICAGO, IL West Orientation Moderate Window Area (WWR=0.30) Note: All cases are westfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE CHICAGO, IL West Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND CHICAGO, IL West Orientation Moderate Window Area (WWR=0.30) kbtu/sfyear B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 16 Air Movement and Control Association International (

19 Chicago, Illinois West Orientation Large Window Area shading devices on an westfacing facade with a large window area Chicago, Illinois. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING CHICAGO, IL West Orientation Large Window Area (WWR=0.60) Note: All cases are westfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE CHICAGO, IL West Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND CHICAGO, IL West Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 17

20 Washington, DC East Orientation Moderate Window Area shading devices on an eastfacing facade with moderate window area Washington, DC. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING WASHINGTON, DC East Orientation Moderate Window Area (WWR=0.30) Note: All cases are eastfacing with a 0.30 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE WASHINGTON, DC East Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND WASHINGTON, DC East Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 18 Air Movement and Control Association International (

21 Washington, DC East Orientation Large Window Area page show the impact of external shading devices on an eastfacing facade with a large window area in a commercial office building in Washington, DC. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING WASHINGTON, DC East Orientation Large Window Area (WWR=0.60) Note: All cases are eastfacing with a 0.60 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE WASHINGTON, DC East Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND WASHINGTON, DC East Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 19

22 Washington, DC South Orientation Moderate Window Area shading devices on an southfacing facade with moderate window area Washington, DC. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING WASHINGTON, DC South Orientation Moderate Window Area (WWR=0.30) Note: All cases are southfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE WASHINGTON, DC South Orientation Moderate Window Area (WWR=0.30) PEAK ELECTRICITY DEMAND WASHINGTON, DC South Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 20 Air Movement and Control Association International (

23 Washington, DC South Orientation Large Window Area shading devices on an southfacing facade with a large window area Washington, DC. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING WASHINGTON, DC South Orientation Large Window Area (WWR=0.60) Note: All cases are southfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE WASHINGTON, DC South Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND WASHINGTON, DC South Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 21

24 Washington, DC West Orientation Moderate Window Area shading devices on an westfacing facade with moderate window area Washington, DC. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING WASHINGTON, DC West Orientation Moderate Window Area (WWR=0.30) Note: All cases are westfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE WASHINGTON, DC West Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND WASHINGTON, DC West Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 22 Air Movement and Control Association International (

25 Washington, DC West Orientation Large Window Area shading devices on an westfacing facade with a large window area Washington, DC. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING WASHINGTON, DC West Orientation Large Window Area (WWR=0.60) Note: All cases are westfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE WASHINGTON, DC West Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND WASHINGTON, DC West Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 23

26 Houston, Texas East Orientation Moderate Window Area shading devices on an eastfacing facade with moderate window area Houston, Texas. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING HOUSTON, TX East Orientation Moderate Window Area (WWR=0.30) Note: All cases are eastfacing with a 0.30 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE HOUSTON, TX East Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND HOUSTON, TX East Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 24 Air Movement and Control Association International (

27 Houston, Texas East Orientation Large Window Area page show the impact of external shading devices on an eastfacing facade with a large window area in a commercial office building in Houston, Texas. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING HOUSTON,TX East Orientation Large Window Area (WWR=0.60) Note: All cases are eastfacing with a 0.60 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE HOUSTON, TX East Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND HOUSTON, TX East Orientation Large Window Area (WWR=0.60) 20 1 kwh/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 25

28 Houston, Texas South Orientation Moderate Window Area shading devices on an southfacing facade with moderate window area Houston, Texas. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING HOUSTON, TX South Orientation Moderate Window Area (WWR=0.30) Note: All cases are southfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE HOUSTON, TX South Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND HOUSTON, TX South Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 26 Air Movement and Control Association International (

29 Houston, Texas South Orientation Large Window Area shading devices on an southfacing facade with a large window area Houston, Texas. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING HOUSTON, TX South Orientation Large Window Area (WWR=0.60) Note: All cases are southfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE HOUSTON, TX South Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND HOUSTON, TX South Orientation Large Window Area (WWR=0.60) 20 1 kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 27

30 Houston, Texas West Orientation Moderate Window Area shading devices on an westfacing facade with moderate window area Houston, Texas. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING HOUSTON, TX West Orientation Moderate Window Area (WWR=0.30) Note: All cases are westfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE HOUSTON, TX West Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND HOUSTON, TX West Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 28 Air Movement and Control Association International (

31 Houston, Texas West Orientation Large Window Area shading devices on an westfacing facade with a large window area Houston, Texas. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING HOUSTON, TX West Orientation Large Window Area (WWR=0.60) Note: All cases are westfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE HOUSTON, TX West Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND HOUSTON, TX West Orientation Large Window Area (WWR=0.60) 20 1 kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 29

32 Phoenix, Arizona East Orientation Moderate Window Area page show the impact of external shading devices on an eastfacing facade with moderate window area in a commercial office building in Phoenix, Arizona. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING PHOENIX, AZ East Orientation Moderate Window Area (WWR=0.30) Note: All cases are eastfacing with a 0.30 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE PHOENIX, AZ East Orientation Moderate Window Area (WWR=0.30) 8.00 PEAK ELECTRICITY DEMAND PHOENIX, AZ East Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 30 Air Movement and Control Association International (

33 Phoenix, Arizona East Orientation Large Window Area page show the impact of external shading devices on an eastfacing facade with a large window area in a commercial office building in Phoenix, Arizona. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING PHOENIX, AZ East Orientation Large Window Area (WWR=0.60) Note: All cases are eastfacing with a 0.60 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE PHOENIX, AZ East Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND PHOENIX, AZ East Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 31

34 Phoenix, Arizona South Orientation Moderate Window Area shading devices on an southfacing facade with moderate window area Phoenix, Arizona. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING PHOENIX, AZ South Orientation Moderate Window Area (WWR=0.30) Note: All cases are southfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE PHOENIX, AZ South Orientation Moderate Window Area (WWR=0.30) 8.00 PEAK ELECTRICITY DEMAND PHOENIX, AZ South Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 32 Air Movement and Control Association International (

35 Phoenix, Arizona South Orientation Large Window Area shading devices on an southfacing facade with a large window area Phoenix, Arizona. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING PHOENIX, AZ South Orientation Large Window Area (WWR=0.60) Note: All cases are southfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE PHOENIX, AZ South Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND PHOENIX, AZ South Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 33

36 Phoenix, Arizona West Orientation Moderate Window Area shading devices on an westfacing facade with moderate window area Phoenix, Arizona. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING PHOENIX, AZ West Orientation Moderate Window Area (WWR=0.30) Note: All cases are westfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE PHOENIX, AZ West Orientation Moderate Window Area (WWR=0.30) 8.00 PEAK ELECTRICITY DEMAND PHOENIX, AZ West Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 34 Air Movement and Control Association International (

37 Phoenix, Arizona West Orientation Large Window Area shading devices on an westfacing facade with a large window area Phoenix, Arizona. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING PHOENIX, AZ West Orientation Large Window Area (WWR=0.60) Note: All cases are westfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE PHOENIX, AZ West Orientation Large Window Area (WWR=0.60) PEAK ELECTRICITY DEMAND PHOENIX, AZ West Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 35

38 Los Angeles, California East Orientation Moderate Window Area page show the impact of external shading devices on an eastfacing facade with moderate window area in a commercial office building in Los Angeles, California. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING LOS ANGELES, CA East Orientation Moderate Window Area (WWR=0.30) Note: All cases are eastfacing with a 0.30 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE LOS ANGELES, CA East Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND LOS ANGELES, CA East Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 36 Air Movement and Control Association International (

39 Los Angeles, California East Orientation Large Window Area shading devices on an eastfacing facade with a large window area in a commercial office building in Los Angeles, California. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING LOS ANGELES, CA East Orientation Large Window Area (WWR=0.60) Note: All cases are eastfacing with a 0.60 windowtowall ratio and include daylighting controls. Annual energy use is expressed in kbtu per square foot of floor area within a 15footdeep perimeter zone. Peak demand is expressed in Watts per square foot of floor area within a 15footdeep point 5 feet from the window for a person facing the side wall. A lower index is better. All results were computed using DOE2.1E for a typical office building. of external shading devices. SHGC=solar heat gain coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE LOS ANGELES, CA East Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND LOS ANGELES, CA East Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE s LowE G LowE B LowE B LowE s LowE G LowE Air Movement and Control Association International ( Page 37

40 Los Angeles, California South Orientation Moderate Window Area shading devices on an southfacing facade with moderate window area Los Angeles, California. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING LOS ANGELES, CA South Orientation Moderate Window Area (WWR=0.30) Note: All cases are southfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE LOS ANGELES, CA South Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND LOS ANGELES, CA South Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 38 Air Movement and Control Association International (

41 Los Angeles, California South Orientation Large Window Area shading devices on an southfacing facade with a large window area in a commercial office building in Los Angeles, California. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING LOS ANGELES, CA South Orientation Large Window Area (WWR=0.60) Note: All cases are southfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE LOS ANGELES, CA South Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND LOS ANGELES, CA South Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 39

42 Los Angeles, California West Orientation Moderate Window Area shading devices on an westfacing facade with moderate window area Los Angeles, California. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING LOS ANGELES, CA West Orientation Moderate Window Area (WWR=0.30) Note: All cases are westfacing with a 0.30 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE LOS ANGELES, CA West Orientation Moderate Window Area (WWR=0.30) 7.00 PEAK ELECTRICITY DEMAND LOS ANGELES, CA West Orientation Moderate Window Area (WWR=0.30) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Page 40 Air Movement and Control Association International (

43 Los Angeles, California West Orientation Large Window Area shading devices on an westfacing facade with a large window area in a commercial office building in Los Angeles, California. analyzed include (), vertical (), shallow overhang (), (), and with, (f). IMPACT OF EXTERIOR SHADING LOS ANGELES, CA West Orientation Large Window Area (WWR=0.60) Note: All cases are westfacing with a 0.60 windowtowall ratio and include daylighting per square foot of floor area within a 15footdeep Watts per square foot of floor area within a 15footdeep computed using DOE2.1E for a typical office building. coefficient, Uvalue=heat transmission in Btu/hrsf f vertical & vertical ANNUAL ENERGY USE LOS ANGELES, CA West Orientation Large Window Area (WWR=0.60) 1 PEAK ELECTRICITY DEMAND LOS ANGELES, CA West Orientation Large Window Area (WWR=0.60) kbtu/sfyr B LowE B LowE LowE G LowE B LowE B LowE LowE G LowE Air Movement and Control Association International ( Page 41

44 Appendix Method for Generating Performance Data INTRODUCTION Window performance was analyzed with computer simulations. Inputs to the simulation included a building module which could be analyzed with different sizes and types of windows. The analysis was based on a default set of window and lighting conditions that includes various climates, window sizes, window types, shading, and daylighting controls. The computer model calculated a number of performance measures such as glare, energy use, and peak demand. This appendix provides a detailed description of the assumptions in the building simulation, the input parameter values, and the performance measures. These methods and assumptions apply to all office performance results throughout the publication. Building energy simulations of commercial window systems were performed using the U.S. Department of Energy s DOE2.1E building energy simulation program (Winkelmann et al. 1993). The DOE2.1E program is the building industry standard that requires as input a geometrical description of the building and a physical description of the building construction, mechanical equipment, enduse load schedules, utility rates, and hourly weather data to determine the energy consumption of the building. DOE2 has been used to develop American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE) 90.1 and California Title24 EnergyEfficiency Standards and to design many commercial buildings over the past twenty years. COMMERCIAL BUILDING PROTOTYPE A generic commercial office building prototype originally developed by the Lawrence Berkeley National Laboratory (LBNL) for ASHRAE SP41 was used for this study. The prototype was modified by the Pacific Northwest National Laboratory (PNNL) (Friedrich and Messinger 1995) in support of the ASHRAE Standard nonresidential building energy standards (ASHRAE 1989). The prototype was further modified by LBNL for this study to reflect ASHRAE Standard (changes to the ASHRAE Standard were not substantive) and to isolate relative differences in energy performance between different window design strategies. The prototype is a synthetic hypothetical building, not a physically real building, with size, shell construction, heating, ventilating, and airconditioning (HVAC) system type, operating schedules, etc. based on the mean prevailing condition among statistical samples and engineering judgment. This analysis relies on relative performance differences between window systems; the intention is not to Figure A1. Floor plan and section of the threestory prototype Table A1. Weather data Page 42 Air Movement and Control Association International (

45 Figure A2. Interior elevation of window wall for windowtowall ratios (WWR) of 0.30 and 0.60 (top to bottom); sections through the overhang and fin are given as well (see Tables 5 and 6) Table A2. ASHRAE insulation values Table A3. Window placement provide absolute data from which a reader may determine energy performance for a specific building. The threestory prototype consists of a ground, intermediate, and rooftop floor (Figure A1). Each floor has four 1500 square foot perimeter zones, each consisting of ten 10 by 15 feet private offices, and a 100 by 100 feet square core zone with a floor area of 10,000 square feet. The floortofloor height is 12 feet with a 9foothigh ceiling and a 3foothigh unconditioned plenum. The total floor area of the model is 48,000 square feet. The building was oriented to true north with each facade facing the four cardinal directions. Six climates were modeled (Table A1) corresponding roughly to the five climate zones defined by the U.S. DOE s Energy Information Administration (EIA 1998). Lightweight construction was used for the building and was the same for each climate: 4inch brick exterior facade, builtup roofing over a 0.75inch plywood deck, and a carpeted, 6inch heavyweight concrete slab on grade. Insulation values for the exterior wall, roof, and floor were obtained from ASHRAE Standard for each climate and are summarized in Table A2. An effective Uvalue was applied to account for the slabtogroundcontact temperature variations of the soil. The interior was specified with adiabatic walls between perimeter offices and standard walls between the perimeter and core zone. These walls were composed of 0.625inch gypsum and metal studs. A 0.5inch acoustical tile ceiling was specified for all occupied zones and inch lightweight concrete floors with a carpet were specified for the two upper level floors. Peak occupant density was 390 square feet per person in the core zones and 275 square feet per person in the perimeter zones. Peak equipment loads were Scheduling corresponded to data from ASHRAE , ELCAP, and PG&E (Friedrich and Messinger 1995). Windows Flushmounted, nonoperable windows were modeled in the exterior wall of each perimeter zone office. Two window sizes were modeled with a fenestration windowtowall area ratio (WWR) (which includes the area of the whole window with frame), of 0.30 and 0.60, where the wall area was defined as the floortofloor exterior wall area and the floortofloor height was 12 feet. Note, the ASHRAE Standard uses this same definition for WWR; however in previous research, WWR was based on the glazed window area (see Table A3 for equivalent WWR values). Figure A2 gives the position of the window in the window wall as seen from the exterior. Table A4. Window properties Air Movement and Control Association International ( Page 43

46 Window position can influence the distribution of heat flux to interior room surfaces and the distribution of daylight within the room. The head height of the framed window was set flush with the ceiling at 9 feet for all window areas. Several types of commercially available windows were modeled in order to determine relative performance impacts for both retrofit and new construction. Glass layers were all 0.25 inches thick. Spectral properties of the glass were obtained from the Optics5 (version 2.0.2) database and input into WINDOW4.1 (windows.lbl.gov/software/default.htm) to derive the whole window properties shown in Table A4. The singlepane window (type A) was modeled with a nonthermally broken, aluminum frame (assuming a retrofit condition) while all doublepane windows were modeled with a thermally broken, aluminum frame. The threepane window was modeled with aluminum inner and outer frames with a polyamide thermal break between the inner and outer frames. Multipane windows were modeled with aluminum or insulated spacers, as indicated in Table A4. The frame width was 3 inches wide in all cases. For multipane windows, all gaps were filled with air. The gap width was 0.5 inches for doublepane windows and 0.79 inches for triplepane. The intermediate layer for the threelayer window was suspended, clear polyethylene (PET) film. Exterior Shades s and vertical were modeled in DOE2.1E as opaque, nonreflective surfaces. These obstructions block diffuse light from the sky and direct sun but reflect no light from the ground. s. The depth of the overhang was set to provide a profile angle of 65 degrees or 55 degrees for a fully shaded window (Figure A2 and Table A5). These solar profile angles roughly correspond to the cooling season of a southfacing perimeter zone in the cold and hot climates and were constrained to depths deemed acceptable by standard practice. The width of the overhang was made the same width as the office module (not the window): 10 feet. The overhang height was set so that its lower surface was flush with the top of the framed window opening. s. A single case was modeled for (Figure A2 and Table A6). The fin depth yields an azimuthal cutoff angle of 26.6 for shading the full window width ( 100 percentshade condition) and 45 degrees for shading half the window width ( 50 percentshade condition). The fin was made the full height of the window and placed flush with the left and right edges of the framed window opening. s and s. When the overhang and were combined, the overhang width was the width of the window. The overhang depth was that for the 55 degree profile angle case. Lighting Recessed fluorescent lighting systems were modeled with a lighting power density of 1.2 throughout the building. Heat from the lighting system was apportioned to the interior space (60 percent) and to the unconditioned plenum (40 percent). Daylighting controls were specified in all cases. The perimeter zone electric lights were dimmed linearly (continuous dimming) so as to provide 50 footcandles at 10 feet from the window wall, centered on the window, and at a work plane height of 2.5 feet. The design work plane illuminance level of 50 footcandles is recommended for performing typical office tasks by the Illuminating Engineering Society. The recommended illuminance level in modern buildings has been changing. The current recommendation is for 30 footcandles where there is intensive visual display terminal (VDT) use and 50 footcandles for filing, intermittent VDT use, and private offices. The reduction in the recommended light level where VDT use is intensive is a response to the reflection problems with cathoderay terminal (CRT) based VDTs. It is generally assumed that higher light levels would be preferred if there were not problems with the VDTs. The recent increase in availability and popularity of flat screen liquid crystal display (LCD) VDTs is likely to change lighting practice and recommendations as these screens are much less prone to veiling reflection problems. The recommendations may return to 50 footcandles, even for intensive VDT use. The electronic dimmable ballasts were modeled with a minimum power consumption of 33 percent and 10 percent minimum light output. Surface reflectances were 70 percent for ceilings, 50 percent for walls, and 20 percent for floors. Mechanical System Five variableairvolume systems with economizers were employed: one each for perimeter zones facing a particular orientation (i.e., northfacing perimeter zones on all three floors were controlled by one system) and one for the three core zones. Such zoning facilitated an analysis of window orientation on heating and cooling energy use. The heating thermostat setpoint was 70 F during occupied hours with a night setback temperature of 55 F; the cooling thermostat setpoint was 75 F with a night setback temperature of 99 F. Heating was provided by a gas boiler and cooling was provided by a hermetic centrifugal chiller and cooling tower. Table A5 depths (ft) Table A6. depths (ft) Page 44 Air Movement and Control Association International (

47 OFFICE PERFORMANCE PARAMETERS Annual Energy Use and Peak Demand All annual energy performance data are given as energy use per perimeter zone floor area (e.g., kwh/sfyr or kbtu/sfyr), unless otherwise noted. Perimeter zone lighting electric energy use data are given without modification. Perimeter zone cooling electric use data were determined using systemlevel extraction loads converted to plantlevel electric use with a fixed coefficient of performance (COP) of 3.0. Fan electric energy use for hours when only cooling is required was then added to this quantity to arrive at total perimeter zone cooling electric use. Perimeter zone other electric use data are all electric end uses that are not included in lighting and cooling, such as convenience outlets, and supply and return fans for heating, heating and cooling, and float periods. Total annual electricity use includes all electricity end uses: lighting, cooling, and other electric end uses. Perimeter zone heating energy use data were determined using systemlevel extraction loads converted to plantlevel energy use with a fixed heating efficiency factor (HEF) of 0.8. Fan electric energy use for hours when only heating is required was not added to this quantity to enable total energy performance comparisons based on fuel type. The COP and HEF efficiency factors represent systemtoplant efficiency, not componentlevel equipment efficiencies such as those given in ASHRAE Such a procedure was necessary since the DOE2.1E program does not separate zonal energy at the plant level. These perimeter zone data enable equitable comparisons to be made across the entire data set. Total annual energy use (electricity and heating energy use) was computed using a sourcesite efficiency of 0.33 for electricity and 1.0 for natural gas. The sourcesite efficiency indicates the generating efficiency of the fuel or utility prior to its use in the simulated commercial building. Peak electric demand data are given for the peak condition that occurs in each perimeter zone and are noncoincident with the whole building s peak condition. Like total annual electricity use, peak demand data includes all electricity end uses: lighting, cooling, and other electric end uses. WholeBuilding HVAC System Capacity The HVAC capacity of the heating and cooling systems was determined at the wholebuilding plant level. DOE2 was allowed to automatically size the plant equipment for each parametric run to ensure realistic partloadratio operations. For these comparisons, note that the perimeter zone window and lighting condition is the same for all orientations. Weighted Glare Index Four types of data are given related to the visual environment: 1) annual average work plane illuminance due to daylight, 2) percent hours that the daylight illuminance is greater than 50 footcandles, 3) annual average glare index, and 4) percent hours that the glare index is greater than 22. These data are given at 5 feet from the window wall, 2.5 feet above the second story floor, and centered on the window wall. The data are based on occupied hours from 7:00 to 17:00 each day of the year exclusive of Saturdays, Sundays, and holidays. A weighted glare index was computed based on these data and are described below. DOE2 computes the hourly daylighting glare indices based on the Hopkinson CornellBRS formula. There are two issues that need to be dealt with. The first is the occupant s view orientation. Glare will be worse facing a window, but research has shown that people tend to be more tolerant of glare through a window. Glare on a side wall will be the best case condition in that if the glare is unacceptable on a side wall, it will only be worse facing the window. It is not clear which orientation is better for this index, as long as the results are scaled appropriately. The index was therefore based on the glare facing the side wall at 5 feet from the window. The second issue is the question of how to evaluate the individual hourly values to get an overall yearly index. Numerical values of the glare index cover a range of values where glare is rated imperceptible by most people on up to values where it is rated uncomfortable. A simple average could easily result in a value of imperceptible glare from individual values that cover the range up to uncomfortable glare. It should be clear that a weighted glare index should be sensitive to fairly infrequent periods of perceptible or uncomfortable glare. The manner in which the glare sensation responds to multiple spatial sources provides a guide as to how to make the weighted glare index sensitive to extreme values. The Hopkinson CornellBRS glare index is actually the logarithm of a glare value. When there are multiple glare sources, the glare sensation is the logarithm of the sum of the glare values. A straight adoption of this transformation for the temporal average results in a weighted glare index that is actually too sensitive, in that even a single excursion returns almost the maximum value, allowing almost no discrimination between this case and one with more excursions. This procedure also gives a single large excursion a worse overall weighted glare index value than a case with multiple just slightly smaller excursions. However, the procedure can be modified by the inclusion of a constant in the transformation to reduce the sensitivity of the average to what seems to be a reasonable compromise. The following formula gives an average that is sensitive to excursions from a base value if they occur at a frequency of 1 percent or more: Gavg = 4*log10(average G' over year) where the G' are G' = 10 (GI/4) and GI are the hourly glare index values from the DOE2 runs. Air Movement and Control Association International ( Page 45