[bldg-sim] Climate Zones and Glass Properties

Since several buildings have been designed (and are still being designed) with glass percentages greater than 50% and up to 80%, I am sending this message again.

What is the basis for envelope properties for vertical glass in different climate zones?

Ex: climate zone tables B-11, B-12, B-13, B-16, B-17 & B-19 for 50% glass in STD-90-2001.

B-10 HDD65=2701-3600 CDD50=5401 + U-fixed=0.46 SHGC-all=0.19

B-11 HDD65=2701-3600 CDD50=3601-5400 U-fixed=0.46 SHGC-all=0.27 Atlanta, GA

B-12 HDD65=2701-3600 CDD50=0-3600 U-fixed=0.73 SHGC-all=0.39

B-13 HDD65=3601-5400 CDD50=3601 + U-fixed=0.46 SHGC-all=0.25

B-16 HDD65=5401-7200 CDD50=3601 + U-fixed=0.46 SHGC-all=0.23

B-17 HDD65=5401-7200 CDD50=1801-3600 U-fixed=0.46 SHGC-all=0.26 Chicago, IL

B-19 HDD65=7201-9000 CDD50=1801 + U-fixed=0.46 SHGC-all=0.26

SC = SHGC / 0.85 approx.

U-Operable = U-fixed + 0.01 approx. Ex: U-fixed = 0.46, U-operable = 0.47 for zone B-17.

Should there be an infiltration rate based on varying annual outdoor air temperatures and building types associated with fixed (pressurized buildings) windows and operable windows? AAMA (American Architectural Manufacturers Association) 101-85 for Heavy Commercial grade fixed window specifies air infiltration of 0.06 cfm per ft2 area of outside frame dimension at 6.24 psf pressure. 10CFR435 indicates 0.15 cfm/ft2 for fixed windows. Neither document shows the outside-inside temperature and height of building basis for the infiltration.

ASHRAE Standard 90 shows a different glass SHGC for the North exposure. Example SHGC-north = 0.36 and SHGC-all = 0.26 for climatic zone B-17 (Chicago). For buildings that have the same glass on all sides can we use the weighted average SHGC? Example: Weighted average SHGC = (0.26*3 + 0.36)/4 = 0.285. Is the north orientation limited to 0 degrees (DOE2 program or180 degrees ASHRAE) or can it be a range from 316 degrees clockwise through 0 degrees to 44 degrees.

I have not looked at the new STD90-2004 climate zone envelope properties yet, but the map shows locations on the sea coast and locations inside the continent belonging to the same climate zone. Glasgow, U.K. is 56 degrees latitude and the annual temperature range is +25 F to +75 F, and Minneapolis, USA is 45 degrees latitude and the annual temperature range is -16 F to +91 F.

Since energy analysis for Std90 and code compliance requires 8760-hour weather data, the climatic zones could be based on the actual HDD65 and CDD50. The weather data accounts for altitude. Example, La Paz, Bolivia is 16 degrees latitude, 13,169 feet elevation and the annual temperature range is +25 F to +63 F, and Acapulco, Mexico is 16 degrees latitude, 16 feet elevation and the annual temperature range is +68 F to +92 F.

During preliminary design we assume that energy efficient Low-E double glass has properties of U = 0.30, SC = 0.35 and VLT = 0.34. The cost of glass increases significantly with more efficient glass. What sort of glass (manufacturer name and model) would ASHRAE Standard 90 recommend for buildings that have more than 50% glass in climate zones B-10 and B-16? Example: 60% to 75% glass (13.5’ floor-floor building with 8’ to 10’ glass height).

Varkie Thomas

SOM