[bldg-sim] Climate Zones and Glass Properties

Varkie Thomas Varkie.Thomas at som.com
Wed Feb 2 12:27:16 PST 2005

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

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

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

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

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


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



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