Exterior Color (Absorp.)

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Hi All,

When I reduce the roofing material absorptance value in my model, under
construction properties, my energy consumption increases instead of
decreasing, which suggests that this input is actually reflectance and not
absorptance. has anyone experience something similar or am I missing
something here? Any input is much appreciated.

Thanks,

Behnam

--
Behnam Jowkar, MASc, BEng, LEED AP BD+C
Mechanical Engineer In Training
p: 416-716-5758
e: behnamjowkar at gmail.com

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When the absorptance is decreased, one would expect the heating load to increase and the cooling load to decrease. The overall energy difference would depend on which increased/decreased more.

Christopher Jones, P.Eng.
Tel: 416.644.4226 ? Toll Free: 1.888.425.7255 x 527

Chris Jones
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This question has surfaced before on the bulletin boards, although more for window SHGC
rather than roof absorptance. If you're seeing something that's counter-intuitive, e.g.,
heating going up with increased absorptance, you should check to see whether the HVAC
system size has changed. What can happen is that the HVAC size will increase due to the
higher cooling loads, so that during the heating season it will be lower on the part-load
curve and result in increased heating energy use.

Joe

Joe Huang
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