i am trying to model a cool roof by changing the absorbency from 0.7 to
0.55. it is the right approach? i am getting an increase in energy costs,
which goes against logic.
When I model cool roofs using ASHRAE Standard 90.1 Appendix G, I change
the absorptance of the roof construction to 0.55, per the
reflectance=0.45 allowance in Table G3.1. Energy savings may be modest,
or even negative, depending on several factors, including climate, roof
U-value, and electric-vs.-gas/heating energy rates. There are good
discussions in the archives regarding the nuances of cool/white roofs.
Rob,
When I model cool roofs using ASHRAE Standard 90.1 Appendix G, I change
the absorptance of the roof construction to 0.55, per the
reflectance=0.45 allowance in Table G3.1. Energy savings may be modest,
or even negative, depending on several factors, including climate, roof
U-value, and electric-vs.-gas/heating energy rates. There are good
discussions in the archives regarding the nuances of cool/white roofs.
Regards,
William Bishop, PE, BEMP, LEED(r) AP
well, that makes me feel a little better. now to explain this to my boss...