[Bldg-sim] Why should roofs have high emissivity?

Brad Painting bradpainting at gmail.com
Sun Nov 29 12:57:22 PST 2009


It seems to me that a roof that emits more radiation will have a greater
warming effect on the building. Some houses in warm climates have radiant
barriers because the aluminum has a *low* emissivity, thus blocking the
infrared radiation. But both LEED and Energy Star suggest high emissivity
for warm climates. Does this make sense?

>From LEED NC Reference Guide v. 2.2:

"To maximize energy savings and minimize heat island effects, materials must
exhibit a high reflectivity and a high emissivity over the life of the
product."

>From Energy Star website:

"In warm and sunny climates highly emissive roof products can help reduce
the cooling load on the building by releasing the remaining heat absorbed
from the sun."

Thanks,

Brad
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