March 2005

Cooling down the house

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Residential roofing products soon will boast "cool" surfaces

by Hashem Akbari and Andre Desjarlais
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Energy-efficient roofing materials are becoming more popular, but most commercially available products are geared toward the low-slope sector. However, research and development are taking place to produce "cool" residential roofing materials.

In 2002, the California Energy Commission asked Lawrence Berkeley National Laboratories (LBNL), Berkeley, Calif., and Oak Ridge National Laboratories (ORNL), Oak Ridge,Tenn., to collaborate with a consortium of 16 manufacturing partners and develop "cool" non-white roofing products that could revolutionize the residential roofing industry.

The commission's goal is to create dark shingles with solar reflectances of at least 0.25 and other nonwhite roofing products—including tile and painted metal—with solar reflectances not less than 0.45. The manufacturing partners have raised the maximum solar reflectance of commercially available dark products to 0.25-0.45 from 0.05-0.25 by reformulating their pigmented coatings. (For a list of the manufacturers, see "Manufacturing partners," page 36.)

Because coatings colored with conventional pigments tend to absorb invisible "near-infrared" (NIR) radiation that bears more than half the power of sunlight (see Figure 1), replacing conventional pigments with "cool" pigments that absorb less NIR radiation can yield similarly colored coatings with higher solar reflectances. These cool coatings lower roof surface temperatures, reducing the need for cooling energy in conditioned buildings and making unconditioned...

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Study about the development of cool, colored roofing materials

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