Use of Radiation Control Coatings to Reduce Building Air-Conditioning Loads

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Abstract
Radiation control coatings (RCCs) are used on building exteriors to reduce the absorption of solar energy. Reduced solar energy absorption results in lower exterior surface temperatures, and, consequently, less heat flow across the building envelope, and reduced electrical requirements to maintain air-conditioned space. Solar reflectance (r) and ambient temperature emittance (e) are key properties for RCC performance. RCC products typically have r values greater than 0.75 and e values greater than 0.8. A review of typical values for r and e along with the dependence of these properties on RCC thickness is presented. The performance of RCCs depends on a number of variables including r, e, solar flux, sol-air temperature, and the thermal resistance of the parts of the building envelope that are coated. The building simulation code DOE-2 has been used to calculate benefits of RCCs for selected values of the previously listed variables. Energy savings can be significant in hot climates where buildings have little or no conventional thermal insulation. RCC technology has potential for reducing cooling loads for buildings in many parts of the world. Computer simulations for buildings located Latitude 25 °N to Latitude 35°N showed reductions in cooling loads due to heat from the roof ranging from 60 to 85%. These reductions were obtained by comparing solar heat gains for flat concrete roof deck with and without an RCC. A research program is currently in progress to evaluate commercially available RCCs.

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