THE EFFECTS OF ROOF ALBEDO MODIFICATION ON COOLING LOADS OF SCALE-MODEL RESIDENCES IN TUCSON, ARIZONA

Data supporting reductions in cooling load and related demand for elec tric power possible from increasing building surface albedo are limite d. Electrical use of wall-mounted air conditioners, roof temperatures, and related environmental factors were monitored during the summer of 1990 on three initially identical 1/4-scale model buildings situated in rock mulch landscapes in Tucson, Arizona. Model thermodynamic prope rties were scaled to approximate thermodynamic similarity with full-si ze buildings. With ceiling insulation of R value 5.28 m(2) K W-1 (R-30 ) installed, increasing roof albedo of the gray composition shingles ( 0.30 albedo, 0.94 emissivity) by painting one roof silver and another white (0.49 and 0.75 albedos, 0.70 and 0.98 emissivities, respectively ) reduced daily total and hourly peak electrical use for air condition ing approximately 5% for the house with white-colored roof compared to either gray or silver-colored roofs. Larger differences were found wi thout ceiling insulation, with daily total and peak hourly demand for houses with white compared to dark brown roofing (0.9 albedo, 0.98 emi ssivity) reduced 28 and 18%, respectively. Computer simulations of dai ly total energy use confirmed comparable savings for similar full-size d buildings. White roofs were 20 to 30 degrees C cooler than either si lver or dark-colored roofs on hot, sunny days, indicating that expecte d cooling due to an increase in albedo may not be realized if it is ac companied by a decrease in emissivity. Light-colored roofs, by maintai ning cooler attic temperatures, may provide savings in addition to tho se presented here by reducing heat gain to air distribution systems lo cated in the attic space.