Cooling energy savings potential of light-colored roofs for residential and commercial buildings in 11 US metropolitan areas

Abstract

The U.S. Environmental Protection Agency (EPA) sponsored this project to estimate potential energy and monetary savings resulting from the implementation of light-colored roofs on residential and commercial buildings in major U.S. metropolitan areas. Light-colored roofs reflect more sunlight than dark roofs, so they keep buildings cooler and reduce air-conditioning demand. Typically, rooftops in the United States are dark, and thus there is a potential for saving energy and money by changing to reflective roofs. Naturally, the expected savings are higher in southern, sunny, and cloudless climates. In this study, we make quantitative estimates of reduction in peak power demand and annual cooling electricity use that would result from increasing the reflectivity of the roofs. Since light-colored roofs also reflect heat in the winter, the estimates of annual electricity savings are a net value corrected for the increased wintertime energy use. Savings estimates only include direct reduction in building energy use and do not account for the indirect benefit that would also occur from the reduction in ambient temperature, i.e. a reduction in the heat island effect. This analysis is based on simulations of building energy use, using the DOE-2 building energy simulation program. Our methodology starts with specifying 11 prototypical buildings: single-family residential (old and new), office (old and new), retail store (old and new), school (primary and secondary), health (hospital and nursing home), and grocery store. Most prototypes are simulated with two heating systems: gas furnace and heat pumps. We then perform DOE-2 simulations of the prototypical buildings, with light and dark roofs, in a variety of climates and obtain estimates of the energy use for air conditioning and heating.