Solar-Reflective “Cool” Walls: Benefits, Technologies, and Implementation

Solar-reflective “cool” pavements are an urban heat island reduction strategy that increases pavement albedo (solar reflectance) to reduce convective heating of the outdoor air, which has the “indirect” effect of decreasing cooling loads in summer and increasing heating loads in winter. Raising pavement albedo also increases the solar flux incident on walls and windows. This “direct” effect of reflective pavement can increase cooling loads in summer and reduce heating loads in winter. In this study we focus on the direct effect of cool pavements, and quantify its impact on the annual conditioning (heating and cooling) energy uses of buildings in California, USA. The study also measures how modifying wall and window properties alter the direct effect. We prepared nine code-compliant building prototypes with external horizontal shading surfaces that represent local roads. To quantify the direct effects of cool pavements, we simulated with EnergyPlus the annual cooling and heating energy uses of each prototype, varying the road albedo, wall absorptance, and window solar heat gain coefficient. We present a physical model that relates each heating and cooling energy use to building properties, and to local road albedo. The results from the building simulations were used to validate the physical model, and to generate relationships that predict the direct effect of pavement albedo change on building energy use.