The impact of the solar absorption coefficient of roof and wall surfaces on energy use and peak demand

Abstract

Climate change, electrification to decarbonize the building sector, and the rise of renewable energy sources have made reducing the peak demand even more important than solely reducing the overall energy use. Solar radiation can have a significant impact on the energy use of buildings. However, previous studies on solar absorption in building envelopes have focused on cool roofs. Less effort has been made to evaluate the impact of solar radiation on heat loss and gain on walls. This paper summarizes a preliminary study to estimate the magnitude of the benefit low solar absorptance surfaces have on reducing peak demand and focuses on simulating a residential building with two types of U.S. code-compliant wall structures, a standard lightweight wall assembly, and a thermally massive mass timber wall, to evaluate the impact of the solar absorption coefficient of the surfaces on the heating and cooling energy use and peak demand. This effort aimed to identify whether a more comprehensive study should be undertaken to develop further the calculation tools previously developed for estimating the energy benefits for roofing systems in the U.S. by adding a similar tool for wall assemblies. Reducing the solar absorption coefficient from 0.9 to 0.3 resulted in up to 46% lower cooling demand and a 70% increase in heating demand depending on the climate. Peak demand reductions for heating and cooling energy were similar to the reduction in heating or cooling energy use. However, the annual energy use changed up to only 12% as lowering the solar absorption coefficient reduces cooling demand but increases heating demand. Whether the total impact overall is harmful or beneficial depends on the climate and type of structure. Additionally, a cool roof calculator was used to estimate the impact of solar radiation on roofs. The learning from this study is that the exterior color and the solar absorption coefficient should be chosen based on the climate to positively impact the energy use profile and peak demand.