Lawrence Berkeley National Laboratory

Cool (solar reflective) roofs and walls can reduce solar heat gain and decrease unwanted heat flowing into indoor spaces. To explore the potential of these strategies to mitigate energy and thermal comfort challenges in Los Angeles, we conducted a study that used EnergyPlus building energy simulations. Our analysis focused on single-family homes in Los Angeles under various historical and future weather conditions, including both typical meteorological year (TMY) and heatwave weather year (HWY) scenarios, based on the COordinated Regional Downscaling EXperiment (CORDEX) framework under the Representative Concentration Pathway (RCP) 8.5. Our study evaluated the impact of cool envelope strategies on heating, ventilation, and air conditioning (HVAC) primary energy intensity savings and thermal comfort improvements. We employed three thermal comfort models: predicted mean vote (PMV), adaptive, and heat stress. Our findings indicate that in Los Angeles, a package of cool roof + walls (reflective roof and reflective walls) can reduce annual HVAC energy consumption by at least 11% for buildings equipped with mechanical cooling systems. They can reduce occupants’ warm thermal discomfort (thermal-sensation-scale-unit-weighted warm exceedance hours) by at least 28% in air-conditioned buildings and by at least 16% in buildings without mechanical cooling systems. Cool envelopes can also lower daily heatwave heat stress by at least 9%.