Simulating the effects of cool roof and PCM (phase change materials) based roof to mitigate UHI (urban heat island) in prominent US cities

UHI (Urban Heat Island) has become a serious concern within major cities due to the increased threat of climate change over time. As UHI intensifies, the energy consumed in urban areas increases through an increase in the cooling demand, and restricts the overall comfort and quality of life in urban regions. UHI mitigation approaches have been widely studied over the past few decades. However, the work presented here evaluates and compares how cool roof and PCM (Phase Change Materials) based roof technologies may perform as UHI mitigation strategies. Detailed thermal energy simulations were conducted with these two strategies over a range of seven climatic zones within the United States. For each mitigation strategy, five different roof types were chosen for the analysis. The results indicate that a higher albedo led to superior energy saving and UHI mitigation for all types of roofing materials. Also, asphalt roofs produced the best results of all the roof types. It was found that insulation did not play a significant role in the reduction of UHI effects. The maximum TRHG (through roof heat gain) flux was 54% lower for the PCM roof than the cool roof at a wide range of albedo. Similarly, the maximum sensible heat flux for the PCM roof type 40% lower than the cool roof technology for varying albedo.