Potential energy and climate benefits of super-cool materials as a rooftop strategy

For decades, reflective rooftops have been used and advocated as cost-effective measures to mitigate the urban heat and reduce building cooling loads. However, their effectiveness has always been limited by shortwave reflectivity and long-wave emissivity of commercially available technologies. Recent advances in coating materials with engineered spectral properties have resulted in inexpensive “super-cool” technologies that can be applied to most surfaces and have albedo and emissivity values greater than 0.96 and 0.97, respectively. This study is an effort to quantify the potential benefits of applying the newly developed materials on building rooftops. To do so, we conducted whole-building energy simulations of archetypical residential and commercial buildings to calculate rooftop surface temperature, sensible heat flux to the ambient, cooling energy saving, and heating energy penalty in 8 U.S. cities with urban heat mitigation plans that include use of high albedo materials. Our results suggest that in all climates, the surface temperature of the super-cool rooftop remains below the ambient air temperature throughout the year, resulting in a negative average daily sensible heat flux of 30–40 W.m⁻². In addition, we found that the new technology can double the cooling energy saving (and heating energy penalty) compared to typical white roofs.