Building roof surfaces can be 30 to 50 °C hotter than the surrounding air in summer, in turn, warming the air through convective heat flux. Advances in material science have enabled rooftop coatings with solar reflectance as high as 0.96 and emissivity approaching 0.97. We use building energy simulations to isolate how improvements in each rooftop radiative property impacts surface temperatures and heat fluxes. The analysis is conducted for two U.S. cities: Phoenix (a hot and arid city), and Atlanta (a hot humid city). Results show that use of rooftop materials with solar reflectance above 0.9 results in surface temperatures that are always below ambient air temperatures, even when the materials have conventional emissivity values. Specifically, increasing rooftop solar reflectance from 0.2 to 0.96, while fixing emissivity at 0.9, results in a mean reduction in the rooftop temperature of about 10 °C. Furthermore, the high reflectance roof results in a cooling of more than 30 W/m² during summer for both cities. On the other hand, increasing emissivity from 0.9 to 0.97 had little impact, suggesting that the focus of development efforts should be maximizing solar reflectance, provided thermal emittance values can be maintained at or above 0.9.

夏季，建筑物屋顶表面的温度可能比周围空气高30至50°C，从而通过对流热通量使空气变暖。材料科学的进步使屋顶涂料的太阳反射率高达0.96，发射率接近0.97。我们使用建筑能耗模拟来隔离每个屋顶辐射特性的改善如何影响表面温度和热通量。该分析是针对美国的两个城市：凤凰城（炎热而干旱的城市）和亚特兰大（炎热潮湿的城市）进行的。结果表明，使用屋顶太阳能反射率高于0.9的材料时，即使材料具有常规的发射率值，其表面温度也始终低于环境空气温度。具体来说，将屋顶的太阳反射率从0.2提高到0.96，同时将发射率固定为0.9，导致屋顶温度平均降低约10°C。此外，高反射率的屋顶导致冷却速度超过30 W / m两个城市在夏季²。另一方面，将发射率从0.9增加到0.97几乎没有影响，这表明开发工作的重点应该是最大化太阳反射率，前提是可以将热发射率值保持在0.9或更高。