Diurnal Selective Radiative Cooling Impact in Mitigating Urban Heat Island Effect

Abstract

This study investigates the impact of diurnal radiative cooling (RC) roof panels RC roofs in mitigating the urban heat island (UHI) at city scale in comparison with high albedo roofs and concrete roofs. A validated microclimate model that embeds a building energy model is used to predict the street level temperature and thermal comfort. The effective radiative properties of RC surface are calculated using their spectral angular properties in a spectral angular atmospheric model. A case study of Beirut city with its morphology and microclimate was simulated on representative days of the year. At the peak of a humid summer day in Beirut, daytime RC roof panels resulted in a reduction in air temperature at the pedestrian level by at least 0.8°C in high building density regions enhancing outdoor thermal comfort. While the RC panel's surface temperature drop was greatest at night, its effect on the microclimate at night was negligible. At lower humidity days, the RC surface temperature was lower, however, RC impact on pedestrian level air temperature was not significantly changed. At moderate and high humidity days, RC panels yielded a similar microclimate influence on pedestrian level air temperature and outdoor thermal comfort to high-performance cool roofs.