Impact of aging, precipitation, and orientation on performance of radiative cooling for building envelope: A field investigation

Abstract

Radiative cooling is an energy-efficient method for providing subambient cooling to the exterior surfaces of buildings. Its performance is influenced by many factors and further investigation is required. This study comprehensively evaluates the cooling performance of a radiative cooling coating under the effect of aging, precipitation, and orientation. The radiative properties of the radiative cooling coating are measured after the temperature cyclic test, ultraviolet (UV) test, and natural aging test in the laboratory. Next, a long-term field experiment is conducted to investigate the radiative cooling performance on sunny and rainy days in the horizontal, south, and west directions. The laboratory results reveal that obvious variations in the radiative properties only occur in the natural aging test, with the shortwave reflectivity decreasing from 0.94 to 0.81. The outdoor results reveal that the subambient cooling effect on a horizontal surface on clear sunny days during daytime decreases from −2.14 °C on August 1 to 0.23 °C on December 1, owing to dust accumulation. In addition, the radiative cooling coating achieves all-day cooling on a rainy day but the cooling ability does not recover immediately after the rainfall. Finally, this study finds that subambient radiative cooling in the horizontal direction is superior to that in the vertical direction, regardless of any weather conditions in our investigation.