Deep sub-ambient radiative cooler design utilizing angular conversion

Abstract

The proportion of electricity consumption used in cooling is significantly higher worldwide. The use of cooling energy produces another heat through the condenser and causes the urban heat island phenomenon. Radiative cooling, which allows passive cooling without energy consumption, solves this problem. However, conventional radiative cooler (RC) facing the sky have a problem with cooling performance depending on the environment due to the absorption of additional heat. Several studies have been conducted to solve these issues, but the cooling performance is poor, or they do not demonstrate differences in cooling performance from conventional RC. In this study, we present radiative cooling structures that achieve not only environmentally independent cooling performance but also block solar irradiance and most atmospheric radiance by using the optical devices with focal points. We confirmed that this structure is 9.9 K and 10.1 K cooler than conventional RC through simulation and outdoor experiment based on daytime in summer, and that even with cheap aluminum foil, the cooler is 5.3K cooler than conventional RC. Our study can be applied to areas such as portable refrigerators, medical devices, and apartment water cooling systems that require high-efficiency cooling and maintaining cooling temperatures even in environmental variables.