Daylong Sub-Ambient Radiative Cooling with Full-Color Exterior Based on Thermal Radiation and Solar Decoupling

Abstract

Terrestrial radiative cooling is an intriguing way to mitigate the accelerating cooling demands in the residential and commercial sectors by offering zero-energy cooling. However, the ultra-white or mirror-like appearance of radiative coolers can be visually sterile and raise safety issues when applied to building facades and vehicles en masse. To overcome the fundamental trade-off between color diversity and cooling performance, a radiatively integrated, conductively insulated material system is proposed that exploits thermal non-equilibrium between colorants and thermal emitters. This allows such radiative coolers to be cooled below the ambient temperature at all times of the day while exhibiting any desired exterior color including black without using vacuum insulation. This work experimentally demonstrates that even black coolers, absorbing 646 W m−2 of solar power under AM1.5 conditions, cool down to a maximum of 6.9 K (average of 3.5 K) below the ambient temperature during the daytime. These systems can potentially be used in outdoor applications, especially in commercial buildings and residential houses, where carbon-free thermal management is in high demand but diversity of colors is also important for visual appeal and comfort.