Daylong sub-ambient radiative cooling with full color exterior

TL;DR

This paper introduces a novel radiative cooling system that maintains sub-ambient temperatures throughout the day while allowing for any exterior color, including black, addressing aesthetic and safety concerns.

Contribution

It presents a thermally integrated, conductively insulated design enabling colored radiative coolers to cool below ambient temperature during daytime, overcoming previous color-performance trade-offs.

Findings

Black coolers absorb 646 W/m² solar radiation

They cool down to 6.9 K below ambient temperature

The system works throughout the daytime

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 broadly applied to building facades and vehicles. To overcome the fundamental trade-off between color diversity and cooling performance, we propose a radiatively integrated, conductively insulated system 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. We experimentally demonstrate that even black coolers, absorbing 646 Wm-2 of solar power under AM1.5 conditions, cools 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.