Radiative cooling to deep sub-freezing temperatures through a 24-h day–night cycle

TLDR

Radiative cooling exploits the 8–13 µm atmospheric transparency window to passively dissipate heat into space, but experimentally demonstrated temperature reductions have been modest despite broad interest in building cooling, renewable energy, and passive refrigeration. The study aims to show that a selective thermal emitter combined with elimination of parasitic thermal load can achieve up to 60 °C temperature reduction from ambient. The authors theoretically design and experimentally implement a selective thermal emitter that minimizes parasitic heat loads to realize large temperature reductions. In a populous sea‑level area, the system achieved an average 37 °C reduction and a peak 42 °C drop during a 24‑h day–night cycle, surpassing previous works.

Abstract

Abstract Radiative cooling technology utilizes the atmospheric transparency window (8–13 μm) to passively dissipate heat from Earth into outer space (3 K). This technology has attracted broad interests from both fundamental sciences and real world applications, ranging from passive building cooling, renewable energy harvesting and passive refrigeration in arid regions. However, the temperature reduction experimentally demonstrated, thus far, has been relatively modest. Here we theoretically show that ultra-large temperature reduction for as much as 60 °C from ambient is achievable by using a selective thermal emitter and by eliminating parasitic thermal load, and experimentally demonstrate a temperature reduction that far exceeds previous works. In a populous area at sea level, we have achieved an average temperature reduction of 37 °C from the ambient air temperature through a 24-h day–night cycle, with a maximal reduction of 42 °C that occurs when the experimental set-up enclosing the emitter is exposed to peak solar irradiance.