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

• Published in: Nature communications Vol. 7; no. 1; pp. 13729 - 5
• Main Authors: Chen, Zhen, Zhu, Linxiao, Raman, Aaswath, Fan, Shanhui
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 13.12.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 140/125; 639/4077/909; 639/624; 639/766/1130/2799; 639/925; Air temperature; Ambient temperature; Arid zones; Atmosphere; Cooling; Freezing; Heat; Humanities and Social Sciences; multidisciplinary; Radiation; Refrigeration; Renewable energy; Science; Science (multidisciplinary); Temperature; United States > US; California
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms13729

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. Radiative cooling relies on the atmosphere’s transparency window. Here the authors achieve up to 42 °C drops in temperature for low thermal loads under diffuse sunlight by improving the selectivity of the emissivity and the thermal management of their devices.