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.
Highlights
Radiative cooling technology utilizes the atmospheric transparency window (8–13 mm) to passively dissipate heat from Earth into outer space (3 K)
Earth’s atmosphere has a transparency window in the wavelength range from 8 to 13 mm that coincides with the peak of the blackbody spectrum of typical terrestrial temperatures B300 K, enabling the process of radiative cooling, that is, radiative ejection of heat from Earth to outer space, and the direct radiative access to this colder heat sink
In a 24 h day–night cycle in winter, the cooler is maintained at a temperature that is at least 33 °C below ambient air temperature, with a maximal temperature reduction of 42 °C, which occurs when the apparatus enclosing the cooler is exposed to peak solar irradiance
Summary
Radiative cooling technology utilizes the atmospheric transparency window (8–13 mm) to passively dissipate heat from Earth into outer space (3 K). The key to such ultra-large temperature reduction is to use highly selective thermal emitter matched to the atmospheric transparency window, and to minimize parasitic heat losses.
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