Climate-dependent enhancement of radiative cooling with mirror structures

Radiative cooling exploits the imbalance between the thermal emission from the radiative cooling surface and the downward atmospheric emission. Since the atmospheric emission power is polar angle-dependent, a mirror structure can be used to increase this imbalance and to amplify the net cooling power. The degree of amplification is determined by various parameters, such as the sky emissivity, the geometry of the mirror structure, and the degree of thermal insulation. A parametric study of aperture mirror-enhanced radiative cooling is presented using a model atmosphere, characterized by an average sky window emissivity and the ambient temperature. A counterintuitive finding is obtained: the aperture mirror structure is more effective in the tropics than in the desert, both in terms of the cooling power and the temperature reduction. The power enhancement obtainable from a relatively simple mirror structure can be significant. For example, in the tropics, the cooling power can be enhanced by more than 40%. The aperture mirror structure holds the potential to be a practical augmentation to improve the stagnant temperature and the response time of radiative cooling devices.