Climate-dependent enhancement of radiative cooling with mirror structures

TL;DR

This study demonstrates that mirror structures can significantly enhance radiative cooling efficiency, especially in tropical regions, by amplifying the atmospheric emission imbalance, with potential practical applications.

Contribution

The paper introduces a parametric model showing how mirror structures can boost radiative cooling, revealing counterintuitive regional effectiveness and quantifying potential power enhancements.

Findings

Mirror structures increase cooling power by over 40% in the tropics.

Effectiveness of mirrors varies with atmospheric conditions and geometry.

Potential for practical improvements in radiative cooling devices.

Abstract

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 the 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, namely that 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 potential to be a practical augmentation to improve the stagnant temperature and the response time of radiative cooling devices.