Radiative Cooling with Angular Shields: Mitigating Atmospheric Radiation and Parasitic Heating

TL;DR

This paper explores the use of angular shields and spectral selectivity to enhance radiative cooling performance, enabling subfreezing temperatures in humid environments without vacuum conditions.

Contribution

It introduces the concept of angular selective thermal emission with shields and analyzes their effectiveness under various environmental conditions.

Findings

Optimal shield angle is 45° under ideal conditions.

Spectral selectivity improves cooling in humid environments.

Angular shields outperform spectral selectivity when parasitic heating is present.

Abstract

Radiative cooling emerged as a possible sustainable solution to the energy hungry vapor compression-based cooling. However, realizing subfreezing temperatures through radiative cooling remains challenging in environments with high humidity and often requires extreme heat management, e.g., by placing the thermal emitter in ultrahigh vacuum conditions. This work theoretically investigates the introduction of angular selective thermal emission through surrounding the emitter with an angular shield. The effect of the spectral selectivity of the emitter, the humidity of the environment, and the introduction of parasitic heating on the cooling performance is studied. The optimal angle for the shield under ideal conditions is shown to be 45{\deg}. In addition, spectral selectivity of thermal emission is necessary to obtain noticeable improvement in the minimum equilibrium temperature. In humid environments, angular selectivity through engineering the thermal emissivity function of the emitter provides a better cooling performance compared to angular shields. Conversely, angular shields performance is superior when introducing parasitic heating. Using angular shields enables cooling emitters to subfreezing temperatures without vacuum and under humid levels higher than the global average.