Influences of atmospheric water vapor on spectral effective emissivity of a single-layer radiative cooling coating

Radiative cooling technology can emit infrared heat to the outer space through the “sky window” for cooling without consuming energy, which had drawn more and more attention. However, some researches reported that there was a significantly different cooling performance at different atmospheric total water vapor columns (TWC) conditions. In this study, taking a simple single-layer radiative cooling coating containing two kinds of particle mixture (SiO2, TiO2) as example, the spectral effective emissivity of the radiative cooling coating was proposed to evaluate the effect of the atmospheric water vapor on the cooling performance. The spectral effective emissivity of the coating was obtained through multiplying spectral emissivity of the coating by the atmospheric transmittivity, where the spectral emissivity was calculated by combining an algorithm for calculating radiative properties of the multi-particle system with the Monte Carlo ray-tracing method (MCRT). The effects of different atmospheric water vapor on the spectral effective emissivity of the simple single-layer radiative cooling coating containing different particles size, volume fraction and thickness were studied to improve the cooling performance of the coating. The results showed that with increasing TWC from 0 to 7000 atm-cm, the average effective emissivity of the simple single-layer coating decreased from 79.5% to 35.3%, with a decrease of 44.2%. The research results are of great significance to the further application development and the design criterion of radiative cooling materials in different atmospheric water vapor environments.