How to rapidly and accurately evaluate the cooling performance of radiative cooling materials?

Radiative cooling materials exhibit great potential for reducing energy consumption in numerous areas. However, owing to the lack of standardized experimental methods and the complexity of model calculation, rapidly and accurately evaluating the cooling performance of radiative cooling materials remains challenging. To address this issue, we propose a new evaluation method that relies solely on the material's radiative properties. First, the calculation accuracies of the hemispherical and spectral-directional emissivity models were compared using the results of three-day field measurements for both radiative cooling and white coatings. The hemispherical emissivity model exhibited slightly higher accuracy and considerably simpler calculation steps than the spectral-directional emissivity model, with the daily, daytime, and nighttime average mean absolute errors between the calculated and measured cooling temperatures all within 2.5( degrees)C. Subsequently, using the hemispherical emissivity model, the cooling performances of radiative cooling materials with shortwave reflectivity (rho(sr)) and hemispherical emissivity (epsilon(lr,he)) varied in the range of 0.80-1.00 under different meteorological conditions were calculated. Based on the calculation results, a new concept termed the cooling potential index (CPI) was proposed and calculated as CPI = rho(sr) + epsilon(lr,he)/18. The index can be used to rapidly evaluate and compare the cooling performances of different radiative cooling materials.