Radiative property tests of cooling coatings: A round robin campaign

Abstract

Radiative cooling is an emerging technology for scenarios requiring space cooling. Radiative property tests of cooling materials are critical for evaluating the cooling performance and energy-saving potential. However, there is a lack of quantitative analysis of the impact of laboratory qualifications on testing results. This study reported a round robin campaign initiated by Chongqing University (China) and participated by seven other academic institutes. In this campaign, six cooling coatings were selected as target materials. The radiative properties — shortwave reflectivity, hemispherical emissivity and atmospheric window emissivity — of the coatings were tested. Based on the testing results, material errors, repeatability errors and reproducibility errors were analyzed. The results revealed that there were certain differences in the radiative properties of the coatings due to their inherent properties. In general, different coatings exhibited varying material errors (0.01%–2.66%), which, although small, were challenging to eliminate. Meanwhile, the radiative property tests showed excellent repeatability, with repeatability errors below 1.00%, confirming that the tests themselves were reliable under proper control. However, significant differences between laboratories (reproducibility errors ranging from 2.03% to 7.40%) suggested that differences in instrument models and operators could lead to significant deviations in the results. This, in turn, severely affected the evaluation accuracy of the coatings’ cooling performance. Therefore, stricter and more detailed protocols are needed to improve the reproducibility for radiative property tests of the coatings.