A new study on passive radiative sky cooling resource maps of China

Abstract

Passive radiative cooling utilizes atmospheric transparency window (8–13 µm) to discharge heat into outer space and inhibits solar absorption. Recently, due to the rapid development of daytime radiative cooling materials synthesized at micro or nano scales, radiative cooling has attracted substantial attention due to its energy-saving potential without generating carbon emissions. This study newly explores radiative cooling resources across China by using the radiative cooling model and extensive meteorological data retrieval. Temporal and spatial variability characteristics of cooling power across seven geographic regions of China are comprehensively analyzed. In particular, the annual, seasonal and daily variations of radiative cooling resources are given in detail. The influence of the spectral properties from different radiative coolers on the cooling potential is clarified. The annual maximum cooling potential is between 36.7 and 71.9 W/m2, among which the humid region of South China demonstrates the lowest cooling power with an average of 48.8 W/m2. In comparison, Northwest China with comparatively dry climate shows the cooling power of 60.1 W/m2 on average. Seasonal distribution of radiative cooling resources varies discrepantly. The cooling power in spring, summer, autumn and winter deviates + 4.02%, −7.22%, −0.34% and + 3.6% from that of annual average, respectively. South China has the lowest cooling potential in all seasons, especially in summer when the net cooling power below 50 W/m2 accounts for the largest geographic share of 42%. In 38.51% of China, the cooling power during the daytime is higher than 60 W/m2, and the ratio at night is reduced to 10.87%. Compared with the ideal broadband cooler, due to the uneven regional distribution of solar radiation, a practical radiative cooler with the solar absorption of 4% and an inferior nonblackbody thermal emittance reduces the annual net cooling power of 15.4% on average. In addition, the practical cooler shows the nighttime cooling power of 24.8% higher than that of the daytime. Finally, a radiative cooling potential-based regional division map is newly displayed, which provides a clear picture for the deployment of radiative cooling technology in China.