Consideration of cooling loss process of the emitter for radiative cooling

Abstract

Sub-ambient daytime radiative cooling (SA-DRC) has been demonstrated by various advanced emitters in recent studies, which have attracted considerable attention from fundamental sciences and potential applications. Apart from emitter's unique radiative properties, the cooling loss of the emitter affects the performance of SA-DRC in actual applications. Although the emitter is fixed in an enclosure space to decrease the effect of ambient wind on the performance of cooling, the cooling loss of the emitter still exists, and an effective heat transfer coefficient between the emitter and ambient air has directly been widely used to predict the magnitude of the cooling loss power. However, this mathematical description is limited, which will lead to a controversial prediction in some cases. In this study, the cooling loss of the emitter was investigated based on a local environment. The simulation was conducted on the basis of four advanced emitters that were reported in recent studies, and the results show that the cooling loss of the emitter increases with the increasing interface temperature of the enclosure space that surrounds the emitter, which weakens the cooling effect of the emitter. A case study shows that the temperature reduction of an infrared-spectral-selective emitter could be degraded from −3.2 °C to 0.1 °C when the interface temperature increases from ambient temperature to 6 °C higher than ambient temperature, which implies that the cooling effect has been entirely destroyed.