Qin Jie, Zhang Zihan, Li Yanwen, Cai Yuanzhu, Zhang Hongqiang, Liu Lianhua, Xu Lijin, Zhang Weidong, Xue Xiao
China Southwest Architectural Design and Research Institute Co., Ltd., Chengdu 610042, China.
Department of Information and Art Design, Henan Forestry Vocational College, Luoyang 471002, China.
Rev Sci Instrum. 2022 May 1;93(5):054901. doi: 10.1063/5.0087494.
The obscure theory of passive subambient daytime radiative cooling (PSDRC) was deduced in a more understandable way using an arithmetic formula rather than integro-differential equations. Based on two boundary conditions of the equations, an innovative radiative cooler was successfully developed to qualitatively observe PSDRC phenomena and quantitatively characterize the cooling effect and cooling power of radiative cooling coatings (RC coatings). The remarkable subambient temperature reduction over 4.0 °C was successfully achieved in a completely open environment without minimizing the parasitic conduction and convection from the ambient. Prominent PSDRC phenomena could even be observed in such an open environment on very cloudy days, which generally compromise the RC. A much more prominent subambient cooling depression of 10.0 °C was observed when a wind shield was employed to minimize the convection. With suppression of convection, the subambient daytime cooling effect on cloudy days was even more noticeable than that occurred on clear sunny days. The subambient cooling effect was still very remarkable even on clear sunny days in the winter. The average cooling power measured on a clear sunny day was 154.8 ± 9.7 W/m, corresponding to an average solar irradiance of 680 ± 90 W/m with a peak value of ∼820 W/m. Both the subambient RC effect and the cooling power measured under real weather conditions using the radiative cooler agreed excellently with the theoretical prediction, sufficiently demonstrating the great innovation, validity, and effectiveness of the device.
利用算术公式而非积分微分方程，以更易懂的方式推导了晦涩的被动低于环境温度日间辐射冷却（PSDRC）理论。基于该方程的两个边界条件，成功开发了一种创新型辐射冷却器，用于定性观察PSDRC现象，并定量表征辐射冷却涂层（RC涂层）的冷却效果和冷却功率。在完全开放的环境中，成功实现了超过4.0°C的显著低于环境温度的降温，且未将来自环境的寄生传导和对流降至最低。即使在非常多云的日子里，在这样的开放环境中也能观察到显著的PSDRC现象，而多云天气通常会影响辐射冷却效果。当使用挡风板来最小化对流时，观察到了更为显著的10.0°C的低于环境温度的冷却降幅。随着对流的抑制，多云天气下低于环境温度的日间冷却效果甚至比晴朗晴天时更为明显。即使在冬季晴朗的晴天，低于环境温度的冷却效果仍然非常显著。在晴朗晴天测得的平均冷却功率为154.8±9.7W/m²，对应平均太阳辐照度为680±90W/m²，峰值约为820W/m²。使用该辐射冷却器在实际天气条件下测得的低于环境温度的辐射冷却效果和冷却功率与理论预测高度吻合，充分证明了该装置的巨大创新性、有效性和实用性。
