Daytime radiative cooling has drawn much attention recently because a target surface can be passively maintained at sub-ambient temperature. In order to implement a daytime radiative cooling device (simply ‘radiative cooler’), strong thermal emission should be focused in the mid-infrared regime (8–13 µm), called ‘atmospheric transparent window’. At the same time, absorption of the solar irradiation should be minimized. In the present study, for optimal performance of daytime radiative cooling, a mixed-integer genetic algorithm was employed to achieve maximal infrared emission as well as minimal solar absorption. The combination of total number of layer, materials, and thickness of each layer in the multilayered radiative cooler were determined through optimization. The optimized multilayer structure exhibited the spectrally-averaged (in the 8–13 µm wavelength range) normal emissivity value of 0.96 and the solar-weighted absorptivity of 0.03. The corresponding net cooling power was found to be 101.0 W/m${}^2,$ and a sub-ambient cooling temperature of $11.2{}^{\circ }$C (i.e., below ambient temperature) was predicted in daytime at air-mas 1.5 condition. Besides, the mechanism of enhanced emission in the infrared region and suppressed absorption in the solar spectrum were thoroughly investigated. We also derived the expected performance of the optimized radiative cooler for various conditions of the environmental parameters, such as convection heat transfer coefficient, ambient temperature, and precipitable water level.

由于目标表面可以被动地保持在低于室温的温度下，因此白天的辐射冷却最近引起了很多关注。为了实现白天的辐射冷却装置（简称为“辐射冷却器”），应将强烈的热辐射集中在称为“大气透明窗口”的中红外区（8-13 µm）中。同时，太阳辐射的吸收应最小化。在本研究中，为使白天的辐射冷却达到最佳性能，采用了混合整数遗传算法来实现最大的红外辐射以及最小的太阳吸收。通过优化确定多层辐射冷却器中层的总数，材料和每层的厚度。优化的多层结构的光谱平均法线发射率值（在8-13 µm波长范围内）为0.96，太阳加权吸收率为0.03。发现相应的净冷却功​​率为101.0 W / m${}^2，$ 且低于室温的冷却温度为 $11.2{}^{\circ }$白天在空气质量为1.5的条件下预测到C（即低于环境温度）。此外，还深入研究了红外区发射增强和太阳光谱吸收抑制的机理。我们还得出了优化的辐射冷却器在各种环境参数条件下的预期性能，例如对流传热系数，环境温度和可沉淀水位。