Performance calibration and standardization of passive radiative cooling

Radiative cooling is a process that surfaces emit thermal energy into outer space. In this work, a method is proposed to consistently and fairly compare different radiative cooling materials under various and repeatable working conditions. A model that accurately replicates the radiative heat transfer in the actual surface–atmosphere–universe system using the surface–surface heat transfer process in a laboratory setup is developed. A novel ilmenite-pigmented polyethylene material that effectively represents the entire atmosphere in the natural radiative cooling phenomenon is created. With the material, it is further proved that the radiative heat transfer in the naturally occurring surface–atmosphere–universe system equals to the laboratory surface–surface heat transfer between the cooling surface and the newly created atmosphere-emulating material. An instrument is constructed accordingly and an experimental protocol is subsequently developed to standardize the assessment of all radiative cooling materials in a repeatable laboratory setting. These will contribute to the field by providing a standard assessing the performance of all developed radiative cooling materials.