Daytime radiative cooling performance and building energy consumption simulation of superhydrophobic calcined kaolin/poly(vinylidene fluoride-co-hexafluoropropylene) coatings

Daytime Radiative Cooling (DRC) is a non-consumptive and non-polluting cooling technology that transfers heat through thermal radiation. Radiative cooling technology can effectively solve the problems of non-renewable energy consumption (e.g., oil) and environmental pollution. This work uses calcined kaolin (CK) modified poly(vinylidene fluoride-co-hexafluoropropylene) (P) to prepare a self-cleaning coating with a radiative cooling function. The self-cleaning property of CK/P coating allows rainwater to easily remove dust adhering to the coating surface, without any influence on its radiative cooling effect. The coating exhibits excellent abrasion resistance and ultraviolet aging resistance to ensure long-term effectiveness of the coating. The extinction coefficient of P is close to zero, which can scatter most of the solar energy. CK has an ultra-high IR emissivity in the 8–13 µm atmospheric transparent window. Thus, the CK/P coating has a solar reflectance of nearly 91% in the wavelength range of 200 to 2500 μm and an IR emissivity of 96% in the transparent atmospheric window. The coating exhibits a cooling effect of −1.95 °C in direct outdoor sunlight. In addition, the coating reduces energy consumption throughout the year as a roof coating for simulated houses, demonstrating the material's feasibility in addressing energy consumption and environmental pollution.