Low-cost waterborne radiative cooling paint for large scale production and application in buildings

Abstract

Passive daytime radiative cooling (PDRC) is a cooling technology with no energy consumption and no pollution generation. It emits self-generated heat to outer space using thermal radiation, thus reducing its temperature. Radiative cooling technology aims to the energy consumption problem of buildings and environmental pollution caused by the use of Freon in compressor air conditioners. Many kinds of radiative cooling coatings have been attempted, but the cost and large-scale practical application have been challenging. This work prepared a composite coating with a radiative cooling function using calcined kaolin (CK) powder and waterborne fluorocarbon (WF). The inexpensive CK has a wide particle size distribution and exhibits high solar reflectivity (RS) and infrared emissivity (EIR). The excellent adhesion and chemical stability of waterborne fluorocarbon (WF) provides a good guarantee for the practical use of the coating. As a result, the CK/WF coating achieves an RS of 91% and an EIR of 95% in the transparent atmospheric window (ATW) of 8–13 µm. The coating demonstrated a temperature decline of 3.8 °C under direct sunlight in the field. The coating meets the conditions for large-scale applications. When used as a roofing material for simulation, it can save up to 30% of energy consumption throughout the year. Overall, the CK/WF coating has outstanding energy saving and pollution reduction performance, which will further advance the radiant cooling material into real-world applications.