Aqueous double‐layer paint of low thickness for sub‐ambient radiative cooling
Benjamin Dopphoopha, Keqiao Li, Chongjia Lin, Baoling Huang
Abstract
Abstract Radiative cooling may serve as a promising option to reduce energy consumption for space cooling. Radiative cooling paints provide a cost‐effective and scalable solution for diverse applications and attract great attention, but the state‐of‐art cooling paints generally use non‐eco‐friendly organic solvents and need large thicknesses (>400 μm) to realize high performance, which leads to high cost and environmental issues in implementation. This work aims to address these challenges by developing eco‐friendly aqueous paints with low thickness (below 150 μm) by adopting a double‐layer design based on a complementary spectrum strategy. The structure consists of a wide bandgap top layer to scatter short‐wavelength light and a bottom layer with high reflectance to visible and near‐infrared (NIR) irradiation. Effects of different design factors are studied using numerical simulation and experiments to attain the optimal design. The resulting Y 2 O 3 –ZnO paints show a strong reflectance of 95.4 % and a high atmospheric window emissivity of 0.93 at a low thickness of 150 μm. Field tests in the subtropic humid climate of Hong Kong demonstrated sub‐ambient cooling of 2 °C at noon and 4 °C at night without shielding convection. The paints also show high robustness and excellent resistance to water and UV light attacks, rendering them promising for large‐scale applications.