Sub-ambient cooling effect and net energy efficiency of a super-amphiphobic self-cleaning passive sub-ambient daytime radiative cooling coating applied to various buildings

Abstract

In this study, a super-amphiphobic passive sub-ambient daytime radiative cooling (PSDRC) coating was applied to various buildings in different climatic regions in China. Irrespective of sunny, cloudy, and rainy weather conditions, the roof and west-facing wall surfaces coated with the PSDRC coating exhibited distinct sub-ambient cooling effects. Compared with the cool-white and grey roof surface temperatures, the roof surface temperature due to PSDRC coating was lower by 10.1 °C and 33.1 °C, respectively. Consequently, the room interior temperatures of different buildings were lower than the ambient air temperature during the day because of heat conduction and convection. The room with a window coated by the PSDRC coating had 18.2 °C lower interior temperature than that with a west-facing glass window. Thus, the PSDRC coating decreased the cooling energy consumption of buildings in the summer but increased the heating energy consumption in the winter. However, the net energy savings were considerable because of low solar irradiance and high heating energy demand when the sub-ambient cooling effect was diminished, which minimised the difference between the roof surface and room interior temperatures of the PSDRC and control buildings. After five-cycle dirt resistance tests, the solar reflectance of the super-amphiphobic PSDRC coating was reduced only by 0.0051. After 2000 h of artificial accelerated weathering tests, the solar reflectance of the superamphiphobic PSDRC coating was attenuated by 0.021 on average. This indicates the significance of the super-amphiphobic self-cleaning capability, which endowed the coating with a long-term sub-ambient cooling effect.