Super-amphiphobic coatings with sub-ambient daytime radiative cooling—Part 2: Cooling effect under real conditions

Abstract

The cooling effect of a super-amphiphobic self-cleaning radiative cooling coating (RC coating) on various substrates was systematically studied under real working conditions and compared with that of conventional cool white coatings. Under direct sunlight, the surface temperature of the RC coatings was always below the ambient air temperature, even up to 12.9 °C on concrete, whereas that of the conventional cool white coatings on concrete reached 4.1 °C above the ambient air temperature. When the RC coatings were applied to industrial facilities such as carbon-steel-based substation cabinets, the temperatures of the coated ceiling surface and interior remained below the ambient temperature, yielding an interior temperature reduction of 13.7 °C relative to the temperature of an unpainted substation cabinet. When applied to outdoor living facilities, including safety helmets, sunshades, and Roman tents with open and closed curtains, the RC coatings could greatly improve the thermal comfort either by reducing the air temperature beneath the open facilities or by significantly lowering the interior temperature of the closed space of the living supplies. Upon application to concrete buildings, the RC coatings reduced the temperatures of the concrete surface, roof surface, and room interior by 25.7, 12.9, and 11.5 °C below the ambient air temperature, respectively, the decrease in the latter two being 9.8 and 4.8 °C, respectively, relative to the buildings coated with 0.88-solar-reflectance conventional cool white coatings. The measured sub-ambient cooling effect agreed with the theoretical prediction. In summary, RC coatings have wide application prospects in cooling energy conservation and emission reduction. Superamphiphobic self-cleaning radiative cooling coatings were applied to industrial and basic facilities, outdoor living supplies and real buildings. The coating surface temperatures over different basements were below ambient air temperature day and night. The air temperatures beneath the coated roofs/ceilings of facilities in open and closed environments were at least 2.5 °C and 9.0 °C lower than those beneath the conventional white facilities in open and closed environments, respectively. • The subambient daytime radiative cooling coatings were applied in various fields. • The coating greatly reduced outdoor products' surface and interior temperature. • The coating enabled the metals' surface temperature to be below that of the ambient. • The coating greatly reduced concrete buildings' surface and interior temperature.