A double-layer radiative cooling coating that utilizes the refractive index difference between layers to achieve extremely high solar reflectivity

Passive daytime radiative cooling(PDRC)technology has great potential in reducing cooling energy consumption.In order to further improve the spectral performance of PDRC coatings,current researchers mostly focus on the selection and size design of functional particles,while ignoring the optical properties enhancement effect caused by the interlayer binder.In this study,based on the principle that the refractive index difference between layers enhanced the backscattering performance of the solar spectrum,we proposed and manufactured a double-layer PDRC coating with polyvinylidene difluoride(PVDF)as the filmforming material in the upper layer and polydimethylsiloxane(PDMS)as the film-forming material in the lower layer,both filled with Al_(2)O_(3) and SiO_(2) particles.The double-layer PDRC coating exhibited excellent spectral performance that a high solar reflectivity of 98%and an emissivity of 0.95 at the“atmospheric window”band.In comparison,the solar spectrum reflectivity of the single-layer PDRC coatings based on PVDF and PDMS of the same thickness was 95%and 94.7%,respectively.Outdoor tests showed that the PDRC coating achieved a temperature decrease of up to 7.1℃ under direct sunlight at noon time.In addition,the PDRC coating had excellent weather resistance,water resistance,and other basic properties.This article opens up a new idea and provides methodological guidance for the design of double-layer PDRC coatings.

Radiative cooling for long-term building energy efficiency:An experimental comparison of seven coatings

Radiative cooling coatings are widely used owing to their excellent cooling performance and energy efficiency.However,there is a lack of comprehensive research on their weather resistance,long-term performance and effects on building load.To fill this research gap,seven coatings were selected for experimental observation and simulation research.The results revealed noticeable differences among different coatings regarding anti-aging properties,cooling performance and building load reduction.Some coatings exhibited yellowing,cracking and peeling after weathering tests,accompanied by a decline in their radiative properties.Long-term tests showed that the cooling performance of all coatings gradually decreased due to natural aging,and the rate of decline was proportional to the weathering of the coatings.Building load simulations revealed the potential effect of coating selection on cooling and heating loads,thereby suggesting that different coatings should be selected based on actual usage scenarios in different climatic zones.