Novel Passive Radiation Cooling Materials with High Emissivity Discovered by FDTD Method

Abstract

The cooling with the traditional condensation method leads to huge energy consumption, while increasing attention has been paid to radiant cooling because of its characteristics of no additional energy consumption and no pollution. In order to obtain materials with higher infrared emissivity and better performance for daytime passive radiation cooling materials, the infrared emissivity of different materials was studied based on the finite-difference time-domain method. A new composite material with high emissivity has been found. The results show that the highest emissivity can reach 99.1% by adding Si3N4, Al2O3 and Fe2O3 particles with volume fractions of 6% and diameters of 50 nm into polydimethylsiloxane. This is the most excellent emissivity ever found. By combining the emitting layer made of polydimethylsiloxane mixed with nanoparticles with the reflecting layer made of Ag foil, the new film material can reach a solar transmissivity of 96.4% and a “sky window” mean emissivity of 94.2%. A new composite material with high emissivity and high reflectivity has been realized. The new composite material can be used as a radiation cooling material with good performance and help to solve the cooling problem caused by energy consumption.