Effect of surface characteristics and atmospheric conditions on radiative heat loss to a clear sky

Abstract The factors influencing the net heat loss of surfaces exposed to atmospheric thermal radiation have been investigated. Measurements of net heat loss as a function of surface temperature, ambient temperature, and humidity, have been carried out on both gray and spectrally selective surfaces. Gray surfaces of high emissivity are found to exhibit the highest net cooling power at temperatures near ambient. Spectrally selective surfaces with spectral emissivities matched to the 8–13 μm atmospheric window exhibit the highest cooling powers at temperatures well below ambient. Conduction heat transfer between the radiating surface and surroundings is shown to significantly limit the net cooling power. The experimental results are in good agreement with an analysis of sky-radiator-ambient heat exchange.