Chapter 6 – MATERIALS FOR RADIATIVE COOLING TO LOW TEMPERATURES

Radiative cooling uses the clear sky as a heat sink. To assess the potential of this free and abundant source of cooling we first present computed data, based on a detailed model of the sky radiance, which show that a cooling power of ∼100 Wm–2 at ambient temperature and a maximum practical temperature difference of ∼25°C can be accomplished. Low temperature applications hinge on materials development. We review work on selectively infrared-emitting surfaces with a focus on silicon-based coatings backed by metal, metallized polymer foils, gas slabs backed by metal, and certain ceramic oxide layers. We also treat infrared-transparent polyethylene-based convection shields with a focus on cellular constructions, as well as coatings and pigments for diminishing the solar transmittance. The results of a few selected field tests are included. Under favourable, but not uncommon, meteorological conditions one can reach temperature differences of 15–20°C during the night and ∼10°C during the day with simple devices.