RADIATIVE COOLING DURING THE DAY - SIMULATIONS AND EXPERIMENTS ON PIGMENTED POLYETHYLENE COVER FOILS

Pigmented foils can promote radiative cooling of an underlying object if they reflect most of the solar light and transmit a part of the thermal radiation in the atmospheric window in the infrared. In this paper we describe the optimization of optical properties, and simulations of thermal performance during the day for pigmented polyethylene foils. The tested pigment materials were ZnS, ZnSe, TiO2, ZrO2 and ZnO. It was found that only ZnS could promote cooling of a black body radiator in an insulated box at noon with the sun in zenith position. A 400 mu m thick ZnS pigmented foil with a pigment volume fraction of 0.15 and a solar reflectance of 0.849 was tested in Tanzania. At noon the temperature was slightly above the ambient, and the heating power was approximately 7.2 Wm(-2). However, this foil proved that cooling of a black surface could be obtained more than 19 hours per day in an arid location close to the equator.