 A radiative air well is designed to cool a substrate by radiating heat to the night sky. The substrate has a low mass so that it cannot hold onto heat, and it is thermally isolated from any mass, including the ground. A typical radiative collector presents a condensing surface at an angle of 30°from the horizontal. The condensing surface is backed by a thick layer of insulating material such as polystyrene foam and supported 2 – 3 metres (7 – 10 ft) above ground level. Such condensers may be conveniently installed on the ridge roofs of low buildings or supported by a simple frame. Although other heights do not typically work quite so well, it may be less expensive or more convenient to mount a collector near to ground level or on a two-storey building.
