Thermal modelling of a night sky radiation cooling system

The thermal modelling of a night sky radiation cooling system suitable for a room situated in the Namib Desert at Gobabeb, Namibia, is considered in this paper. The system consists of the following components: radiator panels, a single water storage tank, room air-to-water natural convection heat exchangers or convectors, circulating pump(s), interconnecting pipe work and temperature sensors and controls. The mathematical equations describing the thermal behaviour of the various system components are given. These equations are solved using an Excel spreadsheet and the hourly panel surface, water storage tank and room temperatures are calculated for a given internally generated heat load and weather pattern. Given the maximum allowable room temperature, the sizes of the system components may be calculated. The results obtained compared favourably with values reported in the literature. It is thus concluded that the thermal model presented can be used with confidence as a design tool for the sizing of a night sky radiation cooling system