An aluminium nocturnal radiator, painted with an appropriate white paint, was established on the roof of the Department of Environmental and Natural Resources Management in Agrinio, Western Greece. The lightweight metallic radiator was used for cooling the ambient air below its initial temperature. The dynamic thermal performance of the system during summer months was calculated using an accurate mathematical model, based on the heat transferred from the air circulating inside the radiator to the ambient air. Furthermore, an extensive validation process was carried out. Thus, the experimental air temperature values at the radiator's outlet were compared with the theoretical ones and a very good agreement was achieved. The validation process was extended for two radiator's paints with different emissivities, in order to investigate the impact of different materials' optical parameters on the system's efficiency. Moreover, the more effective lightweight nocturnal radiator was used to provide space cooling or pre-cooling for the building of the University. Indoor air temperature values of the thermal zone connected with the radiator were compared with those of a similar zone without any cooling system and the results demonstrated a remarkable effectiveness of the system. (C) 2007 Elsevier Ltd. All rights reserved.