Thermal simulation of roof surface evaporative cooling system for India using “TRNSYS”

Abstract

SYNOPSIS Cooling of buildings by employing evaporation of water is a well-recognised concept for the reduction of mechanical cooling loads of buildings, especially in hot and dry climates. Evaporation of water may be used directly inside the building, as in desert coolers which are quite commonly used in tropical countries; this results in reduction of air temperature and increase in humidity of the indoor air. Alternatively, the exposed surface of the roof may be treated with water producing a cooling effect on the inside air without any increase in humidity. The latter method, referred to as roof surface evaporation cooling (RSEC) technique, has been practiced for a long time now, and has been established as an effective passive cooling technique. This paper presents results of a computer simulation carried out using “TRNSYS” for a single zone building treated with a roof surface evaporative cooling system corresponding to five locations in India representing different climatic conditions. The results of the simulation are analysed in terms of performance parameters, namely, discomfort degree hours (DDH) for a conditioned building and monthly cooling load for a conditioned building. Various walls/roof configurations having different U-values have been considered and calculations have been made corresponding to different set-point temperatures (25°C to 30°C) for indoor temperature. It is observed that a reduction in number of DDH and cooling load could be substantial for hot & dry and composite climatic zones, though less effective for warm & humid climates. The effectiveness of the RSEC system as a function of difference in roof composition and External Shade Factor of windows has also been presented.