On thermal performance of an improved roof pond for cooling buildings

In this study, a detailed simulation model is developed for the investigation and analysis of a roof pond with gunny bags (RPWGB) floating on the water surface which was suggested and experimentally investigated in a previous study of the present authors. The model is based on the newly proposed empirical correlation of water evaporation rate from a wetted surface to the ambient air proposed by the present authors, and takes into account the response of buildings as a whole to evaporative cooling. Results by simulations show that, regardless of the type of buildings the technique is applied to, RPWGB has a better cooling performance in terms of the indoor air temperature and heat flux through the roof into pond as compared to a roof covered with wetted gunny bags, which had been widely considered to be one of the most efficient roof cooling techniques. The reason for its higher efficiency is the thermal stratification inside the pond. The simulated results also reveal that the optimal water depth in the RPWGB depends on the roof type in general, and it is about 20 cm for a concrete roof and is about 5 cm for metal-decked roofs.