Numerical Study of Thermal Behaviors in Roof Ponds Under the Hot and Humid Climate

Abstract

The passive cooling of building roofs by use of a water roof pond has been of interest for many years, but the thermal behavior of roof ponds lacks detailed analysis leading to high water depths and inaccurate thermal performance estimations. In this study, the effects of solar radiation, ambient temperature, and constant water evaporation on the thermal behavior in roof ponds with depths of 0.1, 0.2, 0.3 and 0.4 m in 2 roof pond patterns; uncovered with and without water flow, were numerically investigated. The numerical results illustrated temperature gradients in the roof pond systems during exposure to a solar intensity of 638 W/m², and ambient temperatures of 32.93 - 36.67 °C with an initial water temperature of 24.0 - 25.35 °C. In the uncovered roof pond, the water depth of 0.2 m was found to completely prevent heat transfer into the building. The roof pond with a water flow of 0.1 - 0.4 m removes heat away from the roof through water circulation; hence, the suggestion is to use it in combination with a conventional uncovered roof pond as a hybrid-system. The results reveal important information regarding the complex interaction between temperature distribution in water with mixed convection in the roof-pond in a hot and humid climate.