Thermal performance of passive techniques for roofs in tropical climate

Abstract

Problem: Roofs receive the most intense solar heat load among all building envelope surfaces in Equatorial-region. Solar heat gain through roof contributes to a significant portion of building heat load. In tropics where building cooling is needed all-year-round, passive methods to reduce heat gain through roof could provide significant cooling energy-savings. Approach: Currently, the most widely adopted practices to curb the heat flux through roof include using thick building material-layer (30-40 cm-thick concrete) or insulation (5-10 cm-thick). This study investigates the thermal performance of emerging methods: cool roof and green roof. Cool roof works by applying a coating-layer having high-solar-albedo. Green roof works by adding a soil-layer and vegetation. This study numerically compares the heat curbing performances of these technologies under the tropical climate using an experimentally-calibrated EnergyPlus model. Results and discussion: Cool roof performs best in reducing annual net heat gain in tropical climate of Singapore, which receives abundant irradiation. Cool roof reduces heat gain during day-time and promotes heat loss during night-time. Insulation and green roof are effective in curbing heat gain during day-time but they prevent heat loss during night-time. Research limitations: This paper reports the investigation on a flat concrete roof as the base. Investigations on other roof base materials, e.g., metal roof, will be reported in future. Originality: This is the first study that compares performances of cool roof, green roof and insulation against original concrete roof in tropical climate.