Kishor T. Zingre

Thermal performance of passive techniques for roofs in tropical climate

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.

An Investigation of Microclimatic Impact of Cool Coating for Buildings in Low-Latitude and Tropical Climate

This study investigates the impact of cool coating on air-conditioning energy savings and micro-climate of buildings in low-latitude and tropical climate by performing a computational study. The computational study was carried out using Integrated Environmental Solutions (IES) software which is plugged in with Computational Fluid Dynamics (CFD) program [1]. IES simulations (which uses the heat balance equations at building envelope surfaces and in indoor environment) were performed to investigate the roof surface temperature, while CFD simulations (which uses the Finite Volume Method) were performed to investigate the impact on micro-climate above a real-size single storey air-conditioned building. The computational models in the software were validated by comparing the simulations results against the experimental results obtained from the test building in the industrial area of Nanyang Technological University (NTU), Singapore. Results showed that by applying a cool coating having solar reflectivity of 0.8 on the concrete roof with original solar reflectivity of 0.27, the surface temperatures of roof and ceiling can be reduced by up to 17.5°C and 1.2°C respectively in an air-conditioned room maintain at 22°C. In addition, after applying this high solar reflectance coating, a maximum reduction of 1.0°C, 0.7°C and 0.6°C for air temperature at a height of 0.5 m, 1 m and 1.5 m above the roof surface could be achieved.Copyright

An Investigation of Heat Transfer Characteristics of Cool Coating for Building Roofs in the Tropical Climate

Heat transfer characteristics of cool coating for building roofs in the tropical climate have been investigated by formulating a cool roof heat transfer (CRHT) model for transient heat flux through a cool-coated multi-layered roof (MLR). Furthermore, the impact of the cool coating on heat flux through roof was quantified by extending the CRHT model to estimate the equivalent thickness of uncoated roof required and the equivalent thermal insulation material thickness to be added over uncoated roof to achieve the same daily heat gain as for a cool-coated roof. It was observed that the impact of cool coating is much more significant for low R-value (5–15 cm2-K/W) roof materials, such as metal roofs, as compared to high R-value (>800 cm2-K/W) roof materials such as concrete, asphalt shingle, wood shingle, etc.Copyright