Reduction in thermal loading of buildings by high-albedo materials
Lau, Jia Hui.
Date of Issue2013
School of Mechanical and Aerospace Engineering
Thermal loadings from the surrounding of the building into the building interior are a major concern, directly related to the usage of cooling devices to cool the interior of the building. Ambient temperatures in Singapore are relatively higher as compared to countries in other regions due to the Urban Heat Island (UHI) effects encountered and the geographical location on the globe. UHI causes a higher temperature of several degrees Celsius in urban area as compared to its surrounding suburban and rural areas. With the higher temperature, thermal loadings into the interior of the buildings reached a level significantly to cause thermal discomfort to the occupants of the buildings. Mitigation devices such as air-conditioner systems are most commonly used to achieve thermal comfort within the buildings. However, the excessive usage of mitigation devices brings up environmental and energy consumption issues. In the majority of the buildings, roofs are areas highly exposed to the solar irradiation by the Sun, contributing to a major component of thermal loadings into the buildings. Various passive cooling methods had been developed over times to reduce the inward thermal loadings, such as the high albedo roof coating (known as cool roof) and vegetation roof. Among these methods, the high albedo roof possesses some important advantages such as its higher lifespan and the ease of application. This report presents an experimental study on the effect of high albedo roof on the reduction of thermal loadings of the buildings. Effects of the high albedo roof on the roof microclimate, together with the roof surface temperature, heat flux across the roof slab and the power consumption of the air-conditioner required to cool the test building were analysed through the experimental study. Experimental data collected before the high albedo coating was applied onthe roof was used to make a comparison against the results obtained after the coating to evaluate the coating effects on the building roof. The high albedo coating used in this study increases the solar reflectance and the thermal emissivity of the test roof from 0.27 to 0.8 and 0.92 to 0.94 respectively. The results obtained showed the high albedo roof materials used in this study produced significant effect in reducing the roof surface temperature and heat flux across the root slab. Maximum reduction in roof surface temperature was as high as 19.2°C under strong solar irradiation. Reduction in heat flux after the coating was also achieved with the maximum reduction occurring at 73.6W/m2. The obtained results shows that the high albedo material is an effective passive cooling technique to effectively reduced the peak temperature and heat flux across the roof. In addition to this, the efficiency of the air-conditioner unit used in the study also shows a significant improvement. Average electricity consumption of the air-conditioner decreases in the range of 0.3kWh to 0.4kWh. This decrease was attributed by the cooler air drawn in by the air-conditioner condenser for the cooling work. Main reason for the decreased in air temperature at the condenser inlet was due to the reduction in the roof temperature as well as the solar irradiation absorbed by the coated roof surface, reducing the air temperature close to the condenser inlet.
Final Year Project (FYP)
Nanyang Technological University