Cool coating for urban heat island (UHI) effect mitigation - experimental study

• Main Author: Tan, Bing Yu
• Other Authors: Wan Man Pun
• Format: Final Year Project
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/74722
• Institution: Nanyang Technological University

A common phenomenon observed worldwide is the warming of urban built up areas as compared to their rural counterpart. This phenomenon is known as the Urban Heat Island (UHI) effect. As the name suggests, this phenomenon is caused by the urbanisation and development of cities; and human behaviours contribute significantly to the UHI intensity. Singapore, having underwent one of the fastest urbanisation progress in the world, is experiencing the UHI effects all over the island. With more development planned in the future, coupled with the tropical warm climate, Singapore is set to see a worsening of the UHI effect in the future. The UHI effect primary causes thermal discomfort to the population. The measures taken to combat the UHI effects, such as usage of air-conditioning systems, can potentially worsen the UHI situation in Singapore. Hence, it is imperative to research other methods to mitigate the UHI effect. In an urban layout, the roof and the pavements are areas most commonly exposed to the sun. In some situations, these structures are exposed to the sun throughout the day. The building façade and pavements form the urban canyon geometry that hinders radiation from escaping back into the atmosphere. The solar radiation contributes to the heating of structures, and in turn the UHI effect. Various methods have been researched and experimented on to reduce the UHI effects. Out of these methods, one that stand out is the application of cool materials. Cool materials, such as cool paints have surface finishing that has high albedo and thermal emissivity. Compared to the other methods available, cool materials stand out due to the ease of application, environmental friendliness and the ability to protect the surface that they are applied on. This report presents an experimental study on the effect of cool paint on various portion of the urban geometry, namely the building façade, the roof and the pavement. In order to study the cooling capabilities of such paint, the surface temperature, heat flux activities and indoor temperature of the set up was studied. Additionally, the Mean Radiant Temperature (MRT) within the canyon was also tracked in order to study the impacts of the cool paint on its environment. Two units of Prefabricated Bathroom Units (PBUs) were used as the setup, and various combination of paint – conventional, cool, and colours, were used on the setup to evaluate the effects of cool paint on the buildings and the surroundings. The building façade coated with the cool paint were found to have a lower surface temperature as compared to the façade with conventional paint. Both the outer and inner walls of the building experienced a reduction in surface temperature of about 2°C. The application of cool paint on the pavement managed to result in an approximately 4°C maximum surface temperature reduction, with the heat flux activities showing lower rate of absorption and higher heat loss to surrounding. Similarly, this was also observed on the building façade. The application of cool paint to the roof, much like the façade, reduced both the outer and inner surfaces by approximately 3°C. The usage of cool paint also saw a reduction in the Mean Radiant Temperature within the canyon. From the experiments, it can be seen that usage of cool paint can effectively reduce the thermal loading in buildings, and at the same time improve thermal comfortability within the canyon.