Numerical study of cool roof on heat transfer

• Main Author: Kwan, Gladys Yin Siong
• Other Authors: Wan Man Pun
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Mechanical engineering::Energy conservation
• Online Access: http://hdl.handle.net/10356/64988
• Institution: Nanyang Technological University

Cool roofs are an emerging technique with a flourishing interest worldwide of late. The aim of this study is to present the application of cool coating on the roof of an experimental building located in N3.1, Nanyang Technological University, Singapore. The N3.1 building is simulated in eight metropolitan cities for their varying climates and to identify its heat transfer performance after the implementation of four distinct roof types - conventional roof, insulated roof, cool roof and green roof. This specific numerical study employs the use of a whole building energy simulation software, EnergyPlus, which is intended as a shining example of the cool roof capabilities in improving the thermal performance in roofing systems especially in hot and humid climates, particularly in Singapore. This report discusses other roofing systems, the insulated roof and roof with vegetation and the conventional concrete roof to present a holistic coverage of roofing systems commonly used across the developed world. For the vegetated roof, its soil layer thickness, the amount of moisture content in the soil as well as the hydrologic cycle in plants - the evapotranspiration between plants and the atmosphere were investigated. For the cool roof, thermal emittance and solar reflectance were examined as they are two important properties that define the ‘coolness’ of the roof. The component that which contributes most to lowering heat transfer rate in green roof is the soil layer, especially the moist soil. Compared to a conventional concrete roof, moist soil is able to reduce the annual heat gain by almost six times. In cool roof, increasing the thermal emittance from minimum to maximum, reduces the net annual heat transfer rate by as much as ten times and by maximising solar reflectance to 0.9, solar heat gain and temperature lowers significantly due to a lower net annual heat transfer by as much as three times.