Thermal performance of concrete-based roofs in tropical climate

In this work, an analytical Complex Fast Fourier Transform (CFFT) method is used and modified to predict the transient roof temperature and transmitted heat flux through the multilayer roofs of naturally ventilated rooms. A field experiment is carried out on two full-scale roofs to validate the CFFT model. The mean bias error (MBE) and cumulative variation of root mean square error (CVRMBE) in the ceiling temperature prediction using CFFT model are found less than 4% during both sunny and rainy days. After validation, a parameter study is conducted to investigate the impacts of rooftop surface solar reflectivity (from 0.1 to 0.9) and thermal resistance (from 0.1 to 2.5 m2 K/W) on the thermal performance of two types of concrete-based roofs, namely the unventilated and ventilated roofs. Compared to the roofs with solar reflectivity of 0.1, increasing the solar reflectivity by 0.1 reduces the daily heat gain by 11% in both the unventilated and ventilated roofs during a typical weather day in Singapore. Compared with the unventilated roofs, the individual uses of roof ventilation and 2.5-cm expanded polystyrene (EPS) foam insulation reduce the daily roof heat gain by 42% and 68% respectively, and the daily roof heat gain reductions increase to 73% and 84% in the ventilated roofs incorporated with 2.5-cm EPS foam and radiant barrier respectively.