Urban heat island and thermal comfort conditions at micro-climate scale in a tropical planned city

Abstract

The urban heat island (UHI) phenomenon and the outdoor thermal comfort in a planned city need to be reviewed and studied as a climatic issue in the design process. Increasing the temperature and discomfort conditions would be unjustified and not acceptable, unlike the temperature and the discomfort outdoors in a non-planned city that is natural. This study aimed to investigate the UHI phenomenon and outdoor thermal comfort on a micro-scale of the different areas in a planned city. A mobile survey and fixed station measurements were performed to investigate the intra-urban air temperature within the city. The thermal comfort condition of the different hot spots of the urban area in the city was investigated by using Envi-met V4 Beta software. The results indicate that the maximum UHI occurred during the afternoon and reached 3 °C in low-rise residential buildings. The high-rise residential buildings and the Boulevard street are 4 °C lower than low-rise buildings and 1 °C lower than nearby suburban areas. The city's human thermal comfort exceeds the natural range of 30 °C. However, the high-rise residential buildings and the Boulevard street are thermally comfortable most of the daytime hours, while low-rise buildings suffer from a long period of heat stress. The diffuse, reflected solar radiation and the surface temperature have an influence on increasing the Physiologically Equivalent Temperature (PET) thermal index within the city, while the wind velocity and building height are the essential variables reducing the PET thermal index.