Thermal comfort effects of urban design strategies in high-rise urban environments in a sub-tropical climate

Outdoor thermal comfort is associated with the usage pattern of urban open spaces. Thermally uncomfortable outdoor environments could discourage participation in outdoor activities and increase buildings' cooling energy consumption. This article evaluated the effects of various urban design strategies on summertime outdoor thermal conditions, focusing on applications of high-albedo pavement and vegetation. Field measurement was carried out in two high-rise residential quarters in Shanghai. The result of the measurement was used to interpret the numerical simulation. Numerical simulation using ENVI-met was then applied to examine a series of urban design strategies, using the physiological equivalent temperature (PET) as the thermal comfort index. The result shows that an increase of 0.4 in the ground surface albedo overall reduces the thermal comfort, as indicated by an increase of 5-7 degrees C in PET during the day with a marginal decrease of less than 1 degrees C at night. Increasing greenery cover, especially tree cover, improves thermal comfort during the whole period under evaluation. A reduction of up to 15 degrees C in daytime PET is achieved by adding a dense tree cover (LAI = 6.4) over a grass lawn and up to 20 degrees C by adding the tree cover over the hard pavement with an albedo of 0.2.