Assessment on seasonal variations of outdoor thermal comfort with on-site monitoring in a precinct

Abstract

City residents desire to enjoy more outdoor recreational activities, such as walking, cycling and picnicking. The authors' earlier study reported that thermally comfortable environment could be generated in a local space at hot summer in a subtropical city. The present study aims to further assess the variations of the thermal perceptions for the temperate autumn and cool winter in the two same outdoor sites on an campus via on-site monitoring at the pedestrian level winds and thermal parameters at two sample days (sunny and cloudy) in a precinct. The daytime wind directions were also recorded from a nearby urban weather station and used for the analysis on the differences of wind and thermal comfort between the two surveying sites. The instantaneous thermal perceptions were assessed using PET (Physiological Equivalent Temperature) and the PET based index, normalized environmental parameter differences. Results indicate that the wind speed differences become smaller between the two sites due to their different building designs and the changes of wind directions in summer and winter. Not as the hot summer, the PET results note that the space without shading, directly subject to solar radiation, which can provide a thermally comfortable area at a sunny day in the cool seasons. Specifically in winter, wind speed difference is not contributed significantly to improve the thermal comfort while adaptive sunshine can obtain better thermal perception. The results reconfirm the possibility that a local outdoor thermal comfort zone can be built at selected urban spots even in cool seasons and provide a reminder for planners to consider the seasonal impacts in precinct planning within high dense city.