1. Characteristics of Thermal Comfort in Outdoor Environments

The living quality of urban inhabitants is important to urban liveability and receives increasing concern in urban living. Thermal comfort is widely regarded as one of the important issues to urban living, particularly the health and well-being of urban inhabitants. In outdoor environments where urban dwellers spend their time for commuting, leisure, and recreational activities, the thermal environment is more complex due to the constantly changing environmental conditions and the interplay between human body and the ambient environment. Meteorological factors such as air temperature and humidity, solar radiation, and air movement are fundamental parameters of the immediate environment that one is experiencing while metabolic heat generated by human activity and clothing worn by an individual are the two personal attributes that define the human thermal environment. In outdoor environments, peoples’ subjective assessment of thermal comfort is also influenced by psychological expectancy and their thermal history. The major issues associated with outdoor thermal comfort in cities include low urban wind speeds, high temperatures due to urban heat island effects, and limited solar access. In high-density cities, where complex and high-rise urban geometries are common, enhancing urban design is essential for improving outdoor thermal comfort and hence enhancing the usage of outdoor spaces.