A new method to assess spatial variations of outdoor thermal comfort: onsite monitoring results and implications for precinct planning

Publication date: Available online 25 February 2015
Source:Building and Environment
Author(s): Jianlei Niu , Jianlin Liu , Tsz-cheung Lee , Zhang(John) Lin , Cheukming Mak , Kam-Tim Tse , Bo-sin Tang , Kenny C.S. Kwok
Residents wish to have outdoor spaces to enjoy walking, cycling, and other recreational activities, which are often hindered by the unfavorable thermal comfort conditions, especially in the summer. High building densities lower the average wind speed and this intensifies the urban heat island effects at city scale. The conscientious use of building morphology to create local thermal comfort zone at selected spots in a large precinct is becoming a pressing issue for sustainable urbanization. This paper is a proof of concept study via continuous monitoring of the pedestrian level winds and thermal parameters at two sample days in summer, which include instantaneous air temperature, globe temperature, wind speed and humidity. Three outdoor locations at an university campus are chosen and daytime thermal perceptions at the three sites were evaluated using PET (Physiological equivalent temperature). A PET based new index was defined, which is called the thermally-perceivable environmental parameter difference, respectively for the radiant temperature and wind speed. By analyzing the simultaneous differences of radiant temperature, wind speed and air temperature between the monitored spots, it is shown that it was the wind speed and radiant temperature differences that were making significant differences in thermal comfort. This pilot study clearly indicates that wind amplification combined with shading effects can generate thermally comfortable conditions in the open ground floor beneath an elevated building, even on a sunny, hot summer day in a subtropical city. This finding helps to alert city planners of additional options available in precinct planning to encourage outdoor activities.