Thermal comfort in naturally ventilated and air-conditioned buildings in humid subtropical climate zone in China

A thermal comfort field study has been carried out in five cities in the humid subtropical climate zone in China. The survey was performed in naturally ventilated and air-conditioned buildings during the summer season in 2006. There were 229 occupants from 111 buildings who participated in this study and 229 questionnaire responses were collected. Thermal acceptability assessment reveals that the indoor environment in naturally ventilated buildings could not meet the 80% acceptability criteria prescribed by ASHRAE Standard 55, and people tended to feel more comfortable in air-conditioned buildings with the air-conditioned occupants voting with higher acceptability (89%) than the naturally ventilated occupants (58%). The neutral temperatures in naturally ventilated and air-conditioned buildings were 28.3 degrees C and 27.7 degrees C, respectively. The range of accepted temperature in naturally ventilated buildings (25.0 similar to 31.6 degrees C) was wider than that in air-conditioned buildings (25.1 similar to 30.3 degrees C), which suggests that occupants in naturally ventilated buildings seemed to be more tolerant of higher temperatures. Preferred temperatures were 27.9 degrees C and 27.3 degrees C in naturally ventilated and air-conditioned buildings, respectively, both of which were 0.4 degrees C cooler than neutral temperatures. This result suggests that people of hot climates may use words like "slightly cool" to describe their preferred thermal state. The relationship between draught sensation and indoor air velocity at different temperature ranges indicates that indoor air velocity had a significant influence over the occupants' comfort sensation, and air velocities required by occupants increased with the increasing of operative temperatures. Thus, an effective way of natural ventilation which can create the preferred higher air movement is called for. Finally, the indoor set-point temperature of 26 degrees C or even higher in air-conditioned buildings was confirmed as making people comfortable, which supports the regulation in China that in public and office buildings the set-point temperature of air-conditioning system should not be lower than 26 degrees C.