Occupants’ thermal comfort and perceived air quality in natural ventilated classrooms during cold days

Abstract

In north-west China, a number of university classrooms are natural ventilated during cold days when the prevailing mean outdoor air temperature is about 10 °C. This study investigated the students' thermal comfort and perceived air quality in natural ventilated university classrooms under such low outdoor temperature. 30 field-surveys were conducted in seven typical university classrooms during November 2017 in a sub-provincial city of Xi'an located in the north-west of China in the cold climate zone. A total of 992 responses from the university students ages between 17 and 22 years were received. The results showed that the thermal neutral temperature was 20.6 °C; the thermal comfort temperature range was from 19.5 to 21.8 °C; the occupants' preference temperature was 22.78 °C. The thermal dissatisfaction rate was lower than 10% when the indoor operative temperature ranges between 18.3 and 23.8 °C. The percentage of dissatisfied occupants for indoor air quality was higher than 20% in some cases and it was not related to CO2 concentration. Based on the survey results, it was found that the comfort temperature calculated by the aPMV model (China's thermal comfort model for free-running buildings) was higher than the experiment results. The occupant density affected the perceived air quality, but had no effect on thermal sensation. Moreover, the influence factors of perceived air quality including indoor temperature, enthalpy, thermal acceptability and thermal sensation were analyzed. Results showed that the occupants' acceptability of indoor air quality was mainly affected by thermal sensation.