Effects of indoor humidity on building occupants' thermal comfort and evidence in terms of climate adaptation

Similar as temperature, air humidity may affect people's thermal comfort and humidity adaptation may happen when people changing their living conditions. To provide evidence on both effect from humidity on people's thermal comfort and their humidity adaptation, a comparative study has been conducted in a controlled climate chamber. During the experiment, the air temperature was set as 25 degrees C and 28 degrees C respectively and the relative humidity was changing between 20% and 90%. There were twenty four participants involved in this experiment, with half living in High Humidity (HH) regions of China, such as Chongqing, for over 20 years, and another half recently moved to Chongqing from Low Humidity (LH) regions in northwestern China. During the experiment, mean skin temperature was measured as an objective important parameter and subjective questionnaires were used to subjectively collect people's sensations with respect to heat, humidity and sweating. The data collected demonstrated that people living in HH regions showed a better adaptive ability to humidity changes than those came from LH regions. Climate adaptation also reduced the sensitivity of HH subjects' thermal responses. When air humidity was over 70%, subjects started to show stronger thermal responses. Based on these results, an upper limit of humidity of 17 g/kg has been proposed for Chongqing, China. The results from this study will help to broaden the adaptive thermal comfort theory and can provide important references regarding to humidity control for buildings.