Thermal Environment and Comfort in Japanese Dwellings During Summer

Abstract

As people spend the majority of their time indoors, maintaining a comfortable and suitable thermal environment within buildings is essential for improving quality of life. Previous studies in Japan have investigated the wet-bulb globe temperature (WBGT) in indoor environments; however, studies primarily focused on residential buildings are lacking. Therefore, a field survey of 17 Japanese dwellings was carried out during the summer, for which a total of 1166 thermal sensation votes (TSVs) were collected from 23 respondents. The results show that the average indoor air temperature is 26.4 °C, which is 1.6 °C lower than the recommendation for summer temperature by the Japanese government. The variation in globe temperature and WBGT indicates that there are significant differences in cooling usage behavior, with a strong correlation between WBGT and indoor globe temperature. The acceptable indoor globe temperature exhibits a wider range in free-running (FR) mode than in cooling (CL) mode. The mean comfort temperature was 26.9 °C in FR mode, while it was 27.0 °C in CL mode. These findings indicate that the occupants felt comfortable at the high indoor temperature, suggesting there is a possibility to reduce the energy used for cooling.