Field study on occupants’ subjective symptoms attributed to overcooled environments in air-conditioned offices in hot and humid climates of Asia

Indoor thermal environments in various offices in hot and humid climate regions of Asia are overcooled by air conditioning (AC) systems. Overcooled environments affect the occupants’ health and lead to excessive energy consumption. This study aims to clarify the association of occupants’ subjective symptoms with indoor thermal environments through field surveys conducted in Thailand, Indonesia, and Singapore. Indoor thermal measurement and thermal comfort surveys, including a questionnaire about thermal sensation and subjective symptoms, were conducted, targeting 599 occupants in 11 offices. The results showed that the mean indoor operative temperatures (T_op) for all cities were lower than 24°C. More than half of the occupants wore light clothing ensembles (0.30–0.59 clo). Therefore, 42.6% of the occupants’ calculated predicted mean vote (PMV) was less than −0.5. The correlation between indoor temperatures and the actual percentage of occupants who reported subjective symptoms (APSS) was analyzed. The lower T_op and standard new effective temperature (SET*), the more APSS was increased. In each temperature category of below 24.5°C, more than 30% of occupants reported subjective symptoms related to coldness. Therefore, the findings from this study suggest that raising T_op higher than 24.5°C is a first step to minimize the harmful effects of the cooling environments on the occupants’ health in this region. As the number of samples in the higher temperature range was insufficient in this study, further experiments in actual offices are necessary to verify the reduction of occupants who report subjective symptoms while raising the setpoint temperature.