Effect of Changing Temperature Setpoints on Sensation and Comfort in Tropical Region: A Case Study of Air-conditioned Offices in Thailand

摘要

Thermal comfort is a necessary study for indoor environment. In the tropics, people generally stay in a cool environment to maintain comfort, while the outdoor environment is hot and humid throughout the year. Many countries have proposed the temperature setpoint for living in a suitable condition and reducing energy. This study aims to survey the thermal environment in a shared office spaces both in an actual condition and an experimental temperature condition. Five offices in the Bangkok metropolitan, in Thailand were investigated from 2018 to 2019. The setpoint temperature was changed in the range of 22-26 °C to differentiate an occupant's satisfaction compared with previous studies. The questionnaire derived from the ASHARAE standard was distributed to occupants during the survey. The results indicated that the actual condition, the setpoint of case studies ranged between 21°C and 24 °C. Most thermal environments were in the 1.0 clo comfort zone rather than the 0.5 comfort zone, which was more suitable to occupants in the tropics. However, when changing the temperature, the thermal environments were shifted to outside the comfort zone in several cases owing to humidity exceedance. When increasing the temperature, thermal environments could be less controllable in low-operated HVAC (heating, ventilation, and air-conditioning) offices with wider ranges of both air temperature and relative humidity. Thermal sensation vote indicates a similar trend with the warmer-than-neutral vote of a previous study, while the colder-than-neutral vote was much lower. Considering 80% of the acceptable vote, temperature setpoints from 22 °C to 23 °C were suitable to occupants in in low-operated HVAC offices and from 24 °C to 25 °C in high-operated HVAC offices. Occupants in low-operated HVAC offices felt more discomfort than those in high-operated HVAC offices at the same setpoint. Furthermore, it was found that the comfort temperature ranged from 23.7 °C to 24.1°C, indicating the limit of changing to a warmer temperature. The limitation of temperature setpoint may arise from both air-conditioning system and occupants' cooling environment expectation.