Experimental Study on Thermal Comfort Towards Increasing Temperature Set-Points in Air-Conditioned Office Spaces in a Tropical Region: A Case Study in Thailand

Many countries propose indoor temperature set-points of air-conditioned offices to be comfortably sustainable and to reduce energy consumption. Even though there are recommendations for the optimum temperatureset-points, it is questionable how those values could be applied to the actual situation in a tropical region. This study aims to survey thermal performance and estimate thermal comfort in different set-points. In 2019, two air-conditioned office buildings were tested by increasing set-points from the actual value between 23 °C and 25 °C. Data loggers measuring thermal variables were installed in the offices and the questionnaire was distributed to evaluate human response. Considering the ASHRAE psychometric chart, thermal environments of both cases on the day of a normal set-point were low; falling inside in the 1.0 clo zone. Thermal environments gradually moved from the 1.0 clo zone to the 0.5 clo zone, however, some of them were out of both comfort zones due to high absolute humidity. The predicted mean vote (PMV) and the thermal sensation vote (TSV) show that the votes changed from the cold side to the neutral side, and the higher acceptance rate was at warmer temperatures. The comfort temperature calculated from Griffith’s method was found to be 23.6–25.1 °C which was lower than the measured operative temperature. Adaptive clothing behavior is described to confirm a better condition at warmer temperatures. A possibility of increasing cooling set-points at 24–25 °C is applicable to office buildings in the tropics to remain comfortable.