Thermal comfort in classrooms in the tropics

A field study was conducted in classrooms in Singapore, which were mechanically ventilated by fans, to assess their thermal conditions during the students’ lesson hours. Thermal comfort variables were measured at the same time when students and teachers answered a survey on their perception/sensation of the indoor climate. Objective data analysis showed that none of the classes had thermal conditions falling within the comfort zone of ASHRAE standard 55. Occupants found temperature range beyond the comfort zone acceptable. This suggests that the standard is not applicable in free-running buildings in the local climate. A new PMV model, which incorporates two common forms of adaptation-reducing activity pace and expectation, still showed discrepancy in predicting actual thermal sensations, especially at lower temperatures. Comparison of the various methods of assessing thermal acceptability showed that they produce widely disparate results, with the Bedford scale giving the highest level of acceptability. Classroom occupants generally accepted cool thermal sensations more readily than warm thermal sensations.