Thermal preference and comfort assessment in air-conditioned and naturally-ventilated university classrooms under hot and humid conditions in Brazil

The adoption of air-conditioning as a cooling strategy in hot and humid climates is common practice. In such locations, the overcooling of buildings in a concern as this leads to the dissatisfaction of the occupants and unnecessary cooling energy consumption. In this regard, a field study was carried out in the Brazilian city of São Luis (hot and humid equatorial climate) to evaluate the preferred and most comfortable thermal conditions in this context. The investigation took place in air-conditioned and naturally-ventilated classrooms, in which the environmental parameters were measured concomitantly with the application of questionnaires to the undergraduate students for thermal assessment purposes. There was a difference between the preferred thermal sensations (noticeably the “slightly cool”) and the ones considered most comfortable/acceptable (“slightly cool” and “neutral”, equally), which reflected in the preferred and most comfortable temperatures. Thermal comfort in naturally-ventilated classrooms was limited due to high air temperatures and low air speeds. The best thermal conditions in air-conditioned classrooms were found to be between 23–24 °C standard effective temperature, and more than 20% of the students were uncomfortable below 22 °C because of excessive cold when clothing insulation values were close to 0.3 clo. The results also showed that indoor air temperatures can be set as high as 26 °C without impairing thermal comfort, which could aid attempts to minimize the cooling energy consumption in this year-round hot and humid climate.