Influence of recent and long-term exposure to air-conditioned environments on thermal perception in naturally-ventilated classrooms

Air conditioning (AC) systems have been increasingly adopted as the main cooling strategy in Brazilian buildings, and this may affect people's response to hot indoor spaces. A field study was conducted in naturally-ventilated classrooms located in the northeast region of Brazil with the purpose of evaluating the subjective responses of the students as a function of different thermal backgrounds in relation to the use of AC. Indoor microclimatic variables were measured and a questionnaire was applied to the students, in which the thermal perception, air movement perception and cooling strategy preference were recorded. The thermal background of the participants in relation to AC was classified as follows: recent prior exposure (exposure to AC 1 h before the field survey), long-term exposure (routine experience of AC), and hours of AC exposure daily (in cases where long-term exposure was declared). Long-term exposure to AC influenced the thermal perception of the students and significant differences between exposed and unexposed students were observed for a temperature of 28–30 °C (standard effective temperature - SET). The influence of recent prior exposure to AC was negligible compared to that of long-term exposure. Among the students with experience of long-term exposure to indoor AC, those who declared exposure to 12 or more hours daily responded with the warmest thermal sensation (TS) values and the highest percentage of preference for AC as a cooling strategy. Hot discomfort was a key factor in the influence of long-term exposure on human thermal perception.