Investigating students' subjective comfort with window-airing during the cold season: Thermal sensation, humidity, air movement, and perceived air quality

• The effect of natural ventilation rate on students’ comfort in winter was investigated. • Students are more thermally sensitive with forced window openings. • Effect of thermal sensation on comfort is more than 70 %. • Air movement sensation is related to ventilation rates. • Comfort model was proposed to determine indoor temperature settings with window-airing. Balancing the need for indoor air quality and thermal comfort during cold seasons is challenging for naturally ventilated schools. For students' health concerns, opening windows to ventilate during class time could be inevitable in winter, especially during flu season. However, there is a lack of field studies investigating its potential impacts on students' comfort. In this context, this study investigated students' subjective comfort with window airing in winter through a field study in the Mediterranean climate, with a total of 34 field experiments with different window opening scenarios conducted in two university classrooms. The study analyzed the effect of thermal sensation, humidity, air movement, and perceived air quality on students' comfort and identified correlated environmental parameters. The results showed that students' comfort was mainly determined by thermal sensation and air movement, while they were not very sensitive to indoor humidity and air quality. Their thermal sensation was found to be directly determined by the indoor temperature and not correlated with the outdoor temperature. Achieving the required ventilation rate would not cause obvious discomfort in terms of air movement. Moreover, the study validated 4 main adaptive PMV models (nPMV, adPMV, arPMV, and e pm PMV) and found them to be ineffective with forced window openings. The proposed comfort prediction model suggests that to meet the ventilation rate requirement, the indoor temperature should be maintained above 21 °C to avoid causing thermal discomfort problems. The specific practical recommendations are given in the conclusions.