Thermal comfort and indoor air quality challenges in mixed-mode classrooms: Year-Round field study insights from a hot-humid climate

Indoor air quality (IAQ) and thermal comfort in classrooms are critical for students’ health and performance. While air conditioning (AC) reduces heat stress and PM2.5 pollution, it increases energy consumption and contribute to long-term environmental burdens. Unlike air pollutants, which pose direct and long-term health risks, thermal discomfort can sometimes be managed in the short term through behavioral or psychological adaptation, although such adaptation is limited and influenced by environmental conditions. This study presents year-long field measurements from urban and rural elementary schools in Taiwan, assessing thermal conditions, CO2, and PM2.5 in mixed-mode ventilated classrooms. Natural ventilation improved CO2 levels but worsened PM2.5, creating a trade-off. Although individual parameters met acceptable thresholds, optimal indoor environmental quality was achieved only 13 % of the time in urban and 16 % in rural classrooms. PM2.5 had a greater negative effect than CO2 or temperature during naturally ventilated periods. In urban classrooms, AC use increased to 53 %, yet PM2.5 stayed within Grade I only 26 % of the time. CO2 scores were lower in urban classrooms (68) compared to rural ones (89), while thermal comfort scores were higher (90 vs. 73). These findings support integrated, location-specific strategies and promote thermal adaptation for healthier, energy-efficient school environments.