Integrated Environmental, Physiological, and Subjective Evaluation of Thermal Comfort in a Tropical School Classroom

Thermal comfort is crucial for students' concentration, health, and academic performance, yet classrooms in hot and humid climates often suffer from poor ventilation, overcrowding, and limited cooling systems. Existing standards such as 'The American Society of Heating, Refrigerating and Air-Conditioning Engineers' (ASHRAE) 55 and 'International Organization for Standardization' (ISO) 7730, which are largely derived from adult office environments, may not adequately reflect the needs and adaptive behaviors of school-aged children in tropical classroom settings. To address this gap, the present study investigates thermal comfort in a Malaysian secondary school classroom by integrating environmental, physiological, and subjective measurements. All data was collected across three sessions, capturing the progression of indoor temperature throughout the day under different cooling strategies. Environmental parameters were continuously monitored while simultaneously, heart rate data was recorded. A questionnaire survey was also distributed to the students to assess their thermal comfort in the classroom. Two phases were conducted at which a pre-installation phase to establish baseline conditions with only existing ceiling fans (C1), followed by a post-installation phase of using only air-conditioning (AC) at set-point temperature of 24°C (C2) and using only new ceiling fans (C3) to evaluate alternative cooling strategies. The findings show that during case study C1, the classroom was warm at 29.8 °C, the temperature decreased to 22.1 °C (C2), and maintained a comfortable 25.3 °C during C3, with more uniform air movement and acceptable air quality. The physiological data show that students had higher heart rates, lower heart rate variability (Root Mean Square of Successive Differences (RMSSD) = 20 to 25 ms), and higher stress (13 to 14) during C1, while the stress was lowered and RMSSD was improved for C2 and C3. Lastly, subjective data emphasized that in C1 conditions, students felt consistently neutral towards slightly warm with thermal sensation votes (TSV) values of 3.8 to 4.2, while C2 lowered TSV to 2.1 to 2.5, and C3 provided moderate improvement with TSV ranging from 3.2 to 4.0, showing both interventions improved thermal comfort. Thus, by combining objective measurements, physiological data, and subjective assessments, this study provides a comprehensive perspective on classroom thermal comfort dynamics under various cooling strategies.