Improving classroom air quality and ventilation with IoT-driven acoustic and visual CO₂ feedback system

In naturally ventilated classrooms, the air quality and ventilation conditions rely heavily upon window and door opening behaviour of the class teacher. This study aimed to examine the impact of an Internet of Things (IoT)-based CO₂ self-surveillance display system (SAVE unit) on classroom air quality and thermal comfort. The visual-acoustic signalling of classroom ventilation conditions notified the class teacher for opening/closing of classroom doors and windows. The air quality data were collected across baseline (no alarm), S1 (visual alarm) and S2 (visual-acoustic alarm) scenarios. The alarm was triggered to notify a class teacher when CO₂ exceeded 1000 and 1500 ppm with different alarm schemes. Results showed a 19.5 % reduction in CO₂ with visual alarms and 19 % with visual-acoustic alarms. However, PM concentrations (PM₁₀, PM₂.₅, PM₁, PM₀.₁) increased due to window openings, though a daily average of PM₁₀ and PM₂.₅ remained within WHO safe limits. Teacher's decision to open or close windows was primarily influenced by classroom temperature. Higher CO₂ concentration was observed during colder days (S2) due to windows kept closed to avoid uncomfortable classroom temperature and excessive use of heaters. The SAVE unit helped to effectively lowered CO₂, but it also led to higher energy consumption due to heat loss from open windows. While natural ventilation improved air quality, it highlighted the need for balancing energy efficiency and thermal comfort. A holistic signalling system that integrates temperature, air quality, and ventilation parameters would better guide teachers in managing classroom ventilation. Additionally, a school-level ventilation protocol based on IoT-based signalling is recommended to ensure consistent and effective air quality management. This study underscores the importance of real-time data-driven ventilation strategies to optimise indoor air quality, reduce exposure to pollutants, and maintain a comfortable learning environment in classrooms.