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Indoor environmental quality is essential for pupils` health, comfort, and academic performance. However, recent studies indicate that indoor air quality (IAQ) in classrooms is often inadequate. This observational study examines the impact of three ventilation concepts on IAQ and thermal comfort under real-life school conditions: manual window airing combined with CO2 traffic lights, decentralized mechanical ventilation, and centralized mechanical ventilation. Eight classrooms in three elementary schools were monitored from 10/2023 to 04/2024. Continuous long-term measurements covered CO2, PM2.5, VOCs, indoor air temperature, relative humidity and window opening states in the classrooms, and ambient data including PM2.5 at each school. Significant differences were found in all five indoor parameters across the three ventilation concepts. The decentralized ventilation group achieved the lowest CO2 concentrations (18–22% lower), while the window airing group showed the highest PM2.5 levels (mean of 6 µg/m3) and the lowest temperatures (21% of the time below 20 °C). Relative humidity tended to be too low for all concepts, particu-larly with mechanical ventilation (medians below 40%). Windows in the window airing group were opened approximately twice as long. The findings highlight the benefits of well-operated mechanical ventilation systems and underscore the importance of user awareness and system management.
Effective classroom ventilation is essential for indoor environmental quality (IEQ), com fort and health of schoolchildren, who spend substantial time indoors. This controlled observational study compared manual window airing (WA) with decentralized mechanical ventilation (DV) in six classrooms of two elementary schools during the winter infection period. Symptoms of upper respiratory tract infections, salivary biomarkers, well-being, perceived comfort, and classroom-level IEQ were assessed through questionnaires, saliva samples and long-term monitoring. Ninety-eight schoolchildren participated (64 WA, 34 DV). Symptom-based outcomes of the WURSS-K questionnaire showed consistently lower illness burden in group DV, with several parameters reaching statistical significance and an absolute risk reduction of 7.8%. Salivary immunoglobulin A (sIgA) concentrations were also significantly lower in group DV (approximately 39–59%, p ≤ 0.01). Sensitivity analyses showed positive associations of CO2 and PM2.5 with sIgA and indicated that PM2.5 exposure accounted for group differences. Comfort perceptions mirrored measured IEQ: DV classrooms exhibited warmer, more stable thermal conditions, lower CO2 and PM2.5, and slightly better thermal and draught-related impressions. Overall, decentralized mechanical ventilation supported favorable IEQ and comfort and may influence mucosal immune activity through reduced particulate exposure, complementing the observed reduction in symptom burden. A multidimensional approach integrating medical outcomes with continuous IEQ monitoring proved valuable and should be expanded in larger, balanced cohort studies.