Experimental Assessment of Mechanical Ventilation Strategies on Indoor Air Quality in a School Classroom

Indoor air quality in school classrooms is strongly influenced by ventilation strategies, which in most existing buildings rely on manual window opening rather than controlled mechanical systems. This study investigates real indoor CO2 conditions in an Italian secondary school classroom equipped with a decentralised heat recovery ventilation unit (HRV) and evaluates the effectiveness of an automated control strategy in improving air quality. Continuous CO2 monitoring was conducted over two consecutive school years using calibrated sensors. During the first year, ventilation management was left entirely to occupant discretion; in the second, an automated scheduling strategy was implemented via a low-cost smart plug, progressively extending daily HRV operation from 1.5 to 5.0 h across the winter months. During the uncontrolled year, the HRV was never activated despite being installed, and 3.92% of total teaching time during the winter season was spent under Category IV conditions (Delta CO2 > 1350 ppm). The automated strategy during the winter reduced Category IV exposure to 1.63% and was associated with a 32.3% reduction in student absences. These findings confirm that the primary barrier to effective mechanical ventilation in schools is not hardware availability, but the absence of a structured operational strategy.