Abstract
In the post-pandemic era, Signaled Manual Airing (SMA, i.e. windows opening driven by real-time IAQ measurements) is still expected to play a role in schools, either independently or in support of mechanical ventilation (MV) systems, to meet more stringent regulatory requirements for indoor CO₂ levels. The present study in-depth evaluates the impact of SMA on improved levels of CO₂ but also its thermal impact in schools via a dedicated IoT-IAQ monitoring platform equipped with fully tuneable multi-threshold alarm schemes. An aged middle-school building, representative of a large amount of old existing school buildings in Italy (and Europe) and a Northern Italy location, were selected to investigate cold and high humidity winter conditions as the most critical for SMA. The mean indoor CO₂ difference with reference classrooms without alarms ranged from 20% to an impressive nearly 70%. We demonstrate a clear dependence on signalling mode and level of system usage learning. The best results were in fact obtained with acoustically enhanced signalling (acu-SMA).
As downside effect, operating SMA at even moderately cold latitudes caused also thermal discomfort during the coldest days, with worsened response to the alarms. The observed mean CO₂ levels maintained by classroom groups appear to be correlated with the average indoor temperature and its inverse product [CO₂*Tindoor]-1 to a cumulative fatigue function with memory effect, referred as " thermal behavioural fatigue". Bounds of generalization, further developments towards smart hybrid ventilation systems and most suitable Italian regions for pure SMA retrofitting are finally discussed.