Guidance to assess ventilation performance of a classroom based on CO2 monitoring

Since the COVID-19 pandemic, the ventilation of school buildings has attracted considerable attention from the general public and researchers. However, guidance to assess the ventilation performance in classrooms, especially during a pandemic, is still lacking. Therefore, aiming to fill this gap, this study conducted a full-scale laboratory study to monitor the CO2 concentrations at 18 locations in a classroom setting under four different ventilation regimes. Additionally, a field study was carried out in two Dutch secondary schools to monitor the CO2 concentrations in the real classrooms with different ventilation regimes. Both the laboratory and field study findings showed that CO2 concentrations varied a lot between different locations in the same room, especially under natural ventilation conditions. The outcome demonstrates the need of monitoring the CO2 concentration at more than one location in a classroom. Moreover, the monitored CO2 concentration patterns for different ventilation regimes were used to determine the most representative location for CO2 monitoring in classrooms. For naturally ventilated classrooms, the location on the wall opposite to windows and the location on the front wall (nearby the teacher) were recommended. For mechanically ventilated classrooms, one measurement location seemed enough because CO2 was well-mixed under this ventilation regime.