Use of CO₂ feedback as a retrofit solution for improving air quality in naturally ventilated classrooms

Carbon dioxide (CO₂) sensors that provide a green/yellow/red visual indication were installed in pairs of naturally ventilated classrooms during normal school operation. During a two-week period in the heating and the cooling season, teachers and students were instructed to open the windows in response to the CO₂ feedback in one week and open them as they would normally do, without feedback, in the other week. In the cooling season, two pairs of classrooms were monitored, one pair with split cooling in operation and the other pair with no cooling. The resulting indoor environmental conditions in these classrooms and window opening behaviour were monitored. Children also reported their perceptions and symptoms. Resulting energy use was measured and used to estimate annual energy use. Providing CO₂ feedback reduced CO₂ levels. More windows were opened in this condition, and this increased energy use for heating and reduced the cooling requirement. Split-cooling reduced the frequency of window opening when no CO2 feedback was present, suggesting that classroom temperature is the driving factor for this behavioural response. Children liked CO₂ feedback; their perceptions and symptoms were somewhat improved with CO₂ feedback, although many of these changes did not reach formal statistical significance.