The effects of nightly shutdown of ventilation on indoor air pressure difference conditions and TVOC and radon concentrations in Finnish schools and day-care centres

In the Future Spaces research project, the impact of completely shutting down night-time ventilation on measured and experienced indoor air quality was examined in 11 Finnish day-care or school buildings. The study compared a normal situation comparison period defined by measurements during early winter to a consecutive altered situation comparison period defined by measurements during late winter. The effect was evaluated by comparing daily hourly mean values measured during the comparison periods. Modern ventilation systems in new buildings generally keep pressure differentials at a moderate level when properly adjusted and in most cases and the night-time ventilation shutdown does not have a big impact on the air pressure difference conditions over the building envelope. TVOC (Total Volatile Organic Compounds) and radon concentrations increased as expected at night when ventilation was stopped, but this had no significant impact on concentrations during occupied hours when ventilation was restarted 2–3 hours before the arrival of the first building users to ensure clean indoor air. Therefore, the effects on indoor air quality during occupied hours are not an obstacle to stopping ventilation during absence periods for example for energy saving reasons.