Air change rates during sleep in Danish bedrooms

The ongoing project ‘Bedroom Ventilation and Sleep Quality’ investigates the effects of bedroom ventilation on sleep quality and next-day cognitive performance. As part of the project, 84 bedrooms in the Greater Copenhagen area of Denmark were inspected during the 2020 heating season. In the first week, participants slept under environmental conditions that they typically experienced during sleep; in the second week, they slept with the interventions made by opening/closing either the door, or window, or both. As an essential part of the study, the CO₂ concentration in bedrooms was continuously measured. The bedroom window and door status during sleep were obtained the following morning via sleep diary. The air change rates per hour (ACHs) in bedrooms were estimated using the occupant-produced CO₂ concentration decay method. Mechanical ventilation was rarely installed in bedrooms; extract ventilation in the bathroom and kitchen was predominant. Participants typically slept with both bedroom window and door closed. The median ACH was 0.40 h^-1 during sleep under habitual conditions. Opening either the window or door increased bedroom ACH during sleep, but window opening led to better ventilation than the door opening, which was verified by the intervention. These results suggest that the ventilation in most bedrooms is currently insufficient compared with the ventilation requirements prescribed by limited standards, highlighting the urgency to look at its impact on sleep quality and improve bedroom ventilation.