Does window/door opening behaviour during summer affect the bedroom environment and sleep quality in a high-density sub-tropical city

To investigate the effects of window and/or door opening on sleep quality, a two-week field intervention study was performed in 50 bedrooms in the summer in a high-density city (Shanghai). Each participant slept as they did normally in their own bedroom during the first week and changed the state of windows or doors from open to closed or vice versa in the second week. Their bedroom environment and sleep quality were objectively measured. Available data from 256 person-nights in which the intervention was effective were used for analysis of window or door manipulation. The indoor carbon dioxide (CO₂) concentrations were lower and the air temperatures and PM_2.5 concentrations were higher when windows were open. The perceived air freshness and noise intensity were both higher and the duration of REM-sleep (Rapid Eye Movement sleep) was lower in this condition. No significant differences were found in other sleep quality indexes. These results suggest that in a high-density city, the increased indoor temperature, PM_2.5 concentration as well as noise caused by opening windows may disturb sleep and offset the positive effects of improving the ventilation. Thus, window opening should not be recommended as a universal way of achieving bedroom ventilation to promote sleep. Affordable retrofit solutions for bedroom ventilation should take these aspects into account.