The effect of CO₂ controlled bedroom ventilation on sleep and next-day performance

Both sleep and good indoor air quality are generally considered to be important for human health and well-being. In the present study, sleep quality and next-day performance were measured in identical single-occupancy dormitory rooms located in a quiet area North of Copenhagen. The 16 international students participating as subjects, half of them women, were sleeping in their own rooms and maintained their habitual life style, with a few restrictions on alcohol and caffeine consumption. The subjects were exposed to two conditions, each for one week, with one high and one low rate of ventilation, resulting in average CO₂ levels of around 835 and 2395 ppm, respectively. A fan controlled by a CO₂ sensor was used to supply outside air to establish the condition with low CO₂ level. In the condition with high CO₂ concentration the fan was switched off. The subjects were instructed to adjust the electric heater that was installed below the window to ensure thermal comfort and average room temperature did not differ between conditions. The indoor environment was assessed based on online morning questionnaires and physical measurements of room air temperature, relative humidity and CO₂ concentration. The subjects’ sleep quality and next-day performance were assessed from subjective responses that were obtained by using visual analogue scales and the Groningen Sleep Quality scale, from one test of logical thinking, one diagnostic test of cue-utilisation, and in terms of movement data recorded on wristwatch-type actigraphs.

The results show positive effects of a higher ventilation rate on the subjectively assessed freshness of the air, on the subjects’ mental state and their feeling of being rested. There was also a significant and positive effect on the sleep efficiency measured by the actigraphs and the expected significant and positive effect on performance. However, there were some negative effects of the higher ventilation rate on the rated intensity of mouth dryness and skin dryness.