THE EFFECT OF CO2 CONTROLLED BEDROOM VENTILATION ON SLEEP AND NEXT-DAY PERFORMANCE
People spend one third of their life sleeping, 12-14 hours/day during infancy and 7-8 hours/day during adulthood. Good sleep is generally considered to be essential for human health and well-being. Many factors are thought to influence sleep quality, among those the indoor environmental quality (IEQ) parameters which include: air temperature and relative humidity, air velocity, particulate matter concentration, illumination level, sound level and ventilation rate. Bekö et al. (2010) reported that 57% of the bedrooms of Danish children did not fulfil the minimum ventilation requirements stipulated in EN 15251 (2007). Studies by Tynjälä et al. (1999) and Meijer et al. (2000) of children in Finland and Holland respectively showed a strong correlation between sleep quality and the ability to concentrate the next day. Both studies show that good and refreshing sleep is an important determinant of general well-being among adolescents.
The objective of the present study was to investigate the effect of CO2 controlled ventilation on sleep quality and next-day well-being. The working hypothesis was that subjects would sleep better during the night and perform better the following day in the CO2 controlled ventilation condition.
Recorded on wristwatch-type actigraphs and from online morning questionnaires including the Groningen Sleep Quality scale, questions about the sleep environment, next-day well-being and SBS symptoms, and two tests of mental performance. Although no significant effects on the sleep quality scale or on next-day performance could be shown, there were significant and positive effects of an open window on the actigraph-measured sleep latency and on the subjects’ assessment of the freshness of the air, their ability to fall asleep and nasal dryness. There was a negative effect on reported lip dryness.
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.
The experiment reported in this paper is part of an on-going study entitled: “Energy-efficient bedroom ventilation that may improve sleep and next-day well-being” at the International Centre for Indoor Environment and Energy (ICIEE) of the Technical University of Denmark (DTU)
Peter Strøm-Tejsen, Pawel Wargocki, David P. Wyon, and Daria Zukowska
International Centre for Indoor Environment and Energy, Department of Civil Engineering, Technical University of Denmark.
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