Bedroom ventilation and sleep quality

Xiaojun Fan

Research output: Book/ReportPh.D. thesis

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Abstract

Sleep plays a vital role in maintaining human health and well-being. Previous studies have documented that poor indoor environmental quality (IEQ) in bedrooms disturbs sleep quality, but they were mainly focusing on temperature, noise and light; less attention has been paid to indoor air quality (IAQ) in bedrooms as an essential environmental quality factor. IAQ has been shown to affect human health and performance over the past decades when people are awake. Only a few studies have shown that air pollutant exposure during the night affects sleep quality, and most of them have focused on the effects of ambient (outdoor) air pollution. Research is lacking on how bedroom ventilation and IAQ affect sleep quality and thus next-day cognitive performance and well-being. The present work has attempted to fill this gap.

The main objective of this dissertation was to examine how bedroom ventilation affects sleep quality and next-day cognitive performance. The specific objectives included: 1) to quantify the current ventilation levels in actual bedrooms; 2) to estimate the CO2 emission rate from sleeping people that can be used to design, control, and operate bedroom ventilation systems; 3) to recommend ventilation rates for bedrooms that will not disturb sleep quality; and 4) to explore ways to improve bedroom ventilation when mechanical ventilation systems are not installed.

A series of experiments were conducted, including climate chamber studies, cross-sectional studies, and field intervention studies. Specifically, a laboratory chamber study was conducted with 11 subjects to measure the CO2 emission rates from sleeping people and to investigate the effects of increased temperature and reduced ventilation on CO2 emission, sleep quality and the next-day cognitive performance. Some of these findings were later verified in a four-week-long field intervention study in 29 bedrooms in Belgium where the ventilation rates were remotely controlled by the existing extract ventilation systems; the air entered into bedrooms was delivered by trickle vents installed on the windows. A cross-sectional study was conducted in 84 bedrooms in Denmark to measure the ventilation rates during sleep and to examine whether they impact sleep quality; the measurements lasted for one week. The participants were asked to keep the bedroom settings of their bedroom windows and doors unchanged throughout the measurement period. Subsequently, another field intervention study was carried out in 64 bedrooms participating in a cross-sectional study; measurements were made for an additional week. The intervention was made by opening the windows or internal doors if they had been closed in the first week or closing them if they had been open, to investigate the effects of these interventions on bedroom IAQ, sleep quality and next-day performance.

The results from the experiments in the laboratory and in actual bedrooms consistently show that inadequate bedroom ventilation and consequently poor bedroom IAQ negatively affect sleep quality; they also show that this may affect next-day cognitive performance. Specifically, the results of chamber studies with sleeping people showed that when ventilation with outdoor air was reduced (as demonstrated by the increased mean CO2 concentration from 800 ppm to 1,700 ppm), the sleep onset latency increased indicating reduced sleep quality. Self-reported next-day cognitive performance was higher after sleeping with increased ventilation, but it did not change at low ventilation. The analyses of the results from field intervention studies in Belgium showed similar results. The results from 12 bedrooms indicated that when the ventilation was reduced so that mean CO2 concentration increased from 856 ppm to 1,927 ppm, shorter deep sleep, longer light sleep, and more awakenings were observed. Extended analyses of the results from 23 bedrooms showed that when the ventilation was decreased so that the mean CO2 concentration increased from 812 ppm to 1,369 ppm, deep sleep was significantly reduced. In the field intervention studies in Denmark, when the windows were open, the bedrooms were ventilated with outdoor air so that the mean CO2 concentration increased from 761 ppm to 1,820 ppm, sleep duration was significantly longer than when the windows were closed. Objectively measured cognitive performance improved after sleeping with windows open (the CO2 concentration was 761 ppm), but it did not change after sleeping with windows closed (the CO2 concentration was 1,820 ppm). In addition to the effects of bedroom ventilation, the chamber studies also showed that increasing the room temperature from 24°C to 28°C, self-reported sleep quality significantly decreased as indicated by subjective ratings made on the Groningen Sleep Quality Scale (GSQS). The subjects also reported feeling more fatigue and sleepier after sleeping at 28 °C compared with 24°C.

Because CO2 is used as a marker of ventilation and IAQ, the design of ventilation systems requires a knowledge on the rate of occupant CO2 emission, but very few measurements have been made on sleeping people. The present dissertation bridged this gap by measuring CO2 emission rates from sleeping people in the chamber. It was on average 11.0 ± 1.4 L/h per person; this emission rate is for healthy adults who did not suffer from chronic sleep disturbance. The measured CO2 emission rates were not affected by a change in temperature from 24°C to 28°C or when the ventilation was changed so that the mean CO2 concentration changed from 800 ppm to 1,700 ppm. Small differences between the sexes were observed: the CO2 emission rate was on average 11.6 ± 1.0 L/h per person for males and 10.7 ± 1.5 L/h per person for females.

The results from the cross-sectional studies showed large variations in bedroom air change rates (ACHs) at night. The median ACH was 0.4 h-1 and the interquartile range (IQR) was 0.2-0.9 h-1. 67% of the measured bedrooms did not comply with the highest ventilation requirement of 0.7 h-1 stipulated by a European standard. Based on the results obtained in the present study and previously published data, it is recommended that bedroom ventilation with outdoor air should be 10 L/s per person. With an average bedroom size (i.e., 32 m3 in Denmark), this would correspond to an air change rate of around 1.1 h-1.

Sleeping with windows open reduced the CO2 concentration and the concentrations of TVOCs and PM10. Under this condition, the perceived air quality was improved, the air was rated fresher, and the odour intensity was reduced. Sleep duration increased under this condition and the self-reported sleep quality was better. Opening an internal door caused CO2 concentration to decrease from 2,362 ppm to 1,293 ppm but no other effects were seen. Sleeping with a window open is therefore recommended if no other methods can be used to ventilate bedrooms but only if no other negative effects are introduced such as elevated noise, PM levels, and draught discomfort.

This dissertation investigated bedroom ventilation and its effects on sleep quality. It bridges several current research gaps, provides valuable and helpful references for the design, operation and control of bedroom ventilation, highlights the importance of bedroom ventilation and the urgency of improving it, supplements current knowledge of the effects of bedroom temperature on sleep quality and next-day cognitive performance, and advances research on IEQ in bedrooms in the field of sleep research. All these may help to improve human health and well-being.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages169
Publication statusPublished - 2023

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