By Mary Kate McGowan, Associate Editor, News, ASHRAE Journal
A busy mind might not be the only thing to blame if falling and staying asleep is a nightly battle. The temperature and airborne pollutants, as determined by the heating, cooling and ventilation in a bedroom, might be the culprits.
People tend to fall asleep more quickly in bedrooms with comfortable temperatures and good air quality. These conditions also improve sleep quality, according to Pawel Wargocki, Ph.D., Associate Member ASHRAE.
For a good night’s sleep, the bedroom temperature should be set to a comfortable level before going to bed. Published research shows that the temperature is usually lower at bedtime than in the morning. The bedroom temperature’s slight increase during the night helps make the bedroom comfortable the next morning, said Wargocki, an associate professor at the Technical University of Denmark.
“If you really want to fall asleep quickly, avoid overheating,” he said. “When you wake up in a very stuffy environment, it’s not very pleasant.”
People also tend to sleep and feel better the next day when they sleep in a well-ventilated environment, he said.
If a bedroom’s window and door are closed for privacy and energy conservation purposes, the room’s ventilation rate is “so low that carbon dioxide (CO2), an indicator of poor indoor air quality (IAQ), routinely exceeds 2,500 to 3,000 ppm, which is three times the recommended levels,” according to published measurements.
INDOOR ENVIRONMENTAL CONDITIONS’ EFFECT ON SLEEP
Wargocki and his colleagues at the Technical University of Denmark examined the ventilation rate in a bedroom to see how it affected the sleep and next-day performance of a group of college students. The research showed that both sleep quality and next-day performance could be improved by the increasing the clean outdoor air supply rate in bedrooms.
“We know from other research that sleep quality generally affects how we perform the next day,” Wargocki said.
He presented the study during a seminar sponsored by TC 2.1, Physiology and Human Environment, and ASHRAE Standing Standard Project Committee 55, Thermal Environmental Conditions for Human Occupancy, at the 2016 ASHRAE Annual Conference in St. Louis.
Wargocki said only a handful of groups are researching indoor environmental conditions and ventilation in bedrooms, and the research is rarely performed in the subject’s own bedroom.
Many reasons exist for the lack of research in this complex field, including factors that affect sleep quality such as type of bedcovers, sleepwear, external noise disturbance and outdoor climate, according to Wargocki. Other reasons include people not allowing access to the most private part of their home and the lack of availability of simple, unobtrusive instrumentation for measuring sleep quality.
“Our study is one of the first studies of its kind available in literature because most of the research that has been done so far has been in sleep laboratories and in connection with other variables that could affect how well we sleep,” he said.
Wargocki and his fellow researchers performed two experiments in identical student dormitory rooms at the Technical University of Denmark. Sixteen students participated in each two-week period.
The researchers examined different interventions to improve bedroom air quality by increased ventilation and monitored the bedrooms’ carbon dioxide (CO2) levels as a marker of poor IAQ, according to Wargocki.
“We manipulated the ventilation rate in their bedrooms, and in the second experiment they were unaware of the changes we made,” he said. A window was opened in the first experiment, which was regarded as a pilot experiment, he said.
In the main experiment, the rooms had two conditions, increased ventilation and low ventilation (as if the windows stayed closed all night), each condition lasting for one week. Each subject experienced both conditions, in balanced order (i.e., experiencing 50% poor air quality first).
During the ventilated condition, an inaudible outdoor air supply fan was turned on automatically whenever the CO2 concentration increased to above 900 ppm. The fan was off all night during the “low ventilation” condition.
The students could open the windows during the day, but they had to remain closed during the night.
The CO2 concentration in each room ranged from 1,620 ppm to 3,300 ppm with fan off and from 795 ppm to 935 ppm with fan on, according to the research. The average CO2 concentration in the low ventilation condition was 2,395 ppm, with an average of 835 ppm, in the increased ventilation condition.
The students wore wrist-watch-type actigraphs that recorded arm movement to measure how long it took them to fall asleep, how often they woke up during the night, and how long they spent asleep; this information can be used to assess how well they slept.
The following morning, within 10 minutes of waking up, the students completed a self-assessment, online questionnaire asking how well they slept, how long they slept and other relevant questions. The students also performed two online tests that measured their concentration and attention, Wargocki said.
“What we observed was that when the fan was on and air quality improved, as indicated by lower CO2 concentration, it was easier for students to fall asleep, and they spent more time in bed when asleep,” he said, adding that those students also tended to perform better on the cognitive tests.
The students reported the air was fresher when they got up in the condition with fan on and that they felt better and more rested. However, they felt that their mouth and skin were drier, according to Wargocki.
Although the results were obtained with students, it is likely that the results can be generalized to the general population as well as other climatic regions, the research noted.
“Given these findings, it is reasonable to hypothesize that next-day performance would be better after sleeping in the conditions that provide better bedroom air quality. It was possible to show that this was the case, and to my knowledge for the first time ever,” Wargocki noted.
Because people spend almost one-third of their lifetime in a bedroom, Wargocki considers that there should be more research on how the bedroom thermal environment and IAQ affect sleep quality. He also said ASHRAE should play an active role in this endeavor.