A joint research team from Toyohashi University of Technology, National Institute of Advanced Industrial Science and Technology, and the Department of Architecture and Civil Engineering published findings that showed air conditioning (AC) airflow stimulates the body during sleep, even when the velocity of the air is lower than an insensible level. The AC may be affecting sleep conditions. This indicates that some AC settings may have an unintentional negative affect on sleep quality, even if the person feels comfortable through the night.
Warming in urban areas blocks the temperature from cooling down at night. This leads to sweltering heat at night, which severely deteriorates sleep quality; however, the general belief is that better sleep quality can be achieved if the temperature in the room is controlled with an AC. Most people will leave the AC on all night, but there is a general scientific theory that this is bad for health. Additionally, many people will experience chills during sleep, which will cause them to wake up periodically.
The AC system can be set up to configure the airflow velocity in a room; however, no published data has looked at airflow velocity measurement or the influence of airflow to human health and sleep quality.
Professor Kazuyo Tsuzuki led the research team. Subjects were placed in one of two types of bedrooms, each with the same temperature but different airflow velocities. Scientists then compared the body temperature control and depth of sleep using an electroencephalogram (EEG) and subjective reporting by the participants.
Insensible airflow is defined as air velocity that is 0.2 m/s or lower. This means that the person in the room is unaware of the airflow level. For this research, a comparison was made between the two types of airflow: customized AC mean velocity of 0.04 m/s and standard AC mean velocity of 0.14 m/s. All rooms were set at room temperature.
Subjects reported they felt cooler with the higher airflow velocity during sleep and wakefulness. There was no observable difference between length of sleep, skin temperature, rectal temperature, comfort, or sense of coolness or warmth. Standard AC settings automatically lower the airflow velocity when the temperature reaches the setting. It starts to increase again when the temperature rises. The timing of airflow velocity and body movements were compared, along with waking stages, sleep depth, and heart rate.
The results of the study indicated that participants had more body movements, faster heart rates, and more nighttime awakenings in the standard AC room with a mean velocity of 0.14 m/s. This indicates that standard AC settings may influence sleep, as researchers found that subjects have varying sleep depth changes or will roll over once cool air starts to blow into the room.
Only healthy adult male subjects participated in this study. The findings and sample population imply that colder airflow may affect elderly, females, people with lower physical strength, and people with higher sensitivity to cold differently with regard to sleep quality. These findings are expected to help figure out a healthy airflow velocity that would create the best sleeping environment.
Research findings were published in the online journal, Energy and Buildings.
Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development. Her hobbies include hiking in the Rockies, cooking, and reading.