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HOME > No.9, May 2017 > Using an air conditioner in summer may affect sleep quality

Using an air conditioner in summer may affect sleep quality

The research suggests that sleep quality may be affected by subtle insensible airflow By Kazuyo Tsuzuki
Associate Professor Ryoji Inada (left) with his students
Professor Kazuyo Tsuzuk (3rd from right, front raw) with her laboratory members

Professor Kazuyo Tsuzuki, in collaboration with the National Institute of Advanced Industrial Science and Technology and Asahi Kasei Homes, conducted research on the influence of the airflow from air conditioners on sleep. Using an air conditioner helps people to sleep better on sweltering nights. However, researchers found that when airflow is directed at a human body, even at an insensible velocity, it impacts on sleep conditions causing sleeping positions and affects the depth of sleep.

A study by a joint research team including professor Kazuyo Tsuzuki of Toyohashi University of Technology, the Department of Architecture and Civil Engineering, the National Institute of Advanced Industrial Science and Technology and Asahi Kasei Homes, has revealed that airflow from an air conditioner (AC) stimulates the human body while sleeping and impacts on sleep conditions even if the mean airflow velocity is lower than an insensible level. It suggests some AC settings may have an unintentional negative impact on sleep quality despite the comfort the person feels.

Urban warming blocks the temperature from cooling at night. It causes sweltering nights which impact sleep quality. However, high-quality sleep can still be realized if the room temperature is controlled effectively with an AC. The general belief is that having the AC on all night is bad for health. Also, quite a few of us experience chills while sleeping and awakening due to cold temperatures.

Airflow velocity in the sleeping environment can be configured with the AC. However, no data on airflow velocity measurement or research on the influence of AC airflow has been available up to now.

The research team, led by professor Kazuyo Tsuzuki, had the subjects sleep in two bedrooms set to the same temperature using ACs set at different airflow velocities, then made a comparison of the depth of sleep and body temperature control using electroencephalogram (EEG) measurements as well as subjective reporting by the subjects.

Figure 2.
Fig.1 Subject in experiment (before sleeping)

We call the air velocity of 0.2m/s or lower "insensible airflow", in a sense, the person remains unaware of such a low level of airflow. In this study, a comparison was made on the influence of two types of airflow, with mean velocities of 0.14 m/s (general AC) and 0.04 m/s (customized AC), both at a room temperature of 26 °C. Subjects felt cooler with the higher airflow velocity during wakefulness and sleep. However, no significant difference was observed in the feeling of comfort, length of sleep depth, skin temperature, rectal temperature or sense of warmth or coolness in each subject before sleeping. General AC lowers airflow when the room temperature reaches the desired setting and starts increasing the flow again when the temperature is higher. The study compared the correlation between the timing of the airflow starting to blow and body movement, heart rate and waking stage in sleep depth. The results found that the subjects have significantly greater body movements, an increased heart rate and a higher frequency of waking in the room that has the AC with a mean velocity of 0.14 m/s. This suggests the general AC may have some influence on sleep, as we discovered that subjects roll over or their sleep depth changes the moment cool air blows out.

This study was conducted using healthy adult male subjects. It implies that the cold airflow may have a greater impact on the overall sleep of female and elderly subjects with lower physical strength or a greater sensitivity to cold. The result of this study is expected to be a useful clue as to how to configure the airflow velocity of an AC to create a comfortable sleeping environment.

This research is the result of the study conducted by Professor Kazuyo Tsuzuki at the National Institute of Advanced Industrial Science and Technology. The research results were reported online in the Energy and Buildings journal on December 23, 2016.

This research was conducted with the Grants-in-Aid for Scientific Research #21300271 and #25282016 by Ministry of Education, Culture, Sports, Science and Technology and Japan Society for the Promotion of Science.


Morito, N., Tsuzuki, K., Mori, I., and Nishimiya, H. (2017). Effects of two kinds of air conditioner airflow on human sleep and thermoregulation. Energy and Buildings, 138,490-498.










本研究は、都築和代教授が産業技術総合研究所において実施した研究成果です。 また、本研究の成果は2016年12月23日Energy and Building誌にオンライン版で掲載されました。


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Researcher Profile

Kazuyo Tsuzuki
Name Kazuyo Tsuzuki
Affiliation Department of Architecture and Civil Engineering
Title Professor
Fields of Research Building environmental engineering / Environmental ergonomics