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Numerous studies have proven that sleep is important. However, people find it hard to sleep especially when temperatures are rising. Fortunately, due to the invention of air conditioners, people can sleep comfortably and coolly at night. But according to a recent study, although air conditioners help people sleep comfortably, it also has been found to have a negative effect on sleep.

The study, conducted by researchers from the Toyohashi University of Technology, National Institute of Advanced Industrial Science and Technology, and Asahi Kasei Homes, investigated how air conditioner (AC) air flow affect sleep quality of people. In particular, the study examined what type of AC settings is best to ensure not only a comfortable rest but also ensure the quality of sleep of the people in the room with an AC.

The researchers tested two types of AC settings. The first setting has an air velocity of 0.4 m/s or what was considered in the study as lower insensible airflow. The second setting has an air velocity of 0.14 m/s or the standard setting of common air conditioners. Both air conditioning units were set at a temperature of 26 °C.

Ten healthy males participated in the study and their depth of sleep and body temperature were measured. An electroencephalogram (EEG) was used to get accurate measurements and subjective reports of the participants. Moreover, the study correlated the time the air conditioners started cooling the controlled room, the participants' body movements, heart rate, and sleep depth.

The results of the study found that the study's participants reported to experiencing cooler temperatures with the higher air flow velocity or the second AC setting during wakefulness or before sleep. In fact, the researchers found no significant difference between the two AC settings before sleep in regards to the participants' body temperature, feelings of comfort, skin temperature, the length of the depth of sleep, rectal temperature or sense of coolness or warmth.

Although the participants' reported feelings of comfort on both AC settings, participants experiencing the second AC setting were found to experience an increased heart rate, significantly more body movements, and higher frequency of waking up during sleep. This just proves that the common air conditioner settings have an effect on a person's sleep. Meaning the higher the air flow velocity of the air conditioner, the higher the negative impact it has on a person's sleep quality.

In fact, the study recommends the proper configuration of air conditioners to ensure not only comfort and coolness during sleep but also the proper sleeping environment. The study is published in the journal Energy and Buildings and is the first one to investigate the relationship of air flow velocity of air conditioners and sleep quality.