Enjoying sound sleep
even during nights of extreme heat

Why you may need a high-performance AC in your bedroom

Daikin Industries, Ltd.
Content Production: TOYO KEIZAI BRAND STUDIO

The season of hot, sleepless nights is once again upon us. According to the “Daikin 23rd Survey on Attitudes of Modern People Toward Air,” a survey conducted in 2017 by Daikin Industries of 1,300 men and women between the ages of 20 and 70, more than 60% of the people responded either that the hot summer nights make it difficult for them to fall asleep or that the summer heat causes them to wake up in the middle of the night.

Of the people who responded, 55.0% of them answered that they “often”, “sometimes,” or “rarely” argue with their partner over how to use the bedroom air conditioner (Daikin Industries, "Daikin 23rd Survey on Attitudes of Modern People Toward Air").

When you constantly suffer from lack of sleep, not only does it reduce your attention and concentration and affect your daytime performance, but it may also lead to bad health if you are able to recover from the fatigue that follows.

To avoid putting your health at risk, you may decide to use an air conditioner to get a restful night of sleep, but this may prove to be unexpectedly difficult. One reason is that if you live with your family then you may be unable to have your own preferred temperature setting.

The abovementioned “Survey on Attitudes of Modern People Toward Air” also found that 55% of the respondents said that they and their spouses had argued about the overnight temperature settings for the air conditioner.

“The temperature in which a person feels comfortable varies greatly for each individual, so it's difficult to say absolutely, but in general, men tend to find lower temperatures more comfortable than women,” explains Professor Hiroko Kubo of Nara Women's University. It is said that the appropriate temperature for restful sleep is between 26 and 28 degrees℃, but even if you set the air conditioner within that temperature range, heat and cold may feel differently according to the individual and living environment.

So, how can all family members be ensured of sound sleep until the next morning? Professor Kubo proposes, “To get a good night’s sleep, you need to look at the total picture, not just room temperature, but also humidity and airflow.”

Hiroko Kubo
Professor Ph.D.
Faculty of Engineering
Graduate school of Human Centered Engineering
Nara Women’s University

“It's also important to have deep non-rapid eye movement (NREM) sleep, which lasts for about three hours immediately after falling asleep,” says Professor Kubo. When people sleep, they typically alternate between deep NREM sleep, light NREM sleep, and rapid eye movement (REM) sleep stages in cycles ranging from about 80 to 120 minutes in duration.

In particular, the deep NREM sleep stage continues for a lengthy time just after falling asleep, whereas the ratio of the REM sleep stage increases at dawn, but if you can get a good amount of NREM sleep immediately after falling asleep then you are more likely to have quality sleep until morning. The key to entering this NREM sleep stage is changes in “body temperature.”

According to Professor Kubo, “Your body reaches its daily highest temperature in the evening and gradually falls over the course of the night to early morning. In particular, when you first fall asleep, your hands and feet warm up, and, as you enter deep sleep, your body will sweat to release heat and lower your body temperature. In contrast, at dawn, your body temperature rises, causing your sleep to be lighter, and you will gradually wake up.

When trying to sleep in a room with a high indoor temperature, your body will have trouble lowering its own temperature, making it difficult for you to fall into deep NREM sleep. Also, the high humidity in summer also hinders deep sleep. During the hot and humid Japanese summers, it is not uncommon for indoor humidity to rise to nearly 80%. So, if you sweat a great deal just after falling asleep, then that sweat will not easily dissipate in the hot and humid environment, and the resulting heat and discomfort will make falling asleep even more difficult.

Conversely, we hear many people complain, “I feel tired and groggy after sleeping with the air conditioner on at night.”

While many people use a timer function to manage health or save energy, Professor Kubo advises, “For restful sleep, I recommend running the air conditioner all night rather than using a timer.”

Homes and apartments typically allow heat to accumulate in the walls, floors, and ceilings during the day from the strong sunlight during the day. So, even if the air conditioner is set to 25 degrees℃, the room temperature may quickly rise to nearly 30 degrees℃ once the timer shuts off the air conditioner.

“A large part of the health issues caused by air conditioners arises from the cold air blowing directly on the body, or from the air conditioner repeatedly switching on and off to regulate the temperature, which cools the body down due to the low room temperature,” explains Professor Kubo. To prevent both the discomfort caused by heat and humidity and the chills caused by low temperatures, “You must not only control temperature but also humidity.

“If the room temperature is high, it will not feel unbearably hot if the climate itself is dry, and the humidity is low. On summer nights, you can get a restful night of sleep with a room temperature of 26 to 28 degrees℃ and a humidity level of around 50%.”

So, when the room temperature is slightly high, but the humidity is low, the room shouldn’t feel too uncomfortable. Still, if it is hard to sleep, try adjusting the airflow direction to blow air on the family members who are more sensitive to heat. Utilizing total control of temperature, humidity, and airflow can help create an environment where everyone can sleep comfortably.

“Even for those people with a high-performance air conditioner in their living room, many seem indifferent about the air conditioner that they choose for their bedroom and consider it to be a low priority. However, the bedroom is precisely where you need a high-performance air conditioner,” maintains Professor Kubo. In the daytime, you can adjust the temperature according to how you feel by changing the air conditioner settings to suit your preferences or by putting on or removing your jacket, but that's not possible while you're sleeping.

For many years now, HVAC&R specialist manufacturer Daikin Industries has been confronting summer air quality issues. One such issue involved “how to spend a tropical night comfortably.” In this way, Daikin has been taking on the challenge of creating spaces where everyone, regardless of differences in gender, age, or temperature sensitivity, can feel comfortable.

Daikin tackles research to create the perfect air for restful sleep

For example, a sensing technology detects user heart rate and uses it to determine sleep cycle. The room temperature is then adjusted to prevent users from feeling cold for the first three to four hours after falling asleep when their body temperature is low. Likewise, in the early morning, it prevents users from feeling hot in the morning when their body temperature is rising. In addition to temperature, research is conducted on comprehensive control that includes indoor light, sound, and other factors.

By having a high-performance air conditioner in your bedroom, you will be able to control all aspects of your sleep environment to ensure yourself of restful sleep.