Effects of air temperature and humidity on sleeping women by the ventilation and air-conditioner, Japan

. The effect of ventilation system on the sleeping persons has not been well studied. This is because mechanical ventilation systems had not previously been widely used in residential buildings in Japan. However, 24-hour mechanical ventilation is now mandatory in highly airtight and insulated houses. This study compared the temperature and humidity in bedrooms using either regular mechanical ventilation or desiccant ventilation when the air conditioner was switched off by a timer. The experiments investigated the sleep quality, thermoregulatory responses, and thermal comfort of young woman participants during the sleeping period at night. The desiccant ventilation reduces the air temperature and humidity by 1 °C and 20% Rh, respectively. While the air conditioner was turned off, the women’s skin temperatures increased by about 0.5 °C, but did not increase awakenings, as a result, the sleep efficiency was maintained at 96%. Thermal and comfort sensations were obtained significantly on the cooler and more comfortable side with the desiccant ventilation system than without desiccant system.


Introduction
In summer night, the outdoor temperature does not always fall below 25°C in the urban area of Japan. Therefore, people need to use the air conditioning in their bedrooms to sleep well and comfortably. According to the results of a survey, some of people preferred to use air conditioning in their bedrooms for a first few hours while they slept [1]. Because it was found that the people prevented the body from being chilled or catching cold during sleep by the air conditioner. However, there were reports of the people waking up due to increasing air temperature (Ta) when the air conditioning was switched off by a timer.
The desiccant ventilation systems for residential buildings have been developed. Desiccant technology is a ventilation system in which moist outdoor air is passed through dehumidifying adsorbents to remove moisture, and the dried air is then brought indoors. In particular, in the case of high airtightness, high thermal insulation houses completed after 2003, mechanical ventilation is mandatory, so fresh air from outdoors is constantly flowing in.
The combination of desiccant system and air conditioner has not been well studied [2]. In particular, when air conditioners are used on timers, there is no research on how changes in temperature and humidity, as well as ventilation, are affected after the air conditioner is turned off, and how this affects people. In order to investigate the influence of ventilation systems on the indoor environments of a house, sleep experiments were carried out. Although women often complain about cooling due to air-conditioning [3], further data is considered necessary because sleep experiments conducted on woman subjects are limited. Therefore, in this study, sleep experiments were conducted on women in a house with a desiccant ventilation system to clarify the sleeping environment in summer and the effects on the human body during sleep.

Experimental Design
The experiment was conducted in a model house built in Toyohashi City, Aichi Prefecture, by Company S, which is an overnight experience type house (hereafter referred to as 'O House'). Tables 1. and 2. give an overview, and Fig. 1 shows the second-floor plan of the O house where the sleeping experiments were carried out from July to September. This experiment was approved by the Committee for Ethics Concerning Research with Human Subjects of Toyohashi University of Technology. This study was conducted in 2017. The experimental schedule consisted of running the air conditioner at 21:00 with the temperature set to 27 °C. At 23:30, the remote control of the air conditioner was changed to 26 °C and a timer was set for 2 hours. Participants moved to the bedrooms at 23:40, completed a pre-sleep questionnaire, went to bed at midnight and were awakened at 7am by the examiner. The air conditioning was switched off at 1:30 am by the timer.

Measurements
Measurements included bedroom air temperature, globe temperature, relative humidity and wind speed, which were taken near the bedside where the participants slept. The participants' sleep was measured by the Actigraph (AMI) to measure body activity during the experiments. Sleep variables such as sleep onset latency and midawake time were calculated by a software AW2 after the experiment. Skin temperature was measured at eight sites (forehead, chest, back, upper arm, dorsal hand, thigh, lower leg and dorsal foot) and the mean skin temperature was calculated using a formula of the Hardy-Dubois 7-point method. The thermal sensation (TS) was asked on a scale of 9 from very cold (-4) to very hot (+4 ), comfortable sensation(CS) was evaluated on a seven-point scale from very uncomfortable (-3) to very comfortable (+3), and the questionnaires were answered at bedtime and on waking. After waking up in the morning, the OSA sleep questionnaire was used to evaluate the subjective feeling of sleep during the sleeping period, as well as TS and CS during sleep.

Participants
Three participants slept one night. Two participants slept in the master bedroom and one in another room. Participants wore short-sleeved T-shirts and shorts. Totally 22 women participated, of whom 16 were university students (age 20-22 years) and 6 were office workers (age 26-52 yeas). The experiment consisted of three days in one week, alternating between desiccant ventilation and normal ventilation without desiccant ventilation.  Air temperature (Ta) and humidity variations (Rh) in the bedroom are shown in Fig 3 & 4. The Ta was approximately 25°C when the air conditioner was in operation and there were no differences between the different types of ventilation. The Ta increased after 1:30, rising to 28°C with desiccant ventilation and 29°C without desiccant ventilation on waking at 7:00. Rh was approximately 45% throughout the night with using desiccant ventilation, while it was 50% without desiccant ventilation when the air conditioner was running, rose to 65% one hour after the air conditioner was stopped, and remained almost constant thereafter. Fig.5. shows the changes in mean skin temperature during sleeping period. No significant difference was found between desiccant ventilation and mechanical ventilation without desiccant system. Mean skin temperature was similar while the air conditioner is running, however, increased more in mechanical ventilation. There were no effects such as increased mid-sleep awakenings, and there were few differences between humidity conditions in this room temperature range. When the air conditioner was turned off, the participants' skin temperature increased by about 0.5°C, but their mid-wake did not increase and their sleep efficiency was maintained at 96%.

Fig.7. shows average and SD of thermal sensation (TS).
There were no significant differences in TS between conditions before sleep. however, significant differences were found in TS during sleep (P<0.01) and after waking (P<0.01). The participants reported cooler side with desiccant ventilation and hotter side without desiccant ventilation. Similarly, as for thermal comfort sensation (CS), there was no difference in CS with or without desiccant system at bedtime before sleeping, and the participants showed the comfortable side. After awaking up and during sleeping, there was significant differences (P<0.05) with no desiccant system being on the uncomfortable side and with desiccant system being on the neutral sensation.

Individual differences
Participants in the two conditions were grouped according to their sensitivity to heat and cold based on their self-reports. The number of participants' thermal preferences is shown in Table 3. Table 3. Participants   Fig. 9. Thermal sensation for thermal preferences Fig.9. & 10. show the mean and SD of TS for the four groups classified by the two conditions of people are sensitive to heat and people are sensitive to cold with desiccant ventilation and without desiccant ventilation. No difference was found in TS without desiccant ventilation in both people are sensitive to heat and people are sensitive to cold. However, while people are using desiccant ventilation. People who are sensitive to heat felt cooler than people are sensitive to cold while using desiccant ventilation. As for CS, people are sensitive to cold felt more discomfort using mechanical ventilation without desiccant than using desiccant ventilation.

Discussions
During the summer nights, outdoor temperatures dropped but did not fall below 25°C (77°F). Relative humidity, however, remained above 80% overnight, resulting in muggy conditions in the urban area. Indoor relative humidity was 70% when the desiccant system was not in use, because outside air was introduced directly into the room through mechanical ventilation. On the other hand, the desiccant ventilation system kept the relative humidity at about 45%. In particular, the desiccant ventilation system maintained 45% after the air conditioner was turned off by the timer setting. In other words, desiccant ventilation was able to reduce humidity by 20% with or without the air conditioner. The young female participants had 95% sleep efficiency with no increase in mid-awakenings at 28~29°C and 45~65% relative humidity. The mean skin temperature was also maintained at 34.5°C with and without desiccant ventilation, and even after the air conditioner was turned off on a timer. However, thermal and comfort sensations were obtained significantly on the cooler and more comfortable side with the desiccant ventilation system than without desiccant system. Comparison by thermal preference showed that people who are sensitive to heat felt cooler and more comfortable than people who are sensitive to cold when using desiccant ventilation. Sleep experiments on women have very few data due to problems with the menstrual cycle, and we were unable to find any previous studies that examined skin temperature and sleep parameters such as sleep efficiency as well as the effects of humidity. Further experiments should be conducted in the future to accumulate more data.
As thermoergulatory responses and sleep parameters of naked young men were investigated in hot and humid environments, the sleep efficiency was 73% at 35°C 75% [4]. However, there was no significant difference between 29°C 50% and 29°C 75%, with sleep efficiencies of 92.6% and 88.7%, respectively. Since the participants were young women in this experiment and their metabolic rate was lower than that of young men, the effect of humidity may not have been apparent. Nevertheless, the effect of humidity on sensory perception of warmth, coolness, and discomfort was revealed, suggesting that further analysis is necessary.
In the future, we would like to further examine comparisons with male participants and the effects of different cooling times on the human body during sleep.

Conclusions
The desiccant ventilation reduces the air temperature and humidity by 1 °C and 20% Rh, respectively. While the air conditioner was turned off, the participants' skin temperature increased by about 0.5 °C, but did not increase awakenings, as a result, sleep efficiency was maintained at 96%. Thermal and comfort sensations were obtained significantly on the cooler and more comfortable side with the desiccant ventilation system than without desiccant system.