| A good sleep is essential for human body to recover from tiredness,to refresh mind,and to restore energy for maintenance of physical functions.Sleep quality is closely related to thermal environment,and high temperatures have negative impacts on sleep.Summer is long and hot,and air-conditioners and electric fans are commonly used at night in the hot-humid area of China,making temperature and air velocity the key thermal environment parameters for sleep of local people.Previous studies on constant temperatures revealed that a higher thermal comfort was related with a higher sleep quality,and those on dynamic changing temperatures provided some clues for establishing a better sleep thermal environment.It is also suggested that airflow has a great potential for reducing negative impacts of high temperatures on sleep and improving sleep quality.Meanwhile,local people in the hot-humid area of China showed special thermal adaptation and sleep habits.Based on the aforementioned,taking healthy young people in the hot-humid area of China as subjects,the present study is aimed to investigate the effects of air temperature,air velocity and their dynamic change patterns on sleep quality and thermal comfort by conducting climate chamber experiments,to determine the optimal thermal environment parameters and dynamic change patterns for sleep,and to provide scientific references for evaluation,design and control of sleep thermal environment in the hot-humid area.The experiments were conducted in the precisely controlled climate chamber at South China University of Technology(Guangzhou),with typical bedding system of a total insulation of 1.50 clo,and two multi-gear low-noise floor fans for producing airflow.Physiological parameters including PSG,skin temperature and body weight loss were measured.The subjective perceptions on sleep quality and thermal environment were collected through questionnaires.Two groups of 16 subjects(8 male and 8 female)with normal sleep and stable mood were exposed to the constant and dynamic experimental conditions,respectively.Each experiment lasted from 21:30 to 7:30 of the next day(10 h in total).The constant conditions were:(1)air temperature(Ta)27 ℃,relative humidity 50% RH,air velocity(Va)< 0.1 m/s;(2)Ta 29 ℃,50% RH,Va < 0.1 m/s;(3)Ta 29 ℃,50% RH,Va 0.7 m/s.The results showed that significant changes occurred in thermal sensation and comfort before and after sleep,and sleep quality was inevitably disturbed by hot or cold stimulus and not optimal under constant thermal environment.Meanwhile,a great potential of airflow utilization was identified on improving sleep quality.Accordingly,a new definition of thermal neutral temperature for sleeping people was proposed,and the optimal sleep thermal environment was investigated through dynamic changes of air temperature and air velocity.The dynamic air temperature condition was Ta 27 ℃ → 29 ℃,50% RH,Va < 0.1 m/s,and the dynamic air velocity condition was Ta 29 ℃,50% RH,Va 0.7 → < 0.1 m/s,both changing at the midpoint of an 8 h sleep(4 h + 4 h).The results indicated that under the dynamic conditions,thermal sensation maintained neutral both before and after sleep,and sleep quality and thermal comfort were both significantly improved compared to those of the constant conditions.It is therefore concluded that,27 ℃ → 29 ℃ is the thermal neutral temperature for sleeping people with a total bedding insulation of 1.50 clo,and 4 h 27 ℃ + 4 h 29 ℃(50% RH,without airflow)and 4 h 0.7 m/s + 4 h < 0.1 m/s(29 ℃,50% RH)are the optimal dynamic change patterns of air temperature and air velocity,respectively,for healthy young people in the hot-humid area of China. |
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