Effect Of Local Cooling On Thermal Comfort Of People And Sleep Quality

Local cooling has been shown to have the potential to adjust human thermal comfort.Previous studies on local cooling are mainly conducted with subjects in sitting posture.When in a sleeping posture,the distribution of blood flow and the contact area between human body and the environment are different.In this study,the effects of local cooling on thermal comfort were firstly investigated when people in a sleeping posture in a 30?environment.Thirty-six healthy adults participated into this experiment.Local cooling was applied to five parts,including the head-and-neck part,chest-and-abdomen part,upper arm,back and thigh,each for 10 min.The cooling conditions were separated by 30 min of ‘no-cooling'.Thermal sensation and thermal comfort were evaluated with visual analog scales.Physiological parameter(skin temperature,ECG and blood pressure)was measured during the exposure.The results show that: when people in sleeping posture,local cooling of the back is an effective way to improve thermal sensation and thermal comfort.The effects of local conductive cooling applied to sleeping people on thermal comfort and sleep quality were then investigated.Eighteen males slept in a climate chamber of hot environment for 4 nights,in no cooling,back cooling,head(neck)cooling,and back and head(neck)cooling conditions,respectively.Sleep quality was evaluated subjectively using questionnaires in the morning and objectively by analysis of electroencephalogram(EEG),electrooculogram(EOG)and electromyogram(EMG)signals continuously monitored during the sleeping period.The results show that cooling both the back and head(neck)parts resulted in the largest improvement on thermal comfort and sleep quality.Compared with no cooling,the subjects felt cooler and more comfortable,reported higher sleep quality,spent longer time in sleep,had lower number of awakenings,shorter sleep onset and longer stage N3 sleep and REM sleep when the room temperature was 32 oC.Cooling back alone also improved thermal comfort and sleep quality,although their effects are less influential than the back and head(neck)cooling.The mean sleep efficiency was improved from 84.6% in no cooling condition to 95.3% and 92.8%,which suggest very good sleep,in the back and head(neck)cooling and back cooling alone conditions,respectively.Cooling the head(neck)alone slightly improved thermal comfort and subjective sleep quality,and increased stage N3 sleep,but did not induce other improvement on sleep quality.Our results suggest that local conductive cooling applied to large body parts(back and/or head)of sleeping people could efficiently maintain good sleep and improve thermal comfort in hot environment.