Research On Differentiated Thermal Requirement Of Human Body And Thermal Environment Design Parameters For Sleep In Winter

Sleep is the major state in residential buildings,which takes about one-third of human life time.The thermal requirement for comfort is different between waking state and sleeping state in time scale,since the reduction of energy metabolism,the increase of thermal resistance around human body and the absence of behavioral adjustment during sleep.Besides,the thermal requirement difference is also reflected in spatial scale due to the restricted activity scope,and the influence of bed climate on human body becomes prominent accordingly.However,the existing standards of thermal environment design are pertaining to active waking state,and the thermal requirement disparity between active waking state and sleeping state has not been considered.In light of the current situation,field study and experiment in climatic chamber were conducted in the present study to explore the differentiated thermal requirement of human body in sleeping state.In addition,a theoretical model was established to analyze the sleep thermal environment quantitatively.The main research work and results are as follows:(1)Field study was conducted in non-heating residential building in Northwest China during winter,to investigate the usage patterns of bedding system and thermal requirement feature of residents during sleep in winter.Combined with experimental study in climate chamber,the coupling space characteristic of sleeping environment was illuminated.It was observed that the indoor temperature in about 71% of all the surveyed bedrooms was lower than 15°C,and the thermal resistance of bedding system was mainly in the range of 3.0~5.0clo.The discomfort percentage was no more than 15% when residents adopt bed warming methods to moderate the cooling effect on human body.The survey results revealed the importance of bed climate in sleeping thermal comfort,and became the basis and premise of experimental research.(2)Experiment was performed in climate chamber to analyze the thermal requirement difference and relevance between local part and the whole body.The results show that proper disparity in thermal experience between local body parts was observed beneficial to overall thermal comfort level.The skin temperature of trunk was higher than lower body part,and the skin temperature of the covered body should be higher than that of head.The thermal comfort zone of indoor environment perceived on the face was rather wider with indoor temperature range of 10.0~22.0°C,and it is 11.2~18.8°C for the covered body under typical winter bedding system resistance.(3)The two-node thermal comfort model was deduced based on thermal equilibrium theory,including the partial thermal sensation model(PTS)and whole body percent dissatisfied model(WPD).The PTS model predicted thermal sensation of head and covered body separately,and the WPD model associated the partial thermal sensations to make a comprehensive evaluation of the sleeping thermal environment.In addition,the heat dissipation characteristics during sleep was discussed.It was indicated that the heat transfer by conduction could not be neglected for sleeping state,about 30%~40% of total heat loss.(4)Based on the PTS-WPD model in the present study,the thermal environment evaluation method was proposed to qualify the indoor thermal environment in conjunction with bed climate,and a slide scale of physiological parameter was applied to improve the evaluation accuracy.Additionally,the thermal comfort zones for sleeping state were computed including thermal environmental parameters of indoor air temperature,air relative humidity,indoor mean radiant temperature and air temperature in bed climate.The results showed that the matching design of indoor thermal environment with bed climate could satisfy the thermal requirement of sleeping human body,and lower the indoor temperature simultaneously.The indoor temperature for sleep state was 5°C lower than the current international thermal environment design criteria,with bed climate in comfortable zone.This study innovatively proposed the two-segment model on the strength of disparate thermal requirement between head and covered body,and the coupled comfort zone and evaluation method of indoor thermal environment and bed climate were established.For buildings with conventional energy resource,the study results set theoretical foundation for energy supply on-demand.For buildings with renewable energy resource,the comfort zones of coupling sleeping space provide design basis for partial heating in time-spatial scale,which is benefit for ensuring thermal comfort and optimizing energy utilization simultaneously.