Research On Human Thermal Comfort And Evaluation Model Of Local Heating In Cold Environment

With the growth of national economy and the improvement of people’s living standards,the demand for heating in winter is further highlighted.In winter,the indoor thermal environment in some areas without central heating in China is extremely bad and needs to be improved urgently.It is shown that local heating in cold environment has a certain potential to maintain human thermal comfort.On this basis,this paper hopes to explore the effectiveness of local heating in improving human thermal comfort in low temperature environment,and put forward the scientific basis of using local heating to create comfortable thermal environment in low temperature environment.Firstly,the flow field of three kinds of convection and three kinds of radiation local heating equipment commonly used is tested and studied.Under typical working conditions,the temperature field characteristic parameters such as temperature distribution,temperature uniformity and maximum vertical temperature difference,are tested;airflow characteristics such as average air velocity,instantaneous air velocity and turbulence of various equipment are explored;and equipment performance parameters such as response time,heating temperature are also tested.It is found that when local heating by convected equipment,the temperature uniformity in the test area is related to the range and temperature of air supply,and the turbulence degree of air flow increases with the increase of air supply temperature.The response time of radiant local heating equipment is long,and the lower the surface temperature of radiant panel,the worse the heating effect.Secondly,in the artificial climate room,two local heating thermal comfort experiments were carried out on the sitting person.During the experiment,the subjective questionnaire survey was conducted on the subjects,and the skin temperature and clothing surface temperature of the subjects were continuously collected.The fan heater A(tower heater)and the irradiation heater were used respectively as heat sources during the experiments,and three ambient temperatures of 11℃,7℃ and 3℃ and two humidity of 30% and 50% were selected.Six background conditions in total were used in the experiments.It is found that in the process of local heating,the improvement effect of human thermal sensation is obvious,and the acceptability and satisfaction rate of subjects to thermal environment are greatly improved,which proves the effectiveness of local heating in improving human thermal comfort under low temperature environment.In the process of local heating,the skin temperature changes in different parts of human body are different.According to this,the human body is divided into three regions,namely,the core region(chest,back and abdomen),the middle region(upper arm,forearm,thigh and calf)and the end region(head,hands and feet).There is no significant difference in thermal sensation in the core region,but there is no significant difference in thermal sensation between upper arm and forearm,thigh and calf in the middle region.Then,the author compares the differences of subject’s overall thermal sensation vote as well as thermal sensation vote of head,back,chest,forearm,hands,legs and feet under convection and radiation local heating modes,and finds that there is no statistically significant difference,so a new method is established for two typical local heating modes.The mathematical relationship model between local thermal sensation and global thermal sensation,the influence weight coefficients are 0.2(head),0.08(back),0.04(chest),0.18(forearm),0.23(back),0.2(leg)and 0.19(foot).Finally,the thermal environment created by local heating in low temperature environment is a typical non-uniform thermal environment.The research shows that the thermal sensation in non-uniform thermal environment can’t well predict whether the human body is dissatisfied with the thermal environment.Therefore,a prediction model of non-uniform thermal environment dissatisfaction rate is established for local heating in low temperature environment.There are many environmental parameters that affect human thermal comfort in non-uniform thermal environment,so the equivalent temperature EQT is introduced here as an evaluation index.By equivalent sensible heat transfer between each part of human body and real non-uniform thermal environment to sensible heat transfer between human body and imaginary uniform thermal environment,the equivalent temperature ,of imaginary uniform thermal environment around each part of human body is obtained.And using the weights obtained in chapter 4,the overall equivalent temperature ,is calculated.Because the uniformity of human thermal distribution is an important factor affecting human thermal comfort.Based on the overall equivalent temperature ,and the maximum difference of local equivalent temperature?,,the prediction of thermal environment dissatisfaction rate is established which is in good agreement with the predicted value and proves that the model can correctly predict the dissatisfaction rate of human body with thermal environment during local heating in low temperature environment.By using this model,the ranges of ,and ?,are calculated when the PD is controlled at0～20%.Accordingly,a control logic of thermal environment is following put forward.