Study on Human Thermal Comfort within Lower-pressure Environment of Asymptomatic Altitude Reaction
|School||Xi'an University of Architecture and Technology|
|Course||Heating,Gas Supply, Ventilation and Air Conditioning Engineering|
|Keywords||lower-pressure environment of asymptomatic altitude reaction thermal comfort physiological indexes predictive model of thermal sensation dimensional analysis|
Comfortable and healthy thermal environment has active effects on people’s living, working and technical processes. Most of the studies on thermal comfort are carried out under normal pressure condition. The PMV-PPD index, which is widely used, is based on the so called stable and approaching to comfort environment and the testing people are from the Occident. The practical application shows that many factors like geography location, climate condition, living habit, architecture style, heating and air conditioning system style and even the economic level have important influence on human thermal comfort.The climate condition includes temperature, relative humidity, air-flow velocity and atmospheric pressure. Under special conditions, e.g. lower- oxygen lower-pressure altitude environment, it is worthwhile and necessary to do more research work about the applicability of PMV, because the physiological responses of human body and heat exchanges with environment are different from that in normal environment.This paper is supported by the National Natural Science Foundation of China (Project Number 50778091). It emphasizes on thermal comfort problems at altitude below 3000m, viz. asymptomatic altitude reaction regions. Within this region, physiology of human body adapts to the environment change without pathology variation. At high altitude above 3000m, mountain disease is the most chief problem to be solved by physiological and medicinal methods.Main contents of the thesis are as follows.(1) Theoretical research of thermal balance under lower pressure environmentThermal balance is related to environmental factors. Lower-pressure affects human energy balance in the aspects. The first aspect is the change of human heat transfer characteristics. The air density will change with air pressure, which leads to the change of convection and evaporation heat loss rate, and the total heat loss will change likewise. The second aspect is change of respiratory heat loss. According to physiological research, people’s respiration function will change when the oxygen content decreases. The third aspect is change of human metabolic rate due to different oxygen consumption under lower pressure environment.This paper analyzes the body’s convective heat rate under lower-pressure environment. The result shows that the convective heat rate reduces, while the evaporative heat rate increases under lower-pressure environment. New expression about the evaporation heat transfer under low pressure environment is deduced according to Lewis ratio based on the theory of heat-mass-transfer analogue.The respiratory heat loss and metabolic rate change are also studied. The influence of low pressure environment on body respiration and metabolic rate are discussed significantly. The body thermal balance equation under low pressure environment is deduced. Moreover, factors influencing PMV index under low pressure environment are analyzed.(2) Experimental studies on thermal comfort within low pressure environment of asymptomatic altitude reactionBased on orthogonal experiments, the influential importance of factors like temperature, air pressure and air velocity on mean thermal sensation (MTS) is studied under typical clothes heat resistance and activity level. The relationship between thermal comfort and the parameters are obtained. Air temperature is the first significant factor affecting MTS and then is air pressure and air velocity. So, under low pressure environment, the air pressure has direct and important effect on thermal comfort.MTS and thermal neutral temperature (TNT) are used to describe the change of thermal sensation under different pressures. The experimental results indicate that TNT is lower than that in normal environment. The heat exchange between human body and environment are also analyzed.In order to make clear the relationship of all the factors and their effect on thermal comfort, the contrast experiment analyses are carried out. MTS increases when air temperature and mean radiant temperature increase. Under low-pressure environment, tiny air velocity (<0.3m/s) has little effect on MTS of people wearing heavy clothes close to thermal comfort. Under thermal neutral circumstances, relative humidity has little influence on MTS.MTS is compared with PMV index under different experimental conditions. The results indicate that the value and tendency of PMV index with pressure change deviate from the actual thermal sensation under lower-pressure conditions.Besides, physiological data of human body are tested. The significance of pressure influencing the physiological indexes and the trend of physiological indexes are acquired by using T-Test analysis, namely, the two sample equal-variance suppose and the means of two normal distribution test.(3) The found of predictive model of thermal sensation under low pressure environment of asymptomatic altitude reactionCalculation of PMV index is very complex and need to be solved iteratively on computers, which is a disadvantage in engineering application. More important, the PMV index deviates from the actual thermal sensation under lower-pressure environment. In this paper, the main influencing factors are changed to dimensionless parameters by dimensional analysis method. Combining with the experimental data, predictive model of thermal sensation within asymptomatic altitude reaction is founded.