Effects Of Relative Humidity And Its Dynamic Change On Human Thermal Comfort

Relative humidity(RH)is one of the main environmental factors which affect human thermal comfort.For the design and operation of building environment,reasonable setting of RH is not only related to the human comfort,but also related to the consumption of building energy and the application of building energy-saving technologies.In addition,for some special indoor environment such as aircraft cabin environment and so on,suitable RH setting is one of the important ways to improve passenger comfort and the competition of commercial airliners.In view of the significant influence of RH on human thermal comfort,a lot of research work has been carried out in this field both at home and abroad,mainly aiming at the effect of RH or the coupling effect of RH and temperature.However,these studies are often difficult to obtain consistent conclusions,and even get the contradictory conclusions.This may be because that the effect of RH on the thermal comfort is also affected by other important non environmental factors,such as adaptability.And these studies do not distinguish the influence of RH in the steady environment and the change of RH in the dynamic environment.Moreover,few studies have focused on the effect of indoor RH dynamic changes on human thermal comfort.Based on the thermal comfort theory of neurophysiology and the relationship between human psychology,environmental parameters and human physiology in dynamic environment,human psychological state in steady environment can be regarded as the basis for the change of human psychological state in dynamic environment.Therefore,the comprehensive study in steady environment and dynamic environment is an important prerequisite for understanding the effect of RH on human thermal comfort.So,the effect of RH and its dynamic changes on the thermal comfort was studied in this paper and the mechanism was explored.We also established empirical models to predict the thermal comfort and obtained the comfort zone for RH and temperature.And the corresponding environmental control strategy was put forward.It can not only provide references for the operation of the indoor environment,but also provide a basis for further research on the influence of multiple factors such as RH and temperature,wind speed and adaptability on thermal comfort.On the basis of considering the human adaptability ignored in the previous literature,we further verified the influence of RH on thermal comfort,so as to get a deeper and more accurate understanding of RH.In this paper,subjects were exposed to steady environment with different temperatures and RH in climate chamber in different seasons.The results showed that RH had more obvious effects on thermal sensation in non-thermal neutral environment and showed no obvious seasonal differences.Compared with ET*and PMV,SET*can more accurately reflect the compensation effect of RH on thermal sensation.In addition,80%acceptable comfort zones were obtained in this study.The optimum humidity ranges in spring,summer and winter were 7.9-15.1 g/kg,3.3-18.8 g/kg and 2.9-12.8 g/kg(humidity ratio),respectively.The optimum temperature ranges were 21.8-26.2 ~oC,20.2-26.9~oC and 23.2-28.6 ~oC(SET*),respectively.This paper attempts to study the effect of RH on the thermal sensitive TRPs(thermo-receptor)protein to indirectly explore the impact mechanism of RH on human thermal comfort in steady environment from the perspective of molecular biology.Through the exposure experiments of mice at different temperatures and RH in the animal climate chamber,the regulation of thermal sensitive TRPs(Thermoreceptor)protein and HSP70 heat shock protein was studied.The results showed that the changes of RH levels resulted in significant changes in the expression of thermal sensitive TRPs proteins in the skin and brain tissues.This may lead to a difference in the body's perception of the intensity of thermal stimulation.Further analysis showed that RH affected the expression of thermal sensitive TRPs protein indirectly through the compensation effect on temperature,which was the molecular mechanism of the difference of thermal stimulation under different RH conditions.In this paper,the RH dynamic change was divided into RH ramps and RH step-chagne.In the climate chamber RH ramps at different temperatures in aircraft cabin was simulated and the changes of human thermal comfort and skin temperature was studied.The results show that RH ramps had obvious effect on thermal sensation,humidity sensation and perceived air quality especially when in a warm environment.In addition,the linear relationship between SET*and skin temperature and thermal sensation was established,and80%acceptable comfort zone of RH ramps was obtained.When RH ramps,the temperature should be set in the range of 21.3-25.8 oC(SET*),the humidity should be set less than 12.8g/kg(humidity ratio),and the air enthalpy should be set less than 54.7 kJ/kg.For RH step-change,the effect of clothing material must be considered.The exposure experiments of human body with different clothing materials in the RH step changed environment showed that the change of RH had a significant influence on human thermal comfort,and this influence is closely related to clothing material and environmental temperature.The transient effect of RH has the greatest influence on the thermal comfort for human body with cotton clothing,followed by polyester fiber clothing and 60%cotton+40%polyester fiber clothing.Based on the analysis of dynamic thermal comfort neurophysiology model,the thermal sensation of human body with the cotton clothing can be predicted by the skin temperature and the change rate of the skin temperature and that of human body with the other two clothing materials can be well predicted by the skin temperature alone.As for the influence of RH change in dynamic environment,human thermal physiology(skin temperature)and human heat loss have a good correlation with thermal comfort.So,in this paper,human/clothing dynamic heat and moisture transfer model was used to study the transient effect of RH on human thermal physiology and heat exchange,so as to indirectly explore the impact mechanism of RH dynamical change on human thermal comfort.The results showed that the model can well simulate the variation of human skin temperature and total heat loss in the process of RH gradual change and step change in cool and warm environment,and the results were in good agreement with the corresponding human body experiment.Therefore,the mechanism of RH dynamic change to the human thermal sensation can be explained from the aspect of human heat regulation and heat transfer.