Investigation On Thermal Comfort Characteristics And Improvement In Winter For Electric Vehicle Cabin

Vehicle is one of the most frequently used traffic tools,there are more attention focused on optimizing the thermal environment and occupant’s thermal comfort.With the initiative to save energy and reduce CO₂ emissions,electric vehicles（EVs）gradually have been taken more percentage in vehicle consumption market for the past decade.Compare to traditional fuel vehicles which heat the cabin by recycling the waste heat from engines,the heating system of EVs in winter consumes electric energy which shortens its driving range.On the premise of reasonably satisfing the heat demand of occupants in EVs,how to effectively reduce its heating energy consumption is worthy of further exploration by researchers and designers.In previous research,the optimization of occupant thermal comfort and EVs energy consumption is usually investigated separately,and the thermal comfort evaluation indexes and models are mostly proposed based on the building indoor thermal environment.Mean skin temperature（MST）is often used to evaluate human thermal comfort.Currently,there are many calculation methods for MST while the accuracy of the results is different.Moreover,in determining the weight factors of MST,the interaction between local thermal sensation and overall thermal sensation is rarely considered.In addition,as one of the effective methods to improve human thermal comfort,personalized comfort system（PCS）has been reported in the application of building indoor environment,while the application effect on passengers’thermal comfort and the impact on energy consumption of the vehicle still need to be explored.In this study,four heating modes（No heating,PCS,Air conditioning,PCS&AC）are tested.The influences of different heating modes on cabin thermal environment and occupants’thermal comfort are analyzed.The applicability of predicted mean vote（PMV）,standard effective temperature（SET*）and operating temperature(T_op)for evaluating the occupants’thermal comfort is analyzed,and the influence of PCS on EVs heating energy consumption in winter is explored.Besides,based on variation rule of subjects’thermal sensation voting and skin temperature,the applicability of 8 MST calculating methods are compared,and a simpler 3-point measurement method is proposed.The main research results of this paper are:（1）Only PCS heating cannot fully satisfy the occupant’s thermal demand in winter.Both AC and PCS&AC heating modes can improve the occupant’s overall thermal sensation and local thermal sensation to thermal neutral status or above.（2）The trunk part of the occupant（forearm,hand,thigh,calf,foot）is easy to be cool.Considering the actual driving and sitting state,the hand,foot and calf which will be contact with low temperature air directly,the heating demand of the above parts should pay more attention,which can not only effectively improve the occupant’s thermal sensation,but also reduce the unnecessary heating energy consumption.（3）Compared to the occupant’s actual thermal sensation votes,the results of PMV are lower.SET*and T_op both have good linear correlation with TSV,and SET*is more sensitive to the feedback of occupant subjective thermal sensation changes.According to the neutral thermal temperature results obtained from the regression equation,AC heating can reduce the temperature SET values of air conditioners by 2.8℃of SET*and 1.6℃of T_op with the assistance of PCS.（4）There is a linear correlation between the local skin temperature(₆))and the local thermal sensation vote（LTSV）.When-0.5≤LTSV≤+0.5,there is a big difference among the local parts’comfortable body skin temperature range calculated by the regression equation.In the heating design,the phenomenon of local excessive heating or insufficient heating should be avoided.（5）There is a linear correlation between the average skin temperature and the overall thermal sensation,but there are significant differences between the results obtained by different MST calculation methods.In addition,the revised 3-point method proposed in this paper（0.46 for chest,0.2 for head and 0.34 for calf）has the advantages of fewer measurement points,higher accuracy and higher sensitivity,and is more suitable for evaluating the internal thermal comfort of winter electric vehicles in hot summer and cold winter areas.