Research On Thermal Environment And Human Thermal Comfort Of Commercial Vehicle Localized Air Conditioning System Based On Thermoelectric Cooling

The main function of the car air conditioning system is to adjust the temperature and humidity of the car cabin to meet the thermal comfort of the occupants.Commercial vehicles for long-distance transportation have a large cabin and fewer passengers.The human thermal comfort is closely related to the thermal environment around the human body only,and the thermal regulation of the entire car cabin by the air conditioning system will generate a lot of energy waste.Localized air conditioning is a regional thermal regulation technology,which focuses on the thermal comfort requirements of different parts of the human body,and studies the coupling mechanism and precise control method of the human body temperature field and the cabin flow field.Combined with the advantages of thermoelectric cooling,such as high reliability,no refrigerant,no moving parts,and no noise,the localized air conditioning system based on thermoelectric cooling has a good application prospect in energy saving,vehicle electrification and intelligence field.How to form an orderly airflow distribution under the influence of the limited cabin space and external complex environmental factors,improve the thermal comfort of the human body,and build a reasonable local thermal environment has become the main challenge for the application of automotive localized air conditioning.In this paper,the relevant research on the thermal environment of the vehicle cabin under the localized air conditioning of commercial vehicles is carried out,which mainly includes the following parts:(1)Construction of localized air conditioning system for commercial vehicles and analysis of thermoelectric cooling performance.The heat transfer process of the commercial vehicle cabin under natural conditions is analyzed.Based on the basic principle of thermoelectric cooling and the heat transfer law of heat exchangers,a small thermoelectric cooling device(TEC)is developed for the localized air conditioning system for commercial vehicles.The arrangement of the TEC is determined based on the heat load difference of the human body.Equipped with auxiliary accessories such as circulating cooling water circuit,a localized air conditioning system is built.A multi-field coupling model including thermoelectric effect,heat transfer,fluid dynamics is built.The dynamic simulation of the thermoelectric effect is realized,the dynamic response of various performance parameters of the TEC is obtained,and the variation law of the TEC outlet air temperature with the input current is revealed.Experimental tests are carried out to verify the accuracy of the coupling model and obtain the optimal current range of the TEC.(2)Research on the flow field characteristics of localized air conditioning cabin based on multi-point air supply.Considering the velocity inhomogeneity under the diffusion of multi-point jets,the air supply form of symmetrical cross jets for local air conditioning is proposed.The diffusion and attenuation laws of isothermal cross jets are analyzed,and the lateral distribution of fluid parameters with jet distance is obtained.The angle of the TEC airflow is determined.A heat transfer model of the commercial vehicle cabin is built.By analyzing the composition and difference of the heat gain of various parts of the human body under the isothermal jet,combined with the temperature attenuation law of the cross jet,the regulation strategy of the TEC outlet air temperature is obtained.The non-isothermal cross-jet air supply mode is formed,which can reduce the heat exchange difference between the left and right of the human body and improve the horizontal uniformity of the surface temperature.(3)Research on the thermal response of the human body under the multi-point air supply of local air-conditioning.Based on the established commercial vehicle cabin fluid-heat transfer model,a human thermal regulation model is further introduced to simulate the thermal response of the human body under nonisothermal cross-jet.The Fluent-TAITherm co-simulation platform is built to obtain the transient distribution of the cab flow field,and the accuracy of the fluid simulation was verified by the surface airflow temperature measurement experiment of the manikin.Then,the thermal response of the human body in the cab is analyzed under different ambient temperatures and different cabin humidity conditions,and the thermal regulation process of the human body under various working conditions is simulated to obtain the changing laws of human skin temperature,blood regulation and sweat volume.A preliminary assessment of human thermal comfort was carried out using the traditional PMV method.The results show that in the thermal environment constructed by localized air conditioning,high humidity reduces the evaporative heat dissipation and respiration heat dissipation of the human body,which increases the skin temperature and reduces thermal comfort.Finally,skin temperature measurement and sweat amount evaluation experiments are carried out to do the model validation.The results show that for the human body parts such as the hands and feet,which are at the end of the blood circulation and have large individual differences,the model prediction accuracy is not good,and the maximum deviation can reach 2.1 °C.But the skin temperature deviation of most human segments is within 1°C,the overall prediction accuracy of the model is well.Due to the differences of human body,the prediction accuracy of the model for the amount of sweating is not high,and it can be used to judge the sweating situation.(4)Evaluation and verification of thermal comfort of commercial vehicle localized air conditioning cabin.Based on the standard effective temperature SET and equivalent temperature Teq,combined with the localized air conditioning thermal environment of commercial vehicles,a thermal comfort evaluation index was established,and the relationship equation between thermal comfort subjective voting(TSV)and SET and Teq was obtained by fitting.Based on the surface area and local thermal sensitivity of each segment of the human body,the weights of the segments of the human body are determined,and the weighted average is used to obtain the overall thermal comfort index value.The subjective evaluation experiment of thermal comfort in localized air conditioning thermal environment is carried out,and a questionnaire was designed to invite volunteers to participate in the subjective evaluation and scoring.The results show that Teq is closer to the experimental value than SET in the overall thermal comfort evaluation prediction,but the difference between the two is small under colder conditions.In local thermal comfort prediction,the SET prediction value is more accurate.Combined with the difficulty of SET and Teq calculation methods to comprehensively judge,SET is more suitable for the evaluation of human thermal comfort in the local airconditioning thermal environment than the equivalent temperature.The effectiveness of local air conditioning in improving human thermal comfort is also verified by the experimental results.In this paper,the thermal environment and human thermal comfort of commercial vehicle localized air conditioning based on thermoelectric cooling are studied.A numerical simulation method of the special thermal environment of commercial vehicle cabin is proposed,and the construction mechanism of the local temperature control area of the cabin based on multi-point jet air supply is explored.The human body heat transfer process in the thermal environment is analyzed.The human body surface temperature distribution and variation law under the multi-point air supply jet are revealed.Finally,the precise regulation of human thermal comfort is formed.This research is used to solve some common problems in the practical application of automotive local air conditioning and cabin thermal environment research,and to explore new ways to apply automotive thermoelectric cooling technology.