Study On The Key Technology Of Thermal Environment And Occupant’s Thermal Comfort Analysis In Vehicle Cabins

With the development of city and the change of citizens’ lifestyle, vehicles havegradually changed to mass consumer goods from luxury in the past, and become anindispensable part of urban life. People spend more and more time in the vehicle cabins, thenthe thermal environment in vehicle cabins has aroused wide attention from consumers,researchers and car manufacturers. The thermal environment in vehicle cabins is closelyrelated to occupants’ thermal comfort, the air temperature, relative humidity, flow velocity,mean radiant temperature and other environmental factors are known to afect the ridingcomfort of occupants. On the other hand, the thermal environment in vehicle cabins and theoccupants’ thermal comfort are seriously affecting the fuel economy of the vehicle, especiallyfor the electric vehicles. All the energy used for the cabins heating or cooling in electricvehicles is supplied by the main battery which is expected to be used to drive. Operation ofthe air-conditioning system thus has a major influence on battery’s cruising range, which isone of the bottlenecks to restrict electric vehicle’s development. Under this background,thermal environment and occupant’s thermal comfort in vehicle cabins research is not onlythe urgent need to improve the energy efficiency of the vehicle, reduce the impact of theexternal environment on the interior thermal environment, then to achieve scientific andefficient thermal environment thermal management in vehicles cabins; but also fordevelopment of comfortable, energy-efficient thermal environment standards in vehiclescabins providing a scientific basis and theoretical guidance, it has far-reaching significancefor constructing energy-efficient, comfortable and safe vehicles cabins environment.With comprehensive reviewing of the thermal environment and occupant’s thermalcomfort in vehicle cabins research in open literature, this paper analyzed and summarizedtheir advantages and limitations, thus proposed to build a complete transient thermalenvironment and occupant’s thermal comfort analysis system as the main line, put forward theresearch contents in this paper. Firstly, with the purposes of understanding the basic thermalconditions in the cabin of a typical Mittelklasse, the solar radiation inside and outside thecabin, the distribution of temperature and humidity and other environmental variables underdifferent climate in south China were experimental measured and analyzed. Furthermore, themeasurement data would provide the analysis basis and validation data for the subsequentthermal environment numerical study.According to the deficiencies of current occupant’s thermal comfort evaluation methodsin the vehicle cabins thermal environment, this paper tested the skin temperature of occupant’s head, chest, abdomen, back, upper arms, lower arms, hands, thighs, legs and feet under thetransient and non-uniform thermal environment in the cabin, while using the ASHRAE7-points scale to evaluate the local thermal sensation of corresponding body parts, then usingthe mathematical statistical analysis method to investigate the relationship between the skintemperature and the local thermal sensation of corresponding body part. Finally, establishing anew objective occupant’s thermal comfort evaluation methods based on the occupant’s skintemperature, providing scientific and feasible evaluation method for the follow-up study inthis paper and making up the blank of domestic occupant’s thermal comfort evaluationmethod.Based on the conclusions of experimental study and according to the heat transfermathematical model of car body, the numerical calculation model was established andvalidated in this paper. Then, the solar radiation, the wall emitting radiation and theconduction heat transfer process, etc. on the interior wall were simulated; the wall temperaturedistribution and the heat flow flux of different heat transfer process were calculated throughthe established numerical model. Based on the numerical results, this paper, furthermore,analyzed the main influencing factors of surface thermal environment in vehicle cabins. Onthe basis of the benchmark model, this paper investigated means to reduce the influence ofsolar radiation on the thermal environment in vehicle cabins by changing car body features.The resulted showed that it can effectively reduce the impact of the external environmentalconditions on the vehicle cabins by changing the window glass optical properties as well asthe surface characteristics of the car body. These conclusions would provide valuablereferences for the vehicle design and the occupant’s thermal comfort study.In the aspect of “temperature-flow” distribution characteristics investigation in vehiclecabins, this paper firstly theoretically analyzed the computational fluid dynamics model andthe boundary layer treatment approach, discussed the influence of natural heat transfer andobtained the simplification basis of the numerical approach of vehicle cabins. Then couplingthe solid wall heat transfer and the fluid flow and heat transfer model, this paper established acompleted coupled numerical model of thermal environment in vehicle cabins, which canconsider the influences of external environment conditions. With the coupled numericalmodel, this paper simulated the “temperature-flow” dynamic characteristics in vehicle cabinsin the process of air-conditioning refrigeration under south China climate and analyzed thefluid flow and temperature dynamic distribution inside the cabin as well as the generalguidelines of the cabin’s thermal management design.Finally, according to the human thermal regulation theory and mathematical model, based on the occupant geometric model this paper established an occupant thermal regulationnumerical model, this model divided the body of occupant into14different components, andeach component was subdivided into four levels. Then coupling the occupant thermalregulation and the thermal environment numerical model, this paper established a completedcoupled numerical model of occupant’s thermal comfort analysis. With the coupled thermalcomfort analysis model, this paper calculated the occupant’s skin temperature under thetransient and non-uniform thermal environment in vehicle cabin, and used the establishedoccupant’s thermal comfort evaluation method to detailed analyzed occupant’s thermalcomfort in the process of air-conditioning refrigeration, and discussed the general law of theoccupant’s thermal sensation then the thermal comfort in vehicle cabins.The thermal environment coupled simulation methods, the occupant’s thermal comfortevaluation method, as well as the main conclusions obtained in this paper, solved some keycommon technologies, rules and design principles during the thermal environment andoccupant’s thermal comfort analysis in vehicle cabins, enriched and improved the existingresearch system, had a good theory and engineering application value in vehicle design.