A Numerical Model to Evaluate the HVAC Power Demand of Electric Vehicles

There has been a significant increase in demand for electric vehicles (EVs) in recent times due to existing environmental situations and an ever rising concern for energy. Due to the electrification of transportation and customer requirement, there is a concentrated focus on vehicle performance of EVs as a prime criterion. Amongst performances, range anxiety caused by the poor energy densities of the batteries, is one of the major drawbacks in these EVs. Possible mitigation for these scenarios includes, increasing the battery capacity, using dual energy sources and/or optimising the energy demands. After the propulsion system, auxiliary systems have an immense impact on the energy demands, the most significant being the heating ventilation and air-conditioning (HVAC) unit. With that in mind, this study develops a thermal model to analyse the required HVAC power for varying vehicle specifications. To benefit from the simplicity and versatility of one-dimensional (1D) numerical models, the passenger cabin of a city bus was modelled in Matlab Simulink. Next, empirical relations were employed to take external convection, wall conduction, solar radiation and passenger heat generation into account. Additionally, the influence of the forced internal convection of the conditioned air flow in the passenger cabin was modelled and analysed in a three-dimensional (3D) CFD simulation and then transferred into the 1D model. The results of the CFD simulation were also used to validate the 1D model in early stages of development. The model was then used to examine the effect of insulation and reflectivity optimization on the HVAC power consumption at different vehicle speeds. To the best of our knowledge, the model developed in this paper can be used to evaluate the required HVAC power, thus maintaining a required cabin temperature for various heavy vehicle specifications as well as boundary conditions.