Assessment of an Electric-Vehicle HVAC System Using Numerical Simulation and Experimental Validation

With the transition from Internal Combustion Engines Vehicles (ICEVs) to Electric or Hybrid Electric Vehicles (EVs/HEVs), most of the system aggregates and system parameters need to be redefined and recalibrated. This is mainly due to the change in power and transmission system. One of the critical system aggregates is heating ventilating and air-conditioning (HVAC) system as it directly impacts the car interior noise (other than passenger comfort) across all speed ranges. At low speed, interior noise becomes more annoying due to HVAC and electromagnetic noise from traction motor. However, at high speed other auxiliary noise sources are added up to the overall noise sources. Hence it becomes necessary to design and develop the HVAC system which should produce no abnormal noise and overall noise becomes low. The advancement of numerical simulation plays an important role in finalizing the HVAC design and also provides better insight of the products.

The present paper describes the numerical simulation and experimental validation of an electric vehicle HVAC with an aim to minimize the system losses and thereby reducing the overall noise level. Based on the requirements of an electric vehicle from an Indian car manufacturer, HVAC was designed considering compactness and less weight albeit fulfilling the desired performance. Numerical simulation was performed with the help of 3 – dimensional (3D) - CFD (Computational Fluid Dynamics) using CCM+ software. HVAC geometry was cleaned up and meshed appropriately. Areas with flow separation, flow vortices and high turbulent kinetic energy (TKE) were identified in the flow domain. After having deep investigation into those areas, HVAC was modified keeping a view to streamline and eliminate the secondary flows as well as reducing the overall pressure drop across the system. Experiments were carried out on this modified HVAC in a semi-anechoic chamber and noise data was captured. It is observed that a substantial improvement is achieved in overall system resistance and so in blower RPM and hence airborne noise level is reduced substantially.