HVAC Design in Electric Vehicles: Special considerations

A vital aspect of any cabin design is the thermal comfort of passengers, especially the driver. No passenger should experience high temperature variation when the air conditioner or heater is turned on. Passenger comfort depends on the velocity and temperature of air coming out of the HVAC unit. Interior system cabin designers use CFD to efficiently and effectively achieve target velocities and temperatures inside the cabin. In Electric Vehicles, however we face a couple of additional challenges compared to conventional ICE vehicles.

In conventional vehicles most of the noise is generated by the engine. This forces engineers to work quite a lot on engine noise reduction. However, because of a lack of an engine, electric vehicles are quieter. Ironically, this makes the HVAC noise more prominent from the point of view of the passenger’s comfort. Therefore, in EVs it suddenly becomes very important to take care of HVAC-generated noise.

Secondly, in an EV, batteries are the sole power generating device and the efficiency of the vehicle depends on how much additional load the batteries are experiencing. Compared to conventional vehicles where the engine is used for running the Air Conditioning units, in EVs the AC runs on battery power.

As engines generate a lot of heat during operation, this heat is always available for heating the air inside the cabin in one way or another. However, EVs need a heater to heat the cabin, especially in cold weather, putting additional load on the batteries.

The above points emphasize the fact that in EVs it is necessary to design all systems with greater efficiency than in conventional ICE vehicles. For improving efficiency of the HVAC, it is also important to have flow with as less of a pressure drop as possible so that power requirements can be reduced. Flow optimisation using CFD techniques can be a good option in such cases to predict pressure drops and optimise the design.