Cabin and Battery Cooling Performance Trade-off in an Electric Vehicle 2020-28-0004

Electric vehicles (EVs) carries two main anxieties in users which are its range and battery life, hence these are important parameters to be taken care of during electric vehicle development. Range of EV depends on many parameters such as vehicle weight, heating ventilation and air conditioning (HVAC) system, battery cooling system (BCS), traction cooling system (TCS) and other electrical loads, which consumes power from a High Voltage (HV) battery. Severe hot ambient in India requires a big size HVAC system, on the other hand, the battery pack needs refrigerated cooling system to keep its temperature in control. Hence, the major parasitic consumers in an EV are HVAC and BCS. In order to enhance the overall efficiency, a trade-off between these two systems is crucial, as both the systems are served with common compressor and condenser in dual loop refrigerant circuit.

This work comprises of experiments done on an EV with dual loop refrigerant circuit, which has common compressor and condenser unit, where the HVAC circuit has a separate thermostatic expansion valve (TXV) with an evaporator installed for cabin cooling and a separate TXV with chiller installed for battery cooling. Further, batteries are cooled through a secondary loop comprising of coolant pump, coolant and cooling plate on which the batteries are mounted. Stated arrangement avoids multiple refrigerant pumping devices, heat exchangers and saves cost, weight and space, but it comes with a limitation/complexity on individual controls for both HVAC and BCS. This imposes a challenge in meeting the cabin and battery cooling requirement in severe ambient conditions without compromising the target vehicle range.

This paper discusses about thermal strategies such as fan duty, compressor speed and duty optimization without compromising the vehicle range. Adopting Design of Experiments (DOE) approach, worst conditions were simulated for trade-off between HVAC and BCS with a dual loop refrigerant system in 1D simulation. The simulations were performed in KULI software from M/s Magna Steyr.