Application of an on-board electric vehicle air conditioner in the battery cooling system

Overheating is one of the main reasons that accelerates the rate of battery discharge in electric vehicles and leads to the deterioration of its performance over time. Rapid charging of the battery is not beneficial for its longevity, as high currents increase the temperature and can irreversibly damage the internal structure of the battery. At optimal temperatures, the availability of discharge power, charge reception during regenerative braking and battery health are at the best level. Battery life, electric vehicle (EV) drivability, and fuel economy deteriorate as temperatures rise, so the battery cooling system is of great importance for EVs.

Air cooling, which is used in many electric vehicles, is relatively simple and, accordingly, inexpensive. Air cooling can be implemented by simply circulating air around the battery cells, which is the least efficient, or by using a fan to increase airflow. Liquid cooling of the battery, which operates similarly to cooling of the internal combustion engine, is much more complicated and expensive. The coolant is pumped through the channels provided in the battery, where it is heated and fed to the heat exchanger for cooling. But even here, the degree of cooling of the liquid is greater, the lower the temperature of the outside air. Particular inconveniences arise when it is necessary to quickly charge an electric car on a hot day, when the EV controller reduces the charging speed to reduce the temperature.

We propose the use of a standard air conditioning system of an electric car to additionally reduce the temperature of the coolant in the battery circuit before the planned charging. For those purposes, we also propose the elements of the methodology that enable the calculations of the energy required to cool the battery to the required temperature with the sufficient accuracy for engineering practice.