A special evaporator plate enclosed in the battery cell is connected to the air-conditioning system in the vehicle. This is done using what is known as the splitting process on the high-pressure and low-pressure side via tubes and an expansion valve. This means that the interior evaporator and the evaporator plate of the battery (which functions like a standard evaporator) are connected to the same circuit.
The different tasks for the two evaporators result in different requirements for refrigerant flow accordingly. While the interior cooling system aims to satisfy the comfort demands of the passengers, the high-voltage battery must be cooled to varying degrees of intensity depending on the driving situation and the ambient temperature.
These requirements are the defining factors for the complex control of the quantity of evaporated refrigerant. The special design of the evaporator plate and its resulting integration into the battery offer a large contact surface for the heat exchange. This means it is possible to guarantee that the critical maximum temperature of 40 °C is not exceeded.
When the outside temperatures are very low, it is necessary to increase the battery temperature to the ideal battery temperature of at least 15 °C. However, the evaporator plate cannot help in this situation. A cold battery is less powerful than one that has the right temperature. It is also difficult to charge the battery when temperatures are significantly below freezing. In mild hybrids, this can be tolerated: In the extreme case, the hybrid function is only available to a limited extent. It is, however, still possible to drive with the internal combustion engine. On the other hand, a battery heater needs to be fitted in purely electric vehicles so that the vehicle can be started and driven whatever the situation in the winter.
Evaporator plates that are integrated into the battery directly cannot be individually replaced. In the event of damage, the entire battery must always be replaced.