In contrast to combustion engines, which operate across a wide temperature range and rely on cooling, EVs face unique thermal management challenges. Combustion engines generate enough waste heat to provide cabin heating and auxiliary unit operation without significantly impacting efficiency. The gearbox's waste heat can also be managed effectively through a heat exchanger. The only exception is cabin cooling, which traditionally requires an engine-driven air-conditioning compressor and a refrigeration circuit, leading to a reduction in mechanical power in the vehicle.

Conversely, in EVs, the traction battery typically operates at lower temperatures. Extreme cold can reduce battery performance, especially during charging, while excessive heat can pose safety risks. Other components, like electric motors and power electronics in the electric drivetrain, operate across various temperature ranges, but they are so efficient that their waste heat alone is insufficient for cabin heating.

This leads to a dual challenge: cabin air-conditioning requires energy from a heat pump, while the traction battery needs active heating and cooling to maintain its optimal operating temperature window. Consequently, the thermal management system in an EV must strike a balance between four key objectives: maximizing system-level efficiency and range, controlling costs, and optimizing installation space.

In hot environments, electric vehicle batteries can experience elevated temperatures due to external heat and heat generated during operation. High battery temperatures can lead to lower efficiency, accelerated degradation, and shorter overall battery life. Efficient battery cooling is essential to maintain optimal performance and longevity. 

Electric vehicles use electric drives, such as permanently excited synchronous machines (PMSM), in their drive systems. These drives generate heat during operation and their efficiency and performance can be affected by high temperatures. In particular, PMSM motors have magnets in their rotors that can lose their magnetism if the Curie temperature is exceeded. This can lead to demagnetisation of the motor, resulting in a significant loss of efficiency and potentially costly replacement of the motor. 

Air conditioning in electric vehicles plays a dual role in hot environments. On the one hand, it is necessary to ensure passenger comfort, and on the other hand, it is crucial for cooling various components, including the battery and the electric drive. The challenge is to find the right balance between keeping passengers cool and effectively cooling critical vehicle components.

High temperatures can pose a safety risk in e-vehicles. Extremely high temperatures can cause thermal runaway in lithium-ion batteries, which can lead to fires or explosions. Proper thermal management is critical to minimise these safety risks.