THE HEAT PUMP, A KEY DEVICE FOR EVERY ELECTRIC CAR

(Article published in Automotive Innovations magazine, June 2024)

By Piero Facchin

Motors, whether electric or fuel-powered, produce heat when they run. The thermal energy created is often lost, but in order to put it to good use, internal combustion engine cars use a small amount of it to run their heating and ventilation systems.

Electric vehicles (EVs), on the other hand, offer a higher level of efficiency: although motors and batteries produce excess heat that can limit the range, there isn’t enough to power other systems such as heating. So, during winter, EV drivers are either cold or forced to draw extra energy from the battery to power the heater, which is far from ideal.

A heat pump in an EV works on a principle similar to that of a standard refrigerator or air-conditioning system, but adapted to heat and cool the cabin.

Heat pump operation depends on a thermodynamic cycle involving the compression and expansion of a coolant fluid. Here are the key stages in this process:

1. Compression: The cycle begins when the coolant, initially a low-pressure gas, is compressed by an electric compressor. As it is compressed, the gas increases in temperature and pressure.
2. Condensation: The hot, high-pressure gas then passes through a condenser, where it releases its heat to the outside of the vehicle (when used for cabin cooling) or inside to heat the cockpit. During the heat release process, the coolant is condensed and transformed into a liquid.
3. Expansion: The liquid coolant then passes through an expansion valve, reducing its pressure. This expansion quickly reduces the temperature of the coolant, transforming it into a low-temperature, low-pressure mixture of liquid and vapour.
4. Evaporation: This cold mixture enters the evaporator, where it absorbs heat from the air inside the vehicle (for cooling) or from outside (for heating). As it absorbs heat, the coolant evaporates and returns as a low-pressure gas.
5. Return to the compressor: The low-pressure, low-temperature gas goes back to the compressor, where the cycle can start again.

The efficiency of a heat pump in an EV is crucial, as it optimizes battery autonomy by using less energy than traditional heating systems that rely directly on electrical resistance. What’s more, this system can reverse its cycle to provide either heating or cooling, as required, while using fewer components than a separate air-conditioning and heating system, resulting in weight and space savings.

PICTURE CREDIT : Automobile Propre