The principle of the heat pump is basically similar to the system of a refrigerator or an air conditioning system - only in the opposite direction. It is therefore a closed circuit that contains a special liquid or gaseous medium (coolant). The system should be overpressure compared to normal atmospheric pressure.
The main components of the system are compressor, evaporator, condenser (Capacitor) as well as lines, valves and sensors. The liquid refrigerant first enters the evaporator. This is where heat is exchanged and the state of aggregation of the coolant changes: the air cools and the working medium heats up until it finally exits the evaporator in gaseous form. The now gaseous medium is now passed through the compressor and compressed therein. Due to the increased pressure, the volume of the gas decreases and the temperature of the medium increases. The now gaseous coolant, which has a high pressure and high temperature, continues to the condenser. This is where it releases its thermal energy, for example to heat up the interior of a vehicle. By removing heat, the coolant returns to its liquid state. After passing through a throttle, the gaseous medium expands and cools down further, now reaches the right-hand evaporator and absorbs heat energy from the environment through heat exchange. The air in the evaporator cools down and that of the medium rises. It exits the evaporator in gaseous form and flows back to the compressor. The cycle process can thus be continued continuously.
Since the waste heat from the engine in an electric vehicle is often insufficient to heat the passenger compartment sufficiently, alternative heating systems have to be installed here. These mostly electric heaters require energy for operation, which is usually taken from the traction battery, which affects the range. Some manufacturers now combine electric PTC heaters with heat pumps, so that the heating loads of the electric heater only have a minor effect on the range of the vehicle.
Addendum
Source: text and video green car magazine
Cover picture: Energy-saving heat pump - Coypright AngelaStolle @ fotolia.com
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