Heat Pump
A heat pump is a climate-control system that moves heat between the vehicle and its surroundings instead of producing all cabin heat directly with an electrical resistance heater.
Efficiency and COP
For heating, the coefficient of performance (COP) is the useful heat output divided by the electrical input, measured on the same basis and under stated operating conditions. A heat pump can have a COP above 1 because it moves heat rather than converting all of its input electricity into heat.
COP is not constant. Outside temperature, humidity, refrigerant temperatures, heat-exchanger conditions, available waste heat, cabin demand, and defrost operation can all change it.
An electric resistance heater creates heat directly from electrical input. A Electric Resistance Heater and PTC Heater is one such design. Resistance heat is a separate heat source, not part of the heat-pump COP claim. An EV may use it as backup or supplement when rapid warm-up or additional heat is required.
Why it matters in an EV
Cabin heating draws energy from the traction battery unless another energy source is available. Under suitable conditions, a heat pump can reduce the electrical energy needed for a given cabin-heating demand compared with resistance heating.
The presence of a heat pump does not establish a fixed winter-range improvement. System design, weather, trip length, software, and preconditioning all affect the result. Preconditioning while plugged in can also change how much of the conditioning energy comes from the charger rather than the traction battery.
See Heating, Ventilation and Air Conditioning for the relationship among cabin conditioning, battery heat, preconditioning, and cold-weather energy use.