Heating system, a key element in an electric model
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Heating system, a key element in an electric model
Before we look at the different types of heating systems in electric vehicles, which are of concern to many users, particularly in winter, let’s first take a look at how heating works in a combustion engine vehicle.
Heating in internal combustion vehicles
Internal combustion engine vehicles use a cooling system designed to maintain the engine at an optimum temperature, generally around 90°C. This system relies on a heat transfer fluid (coolant) circulating around the cylinders to absorb the heat generated by the engine. Once heated, the liquid is pumped by a water pump to a radiator at the front of the vehicle, where it is cooled before returning to the engine to repeat the process.
Some of this excess heat is recovered to heat the passenger compartment. When the user activates the heating control, a valve redirects some of the hot liquid to a radiator located in the passenger compartment. This radiator heats up, and a fan distributes the heat throughout the cabin. This simple and ingenious process consumes no additional energy, as it uses the heat produced naturally by the engine. This heat production is similar to domestic oil or gas heating, which uses a boiler to heat the water in the system.
Heating in electric vehicles
In electric vehicles, heating is based on different principles and the energy requirements for heating the passenger compartment are greater, as the absence of an internal combustion engine means that there is no source of ‘free’ heat. Although electric vehicles are also equipped with cooling circuits for the battery and motors (depending on the technology), these circuits are not used to heat the passenger compartment. Heating is therefore provided either by a thermal convector fitted with a heating resistor (PTC – Positive Temperature Coefficient), or by a heat pump (PAC).
Here’s a comparison of the two systems
Resistance heating: simple but high consumption
Resistance heating is based on the Joule effect, a physical phenomenon in which the passage of an electric current through a resistor generates heat. This heat is then diffused into the passenger compartment using a fan. This system works in a similar way to a small fan heater, which heats the air using a resistor before propelling it into the space using a fan.
However, this type of heating is particularly energy-intensive. Its power can vary between 1 kW and 5 kW. This high energy consumption has a significant impact on the range of electric vehicles, making energy management even more crucial in winter. For example, some vehicles can lose up to 80 km of range with the heater switched on.
Advantages :
- Simple, robust and inexpensive technology.
- Rapid heat production, even in very cold weather.
Disadvantages :
- High energy consumption, which can considerably reduce range.
- Limited efficiency: 1 kW of electricity produces 1 kW of heat.
Heat pump heating: efficient but complex
A heat pump, on the other hand, operates on the principle of the thermodynamic or refrigeration cycle, similar to that of a refrigerator or reversible air conditioning system. It captures heat from the outside air or from other sources (such as the battery cooling system) and transfers it to the passenger compartment. This process uses a refrigerant that goes through various phases: compression, condensation, expansion and evaporation. This cycle can produce both heat and cold.
The Coefficient of Performance (COP) of a heat pump generally varies between 2 and 5. This means that with a COP of 3, for every 1 kWh of electricity consumed, the heat pump gives off 3 kWh of heat. However, the COP decreases as the outside temperature drops: the colder it gets, the lower the efficiency. Below a certain temperature, an auxiliary electrical resistance is used to heat the passenger compartment, which temporarily increases energy consumption, particularly when starting up the vehicle at very low outside temperatures.
This equipment is similar to reversible air/air air-conditioning systems that can be installed in the home to heat in winter and cool in summer.
Advantages :
- High energy efficiency: a COP of 2 to 5 means that 1 kW of electricity consumed can produce up to 5 kWh of heat
- Reduced impact on range thanks to lower power consumption.
- Versatility: can heat in winter and cool in summer
Disadvantages :
- Higher manufacturing and installation costs (+/- €1,000 as an option).
- Reduced performance at low temperatures, requiring a back-up electric heater at start-up.
- Technical complexity, implying potentially more costly maintenance.
Comparison of the Two Technologies :
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Conclusion:
The choice between resistance or heat pump heating depends on the builder’s priorities and the user’s needs. If the aim is to minimise initial costs and simplify design, resistance heating is a suitable solution.
On the other hand, for users looking for maximum autonomy, particularly in temperate climates, heat pumps are a wise choice. More and more manufacturers are incorporating heat pumps into their vehicles, or offering them as an option at a fairly substantial extra cost (+/- €1,000), because they represent a compromise between energy efficiency and user comfort.