One of the main differences between heating, ventilation, and cooling (HVAC) systems in internal combustion engine (ICE) vehicles and electric vehicles (EVs) is their power source. That difference results in several differences in implementation choices.
This FAQ begins by looking at the different power sources used in ICE vehicle HVAC systems compared with their EV counterparts, looks at alternative implementations for cabin heating like fan heaters, heat pumps, and high-voltage heaters, and closes by looking at the implications for EV drivers and passengers.
In an IEC vehicle, the HVAC system uses a refrigerant that can receive heat from the heater or is cooled by a radiator. The refrigerant is circulated at high pressure using a compressor driven with a pulley and belt system attached to the ICE.
The operation of the HVAC system in an EV is quite similar. The primary difference is that instead of using a pulley and belt system driven off the ICE, the system in an EV uses an electric compressor powered by the main battery. These compressors are self-contained systems, including the electric motor, an inverter motor drive, and a separator that keeps the compressor oil and the refrigerant from mixing (Figure 1).
Figure 1. An HVAC unit in an EV is a self-contained system including the compressor assembly, electric motor, and drive electronics (Image: Guchen Compressor).
Similar systems can be used for the battery cooling system and for producing the hydraulic drives needed for electric tractors, excavators, and other heavy-duty electrified equipment. In the case of the HVAC application, an advantage of the EV system is that it can run even when the car is parked and the motor is off, which is not true for ICE-driven HVAC systems.
Heating is different
In an IEC vehicle, the engine is typically the primary heat source for warming the cabin. That’s not possible in an EV, so other approaches have been developed. For basic heating, a simple electric heater with a blower can be used to heat the cabin.
These heaters can draw relatively little power in mild climates but significantly reduce the driving range in extremely cold temperatures. In sub-zero temperatures, the driving range can be cut in half, limiting the usefulness of this solution to small cars primarily used in city centers and not taken out for extended road trips during very cold weather conditions.
Heat pumps
Heat pumps have been used in EVs for several years. They can improve the efficiency of the HVAC system by recycling or harvesting waste heat from power electric modules, including motor drivers, dc/dc converters, inverters, onboard chargers, and from the battery pack.
The heat pump uses the captured heat to vaporize the refrigerant, which is discharged from the compressor and sent through the condenser to be returned to a liquid state. This process generates additional heat that is also recovered by the heat pump and used to warm the cabin. Harvested heat reduces the battery’s load, cutting the HVAC system energy consumption and maximizing driving range (Figure 2).
Figure 2. A heat pump in an EV harvests heat from a variety of systems, reducing energy consumption and maximizing driving range (Image: Hyundai).
What’s a high-voltage heater?
Another approach is called a high-voltage heater (HVH). In contrast with heat pumps that use a refrigerant, HVH technology employs water as the heat transfer medium. They are simpler in construction and can be lighter since a compressor is unnecessary. A typical HVH system can operate with supply voltages from 100 to 450 V with a maximum heating power of up to 7 kW. HVH systems are commonly found in large vehicles like trucks and buses.
In the case of trucks, it’s often used to provide heat to the driver’s cabin while the vehicle is parked. It’s also found in some passenger EVs that combine one or more of the systems described above to realize the maximum performance across the broadest range of uses.
Usage considerations
Given the desire for both comfort and maximum driving range, there are several considerations for EV drivers using HVAC systems. Some EVs have heated and cooled seats that maximize the impact of the system and enable the interior temperature to be set lower or higher than normal and still maintain comfort. Plus, there are ways to reduce the need for heating like:
- Preheating the car’s interior before beginning a trip. This can be accomplished by plugging into a charger and heating the interior or simply parking the car in a sunny location and letting the greenhouse effect heat the cabin.
- Driving in economy mode will reduce the energy consumption of many vehicle systems and make more battery energy available for the HVAC system.
Summary
The IEC in a conventional vehicle provides the rotational power for the air conditioning compressor and thermal energy for the heater. Since there is no IEC in an EV, different energy sources are used that result in different system implementations, including electric compressors for air conditioning and various heating technologies like fan heaters, heat pumps, and high-voltage heaters.
References
- 320 V electric compressor, Guchen Compressor
- Air Conditioning in an EV, Knauf Industries Automotive
- Recycling More Heat: Hyundai and Kia Turn Up EV Efficiency with New Heat Pump Technology, Hyundai
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Filed Under: Electrification, FAQs, Featured