Reports indicate that Volkswagen temporarily discontinued offering the heat pump system on its MEB platform electric vehicles (ID.4, Q4 e-tron, etc.). Although Volkswagen states that this is “due to the ongoing shortage of semi-conductors”, other factors are likely to have affected this decision. These include the fundamental value of heat pump systems, and because VW realized through customer feedback and internal testing that its original estimate of range improvement value was “off by more than 10%”.
A heat pump offers significant performance improvement at moderate ambient temperatures, but lower performance improvement for high ambient temperature cooling and diminishing benefit at low ambient temperatures (see the diagram below). Heat pumps are costly, resulting in US$150-400 in additional cost. Furthermore, the CO2 (R744) refrigerant heat pump used by VW for MEB vehicles is more expensive than R1234YF based heat pumps.
Data Sources: VW, Mahle, Valeo, Chosun Univ., The ITB Group
Heat pumps offer advantages, but come at a cost
An EV heating and cooling system is important for maximizing vehicle range and charging rates. Heating is particularly critical since simple electric heating technologies have a low Coefficient of Performance (COP) of nearly 1.0. In comparison, A/C cooling is efficient with typical COPs from 2-3. System COP is a measure of thermal efficiency that is a ratio of output energy divided by input energy. Heating also can involve a higher Delta T than cooling (difference in temperature of the cabin or battery vs. the target temperature). This higher Delta T requires more thermal power, for a longer time, to condition the vehicle. Heat pumps improve heating efficiency by using energy from the ambient air or other sources to achieve a COP of up to 3.0. See exhibit.
To accomplish this COP improvement, a heat pump system requires additional refrigerant and coolant system cost on the order of $150-400. Refrigerant valves alone, for a reversible refrigerant heat pump system, can cost $100-250. Automakers charge on the order of $1000 for the heat pump feature. Additionally, the mass of a heat pump system can range from 5-15kg. The customer value of a heat pump is derived from its efficiency improvement effect versus design complexity, cost, and mass.
Low temperature performance is a key determinant of BEV thermal system value
A heat pump can offer high efficiency with a COP of 3.0 at moderate ambient temperatures. Unfortunately, as the ambient temperature diminishes the efficiency of a heat pump drops. This is important because highway driving at low ambient temperature results in a worst-case condition for driving range. There are three primary causes of range reduction at highway speeds in cold ambient conditions: battery inefficiency, aerodynamic drag, and cabin thermal conditioning power. For highway driving in cold conditions, the share of losses is dominated by battery and aerodynamic effects, and cabin losses account for 5-10%. With a system COP of 1.5 and losses of 5-10%, the benefit of a heat pump for cabin conditioning would be on the order of 1.7 -3.3%. Then the mass of the heat pump system slightly reduces the overall impact of a heat pump.
Although heat pump systems on average save energy and increase range, it is not surprising that customers don’t notice the small heat pump benefit in cold highway driving. Coolant waste heat recovery and multiple-source heat pumps may provide greater range improvement than air-source heat pumps in cold conditions.
Alternatives to improve vehicle range
Automakers are choosing a range of alternatives to improve BEV range. Some companies like BMW, Ford, Mercedes-Benz, and Toyota focus on coolant waste heat recovery, which can be used to heat the battery as well as the cabin. Key to maximizing performance is using waste energy, not just from the ambient environment, but also from the vehicle. Waste heat recovery from the motor/inverter/battery can deliver as much as 500W using a 20W pump for a COP of up to 25 by adding coolant control hardware and software.
Cabin comfort improvement alternatives include localized heating and cooling devices which are more efficient than conditioning the air alone. The cabin can also be made more efficient by applying higher levels of air circulation. For higher cabin air recirculation levels, intelligent algorithms and in some cases new hardware are necessary to manage cabin carbon dioxide and humidity build-up.
The path forward
Volkswagen is reported to be developing hardware and software improvements to improve heat pump effectiveness but has not provided timing for when it may resume production of MEB vehicles with heat pumps. ITB expects significant thermal system design refinement for BEVs over the next ten years, particularly to lower thermal system cost for improved value by all automakers.
ITB provides insights into changing vehicle thermal technologies and markets
ITB has dialogue with companies throughout the automotive value chain to determine unmet needs and innovations for improved thermal system value. In our 2023 research, ITB dives deeply into markets, designs, and materials for electrified vehicle thermal management plus initiatives for BEV range improvement and rapid charging. This includes differences across global regions, vehicle powertrain types, and OEMs. Contact The ITB Group to learn more about changing technology markets.
