Cooling and Heating: In traditional combustion engines, an intricate and robust thermal management system minimizes the impact on fuel consumption and, consequently, range. However, this issue is magnified in pure EVs, particularly during cold weather. These vehicles face a challenge: they produce very little waste heat that could be utilized.
For EVs, key factors influencing buyer acceptance depend on thermal management: battery lifespan, vehicle range, drive performance, and fast-charging capability.
At any given moment and under all climatic conditions, every component of the drive system requires the right temperature.
Moreover, thermal management ensures a comfortable climate inside the vehicle—a comfort for the driver that is not only pleasant but also a safety factor. Ideally, interior climate control should have minimal impact on range. That's the theory.
In practice, things are more complicated. For conventional combustion engines, heating the interior in winter is not an issue, thanks to the abundance of waste heat from the engine. However, this heat source is completely absent in pure EVs.
And how does this affect the range or the performance of the drive battery?
MAHLE engineers investigated the heating and cooling requirements for a compact class EV. They found that at minus 15 degrees Celsius, about 4.5 kilowatts of heating power is necessary to maintain an interior temperature of 22 degrees Celsius.
This heating power is comprised of two kilowatts lost through convection and thermal radiation through windows and the bodywork to the surroundings, and 2.5 kilowatts discharged to the environment through the vehicle's ventilation system.
Electric motors and power electronics have very high efficiency rates. For a compact class EV with an assumed drive power of about 2.5 kilowatts during city driving, this results in a mere 0.4 kilowatts of heat available to the coolant.
These figures quickly make it clear that this is far from sufficient to heat the interior accordingly. Therefore, the heating power must come from the battery, costing range.
This example illustrates the extent to which interior heating competes with propulsion. The majority of newly registered EVs are still equipped with an electric high-voltage heater. This heater has a high energy demand because it can only convert one kilowatt of electricity into one kilowatt of heat. To maintain the interior at 22 degrees under the described conditions, nearly twice as much energy must be used for heating as is needed for propulsion, significantly reducing the range.
MAHLE has thus developed an efficient alternative, opting for a combination of an electric high-voltage heater and a heat pump. The heat pump contributes significantly to increasing the range due to its much higher efficiency, while the electric heater covers the critical operating conditions of the heat pump. How this system works will be explained in an upcoming post.