Waste heat recovery
Turning motor, inverter and even cabin-air heat into free warmth.
- Explain waste heat recovery at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real vehicle
Overview
Every watt of motor and inverter loss is heat that would otherwise be thrown away. Capturing even a portion of it before it reaches the radiator reduces the load on the heat pump and PTC heater.
In depth
Sources worth capturing
Motor and inverter losses, exhaust cabin air before it is vented outside, and even the battery's own resistive losses during discharge are all usable low-grade heat sources. An evaporator plumbed into the powertrain loop lets the heat pump extract this heat rather than generating fresh heat from electricity.
Motor losses are proportionally largest relative to road load at low speed, exactly when the car has the least aerodynamic heat generation to spare — making waste heat recovery most valuable in city driving.
Key takeaways
- Motor, inverter and exhaust cabin air are all usable waste heat sources.
- Recovering waste heat reduces the electrical load needed for cabin and battery heating.
- The benefit is largest in low-speed, stop-and-go driving.
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