How to design heating and cooling systems for HEV/EVs

Co-authored by Kevin Stauder, systems engineer, automotive body electronics and lighting

For decades, the internal combustion engine (ICE) has run the car as well as the heating and cooling systems. As the automotive industry electrifies and transitions to hybrid electric vehicles (HEVs) with small combustion engines or fully electric vehicles (EVs) with no engine at all, how will the heating, ventilation and air-conditioning (HVAC) systems work?

In this white paper, we will describe the new heating and cooling control modules in 48-V, 400-V or 800-V HEVs and EVs. From there, you will learn about the unique subsystems in these modules with examples and system diagrams, and we’ll finish by reviewing functional solutions for these subsystems to help you start planning your implementation.

First let’s discuss the basics of how a combustion engine works in a HVAC system. In a vehicle with an ICE, the engine is the foundation for the heating and cooling system. For cooling, the air from the blower fan enters the evaporator, where the refrigerant cools the air. The air conditioner (AC) compressor, which is driven by the engine, then compresses the refrigerant exiting the evaporator. Similarly, for heating the air, heat generated by the engine is transferred to the coolant. This warm coolant enters the heater core, which heats the air that will blow into the cabin. That is how the engine plays a foundational role in the heating and cooling of a vehicle cabin.

In HEV/EVs, the sizing or the absence of a combustion engine requires the introduction of two additional components that play a key role in the HVAC system.

  1. A brushless DC (BLDC) motor, which is a type of DC motor that rotates the AC compressor, instead of the engine
  2. A positive temperature coefficient (PTC) heater or alternatively, a heat pump, that heats the coolant, rather than the engine.

With the exception of these components, the rest of the heating and cooling system infrastructure is the same as it is in a vehicle with an ICE. As noted, the BLDC motor and PTC heater or heat pump are needed in the absence of an engine and bring separate challenges in power consumption, control of the motor and the resistive heater and overall HVAC control.

To learn more about the unique subsystems in these modules and functional solutions, read the white paper below.

Read "How to design heating and cooling systems for HEV/EVs."