Electrified vehicles, heating, ventilation and air-conditioning

Taurayi Raymond Sewera

THIS week we tackle electrified vehicles, heating, ventilation and air-conditioning.

The environment of any vehicle that has occupants must be controlled for their comfort.

Keeping the cabin environment controlled minimises operator fatigue, which allows for extended operator usage.

EV Heat Pump

Along with operator comfort, the ability to control cabin temperature keeps the related electronics within efficient operation range.

In other words, it puts less thermal stress on the material that make up the interior components of the cabin, which also allows for longer life of the components.

However, keeping control of the interior temperature will also impact (reduce) the range of a battery electric vehicle (BEV) or plug-in hybrid electric vehicle (PHEV) high-voltage battery pack — or fuel economy of a hybrid electric vehicle (HEV) — as it will provide energy to the heating, ventilation and air-conditioning (HVAC) system.

Audi e-tron GT Li-Ion Battery Cooling System

Understanding how all of these temperature control systems operate with each other will allow the technician to diagnose failures within these systems.

Let us talk about electric air-conditioning systems in cabin and battery pack cooling.

A BEV is more efficient at thermal management than a conventional internal combustion engine (ICE)-powered vehicle.

Allowing these components to overheat could cause thermal runaway (high-voltage battery pack) and reduce components life.

Audi e-tron High Voltage Battery Cooling System

For example, separate cooling loop systems can be designed for the high-voltage battery pack, power electronics and electric transmission/drive units and engine for HEV and plug-in PHEV only.

When multiple cooling systems are used in a vehicle, it can be more complex to maintain and diagnose the root cause of what is causing the thermal issue.

To help combat this issue, the original equipment manufacturers (OEMs) have come up with a couple of different ways to heat the cabin.

The first is through a resistive heating element, allowing the vehicle to be heated through electrical current.

This is a quick way to heat the cabin and is very efficient.

The downside to this type of heating is it utilises a lot of electrical potential from the battery pack, reducing the range of the vehicle.

In fact, the resistive electrical heating can reduce the vehicle range from 40 percent to 50 percent in extremely cold weather, when the cabin heating demand is high.

Audi e-tron HV Battery Cooling System Exploded View

With this type of system, you still need a separate air-conditioning (AC) system to cool the vehicle.

This is done by using an AC compressor that uses similar internal components to a conventional AC compressor.

However, the compressor used in HEVs, PHEVs and BEVs cannot be driven by a traditional drive belt due to the engine auto-stop mode in HEVs and PHEVs, or if the vehicle is not equipped with an engine (as in BEVs).

In this case, the AC compressor is powered by the high-voltage system.

Operating an electric AC system will also deplete the battery pack if its efficiency is not optimised and does not work in tandem with other systems on the vehicle.

Hyundai Heat Pump for EVs

This is being experienced in Zimbabwe, as we are importing used HEVs, PHEVs and BEVs from Japan, where temperatures can be extremely cold, and these vehicles are mostly using these electrical heating components and systems.

To help with efficiency in AC systems, a majority of new EVs operate with a R-1234yf refrigerant, which helps increase efficiency through the lower amount of refrigerant in the system.

Battery pack heating and cooling systems are controlled by uniquely designed cooling systems.

Depending on application, the battery cells are cooled by one of the following:

Routing cool cabin air (air cooled by the HVAC system) into the battery pack

A thermal-cooled heat sink or cold plate (with liquid or AC low-pressure gas circulating in the cold plate)

Coolant transferring a liquid or AC low-pressure gas through a network of cooling tubes or passages routed in between or into battery modules/cells throughout the entire battery pack.

The coolant is circulated through the pack to absorb the heat generated during the propulsion, regenerative (regen) or battery charging electrical conversion process.

When molecules move from the anode (negative electrode) to the cathode (positive electrode) or vice versa, they generate heat that must be removed, or the separator electrolyte interphase (SEI) layer in the cell will grow (thicken) and reduce the volume of lithium positive ion, along with other negative operating effects.

EV HVAC Syatem Concept

This reduces module or cell capacity and power.

If the module or cell temperature is not maintained and elevates beyond the maximum operating temperature, it will become unstable and may become uncontrollable, which may cause thermal runaway.

When thermal runaway occurs, a vehicle fire could occur, which poses danger to the vehicle’s occupants or cause the vehicle to become unstable.

Controlling the heat generated through electric drive process is key to maintaining occupants’ safety and vehicle longevity.

When the ambient temperature is below the pack’s operating rating, the vehicle must heat up the pack to allow recharging and proper operation.

To be continued…

Taurayi Raymond Sewera is ASE & Autocate Association-certified World Class Master Technician with 39ASEs, ASE Advanced Level Specialist L1, L2, L3 and L4. He is also an AMI-accredited master electric vehicles and master automotive manager, ACDC-certified master hybrid and electric vehicles technician. Taurayi is the founder and CEO of TauRay Automotive. He can be contacted on +263 77 234 1193, +263 77 235 7296 or rtsewera@gmail.com