Thermal Management in the Electric Age

Across the country, commercial fleets of all sizes and duty cycles are transitioning from internal combustion engine (ICE) vehicles to electric vehicles (EVs). A shift of this magnitude comes with challenges, including higher vehicle acquisition costs and the need for charging infrastructure. However, the total cost of ownership (TCO) of commercial EVs will likely outperform ICE vehicles as soon as 2025. Given the increasing availability of all classes of EVs and their improving range, the need to reduce carbon emissions, and government incentives and regulations that encourage adoption, the commercial EV market is primed for growth.

Questions about how commercial electric vehicles will perform compared to their ICE cousins occupy the minds of fleet operators. Can a battery store enough energy to reliably power rugged medium- and heavy-duty vehicles? Will those EV systems withstand regular use in harsh, dirty environments? Which technologies best protect and optimize the performance of commercial EV components? Appearing on this list with increasing frequency are questions about whether EVs require seasonal, temperature-related preparation similar to the winterization ICE vehicles undergo. The answer is a qualified yes because the most important aspects of EV winterization happen in manufacturing, not at the depot.

The lithium-ion (Li-ion) batteries in modern EVs are larger versions of those found in virtually all smartphones. Anyone who has ever left a phone in the sun or in a car on a cold night knows that temperature extremes in either direction negatively affect a phone’s battery life and performance. Similarly, maintaining the right battery temperature range is essential for reliable EV operation.

In cold temperatures, the chemical reactions inside Li-ion batteries slow down, increasing internal resistance, which reduces battery capacity and, in turn, reduces vehicle range. Cold temperatures also result in slower charging. On the other end of the mercury, high temperatures cause chemical reactions in the battery to speed up, draining the battery more rapidly. If a battery is continually exposed to temperature extremes, it will degrade over time.

The good news is that vehicular thermal management is well-trodden ground. Some companies have more than 100 years of experience in the field. Thermal management companies have developed new technologies and methods, including high-fidelity temperature control for EV components using refrigeration and heating circuits with sensors and sophisticated controls. Using these technologies help make electrified commercial vehicles viable in even the most severe environments.

What Is Battery Thermal Management?

Battery thermal management is one of the less visible but critical frontiers in EV transportation. Ambient temperature impacts the range, charging time and the working lifetime of batteries. For rugged specialty and commercial EV platforms, however, battery thermal management systems (BTMSs) must efficiently manage battery temperatures, be able to accommodate novel space constraints, and survive unforgiving and often dirty operating environments.

For peak performance during charging and operation, what is effectively a double-duty cycle, battery pack temperature should ideally remain between 25°C and 35°C (77°F and 95°F). As such, a BTMS should heat and cool the battery pack with which it is paired. In practice, if the ambient temperature drops too low, the BTMS heating loop will increase the temperature of the coolant circulating within it until the battery pack temperature reaches the ideal range. Once the vehicle is in operation—or while charging—the BTMS removes the resulting heat from the battery pack to prevent overheating. The switch between cooling and heating, as well as the intensity of each, are managed automatically by the system.

A key consideration in a BTMS design is optimizing temperature control while minimizing power consumption. A BTMS, therefore, may have an active loop with a refrigerant circuit to remove heat in hotter temperatures and a passive loop with a radiator and fans—which draws less power—if the ambient temperature is moderate. For off-highway applications, BTMSs can be designed to protect fans or exposed heat transfer modules from potential clogging by dirt and debris. As with all batteries of this type, maintaining optimal thermal conditions shortens charging time and maximizes the range and battery lifetime.

Other Considerations for Thermal Management

The inverters, converters, traction motors and related power electronics that charge the batteries or turn battery-stored electrical energy into kinetic energy are similarly affected by ambient and operating temperatures. Given the weight, payloads and workloads of heavy-duty commercial EVs, their powertrain electronics require significantly more power than the average light-duty or consumer passenger EV. With more and higher power comes more heat. More heat means more stress on electrical components and as a result, more vulnerability to compromised performance, durability and safety.

With inverters, for example, power output is limited by the maximum temperature threshold of the power module, impacting performance. It may even shutdown without intervention from a BTMS.

Commercial EVs are typically equipped with a cooling package for inverters, converters and traction motors, each with a coolant loop to cool the power electronics, which is then routed through the cooling package to reject the heat to ambient. This circuit keeps the power electronics within the temperature range that ensures the best performance and the lowest risk of damage to sensitive components. In most commercial applications—where unexpected downtime is unacceptable—reliable thermal management of drivetrain electronics protects the asset and the operation it serves.A fully electric, North-American-style fire truck with a BTMSVector Group

Changing Fuel & Changing Habits

As a massive wave of resources flows toward domestic engineering, manufacturing and EV infrastructure, more platforms across all transportation segments will be electrified. The shift from hydrocarbons to electricity is nothing short of an engineering revolution in which the similarities between the two are mostly optical. While little re-training is required of the professional drivers who switch over to operating these vehicles, a few important adjustments to old habits are unavoidable.

A large earth mover or a truck that pulls heavy loads requires a larger battery pack, which means more thermal mass. When heated indoor parking is unavailable, the larger the battery pack is, the longer it takes to reach equilibrium with ambient temperature. This means it will take longer to warm the battery pack to optimal operating temperature again. Connecting to a charger whenever stationary, especially in the cold, allows a BTMS to protect the battery pack and mitigates the risk of a cold-battery performance reduction of up to 40%.

Also, the battery draw from cabin heating is responsible for nearly two-thirds of range reduction in cold weather. Drivers who rely more on in-cabin comfort features like heated seats and steering wheels and turning heaters off when not in the vehicle, will also get more range between charging sessions.

Electricity in the Fast Lane

After nearly two centuries of innovations in motorized transportation, EV technology is now viable across dozens of vehicle segments. Engineers have made advancements in thermal management that are putting commercial and rugged specialty EVs on the path to outperform their ICE predecessors. Backed by the spirit of innovation, rapidly growing demand, incentives and guidelines from governments, and broad support to reduce transportation emissions, the electrification of commercial transportation is already more advanced than most prognosticators thought it would be.