Photo courtesy of Carrier Transicold
Comfort Pro Electric Apu On Rig 60883348855b3

Latest developments in electric APUs

May 26, 2021
Battery-powered auxiliary power units can help to reduce emissions, fuel costs, and engine wear.

Examining the goals of a fleet’s operations will most likely yield a litany of objectives surrounding efficiency and cost savings. This is true of any department, though such objectives reign supreme for the maintenance team.

Whether finding cost savings in vehicle operation or in maintenance practices, solutions that serve both avenues are always enticing and should be examined to enhance the way a fleet operates. One such solution comes in the form of auxiliary power units (APUs). Particularly, it serves fleets to look beyond diesel-powered APUs as the only available solution and consider alternatively powered solutions, specifically electric, battery-powered APUs.

What is an electric APU?

An electric APU is a battery-based power system that can operate specific vehicle systems without the need to have the vehicle’s engine running. The basic electric APU may consist of a battery, or bank of batteries, a compressor, and possibly an inverter, along with hardware and software integrations to connect to specific vehicle systems, such as the in-cab heating and cooling, the vehicle computer system, and others.

“Today’s electric APUs are battery-powered,” said Ryan Rubly, product manager, alternative power for Carrier Transicold, Truck/Trailer/Rail Americas. “The standard ComfortPro electric APU [offered by Carrier Transicold] uses four Group 31 AGM batteries that are charged by the truck’s alternator.”

Though, AGM batteries are not exclusively the power-source standard for electric APUs, as Xantrex offers the Freedom e-GEN Lithium Ion System, which utilizes lithium iron phosphate batteries.

What does an electric APU do?

Electric APUs can serve a range of purposes and functions for vehicle system operation, primary of those being to provide air conditioning and heating to the cabin. “The primary function of the APU, such as those in Carrier Transicold’s ComfortPro APU family, is to provide climate control for the truck cab so the driver doesn’t idle the truck to maintain comfort during rest breaks,” Rubly said.

Mission Critical Electronics recently announced a technical partnership with ZeroRPM, which has furthered the capabilities of the Xantrex Freedom e-GEN Lithium Ion System to include additional air conditioning operations.

“The e-GEN core system is intended for hotel operations,” said Don Wilson, applications engineer at Xantrex, a Mission Critical Electronics brand. “So, we are just doing the hotel electrification, including [systems such as] the Bergstrom air conditioner. It is a DC air conditioner meant to cool the sleeper. Our e-GEN [system] does that very well.

“The integration with ZeroRPM allows us to actually run the dash air too,” Wilson continued. “You could power just the Bergstrom [vehicle climate control system] or just the sleeper air conditioner; you could do just the dash; or a combination of both.”

Wilson relayed that the integration of the ZeroRPM System into the e-GEN core allows flexibility and extended options in climate control, particularly beneficial for vehicles operating in hot climates.

Beyond air conditioning, electric APUs can power hotel loads as well, though additional specifications are typically required.

“Some APUs can also serve as a power source for hotel loads and offer features that support the truck power plant, such as engine warming,” Rubly explained. “In the Carrier Transicold ComfortPro platform, most of our diesel systems are fully featured, meaning that in addition to climate control they also provide engine warming, battery charging, and power for hotel loads. The standard ComfortPro electric APU is primarily a cab air conditioning system. However, other capabilities can be added by specifying different options, such as a fuel-fired heater, an inverter for hotel loads, and a heater for truck engine preheating.”

Xantrex’s Wilson spoke to the e-GEN system and the utilization of the ZeroRPM integration that allows for cabin heating.

“Instead of running electric heaters, that diesel engine stores a lot of heat when you shut it off,” Wilson said. “We can still circulate the coolant into the heater core and get that heat out of there. But eventually that engine is going to cool down … One of the features that can be added on is the ability to start the truck. So, when the battery gets low, what it would do is it would start the engine, build up that heat again, shut off the engine, and then use that to run heat.”

Wilson reiterated that air conditioning is operated electrically off a battery, though emphasized that were the battery to get to a point where it is too low to run the compressor, the engine could be started and charge the battery.

Furthermore, Wilson said that the ZeroRPM System components of the electric APU can operate more than just the dash air conditioning, including the radio and “anything that you would normally run with the engine on that you don’t get with the engine off.”

The ZeroRPM System also captures all the data associated with the engine-off technology – utilizing the company’s Intellimetrics software to give users detailed insight into how the system performs. A secure portal provides customized reports and graphs of fuel savings, emissions reduction, and vehicle usage. “It pulls in runtime, downtime, hours, and stores it all,” Wilson said.

Electric APU considerations and challenges

Understanding the operational capacity of an electric APU is one thing; understanding how its performance impacts the vehicle’s operation, the fleet’s business operation, and the maintenance implications can help determine whether electric APUs will work for a fleet.

Essentially, operating an electric APU versus idling a vehicle’s engine will provide a windfall of benefits stemming from the reduction of the vehicle’s engine runtime.

“Since it is an engineless system, an electric APU provides air conditioning comfort without fuel consumption, idling noise, and related emissions,” Rubly said. “This saves fuel and related emissions, providing regulatory compliance in cities, regions, and states where anti-idling laws exist. Reducing the amount of time a truck idles also cuts wear and tear on the truck engine, which can provide long-term maintenance benefits.

“While initial cost is a factor in an APU purchase, the most important consideration is lifecycle cost and payback period,” Rubly continued. “Whether diesel or electric, payback from fuel savings starts the moment the truck engine is shut off and the APU is engaged … Over time, the use of the APU can help extend truck service intervals, helping to control operating costs, which adds to return on investment.”

Beyond vehicle operations, insight from Xantrex’s Freedom e-Gen System with ZeroRPM System integration can provide data from its use of Intellimetrics to create the opportunity for operational efficiencies from a management perspective.

“When we’re talking about engines, a lot of people look at miles, but it is really hours,” Wilson suggested. “We can help not only identify the hours that we have used if we needed to start the engine, but also compare it to an existing vehicle and see how many hours you have saved.”

“You can see information by vehicle,” said Mitul Chandrani, director of marketing, Xantrex Business, Mission Critical Electronics, speaking to the capabilities of the data management portal from their offering of the ZeroRPM System integration. “If a fleet has 25 vehicles, you can see information by vehicle, and then you can also see a consolidated dashboard of all savings in fuel, how much CO2 has been prevented from atmosphere from these vehicles, [et cetera].”

Wilson further spoke to the sort of data captured and how it can serve to better the practices by users.

“One of the things about the auto-start feature is if the system doesn’t work for whatever reason, the driver can override that and manually start his engine,” he said. “Well, that kind of information is logged. There are stories told of the truck ‘tattle-taling’ on the driver for misbehaving and using engine power when he should be using the system.”

Though providing multiple benefits, electric APU integration and operation doesn’t come without potential challenges.

“Traditionally, diesel APUs provide a greater range of capabilities, including higher capacity, continuous air conditioning and heating in climate extremes, as well as ample continuous power for hotel loads,” Rubly explained. “This can be especially important to long-haul operators, who are subject to the 34-hour restart rule that may result in an extended break ‘at home’ in the truck cab while on the road. In contrast, electric APUs tend to be chosen by regional carriers where the driver may need air conditioning for a single overnight trip.”

Specific to the use of lithium batteries, Wilson advised of system-specification challenges.

“The only drawback when we’re dealing with lithium batteries [is that] lithium batteries can’t be left out in the cold; they can’t be left out in the heat,” Wilson said. “They have to be in the cab, which means you have to add a battery in the sleeper.”

He added that while lithium batteries must avoid extreme temperatures, the size of the battery pack is about half that of the traditional lead battery setup. Wilson explained that compared to a system utilizing Group 27 batteries – typically a set of four – to get the electrical equivalent in a lithium battery powered system requires the space of less than two Group 27 batteries, in terms of volume.

Maintenance, charging, and battery management

Aside from fuel, noise, and emission reductions, arguably the greatest benefit offered by electric APUs is the reduction in maintenance requirements.

“Electric APUs are also selected for their low-maintenance aspects,” Rubly stated. “With a simpler design than [diesel] APU systems and only a few moving parts, there is far less to service with an electric APU, and there is no engine-related maintenance such as oil changes and various filter replacements.”

The closed-system nature of electric APUs creates an environment to be seemingly simple in terms of maintaining its operation and performance capabilities.

“That’s the beauty of it – because everything is electronic other than the compressor itself and the Freon lines, there are no different maintenance [requirements] than you would have on the truck anyway,” Wilson advised. “The compressor itself is fully enclosed; you never really need to touch it.

“If you ended up with a Freon leak, you would handle that the same way you would handle it if it was just in the truck,” he added.

From a maintenance perspective, electric APUs inherently require proper battery management.

“Electric APUs are generally charged via the truck engine alternator,” Rubly explained. “Carrier Transicold’s ComfortPro electric and diesel APUs offer optional shore power kits that allow the driver to power the APU from any 115V outlet, providing climate control and battery charging while utilizing zero fuel.” He added that the ComfortPro electric APU can provide 7,500 Btu/h of air conditioning for up to 11 hours under normal operating conditions.

Along with understanding the charging needs of the battery, a fleet should remain cognizant of battery lifecycle expectations and when to perform appropriate replacements.

“Battery changeouts are the main maintenance requirement of electric APUs,” Rubly said. “With AGM batteries used in most systems, battery changes may be necessary in a 24- to 36-month timeframe, depending on use and number of charge cycles.”

However, fleets need be aware of the type of battery utilized in an electric APU system, as maintenance and replacement intervals can vary drastically.

“The lithium battery should have, in normal usage, at least a 10-year life span before it even needs to be touched,” Wilson stated.

Battery technology and the future of electric APUs

Electric APUs are available on the market today. Though, as the horizon nears with impending regulations for emissions, idle hours, noise pollution, and the industry’s goal of electrification, an understanding of the future of battery technology, and its applications to the electric APU space, is important.

“The emerging technology is going to be [focused on] how to store energy,” Wilson said. “Before, it was lead batteries. Big, heavy, and they go bad after a couple of years because we really work them to death in this market.” Wilson confirmed the industry more readily continues to adopt lithium battery technology as a replacement for AGM batteries.

“Lead [batteries] will always have their place in starting the engine; lithium batteries, they just can’t do that kind of load in starting an engine. But for lightweight, long-term storage, lithium – right now – is a way to go.”

Lithium-ion batteries may receive negative attention today as potentially dangerous, though Wilson heeded a generalization of the lithium category is inappropriate.

“Lithium scares a lot of people,” he said. “It doesn’t need to scare you as long as you understand it, but everybody just throws out lithium like it is all the same. There are six different chemistries of mainstream lithium batteries; some are safer than others, and some are more volatile.”

For instance, there is a distinct difference in chemistry and application for lithium cobalt batteries compared to lithium iron phosphate batteries. Wilson explained that while the lithium cobalt battery is used for lightweight, small-energy storage, for applications in the cellphone, airline, and car industries, it can be more volatile.

“When we are talking about energy storage in a vehicle – not to drive the vehicle like a Tesla – but storage in a vehicle for electrical loads, lithium iron phosphate batteries are way less volatile,” Wilson advised. “You don’t have the burning problems with lithium iron phosphate that you do with lithium cobalt. And so, when you look at safe energy storage, lithium can be scary, but if you are looking at the right chemistry, it is really not.”

Xantrex utilizes lithium iron phosphate chemistry in their lithium-ion batteries. In creating such a battery composition, Wilson stated that to utilize such a chemistry, about a 10 percent addition in weight and about a 10 percent addition in size was necessary, which was a decisively acceptable trade-off for the safety offerings.

“They are UL Listed,” Wilson said of Xantrex lithium iron phosphate batteries. Underwriter Laboratories (UL) is an independent safety science company that provides third-party certification and can approve UL Listing. UL Listing means that the company has tested representative samples of a product and determined that the product meets specific, defined requirements. These requirements are often based on UL’s published and nationally recognized Standards for Safety. “I like the UL Listing because it means somebody else, who doesn’t care how many batteries we sell, looked at it and made sure it was safe,” he added.

Integration of such battery technologies into a fleet’s operations today can help with plans for the future when regulations may move the industry toward expanded electrification adoption. Exploring electric APU specification today, even in limited capacity, can help a fleet understand which vehicles, applications, routes, etc. may be most positively impacted with such technology. Beyond that, testing electric APUs in a fleet today provides valuable feedback should extensive fleet-wide specification become necessary down the road with federal regulations requiring reduced greenhouse gas emissions and more efficient technologies. But aside from just planning for the future, electric APUs can be implemented today – and they offer benefits across multiple channels for a fleet’s organization.

About the Author

Tyler Fussner | Associate Editor | Fleet Maintenance

Tyler Fussner is Managing Editor - Community Manager at Supply Chain Connect, part of the Design & Engineering Group at Endeavor Business Media.

Previously, Fussner served as the Associate Editor for Fleet Maintenance magazine. As part of Endeavor's Commercial Vehicle Group, his work has been published in FleetOwner magazine, as well as Bulk TransporterRefrigerated Transporter, and Trailer-Body Builders.

Fussner's May 2022 print feature 'The dawn of hydrogen trucks' was named the best single technology article in B2B by the judges of the 2022 Folio: Eddie and Ozzie Awards. Fussner was also awarded Silver in the Technical Article category for the Trade Association Business Publications International (TABPI) 2021 Tabbie Awards.

Fussner previously served as Assistant Editor for Endeavor's Transportation Group on the PTEN, Professional Distributor, and VehicleServicePros.com brands.

Fussner studied professional writing and publishing at the University of Wisconsin-Whitewater. He has experience in shop operations, is a Michelin Certified Tire Technician, and a Michelin Certified Tire Salesperson.

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