APUs: The Good, The Bad and The Ugly

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TORONTO – On a recent driving trip between Toronto and Chicago, I encountered an unusual situation: a quiet rest area.

Of the 26 trucks I counted lined up in the parking stalls, only two were idling. I’m not sure how long they had been there or whether they were in the process of coming or going, but I thought perhaps the tide has finally turned.

Strolling through truck stops and rest areas in recent years was to be bombarded by noise from the idling engines, usually set at high-idle of around 800 to 1,000 rpm to maintain oil pressure and/or pressure in the air-conditioning compressor and the heat in the cab heater core – or so the thinking went.

On nights when temperatures dropped to low- to mid-teens Celsius, I could never figure out whether the driver had the heater or the air conditioner going. Neither was necessary, which made running the big engine at high idle all the more ridiculous. 

An accepted rule of thumb says every 10 percent of idle time equates to about a one-percent penalty in fuel economy. Those chaps, idling away a cool fall evening, were likely hurting their overall fuel economy by about three percent. Not to mention the money wasted at a gallon an hour burned over eight hours. Clearly there is work to be done.

“Some small to medium-size fleets just aren’t onboard yet with the entire idle-reduction savings,” says John Dennehy, vice president of marketing at cab-heater supplier Espar Products.

“I still see 50 percent of vehicles out there that still aren’t implementing idle reduction.”

Unfortunately, Dennehy’s estimates are probably accurate, and that amounts to a lot of fuel used in a pretty unproductive manner. As for why uptake is still relatively low, the reasons run the gamut, and most are valid.

Diesel auxiliary power units (APUs) tend to be heavy and they take up precious frame space. Some have reliability issues, they require maintenance and they can be noisy. The big advantage to a diesel APU is that it will keep running long after a battery-powered auxiliary-power system has coughed up its last amp.

The electric systems, while generally lighter in both weight and maintenance, have duty cycles limited by their ability to recharge. While most systems now claim reasonable output for eight- to 10-hours, once the batteries are depleted they must be recharged.

That might not be a problem in high-mileage applications where the truck runs eight to 10 hours a day. However, when the truck doesn’t run long enough, the available charge will be limited. This can also be a problem during an HOS reset interval in hot weather, where the truck is parked for 36 hours or more and air conditioning is required.

And there’s another menace to electric APUs: CPAP machines. Drivers with sleep apnea require continuous positive air pressure machines to ensure a good night’s rest, and some of those machines draw a lot of current, limiting the effectiveness of a battery-powered system.

Electric APUs also require deep-cycle batteries, which aren’t good at starting trucks, and a heavy-duty high-output alternator. Both can add to the overall system cost.

Owner-operator, Greg Decker of Airdrie, Alta., has used diesel APUs for years and has run several different brands. He now has a popular unit that he says does an adequate job of cooling the cab when it’s not extremely hot, but has a harder time warming the cab in the minus-40 Alberta winters.

He supplements the APU’s output with a small space heater in winter and plugs a block-and-coolant heater into the APU for engine heating. The unit has a closed-circuit HVAC loop, which Decker prefers to tapping into the truck’s system.

“I had a coolant line fail on a previous unit,” he says. “It drained all the coolant from the truck and left me stranded with a huge service-call charge.”

The diesel APU works for Decker, but he cautions prospective adaptors to do a lot of research before bolting one to the truck.

“I would rate the reliability and performance as good,” he says. “I don’t think there is a perfect APU on the market. Buyers have to do their research and try to buy a unit that matches their price, duty requirements, mechanical abilities and the availability of service locations in areas they operate.”   

What’s Around the Corner?

While developing their SuperTruck for the U.S. Department of Energy’s test program, engineers at Cummins and Peterbilt developed a system that used four 3,300-watt/hour lithium-ion (LI) batteries. Results showed it did a better job at powering real-world demand than what is commercially available, but there’s a reason why it’s not commercially available.

As Cummins’ team leader, David Koberlein explains, “Those batteries are heavy and expensive.

“The capacity of this system is 13.2 kw/hr, which is significantly higher than current systems that support just HVAC systems,” he says. “We were able to run a fleet-specified load on the system, including a CPAP machine, microwave, TV monitor and other typical hotel loads, and we recharged from zero within six hours of the start of the truck.”

That sounds promising, but LI batteries on that scale are still not cost effective for use as a truck APU.

The ROI just isn’t there yet.

Espar’s parent company, Eberspaecher, announced at the IAA truck show in Hanover in September that it expects to have a fuel-cell APU that converts diesel very efficiently to electricity in production by 2017. The company says the system would be most efficient when used to power almost all of the truck’s auxiliary loads, including air compressors, water pumps, heaters and air conditioners.

Using catalytic convertors and reformers, diesel fuel is converted to “fuel gas” which is used to produce electricity. Eberspaecher claims they can get the same output with about the energy input, and nitrogen oxide, carbon monoxide and particulate emissions are 90 percent less compared with a diesel-engine APU.

Development is hardly at a standstill, but some revolutionary change from our traditional sources of auxiliary power is still a few years away.

Meantime, when alternatives fail or leave you wanting, it’s worth remembering that trucks bearing the Certified Clean Idle sticker are allowed to idle even in areas with idling restrictions.

If your APU works in, say 80 percent of the situations you find yourself in, that’s fine. Idle for the remainder or get a motel. And if your truck is older and doesn’t bear one of the aforementioned stickers, you can get one on eBay for $4.99.

 

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Jim Park was a CDL driver and owner-operator from 1978 until 1998, when he began his second career as a trucking journalist. During that career transition, he hosted an overnight radio show on a Hamilton, Ontario radio station and later went on to anchor the trucking news in SiriusXM's Road Dog Trucking channel. Jim is a regular contributor to Today's Trucking and Trucknews.com, and produces Focus On and On the Spot test drive videos.


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