The nuts and bolts of APUs

How to select and maintain the appropriate auxiliary power unit (APU)

With the proliferation of anti-idling regulations, the need to reduce fuel costs and emissions and the urgency to keep drivers, fleets are turning to auxiliary power units (APUs) to provide creature comforts without the need for running a truck's engine. However, if not properly selected, operated and maintained, APUs can create service and repair issues.

In simplest terms, a truck APU is a device that provides climate control and converts DC to AC power for driver creature comforts without the need to idle the engine.

Idling the engine maintains a comfortable environment for drivers but it wastes energy. An hour of idling time consumes about one gallon of diesel fuel, whereas APUs consume far less. Fuel is one of a fleet's largest large expenses.

Even though diesel engines are efficient when idling, constantly running high horsepower engines at low rpm combusts fuel incompletely. What's more, continual operation of an engine at low speed causes additional wear on internal parts compared with road speed rpm.

Along with consuming significant amounts of diesel fuel and emitting large amounts of pollution, long periods of idling heavy duty truck engines accelerates engine wear and tear and causes noise and vibrations.

The matter of selecting the appropriate APU is complicated because of the wide variety of units to choose from. Configurations include diesel-powered engine-based, shore power, thermal storage systems, hybrid systems and pure electrified system. As would be expected, each type of design has its advantages.

APU manufacturers advise that the expectations of the unit and its operational requirements must be considered to ensure that the APU chosen will perform as desired. Other important elements to take into account are systems placement and installation, as reliability problems tend to be in large part due to improper installation.

When purchasing APUs, Dean J. Lande, manager of business development for Carrier Transicold says there are seven key criteria fleets should consider:

Performance (diesel vs. battery) - "Diesel APUs tend to provide more consistent performance over longer periods of time and are not dependent on batteries that need to be recharged every four to eight hours," he says. "Especially for fleets that travel through the hotter region of the southern tier states, it is very important to ask whether the APU will provide at least eight hours of continuous cooling. Battery-powered systems tend to under-perform diesel APUs in this region."

Lifecycle cost - Lifecycle cost includes initial purchase price plus both operating and maintenance costs. Diesel APU buyers must budget for oil and filter changes, so extended service intervals are important. Buyers of battery systems must budget for potential battery replacement.

Warranty - It is necessary to understand what components are covered under the manufacturer's standard warranty and for how long, recommends Lande. Look for standard warranty packages that cover big-ticket major components such as engines, compressors, generators, evaporators and condensers. Determine if the manufacturer provides an extended warranty option. "It is important to compare among manufacturers, not just cost, but what specific components are covered," he says. "Look for the lowest cost coverage that covers the most major components."

• Service network - For fleets that travel long distances, it's best to go with manufacturers that provide nationwide service support. "If an APU problem arises on the road, you don't want your drivers to find themselves in a situation where no one knows how to service it."

• Installation time - Shorter install times typically reduce overall acquisition cost. Truck OEMs are beginning to offer preconfigured cabs to accommodate an APU, which "drastically cuts down on installation time, saving money," notes Lande.

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