What You Need to Know About APUs
January 2013, Work Truck - Feature
As anti-idling laws become more prevalent across the U.S., medium- and heavy-duty truck fleets are turning to onboard generators, called auxiliary power units (APUs), to operate accessory equipment — such as heating and air conditioning systems for sleeper cabs, halogen lamps for nighttime jobsites, and hoists for aerial bucket trucks or service cranes — without having to idle the main engine.
Considering that the industry averages fuel consumption at idle, for a Class 8 tractor, ranges from 0.6 gallons to 1.1 gallons, according to Thermo King, APUs enable truck fleets to substantially reduce fuel costs while still powering the amenities and tools drivers and crews need to perform their jobs most productively.
But, with a per-vehicle cost of $6,000 to $10,000 (plus installation), and various options to evaluate, the process for selecting the right APU for the application and budget can be daunting.
Combustion-Power vs. All-Electric APUs
The APU market is essentially divided into two types: combustion-power and all-electric (battery power). Although most combustion-powered APUs are fueled by diesel, there are units available that operate on alternative fuels, such as natural gas and propane autogas.
But, which APU type is better? The answer depends on the truck’s application.
“With diesel-powered APUs, there’s virtually unlimited power available to heat and cool as long as fuel is in the APU,” said Bill O’Shea, fleet sales director with Fontaine Modification, a company that installs APUs for OEMs and fleet customers, in addition to other custom services that tailor vehicles for specific vocational applications.
“Battery-powered APUs have the advantage of no noise, but have limited run times. Yet, that technology is getting better by the month with more advancements,” O’Shea added.
According to O’Shea, the diesel-powered APUs represent 70 percent of the APUs the company installs for its major fleet customers.
“With the electric APU, you have a captive amount of energy,” said Paul Barbaro, product manager, auxiliary power units for Thermo King, which manufactures both APU types. “You have four APU batteries, with limited ability to leach off the tractor batteries, so you have limited heating, ventilation and air conditioning (HVAC) capability. When the batteries go dead, there’s no way that you can just start the unit back up again and [instantly] create more APU capacity.”