• Product features --Always compare product features among various APUs, he stresses. For example, if routes cover the Northeast, Midwest or Canada, in the winter it helps if the APU has a truck-engine heating option in order to avoid cold starts. Or, if drivers watch TV when resting or like to store fresh food in an onboard refrigerator, be sure to spec an APU that provides enough power to the cab to run these devices.
• Ease of use - APUs should be simple for drivers to operate. Fleets need to be aware that in California, diesel-powered APUs used on Class 8 tractors equipped with model year 2007 or newer engines require an additional emissions reduction device, such as a diesel particulate filter (DPF), he says.
The average over-the-road tractor idles approximately 2,400 hours per year, according to Dwayne Cowan, APU product manager for Thermo King, a business of Ingersoll Rand. A fleet can save on average 0.8 gallons per hour idling with an APU vs. tractor engine. If fuel is $3 per gallon,
When deciding between a battery-based or engine-based APU system, battery-based have reduced install time and less overall maintenance, Cowan says. Engine-based APUs have an advantage in cooling and hotel loads, plus provide tractor engine warming and charge tractor batteries.
Because fleet suitability is a major factor in APU selection, he says careful thought needs to be given to the following:
• Battery-based system alternator size requirements
• What are the tractor operating days?
• What is the desired runtime of the HVAC system?
• What is the ambient temperature and the desired temperature in the bunk?
• Is the layover mostly during the day or night? Daytime layover will reduce the runtime of a battery-based system due to the increased solar load.
• What is the cab insulation and age of tractor?
• Are the sleeper and window curtains closed?
• What are the expected hotel loads?
• Does the tractor have multiple stops during a route? If so, how many stops and duration of each stop? Does the driver run the auxiliary HVAC during each stop? If this is the case, what is the typical time between stops for recharging the batteries?
• If there are not multiple stops, what is the typical drive time between rest periods? The longer drive time between stops will provide additional time to recharge batteries for battery based system.
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