Auxiliary Heating Systems 101

Essential considerations for choosing reliable, easy-to-maintain units


Anti-idling laws, high fuel prices and unnecessary engine wear are causing fleet operators to look for alternative ways to keep drivers in a comfortable environment when temperatures drop. The use of auxiliary heating systems is one method for heating the truck cab and sleeper without having to run a truck's engine.

While an idling engine maintains a comfortable environment for drivers, it wastes energy. Even though diesel engines are efficient when idling, constantly running high horsepower engines at low rpm combusts fuel incompletely. What's more, continually operating the engine at low speed causes additional wear on internal parts compared with road speed rpm, and that increases maintenance costs and shortens engine life.

By using an auxiliary heating system to heat the cab, a truck's engine can be shut off, so far less fuel is used and fewer diesel emissions emitted. Since the engine isn't running as much, there is reduced the wear on the engine and other related mechanical components.

On average, heavy duty diesel truck engines consume 1 to 1.5 gallons of diesel fuel per hour while idling. When operating on the road, these engines consume around 6 or more gallons per hour.

The amount of operational savings that can be realized from auxiliary heaters will depend, naturally, on how well the system is matched to requirements and needs. That is no small feat, as there is a very wide variety of designs and models to pick from.

There are auxiliary cab and sleeper heater systems that come with engine heating capability, and full auxiliary power units (APUs) that come with added functions as well. APUs are offered by truck OEMs as original equipment and from a variety of manufacturers for new and aftermarket installation.

APUs come in various styles and arrangement. There are models that are powered by diesel or propane. The typical major components are a small engine, an alternator and the heating, ventilating and air conditioning (HVAC) system.

There are hybrid and electric APUs for which batteries and an inverted charger are important components. One hybrid system, introduced earlier this year, combines the Bergstrom NITE Plus System no-idle climate control system with a Kohler DC power unit.

With this hybrid system, when the power levels of the four deep-cycle AGM batteries decrease to low voltage levels, the low-battery indicator is triggered and the Kohler DC power unit begins to recharge the batteries while keeping the Bergstrom NITE Plus System operating uninterrupted, explains Stacy Peshkopia, marketing manager, Kohler Power Systems. Should the truck's batteries also be depleted, the power unit is able to recharge them with the use of the specified bi-directional separator, and at no risk of overcharging either bank of batteries.

In heating mode, 0.05 gallons per hour are consumed, she says, while 0.10 grams per hour is used when the hybrid power system is in recharge mode. When the system is in the air-conditioning mode, it uses no fuel because it operates solely on the Bergstrom system.

Some vehicle APUs can also use an external shore power connection for their heating and cooling functions. Fuel-cell powered APUs as a way to reduce idling on large trucks is under development and has been demonstrated.

Another alternative heating solution is the Autotherm Energy Recovery System (ERS). It automatically continues operation of the vehicle's heater every time the engine is turned off.

By circulating the same amount of hot water to the cab heater as the engine pump and keeping the fan operating, the Autotherm ERS keeps the cab interior warm for hours whether the operator is in the vehicle or out of it, says Frank Perhats of the Autotherm Division of Enthal Systems.

The cooling system of any vehicle that has been driven on the road for a half hour or longer has reached optimum operating temperature and is, therefore, a storehouse of useable energy, he explains. In most trucks, this energy is slowly dissipated to the vehicle exterior when the engine is off.

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