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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.

In a few minutes, the cab interior becomes too cold to occupy comfortably because the engine driven pump is no longer running and circulating hot water to the heater. Autotherm ERS captures this heat and puts it to use warming the cab.

MIXED CAPABILITIES

Choices of auxiliary heating systems range from dedicated heaters to auxiliary power units. These can provide not just heating, but air conditioning and other benefits, such as power for "hotel loads" (electricity for in-cab appliances, computers, TVs and personal devices), battery charging and engine warming.

The Pony Pack 200 APU has its own compressor and alternator. If the truck's compressor and/or alternator fails, the APU's compressor and alternator provide enough engine support to allow the truck to continue to function until it can be repaired at a preferred shop, says Rex Greer, president of Pony Pack.

There are APUs that have the ability to provide a combination of engine, cab and fuel pre-heating, John Dennehy, Espar Products' vice president of marketing and communications, says. These effectively remove fuel gelling issues from winter operation.

"Pre-heated engines start easier and dramatically reduce cold start engine wear and cranking system stress for maintenance cost savings," he notes. "Cold start white smoke is eliminated extending the life and regeneration cycles of diesel particulate filters for lower cost of ownership."

"While heating-only units are less costly, an APU with cooling may be a more practical option for truck operators whose routes go through warmer climates," observes Dean J. Lande, manager of business development, Carrier Transicold. "Fuel savings and greater versatility when complying with anti-idling regulations are also benefits with APUs."

Making the appropriate selection of an auxiliary heating system involves a range of considerations. These include such factors as capacity needed based on the climate where the vehicles operate; size of the cab and sleeper compartment; placement, mounting and installation of the system; how the system is integrated into the vehicle; system weight; desired features; and maintenance requirements.

OUTPUT CONCERNS

A good starting point for selecting an auxiliary heating system is to figure the expectations of the unit and the operational requirements. Among the types of questions that need to be answered: Will the APU to be used to supply additional power for hotel loads? How much heating and cooling is wanted? What is the heater's capacity?

High BTU (British Thermal Unit) output is important for both heating and cooling, observes Jill Tolstedt, sales and marketing manager, Tridako Energy Systems. The heater's capacity and the outside temperature determine how long it will take a system to heat or cool the environment. The higher the BTU rating, the more fuel that will be burned.

As a rule of thumb, maintaining a comfortable inside temperature when the outside temperature is 32 degrees Fahrenheit requires 20 BTUs for every cubic foot of space.

BTU is a standard unit of measurement used to denote both the amount of heat energy in fuels and the ability of appliances and air conditioning systems to produce heating or cooling. One BTU is the amount of heat required to increase the temperature of a pint of water (which weighs 16 ounces) by one degree Fahrenheit.

A truck sleeper with an 80-inch double bunk sleeper has a volume of 320 cubic feet. Therefore, it would require a heater with 6,400 BTUs. For larger sleepers, or for trucks that operate in extreme cold climates, heaters with much higher BTUs would be needed.

A vehicle's insulation also needs to be considered as well. The poorer the insulation, the more heating/cooling required.

Insulation can be improved by insulating the floors with foam under the carpet, installing extra insulation in the cab and sleeper and adding heavy duty or thermal curtains to separate the sleeper compartment from the cab. These things will also reduce the amount of time it takes for the auxiliary heating system to warm things up or cool things down.

VEHICLE USE

Vehicle application and operation must be analyzed in order to determine how often and how long the truck idles to heat or cool the cab or sleeper, says Pony Pack's Greer.

For a driver that will be spending a night in his truck every other night or so, a battery-powered auxiliary heating system that can provide up to 8 hours or so of operation might suffice, he says. On the other hand, a driver who will have to do his 34-hour Hours-of-Service reset in his truck will need a much larger capacity system.

Trucks running in the arid Southwest will have different heating and cooling requirements that those operating in the Northwest Territories, he adds.

It is also advisable to compare the airflow of auxiliary heating systems, measured in cubic feet per minute (cfm), as well as their fuel consumption, measured in grams per hour (gph).