Idling Roundup
Spec’ing for comfort
A thorough review of your needs will tell you what to spec on your truck and what power needs you will run into for key-off comfort

By Paul Abelson, senior technical editor

In virtually every major purchase decision in trucking, trade-offs must be made. Should I get the 14- or 15-liter engine that delivers more power and torque or the more fuel-efficient 12- or 13- liter one that saves weight and gets better fuel economy? Should I get the 18-speed transmission that gives the most flexibility and control or the 10-speed that weighs less and costs much less? Or should I get an automated manual that costs more initially but saves money over years of use? Should I get ribbed drive tires for better fuel economy or lug-design tires for better traction?

In all cases, decisions must be made based on each individual circumstance. Before you can make your decisions, you need to know what your options are. What is available? What are each alternative’s advantages and disadvantages?

Idle-reduction gear is no different.

Start by defining your needs. How warm or cold will it get where you will operate? What temperature range will your device or devices have to cover? Should you cover the entire temperature range or can you “make do” at the extremes? If you are needing the extremes covered, your costs will be higher.

In the 1980s, the U.S. Army was having an inordinate number of armored tank heater failures. During the same period, our NATO Allies, Britain and Germany, had virtually none. Our specification was written in 1942, just after Japan sent an invasion force to the Alaskan islands of Kiska and Attu. Planners envisioned Sherman tanks fighting in Alaska in mid-winter in temperatures below minus 40 degrees.

They specified a 60,000 Btu heater for those extreme conditions. They never considered more common temperatures, between freezing and minus 10 degrees. The heaters would “short cycle” quickly, reaching desired warmth and shutting down, only to start over again minutes later. That burned up motors and igniters. Our Allies specified heaters with about half the capacity that ran continuously without breakdown. If it wasn’t warm enough, soldiers put on more sweaters.

This is a principle common to all heating, ventilation and air conditioning units. They should be designed for the most common operating range, not for the extreme. Since most wear and tear occurs on start-up, avoid short-cycling. Spec’ing for extremes not only costs more, heat and air units don’t work as well.

Idle-reduction equipment is primarily heat and air units. The equipment you select should provide heat in winter, cooling in summer and power for “hotel loads,” the creature comforts that you would expect when staying in a hotel. They include lighting, entertainment such as TV, stereo, DVR, etc., and cooking needs, including food refrigeration.

Power can come from a variety of sources, often in combination. Batteries can provide electricity to run heat and air units as well as hotel loads, but they need to be recharged. That can come from an alternator turned by your truck’s engine or by a smaller auxiliary engine turning its own generator or alternator. It can also come from a shore power unit, if it is available and you have the wiring and devices needed to use it. To use it, you may need to convert 120-volt alternating current (AC) to 12-volt direct current (DC), and internal wiring to move current from your plug-in point to the batteries.

Batteries fit three major types: starting, deep cycle and absorbed glass mat. Starter batteries deliver high current for short times. Deep cycle delivers lower peak current, but over a much longer period. Glass mat batteries provide the best of both, but are heavier and more expensive. If you combine starter batteries and deep cycle batteries for hotel loads, use an isolator in the charging circuit to allow each type to charge fully.

Although “certified idle” engines are legal and increasingly available, avoid using your big engine for hotel loads. Engines consume fuel at three to four times the rate of auxiliary power units or generators. The names are often used interchangeably, but generators provide only electricity while APUs have their own air conditioning compressors and often full A/C systems with ducts to the cab or sleeper. Generators, or gen sets, can feed individual units or maintain batteries.

Run continuously, both types consume about 0.2 to 0.3 gallons of diesel per hour. Properly sized, these auxiliary engines can keep the heat and air system along with all hotel loads operating while recharging batteries provided they have fuel.

If you can schedule extended down time out of the truck, battery power may be a better alternative, especially if supplemented with shore power. An extra bank of deep cycle or absorbed glass mat batteries can provide a great deal of power.

To be sure, calculate your needs. TMC’s Recommended Practice RP136A, Managed/Isolated Battery Systems for Electric Start Systems contains a table of typical electric current draws for such things as dome and reading lights, air-circulating fans, heater blower motors and even a refrigerator. Values are for 12-volt systems. For microwaves, hot plates, TVs, entertainment systems, and heat and air systems, check manufacturers’ specifications. If using 120-volt systems, multiply the amp rating by 10 to get 12-volt current draw into your inverter, and add 25 to 30 percent to the total for internal losses through the inverter. Size cables and fuses accordingly.

If you have shore power or an APU or generator/inverter producing household current, you can use a low-cost ceramic heater in your bunk. For less than $100, you can find models with thermostat controls at most hardware stores. Do not use them with battery power. In addition to electric heat, a generator or APU can provide hot water from its cooling system. The truck’s engine and cab and bunk heaters can use this hot water.

Perhaps the most efficient heat sources are fuel-fired heaters. Espar and Webasto are most popular. Fuel consumption usually ranges between 0.05 and 0.10 gallons of diesel per hour, for outputs of 6,000 or 12,000 Btu per hour. Older heaters cycled on and off, but the latest cut output to as low as 3,000 Btu to maintain comfortable levels without short-cycling.

Self-contained air conditioners are available in both 12-volt and 120-volt models, with cooling capacities to match your climate and volume needs. Remember, too much capacity leads to destructive short-cycling.

Bergstrom, makers of the NITE System that uses their battery powered A/C with a fuel-fired heater just announced a partnership with eNow to use solar charging to provide electricity for the A/C.

These options need careful evaluation to meet your needs. Another alternative is technology that starts and stops the engine. Idle Smart measures interior and ambient (outside) temperatures as well as engine and battery conditions. Its electronic controls weigh less than 5 pounds. Idle Smart cuts idle time by an average of 70 percent but still maintains driver comfort using the truck’s heat and air units. A one-time installation will take less than three hours and it can be moved to a new truck.

For added comfort, beef up your truck’s insulation. It will make all your devices more efficient. LL

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