Thermo King discusses Auxiliary Power Units

Oct. 1, 2007
A number of factors are creating a growing need for Auxiliary Power Units (APU) on sleeper cab tractors. Chief among them: fuel prices keep rising and

A number of factors are creating a growing need for Auxiliary Power Units (APU) on sleeper cab tractors. Chief among them: fuel prices keep rising and are a significant portion of the operating cost for fleets and owner operators; anti-idle laws that prohibit truck idling — done to keep drivers comfortable, engines warm, and batteries charged — are growing in coverage and enforcement, and continuing environmental concerns over diesel emissions.

A typical over-the-road tractor will idle approximately 2,400 hours a year. It is estimated that idling burns 5 percent of all fuel used in US, amounting to about 1.2 billion gallons.

Approximately 2.3 million diesel trucks are in the US, of which some 600,000 are equipped with sleeper cabs. These are ideal candidates for APUs to handle complete climate control, as well as perform other functions, including providing onboard power.

Research shows that idling a diesel engine for an hour produces 10.44 pounds of House Gases (GHGs). A year's worth of idling produces more than 12.5 tons of GHGs. Furthermore, 60 percent of all vehicle particulate matter in the air comes from heavy duty diesels.

To address the matter of APUs, Thermo King put on an Idle Reduction Seminar at the Great American Trucking Show. Presenters were the company's Tom Kampf, product manager, climate control technologies, and Leonard “Bud” Rodowick, manager, fleet performance.


The savings provided by an integrated APU are significant, said Kampf. Assuming one gallon is burned per hour at idle, 2,400 hours per year of idling, and diesel fuel at $2.80 per gallon, a fleet spends $6,720 on idling a year per truck.

With an APU, only about 0.10 of a gallon of diesel is burned per hour. Using the same figures, he said an APU would only burn $672 worth of fuel per year — a savings of more than $6,000 per year or $500 per month

Figuring an APU costs approximately $9,000, and that is financed at a rate of 13.5 percent for 36 months, the cost for the APU would be about $307 per month. That results in a savings of $193 in fuel costs per month, or $193 in positive cash flow per month

Kampf noted that there are also tax savings available because of the dual use of fuel in the tractor and its APU.


There is a growing trend by states and municipalities to adopt anti-idling regulations. Thermo King says the following states have some form of anti-idle rules: Arizona, California, Colorado, Connecticut, Delaware, District of Columbia, Georgia, Hawaii, Illinois, Maryland, Minnesota, Mississippi, Missouri, New Hampshire, New Jersey, New York, Pennsylvania, Texas, Utah, and Virginia.

At least four states — Arkansas, Kansas, New Mexico, and Oregon — allow a 400-pound weight exemption for an APU


Fleets typically use two ways to validate their savings with an APU — the standard GPH (gallon per hour), which is that engines will consume about a gallon an hour idling, vs. APU fuel consumption, which is much less, said Thermo King's Rodowick, manager, fleet performance. The difference is fuel/cost savings per truck.

Downloads from engine electronic control modules have shown that idle reduction translates to mpg improvement because fewer gallons are used for idling, so there is more miles per gallon driven

With the new ultra low sulfur diesel (ULSD), the reduced sulfur content is causing the diesel to burn faster, testing from the American Transportation Research Institute (ATRI) has found.

While there is not enough data to determine how significant a reduction there is, Rodowick said fleets are experiencing as much as a five to 10 percent reduction in fuel mileage. What's more, many newer diesel engines are not getting the fuel economy of older engine designs. All the more reason to consider an APU, he said.

Drivers play a significant role in fleet fuel economy, he said, noting that TMC (Technology & Maintenance Council) believes that driver performance can account for as much as a 35% difference in fuel economy performance.

In concluding the seminar, Rodowick said the “green squeeze” — idling laws, US EPA emission standards, and higher fuel costs — are not going away. Fleets need to identify their solutions and then re-establish what they want their mpg rate to be.

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