(Minneapolis - October 6, 2008) - Most people are familiar with engine-driven air conditioning systems, mainly through their lack of cooling power during moments when needed most such as rush hour on a 98 degrees F day. Once traffic starts moving again, the air conditioning begins to cool down the car once again. A conventional bus that idles 50 percent of the time with an engine-driven compressor has a much larger challenge. It needs to keep a bus load of people cool and comfortable. And those people do not care if the bus is moving or not. It takes a very large air conditioner with a very large compressor to provide ample cooling at engine idle speeds. Thermo King has come up with a solution: an air conditioner that is NOT dependent on engine speed for capacity, but rather an electric compressor. And Portland, Oregon's TriMet bus company had the chance to try it.
The idea of having an all-electric air conditioner on a conventional diesel engine-driven bus was exciting for TriMet's bus maintenance director Tony Bryant, who believed that there would be fuel savings from such a system. With these potential benefits in mind, TriMet agreed to test the unit last year and compare the results to 20 other units from the same fleet.
After one year of monitoring and recording, Bryant said "Like a lot of transit maintenance managers, we're about getting results. The Thermo King system has had negligible maintenance costs and given us a 2-3 percent average yearly fuel savings to boot."
This "dream system" is not dependent on engine speed for capacity. It operates with an electric compressor, offering consistent capacity no matter the ambient temperature or bus speed.
"Part of what we do at Thermo King is to make sure our customers are comfortable with new technology. We allow customers to see the actual benefits in a fleet environment prior to making any major decisions," says Don Nielsen, engineering manager at Thermo King. "No one wants to be stuck with 'it sounded good but didnÃ¢â‚¬â„¢t work very well' technology."
Of course, with any testing there are issues and challenges to overcome. Aside from some normal tweaks and upgrades at the beginning of the test, the fuel mileage on the test unit was not as good as on the rest of the fleet. "Although the test was somewhat skewed by measuring one sample against the average of 20, we felt that we should be seeing better results," said Nielsen. "The test unit was delivering more capacity than the conventional unit and it was delivering it all the time, even when the engine was idling." Once software was installed to provide better capacity control on the electric HVAC, the fuel economy improved dramatically, exceeding the fleet average by as much as seven percent in some months.
After the testing in Portland, two facts became obvious; the electric air conditioner could be smaller and still deliver the same amount of cooling as the conventional air conditioner and that there is a cost for cooling. "When comparing systems and refrigerants, it's very important for customers to understand that the comparison must be based on the same amount of cooling," says Nielsen. "When you do that, efficiency will win every time."
Thermo King Corporation, a business unit of diversified industrial firm Ingersoll-Rand Company Limited, was founded in 1938 and manufactures transport temperature control systems for a variety of mobile applications, including trailers, truck bodies, buses, shipboard containers and railway cars. The company operates 10 manufacturing facilities and 17 parts distribution centers worldwide. Sales and service is provided by a global dealer network of 865 independently owned companies in 75 countries. For more information, access the Thermo King web site at www.thermoking.com.
Thermo King Corporation, a business unit of diversified industrial firm Ingersoll Rand Company Limited, was founded in 1938 and manufactures transport temperature control systems for a variety of mobile applications, including trailers, truck bodies, buses, shipboard containers and railway cars. The company operates 10 manufacturing facilities and 17 parts distribution centers worldwide. Sales and service is provided by a global dealer network of 865 independently owned companies in 75 countries.
Mike O'Brien, Thermo King Corporation