(Minneapolis - April 17, 2008) - Since launching the screw compressor more than 15 years ago after extensive development and testing, Thermo King has seen it start to become the compressor choice for bus HVAC. Thermo King has invested millions of dollars in research, development and tooling to ensure that the most precise tolerances are maintained to maximize the reliability of this technology, with the payoff being an 80 percent reduction in moving parts as compared to a reciprocating compressor.
This reduction in moving parts greatly reduces the chance of breakdowns and helps make Thermo King's HVAC systems the most reliable on the market. Today, there are more than 40,000 screw compressors in service in North America, and one early installation of 20+ compressors have operated for more than 28,000 hours each without a failure. Big Power in Demanding Climates.
Given the reliability and performance benefits the screw compressor provides, more and more customers are choosing to go with this technology for their fleets. Valley Metro, located in Phoenix, Ariz., provides bus service in one of the most severe climates in North America and requires efficient and reliable HVAC systems to keep the customers cool. Operating buses in temperatures exceeding 110 degrees Fahrenheit, day in and day out during the summer, has made Dave Hyink, Valley Metro fleet and facilities supervisor, impressed with the performance of the screw compressor and R-407C refrigerant. "It's the best cooling unit that's ever been in the valley," reports Hyink. The unique combination of the S391 screw compressor and the high performance refrigerant R-407C used by Valley Metro is a solution offered only by Thermo King.
While the S391 with R-407C provides an excellent solution, some former R-22 customers have decided to use the refrigerant R-134a exclusively. However, because these customers still need the higher cooling capacities you get with R-22 and R-407C at engine idle speeds, these customers have chosen to go with the Thermo King S616 compressor. Former R-22 customers, like Sky Harbor Airport in Phoenix, who use this combination of the S616 with R-134a, have not experienced any decline in cooling performance.
Built for Fuel Savings with fuel costs at all-time highs, the screw compressor can save gallons of fuel per day for customers using reheat. "Reheat is a mode of operation that introduces heat into the refrigeration cycle to stabilize the temperature as it reaches set point", says Don Nielsen, engineering manager, Thermo King. "Most North American transit operators use reheat to balance the cooling load during light load conditions and also to keep the windows from fogging up." The screw compressor can stabilize the load by "unloading" some of its pumping ability during these conditions. This reduces the amount of energy used during reheat, resulting in less horsepower required from the engine to drive the compressor. Less horsepower means less fuel used, which in turn means big savings. Just how much fuel can you save with the screw compressor? That depends on how much reheat you use. An operating profile of your fleet that includes local climatic conditions, light and peak load conditions, number of days per year that air conditioning is used, hours of operation per day and engine data will provide the fuel savings you can expect. While testing a bus from a large Midwestern fleet in the Thermo King Testing Center, the bus operator was able to witness the reduction in engine horsepower load when the compressor unloaded, and the results were quite impressive.
What about operators who don't use reheat in their operation? For operators that cycle the clutch off when the temperature reaches set point, the most efficient solution available is the screw compressor with the high performance refrigerant R-407C. The bus will cool down faster and the temperature will recover faster after door openings, which adds up to the compressor running less, using less horsepower off the engine and saving money.
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