Compressors that run on frictionless bearings are an enticing prospect. Dan Foss Turbocor, Inc. is now marketing a line of compressors that use magnetic bearings to provide essentially frictionless operation. These compressors have been on the market for about three years, and now McQuay International is incorporating the compressors into their new line of frictionless chillers.

Using innovative technology that levitates the compressor shaft in a magnetic field, the compressors operate without metal-to-metal contact, making them more efficient, and eliminating the need for an oil management system. Turbocor has recently received three prestigious awards for this design: the ASHRAE/AHR Expo "Energy Innovation" Award in 2003, the Natural Resources Canada's Energy Efficiency Award in 2003, and the U.S. Environmental Protection Agency’s Climate Protection Award in 2004.

How are they different?Here are some of the features, benefits, and concerns to help you decide whether frictionless compressors (or McQuay’s frictionless chillers) are right for you. Each feature is discussed in more detail below.

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Probably the best operating boiler can achieve ~80% or +/-2%.

Historically, boiler efficiency has been limited due to the minimum temperature allowed for the auxiliary equipment. Heat lost up the stack was in exchange for keeping the flue gas temperature above the water vapor dew point to protect the air heater or economizer from acid corrosion. If water vapor was allowed to condense out, rapid deterioration, due to acid corrosion, of the outlet duct and stack would also occur.

The contribution of dry flue gas is ~9-12% & ~5-8% due to presence of humidity & water in combustion products. The reason is that the flue gas temperature (generally 170 - 200°C) is limited by dew point to avoid condensation of downstream exchangers.

With the development of CHX™ condensing heat exchangers, boiler efficiency can now approach 90%. Approximately 1% gain in boiler efficiency can be expected for every 20° C reduction in flue gas stack temperature. Therefore if we can lower it to ~90°C or so, we can practically recover more heat with total thermal efficiency increase from 80% to ~88% or so.