Frictonless compressor technology
New compressor makes chillers cleaner, quieter, and more energy-efficient new compressor technology intro- THE BEARINGS Traditional centrifugal compressors use roller duced during the 2003 International Air-Conditioning, Heating, Refrig- bearings and hydrodynamic bearings, both of erating Exposition (AHR Expo), held last January which consume power and require oil and a lubrication system. Recently, ceramic in Chicago, may have a significant effect on the future of mid-range By HUGH CROWTHER, PE, roller bearings, which avoid issues and related to oil and reduce power conchillers and rooftop applications EUGENE SMITHART, PE sumption, were introduced to the in water-cooled, evaporatively HVAC industry. The lubrication of cooled, and air-cooled chilledwater and direct-expansion (DX) systems. these bearings is provided by the refrigerant itself. 1 Designed and optimized to take full advantage of magnetic-bearing technology, the compressor was awarded Touchdown Permanent-magnet the first AHR Expo Innovation bearings synchronous motor Award in the energy category, as well as Canada’s Energy Efficiency Award for its potential to reduce utility-genShaft and
Compressor impellers erated greenhouse-gas emissions. The cooling compressor is key to a new watercooled centrifugal-chiller design, with Inlet-guide-vane Magnetic bearings Air-Conditioning and Refrigeration assembly and bearing sensors Institute (ARI) tests indicating integrated part-load values (IPLVs) not normally seen with conventional chillers in this tonnage range. This article describes this new The TT300 compressor’s onboard digital electronics manage operation compressor technology and its first use while providing external control and Web-enabled access to a full array of in an ARI-certified chiller design. performance and reliability information. A Hugh Crowther, PE, is the global director of applications for McQuay International in Minneapolis. With more than 15 years of experience in large-HVAC-system design, he has written numerous articles and application guides related to HVAC design. Contact him at hugh. [email protected] com. Eugene (“Smitty”) Smithart, PE, is vice president of sales and marketing for Turbocor in La Crosse, Wis. With nearly 30 years of experience, he is well-known in the HVACR industry, having published numerous articles and been involved in a number of industry-changing initiatives.
A recipient of the U. S. Environmental Protection Agency’s Climate Protection Award, he can be contacted at [email protected] com. F R I C T I O N L E S S Magnetic-bearing technology is significantly different. A digitally controlled magnetic-bearing system, consisting of both permanent magnets and electromagnets, replaces conventional lubricated bearings. The frictionless compressor shaft is the compressor’s only moving component. It rotates on a levitated magnetic cushion (Figure 1). Magnetic bearings—two radial and one axial— hold the shaft in position (Figure 2).
When the magnetic bearings are energized, the motor and impellers, which are keyed directly to the magnetic shaft, levitate. Permanent-magnetic bearings do the primary work, while digitally controlled electromagnets provide the fine positioning. Four positioning signals per bearing hold the levitated assembly to a tolerance of 0. 00002 in. As the levitated assembly moves from the center point, the electromagnets’ intensity is adjusted to correct the position. These adjustments occur 6 million times a minute. The software has been designed to automatically compensate for any out-of-balance condition in the levitated assembly.
Target sleeve Y-axis position sensor Channels 0-1 X-axis position sensor Channels 2-3 Channel 4 X-axis position sensor Impellers Z-axis Sensor Front position ring radial sensor bearing Motor Sensor ring Rear radial bearing Axial bearing FIGURE 2. A digitally controlled magnetic-bearing system consisting of two radial and one axial bearing levitate the compressor’s rotor shaft and impellers during rotation. fail, the touchdown bearings (also known as backup bearings) are used to prevent a compressor failure. The compressor uses capacitors to smooth ripples in the DC link in the motor drive. Instantaneously after a power failure, the motor becomes a “generator,” using its angular momentum to create electricity (sometimes known as back EMF) and keeping the capacitors charged during the brief coastdown period. The capacitors, in turn, provide SHUTDOWNS AND POWER FAILURES enough power to maintain levitation When the compressor is not running, during coastdown, allowing the motor the shaft assembly rests on graphite-lined, rotor to stop and delevitate. This feature radially located touchdown bearings. The allows the compressor to see a power magnetic bearings normally position the outage as a normal shutdown.