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Magnetic Bearing Compressors Improve Chiller Efficiency

Key Points
  • Magnetic bearings suspend the rotor shaft in a magnetic field, providing non-contact operation.
  • Benefits of magnetic bearing technology include energy savings and lower maintenance costs.
  • One facility saved $26,000 a year after installing a chiller with a magnetic bearing compressor.

Chiller plantChillers are used widely for cooling and refrigeration in commercial facilities, but they consume a lot of energy. Variable speed chillers using unique magnetic bearing compressor technology offer an efficient alternative to conventional units. Magnetic bearing compressors provide benefits in energy savings, less maintenance and quieter operation.

How they work

Compressors are the main components of chillers, pumping gaseous refrigerant through the system and condensing it into liquid. Rotors spin inside the compressor, while bearings help support and position the rotor. Conventional bearings come into contact with the rotor,  requiring lubrication. Magnetic bearings provide non-contact operation by suspending the rotor shaft in a magnetic field, eliminating friction losses and the need for lubrication.

Components of a magnetic bearing system include electromagnets, position sensors, a power amplifier and a signal processor. The sensors pick up any change in the position of the rotor and communicate that information to the signal processor. The processor initiates a response to the amplifier, which supplies current to the electromagnets, altering their magnetic force to bring the rotor back to the desired position. This process repeats itself continuously during operation.

The benefits

Magnetic bearing compressors offer significant advantages compared to conventional units:  

  • Energy savings. Magnetic bearing compressors are more efficient under part-load conditions, which chillers operate at most of the time. Cooling efficiency is increased by up to 5 percent, according to the U.S. General Services Administration.
  • Low maintenance. Maintenance requirements for magnetic bearing compressors are simpler because of lubrication-free operation and the elimination of such parts as filters, seals and piping.
  • Flexibility. Magnetic bearing compressor technology is appropriate for new construction, as well as major renovations and chiller retrofits.

Other advantages include quieter operation and a wide temperature range. Despite these benefits, there is some concern about the overall reliability of magnetic bearing drives and the 'coast down' effect that occurs during a power outage.

Case study: magnetic bearing compressor makes waves

Magnetic bearing compressors typically cost more than conventional units, but they can provide a good return on investment. A U.S. Navy facility in Newport, Rhode Island added a new, 90-ton variable speed chiller equipped with a magnetic bearing compressor alongside its two 100-ton chillers with reciprocating compressors. The new chiller provided energy savings of 65 percent. Utility cost savings of $26,000 a year resulted in a simple payback of less than four years. 


Image source: U.S. Department of Energy

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