U.S. Department of Energy - Energy Efficiency and Renewable Energy

Federal Energy Management Program

FEMP Technology Brief: Magnetic-Bearing Chiller Compressors

Technology Ideal for Partial Loads

This photo shows a newly installed magnetic-bearing  chiller compressor.

Navy Region Southwest, San Diego CA. Photo courtesy of the Navy Techval Program.

Centrifugal, two-stage, magnetic-bearing chiller compressors equipped with variable-speed drives are a relatively new technology that operates at a high efficiency. Based on this case study, independent analysis by the U.S. Department of the Navy has verified that magnetic bearing compressors operate more efficiently than reciprocating and screw compressors, especially during partial load conditions. The magnetic bearings allow the compressor to operate without the use of oil for lubrication, which reduces energy losses due to friction and increases the heat transfer efficiency of the chiller, because no oil enters the evaporator or the condenser. A variable speed drive on the motor allows the compressor to operate much more efficiently at partial loads than standard compressors. The oil-free system also eliminates the need for oil maintenance, resulting in operations and maintenance (O&M) savings.

Agency Technology Evaluation Program

Technology Description
Magnetic-bearing chiller compressors are oil-free, variable speed compressors that can be installed as a retrofit to an existing chiller or within a new chiller. Digital, internally controlled, magnetic bearings reduce friction and eliminate the need for oil lubrication. The compressor is manufactured by a single company, but many manufacturers include this new compressor as part of a chiller package.

Technology Evaluation Program
Navy Techval

Savings and Benefits

  • 49% average power savings achieved
  • 6.4 years average ROI
  • Quiet operation
  • Light weight
  • Low start-up power draw
  • Reduced maintenance costs

Potential Applications

  • Nationwide application
  • Partial load applications on chillers achieve the most savings
This color illustration shows a cut-away image of the mechanical configuration of the compressor.

Image courtesy of the Navy Techval Program.

The Navy Technology Validation Program (Navy Techval) was established in 2004 to identify technologies that show large energy savings, show promise in a variety of applications and locations, reduce maintenance costs, lower the Navy's energy bill, meet federal mandates, and reduce technology implementation barriers. The Navy Techval Program demonstrates commercially available emerging technologies that look promising for use at shore facilities but are not yet in widespread use. This technology brief highlights the drivers, savings, and benefits found in the demonstration of the magnetic bearing chiller compressors.

What were the Benefits?

In addition to this case study's energy savings noted below, the magnetic bearing compressors feature:

  • Quiet operation
  • Light weight – allowing for faster installation
  • Low startup draw – about 2 amps, which can reduce capacity/peak power requirements for a backup generator
  • Reduced maintenance costs – due to no oil use.

What were the Savings?

Power savings averaged 49% across three case study sites. Magnetic bearing compressors were installed in each of the sites shown in the table below. The San Diego and Jacksonville, Florida, studies were both compressor retrofits, while the Newport study involved installation of a new chiller. In these case studies, the largest savings were experienced at the Newport, Rhode Island, location.

Energy savings were assessed for retrofits in three different Navy facilities as part of the Navy's Techval program between 2005 and 2007. The results are presented in the table below.

New chiller technology Techval demonstration summary
Project Site Project Type $/kWh Tons Annual kWh savings Annual Energy $ Savings % Savings Cost $/Ton Payback (years)
"San Diego" Add a third compressor $0.121 240 176,717 $21,206 40% $178,787 $744 8.4
"Newport" Install a new chiller $0.115 80 227,760 $26,192 65% $100,783 $1260 3.8
"JAX" Retrofit compressor with condensing water reset $0.054 120 284,407 $15,358 41% $107,592 $897 7.0

Operations and Maintenance
Based on manufacturer recommendations over 10 years, maintenance labor and costs are estimated to be approximately 96 person-hours in labor and $500 in materials.

Potential Applications

A magnetic-bearing chiller compressor can be installed as part of a new chiller installation or a retrofit on an existing chiller when the existing evaporator and condenser are in good condition. The technology is ideally suited for chillers that run at partial load for most of the year. Energy savings are reduced at, or near, full load. The technology may require an upgrade of controls to extract the most savings from a retrofit. Magnetic bearing compressors can be applied to air-cooled and water-cooled chillers.

Lessons Learned

The Jacksonville demonstration revealed another opportunity for increased energy savings. The new compressor technology is capable of operating with lower condenser water supply temperatures compared to some conventional compressor systems. This resulted in an additional improvement in efficiency.

The new variable-speed centrifugal compressor technology is a notable improvement over existing reciprocating and screw compressors. In addition to energy and cost savings, the new technology is lighter and quieter.

Achieving Energy Savings in Your Facility

Regulatory Requirements
Magnetic-bearing chiller compressors can help meet Federal agency energy use reduction requirements.

  • Conduct an inventory of existing chiller compressors
  • Identify older chillers that are due to be replaced
  • Create a replacement schedule and evaluate the feasibility of magnetic bearing chiller compressors when chillers are being replaced. 
  • Monitor the energy savings associated with the compressor. If savings are evident in only a few locations, identify what's different about those locations and replicate in similar locations.
  • FEMP provides support to Federal agencies looking to fund energy efficiency projects. FEMP's Project Funding section provides detailed information and identifies where assistance is available to implement energy projects.

More Information

See Magnetic Bearing Chiller Compressor.

For more information about the Navy Techval Program or magnetic-bearing chiller compressors, contact:
Paul Kistler, P.E., C.E.M.
Naval Facilities Engineering Command-Engineering Service Center
U.S. Department of the Navy
1100 23rd Avenue
Port Hueneme, CA 93043
Phone: 805-982-1387

For more information about FEMP's Technology Deployment Program, contact David Catarious at 202-586-8121.

Technology Deployment Working Group

In support of the Federal Government's dedication to improving its energy efficiency, an interagency advisory committee was formed to accelerate deployment of innovative clean energy technologies in the federal sector. The Senior Executive Committee for Technology Deployment, a subcommittee of the Interagency Technology Deployment Working Group, brings together leaders of technology deployment programs from across the federal government to reduce energy use in agency facilities. The Technology Briefs are produced to share knowledge gained through the various technology evaluation programs. This Technology Brief on magnetic bearing chiller compressors is a compilation of experiences from the Navy Techval evaluation program.