A significant effort is being made to improve the fuel economy and environmental friendliness of maritime fleets. Most of the efforts have been placed on the diesel engines and lubricants used for propulsion and shipboard electrical generation needs. However, there is another key shipboard system that can make a significant contribution today- the integration of high-efficiency compressors.
These systems can reduce onboard chillers’ fuel consumption by better than 25 percent, increase cooling capacity by at least 50 percent, improve reliability by more than 50 percent, meet environmental objectives of reducing refrigerant leakage by 90 percent and eliminate hazardous oily waste.
As part of an American Recovery and Reinvestment Act program, the U.S. Navy has spearheaded an initiative to integrate high-efficiency small and large capacity compressors to mate with existing shipboard R-134a refrigerant chiller heat exchangers shells to dramatically improve chiller capacity and performance. YORK® Navy Systems, a Johnson Controls Company, is leading the chiller prototype development program.
The compressors are comprised of a variable speed, two-stage compressor with Calnetix Technologies’ Powerflux™ oil-free magnetic bearings and a Calnetix Magnaforce™ high-speed permanent magnet motor. The marine chiller systems are projected to save 1,000 barrels of oils per year per ship, all with no change in the system’s weight or seawater chiller capacity.
In addition, the Navy chilled water plants provide mission-critical cooling to weapons as well as command and control systems in addition to crew comfort. As these chiller systems advance to include high-energy radars and directed energy weapons, the cooling demand along with acquisition, fuel and life cycle cost will increase dramatically.
Navy chillers also must be very robust and operate for 35-50 years in extreme environments, such as weapons-effect shock, ship heavy-weather vibration and Arctic as well as tropic conditions. The high-efficiency compressors being built under the Navy’s initiative will be able to work under these circumstances while also providing space, weight, power, cost and environmental benefits.
The new marine chiller systems with variable speed motor capabilities and magnetic bearings are proving to be 200 percent more effective than the existing systems for the following reasons:
Powerflux™ magnetic bearings do away with the oil lubrication system. This eliminates the need for valves and fittings that are sources of refrigerant leakages while getting rid of oil changes and the hazardous waste disposal processes. It also frees up valuable space onboard once used for oil stowage requirements.
Vericycle™ variable speed drives remove the complex mechanical vanes typically used to throttle compressor refrigerant flow and reduce the starting in-rush current by at least 75 percent. Doing so improves reliability and lowers stress to the ship’s electrical distribution system.
Together, Magnaforce™ PM motors and Vericycle™ variable speed drives eliminate the need for complex and costly speed increasing gears. This allows a compact, simple, two-stage compressor that provides improved cooling efficiency and allows the compressor-motor to be a single; easily tested and replaceable module.
The compressor system successfully passed Navy MIL-STD-167 vibration and MIL-S-901D shock testing requirements in 2013. Production units underwent further testing in 2015 in preparation for the first ship installation in 2016.
Test Results and Analytical Predictions for MIL-STD-167 Vibration Testing of a Direct Drive Compressor Supported on AMB
Comparative Study of Axial/Radial Magnetic Bearing Arrangements for Turbocompressor Applications
Advantages of PM Machines for High-Speed Applications
Advantages of Magnetic Bearings
High-Speed Air Compressor for Industrial Applications
How PM Motor Generators Work