MAE 435 Informal Written Report #2
Magnetic Couplings Group
Project Advisor:
Dr. Praveen Malali
Members:
Charles Nipp
Carol Catoire
Stacey House
Mackenzie Payment
The project goal for the magnetic couplings group was to prove the ability of the magnetic coupling to tolerate misalignment between a motor and load shaft and to show energy savings with the use of a magnetic coupling as compared to a mechanical coupling. The group worked with Old Dominion’s Facilities engineering group and FluxDrive, the magnetic coupling manufacturer, to select and install two magnetic couplings on the Old Dominion campus. Magnetic couplings were installed on a chilled water pump in Constant Hall and on the Thermo-Fluids lab wind tunnel in Kaufman Hall.
Vibration testing was performed to prove the magnetic coupling’s ability to tolerate shaft misalignment. Flux Drive reported that the magnetic coupling can tolerate up to 0.100 inch of misalignment between the motor and load shafts. Vibration testing was conducted using a machinery analyzer with a magnetic accelerometer. Vibration was measured in the axial, horizontal, and vertical directions on the front and rear motor bearings and the load side bearings.
Vibration testing began on the wind tunnel. When angular misalignment was induced by moving the motor horizontally, the axial play of the motor allowed the magnetic coupling to snap closed. This will likely happen each time alignment is changed. In addition, the motor would not move more than 0.002” out of alignment and testing required the shafts to be 0.100 inch out of alignment. Due to the combination of these two issues, vibration testing was moved to the chilled water pump installation.
Baseline measurements for both installations showed an increase in vibration after the magnetic coupling was installed. Vibration testing was performed on the chilled water pump installation andthe magnetic coupling was able to tolerate vertical misalignment between the motor and load shafts of up to 0.060 inch, but was not able to tolerate 0.090 inch vertical misalignment. Only minor variances in vibration were found when the magnetic coupling was misaligned.
Air gap spacer testing was performed on the chilled water pump installation to prove and define the energy savings potential of the magnetic coupling. Flux Drive reported that a 10% speed reduction would result in 16% energy savings. This testing consisted of adding air gap spacers between the hubs of the magnetic coupling to increase the air gap and the slip between the motor and load shafts. The increase in slip caused reduction in load speed, flow rate and power consumption. Power consumption was measured using a power logger connected directly into the chilled water pump power panel. The power savings expected were to be from a power spike at start-up and through the use of the magnetic coupling and the air gap spacers.
Power testing showed a 0.3 kilowatt spike at start of the chilled water pump. Based on 276 starts a year for the chilled water pump, annual savings were calculated to be $0.11. Power savings through the use of the magnetic coupling were 1.81 kilowatts per hour. Based on 18.2 hours a day and running for 178.5 days a year, annual savings totaled $470.41. Overall, the power savings equated to an average of 15.2% for the magnetic coupling for all the air gap spacer configurations.
Two optimum operating conditions for the magnetic coupling are being reviewed. One option is to alternate between the mechanical and magnetic coupling pumps for peak times and the second is to obtain another magnetic coupling and alternate the air gap spacer configurations in the magnetic couplings. Energy savings are possible with both options and are greater with the second option. The payback period will be determined for both optimum operating conditions. The life cycle cost analysis for the magnetic coupling is being worked and is considering both operating conditions.
Work on the design changes for the magnetic coupling in underway and is on track to be completed as scheduled. Design changes are focused on ways to make the air gap spacer installation easier and to address the difficulties encountered when testing with the magnetic coupling. Also, Flux Drive will be provided with information based on testing and experience using the magnetic coupling.