April 20, 2012
Return on Alignment–Energy Savings
By Michael Keohane
Although the benefits of precision shaft alignment are well known to companies that do have a good shaft alignment program, it remains a fact that many machines are still not precision aligned. This can be attributed to difficulty in figuring out the return on investment. It is difficult because good alignment practices lead to cost avoidance. This is much harder to measure than cost of acquisition. While most organizations know their overall cost of maintenance, they do not know such critical things such as meantime between failure or the total cost of operating an asset. It is not always easy to figure out.
Energy savings for shaft alignment are seemingly easy to measure but the source of some controversy because the savings are difficult to pin down to shaft alignment. Some studies show energy savings of 3% – 10%:
Precision Alignment Provides Big Reductions in Electricity Consumption
- Reliability Magazine May/June 1995, Gord Cybolsky & Pat Pathn, Accuride Canada
Reducing Power Loss Through Shaft Alignment
- P/PM Technology October 1993, Ming Xu, et al.
Other studies indicate that perhaps the energy savings are not that great:
No Significant Measurable AMP Correlation When Brought from Coupling Tolerance to Precision Alignment Tolerance
- Rotating Machinery Energy Loss Due to Misalignment, Energy Conversion Engineering Conference 1996,Gaberson and Cappillino
- Motor Shaft Misalignment Vs. Efficiency Analysis,P/PM Technology October 1997, J. Wesley Hines, et al.
Even these studies showed energy savings do exist but are closer to 1%-1.5%. So here’s the question: is a 1% energy savings significant?
Here is an example:
- 1% drop on a 480 volt motor running 8400 hours/yr drawing 50 amps (~40hp) with a cost of $0.07/kWhr
- kW Reduction = (480V)(0.5A)(0.92PF)(1.732)/1000
- 0.38 kW reduction
- Total Savings = 8400 hours/yr x 0.38kW drop x $0.07/kWhr = $225 for this one machine
- Total Plant savings for 50 machines, averaging 50A, if 50% are misaligned
The assumption is a 1% energy savings is a 0.5A drop on a total of twenty five 50A motors. In addition, we assumed this savings was realized on 50% of the machines since historically misalignment is the root cause or premature failure of around 50% of the assets.
The conclusion is that energy savings can be realized through precision alignment in even the most conservative estimates. Would these savings alone be enough?