By Ron Marshall for the Compressed Air Challenge
A metal fabrication facility ran two separate systems to feed tools and equipment in two shops on their premises. One compressor ran load/unload, the other was a VSD controlled compressor.
The plant maintenance engineer attended a Compressed Air Challenge seminar, and as a result, came to realize how much compressed air costs and what to do about it. Inspired by what he learned, he went out and purchased flowmeters—and used his existing power measurement instruments to do a self-assessment of his system efficiency. The data logging showed that both systems were lightly load and running very inefficiently. Because the system piping for both systems are very close together, there was an opportunity to tie the systems together and save power.
This had to be done on an emergency basis one particular day, because the smaller compressor unexpectedly failed. Because he expected some significant savings, the plant engineer measured the new flow and power of the remaining compressor and calculated the system efficiency. The analysis showed that even though there were savings, the VSD compressor was operating at a specific power as high as 60 kW per 100 cfm, very poor for a compressor of this type. Normal is about 25 kW per cfm at minimum speed.
The plant engineer did not realize that this type of compressor, even though it is a VSD controlled unit, comes from the factory with default set to modulate at lighter loads. This modulation pushes the compressor into very inefficient operation at near minimum compressor speed. Typically, the supplier of this equipment adjusts the compressor so that this modulation does not happen. The adjustment was forgotten on this unit.
The manufacturer was contracted and offered to make the adjustment to get things back within specification. Estimated savings for the combining of the two systems adds up to $9,600 per year, for a 43% savings in energy costs.
Learn more about system optimization in our next Compressed Air Challenge seminar in your area. Visit www.compressedairchallenge.org for more information.