By Ron Marshall for the Compressed Air Challenge
A sheet metal processor went through a plant expansion that more than doubled the size of its facility. To be safe the plant engineer doubled the size of their air compressor to 50 hp from the original 25 hp.
The original unit was installed with a 120-gal tank and 1-in. lines; thinking that this worked very well, the Engineer installed the new larger compressor with the same size pipes and tank. The new compressor was activated and became the main unit, with the older 25-hp model put in standby.
An auditor assessed the system as part of a program offered by the power utility. The auditor noticed that the 50-hp compressor was very lightly loaded at an average of 7% of its capacity—but running all the time. When it loaded, it cycled very frequently, even though the control was set with a very wide pressure band.
Further investigation showed high differential due to undersized piping was causing restriction, resulting in the compressor control to work improperly with system storage. A 50-hp compressor needs piping of 1.5- to 2-in. size. The local 120-gal receiver was much too small for the compressor; recommended sizing would be between 1,000 and 2,000 gal to allow the compressor to operate with reduced cycles, and even turn off between load operations. This inefficient operation caused the compressor specific power to be 92 kW per 100 cfm produced, more than 4 times the optimal level.
It turned out the plant had expanded but the machinery installed was mostly hydraulic. Most of the new building was being used for storage of product. There was no real need for a new, larger compressor. The new unit was grossly oversized. The auditor pointed out that the old compressor was more appropriately sized to handle the small load, but even it was oversized. This smaller unit was placed into service for a test, and the power consumption immediately dropped by 40%. Further to this, if large storage is installed, the 25 hp or even the 50 hp unit could turn off between cycles, saving an estimated 74% in power costs.
Learn more about compressor efficiency in our next Compressed Air Challenge seminar in your area. Visit www.compressedairchallenge.org for more information.
William K. says
It is often quite valuable to know the requirements for a system prior to the design and build activities. Guesses made with no basis in data are seldom as good as we would want them to be. The posting verifies this assertion.
In the electrical area we have a policy in place to not cut the wire until we know how long it should be, and what gauge it needs to be.
Skylar Williams says
When you increase the size of your facility it doesn’t surprise me that you would need larger piping for your compressed air systems. Luckily they were able to figure out what the problem was so they could get it fixed and continue working. My husband works in a shop and they are about to expand, so I imagine they will have to also upgrade the piping.