What’s your air compressor control strategy?

Feb. 25, 2017

If you don't know, you likely have problems with efficiency.

Compressed air is a costly energy source for the tools and equipment your plant, and it should be produced and used wisely. The typical power conversion ratio of an air compressor is eight units of energy in for every one unit of energy out, but this is achieved only with very good compressor control. If your compressors are poorly controlled, this ratio can more than double.

So what is your compressor control strategy? If you don’t know, then there are likely problems with your system efficiency. So often the compressors are installed and just left at the factory default settings or have the settings determined by the maintenance service personnel.

What's the problem with that? Well, the people determining your strategy may have other priorities. They may benefit if your compressors run longer and require more maintenance. A poorly thought-out compressor control strategy usually results in plant pressures that are higher than needed, air compressors that are running longer than required, and system configuration missing valuable components, such as storage receivers.

The planning for the control strategy should start when the compressors are purchased. Typically, compressors are purchased in a bid process in which one vendor is competing against another. This often results in vendors offering lower-price options with valuable energy-savings features missing so they don’t lose the sale. If there is a choice, often a lower-quality, less-efficient compressor may be offered rather than a premium efficiency model. Perhaps little or no storage receiver capacity might be offered, dooming the compressor to lower efficiency for its lifetime.

When the compressor is installed, the plant operators may leave it up to the installers to set up the unit. Perhaps it is a compressor that is rated at 125 psi, so that’s where the unit is set, but this setting may be far higher than is actually needed in the plant. This higher pressure causes more air to flow in the plant and more energy consumption by the compressor. If multiple compressors are installed, it is not uncommon to see the units all set to the same pressure, resulting in the compressors fighting for control and running many wasteful hours in the unloaded condition. Often, too, energy-saving features such as auto-start are not activated, resulting in higher-than-desired compressor-run hours and inefficient compressor operation.

Good control strategy would start with the selection of efficient compressors. The most-efficient compressors would be selected to reduce lifecycle cost by referring to the Compressed Air and Gas Institute (CAGI) data sheets. Large storage would be purchased with the compressors to ensure good compressor operation and connected with properly sized piping to reduce any compressor room restrictions.  Efficient components would be selected so that dryers, filters, drains, coolers, pressure regulating valves would all help to reduce the energy costs of the system. Finally, the compressor pressure set points would be selected so that reasonable plant pressures would result. If a single compressor runs feeding partial loads, this compressor should be selected for the best part load efficiency. If multiple compressors must run, then all the compressors except one should be fully loaded or off. The remaining unit, again, must be the one with the best efficiency. If there are more than three compressors in a system, or if the compressors are located in separate rooms, then an external compressor controller may be required to properly orchestrate the control.

You can get help with this by calling a reputable compressed air service provider, preferably someone who has attended a Compressed Air Challenge level 1 or 2 seminar. Or you might be able to do it yourself. Learn more about compressor control at Compressed Air Challenge's next Fundamentals of Compressed Air Systems seminar.  Check out the calendar at www.compressedairchallenge.org.

About the Author

Ron Marshall

Ron Marshall first developed his skills as an industrial compressed air systems expert at Manitoba Hydro, where he worked for 38 years, supporting more than 600 energy efficiency projects. He now operates his own compressed air energy efficiency consulting firm where he provides technical advice, system auditing, and training.  Ron is a level 2 instructor with Compressed Air Challenge and conducts training internationally. Contact him at [email protected].Want to learn more about compressed air? We would suggest sending key staff to one of our Compressed Air Challenge seminars to help them learn what is possible. To learn more about upcoming training opportunities visit the CAC calendar at https://www.compressedairchallenge.org/calendar.

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