Managing compressed air systems

In a period that has seen increased revenue hard to come by, companies have been forced to squeeze even tighter on operating expenses. When you look behind the scenes of a 'healthy company,' you may see double-digit earnings but with revenue increases as low as 2%.


Focus on the air system
Focus on the compressor
How to buy
The tough part
What can go wrong?
Monitoring from a distance

In a period that has seen increased revenue hard to come by, companies have been forced to squeeze even tighter on operating expenses. When you look behind the scenes of a "healthy company," you may see double-digit earnings but with revenue increases as low as 2%. There are painful ways to increase earnings without increasing revenues, such as layoffs, and cutbacks on capital spending, but there is also a painless way to increase earnings, and that is by simply stopping the bleeding.

Focus on the air system

The bleeding refers to the money that is being wasted on inefficient compressed air systems in manufacturing facilities throughout the world. Most companies are painfully unaware of the cost of waste present in their current air system.

If you want to know where savings can be found, follow the money. One way to do that is by focusing on your air system, which typically uses 10% of the energy in your facility. The Department of Energy, the Compressed Air Challenge, and the Compressed Air and Gas Institute (CAGI) have hosted seminars to educate plant managers on how to make their facilities more energy efficient. There are simple lessons that can be learned and implemented immediately.

These include:

  • Measuring the baseline (kW, pressure, and flow)

  • Identifying inappropriate uses of compressed air

  • Fixing leaks

  • Increasing air receiver capacity

  • Fine tuning compressor controls.

    • Audits

      Another emerging trend in the industry is air system audits. It is important to distinguish between the various types of air system reviews that are available, since they vary in quality and effectiveness. The Compressed Air Challenge has identified three types of analyses of compressed air systems.

      Walk-through evaluation (

      A walk-through evaluation is an overview of a plant compressed air system identifying the types, needs, and appropriateness of end uses, pressures, and air quality requirements.

      • The distribution system is analyzed for any apparent problems of size, pressure drops, storage, leaks, and drains.

      • The supply side is analyzed for types of compressors, and the types, suitability, and settings of capacity controls.

      • A simple block diagram of the system is drawn.

      • Maintenance procedures and training also are analyzed.

      • Written report of findings and proposed solutions is submitted.

      • Solution and product neutrality should be maintained with any recommendations.

        • System assessment (2%%MDASSML%%5 days)

          A system assessment is more detailed than a walk-through evaluation of a plant compressed air system.

          • In addition to identifying the items and problems of the walk-through evaluation, readings are taken at appropriate locations to identify the dynamics of the system.

          • Besides a simple block diagram of the system, a pressure profile and a demand profile are made to help identify potential problems and how they could be resolved.

          • Again, maintenance procedures and training are reviewed.

          • A written report of findings and recommendations is submitted.

          • Solution and product neutrality should be maintained with any commendations.

            • System audit (3%%MDASSML%%10 days)

              A system audit is similar to a system assessment but in more depth and detail.

              • Data logging of readings throughout the system is conducted for an indepth analysis of the dynamics of the system and resulting problems.

              • Again, maintenance procedures and training are reviewed.

              • The objective is a proper alignment of the supply side and the demand side for optimum efficiency, energy savings, and reliability. A baseline is established, against which the results of any proposed changes are measured.

              • A comprehensive written report of all findings, recommendations, and results is submitted.

              • Solution and product neutrality should be maintained with any recommendations.

                • Focus on the compressor

                  In recent years technology has been developed to improve compressor efficiency. There are two major ways to reduce compressor horsepower. One is with a variable-speed drive (VSD) compressor, the other is using multiple traditional compressors with a master sequencing control.

                  In applications with varying demands, the VSD compressor may be the answer. A VSD compressor controls capacity output by controlling the speed of the motor. As the compressor turns slower, the compressed air exiting the compressor is reduced. The VSD compressor shines when plant air demand is 60% or less of the compressor's capacity. Traditional compressors became less efficient in this range.

                  VSD compressors are more costly than standard compressors if they run at 100% capacity, since extra energy is lost with the addition of the VSD itself. Although the initial cost of a VSD compressor is more than other types of compressors, the energy savings more than make up for the difference, if the compressor is applied correctly.

                  Since VSD compressors have become popular, some plants question whether a VSD can be retrofitted onto an existing compressor. The answer is yes, but using a fixed-speed air end at variable speeds (capacities) may not result in significant energy savings. An air end designed to run at variable speeds will operate throughout a wider range of capacities (Fig. 1).

                  The goal in managing any air system is to use the lowest possible brake horsepower. If demand fluctuates between 20% and 90%, the VSD compressor will most likely be the low-horsepower answer.

                  Another trend in plants is to replace larger compressors with two or more smaller compressors. Assume a facility requires a 200-hp air compressor to handle peak loads, but the second shift requires only half of that capacity. You can purchase one 200-hp compressor or two 100-hp compressors. It's important to note that it can be 65% to 75% more costly to operate a 200-hp compressor at 50% load than it is to operate one 100-hp compressor at full load, with the other 100-hp compressor turned off.

                  Multiple units will also benefit from advanced sequencing controls that are on the market. Some sequencers are a built-in component of the compressor's controller. Stand-alone sequencers are also available. These can accept inputs from various types of compressors (rotary screw, reciprocating, and centrifugal). The main purpose of the sequencer is to manage the horsepower being used. The sequencer constantly monitors the plant air pressure and only turns on compressors as needed. The better sequencers will make sure that, in multiple-compressor installations, only one unit will be running partially loaded, while any others that are on are operating at full load.

                  Before deciding what type of compressor or controller to use, it is critical to understand the demands of the system. Demands can change from one shift to the next. A plant air system that supports a rather static demand of air for a particular, unchanging process will be designed quite differently than one that has wide fluctuations in air demand (Fig. 2).

                  A good compressed air audit will provide detailed information of a plant's air demands over a week's time. This valuable information can help in deciding what type of compressor or compressors are right for an air system.

                  How to buy

                  How to make sense of the different types of compressors on the market? The Compressed Air and Gas Institute has worked with compressor manufacturers to develop Compressed Air Equipment Data Sheets. These sheets make it easier to compare the efficiencies of various compressors and air system components (Fig. 3).

                  The total cost of ownership needs to be considered when purchasing an air compressor. Far and away the most important element is the cost of electricity needed to run the compressor (65%). The cost of replacement parts and maintenance is also significant (20%), while the initial cost of the compressor (15%) is the least expensive.

                  The tough part

                  Taking care of an air system is similar to taking care of oneself. It's one thing to lose 20%%MDASSML%%30 lb; the hard part is maintaining that weight. The same is true for an air system. It is one thing to design the perfect air system that has all the right components, but it is another thing to maintain it. A well-designed system that is poorly maintained can easily cost tens of thousands of dollars to a company.

                  What can go wrong?

                  The minute a plant air system is turned on, it's efficiency immediately begins to decline, filters begin to clog, leaks begin to appear, and seasons change, affecting the function of drains. The past 10 yr has seen a sharp decline in plant maintenance personnel (another way to increase earnings without increasing revenues). This short-term savings for plants can turn out to be a costly mistake if they haven't found a company to help with air system maintenance.

                  Over time, any filter, whether it is filtering particulate, lubricant, or water, will begin to clog, making it more difficult for compressed air to travel through. The end result? Pressure drop in the system.

                  Any drop in pressure is an unrecoverable loss of energy. As pressure drops in the plant, it must be increased in the system for tools and processes to receive air at their minimum required pressure. Since every 2-psig increase in pressure results in a 1% increase in bhp used, it doesn't take long to see operating costs skyrocket.

                  Leaks seem to be inherent with any air system but minimizing leakage to 10% of capacity is necessary to avoid costly electric bills. Many plants average 30% leakage. A proper waste management system helps minimize leakage and identifies any inappropriate uses of compressed air (which includes using it to cool employees or sweep floors).

                  Monitoring from a distance

                  Since many companies do not have the time or the personnel to keep an eye on their air system, some are turning to remote monitoring as a way to prevent major losses. Controllers are now available that allow information to be fed to a central location where all plant equipment can be monitored. There are systems that allow you to log online and view the operation of a compressor from a web site.


                  Another trend that started a few years ago is what is known as "air-over-the fence." This is when a company completely takes over a compressed air system, being responsible for the equipment and its upkeep. You, in turn, pay a monthly utility bill for the air used. Those who have chosen this route have done so because of their unwillingness to take the time or don't have the personnel to manage the system. Buying air by the cubic foot is not cheap. Purchasing a maintenance contract will most likely be less expensive. But the message is clear: If you want to stop the bleeding, the system has to be managed by someone.

                  Plant Engineering magazine extends its appreciation to Michael O'Connor and the Compressed Air and Gas Institute (CAGI) for preparing this special report.

                  For more information on the subjects in this article contact CAGI at or visit their web site, .

                  Michael O'Connor has spent the last 15 years in the compressor industry and is currently the Manager of Training and Development at Gardner Denver Inc., Quincy, IL. He has written, directed, and produced over 50 videos and several audio programs covering various compressor products and topics including the last CAGI video entitled "Air Treatment." He has also served on Educational and Promotional Marketing Committees of CAGI for the past 7 years.

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