How Much Is Your Air System Really Costing?
EP Editorial Staff | May 17, 2011
While you may not be able to run your operations without it, you probably can make your compressed air equipment run more efficiently and economically.
By Ron Marshall and Bill Scales for Compressed Air Challenge
Compressed air equipment is rarely installed with instrumentation that can supply a baseline to monitor system energy performance and related expenses. End-users are often blind to the real operating costs—and may be unaware of the consequences of the problems plaguing their systems and associated compressed air-powered machinery. Studies have shown that a few hours of basic awareness training can go a long way in increasing system efficiency. This “efficiency” training often generates significant side benefits in the form of a more productive and reliable system due to more stable pressure, improved compressed air system reliability and increased plant productivity.
Back to the question
So, how much is your compressed air system really costing your organization? Odds are that your management information system can track and control your pencil and paper clip purchases down to the penny, but to put an exact number on the cost of your compressed air, well, that’s another story…
If you go to your compressor room and look around, you may understand the reason for the lack of information. The room will probably be a noisy, hot and dirty place. The equipment within will have assorted instrumentation options to observe system temperatures, pressures and operating hours, but any indication of flow and power consumption will be missing.
Track down your operators and ask about their operating strategy and compressor-control coordination plan. More times than not, the question will be met with a blank stare. The reality of the situation will be that the plan and coordination strategy will be left to the default settings of the compressor manufacturer—or up to a well-meaning, but untrained operator.
Air is not free
Many end-users think air is free: They simply don’t know what it costs to operate their compressors, nor can they assess the cost of using 10, 50 or 100 cubic feet per minute of something they think of as “free.” Many are surprised to discover that the operating costs throughout the life of compressed air equipment greatly exceed the initial purchase price—in fact, in most cases, energy cost alone in the first year of operation will exceed the purchase price of the equipment. It’s essential to determine the current annual costs in dollars and communicate the situation to all involved. In this way, better decisions can be made on new equipment selection and mode of operation of existing equipment.
1 Horsepower Motor
Fig. 1. Energy cost comparison of air vs. electric (Source: Compressed Air Challenge)
Compressed air vs. other energy sources
Although compressed air is a necessary part of most plant operations, it is not the most efficient source of energy in a plant (see Fig. 1). To operate a 1 hp air motor requires 7-8 horsepower of electrical power into the compressor. At higher-than-typical pressures, even more power is needed.
- 30 scfm @ 90 psig is required by the 1 hp air motor.
- 6-7 bhp at the compressor shaft is required for 30 scfm.
- 7-8 hp electrical power input to the compressor is required for 6-7 bhp at the shaft of the compression element.
- The overall efficiency of a typical compressed air system can be as low as 10-15%.
Annual energy costs for a 1 hp air motor vs. a 1 hp electric motor in a 5-day-per-week, 2-shift operation, at $0.05/kWh is $1164 (compressed air) vs. $194 (electric). This means the compressed-air-powered motor can cost more for the same power output—significantly more if plant pressures are higher than the estimated level of 90 psi.
The cost of poor system performance
Systems with leaks waste money: Leaks make a system less efficient and increase the cost per unit of air produced. Figure 2 shows the cost of leaks through a perfect orifice in a compressed air system.
Fig. 2. The costs of air leakage (Source: Compressed Air Challenge)
Note: Costs calculated using electricity rate of $0.05 per kWh, assuming constant operation, 100 psig and a typical compressor.
The cost of operating (first-cut estimate)
You can do a first-cut estimate of your compressed air costs to find out what’s at stake by adding up the nameplate horsepower of your normally running compressors and doing some simple ratios. The cost of operating a 100 hp compressor for 8760 hours at $0.10/kwh is approximately $68,790. At 4000 hours and $0.08/kWh, the cost is 4000/8760 x $0.08/$0.10 x $67,790—or $25,130. (For instructions on more detailed calculations, refer to Compressed Air Tip Sheet 1 “Determine the Cost of Compressed Air for Your Plant,” in the online library at www.compressedairchallenge.org.)
Rationale for compressed air
Almost every sector of the economy utilizes compressed air systems, and there are thousands of different uses for them. Consider just the manufacturing sector, which relies on compressed air for powering pneumatic tools, packaging, automation equipment, conveyors and control-system applications, among others. Many manufacturing industries also use compressed air and gas for combustion and process operations such as oxidation, fractionation, cryogenics, refrigeration, filtration, dehydration and aeration.
There are countless applications where compressed air is the best overall solution. If, however, other, more cost-effective sources of power are available, compressed air is probably being used inappropriately: While ambient or atmospheric air may be free, its compressed form is
expensive. When compressed air is needed to make a product, it should be used wisely. If you want to cut costs, you need to be aware of these very real compressed air facts of life:
- It is often the least-efficient source of energy in a plant.
- It is often the biggest end-use of a plant’s electricity.
- It is frequently used inappropriately.
- It should be viewed as a system that can be managed.
- Its costs can be measured and controlled.
The typical system
A compressed air system consists of a supply side (that includes compressors and air treatment), as well as a demand side (that includes distribution and storage systems and end-use equipment). A properly managed supply side will result in clean, dry, stable air being delivered at the appropriate pressure in a dependable, cost-effective manner. A properly managed demand side minimizes wasted air and uses compressed air for appropriate applications. Improving and maintaining peak compressed air system performance requires addressing both the supply and demand sides of the system, as well as their interaction (as shown in the opening image of the article).
Hundreds of manufacturers produce the various pieces of equipment that are used in a compressed air system—from compressor packages to end-use tools. There are generally many different options for accomplishing a given task with compressed air, and it is important to apply the equipment properly. Often, if a system is performing poorly, it is not because the equipment is faulty, but because it has been applied improperly or poorly maintained. Almost every compressed air system (from a modern one in a 2-year-old plant to equipment that has been modified and updated over a 40-year span) has room for performance improvement.
Take a systems approach…
Improving and maintaining peak compressed air system performance requires not only addressing individual components, but also analyzing both the supply and demand sides of the system and how they interact (see Fig. 3). This practice is often referred to as a “systems approach” because the focus is shifted away from components to total system performance. Taking a systems approach usually involves the following:
- Developing a basic block diagram of your system.
- Measuring the baseline (kW, pressures, cfm consumption, leak load) and determining costs, with available tools.
- Working with your compressed air system specialist to implement an appropriate compressor control strategy.
- Once controls are adjusted, remeasuring to get more accurate readings of kW and pressures and to determine leak load.
- Walking through to check for obvious preventive maintenance items and other opportunities to reduce costs and improve performance.
- Identifying and fixing leaks and correcting inappropriate uses (knowing costs, remeasuring and adjusting controls as above).
Understanding your system
U.S. Department of Energy (USDOE) research has shown that 75% of compressed air equipment operators have received no formal training in system efficiency. With this level of education (and lack of awareness regarding the true costs of compressed air and what can be done about them), it’s not surprising that a significant number of these systems run inefficiently. System operators need to understand their system problems—as well as the solutions they can use to deal with them.
One way to address this need is efficiency-awareness training. The Compressed Air Challenge (CAC) has developed two levels of training to aid in this type of awareness: “Fundamentals of Compressed Air Systems” and “Advanced Management of Compressed Air Systems.” In 2010, the organization launched Fundamentals of Compressed Air Systems WE (web-edition).
These highly rated sessions have been proven by USDOE studies to encourage positive system changes. A very high portion of end-users reported using materials directly from the training to make efficiency improvements to their compressed air systems. In fact, 76% percent of the sample end-user representatives reported that they had made significant capital and/or operating improvements to their compressed air system since attending the CAC training. As a point of reference, compressed air system efficiency experts find that, for the typical compressed air system, 30% of system energy usage can be saved through cost-effective measures.
The studies also showed that end-users who implemented compressed air system efficiency measures also experienced significant non-energy benefits. End-users reported experiencing benefits such as reduced downtime, improved system reliability, reduced moisture and contamination in the system air, more consistent system pressure and restored delivery of adequate pressure to all system components.
It’s your move
You are invited to start your journey to greater understanding of your compressor air system cost and what to do about it. The CAC Training Calendar provides links to registration and location information for training sessions, including other in-person sessions in various parts of the country. This calendar and other resources are available on the CAC Website, www.compressedairchallenge.org. UM
Ron Marshall, industrial systems officer with Manitoba Hydro’s Customer Engineering Services (Winnipeg, MB), and Bill Scales, CEO of Scales Industrial Technologies, Inc. (Carle Place, NY), are members of the Compressed Air Challenge® (CAC). A partner organization of the USDOE Industrial Technology Program, CAC is a voluntary collaboration of North American industrial users, manufacturers, distributors (and their associations), consultants, state research and development agencies, energy-efficiency organizations and utilities working together to provide resources that educate industry about optimizing their compressed air systems. The CAC has trained over 13,000 compressed air users since 1999. To learn how you can get involved in this important initiative, email: firstname.lastname@example.org.
Recommendation: Learn the Best Practices
A highly recommended resource for any compressed air system operator is Best Practices for Compressed Air Systems Second Edition. This 325-page manual will provide readers with the informational tools necessary to reduce the operating costs associated with the use of compressed air and improve the reliability of the entire system. This single resource addresses the improvement opportunities in all aspects of a compressed air system from end uses to the air entering the compressor inlet filter. The manual provides the “how to” information to implement recommendations that will achieve peak performance and reliability of the system at the lowest operating cost. This resource is a free benefit of attendance at CAC’s Fundamentals training seminars and also is available for purchase through the online CAC Bookstore (www.compressedairchallenge.org/bookstore/index.html).
For more info, enter 261 at www.MT-freeinfo.com