Baseline and monitor efficiency of compressed air systems

Convert measurements to dollars to win funding for upgrades.

By Bill Scales and Ron Marshall

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There have been many excellent articles written about ways to reduce compressed air operating costs. This often is achieved by beginning an awareness campaign and assigning a person the responsibility of justifying, implementing and verifying the improvements. Perhaps you, or someone you know, has taken up this challenge. Fixing leaks, reducing potentially inappropriate uses, adding more air receivers, reducing pressures, optimizing control strategies and recovering heat are good strategies and worthy of consideration. However, in these times of limited resources, choosing the best options within the available budget is important.

Air is free, right?

Figure 1. The cost structure for the first 10 years of an air compressor’s use can surprise many executives. (Compressed Air Challenge)
Figure 1. The cost structure for the first 10 years of an air compressor’s use can surprise many executives. (Compressed Air Challenge)

Most companies don’t know what it costs to operate their air compressors, nor can they assess the cost of using 10, 50 or 100 cubic feet per minute. Many are surprised to discover that the operating costs throughout the life of compressed air equipment greatly exceed the initial purchase price (Figure 1). In fact, in most cases, the annual energy cost alone will exceed the purchase price in the first year of operation. It’s essential to determine the current annual costs in dollars and communicate this to all involved. In this way, better decisions can be made on new equipment selection and mode of operation of existing equipment.

If you want to cut costs, realize that compressed air:

  • Isn’t the most efficient source of energy in a plant
  • Often is the biggest end use of a plant’s electricity
  • Is frequently used inappropriately
  • Should be viewed as a system that can be managed
  • Has costs that can be measured

A good management axiom is, “If you can’t measure it, you can’t manage it.” If the plant is monitoring the power and tracking the total compressor energy consumption, management’s first step is much easier. However, where do you start if your plant doesn’t monitor and measure the input power (kW) and output cfm?

Get with the plan

The Compressed Air Challenge (CAC) has developed a seven-step action plan that is the centerpiece of its popular Fundamentals of Compressed Air training program. Plant personnel can use the steps in this action plan to better understand the system and what it costs to operate. This can help focus on areas of potential improvement that lead to reduced costs. Successful plan implementation also should ensure that any savings from successful improvements are communicated to management to pave the way for the funding that additional future projects will require.

A complete discussion of the Seven Step Action Plan is beyond the scope of this article and is best left to the participants in any given Fundamentals course. You can visit the Compressed Air Challenge website for more information.

Where are you now?

A key element in the plan is the need to baseline your system by taking measurements that quantify the effectiveness or efficiency of the compressed air system as it is before modification. The baseline figures establish where you are now in terms of system efficiency, cost, reliability and other measurements. It’s used for comparison purposes against which the performance of an improved system can be evaluated and reported to management. Measurements of power, energy, pressure, leak load, flow and temperature normally are required to best establish the baseline, and are taken before and after making changes.

Improving system efficiency and increasing the output (cfm) for every unit of input power (kW) is what characterizes a successful outcome. Prove that your improvement efforts work by reporting them by using terms that can be converted to dollars saved. This is the language that upper management understands and often is a key to determining your ultimate success.

It’s a system

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. This practice often is referred to as taking a “systems approach,” because the focus is shifted away from individual components to total system performance.

On the supply side, an important step in developing awareness of the compressed air system operation is to calculate what it costs to produce the compressed air. This exercise can be very simple or extremely complex, depending on the size of the air system and the accuracy of the desired result. Measuring and recording kW is, by far, the most preferred method to determine input power. However, if there isn’t any metering, it’s possible to approximate the annual energy cost using a standard formula and a clamp-on ammeter/voltmeter.

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