Synopsis: Rarely does an industrial user know exactly how much their compressed air is costing or the efficiency of their system. Measurement of key performance indicators (KPIs), also called energy performance indicators (EnPIs), can show facility managers the big picture in terms of current costs and potential savings. To truly manage any system, you must measure it. Four compressed air EnPIs are discussed in this article, when monitored these can tell energy managers a lot about how the system is operating. EnPIs can be used to initiate action to correct deficiencies, or to show improvements after the actions are taken. Some information about available free web-based training on these indicators is given.
Figure 1: Energy Performance Indicators (EnPIs)and Energy Baselines (EnBs) can be used to compare system performance between two different reporting periods (Source CSA 837-16).
Quick, answer these questions, how much compressed air are your compressors producing? How much electricity do they use? What is your system efficiency? How much leakage waste do you have?
Are you stumped? Very rarely can a compressed air system manager answer even the first question, let alone all of them.
Compressed air systems are typically the most ignored of all the many plant utilities, in terms of energy efficiency and waste, yet the air compressors and associated equipment usually consume considerable electrical energy, averaging 10 percent of all industrial motor load. But, once a focus is put on these troublesome systems, by setting up a good system of measurement and analysis, very significant energy savings can easily be found.
To answer the questions posed at the beginning of this message, some measurement must be done. And if your measurement system is properly designed and applied, you won’t even have to get off your chair to answer them, you will be able to track system key performance indicators over days, weeks, months and years, ensuring things are operating correctly and efficiently.
Like any system, to properly manage your compressed air utility you must measure it. Using accurate and relevant measurements, calculations of key performance indicators (KPIs), or energy performance indicators (EnPIs) can be done. These indicators must then be compared to some benchmarks or goals to determine if the readings are as expected, or if improvements can be made.
Some recommended key indicators for compressed air systems:
System specific power – Often measured in kilowatts per 100 cfm or kW per m3 per minute, this indicator tells how efficiency the compressed air is being produced. A good system will be producing air at under 6.7 kW per m3 (19 kW per 100 cfm), a bad one can be over 32 kW per m3 (90 kW/100 cfm). Improvements to this indicator can be gained by upgrading compressors to more efficient styles, by applying efficient methods of control, such as variable frequency drives or cycling refrigerated air dryers, and by reducing discharge pressure.
Total energy consumption – This is a measure of how much total energy in kilowatt hours a compressed air system consumes over a measurement period. It is possible to produce the air very efficiently, yet waste large amounts of energy through leakage and inappropriate use, like when high pressure compressed air is used for blowing dust or cooling equipment. Improvements to this key indicator are often achieved by improving the system specific power and/or reducing flow through waste reduction. Often a large reduction in total energy can be gained by reducing total operating hours by turning the compressors off during non-production times.
Specific Energy Consumption – The ratio of the compressed air energy consumed per product output of the plant, such as kWh per tonne or kWh per 1,000 board feet. This indicator is important if a large amount of energy is expended to produce a specific product, and there is good correlation between compressed air usage and product output.
Leakage as a percentage of production flow – This indicator shows how much system waste occurs when there is no production. This measurement is easy to do in a shift-oriented plant, but difficult to measure in a location where production never shuts down. A good number for this indicator is less than 15 percent of production average compressed air flow. Above this level would indicate some leakage detection and repair work is required.
Of course, basic measurements like pressure, flow, dew point, critical temperatures are also important and should be monitored.
The correct instrumentation needed to do these measurements is readily available on the market and can be purchased at reasonable cost. Once the data is measured and recorded in a time sampled database it is usually quite easy to set up automatic calculation of these key indicators. More and more SaaS companies are offering data aggregation services, where the data from the installed instruments can be sent to a cloud database and then displayed on an easy to understand dashboard. These dashboards are where you can get the answers to critical questions about your compressed air system.
Figure 2: Measured Key Parameters can be captured and visualized on web-based dashboard to show the performance of the compressed air system (Source CSA 837-16).
There is really no excuse these days for letting your compressed air system run wild.
More information on these EnPIs can be found in Canadian Standards Association (CSA) standard C837-16. Some free computer-based training has been developed to explain the why and how of monitoring these indicators. This training can be accessed here (a sign up is required).