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Watch your compressed air numbers

Aug. 20, 2020
There’s no excuse these days for letting your compressed air system run wild.

Quick, how much compressed air are your compressors producing? What is your system efficiency? How much leakage waste do you have?

Very rarely can a plant professional even answer the first question, let alone all of them. Compressed air systems are typically the most ignored of all the plant utilities in terms of energy efficiency and waste, yet in most plants air compressors and associated equipment consume considerable electrical energy. But, once a focus is put on these troublesome systems, significant energy savings can be gained by applying common efficiency measures.

To answer the questions posed at the beginning of this post, some measurement must be done. And if you do your measurement right, you won’t even have to get off your chair to answer them and to be able to track their levels over days, weeks, months, and years.

Like any system, to properly manage your compressed air utility you must measure it, and the measurements and calculations of key performance indicators must be compared to some set benchmarks or goals to determine if the readings are as expected or not as desired.

Some indicators for a compressed air systems include the following:

System specific power – Often measured in “kilowatts per 100 cfm” or “kW per cubic meter per minute”, this indicator tells how efficiency the compressed air is being produced. A good system will produce air at under 19 kW per 100 cfm, whereas a bad one can be more than 90 kW/100 cfm. Improvements to this measure can be gained by upgrading compressors to more efficient styles and applying efficient methods of control, such as variable frequency drives or cycling refrigerated air dryers.

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 energy through leakage and inappropriate use of compressed air, like using high pressure compressed air for blowing dust. Improvements to this measure are gained by improving the system specific power and/or reducing waste.

Specific energy consumption – The ratio of the compressed air energy consumed per product output of the plant, such as “kWh per ton” or “kWh per 1,000 board feet”. This indicator is important if a large amount of energy is expended to produce a specific product.

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 in a location where the production never shuts down. A good number for this indicator is less than 15 percent of production average flow. Any reading above this 15% mark indicate that some leakage detection and repair work likely is required.

Of course basic indicators like pressure, flow, dewpoint, and critical temperature are also important and should be monitored.

The instrumentation required to take these measurements and do these calculations is readily available at a reasonable cost. More and more companies are offering data aggregation services, where the data from the instruments can be sent to the cloud and displayed on an easy to understand dashboard. This dashboard is where you answer the critical questions about your compressed air system.

There is really no excuse these days for letting your compressed air system run wild.

About the Author: Ron Marshall

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