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Compressed Air Efficiency: First Steps

This article discusses how to get started on optimizing any compressed air system and the important first steps on the journey to success.

Ron Marshall

Do you want to get your compressed air system under control?  It doesn’t have to be too complicated: there are some very simple first steps that involve your eyes, ears, hands and perhaps using a pencil, clipboard and a smartphone.  Using these, and following this checklist you can usually determine if there is any potential for improvements to your system that might involve more complicated study.

Here are some steps to consider:

Step 1: Gather data

Compressed air systems can be complex, the first steps get you organized.  

  • Have a look at your system and draw out how all the compressors, dryers, filters, receivers, drains and pipes are connected.  
  • Check out component nameplates, receiver volumes, pipe sizes and record them for future reference.  
  • Are there any centrifugal compressors, if so, are they blowing off?
  • Look for an external compressor controller, is there one on the wall and is it active?
  • Look at system pressure gauges, record the pressure at various points of the system, including the air compressors and at the far end of the system.  
  • While at the compressors observe the pressure settings programmed into each one and record the loaded and running hours of each unit. 
  • Inspect all condensate drains for presence of moisture.
  • Check compressor room temperatures and feel the temperature of the air at the discharge of each compressor with your hand.  
  • Note the input temperature of refrigerated dryers and compare to the outlet temperature.
  • Using a convenient air nozzle or hose, spray some compressed air on your hand or a white tissue.  It should be dry and no contaminants.
  • During on-production time, on evenings or weekends, record the length of time a single running compressor spends loaded versus unloaded.  If VSD then record the rpm.
  • Take a walk around a quiet plant and listen, how many leaks do you hear?

Step 2: Analyze the data

Once you have basic information then have a look at what you found. Improvement potential is indicated as follows:

  • Check your drawing and see if any dryer filter component has potential to be overloaded, for example 1,000 cfm (28 m3/min) rated compressor feeding an 800 cfm (22.6 m3/min) air dryer. Overloading causes poor performance and excessive pressure drop.
  • Look at the nameplates; are your compressors more than 20 years old?  Significant advances in unit efficiency have occurred over the past number of years and replacement of an old and failing compressor can yield some excellent savings.
  • Do you have more than 3 active compressors? If so, and you don’t have an active  compressor controller, then there is likely potential for savings.
  • Check the compressor type. Are any of the compressors capable of operating in inlet modulating mode (you may need help from your service provider for this)?  If so, modulation mode is the most inefficient way to control lubricated screw compressors – savings in adjusting how these compressors are controlled is almost guaranteed.
  • Are any centrifugal compressors blowing off?  If so, savings are very possible with better control and compressor optimization.
  • Compare the readings you took from the pressure gauges. What is the pressure loss across your system?If it exceeds 5% in the compressor room and 2% in distribution pipes it is likely showing undersized components.
  • Check compressor operating pressure – if these exceed 100 psi (6.9 bar) it is likely too high.
  • Have a look at the ratio of loaded versus running hours of your compressors. If the ratio of hours is less than 80%, then better control will likely save money.  For more accurate readings take these measurements again spaced one week apart and subtract to determine the present ratio.  For VSD compressors take the ratio of detected speed divided by maximum speed (on nameplate).
  • If there were large amounts of water or lubricant discovered at any drain in the system, or if drains are constantly passing air, you can likely save energy and improve air quality by optimizing.  If water or lubricant is detected at the outlet of the compressor room, you have a problem and should investigate.
  • If the compressor room is very hot, has a large negative pressure, or the discharge of the compressors is uncomfortably hot to touch, this spells trouble with compressor cooling and can overload system air dryers.
  • If the test of dryer temperatures showed uncomfortably hot temperatures and no temperature difference across inlet and outlet of a refrigerated air dryer then suspect problems.
  • When testing at low loads take the ratio of loaded hours and divide by loaded plus unloaded hours.  Multiply this ratio by the output capacity of the compressor.  This calculates the non-productive loading of your system, almost always leaks or inappropriate uses of compressed air.  It should be less than 15% of the full load capacity of your system (total of all the normally running compressors).  Check with maintenance: if there is not regular leakage detection and repair program in the plant then your leak level is likely way too high.
  • If your plant sounds like a pit of vipers due to excess leaks, get busy!

In looking at all these simple checks, if you find you have potential for improvement it is a sign you should call in some expertise.  Measuring a system with data logging equipment and calculating potential savings based on simple improvement measures can and should be done by someone with experience and expertise in compressed air management and who is independent from equipment sales.  Luckily there are many options for this assessment.  Call someone today!

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