You may have heard that compressed air is one of the most expensive utilities in an industrial plant. It's a fact that compressed air is a poor way to transmit energy to an industrial machine or tool if you want superior efficiency. That being said, it is unlikely that in the name of energy efficiency alone, you'll convert all of your industrial tools and equipment to direct-drive electric. Compressed air will never disappear from industrial plants; it is a very useful utility.
Compressed air system costs vary widely. This is because the efficiency of systems is often ignored, as there often are more important issues in running a system. (Chief among these are keeping the pressure at a constant reliable level and maintaining adequate air quality so that production runs smoothly.) Sometimes systems run at excellent efficiency; at other times, factors related to equipment characteristics, system design, flow characteristics, and maintenance levels can cause things to go very wrong.
The good news is you can do something about it.
This article outlines 13 ways to optimize your compressed air system for increased energy efficiency. Although certain points discussed in this article may relate just to the supply side of the system, or to the demand side, everything in compressed air systems is interrelated – items on the demand side can affect how the equipment on the supply side operates. In all cases, the best compressed air system efficiency occurs when both sides of the system are optimized at the same time by taking a holistic systems approach.
1. Get awareness training
With regards to compressed air, what you and your employees don’t know will hurt you. It is very common to see surprised looks on people’s faces when they discover how much it is costing to run their compressed air systems, and how little mechanical energy they receive for the expenditure. Compressed air system awareness training is the best first step in optimizing your system by teaching you how to understand your equipment and how it is running. This knowledge is an important key to getting your costs in line.
The Department of Energy studied compressed air awareness training and found that attending the training helped more than 75% of attendees initiate positive action1. This action includes replacing inefficient equipment, changing maintenance procedures, and doing low cost/no cost measures such as leak detection and repair to reduce system waste (Figure 1). The study found that every dollar invested in compressed air training paid back at a rate of more than 80 times the initial outlay. More information on training for your staff can be found by visiting the Compressed Air Challenge website (www.compressedairchallenge.org).
2. Monitor your compressed air system
In order to get a handle on your compressed air system costs you must measure your system. A system that is not measured can’t be effectively managed. Creating a baseline is important in understanding the challenges involved in improving the efficiency, air quality, air stability and reliability of your system. To monitor you must measure key parameters like pressure, flow, power, and dew point over a period of time. Once collected, these data need to be analyzed to see if there are any issues.
For example, if your air compressors are rated at 18 kW input for every 100 cfm output, but system measurements reveal that your system is consuming 40 kW per 100 cfm, this is a pretty clear indicator that there is likely an efficiency problem. If you make adjustments to improve the situation, the system monitors will tell you if your efforts were successful, how much you saved, and if any other important system parameters have been affected by the change.
More and more factories are implementing permanent monitoring of their compressed air systems so that system parameters can constantly be monitored and adjusted. This is an exceptionally good practice, but good results can be still be obtained by bringing in temporary metering. The measurement and analysis of your system using the services of a qualified compressed air auditor can point you in the right direction.
3. Implement efficient compressor and dryer control
Are your compressors and dryers being controlled efficiently? In what control mode are they operating? It is rare to find a compressed air system operator with the answer to these questions. The control of the air compressors and associated equipment like air dryers is very important to the efficiency and reliability of the system.
With regard to individual compressor controls there are various common modes of operation, with some more efficient than others. Some common modes are start/stop, inlet modulation, load/unload, variable capacity control, and variable speed. Of these modes inlet modulation is the least efficient way to control any compressor that is running at part load, but may be acceptable if the compressor is always at or near full load. The variable speed mode is the most efficient way of controlling compressors at part loads but may not be the most efficient at full loads. If you have a mix of control modes, some thought and planning needs to go into setting up and coordinating multiple compressor systems.