There are five key compressed air system topics that deserve attention if your quest is to reduce compressed air costs. These areas capture some of the most common efficiency problem areas in any system, and represent potential improvement topics to address if you want to reduce your compressed air energy costs.
Compressor Control – Air compressors have a wide range of control modes for local control. Also, if more than one compressor must run, the control of multiple compressors in a system is important. Very often compressor controls will be set and forgotten, running in inefficient control modes like modulation or blow-off. Over time, even efficient control modes like load/unload and variable frequency can have setpoints drift or become adjusted incorrectly. If you don’t know your modes and strategies, then check with your service provider and find out how your compressors are being controlled and what coordination plan is in place.
System Pressure – The higher the discharge pressure, the more energy a compressor consumes per unit output – about 1% extra energy for every 2 psi pressure increase. And any unregulated air consumer will consume about 1% more air for every 1 psi in extra pressure, as this added flow requires the compressor to consume more energy. This extra energy use all adds up to increased electricity costs. If your average system is running above 100 psi, then it is likely that some savings can be gained by optimizing your system pressure. Investigate the reason for high pressure.
Air Drying – Very often the air dryers and condensate removal elements are forgotten when it comes to optimizing your system. Standard non-cycling refrigerated dryers run at about the same power level at zero flow as they do at 100 percent flow, often with timer-controlled water drains blasting for no reason. Modern cycling style dryers reduce their energy consumption as the moisture load reduces, saving energy. Airless drains or float type drains can be retrofitted onto dryers and filters to save compressed air and costs.
Drying compressed air with desiccant dryers can cost 3 to 5 times that of a refrigerated dryer. The worst waste is using this type of dryer when a refrigerated dryer will do. But, if you have a desiccant dryer, check to ensure the units are controlled on dew-point demand rather than running on fixed cycle. Uncontrolled desiccant dryers can easily waste thousands of dollars a year in compressed air. Investigate your dryer and condensate removal system to see what you have working for you.
System Leakage – System waste through leakage is a common target area for efficiency improvement, and leakage detection and repair should be a regular maintenance item in any plant. In the worst-performing plants, general leakage can consume 80% or more of the compressed air produced by the air compressors. Target having leakage below 10% of the average compressed air flow. Realize that to gain full savings from leakage, the compressors must be controlled in an efficient manner; if they are not, then all you may get is higher system pressure. If you don’t know what your leakage percentage is then it is time to take action.
Key Indicator Monitoring – It is not possible to properly manage a system that is not properly measured. Often missing on a compressed air system are the measuring and reporting systems that can track system key performance indicators, like specific power and energy consumption. A good measurement system should track system pressures, power consumption, flows, dew point, and critical temperatures; they also should be displayed on an easily viewed dashboard to ensure that any efficiency or other problems can easily be detected. If these reporting systems are missing from your system, then you should consider installation of permanent reporting; or, as a stopgap measure, consider bringing in professionals who can measure your systems on a temporary basis.
About the Author: Ron Marshall
