13 ways to optimize your compressed air system

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.

By Ron Marshall, Compressed Air Challenge

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A variety of control systems of varying complexity are widely available, and can be installed on compressed air systems to help coordinate compressors operation. This includes ensuring that correct compressors are running at any given time, that equipment is running efficiently, and that the system pressure is kept within specified limits. Implementing controls may be as simple as using what is already built into the onboard compressor control systems, or by the use of more complex external master control systems. There are system controllers now available that can also help you monitor your compressed air system to ensure your efficiency remains within acceptable limits.

Air dryer control is often a forgotten element in a system management effort, especially where desiccant style dryers are used. If your system has non-cycling refrigerated dryers, then you can reduce energy costs by making sure that any spare dryers are turned off if their associated compressors are not running. For desiccant dryers, there are dewpoint controls that can greatly reduce the dryer purge demand if the dryers are experiencing flows that are less than rated conditions. It is not uncommon to find desiccant air dryer purge making up the largest component of the compressed air demand in an industrial plant, in some extreme cases even more than the demand consumed by production machinery.

ca4.jpg4.    Boost efficiency via equipment replacement

The compressed air industry has changed for the better. Manufacturers are very aware that their customers are interested in energy efficiency, and so they have redesigned their equipment to be more efficient. When it comes time to do an expensive major overhaul on your old air compressors, keep in mind that the old equipment may not be up to present day standards. Rather than repairing an old inefficient compressor or compressor motor, it may be in your best interested to look at replacing the equipment with a brand new more efficient unit. This replacement can reduce operating costs going forward and pay for the replacement costs in a short period of time.

When calculating the operating costs savings and choosing what model of new compressor to purchase the Compressed Air and Gas Institute (CAGI) data sheets for the make and model in question can be used to compare various options. Most major compressed air companies have their CAGI sheets published on their websites. The data from these sheets can be used an inputs for your economic analysis in deciding to fix or replace and what compressor to choose. Data sheets are also available for refrigerated air dryers and may help you choose an efficient cycling dryer to replace an old non-cycling unit containing ozone depleting refrigerants.

ca5.jpg5.    Install storage receivers

The use of storage receivers can improve your overall system efficiency in a number of ways. For example, using a main air receiver at the compressor room can make load/unload compressor control more efficient. In the past it was thought that lubricated screw type compressors only needed about one gallon of storage capacity for every cfm of rated compressor output. But this has proven incorrect if efficiency is the goal. The addition of 5 gallons of capacity per cfm or more has excellent benefits in reducing the effects of rapid cycling of screw compressors. Figure 2 shows the effect of adding storage which makes the compressor operate more closely to the “ideal compressor.”

Having significant storage at the compressor room also can help the compressors ride out transient high flow compressed air demands that might cause another compressor to start unnecessarily, or might require a compressor to run continually and inefficiently in unloaded mode to avoid low pressure events, both of which would needlessly increase power costs,

Well placed storage receivers located in industrial facilities on the plant floor can also be of benefit. Storage receivers can be placed near machines that consume short duration high flows of compressed air that might cause localized low pressure events that affects other pressure sensitive equipment. Use of storage to supply these transient events can smooth out these high flows so as not to cause the start of an extra air compressor or cause localized low pressure.

And if production machinery is being affected by localized pressure fluctuations, storage receivers protected by check valves can be installed to protect this equipment from short term transient low pressure events. This can prevent the need to increase the plant pressures to compensate.

6.    Lower the compressed air pressure

The higher the discharge pressure, the more power an air compressor consumes. A general rule of thumb states that around 100 psi, and at a constant flow, the compressor power requirement increases about 1% for each 2 psi increase. Therefore, if this discharge pressure can be reduced some compressed air system savings can be gained.

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