The easiest but potentially the most expensive way to improve your compressed air operations is to hire someone to do a compressed air audit. A team of experienced, professional compressed air wizards will visit your plant, spend days measuring pressures and examining your system, and give you a list of all the things that are wrong. In many cases, along with repairing leaks, poor piping and other relatively minor problems, they’ll advise you spend tens of thousands of dollars on new compressors and controls.
And they’ll be right. Following the recommendations of an audit usually pays for itself in a short time by saving those tens of thousands of dollars in operating expenses.
You are likely to benefit from such an audit, but it may make sense to know what the audit team is likely to find so you can identify the typical problems yourself. To that end, we asked some top compressor manufacturers and service companies to tell us what they usually find. Listed below are their 10 most typical, highest-payback audit items.
One caveat, though: Fixing these before doing a full system audit can make it more difficult to justify the higher-cost improvements. “Often, many parts of a system upgrade that improve the quality, reliability and repeatability of the system are financed in conjunction with the reductions in waste,” says Mark Krisa, air audit manager at Plant Air Technology (www.plantair.com). “Energy reductions associated with your efforts cannot be incorporated into future return on investment projects.”
In other words, if you fix all the low-hanging fruit, when you do an audit the payback on the investment won’t be as high. It’s a numbers game, but it might be important in determining who pays what, and whose budget it comes out of. The numbers game may decide which you do first: the professional audit or your own list of low-cost repairs.
1. Plug those leaks
“One of the most common problems is leaks,” says Wayne Perry, technical director, Kaeser Compressors (www.kaeser.com). “Studies indicate that as much as 35% of the compressed air produced in the market today is wasted to leaks, and everyone has leaks.” Identifying and correcting them may save not only the purchase price of a compressor, but reduce the amount of energy needed to run the compressor.
“It has been our experience that plants which have no formal, monitored, disciplined, compressed air leak-management program will have a cumulative leak level equal to 30% to 50% of the total air demand,” adds Henry van Ormer, engineer and owner of Air Power USA (www.airpowerusainc.com). Every 8 cfm to 12 cfm leak can cost you $800 to $1,200 per year.
Van Ormer suggests setting up a short-term leak inspection program so that every sector of the plant is inspected once each quarter to identify and repair leaks. “Inspections should be conducted with a high-quality ultrasonic leak locator during production and nonproduction,” he recommends. “A record should be kept of all findings, corrective measures and overall results.”
Afterward, he suggests setting up programs to monitor the air flow to each department and making each department responsible for identifying its air usage as a measurable part of the expense for that area.
If you get rid of leaks, you might cause other problems. “Elimination of waste, such as leakage and artificial demand, may result in reduced loading on compressors that are not equipped to turn down efficiently,” says Mike Bakalyar, manager, enhanced services, Gardner Denver (www.gardnerdenver.com). Dynamic efficiency may actually degrade, resulting in very little positive effect on energy usage (Table 1). Waste has been reduced, but the cost recovery shifts to compressor controls.
|Leaking system||Tight system||Tight plus controls|
|Process demand*||1,500 cfm||1,200 cfm|
|Demand reduction||300 cfm (20%)|
|Power||259 kW||243.5 kW||206.9 kW|
|Dynamic efficiency||5.8 cfm/kW||4.9 cfm/kW||5.8 cfm/kW|
|Annual energy cost*||$108,780||$102,270||$86,898|
|Net savings||$6,510 (6%)||$21,882 (20%)|
|*Example system at 90 psi and $0.05/kWh|
“The campaign to reduce leaks must be complemented with configuration and control improvements that will allow the air generation to turn down with the reduced demand,” he says.
2. Down with overpressurization
Excessive pressure increases leaks and wastes money. “Some end users will actually increase pressure in an attempt to compensate for capacity issues,” Perry says. “In fact, increasing pressure will have the opposite effect on air flow and often exacerbate the problem. There is also a proportional relationship between pressure and power consumption – for every 10 psi in excess pressure there is a 5% increase in power cost.”