An important part of any energy efficiency project is verification of the project post installation. Checking out the baseline of the new system and comparing it with the old consumption proves the savings … and gives you the confidence that everything is working okay.
The chart shown at right shows a real system with a lightly loaded online/offline compressor. The readings showed the system, with one running compressor, was running at a system specific power of about 200 kW/100 cfm, which was off the chart. Specific power is like a gas mileage rating for air compressors. Normal in this case would be about 20 kW per 100 cfm — so the old way of running the compressor consumed about 10 times normal in the measured condition.
About midway through the chart, the compressor was changed to a VSD-controlled unit. The specific power immediately fell to about 40 kW/100 cfm, good, but not near the expected number. Fortunately, the site had a web connected compressor monitor installed on the system, and a compressed air auditor immediately diagnosed the problem from his office: the compressor unload timer was set too long, and the compressor discharge pressure setting was too high, wasting power.
The service personnel on site quickly adjusted the parameters and the specific power fell to normal levels. It is best not to totally rely on compressor techs to correctly set the compressors up, sometimes things are missed. The saying “you can’t manage what you don’t measure” certainly comes into play in this case.
The compressor monitor also later detected problems with the air dryer (the plant personnel forgot to turn it on), and an excessive amount of leaks, both of which were corrected in a timely manner so the system could qualify for the maximum in utility incentives.
The auditor also estimates the monitor has saved him two trips to site and eight hours of wasted effort. A good benefit to all!