Plant Air Compressor Deliveries
 |
5.0 to 5.3 cfm/hp 4.5 to 5.0 cfm/hp 4.25 to 4.5 cfm/hp 4.0 to 4.25 cfm/hp |
What Price is Efficiency:
Comparing a 1000cfm rated machine operating at 4 cfm/hp vs. 5.25cfm/hp, the
difference would be $25,000 per year in electrical costs. (Based on 8500
hrs/yr @ $.05/kWh and $7/kW).
Performance Curves
Important conclusion drawn from the performance test:
- The compressor was rated at over 1,000cfm at 100psig but was only able to deliver 799scfm at 100psig.
- The modulating valve was prematurely closing the inlet on the compressors starting at 95 psig.
Imagine there are four of these compressors in the plant (1,000scfm each) plus a backup. If the plant air demand was 3800scfm and just two of the four had this problem (a 200cfm shortfall in air production), then the total capacity from the compressors would only be 3,600scfm and the backup compressor would be forced to run to keep up with demand. The facility may also begin to contemplate purchasing a new compressor because they are "running without backup" now.
At tests of over 230 plants, 80% of compressors tested which featured modulating inlet valves exhibited the graphed behavior above of not producing their rated air flow.
Power Capacity Characteristics
Some considerations which influence which type of controls are
best for the compressor in your plant include:
- Choose the control type which is most efficient for the operating range where the compressor will run.
- If the compressor will operate fully loaded 100% of the time, first cost may be the driving influence.
- A more efficient compressor is likely to have a more expensive first cost. However, life cycle costs should be analyzed to determine the true cost of ownership.
For additional information or assistance, contact Kelly Beiermann, Nebraska Public Power District.
Note: We encourage requests from Nebraska customers. Businesses outside of Nebraska will be directed to their utility for further information.
Source: Airometrix Mfg., Inc. 1999-2003
