A medium-sized tire shop was having troubles with pressure during their busy times. In the spring and fall, during agricultural planting season, the pressure went way down when servicing the many farm implement tires coming in. And the shop’s compressor would cut out when they needed it the most — a very frustrating experience.
A compressor supplier was called in to assist with the problem, they checked out the existing 15-hp screw compressor and indeed proclaimed it to be too small. But they just happened to have a nice 50-hp fixed speed compressor on sale — a very good deal! After installation the pressure problems went away, making for a very happy customer.
One day a compressed air auditor was asked to assess the compressed air system for efficiency. He found that the new compressor turned off regularly during the operating time due to automatic shutdown, but was very lightly loaded, running loaded only 20% of the run time, and at an average of about 10% of capacity through all hours.
Through the almost 5-year life of the compressor, the unit had consumed $22,000 worth of electricity — while producing no air output in the unloaded condition. The specific power calculates to about 42 kW per 100 cfm output, about double what an efficient compressor would be running. Not such a super deal after all!! The unloaded 50-hp compressor consumes more power when unloaded than the fully loaded 15-hp unit.
An inspection of the compressor room where the 15-hp compressor is installed revealed a lack of ventilation; actually no ventilation ducts were ever installed. This explains the failure during high loads.
The customer is now considering the options to right-size their compressor for more efficient operation.