Based on 5,000 hours/year at $0.05/kWh

* An air motor will require about 7hp of compressor capacity or 27-30cfm of air to obtain 1hp output from the air motor.

Why is Compressed Air so Inefficient?

Motor energy is converted to heat in the compression process.

• As shown above, the energy available to do useful work is less than 20% of the compressor input energy.
• If the air is compressed to 100 or 110 psig, by time it is cooled, dried and delivered to the point of use, the pressure may only be 85-95psi.
• Depending on the application, the air may be regulated down, or exhausted at greater than atmospheric pressure (10-14 psig exhaust for air tools).
• A typical air tool application may have an overall efficiency of only 12-15% efficiency and an application where the air is regulated down to 50psig prior to use would have an overall efficiency of only 7-9%.

Life Cycle Cost Analysis of a Compressor

In deciding what compressor to purchase, there may be more important factors than cost. The graph below shows a 10 year life cycle cost for a screw compressor.

@ $0.06/kwh, a single stage rotary screw compressor costs about $10,000/year per 100cfm to operate!
(electricity only, based on 8,000 hrs/yr. runtime)

When selecting a compressor, the following should be taken into consideration:

• What is the total cost of ownership?
• What type of controls will best suit my operation?
• Two stage compressors will likely save money in the long run.

Plant Air Compressor Deliveries

5.0 to 5.3 cfm/hp · H/D 2 Stage Water Cooled Recips. 4.5 to 5.0 cfm/hp · Multistage Centrifs. · 2 Stage Rotary Screw · Higher Speed 2 Stage Recips. 4.25 to 4.5 cfm/hp · Lower Rotor Speed Single Stage Oil Flooded Screw 4.0 to 4.25 cfm/hp · Most Single Stage Oil Flooded Screw

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).

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