Compressed Air Operating Cost Estimator

Instructions

The Compressed Air Operating Cost Estimator is intended to estimate the cost of operating one or more air compressors, but does not consider the cost of auxiliary systems such as dryers, cooling systems, or controls. Information about your air compressor(s), electricity costs, and operating characteristics will be used to estimate the annual cost of operation.

Inputs

• Air compressor power - typically the nominal full-load horsepower of your compressor(s). Auxiliary equipment power can be added into this number if the operating characteristics are similar to the compressor. This can affect the accuracy of the results, either positively or negatively, if the operating characteristics are known or unknown.
• Motor efficiency - the nominal full-load efficiency of the electric motor that drives the air compressor. The estimator will use this number for all operational loads. If the motor efficiency is known to change dramatically over the operational curve of the compressor, you may use the estimator to seperately enter the proper efficiency at each operational point for a more accurate estimate.
• Average annual energy rate - the average annual marginal cost of energy per kWh.
• Average annual demand rate - the average annual marginal cost of demand per kW.
• Compressor fully loaded - the annual hours of operation and load factor when the air compressor is at it's highest load. This is typically 100%, but may be less for variable-speed units. Additionally, an average load can be calculated for a compressor with unloading controls by monitoring the load profile and taking a time average of the load. Contact the Clearinghouse if you need assistance with this process.
• Compressor partially loaded - the annual hours of operation and load factor when the air compressor is partially loaded. Compressors with on/off controls only should set the hours partially loaded to zero. For 2-step controls, this should reflect the number of hours that the compressor is unloaded but running and the load factor can be measured by comparing full load amps to unloaded amps. For variable speed units, the compressor controls should display percentage load.
• Compressor weekend load - the annual hours of operation that the compressor is left on when the facility is unoccupied, and the load factor in that state. Hopefully these numbers are zero, but there are some instances when compressed air is critical for systems on standby, and the compressed air system cannot be shut down.

Outputs

• Annual energy cost fully loaded - the annual energy cost to operate the compressor(s) at the fully loaded condition.
• Annual energy cost partially loaded - the annual energy cost to operate the compressor(s) at the partially loaded condition.
• Annual energy cost weekend load - the annual energy cost to operate the compressor(s) in the weekend condition.
• Annual demand cost - the annual demand charge to operate the compressor(s).
• Total annual cost - the sum of the costs.

Estimated cost per cfm

After calculating cost, it is sometimes helpful to understand the cost per cfm of compressed air so that you can estimate the cost to run a specific piece of equipment. This calculation is only valid for equipment that runs at constant flow while the compressor is at full load, but gives a ballpark number to use when comparing operating costs of equipment. For this calculation, we calculate the operating cost as if the compressor ran fully loaded all the time (8760 hours/year) and divide that cost by the full load cfm of the compressor.

If you need to calculate an actual operating cost, please contact the Clearinghouse.

Contact the Arkansas Industrial Energy Clearinghouse if you need assistance with this calculator.