Of the set of air compressors, at part load the most efficient compressor should be used to save energy.
Most industrial facilities need some form of compressed air, whether for running a simple air tool or for more complicated tasks such as operation of pneumatic controls.
Approximately 10% of the electricity consumed in a plant is for generating compressed air. For some facilities, this may account for 30% or more of the electricity consumed. Compressed air is being an on-site generated utility, very often the cost of generation is not known. Compressed air is one of the most expensive sources of energy in a plant.
Air being commonly considered free, the efficiency of the air compressors is generally a neglected area. Thus in a battery of air compressors, the choice of air compressor to be used to cater to part loads is generally arbitrary.
At part loads it would be worth while to put to duty the most efficient air compressor in order to reduce the electricity consumption.
The formula for calculating the efficiency of air compressors is as presented below.
(bhp) x (0.746) x (# of operating hours) x (Rs./kWh) x (% time) x (% full load bhp)
Bhp - Compressor shaft horsepower (frequently higher than the motor nameplate horsepower—check equipment specification)
Percent time - percentage of time running at this operating level
Percent full - load bhp—bhp as percentage of full-load bhp at this operating level
Motor efficiency - motor efficiency at this operating level
Alternatively FAD monitoring systems have the capability to calculate these efficiencies online thereby enabling intelligent and economical operations.