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Efficiency
Efficiency measures how well something turns inputs into useful outputs. It is the ratio of useful output to total input, expressed as a percentage. Efficiency is never 100% due to friction, leakage and resistance losses.
What Is Efficiency in Compressors?
Efficiency indicates how effectively a compressor converts electrical energy into compressed air energy. It is expressed as the ratio of the power delivered in the form of compressed air to the total electrical power the motor consumes. An efficient compressor delivers more compressed air for each unit of energy it consumes.
Since energy consumption is one of the largest expenses of operating an air compressor over its lifetime, efficiency plays a valuable role in determining the total cost of owning this asset. Improving efficiency could reduce energy costs for industries.
FAQs
Specific Power is the common metric, measured in kilowatts per 100 cubic feet per minute (cfm). A lower Specific Power signals a more efficient unit because it means less energy is used to generate the same amount of air.
Specific Power = kW / cfm * 100
Engineers use other efficiency-focused metrics, such as adiabatic and volumetric.
Air compressor efficiency depends on the application:
- Centrifugal compressors are the most efficient for considerably large, continuous air demands.
- Rotary screw compressors are highly efficient for diverse industrial use cases.
- Reciprocating piston compressors are efficient for small, intermittent uses.
- Variable speed drive (VSD) compressors are efficient for applications where air usage fluctuates.
Yes, for higher pressure applications typically above 100 pounds per square inch (psi), a two-stage compressor is considerably more efficient. By splitting the compression work into two steps with cooling in between, the compressor lowers the total energy required to reach the final pressure, delivering better energy efficiency.
Several factors impact compressor efficiency:
- Operating pressure: Running a compressor at a higher pressure than necessary consumes more energy.
- Air leaks: Air leaks force the compressor to run longer and more frequently to maintain pressure, reducing energy efficiency.
- Maintenance: Skipping regular maintenance clogs the filters, driving the compressor to work harder to draw in air and compress it, which increases energy consumption.
- Air intake quality: The temperature, composition and humidity of intake air affect compressor efficiency. Cool, clean, dry air is more efficient to compress.
Every compressor efficiency calculation must first determine the power consumption or kW and the air output or cfm to establish the Specific Power.
kW for single-phase power = Voltage * amperage * power factor
kW for three-phase power = (Voltage * amperage * power factor * 1.732) / 1000
Note: Power factor is a measure of electrical efficiency. 1.732 or the square root of 3 converts the measurements from a three-phase system into the correct total power.
cfm = (Tank volume [gallons]* (cut-out pressure [psi] – cut-in pressure [psi])) / (7.48 * 14.7 * time [minutes])
Note: This formula calculates the output using a pump-up test, which measures the time it takes to fill the receiver tank. The number 7.48 converts gallons to cubic feet, and 14.7 is standard atmospheric pressure in psi.
The first and most effective step is conducting an air leak audit. Finding and fixing leaks improves energy efficiency and saves money.
A pressure drop is the loss of pressure as air moves from the compressor through pipes, filters and hoses to the point of use. A high pressure drop demands running the compressor at a higher pressure to compensate, increasing energy consumption. Optimize piping size with Quincy Compressor’s solutions and minimize bends and restrictions to reduce pressure drop and enhance compressor efficiency.
Additional Resources
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