Wednesday, July 12

What Is Isentropic Efficiency?

It is no secret that the highest cost to compressed air is the energy consumed by the machines. While new technologies are constantly evolving in the compressor world to help better these efficiencies and energy consumptions, it is still important to be aware of how your compressor is utilizing energy- and this is exactly what isentropic efficiency is all about!

Isentropic Efficiency Meaning

Isentropic efficiency refers to how a compressor converts electrical energy into working compressed air energy. The CAGI formula used is designed to provide a percentage number outlining how efficiently a compressor does this. The higher the percentage, the more efficient the compressor is at converting electrical energy into compressed air, the lower the percentage, the more energy loss your system is observing. This formula should serve as a baseline calculation, as it assumes your compressor is operating at an ideal performance level. However, we know that many different factors will contribute to your system, not always being an ideal compressor system operating at perfect efficiency. Things like friction losses, pressure drops, leaks, contaminant collection, or other obstacles can occur to reduce your compressed air system’s effectiveness. This calculation can be used as a good comparison between compressors because isentropic efficiency is calculated and measured independently of compression technology or compressor type. It is not a direct measurement and thus does not change with changes in pressure as it is derived from power consumption, pressure ratio, and delivered capacity.


Isentropic Efficiency (%) = (Energy (kW) for the Ideal Consumption Process) / (Actual Energy (kW) Consumed)

How is Specific Power Factored In?

Specific power is another energy-use metric that breaks down energy consumption per unit of delivered capacity. Unlike isentropic efficiency, specific power utilizes full load operating pressures to calculate a direct measurement, making the values different for different compressors, and thus a poor comparison metric between systems. A lower specific power value indicates less energy used to pressurize a certain volume of air and thus a more efficient machine. This also means that specific power and isentropic efficiency are inverses of each other. So, the higher the isentropic efficiency, the lower the specific power.

In Summary…

Utilizing both isentropic efficiency and specific power when evaluating energy usage, will provide the best insights when evaluating energy consumption and deciding on a compressed air system. The isentropic efficiency value can be used in comparison realms, while specific power is the industry standard for estimating energy consumption over time for specific compressor types. 



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