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# Compressed Air Energy Calculations at Different Operating Pressures and Flow

## Compressed Air Energy Calculations at Different Operating Pressures and Flow

(OP)
I have a client who is wanting a high-level economic analysis done on retrofitting their air compressor.

The CAGI data sheets show a BHP rating for the compressor, along with the max operating pressure and rated full load acfm.

My question is how to model performance and energy consumption when operating at a lower operating pressure and capacity for the purpose of potential energy cost savings?

### RE: Compressed Air Energy Calculations at Different Operating Pressures and Flow

Wouldn't you use a regulator to lower the output pressure. I assume it has an air receiver. Size of the receiver along with system downstream operating pressure will reduce the duty cycle of the compressor. I believe that is where you would see your energy savings.

### RE: Compressed Air Energy Calculations at Different Operating Pressures and Flow

(OP)
MFJewell,

I am looking for an analysis method to estimate compressor performance based on operating parameters that are different then what's driving the CAGI data sheet.

Example

The CAGI data sheet says a certain compressor is rated at 495 acfm at 100psig with a 89kW input and 0.941 eff.

what could I expect if that compressor was operated at 90 psig on a system that required 400 acfm. what could i expect the input power to be?

### RE: Compressed Air Energy Calculations at Different Operating Pressures and Flow

All the compressor systems I have worked with/on have had a single output from the compressor. The compressors fed large receivers. The larger the receiver, the lower the duty cycle on the compressor (dependent on system demand).

I would think the compressor output is most likely constant on the system you are trying to analyze (with downstream use variable and/or less than the rated output of the compressor). How do you plan to change the compressor output? Typically the system pressure and flow are controlled by control valves and regulators.

Anyway, you can use some basic air compression equations to calculate work required. Google or pull out a thermodynamics book.

### RE: Compressed Air Energy Calculations at Different Operating Pressures and Flow

(OP)
I suppose you're right.

Now that I am reasoning it out to myself I suppose the compressor will shut off, or dump the flow and run unloaded, once the pressure set-point is reached. Then turn back on once the receivers and line pressure falls below the the Cut-In pressure.

Thank you for your insight and experience on the subject.

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