KEVOS® MAKEOS · Pneumatics
Air Compressor Power
What shaft power does it take to compress this air flow to this pressure?
Theoretical isothermal and adiabatic power to compress a flow of free air in one or more intercooled stages, and the shaft power with an overall efficiency.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Air flow (free air delivery) | m³/min | Flow of air measured at inlet conditions (free air delivery). |
| Discharge pressure (gauge) | bar | Discharge pressure at the compressor outlet. |
| Inlet pressure (absolute) | bar | Absolute inlet pressure (1.013 bar at sea level; lower at altitude or with inlet filter loss). |
| Compression stages (intercooled) | stages | Number of stages with perfect intercooling and equal pressure ratios. |
| Ratio of specific heats | 1.4 for air. | |
| Overall efficiency (adiabatic to shaft) | % | Ratio of theoretical adiabatic power to shaft power, from the compressor maker (often 65–85%). |
Method and formulas
- Isothermal: P = p₁ Q ln(p₂ ÷ p₁).
- Adiabatic with N stages: P = N × k/(k − 1) × p₁ Q [(p₂ ÷ p₁)^((k − 1)/(N k)) − 1].
- Shaft power = adiabatic ÷ efficiency; specific power = shaft kW ÷ flow (m³/min).
- Example: 10 m³/min to 7 bar g in one stage needs about 63.475 kW at the shaft.
Limitations
- Theoretical power with an overall efficiency; real compressors also lose energy at part load and in dryers.
- Moisture in the air is ignored.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate compressor motor size for a demand
- Compare single and two-stage compression
- Estimate specific power for energy studies
Who it is for
- Maintenance engineers
- Energy and utilities managers
- Design engineers
What you get
- Pressure ratio
- Isothermal power
- Adiabatic power
- Shaft power and specific power
Interpreting the result
- Compare specific power with maker data (kW per m³/min) to judge an existing compressor.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3032–3041. Topic reference; no source tables or recommended settings are reproduced.
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