Horsepower required to Compress Air

The horsepower required to adiabatic compression of air can be calculated with the calculator below:

N - number of stages

V - volume flow of compressed air at atmospheric pressure (cfm, ft³/min)

k - adiabatic expansion coefficient

P₂- absolute final pressure (psi)

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Theoretical horsepower required to compress one cubic foot of free air (atmospheric pressure) for single-staged, two-staged and three-staged compressors are indicated in the diagram below. In general - plus 15-20% friction.

• 1 cfm (ft³/min) = 1.7 m³/h = 0.47 l/s = 28.3 l/min
  
• 1 psi (lb/in²) = 6894.8 Pa (N/m²) =  6.895×10^-2 bar
• 1 hp = 745.7 W

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The power required for adiabatic (process without transfer of heat) compression of air can be expressed as

HP = (144 N P₁ V k / (33000 (k - 1))) ((P₂ / P₁)^{(k - 1) / (N k)} - 1)                                (1)

where

HP = horsepower

N = number of compression stages

k = 1.41 = adiabatic expansion coefficient

P₁ = absolute initial atmospheric pressure (psi) (14.7 psi at sea level)

P₂= absolute final pressure after compression (psi)

V = volume of air at atmospheric pressure - standard or free air (scfm, ft³/min)

• adiabatic compression (or expansion) takes place without transmission of heat