SCFM versus ACFM and ICFMActual air compressor capacity (ACFM) versus standard air capacity (SCFM) and inlet air capacity (ICFM)SCFM - Standard Cubic Feet per MinuteIt is common to rate the compressed air consumption in Standard Cubic Feet per Minute - SCFM. The SCFM - Standard Cubic Feet per Minute - determines the weight of air to fixed or "Standard" conditions. There are several definitions of SCFM. The most common used in the United States is with "sea-level" properties:

14.696 Pounds per Square Inch (psia) 60 Degrees Fahrenheit (oF) (520oR) 0% Relative Humidity (RH)

Europeans normally use one ata and 0 oC as SCFM.

ACFM - Actual Cubic Feet per Minute

Unfortunately, real life "actual conditions" are seldom "standard conditions". When

pressure is applied a volume of air - it gets smaller vacuum is applied to a volume of air - it expand

Actual air volume flow is often termed ACFM - Actual Cubic Feet per Minute. Actual Cubic Feet per Minute - ACFM, depends on the

pressure temperature humidity

of the actual air. The conversion from SCFM to ACFM can be expressed as ACFM = SCFM [Pstd / (Pact - Psat )](Tact / Tstd) where ACFM = Actual Cubic Feet per Minute SCFM = Standard Cubic Feet per Minute Pstd = Standard absolute air pressure (psia) Pact = absolute pressure at the actual level (psia) Psat = Saturation pressure at the actual temperature (psi) = Actual relative humidity Tact = Actual ambient air temperature (oR) Tstd = Standard temperature (oR) (1)

Online SCFM - ACFM CalculatorThe calculator below can used to calculate ACFM:100

SCFM Standard absolute air pressure (psia) Actual absolute air pressure (psia)

14.7

24

0.5069

Saturation pressure at the actual temperature (psia) Actual relative humidity Actual ambient air temperature (oR) Standard air temperature (oR) temperature converter pressure converter

0.80

540

520

Example - SCFM to ACFM

The actual CFM of a compressor operating at "non-standard" conditions like

elevation 5000 feet (1500 m) - atmospheric pressure Pact = 12.23 psia temperature 80oF - absolute temperature Tact = 540oR saturation pressure Psat = 0.5069 psia relative humidity = 80% demand 100 SCFM

can be calculated as ACFM = (100 SCFM) [(14.7 psia) / ((12.23 psia) - (0.5069 psia) (80 / 100))]((540 oR) / (520 oR)) = 129.1

ICFM - Inlet Cubic Feet per MinuteInlet Cubic Feet per Minute - ICFM - is used by compressor vendors to establish conditions in front of additional equipment like inlet filter, blower or booster. When air passes through the filter there will be a pressure drop. The conversion from ICFM to ACFM can be expressed as ACFM = ICFM (Pact / Pf) (Tf / Tact) where ICFM = Inlet Cubic Feet per Minute Pf = Pressure after filter or inlet equipment (psia) Tf = Temperature after filter or inlet equipment (oR) (2)

Note!The Ideal Gas Law is accurate only at relatively low pressures and high temperatures. To account for the deviation from the ideal situation, another factor is included. It is called the Gas Compressibility Factor, or Z-factor. This correction factor is dependent on pressure and temperature for each gas considered. The True Gas Law, or the Non-Ideal Gas Law, becomes: P V = Z n R T (3) where Z = Gas Compressibility Factor n = number of moles of gas present