These are the TOP TEN “Rules of Thumb” for compressed air, designed to answer the most frequently asked questions by industrial air compressor users.
1. Expected CFM per Horsepower Delivery @ 100 PSIG:
o For “home owner” air compressors — 2 to 2.5 CFM per HP
o For 2-stage air-cooled industrial air compressors—-3.5 CFM per HP
o For small screw vane air compressors (25 HP or less) 4 CFM per HP
o For large piston, screw and centrifugal air compressors: 4.5 to 5 CFM per HP
NOTE: THE MORE CFM PER HP, THE LESS ENERGY USED.
2. Air Reservoir Size Required for These Inlet Control Types:
o Modulating Control—————0 to 1 gallon per CFM
o Online/Offline—————- 3 to 4 gallons per CFM
o Stop-Start/Variable Speed– 4 to 6 gallons per CFM
NOTE: THE MORE AIR STORAGE – THE LESS ENERGY USED
3. Amperage per horsepower:
115 volts——- 1 phase——– 10 amps per horsepower
230 volts——- 1 phase——– 5 amps per horsepower
208 volts——- 3 phase——– 3 amps per horsepower
230 volts——- 3 phase——– 2.5 amps per horsepower
460 volts——- 3 phase——– 1.25 amps per horsepower
574 volts——- 3 phase——– 1 amp per horsepower
NOTE: THE MORE ENERGY EFFICIENT THE MOTOR, THE LESS ENERGY USED.
4. Air Line Size by CFM and Pressure Drop:
o Compressor room header — 0.25 PSIG pressure drop per 100 feet of piping
o Main line—————-0.5 PSIG pressure drop per 100 feet of pipe
o Loop line—————-1 PSIG pressure drop per 100 feet of tubing
o Branch—————2 PSIG pressure drop per 100 feet of pipe
NOTE: THE LESS AIR PRESSURE DROP – THE LESS ENERGY USED.
5. Size your compressed air line filters to be twice (2x) the CFM flow rate of your compressor.
o This will reduce your pressure drop by 2-3 PSIG and save an additional 1% in electrical energy costs.
o Elements will last twice as long (2x) and this can save you maintenance costs.
6. Reducing the air compressor pressure settings by 2 PSIG will result in a 1% energy savings.
7. Reducing the air compressor inlet air temperature by 10°F will result in a 2% energy savings.
8. The average energy cost to run an air compressor is approximately $0.10 per horsepower per hour.
9. Compressed air system leaks totaling the size of a 1/4″ hole, at 100 PSIG, running 24 hours a day, will waste approximately $15,000 in electrical energy per year.
10 Using synthetic compressor lubricants can save you up to 9% in the energy cost of operating your compressor compared to using a non-synthetic lubricant.
COMPRESSED AIR DEFINITIONS:
CFM= Cubic Feet Per Minute – Volumetric Airflow Rate.
Inlet pressure = The actual pressure at the inlet flange of the compressor.
PSIG = Pounds per square inch gauge
AMPS=Abbreviation for the plural of Ampere, a unit of electrical current
Pressure = Force per unit area, measured in pounds per square inch (psi).
Pressure Dew Point = For a given pressure, the temperature at which water will begin to condense out of air.
Inlet temperature = The total temperature at the inlet connection of the compressor.
Knowing these “Rules of Thumb” can help you understand many of the basics of compressed air. Applying these tips can help you save time, energy, and money.
