These are the TOP TEN “Rules of Thumb” for compressed air, designed to answer the questions most frequently asked by users of industrial air compressors.
1. Expected CFM Per Horsepower Delivery @ 100 PSIG:
o For “homeowner” air compressors — 2 to 2.5 CFM per HP
o For air-cooled 2-stage industrial air compressors—-3.5 CFM per HP
o For small vane and screw 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. Size of air reservoir required for these types of inlet control:
o Modulation 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 IS, THE LESS ENERGY IS 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 tubing
o Loop line—————–1 PSIG pressure drop per 100 feet of tubing
or 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% on electrical costs.
o Elements will last twice as long (2x) and this can save you maintenance costs.
6. Reducing air compressor pressure settings by 2 PSIG will result in 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 about $0.10 per horsepower per hour.
9. Compressed air system leaks totaling the size of a 1/4″ orifice, 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% on 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 compressor inlet flange.
PSIG = Pounds per square inch gauge
AMPS=Abbreviation of the plural of Ampere, a unit of electric 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 in air.
Inlet temperature = The total temperature at the compressor inlet connection.
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.