Compressed Air Basics

The Department of Energy (DOE) has determined that air compressors are one of the largest users of electricity in industry. Although at one time the DOE considered electric motors as the largest user of electricity, savings through improved electric motor efficiency are dwarfed by those available through improving the compressed air system design and operation.

Energy savings through improved design and operation of the air system can range from 20-50%. Most facilities consider compressed air a utility on par with electricity, gas, and water. Unlike other utilities, few people know their cost per CFM.

What are your costs per CFM?

Here is a good way to find out

• Assumptions
  • Motor Service Factor = 110%
  • Power Factor = 0.9
• A typical compressor produces 4 CFM per 1 HP
• 1 HP = 110% x 0.746 KW/0.9= 0.912 KW
• Therefore,1 CFM = 0.228 kW
• At 0.06 $/kW/hr : 1 CFM = $0.0137/hr
• Therefore, 10 CFM over 8000 hr will cost: 10 x 8000 x .0137 = $1096.

Where are your savings?

In a typical plant, air leaks account for 20% of the total air usage!

Standard plant system using Basic Air System Drawing

• 8000 hr per year operation
• Electrical costs = 0.06 $/kwhr
• Line pressure = 100 PSIG
• Plant Demand (CFM) ; 400CFM
• Air leaks (CFM) ; 20% ; 80CFM
• Total Compressor Demand ; 480CFM

Electrical Cost for Compressed Air

Leaks are also creating enough additional load to mandate operation of both compressors.

• No Standby Unit
• No preventative maintenance can be performed on either compressor

The number of leaks required to create 80 CFM at 100 PSIG:

• Three, 1/8" air leaks ; 78 CFM or
• One, 1/4" air leak ; 100 CFM

How many leaks do YOU have?