Energy Savings in Compressed Air Systems
Evaluating Compressor Efficiency
Cost-justifying More Efficient Compressors
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Achieve Significant Savings Through Improved Energy Management
Waste Heat Recovery and the Importance of Maintenance
Add to your savings with waste heat recovery, flow controller and maintenance.
 
Waste heat recovered from compressors can be used for heating.
     The heat generated by air compressors can be used effectively within a plant for space heating and/or process water heating. Considerable energy savings result in short payback periods
.
     Process heating: Heated water is available from units equipped with water-cooled oil coolers and after-coolers. Generally, these units can effectively discharge the water at temperatures between 130 degrees F and 160 degrees F.
 
     Space heating is essentially accomplished by ducting the heated cooling air from the compressor package to an area that requires heating. If ductwork is used, be careful not to exceed the manufacturer's maximum back-pressure allowance. When space heating is used in the winter, arrangements should be made in the ductwork to return some of the heated air to the compressor room in order to maintain a 60 degrees Fahrenheit room temperature. This ensures that the air discharged is at comfortable levels.
 
     Waste heat recovery is particularly effective when the primary air compressor package is an oil-cooled rotary-screw type.
 
     Estimating the real energy savings in dollars must include identifying the actual cost of the current source of energy (natural gas, electric, propane etc.). (See Energy Savings Through Heat Recovery.)
Use of flow controllers.
     Most compressed air systems operate at artificially high pressures to compensate for flow fluctuations and downstream pressure drops caused by lack of "real" storage and improperly designed piping systems. Even if additional compressor capacity is available, the time delay caused by bringing the necessary compressor(s) on-line would cause unacceptable pressure drop.
 
     Operating at these artificially high pressures requires up to 25% more compressor capacity than actually needed. This 25% in wasted operating cost can be eliminated by reduced leakage and elimination of artificial demand.

 
 
     A flow controller separates the supply side (compressors, dryers and filters) from the demand side (distribution system). It creates "real" storage within the receiver tank(s) by accumulating compressed air without delivering it downstream. The air pressure only increases upstream of the air receiver, while the flow controller delivers the needed flow downstream at a constant, lower system pressure. This reduces the actual flow demand by virtually eliminating artificial demand and substantially reducing leakage.
 
The importance of maintenance to energy savings.
Well-Maintained vs Poorly Maintained Compressor 
Effect on Energy Costs 
100 hp rotary-screw package (10 cents kWh; 8,760 hrs.) 
Estimated annual full load power costs = $75,000
Poorly Maintained Well Maintained
Dirty oil filter
-1%
Clean oil filter
Hot running oil
-2%
Cooler running oil
Mineral oil
-2%
Synthetic oil
Dirty inlet filter
-1%
Clean inlet filter
Fouled air/oil separator
-2%
Normal running air/oil separator
Total Energy Cost
$81,000
Total Energy Cost
$75,000
Potential Loss
$6,000
Potential Savings
$6,000
 
 
     Leaks are expensive. Statistics show that the average system wastes between 25 and 35% to leaks. In a compressed air system of 1,000 cfm, 30% leaks equals 300 cfm. That translates into savings of 60 hp or $45,000 annually.
 
     A formalized program of leak monitoring and repair is essential to control costs. As a start, monitor all the flow needed during off periods.
 
     Equip maintenance personnel with proper leak detection equipment, and train them in how to use it. Establish a routine for regular leak inspections. Involve both maintenance and production personnel.
 
     Establish accountability of air usage as part of the production expense. Use flow controllers and sequencers to reduce system pressure and compressed air consumption.
 
     A well-maintained compressor not only serves you better with less downtime and repairs, but will save you electrical power costs too.
Evaluating Compressor Efficiency / Cost-justifying More Efficient Compressors
 

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