| 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 |
