| Look beyond the
purchase price. |
| As indicated previously, over a 10 year period,
the electrical power costs of a compressed air system impact the bottom-line
far beyond initial price and maintenance. How can we evaluate the true
impact each element of the compressed air system has on the electrical
power costs? |
| The air compressor package. |
The air compressor package has a very significant
impact on overall operating power costs. There are other pieces of equipment
in a compressed air system that support the air compressor. These also
impact on power costs, both directly and indirectly. But the core of it
all is the air compressor package. Energy wasted at the air compressor
site can never be recovered.
|
|
| What are the components of an energy efficient
compressor? |
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Compressor element (airend) - performance can vary up to 20% depending
on what airend size and style are used.
|
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Drive motor efficiency - there are high efficiency motors available
which can save up to 5% in power consumption. Referring to the previous
example, a 100 hp compressor would save $3,750 annually.
|
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Compressor controls - are an important part of the air compressor
package, matching compressor supply to demand. As outlined previously,
the right control type (dual control) is essential for efficient operation.
Maximum savings of 45% are possible. Any reduction in air usage in a system
accomplished by good demand side management (adequate storage and flow
controller) can be translated into real power cost savings by the control
system, and none does this better than dual control.
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|
|
State-of-the-art
control systems generate large savings.
|
| Sequencing compressors/controls. |
| A microprocessor-integrated sequencer allows
the system to maintain a stable system pressure and ensures that only needed
compressor units are operating at their most efficient level. |
| User-friendly, PLC-based sequencers can mix
and match compressor supply to demand, including automatically shutting
off units not needed, and bringing on backup units as required. |
| Sophisticated sequencers not only sequence
and select units as required, but ensure that no more than one unit in
a multiple-unit installation will be operating at inefficient part load.
All other units will be operating efficiently at full load. |
| Electrical power savings result from operating
fewer compressors at a lower pressure than with conventionally controlled
compressors. |
Efficiency Rules of Thumb
| ? Most air compressors
deliver 4 to 5 cfm per hp at 100 psig discharge pressure.
? Every 2 psig of pressure
increases or decreases the power draw of an air compressor 1%.
? Every 10 degrees Fahrenheit
change in inlet air temperature affects the efficiency about 1%. Colder
temperature increases and warmer temperature decreases efficiency.
? Power cost for 1 hp
for 3 shifts, 7 days a week (8,760 hours) at 10 cents/kWh = about $750/year.
? A 50 hp compressor rejects
approximately 126,000 Btu per hour. Approximately 119,000 Btu/hr of this
is recoverable.
? Size control air receiver
located after compressor for about 1 gallon capacity per cfm of compressor
capacity.
? Size storage air receiver
for about 2-4 gallon capacity per cfm of compressor capacity. This results
in an effective demand side control management system.
? Total pressure drop
across all compressed air system components, including piping, should not
exceed 15 psi. |
|
| Reduce pressure
drop in system components. |
| When buying or replacing equipment, make sure
it maintains low pressure drop over its entire service life. Also, ensure
that filters and dryer are sized and maintained properly. The total pressure
drop across all compressed air system components, including piping, should
not exceed 15 psi. |
|
Evaluating
Compressor Efficiency / Waste Heat
Recovery and the Importance of Maintenance
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| © Copyright 1998 Maintenance Resources, Inc. |
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