The advantages of adding controls to your air system include:
- Reduced energy costs (10 to 25
- Reduced maintenance
Controls reduce energy costs by
improving pressure control and improving multiple compressor
operation. The reduction in constant pressure spikes reduces the
number of leaks and stress on the entire air system. Monitoring the
compressor's condition also reduces maintenance costs.
To identify the proper control system
for your air system, first determine the level of automation,
reporting, and monitoring you need. Do you require:
- Analog compressor condition
- Electronic pressure control?
- Multi-compressor system pressure
- Condition trending reports?
- An interface for system
- The ability to remotely control the
air system at multiple locations?
Dual Control is a combination of Constant Speed Control and
Automatic Start/Stop Control. Automatic Start/Stop is the simplest
form of compressor control. At a set low pressure point a signal is
sent to start the compressor. The compressor runs until the
pressure reaches the upper set point. This cycle repeats as the
pressure fluctuates. Care must be taken to limit the numbers of
starts to less than 6 per hour. More than 6 starts per hour can
damage the electric motor. Constant speed control keeps the motor
running continuously and as the pressure falls to a lower set point
the compressor is put into a loaded position. In a loaded position
the inlet valve is closed allowing air to be compressed. Once the
upper pressure set point is reached the compressor goes into an
unloaded condition where the inlet valve is kept open and the
entering air is bypassed to atmosphere. This eliminates the problem
of frequent starts on the electric motor. A manual switch allows
selection of the mode that best suits the demand for compressed
A compressor that runs in constant
speed control during periods of low demand wastes energy. A
compressor that operates under auto start/stop during high air
demand periods can damage the compressor's electric motor. An Auto
Dual Controller such as the AutoTrol can automatically alternate to
the appropriate mode to save energy. The unit works with any
reciprocating compressor with head unloaders or a rotary screw
compressor that has on/off control. The AutoTrol quickly pays for
itself in energy savings.
In addition to managing pressure,
many controllers monitor or control:
- Automatic drain valves
- Low oil emergency shutdown
- Inlet air temperature
- Outlet compressed air
- Hours of operation
Flow controllers supply consistent
air pressure, making pneumatic devices more efficient while
optimizing the compressors operation. Flow controllers reduce a
plant's costs two ways:
- Reduced horsepower consumption saves
- Efficient operation of the compressor
reduces maintenance expenses.
Intermediate Controls (Demand
A proper compressed air system must
provide a minimum amount of compressed air at a minimum pressure to
satisfy all demands at all times. Those systems that perform
without an intermediate control cost more to operate because it is
forced to operate at a higher pressure than actually required to
meet demands. At higher pressures the cost to compress the air is
higher and any leak will lose more air. This is referred to as
artificial demand. Artificial demand is wasteful and very costly.
An intermediate controller with proper air storage will
dramatically reduce the operating cost of a compressed air
The intermediate controller is
located at the intermediate point of the system. This is downstream
of the filtration and drying equipment (supply side) and upstream
of the main piping distribution system (demand side).
An intermediate controller
1. Establish a stable pressure without a large pressure drop
2. Operate over a wide range of pressures and flows
3. Be responsive to handle system dynamics while maintaining the
4. Ensure it will not shut down production in the event of a
malfunction or control failure
Intermediate controllers operate by
monitoring deviations in pressure on the demand side in relation to
the set balance point pressure. A signal is sent to the controller
that quickly increases or decreases flow to correct the demand side
pressure. This keeps the pressure at the lowest possible pressure
and supplies proper flow.
Storage is an important part of a
system. Storage isolates the compressors from the demand side. Peak
air demands in a properly sized system will use the storage air
that allows the compressors to function in a more stable
Microprocessor control systems
utilize pressure transducers. The pressure accuracy allows pressure
differential to be as low as 2 PSIG (0.13 bar). These models offer
users the ability to program the controller to sequence multiple
compressors. The system operates all of the compressors in a common
pressure range, allowing for the highest energy savings. According
to the manufacturer and model, between 2 and 16 compressors can be
combined. These controllers either work off of several pressure
transducers or one, depending on the particular controller.
The controller balances the load,
distributing it evenly across all of the compressors. By managing
multiple compressors, controllers eliminate compressors working
against each other. This ensures constant pressure to the
compressed air users and equipment. While improving the plant's
compressed air delivery, controllers save the plant money by
reducing electric costs and minimizing compressor maintenance.
Controllers also monitor intake air
temperature, outlet compressed air temperature, outlet flow (cfm),
and other critical measurements. You can access this information at
a touch of a button from the LCD screen. And, the controller saves
this information and allows you to retrieve it to produce reports.
From these reports you can track how your compressor is operating
to plan preventive maintenance.
A Microprocessor control with remote
monitoring has all of the features of a Multiple Compressor Flow
Controller and allows users to manage compressors from remote
locations. For example, an operator in California can manage
compressors in Georgia.
Flow controllers reduce a plant's energy consumption by keeping
the compressed air system running efficiently. A compressor's
electric motor runs less when a flow controller manages the air
distribution, which reduces electric consumption. The flow
controller shuts down the compressor when demand is low and
automatically restarts the compressor when demand increases. The
savings can be significant.
Cost Savings Example:
This example represents one 220 HP (1000 cfm) compressor at 100
psig running one shift; a shift equals 2,920 hours.
KW Conversion Factor = .746
Motor Efficiency = .93
Electric Cost a KWH = .07
Horsepower x KW Conversion Factor / Motor Efficiency x Operating
Hours x Electric Cost a KWH = Power Cost
220 x .746 / .93 x 2,920 x 0.07 = $36,071
If you add a flow controller to the compressor package and reduce
how long the compressor runs a day by 2 hours, you eliminate 730
hours of operation a year.
2,920 - 730 = 2,190
220 x .746 / .93 x 2190 x .07 =$27,053
$36,071 - $27,053 = $9,018
This is an annual savings of $9,018
downstream of a dryer, a dew point monitor enables you to monitor
the compressed air dew point and alerts you when dew point is out
of specification. Dew point monitors help you manage your
compressed air system and ensure proper air dryer operation.
A carbon monoxide monitor is
recommended for all compressed air breathing systems. Colorless,
odorless, and tasteless, carbon monoxide is typically the most
toxic common contaminant in compressed air. An accurate and
dependable carbon monoxide monitor protects against potential
carbon monoxide poisoning. The monitor has an alarm feature, which
is set by the user. If carbon monoxide exceeds the level an alarm
sounds. A digital display continuously indicates the level of
carbon monoxide detected in ppm.
Most controllers can be wall, track or panel mounted. All require
electricity. Most accept 120/240 VAC 50/60 Hz. They are generally
available in NEMA 4, NEMA 12 and NEMA 7 enclosures. Installation
requirements vary from model to model. For more information, while
specifying a controller on eCompressedair, check the catalog pages
for the models you are interested in. A .pdf of the manufacturers'
literature is also available from the catalog page.