Features
The ComfortMiser Compressor Control is designed to operate a
parallel, multiple staged compressor rack or group of
parallel reciprocating or scroll compressors on a single
suction group.
Suction
Pressure Control
The CMC will maintain the
suction pressure as close as the Suction Pressure
Setpoint by turning on/off the compressor and the unloaders.
The CMC will initially
start the compressors in the fully unloaded (lowest
capacity) configurations. Should additional capacity be
required, the CMC, after a calculated delay, will turn
off (add capacity) the next available unloader. Each
unloader will be staged sequentially, in a First On-Last
Off (FILO) sequence. If all the unloaders assigned
to the running compressors have been turned off, then
the CMC will turn on the next compressor.
If the suction pressure is
lower than setpoint, after a calculated delay, the CMC
will turn on (reduce capacity) the next unloader
assigned to the running compressor. if all the unloaders
on the running compressors have been turned on, then it
will turn off the next compressor. The delay time is
calculated automatically using the suction differential
and the rate of change of the suction.
A minimum runtime can be
adjusted at the Compressor Cycling Speed menu.
When the suction pressure is
higher than the suction pressure high alarm limit, the
CMC will turn off/on the next unloader/compressor step
with no time delay.
When the suction pressure is
lower than the suction pressure low alarm limit, the CMC
will turn on/off the next unloader/compressor step with
no delay.
When the Defrost Status
Input is closed, the CMC will maintain at lease one
compressor running, providing enough refrigerant for
cool gas or hot gas defrost. The use of this Defrost
Input is optional and is application dependent.
The CMC will go into alarm
stage and turn off the alarm relay when the suction
pressure reaches its high alarm limit for more than 30
minutes or the suction pressure is below its low alarm
limit for more than 30 minutes.
Booster
Compressor (Satellite) Control
Satellite control is
optional. The CMC is capable of controlling a single
Booster Compressor (Satellite Compressor) based upon a
temperature sensor and a control setpoint/differential.
The CMC will cycle the Booster Compressor as needed and
will go into alarm stage and activate the System Alarm
Relay when the room temperature exceeds a high alarm
limit for 30 minutes or the room temperature is below
its low alarm limit for more than 30 minutes.
Suction
Pressure Reset (SPR) - Load Shedding
The CMC can raise the
Suction Setpoint up to eight pounds based upon the
temperature of the SPR (Room 1) Temperature Probe.
When the room temperature is satisfied and the Suction
Pressure is below the Suction Pressure Setpoint, the CMC
will increase the Suction Pressure Setpoint by
increments of one pound every few minutes until it
reaches a maximum offset of eight pounds.
Should the room temperature
increase above the SPR setpoint, the CMC will restore
the original Suction Pressure Setpoint.
Monitor Head
Pressure
Head pressure monitoring is
optional. The CMC will monitor a 0-500PSIG
Head/Discharge Pressure transducer. The CMC will
go into alarm stage and turn off the alarm relay when
the head pressure exceeds a high alarm limit for more
than 90 seconds or the head pressure is below its low
alarm limit for more than six minutes.
The Head Pressure input can
be used as high side suction input on split suction
system with high side and low side interlock.
Compressor/Unloader Staging Methods
Sequential - The stages will be activated and
deactivated in a First In and Last Out method. The
first compressor will have the longest runtime and the
last compressor has the least runtime. The method is
suitable for those rack design requires first
compressor running most of time for proper oil
distribution.
Round Robin - The stages will be
activated and deactivated in a First In and First Out
method. These This will maintain even run times on
participate compressors. It also prevent the
lubrication oil from migrating out of the compressors.
Combination of
Sequential and Round-Robin - For parallel racks with
two different sizes of compressors or one compressor
with an unloader. Will activate the sequential
compressors via the FILO format, then will activate
the round-robin compressors randomly. The sequential
compressors will be de-activated last.
Mix Match - On parallel racks with
different compressor sizes. The user sets the order of
which the compressors will activate and de-activate in
order to smooth the rack operating step sizes.
Unloaders - The CMC can operate
up to six unloaders per rack. Each unloader can be
assigned to any of the parallel compressors. The
unloaders will operate on an accelerated algorithm as
compared to the compressor algorithm. When a
compressor with an assigned unloader is activated, the
compressor will initially start unloaded. If the CMC
requires an increase in the rack load, the compressor
will then be fully loaded before an additional
compressor is activated.
Compressor 1 Swing
Staging - When
the rack is set up to run in a combination of one
sequential compressor and more than one round-robin
compressor mode, the first sequential compressor will
operate as the swing compressor. This compressor,
usually a smaller compressor, will swing in / swing
out (turned on / turned off) between activation of the
round-robin (bigger) compressors. The smaller
compressor will act as a half step, smoothing out the
performance of the rack.
Unloader 1 Swing
Staging - The
first unloader can be activated as a Swing Unloader.
It will swing in / swing out (Load / Unload) between
compressor staging steps, effectively adding a half
step to the staging, smoothing out the performance of
the rack.
Air
Conditioning Mode
Select this option if this
control is used for controlling the air conditioning
rack. When this option is selected, the Defrost Status
Input (dry contact) is used to put this control into and
idle mode. When the Defrost Status Input is closed, this
control will turn off all the compressors and enter into
the idle mode. The message, "A/C OFF" will flash on the
display. The suction pressure will still be monitored.
If the suction pressure drifts up to 50 LBS, the
compressors will turn on and start pumping down the
suction pressure until it reaches 5 LBS. At that time
all compressors will be turned off. When the defrost
input is opened, normal compressor cycling will resume.
Mechanical
Backup
Mechanical pressure controls
can be installed on the rack and operate in two
different methods.
Series Switchback - The CMC is configured to operate the
compressors by de-energizing the control relays
(Select Compressor Relay N.C. mode in SYSTEM CONFIG
MENU). The mechanical low pressure control is wired in
series with the CMC. If the Control fails or in
suction high/low alarm, all compressor relays will be
activated and the low pressure mechanical controllers
will cut out the compressors when the suction goes
below their settings. NOTE: This method is only
possible with the addition of a timing relay in series
with the compressor contactor coil voltage to prevent
short cycling on start-up.
Parallel Switchback
- The CMC is configured to operate the
compressors by energizing the control relays (Select
Compressor Relay N.O. mode in SYSTEM CONFIG MENU). The
mechanical low and high pressure controls are wired in
parallel to the CMC with the line voltage to the
backup wire through a "Switchback" time delay relay
controlled by the Alarm Relay. If the Control fails or
in suction high/low alarm, all control relays are
de-energized, the Switchback relay is energized and
power is switched to the backups. The mechanical
backup controls now operate the compressors based upon
their Cut-In and Cut-Out settings. With this method,
the backup settings can be set to run the rack as
closely to the suction set point as possible.
Oil
Pressure Monitoring
The CMC can monitor up to
two oil pressure transducers or digital inputs.
The Oil Pressure control scheme can be assigned to
either activate alarms, or to shut down specific
compressors should the oil controls indicate a Low Oil
condition.
The Oil Pressure Monitor can
be configured as a pressure sensor or a digital input.
Pressure - The CMC
monitors an oil pressure transducer and calculates the
pressure differential. An Oil Pressure Differential
Setpoint can be assigned. The CMC can shutdown a
specific compressor or the entire system and activate an alarm when the oil pressure
differential is below the Low Oil Pressure
Differential Alarm Setpoint for a user defined delay
period.
Digital - The digital signal from a
oil control monitor such as a Copeland Centronics Module
is monitored by the CMC. The CMC can shutdown a
specific compressor or the entire system and activate an alarm when the
digital signal is closed.
Receiver
Level Monitoring
The CMC can monitor an
analog receiver level sensor or a digital float and
activate alarms should the receiver level be below a
user configurable level. If the sensor is an
analog sensor, the CMC can be configured with two alarm
levels, one for alarm indication, a lower level for
system shutdown.
The Receiver Sensors can be
configured for a wide variety of sensor: 4-20ma,
0-5VDC, 1-2VDC, 1-6VDC etc...
Monitoring
and Alarming
The CMC monitors six
separate sensors and activates alarms based upon user
definable alarm setpoints. These alarms include:
Low Suction Pressure - The CMC
will shutdown all compressor operations and activate
alarms when the suction pressure is below the Low
Suction Alarm Setpoint for a user defined delay period
High Suction Pressure - The CMC
will shutdown all compressor operations and activate
alarms when the suction pressure exceeds the High
Suction Alarm Setpoint for a user defined delay period
Low Oil Pressure
Differential - The CMC monitors an oil
pressure transducer and calculates the pressure
differential. The CMC will shutdown the compressor
operation and activate an alarm when the oil pressure
differential is below the Low Oil Pressure
Differential Alarm Setpoint for a user defined delay
period
High Head Pressure - The CMC
monitors the Head/Discharge Pressure Transducer and
will shutdown the compressor operation and activate an
alarm when the head pressure exceeds the High Head
Pressure Alarm Setpoint for a user defined delay
period
Low Head Pressure - The CMC monitors
the Head/Discharge Pressure Transducer and activates
an alarm when the head pressure is below the Low Head
Pressure Alarm Setpoint for a user defined delay
period
High/Low Room Temperature
- The CMC
can monitor upto two temperature sensors located in a
refrigerated spaces. The CMC activates an alarm when
the space temperatures exceeds the High
Temperature Alarm Setpoint for a user defined delay
period or goes below the Low Temperature Alarm
Setpoint for a user defined delay period
Low Receiver Level - The CMC
monitors receiver level indicator, either a digital
signal from a float switch or an analog signal from a
float level sensor. The CMC activates an alarm
when the receiver level is below the Low Receiver
Level Setpoint. Should the analog sensor level
drop below a Shutdown Level, the CMC will shutdown
operation of the compressors.
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