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The master/slave assembly can operate with constant or
variable flow. In the case of variable flow each machine
must control its own water pump and automatically shut
down the pump, if the cooling capacity is zero. For constant
flow operation the pumps for each unit are continuously
operating, if the system is operating. The master unit can
control a common pump that will be activated, when the
system is started. In this case the slave unit pump is not used.
All control commands to the master/slave assembly (start/
stop, setpoint, heating/cooling operation, load shedding,
etc.) are handled by the unit which is configured as the
master, and must therefore only be applied to the master
unit. They will be transmitted automatically to the slave
unit. The master unit can be controlled locally, remotely or
by CCN com-mands. Therefore to start up the assembly,
simply validate the Master operating type (MASt) on the
master unit. If the Master has been configured for remote
control then use the remote volt-free contacts for unit
start/stop. The slave unit must stay in CCN operating type
continuously. To stop the master/slave assembly, select
Local Off (LOFF) on the master unit or use the remote
volt-free contacts if the unit has been configured for
remote control.
One of the functions of the master unit (depending on its
configuration) may be the designation, whether the master
or slave is to be the lead machine or the follower. The roles
of lead machine and follower will be reversed when the
differ-ence in running hours between the two units exceeds
a con-figurable value, ensuring that the running times of
the two units are automatically equalised. The changeover
between lead machine and follower may take place when
the assembly is started up, or even whilst running. The
running time balancing function is not active if it has not
been configured: in this case the lead machine is always the
master unit.
The lead machine will always be started first. When the
lead machine is at its full available capacity, start-up delay
(configurable) is initialised on the follower. When this
delay has expired, and if the error on the control point is
greater than 1.7°C, the follower unit is authorised to start
and the pump is activated. The follower will automatically
use the master unit active setpoint. The lead machine will be
held at its full available capacity for as long as the active
capacity on the follower is not zero. When the follower
unit receives a command to stop, its evaporator water
pump is turned off with 20 seconds delay.
In the event of a communication fault between the two
units, each shall return to an autonomous operating mode
until the fault is cleared. If the master unit is halted due to
an alarm, the slave unit is authorised to start without prior
conditions.
ATTENTION: For heat pumps operating in master/slave
mode and with leaving water temperature control the first
AUX2 fan board must be replaced by the AUX1 board
and connected to a common temperature sensor.
This option requires the installation of an additional board.
This board allows control of:
• A heat reclaim condenser pump,
• A heat reclaim condenser heater,
• Two solenoid valves to shut off the heat reclaim coil
(one for each circuit),
• Two solenoid drain valves for the heat reclaim coil
(one for each circuit),
• Two solenoid valves to shut off the water condenser
(one for each circuit),
• Two solenoid drain valves for the water condenser
(one for each circuit).
Selecting the heat reclaim mode can be done with either
the local interface or remotely with the (recl_sw) contact or
by CCN.
The heat reclaim function is active when: the heat reclaim
entering water temperature is lower than the heat reclaim
setpoint, minus half of the heat reclaim dead band.
The heat reclaim function is not active when: the heat
reclaim entering water temperature is higher than the heat
reclaim setpoint, plus half of the heat reclaim dead band.
In the dead band the function remains in its active mode.
The default value of the dead band is 4.4 K. This value can
be modified by Carrier Service.
Changeover procedure from cooling to heat reclaim mode:
• Start-up of the condenser pump.
• Verification of the condenser flow switch control
contact. If this remains open after one minute of
condenser pump operation, the circuit remains in
cooling mode and an alarm will be activated.
• As soon as the saturated condensing temperature
reaches 30°C, the pumpdown sequence is activated.
• Pumpdown: opening of the condenser water inlet
valve and closing of the air condenser air valves 3
seconds later.
• After one minute or when the subcooling value is
above -10°C the heat reclaim function is effective.
The direct-expansion free-cooling principle is to circulate
the liquid refrigerant with a pump and to condense it to a
lower temperature at the condenser when the outside
temperature is low (below the setpoint). The performance
achieved is huge, as only a pump and fans are activated.
This option requires the installation of an additional board
for each circuit. These boards allow control of:
• a three-way compressor shut-off valve
• a refrigerant pump.
The following sensors are connected to each board:
• a pump suction pressure sensor
• a pump discharge pressure sensor
• a potentiometer to copy the position of the three-way
valve.
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