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5.11 - Defrost function
Defrost is activated, when the unit is in heating mode, in order
to reduce frost build-up on the air heat exchanger. The defrost
cycle can only be applied to one circuit at a time. During the
defrost cycle the fans of that circuit are stopped, and the four-
way refrigerant valve is reversed, forcing the circuit to cooling
mode. The fan can temporarily be restarted during the defrost
cycle. The defrost cycle is fully automatic and does not require
any setting. A condensate heater prevents ice formation at the
bottom of the heat exchangers, if the defrost cycles are taking
place at low outdoor temperature.
5.12 - Additional electric heater stage control
The heat pump units can control up to four additional electric
heating stages.
The electric heating stages are activated to complement the
heating capacity when the following conditions are satisfied:
- The unit uses 100% of the available heating capacity, or the
unit is limited in its operation by a protection mode (low
suction temperature, hot gas or defrost sequence in
progress protection), and in all cases cannot satisfy the
heating load.
- The outdoor temperature is below a configured threshold
(see User 1 configuration).
- The unit demand limit is not active.
The user may configure the last available electric heating stages
as a safety stage. In this case, the safety stage is only activated in
addition to the other stages if there is a machine fault, preventing
the use of the heating capacity. The other electric heating stages
will continue to operate as described above.
5.13 - Control of a boiler
NOTE: The control of the electric heating stages or of a
boiler is not authorised for slave units.
The unit can control the start-up of a boiler, if it is in heating
mode. When the boiler is operating, the unit water pump is
stopped.
A heat pump unit and a boiler cannot operate together. In this
case the boiler output is activated in the following conditions:
- The unit is in heating mode, but a fault prevents the use of
the heat pump capacity.
- The unit is in heating mode, but works at a very low
outdoor temperature, making the heat pump capacity
insufficient. The outdoor air temperature threshold for use
of the boiler is fixed at -10°C, but this value can be
adjusted in the User 1 menu.
5.14 - Master/slave assembly
Two PRO-DIALOG units can be linked to produce a master/
slave assembly. The two machines are interconnected over the
CCN bus. All parameters required for the master/slave function
must be configured through the Service configuration menu.
Master/slave operation requires the connection of a temperature
probe at the common manifold on each machine, if the heat
exchanger leaving water temperature is controlled.
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 (con-
figurable) 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 com-
mand 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.
5.15 - Controlling Pro-Dialog units with a System
Manager
Up to eight PRO-DIALOG units (or System Manager
compatible units) can be controlled by one control module of
the FSM, CSM III or HSM type which can handle multitasking
of control functions such as starting units in sequence.