Carrier 30RA/RH Defrost function, Additional electric heater stage control, Control of a boiler

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

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

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.

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.

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