Carrier 30GK manual High pressure load shedding function, Pumping down, Master/slave assembly

LOCAL OPERATING MODE

PARAMETER STATUS

HEATING/	LOCAL	SCHEDULE 2	ACTIVE SETPOINT
COOLING	SETPOINT	PROGRAM STATUS
OPERATING	SELECTION
MODE
cooling	sp 1	-	cooling setpoint 1
cooling	sp2	-	cooling setpoint 2
heating	-	-	heating setpoint
holidays	auto	occupied	cooling setpoint 1
holidays	auto	unoccupied	cooling setpoint 2
REMOTE OPERATING MODE
PARAMETER STATUS
HEATING/	CONTROL	SCHEDULE 2	ACTIVE SETPOINT
COOLING	CONTACT	PROGRAM STATUS
OPOERATING
MODE
heating	-	-	heating setpoint
cooling	sp 1	-	cooling setpoint 1
cooling	sp2	-	cooling setpoint 2
-	holidays	occupied	cooling setpoint 1
-	holidays	unoccupied	cooling setpoint 2
CCN OPERATING MODE
PARAMETER STATUS
HEATING/COOLING		SCHEDULE 2	ACTIVE SETPOINT
OPERATING MODE		PROGRAM STATUS
cooling		occupied	cooling setpoint 1
cooling		unoccupied	cooling setpoint 2
heating		-	heating setpoint

5.17 - High pressure load shedding function

This function does not require an additional board. It prevents high pressure a break on a circuit by the following means:

•Preventing any capacity increase on the circuit once the high pressure value has reached an initial threshold.

•Shedding one or more capacity stages once a second protection threshold has been reached.

In the event of capacity stages being shed, no capacity increase will be authorised on the circuit concerned for a period of 5 minutes.

5.18 - Pumping down

When the lead compressor in each circuit is started or stopped, that circuit goes through a pumping down cycle to purge the evaporator and suction line of refrigerant. The maximum duration of this cycle is 3 minutes.

5.19 - Master/slave assembly

Two PRO-DIALOG Plus 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 opera- ting. 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 trans- mitted automatically to the slave unit. The master unit can be controlled locally, remotely or by CCN commands. Therefore to start up the assembly, simply validate the Master operating type (MASt) on the master unit. If the Master has been confi- gured 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 con- figuration) 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 difference in running hours between the two units exceeds a configurable 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 (confi- gurable) 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 set- point. The lead machine will be held at its full available capa- city 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.

5.20- Controlling Pro-Dialog Plus units with a System Manager

Up to eight PRO-DIALOG Plus units (or System Manager compatible units) can be controlled by one control module of the FSM or CSM III type which can handle multi-tasking of control functions such as starting units in sequence.

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