Carrier 30GK Evaporator water pump control, Control interlock contact, Evaporator heater control

5.3 - Evaporator water pump control 5.5 - Control interlock contact

The unit can control one or two evaporator water pumps. The evaporator water pump is turned on when this option is confi- gured (see User configuration) and when the unit is in one of the on modes described above or in delay mode. Since the minimum value for the delay at start-up is 1 minute (configurable between 1 and 15 minutes), the pump will run for at least one minute before the first compressor starts.

The pump is kept running for 20 seconds after the unit goes to stop mode. The pump keeps working when the unit switches from heating to cooling mode or vice-versa. It is turned off if the unit is shut down due to an alarm unless the fault is a frost protection error.

The pump can be started in particular operating conditions when the evaporator heater is active. See section 5.19 for the particular evaporator pump control for the follower unit (master/slave assembly). If two pumps are controlled and the reversing function has been selected (see User 1 configuration), the control tries to limit the pump run time delta to the configured pump change-over delay. If this delay has elapsed, the pump reversing function is activated, when the unit is running. During the reversing function both pumps run together for two seconds. If a pump has failed and a secondary pump is available, the unit is stopped and started again with this pump.

The control provides a means to automatically start the pump each day at 14.00 hours for 2 seconds when the unit is off. If the unit is fitted with two pumps, the first pump is started on odd days and the second pump is started on even days. Starting the pump periodically for few seconds increases the life-time of the pump bearings and the tightness of the pump seal.

NOTE: If this function is used, there should not be any chilled water pump interlock between terminals 34 and 35 (see section 3.4).

5.4 - Condenser water pump control

Only available on water-cooled units and air-cooled units with heat reclaim.

The condenser pump can be controlled by two modes, depend- ing on the configuration (only accessible by Carrier Service).

1 - Control based on unit start/stop control. In this case it is controlled in the same way as the evaporator pump.

2 - Control based on compressor status. In this case the pump is activated at the same time as the first compressor. It only switches off when no compressor is activated.

This contact can control the status of the water loop. Its function is to prevent unit start-up, if it is open and if the start- up delay has passed. Furthermore, this contact must remain closed when the unit is not in local off, remote or CCN control mode. Opening this contact for more than 8 seconds while the unit is operating, will cause immediate shut-down of the faulty unit.

5.6 - Evaporator heater control

The evaporator heater can be activated to protect an evaporator that may be damaged by ice, if the unit is shut down for a long period at low outdoor air temperature. If the heater is not sufficient to increase the water temperature, the evaporator pump can be started.

NOTE: The evaporator heater control parameters may be modified using the Service Configuration menu.

5.7 - Control point

Control point represents the leaving water temperature that the unit must produce.

•In cooling mode: control point = active setpoint + reset

•In heating mode: control point = active setpoint - reset

5.7.1 - Active setpoint

Two setpoints can be selected as active in cooling mode. Usually, the second setpoint is used for unoccupied periods or for ice storage (medium or low brine unit). A single setpoint is available in heating mode.

Depending on the current operating mode, the active setpoint can be selected with the operating type selector button, or with the user’s volt-free contacts, or with network commands (see section 3.4).

5.7.2 - Reset

Reset means that the active setpoint is modified so that less machine capacity is required (in cooling mode, the setpoint is increased, in heating mode it is decreased). This modification is in general a reaction to a drop in the load. For the Pro-Dialog Plus control system, the source of the reset can be configured in the User 1 configuration: it can be based on an external 0-10 V signal, provided either by the outdoor temperature (that gives a measure of the load trends for the building) or by the return water temperature (delta T that gives an average building load). In response to a drop in the outdoor temperature or to a drop in delta T, the cooling setpoint is normally reset upwards in order to optimise unit performance:

In both cases the reset parameters, i.e. slope, source and maxi- mum value, are configurable in the Setpoints menu (see section 4.5.4). Reset is a linear function based on three parameters.

•A reference at which reset is zero (outdoor temperature or delta T - no reset value).

•A reference at which reset is maximum (outdoor temperature or delta T - full reset value).

•The maximum reset value.

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