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5.2 - Heating/cooling operation
5.2.1 - General
The heating/cooling selection applies to 30RW (liquid chillers)
units, controlling a boiler or equipped with a heat pump option.
5.2.2 - Heating/cooling or heat reclaim selection
The table below summarises the unit heating/cooling or heat
reclaim operation, based on the following parameters:
-
Control type: indicates whether the unit operates in local,
remote or CCN mode. See section 5.1.
-
Unit on/off status: indicates whether the unit is shut
down (not authorised to start) or in operation (or
authorised to start).
-
Heating/cooling or heat reclaim selection in local
mode: operating mode selected via the user interface. See
Information menu.
-
Remote heating/cooling or heat reclaim contacts: these
contacts are only active if the unit is under remote control.
See sections 3.6.
-
HC_SEL: this network command permits heating/cooling
control, if the unit is in CCN operating mode.
-
RECL_SEL: this network command permits heat reclaim
mode control, if the unit is in CCN mode. The heat
reclaim mode is only accessible for 30RW and cooling
only units. It requires a specific configuration.
5.3 - Evaporator water pump control
The unit can control one or two evaporator water pumps. The
evaporator water pump is turned on when this option is config-
ured (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 before the unit goes to stop mode. It is turned off if
the unit is shut down due to an alarm unless the fault is a frost
protection error. See section 5.14 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 second 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.
28
5.4 - Condenser water pump control
The unit can control one or two condenser water pumps. These
pumps can be fixed-speed or variable-speed pumps. Depending
on the configuration the pump can start:
-
When the unit is in one of the modes described above.
-
When at least one compressor is operating.
It is turned off if the unit is shut down due to an alarm.
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 second 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.
5.5 - Control interlock contact
This contact checks the status of a loop (water flow switch and
customer safety loop, see section 3.6). It prevents the unit from
starting if it is open when the delay at start-up has expired. This
open contact leads to an alarm shut-down, if the unit is
running.
5.6 - Control point
The control point represents the water temperature that the unit
must produce. The evaporator or condenser return water
temperature is controlled by default, but the evaporator or
condenser leaving water temperature can also be controlled
(requires a Service configuration modification).
Control point = active setpoint + reset
5.6.1 - Active setpoint
Two setpoints can be selected as active in cooling mode and
three in heating mode. Usually, the second cooling setpoint is
used for unoccupied periods or for ice storage (brine unit). The
second setpoint in heating mode is used for unoccupied
periods, and the third heating setpoint is used for holiday
periods or public holidays. Depending on the current opera-
tions, the active setpoint can be selected by choosing the item
in the Information menu, with the user's volt-free contacts,
with network commands or with the setpoint timer program
(schedule 2).
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