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If the address assignments placed into the LAG ADDRESS and STANDBY ADDRESS
values conflict, the lead/lag will be disabled and an alert (!) message will occur. For example, if
the LAG ADDRESS matches the lead machine’s address, the lead/lag will be disabled and an
alert (!) message will occur. The lead/lag maintenance screen (MAINT04) will display the
message ‘INVALID CONFIG’ in the LEAD/LAG CONFIGURATION and CURRENT MODE
fields.
The lead chiller responds to normal start/stop controls such as occupancy schedule, forced
start/stop, and remote start contact inputs. After completing start up and ramp loading, the PIC
evaluates the need for additional capacity. If additional capacity is needed, the PIC initiates the
start up of the chiller configured at the LAG ADDRESS. If the lag chiller is faulted (in alarm) or is
in the OFF or LOCAL modes, then the chiller at the STANDBY ADDRESS (if configured) is
requested to start. After the second chiller is started and is running, the lead chiller shall monitor
conditions and evaluate whether the capacity has reduced enough for the lead chiller to sustain
the system alone. If the capacity is reduced enough for the lead chiller to sustain the CONTROL
POINT temperatures alone, then the operating lag chiller is stopped.
If the lead chiller is stopped in CCN mode for any reason other than an alarm (*) condition,
then the lag and standby chillers are stopped. If the configured lead chiller stops for and alarm
condition, then the configured lag chiller takes the lead chiller’s place as the lead chiller and the
standby chiller serves as the lag chiller.