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Lead/Lag Chiller Configuration and Operation
The configured lead chiller is identified when the LEAD/LAG SELECT value for that chiller is
configured to the value of ‘‘1.’’ The configured lag chiller is identified when the LEAD/LAG
SELECT for that chiller is configured to the value of ‘‘2.’’ The standby chiller is configured to a
value of ‘‘3.’’ A value of ‘‘0’’ disables the lead/lag in that chiller.
To configure the LAG ADDRESS value on the LEAD/LAG Configuration table, always use
the address of the other chiller on the system for this value. Using this address will make it
easier to rotate the lead and lag machines.
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