Lead/Lag Chiller Configuration and Operation
The configured lead chil ler is ide ntified when the LEAD/L A G SE LE C T value for that chiller is
configured to t he value of ‘‘1 .’’ The config ured lag chiller is identified wh en the LEAD/L AG
SELECT for that chille r is co nf igured to the value of ‘‘2.’’ The standby chiller is co nf igured to a
value of ‘‘3.’’ A value of ‘‘0 ’’ disables the lead/lag in that chiller.
To configure the LAG ADDRESS value on the L EAD/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 rota te the lead and lag machines.
If the address assignments placed into the LAG ADDRESS and STANDBY ADDRESS
values conflic t, the lead/lag w ill be disable d and an alert (!) message will occur. For exa mple, 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 CONF IG’ in the LEAD/LAG CONF IG UR ATION and CURRENT MODE
fields.
The lead chiller respond s to normal start/stop con trols such as occupanc y sch edule, forced
start/stop, and remot e start contact inputs. Aft er completing start up an d ramp loading, the PIC
evaluates the need for additional capacity. If a dditional capacity is needed, the PIC initiates t he
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