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Lead/Lag Control
Lead/Lag is a control system process that automatically starts and stops a lag or second
chiller in a 2-chiller water system. Refer to Figure 16 and Figure 17 for menu, table, and screen
selection information. On machines that have PSIO software with Lead/Lag capability, it is
possible to utilize the PIC controls to perform the lead/lag function on 2 machines. A third
machine can be added to the lead/lag system as a standby chiller to start up in case the lead or
lag chiller in the system has shut down during an alarm condition and additional cooling is
required.
Note:
Lead/lag configuration is viewed and edited under Lead/Lag in the Equipment Configura-
tion table (located in the Service menu). Lead/lag status during machine operation is
viewed in the MAINT04 table in the Control Algorithm Status table. See Table 2.
Lead/Lag System Requirements:
• all machines must have PSIO software capable of performing the lead/lag function
• water pumps MUST be energized from the PIC controls
• water flows should be constant
• CCN Time Schedules for all machines must be identical
Operation Features:
• 2 chiller lead/lag
• addition of a third chiller for backup
• manual rotation of lead chiller
• load balancing if configured
• staggered restart of the chillers after a power failure
• chillers may be piped in parallel or in series chilled water flow