Lead/lag control – Carrier 17/19EX User Manual
Page 96
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
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
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