Carrier 19XL - Manual (Page 101)

Standby Chiller Configuration and Operation
The configured standby chiller is identified as such by having the LEAD/LAG SELECT
configured to the value of ‘‘3.’’ The standby chiller can only operate as a replacement for the lag
chiller if one of the other two chillers is in an alarm (*) condition (as shown on the LID panel). If
both lead and lag chillers are in an alarm (*) condition, the standby chiller shall default to
operate in CCN mode based on its configured Occupancy Schedule and remote contacts input.
Lag Chiller Start-Up Requirements
Before the lag chiller can be started, the following conditions must be met:
1. Lead chiller ramp loading must be complete.
2. Lead chiller CHILLED WATER temperature must be greater than the CONTROL POINT
plus 1/2 the WATER/BRINE DEADBAND.
Note: The chilled water temperature sensor may be the leaving chilled water sensor, the return
water sensor, the common supply water sensor, or the common return water sensor,
depending on which options are configured and enabled.
3. Lead chiller ACTIVE DEMAND LIMIT value must be greater than 95% of full load amps.
4. Lead chiller temperature pulldown rate of the CHILLED WATER temperature is less than
0.5° F (0.27° C) per minute.
5. The lag chiller status indicates it is in CCN mode and is not faulted. If the current lag chiller
is in an alarm condition, then the standby chiller becomes the active lag chiller, if it is
configured and available.