Standby Chiller Configuration and Operation
The configured standby c hi ller is identified as such by ha ving the LEAD/LAG SELE CT
configured to the val ue of ‘‘3.’’ The stand by chiller can only o perate as a replacemen t for the lag
chiller if one of the othe r two chillers is in an alarm (*) con dition (as shown on the LID pa nel). If
both lead and lag chiller s ar e in an alarm (*) condition, th e standby chiller shall def ault to
operate in CCN mode based on its configured Occupancy S c hed ule and remote contact s input .
Lag Chiller Start-Up Requirements
Before the lag chiller c an be started, the following conditions must be met:
1. Lead chiller ramp loading must be complete.
2. Lead chiller CHILLED WATER temperature must be gr eat er than the CONTROL POINT
plus 1/2 the WATER/BRI NE DEADBAND.
Note: The chilled water te mperature sensor may b e the leaving chilled w ater sensor, the ret urn
water sensor, the comm on s up ply water sensor, or the c om m on return water sensor,
depending on which optio ns are configured and enab led.
3. Lead chiller ACTIVE DEMAND LIMIT value must be greater than 95% of full load amps.
4. Lead chiller temperat ure pulldown rate of the CHI LLED WATER temperature is less than
0.5° F (0.27° C) per minute.
5. The lag chiller status indi cates it is in CCN mode and is not fa ult ed. If the current lag chil ler
is in an alarm condition, then the standby chiller be comes the active lag chi ller, if it is
configured and avail able.