Operation Features:
·2 chiller lead/lag
·addition of a third chiller for backup
·manual rotation of lead chiller
·load balancing if con®gured
·staggered restart of the chillers after a power failure
·chillers may be piped in parallel or in series chilled water ¯ow
COMMON POINT SENSOR INSTALLATION Ð Lead/ lag operation does not require a common chilled water point sensor. Common point sensors can be added to the 8-input option module, if desired. Refer to the certi®ed drawings for termination of sensor leads.
NOTE: If the common point sensor option is chosen on a chilled water system, both chillers should have their own 8-input option module and common point sensor installed. Each chiller will use its own common point sensor for control, when that chiller is designated as the lead chiller. The PIC cannot read the value of common point sensors installed on other chill- ers in the chilled water system.
When installing chillers in series, a common point sensor should be used. If a common point sensor is not used, the leaving chilled water sensor of the upstream chiller must be moved into the leaving chilled water pipe of the downstream chiller.
If return chilled water control is required on chillers piped in series, the common point return chilled water sensor should be installed. If this sensor is not installed, the return chilled water sensor of the downstream chiller must be relocated to the return chilled water pipe of the upstream chiller.
To properly control the common supply point temperature sensor when chillers are piped in parallel, the water ¯ow through the shutdown chillers must be isolated so that no water by- pass around the operating chiller occurs. The common point sensor option must not be used if water bypass around the operating chiller is occurring.
CHILLER COMMUNICATION WIRING Ð Refer to the chiller's Installation Instructions or to the Carrier Comfort Network Interface section on page 48 of this manual for information on chiller communication wiring.
LEAD/LAG OPERATION Ð The PIC control provides the ability to operate 2 chillers in the LEAD/LAG mode. It also provides the additional ability to start a designated standby chiller when either the lead or lag chiller is faulted and capacity requirements are not met. The lead/lag option op- erates in CCN mode only. If any other chiller con®gured for lead/lag is set to the LOCAL or OFF modes, it will be un- available for lead/lag operation.
NOTE: Lead/lag con®guration is viewed and edited in Lead/ Lag, under the Equipment Con®guration table of the Service menu. Lead/lag status during chiller operation is viewed in the MAINT04 table in the Control Algorithm Status table.
Lead/Lag Chiller Con®guration and Operation Ð The con- ®gured lead chiller is identi®ed when the LEAD/LAG SELECT value for that chiller is con®gured to the value of ``1.'' The con®gured lag chiller is identi®ed when the LEAD/ LAG SELECT for that chiller is con®gured to the value of ``2.'' The standby chiller is con®gured to a value of ``3.'' A value of ``0'' disables the lead/lag in that chiller.
To con®gure the LAG ADDRESS value on the LEAD/ LAG Con®guration table, always use the address of the other chiller on the system for this value. Using this address will make it easier to rotate the lead and lag chillers.
If the address assignments placed into the LAG ADDRESS and STANDBY ADDRESS values con¯ict, the lead/ lag will be disabled and an alert (!) message will occur. For example, if the LAG ADDRESS matches the lead chiller'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 CONFIG' in the LEAD/LAG CONFIGURATION and CURRENT MODE ®elds.
The lead chiller responds to normal start/stop controls such as occupancy schedule, forced start/stop, and remote start contact inputs. After completing start up and ramp loading, the PIC evaluates the need for additional capacity. If addi- tional capacity is needed, the PIC initiates the start up of the chiller con®gured 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 con®gured) is requested to start. After the second chiller is started and is running, the lead chiller shall monitor conditions and evalu- ate whether the capacity has reduced enough for the lead chiller to sustain the system alone. If the capacity is reduced enough for the lead chiller to sustain the CONTROL POINT temperatures alone, then the operating lag chiller is stopped.
If the lead chiller is stopped in CCN mode for any reason other than an alarm (*) condition, then the lag and standby chillers are stopped. If the con®gured lead chiller stops for and alarm condition, then the con®gured lag chiller takes the lead chiller's place as the lead chiller and the standby chiller serves as the lag chiller.
If the con®gured lead chiller does not complete the start- up before the PRESTART FAULT TIMER (user con®gured value) elapses, then the lag chiller shall be started and the lead chiller will shut down. The lead chiller then monitors the start request from the acting lead chiller to start. The PRE- START FAULT TIMER is initiated at the time of a start request. The PRESTART FAULT TIMER's function is to provide a timeout in the event that there is a prestart alert condition preventing the chiller from starting in a timely man- ner. The timer is con®gured under Lead/Lag, found in the Equipment Con®guration table of the Service menu.
If the lag chiller does not achieve start-up before the PRESTART FAULT TIMER elapses, then the lag chiller shall be stopped and the standby chiller will be requested to start, if con®gured and ready.
Standby Chiller Con®guration and Operation Ð The con- ®gured standby chiller is identi®ed as such by having the LEAD/LAG SELECT con®gured 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 con®gured Occupancy Schedule and remote contacts input.
Lag Chiller Start-Up Requirements Ð 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 con®gured and enabled.
3.Lead chiller ACTIVE DEMAND LIMIT value must be greater than 95% of full load amps.
