Common Point Sensor Usage And; Chiller Communication Wiring; Lead/Lag Operation - Carrier AquaEdge 19XRV series Operation, Maintenance And Installation Manual

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. Refer to Fig. 20 and 21 for
menu, table, and screen selection information.
NOTE: The lead/lag function can be configured on the LEAD-
LAG screen, which is accessed from the SERVICE menu and
EQUIPMENT SERVICE table. See Table 4, Example 22.
Lead/lag status during chiller operation can be viewed on the
LL_MAINT display screen, which is accessed from the
SERVICE menu and CONTROL ALGORITHM STATUS
table. See Table 4, Example 13.
Lead/Lag System Requirements:
• all chillers in the system must have software capable of per-
forming the lead/lag function
• water pumps MUST be energized from the PIC III controls
• water flows should be constant
• the CCN time schedules for all chillers 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
COMMON POINT SENSOR USAGE AND INSTALLA-
TION — Lead/lag operation does not require a common
chilled water point sensor. However, common point sensors
(Spare Temp #1 and #2) may be added to the CCM module, if
desired.
NOTE: If the common point sensor option is chosen on a
chilled water system, each chiller should have its own common
point sensor installed. Each chiller uses its own common point
sensor for control when that chiller is designated as the lead
chiller. The PIC III cannot read the value of common point
sensors installed on the other chillers in the chilled water
system.
If leaving chilled water control (ECW CONTROL OPTION
is set to 0 [DSABLE] TEMP_CTL screen) and a common
point sensor is desired (COMMON SENSOR OPTION in
LEADLAG screen selected as 1) then the sensor is wired in
Spare Temp #1 position on the CCM (terminals J4-25 and
J4-26).
If the entering chilled water control option (ECW CON-
TROL OPTION) is enabled (configured in TEMP_CTL
screen) and a common point sensor is desired (COMMON
SENSOR OPTION in LEADLAG screen selected as 1) then
the sensor is wired in Spare Temp #2 position on the CCM
(terminals J4-27 and J4-28).
When installing chillers in series, either a common point
sensor should be used (preferred), or the LEAVING CHILLED
WATER sensor of the upstream chiller must be moved into the
leaving chilled water pipe of the downstream chiller. In this
application the COMMON SENSOR OPTION should only be
enabled for the upstream chiller if that chiller is configured as
the Lead.
If ENTERING CHILLED WATER control is required on
chillers piped in series, either the common point return chilled
water sensor should be used (preferred), or the LEAVING
CHILLED WATER sensor of the downstream chiller must be
relocated to the LEAVING CHILLED WATER pipe of the
upstream chiller. In this application, the COMMON SENSOR
OPTION should only be enabled for the downstream chiller if
that chiller is configured as the lead. Note that ENTERING
CHILLED WATER control is not recommended for chillers
installed in series due to potential control stability problems.
To properly control the LEAVING CHILLED WATER
TEMPERATURE when chillers are piped in parallel, the water
flow through the shutdown chiller(s) should be isolated so that
no water bypass around the operating chiller occurs. However,
if water bypass around the operating chiller is unavoidable, a
common point sensor in the mixed LEAVING CHILLED
WATER piping should be provided and enabled for the Lead
chiller.
CHILLER COMMUNICATION WIRING — Refer to the
chiller's Installation Instructions, Carrier Comfort Network
Interface section for information on chiller communication
wiring.
LEAD/LAG OPERATION — The PIC III not only has the
ability to operate 2 chillers in lead/lag, but it can also start a
designated standby chiller when either the lead or lag chiller is
faulted and capacity requirements are not met. The lead/lag
option only operates when the chillers are in CCN mode. If any
other chiller configured for lead/lag is set to the LOCAL or
OFF modes, it will be unavailable for lead/lag operation.
Lead/Lag Chiller Configuration and Operation
• A chiller is designated the lead chiller when its LEADLAG:
CONFIGURATION value on the LEADLAG screen is set
to "1."
• A chiller is designated the lag chiller when its LEADLAG:
CONFIGURATION value is set to "2."
• A chiller is designated as a standby chiller when its LEAD-
LAG: CONFIGURATION value is set to "3."
• A value of "0" disables the lead/lag designation of a chiller.
This setting should also be used when "normal" operation
without regard to lead/lag rules is desired (in LOCAL or
CCN mode).
When configuring the LAG ADDRESS value on the
LEADLAG screen of chiller "A" enter the address of the
chiller on the system which will serve as lag when/if chiller
"A" is configured as lead. For example, if you are configuring
chiller A, enter the address for chiller B as the lag address. If
you are configuring chiller B, enter the address for chiller A as
the lag address. This makes it easier to rotate the lead and lag
chillers. Note that only the lag and standby chiller addresses
specified in the configured lead chiller's table are relevant at a
given time.
If the address assignments in the LAG ADDRESS
and STANDBY ADDRESS parameters conflict, the lead/lag
function is disabled and an alert (!) message displays. For
example, if the LAG ADDRESS matches the lead chiller's
address, the lead/lag will be disabled and an alert (!) message
displayed. The lead/lag maintenance screen (LL_MAINT) dis-
plays the message 'INVALID CONFIG' in the LEADLAG:
CONFIGURATION and CURRENT MODE fields.
The lead chiller responds to normal start/stop controls such
as the occupancy schedule, a forced start or stop, and remote
start contact inputs. After completing start-up and ramp
loading, the PIC III evaluates the need for additional capacity.
If additional capacity is needed, the PIC III initiates the start-up
of the chiller configured at the LAG ADDRESS. If the lag
chiller is faulted (in alarm) or is in the OFF or LOCAL modes,
the chiller at the STANDBY ADDRESS (if configured) is
requested to start. After the second chiller is started and is
running, the lead chiller monitors conditions and evaluates
whether the capacity has been 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, the lag and standby chillers
are also stopped. If the configured lead chiller stops for an
alarm condition, the configured lag chiller takes the lead
chiller's place as the lead chiller, and the standby chiller serves
as the lag chiller.
The PRESTART FAULT TIMER provides a timeout if there
is a prestart alert condition that prevents a chiller from starting
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