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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.
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.
When installing chillers in series, a common point sensor
should be used. If a common point sensor is not used, the leav-
ing 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 flow
through the shutdown chillers must be isolated so no water by-
pass around the operating chiller occurs. The common point
sensor option must not be used if water bypass around the oper-
ating chiller is occurring.
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 II 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 op-
tion 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 LEAD/
LAG CONFIGURATION value on the LEADLAG
screen is set to "1."
• A chiller is designated the lag chiller when its LEAD/
LAG 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.
To configure the LAG ADDRESS value on the LEADLAG
screen, always enter the address of the other chiller on the sys-
tem. For example, if you are configuring chiller A, enter the ad-
dress 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.
If the address assignments in the LAG ADDRESS and
STANDBY ADDRESS parameters conflict, the lead/lag func-
tion 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) displays the
message 'INVALID CONFIG' in the LEAD/LAG: CONFIGU-
RATION 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 load-
ing, the PIC II evaluates the need for additional capacity. If ad-
ditional capacity is needed, the PIC II 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 ca-
pacity 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 chill-
er's place as the lead chiller, and the standby chiller serves as
the lag chiller.
If the configured lead chiller does not complete the start-up
before the PRESTART FAULT TIMER (a user-configured val-
ue) elapses, then the lag chiller starts and the lead chiller shuts
down. The lead chiller then monitors the start request from the
acting lead chiller. The PRESTART FAULT TIMER is initiated
at the time of a start request. The PRESTART FAULT TIMER
provides a timeout if there is a prestart alert condition that pre-
vents the chiller from starting in a timely manner. The PRE-
START FAULT TIMER parameter is on the LEAD-LAG
screen, which is accessed from the EQUIPMENT SERVICE
table of the SERVICE menu.
If the lag chiller does not achieve start-up before the PRE-
START FAULT TIMER elapses, the lag chiller stops, and the
standby chiller is requested to start, if configured and ready.
Standby Chiller Configuration and Operation — A chiller is
designated as a standby chiller when its LEAD/LAG CONFIG-
URATION value on the LEADLAG screen is set to "3." The
standby chiller can operate as a replacement for the lag chiller
only if one of the other two chillers is in an alarm (*) condition
(as shown on the CVC panel). If both lead and lag chillers are
in an alarm (*) condition, the standby chiller defaults 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 chilled water temperature must be greater than
the CONTROL POINT temperature (see the MAIN-
STAT screen) plus 1/2 the CHILLED WATER DEAD-
BAND temperature (see the SETUP1 screen).
NOTE: The chilled water temperature sensor may be
the leaving chilled water sensor, the return water sen-
sor, 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 (see theMAIN-
STAT screen) value must be greater than 95% of full
load amps.
4. Lead chiller temperature pulldown rate (TEMP PULL-
DOWN DEG/MIN on the TEMP_CTL screen) of the
chilled water temperature is less than 0.5º F (0.27º C)
per minute.
5. The lag chiller status indicates it is in CCN mode and
is not in an alarm condition. If the current lag chiller is
in an alarm condition, the standby chiller becomes the
active lag chiller, if it is configured and available.
6. The configured LAG START TIMER entry has elapsed.
The LAG START TIMER starts when the lead chiller
ramp loading is completed. The LAG START TIMER
entry is on the LEADLAG screen, which is accessed
from the EQUIPMENT SERVICE table of the
SERVICE menu.
When all the above requirements have been met, the lag
chiller is commanded to a STARTUP mode (SUPVSR flashing
next to the point value on the STATUS table). The PIC II
control then monitors the lag chiller for a successful start. If the
lag chiller fails to start, the standby chiller, if configured is
started.
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