Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual page 46

The PRESTART FAULT TIMER provides a timeout if there
is a prestart alert condition that prevents a chiller from
starting in a timely manner. If the configured lead chiller
does not complete its start-up before the PRESTART
FAULT TIMER (a user-configured value) elapses, then the
lag chiller starts, and the lead chiller shuts down. The lead
chiller then monitors the lag, acting as the lead, for a start
request. The PRESTART FAULT TIMER parameter is on
the LEADLAG screen, which is accessed from the EQUIP-
MENT 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.
5.27.3 - Standby chiller configuration and operation
A chiller is designated as a standby chiller when its LEAD-
LAG: CONFIGURATION 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 ICVC panel). If
both lead and lag chillers are in an alarm (*) condition, the
standby chiller defaults to operate in CCN mode and will
operate based on its configured CCN occupancy schedule
and remote contacts input.
5.27.4 - 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.
. Lead chilled water temperature must be greater than
the CONTROL POINT temperature (see the MAIN-
STAT screen) plus 1/ 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 the
MAINSTAT 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 0.7 K per minute
for a sustained period of 100 seconds.
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 (indicated by
"CONTRL" flashing next to the CHILLER START/STOP
parameter in the MAINSTAT screen). The PIC III 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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5.27.5 - Lag chiller yhutdown Requirements
The following conditions must be met in order for the lag
chiller to be stopped.
1. Lead chiller AVERAGE LINE CURRENT or MOTOR
PERCENT KILOWATTS (on the MAINSTAT
screen) is less than the lead chiller percent capacity.
NOTE: Lead Chiller Percent Capacity = 115 – LAG
% CAPACITY. The LAG % CAPACITY parameter
is on the LEADLAG screen, which is accessed from
the EQUIPMENT SERVICE table on the SERVICE
menu.
. The lead chiller chilled water temperature is less than
the CONTROL POINT temperature (see the MAIN-
STAT screen) plus 1/ the CHILLED WATER DEAD-
BAND temperature (see the SETUP1 screen).
3. The configured LAG STOP TIMER entry has elapsed.
The LAG STOP TIMER starts when the lead chiller
chilled water temperature is less than the chilled water
CONTROL POINT plus 1/ of the CHILLED WATER
DEADBAND and the lead chiller compressor motor
load (MOTOR PERCENT KILOWATT or AVERAGE
LINE CURRENT on the MAINSTAT screen) is less
than the lead chiller percent capacity.
NOTE: Lead Chiller Percent Capacity = 115 – LAG %
CAPACITY. The LAG % CAPACITY parameter is on the
LEADLAG screen, which is accessed from the EQUIP-
MENT SERVICE table on the SERVICE menu.
5.27.6 - Faulted chiller operation
If the lead chiller shuts down because of an alarm (*) condi-
tion, it stops communicating to the lag and standby chillers.
After 30 seconds, the lag chiller becomes the acting lead
chiller and starts and stops the standby chiller, if necessary.
If the lag chiller goes into alarm when the lead chiller is
also in alarm, the standby chiller reverts to a stand-alone
CCN mode of operation.
If the lead chiller is in an alarm (*) condition (as shown on
the ICVC panel), press the ReSet softkey to clear the
alarm. The chiller is placed in CCN mode. The lead chiller
communicates and monitors the RUN STATUS of the lag
and standby chillers. If both the lag and standby chillers are
running, the lead chiller does not attempt to start and does
not assume the role of lead chiller until either the lag or
standby chiller shuts down. If only one chiller is running,
the lead chiller waits for a start request from the operating
chiller. When the configured lead chiller starts, it assumes
its role as lead chiller.
If the lag chiller is the only chiller running when the lead
chiller assumes its role as a lead chiller then the lag chiller
will perform a RECOVERY START REQUEST (LL_
MAINT screen). The lead chiller will start up when the
following conditions are met.
1. Lag chiller ramp loading must be complete.
. Lag CHILLED WATER TEMP (MAINSTAT screen)
is greater than CONTROL POINT plus 1/ the
CHILLED WATER DEADBAND temperature.
3. Lag chiller ACTIVE DEMAND LIMIT value must
be greater than 95% of full load amps.