Faulted Chiller Operation - Carrier 19XR Start-Up, Operation And Maintenance Instructions Manual

running, the lead chiller monitors conditions and eval-
uates 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 chill-
ers 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.
If the configured lead chiller does not complete the 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 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 condi-
tion that prevents the chiller from starting in a timely man-
ner. The PRESTART FAULT TIMER parameter is on the LEAD-
LAG screen, which is accessed from the EQUIPMENT SERV-
ICE table of the SERVICE menu.
If the lag chiller does not achieve start-up before the
PRESTART 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
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 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 con-
figured 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 MAINSTAT screen)
plus 1/2 the CHILLED WATER DEADBAND tempera-
ture (see the SETUP1 screen).
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 wa-
ter 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 0.5° F (0.27° 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 ac-
tive 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 flash-
ing 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.
Lag Chiller Shutdown Requirements — The following con-
ditions must be met in order for the lag chiller to be stopped.
1. Lead chiller compressor motor average line current or load
value (MOTOR PERCENT KILOWATTS on the MAIN-
STAT screen) is less than the lead chiller percent
capacity.
NOTE: Lead chiller percent capacity = 115 – LAG PER-
CENT CAPACITY. The LAG PERCENT CAPACITY
parameter is on the LEADLAG screen, which is accessed
from the EQUIPMENT SERVICE table on the SERV-
ICE menu.
2. The lead chiller chilled water temperature is less than
the CONTROL POINT temperature (see the MAINSTAT
screen) plus 1 ⁄ the CHILLED WATER DEADBAND tem-
2
perature (see the SETUP1 screen).
3. The configured LAG STOP TIME entry has elapsed. The
LAG STOP TIMER starts when the lead chiller chilled
water temperature is less than the chilled water
CONTROL POINT plus 1/2 of the CHILLED WATER
DEADBAND and the lead chiller compressor motor load
(MOTOR PERCENT KILOWATT or AVERAGE LINE CUR-
RENT on the MAINSTAT screen) is less than the lead
chiller percent capacity.
NOTE: Lead chiller percent capacity = 115 – LAG PER-
CENT CAPACITY. The LAG PERCENT CAPACITY param-
eter is on the LEADLAG screen, which is accessed from the
EQUIPMENT SERVICE table on the SERVICE menu.
FAULTED CHILLER OPERATION — If the lead chiller
shuts down because of an alarm (*) condition, it stops com-
municating 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 CVC 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.
2. Lag CHILLED WATER TEMP (MAINSTAT screen) is
greater than CONTROL POINT plus 1/2 the CHILLED
WATER DEADBAND temperature.
3. Lag chiller ACTIVE DEMAND LIMIT value must be greater
than 95% of full load amps.
4. Lag chiller temperature pulldown rate (TEMP PULL-
DOWN DEG/MIN) of the chilled water temperature is less
than 0.5 F (0.27 C) per minute.
5. The standby chiller is not running as a lag chiller.
6. The configured LAG START TIMER has elapsed. The LAG
START TIMER is started when ramp loading is
completed.
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