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 chiller CHILLEDWATER 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 wa-
ter sensor, depending on which options are configured and
enabled.
3. Lead chiller ACTIVE DEMAND LIMIT value must be greater
than 95% of full load amps.
4. Lead chiller temperature pulldown rate 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 faulted. If the current lag chiller is in an alarm con-
dition, then 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 shall be started when the lead
chiller ramp loading is completed. The LAG START TIMER
entry is accessed by selecting Lead/Lag from the Equip-
ment Configuration table of the Service menu.
When all of the above requirements have been met, the
lag chiller is forced to a START mode. The PIC 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 LOAD value is less
than the lead chiller percent capacity plus 15%.
NOTE: Lead chiller percent capacity = 100 – LAG PER-
CENT CAPACITY
The LAG PERCENT CAPACITY value is configured on
the Lead/Lag Configuration screen.
2. The lead chiller chilled water temperature is less than
the CONTROL POINT plus 1/2 of the WATER/BRINE
DEADBAND.
3. The configured LAG STOP TIMER entry has elapsed. The
LAG STOP TIMER is started when the LEAVING CHILLED
WATER temperature is less than the CHILLED WATER
CONTROL POINT plus 1/2 of the WATER/BRINE DEAD-
BAND and the lead chiller COMPRESSOR MOTOR LOAD
is less than the lead chiller percent capacity plus 15%.
The timer is ignored if the chilled water temperature reaches
3° F (1.67° C) below the CONTROL POINT and the lead
chiller COMPRESSOR MOTOR LOAD value is less than
the lead chiller percent capacity plus 15%.
FAULTED CHILLER OPERATION — If the lead chiller
shuts down on an alarm (*) condition, it stops communica-
tion to the lag and standby chillers. After 30 seconds, the lag
chiller will now become the acting lead chiller and will start
and stop the standby chiller, if necessary.
If the lag chiller faults when the lead chiller is also faulted,
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 LID panel), the RESET softkey is pressed to clear the
alarm, and the chiller is placed in the CCN mode, the lead
chiller will now communicate and monitor the RUN STA-
TUS of the lag and standby chillers. If both the lag and standby
chillers are running, the lead chiller will not attempt to start
and will 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 will wait for a start request from the
operating chiller. When the configured lead chiller starts, it
assumes its role as lead chiller.
LOAD BALANCING — When the LOAD BALANCE OP-
TION is enabled, the lead chiller will set the ACTIVE DE-
MAND LIMIT in the lag chiller to the lead chiller’s COM-
PRESSOR MOTOR LOAD value. This value has limits of
40% to 100%. When setting the lag chiller ACTIVE DE-
MAND LIMIT, the CONTROL POINT shall be modified to
a value of 3° F (1.67° C) less than the lead chiller’s CON-
TROL POINT value. If the LOAD BALANCE OPTION is
disabled, the ACTIVE DEMAND LIMIT and the CONTROL
POINT are forced to the same value as the lead chiller.
AUTO. RESTARTAFTER POWER FAILURE — When an
autorestart condition occurs, each chiller may have a delay
added to the start-up sequence, depending on its lead/lag con-
figuration. The lead chiller does not have a delay. The lag
chiller has a 45-second delay. The standby chiller has a
90-second delay. The delay time is added after the chiller
water flow verification. The PIC controls ensure that the guide
vanes are closed. After the guide vane position is confirmed,
the delay for lag and standby chiller occurs prior to ener-
gizing the oil pump. The normal start-up sequence then con-
tinues. The auto. restart delay sequence occurs whether the
chiller is in CCN or LOCAL mode and is intended to stag-
ger the compressor motors from being energized simulta-
neously. This will help reduce the inrush demands on the
building power system.
Ice Build Control — Ice build control automatically sets
the chilled WATER/BRINE CONTROL POINT of the ma-
chine from normal operation set point temperature to a tem-
perature where an ice building operation for thermal storage
can be accomplished.
NOTE: For ice build control to properly operate, the PIC
controls must be placed in CCN mode. See Fig. 16 and 17.
The PIC can be configured for ice build operation. Con-
figuration of ice build control is accomplished through en-
tries in the Config table, Ice Build Setpoint table, and the Ice
Build Time Schedule table. Figures 16 and 17 show how to
access each entry.
The Ice Build Time Schedule defines the period during
which ice build is active if the ice build option is EN-
ABLED. If the Ice Build Time Schedule overlaps other sched-
ules defining time, then the Ice Build Time Schedule shall
take priority. During the ice build period, the WATER/
BRINE CONTROL POINT is set to the ICE BUILD SET-
POINT for temperature control. The ICE BUILD RECYCLE
OPTION and ICE BUILD TERMINATION entries from a screen
in the Config (configuration) table provide options for ma-
chine recycle and termination of ice build cycle, respec-
tively. Termination of ice build can result from the ENTER-
ING CHILLED WATER (brine) temperature being less than
the ICE BUILD SETPOINT, opening the REMOTE CON-
TACTS INPUT from an ice level indicator, or reaching the
end of the Ice Build Time Schedule.
ICE BUILD INITIATION — The Ice Build Time Schedule
provides the means for activating ice build. The ice build
time table is named OCCPC02S.
If the Ice Build Time Schedule is OCCUPIED and the ICE
BUILD OPTION is ENABLED, then ice build is active and
the following events automatically take place (unless over-
ridden by a higher authority CCN device):
1. Force CHILLER START/STOP to START.
2. Force WATER/BRINE CONTROL POINT to the ICE BUILD
SETPOINT.
3. Remove any force (Auto) on the ACTIVE DEMAND LIMIT.
42
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