FAULTED CHILLER OPERATION — If the lead chiller
shuts down because of an alarm (*) condition, it stops com-
municating with the lag and standby chillers. After 30 sec-
onds, the lag chiller becomes the acting lead chiller and starts
and stops 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 (indicated
on the LID ), the RESET softkey is pressed to clear the
alarm, and the lead 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 of
lead chiller.
LOAD BALANCING — When the LOAD BALANCE OP-
TION (LEAD/LAG screen) is enabled, the lead chiller sets
the ACTIVE DEMAND LIMIT in the lag chiller to the lead
chiller’s COMPRESSOR MOTOR LOAD value. This value
has limits of 40% to 100%. When setting the lag chiller AC-
TIVE DEMAND LIMIT, the WATER/BRINE CONTROL POINT
is modified to a value of 3° F (1.67° C) less than the lead
chiller’s WATER/BRINE CONTROL POINT value. If the LOAD
BALANCE OPTION is disabled, the ACTIVE DEMAND LIMIT
and the WATER/BRINE CONTROL POINT are forced to the
same value as the lead chiller.
AUTO. RESTART AFTER POWER FAILURE — When an
auto. restart 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 chillers occurs before 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 motor start-up times. This helps reduce
the in-rush of demand on the building power system.
Ice Build Control —
Ice build control automatically sets
the chilled WATER/BRINE CONTROL POINT of the chiller
from a normal operation set point temperature to a tempera-
ture that allows an ice building operation for thermal
storage.
NOTE: For ice build control to operate properly, the PIC
controls must be placed in CCN mode.
The PIC can be configured for ice build operation by chang-
ing entries on the:
• CONFIG screen, accessed from the SERVICE menu
• OCCPC02S screen (ice build time schedule), accessed from
the SCHEDULE menu
• SETPOINT screen, accessed from the SETPOINT menu.
Figures 15 and 16 show how to access each screen.
The ice build time schedule defines the periods during which
the ice build option can be activated, if the ice build option
is enabled. If the ice build time schedule overlaps other sched-
ules, the ice build time schedule takes priority. During an ice
build period, the WATER/BRINE CONTROL POINT is set to
the ICE BUILD SETPOINT (SETPOINT screen) for tem-
perature control.
The ICE BUILD RECYCLE OPTION and ICE BUILD
TERMINATION parameters are on the CONFIG screen. The
ice build recycle option can be enabled or disabled from this
screen; the ice build termination value can be set to 0, 1, or
2, depending on the factor that determines termination (tem-
perature, contacts, or both). Ice build termination can occur
when:
• the ENTERING CHILLED WATER temperature is less than
the ICE BUILD SETPOINT
• the REMOTE CONTACTS INPUT (STATUS01 screen) is
opened based on input from an ice level indicator
• the end of the ice build time schedule has been reached.
ICE BUILD INITIATION — The ice build option is acti-
vated via the ice build time schedule on the OCCPC02S screen.
If the current time is set as an ice build time on the OCCPC02S
screen and the ICE BUILD OPTION on the CONFIG screen
is enabled, then the ice build option is active and the fol-
lowing events automatically take place (unless overridden
by a higher authority CCN device):
1. CHILLER START/STOP is forced to START.
2. The WATER/BRINE CONTROL POINT is forced to the
ICE BUILD SETPOINT.
3. Any force (Auto) on the ACTIVE DEMAND LIMIT is
removed.
NOTE: Items 1-3 (shown above) do not occur if the chiller
is configured and operating as a lag or standby chiller for
lead/lag operation and is actively controlled by a lead chiller.
The lead chiller communicates the ICE BUILD SETPOINT,
desired CHILLER START/STOP state, and ACTIVE DE-
MAND LIMIT to the lag or standby chiller as required for
ice build, if configured to do so.
START-UP/RECYCLE OPERATION — If the chiller is not
running when ice build activates, then the PIC checks the
following
parameters,
based
on
the
ICE
BUILD
TERMINATION value, to avoid starting the compressor
unnecessarily:
• if the ICE BUILD TERMINATION parameter is set to 0
(temperature only), and the ENTERING CHILLED WA-
TER temperature is less than or equal to the ICE BUILD
SETPOINT;
• if the ICE BUILD TERMINATION parameter is set to 1
(contacts only) and the remote contacts are open;
• if the ICE BUILD TERMINATION parameter is set to 3
(both temperature and contacts), the ENTERING CHILLED
WATER temperature is less than or equal to the ICE BUILD
SETPOINT, and the remote contacts are open.
The ICE BUILD RECYCLE OPTION determines whether
or not the PIC goes into a RECYCLE mode. If the ICE BUILD
RECYCLE OPTION is set to DSABLE (disable) when the
ice build terminates, the PIC reverts to normal temperature
control duty. If the ICE BUILD RECYCLE OPTION is set to
ENABLE, when ice build terminates, the PIC goes into an
ice build recycle mode and the chilled water pump relay re-
mains energized to keep the chilled water flowing. If the EN-
TERING CHILLED WATER (brine) temperature increases above
the ICE BUILD SETPOINT plus the RECYCLE RESTART
DELTA T value, the compressor restarts and controls the chilled
water/brine temperature to the ICE BUILD SETPOINT.
40
