44
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
MAINSTAT screen) is less than the lead chiller per-
cent capacity.
NOTE: Lead chiller percent capacity = 115 —
LAG
PERCENT CAPACITY
. The
LAG PERCENT CAPAC-
ITY
parameter is on the LEADLAG screen, which is
accessed from the EQUIPMENT SERVICE table on
the SERVICE menu.
2. The lead chiller chilled water temperature is less than
the
CONTROL POINT
temperature (see the MAIN-
STAT screen) plus the
CHILLED WATER DEAD-
BAND
temperature (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 CURRENT
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 commu-
nicating 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 softkey to clear the alarm.
The chiller is placed in CCN mode. The lead chiller communi-
cates 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 condi-
tions 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.
LOAD BALANCING — When the
LOAD BALANCE OP-
TION
(see LEADLAG screen) is enabled, the lead chiller sets
the
ACTIVE DEMAND LIMIT
in the lag chiller to the lead
chiller’s compressor motor load value
MOTOR PERCENT
KILOWATTS
or
AVERAGE LINE CURRENT
on the MAIN-
STAT screen). This value has limits of 40% to 100%. When the
lag chiller
ACTIVE DEMAND LIMIT
is set, the
CONTROL
POINT
must be modified to a value of 3º F (1.67º C) less than
the lead chiller’s
CONTROL POINT
value. If the
LOAD BAL-
ANCE OPTION
is disabled, the
ACTIVE DEMAND LIMIT
and the
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 chill-
er has a 45-second delay. The standby chiller has a 90-second
delay. The delay time is added after the chiller water flow is
verified. The PIC II ensures adequate time for the slide valve to
unload. After the slide valve unload timer (start-up screen) has
expired, the 45 and 90 second delays for The lag and standby
chillers occurs prior to energizing 1CR. The normal start-up se-
quence then continues. The auto. restart delay sequence occurs
whether the chiller is in CCN or LOCAL mode and is intended
to stagger the compressor motor starts. Preventing the motors
from starting simultaneously helps reduce the inrush demands
on the building power system.
Ice Build Control —
The ice build control option auto-
matically sets the
CONTROL POINT
of the chiller to a temper-
ature that allows ice building for thermal storage.
NOTE: For ice build control to operate properly, the PIC II
must be in CCN mode.
NOTE: See Fig. 20 and 21 for more information on ice build-
related menus.
The PIC II can be configured for ice build operation.
• From the SERVICE menu, access the EQUIPMENT
SERVICE table. From there, select the OPTIONS screen
to enable or disable the
ICE BUILD OPTION
. See
Table 3, Example 16.
•The
ICE BUILD SETPOINT
can be configured from the
SETPOINT display, which is accessed from the PIC II
main menu. See Table 3, Example 8.
• The ice build schedule can be viewed or modified from
the SCHEDULE table. From this table, select the ice
build schedule (OCCPC02S) screen. See Fig. 22 and the
section on Time Schedule Operation, page 24, for more
information on modifying chiller schedules.
The ice build time schedule defines the period(s) during
which ice build is active if the ice build option is enabled. If the
ice build time schedule overlaps other schedules, the ice build
time schedule takes priority. During the ice build period, the
CONTROL POINT
is set to the
ICE BUILD SETPOINT
for
temperature control. The
ICE BUILD RECYCLE
and I
CE
BUILD TERMINATION
parameters, accessed from the
OPTIONS screen, allow the chiller operator to recycle or ter-
minate the ice build cycle. The ice build cycle can be config-
ured to terminate if:
•the
ENTERING CHILLED WATER
temperature is less
than the
ICE BUILD SETPOINT.
In this case, the opera-
tor sets the
ICE BUILD TERMINATION
parameter to 0
on the OPTIONS screen.
• the REMOTE CONTACT inputs from an ice level indi-
cator are opened. In this case, the operator sets the
ICE
BUILD TERMINATION
parameter to 1 on the
OPTIONS screen.
• the chilled water temperature is less than the ice build
set point and the remote contact inputs from an ice level
indicator are open. In this case, the operator sets the
ICE BUILD TERMINATION
parameter to 2 on the
OPTIONS screen.
• the end of the ice build time schedule has been reached.
RESET
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