5
A START INITIATED: Prestart checks are made, evaporator water pump started.
B Condenser water pump started (5 seconds after A).
C Water flows verified (30 seconds to 5 minutes maximum after B). Chilled water
temperature checked against control point. Guide vanes checked for closure.
Oil pump started, tower fan control enabled.
D Oil pressure verified (15 seconds minimum, 300 seconds after C)
E Compressor motor starts, compressor on-time and service on-time start, 15-
minute inhibit timer starts (10 seconds after D), total compressor starts advances
by one, and the number of starts over a 12-hour period advances by one.
F SHUTDOWN INITIATED - Compressor motor stops, compressor on-time and
service on-time stop and 1-minute inhibit timer starts.
G Oil pump and evaporator pumps deenergised (60 seconds after F). Condenser
pump and tower fan control may continue to operate if condenser pressure is
high. Evaporator pump may continue if in RECYCLE mode.
O/A Restart permitted (both inhibit timers expired: minimum of 15 minutes after E;
minimum of 1 minute after F).
Machine safeties,
evaporator pump
Condenser water pump
Water flow, chilled water
temp., guide vanes, oil
pump, tower fan control
Oil pressure
Compressor, compressor on-
time and service on-time
15-minute start-to-start
1-minute stop-to-start
Com-
pressor
running
Time
6.2 - Shutdown sequence
Chiller shutdown begins if any of the following occurs:
•
the STOP button is pressed for at least one second (the
alarm light blinks once to confirm the stop command)
•
a recycle condition is present (see Chilled Water
Recycle Mode section)
•
the time schedule has gone into unoccupied mode
•
the chiller protective limit has been reached and chiller
is in alarm
•
the start/stop status is overridden to stop from the
CCN network or the ICVC
When a stop signal occurs, the shutdown sequence first stops
the compressor by deactivating the VFD output to the motor.
A status message of “SHUTDOWN IN PROGRESS,
COMPRESSOR DEENERGISED” is displayed, and the
compressor on-time and service on-time stop. The guide
vanes are then brought to the closed position. The oil pump
relay and the chilled water/brine pump relay shut down 60
seconds after the compressor stops. The condenser water
pump shuts down at the same time if the
ENTERING
CONDENSER WATER
temperature is greater than or equal
to 46.1°C and the
CONDENSER REFRIG TEMP
is greater
than the
CONDENSER FREEZE POINT
plus .8 K. The
stop-to-start timer now begins to count down. If the start-
to-start timer value is still greater than the value of the
start-to-stop timer, then this time displays on the ICVC.
Certain conditions that occur during shutdown can change
this sequence.
•
If the AVERAGE LINE CURRENT is greater than
5% after shutdown, the oil pump and chilled water
pump remain energised and the alarm is displayed.
•
The condenser pump shuts down when the
CONDEN-
SER PRESSURE
is less than the
COND PRESS
OVERRIDE
threshold minus 4.1 kPa and the
CON-
DENSER REFRIG TEMP
is less than or equal to the
ENTERING CONDENSER WATER
temperature
plus 1.6 K.
•
If the chiller shuts down due to low refrigerant tempe-
rature, the chilled water pump continues to run until
the
LEAVING CHILLED WATER
temperature is
greater than the
CONTROL POINT
temperature,
plus .8 K).
6.2.1 - Automatic soft stop amps threshold
The soft stop amps threshold feature closes the guide vanes
of the compressor automatically if a non-recycle, non-alarm
stop signal occurs before the compressor motor is
deenergised.
Any time the compressor is directed to STOP (except in
the cases of a fault or recycle shutdown), the guide vanes
are directed to close, and the compressor shuts off when
any of the following is true:
•
AVERAGE LINE CURRENT (%) drops below the
SOFT STOP AMPS THRESHOLD
•
ACTUAL GUIDE VANE POSITION drops below 4%
•
4 minutes have elapsed
•
the STOP button is pressed twice
Compressor ontime and service ontime timers start, and the
compressor
STARTS IN 12 HOURS
counter and the number
of starts over a 1-hour period counter advance by one.
Failure to verify any of the requirements up to this point
will result in the PIC III aborting the start and displaying the
applicable pre-start mode of failure on the ICVC default
screen. A pre-start failure does not advance the
STARTS
IN 12 HOURS
counter. Any failure after the VFD has
energised results in a safety shutdown, advances the starts
in 1 hours counter by one, and displays the applicable
shutdown status on the ICVC display. The minimum time
to complete the entire prestart sequence is approximately
185 seconds.
Fig. 15 - Control sequence
