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SECTION 2 - PRE-STARTUP AND SYSTEM OPERATING PROCEDURES
SHUT DOWN SEQUENCE OF OPERATION
Normal (Controlled) Stop
The chiller capacity will be reduced to perform a con-
trolled shutdown. This will slightly decrease the sud-
den loss of steam load when the chiller trips, thus pos-
sibly preventing boiler relief valves from lifting. The
following sequence is applicable when the Speed Con-
trol Mode is set for Variable:
1. To initiate the controlled stop, push the SOFT
SHUTDOWN key on the OptiView™ Control
Center HOME screen or open one of the remote
cycling contacts (if connected to the chiller pan-
el). The message "CHILLER UNLOADING BE-
FORE SHUTDOWN" is displayed.
2. The present LCLT Controller SP (Local/Remote
setpoint, whichever is selected) is ramped up to
a value equal to the return chiller liquid temp +5
°F and the chiller capacity controls begin unload-
ing the chiller. At the same time, a Soft Shutdown
timer (TDSP9-Soft Shutdown Rampdown Timer,
adjustable 2-20 minutes on the Time Setpoints
Screen) is enabled. The unloading begins with
speed reduction to the calculated anti-surge mini-
mum speed. When the speed has decreased to the
calculated anti-surge minimum speed, the PRV
will close to the calculated anti-surge minimum
vane position. While the vanes are closing and
the head is decreasing, the speed will continue
to ramp down to the lower calculated anti-surge
minimum speed.
When the PRV position feedback signal is equal
to the calculated anti-surge minimum vane posi-
tion, the hot gas valve will begin opening. While
the hot gas valve is opening and the head is de-
creasing, the speed will continue to ramp down
to the lower calculated anti-surge minimum speed
and the vanes will continue to close to the lower
calculated anti-surge minimum.
3. The chiller will be shutdown when the hot gas
valve signal has increased to 95% (if HGV is En-
abled) or the Soft Shutdown logic has been un-
loading the chiller longer than the TDSP9-Soft
Shutdown Rampdown Timeout minutes entered
on the Time Setpoints Screen (if HGV is Dis-
abled).
36
Automatic Start: When the Soft Shutdown is initi-
ated, the Main Steam Inlet Valve control output
is first decreased (ramped down at 5 %/second)
until it is equal to or less than the current output to
the Governor Valve. From this point as the chiller
unloads and until it is shutdown, the Main Steam
Inlet Valve output will equal the Governor Valve
output. When the two valve signals are tracking,
the present LCLT Controller SP (Local/Remote
setpoint, whichever is selected) is ramped up to a
value equal to the return chiller liquid temp +5 °F
and the chiller capacity controls begin unloading
the chiller as described above.
Chillers manufactured after December 2006 ARE
NOT supplied with a separate automatic main
steam inlet valve.
When the Speed Control Mode is set for Fixed,
the unloading sequence begins with the PRV and
proceeds to the hot gas valve as described above.
Immediate Stop
1. On the front of the OptiView™ Control Center,
place the keypad switch in the (O) STOP/RESET
position to immediately trip the turbine without
the unloading delay. In the event that the STOP/
RESET switch fails to trip the turbine, push the
hand trip knob on the turbine.
The oil pumps will continue to run
through their normal shutdown sequence
after any of the above operations. If all
motors must be stopped for safety reasons,
the 120 VAC power supply to the chiller
panel must be shut off by an external
EMERGENCY STOP switch contact (sup-
plied by others).
Post Trip Shutdown Sequence
1. When a turbine trip is initiated, the main start
relay (K18 on the I/O board) is immediately de-
energized. This de-energizes the the turbine trip
solenoid, which causes the pneumatic turbine trip
valve to close. The compressor pre-rotation vanes
are closed, the compressor Variable Geometry
Diffuser (VGD) is opened, and the hot gas valve
and subcooler level control valve are opened. The
main steam inlet isolation valve should be closed
at this time.
FORM 160.67-O2
ISSUE DATE: 10/9/2020
JOHNSON CONTROLS
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