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 CVC/ICVC
When a stop signal occurs, the shutdown sequence first stops the compressor by deactivating the start relay (1CR). A status message of “SHUTDOWN IN PROGRESS, COM- PRESSOR DEENERGIZED” is displayed, and the compres- sor ontime and service ontime 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 tem- perature is greater than or equal to 115 F (46.1 C) and the CONDENSER REFRIG TEMP is greater than the CONDENS- ER FREEZE POINT plus 5 F (–15.0 C). 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 CVC/ICVC.
Certain conditions that occur during shutdown can change this sequence.
•If the AVERAGE LINE CURRENT is greater than 5% after shutdown, or the starter contacts remain energized, the oil pump and chilled water pump remain energized and the alarm is displayed.
•The condenser pump shuts down when the CON- DENSER PRESSURE is less than the COND PRESS OVERRIDE threshold minus 3.5 psi (24.1 kPa) and the CONDENSER REFRIG TEMP is less than or equal to the
ENTERING CONDENSER WATER temperature plus 3° F (–1.6°C).
•If the chiller shuts down due to low refrigerant tempera- ture, the chilled water pump continues to run until the
LEAVING CHILLED WATER temperature is greater than the CONTROL POINT temperature, plus 5° F (3° C).
Automatic Soft Stop Amps Threshold — The soft stop amps threshold feature closes the guide vanes of the com- pressor automatically if a non-recycle, non-alarm stop signal occurs before the compressor motor is deenergized.
If the STOP button is pressed, the guide vanes close to a preset amperage percent until the guide vane is less than 4% open or 4 minutes have passed. The compressor then shuts off.
If the chiller enters an alarm state or if the compressor enters a RECYCLE mode, the compressor deenergizes immediately.
To activate the soft stop amps threshold feature, scroll to the bottom of OPTIONS screen on the CVC/ICVC. Use the
INCREASE or DECREASE softkey to set the SOFT STOP AMPS THRESHOLD parameter to the percent of amps at which the motor will shut down. The default setting is 100% amps (no soft stop). The range is 40 to 100%.
When the soft stop amps threshold feature is being applied, a status message, “SHUTDOWN IN PROGRESS, COM- PRESSOR UNLOADING” displays on the CVC/ICVC.
The soft stop amps threshold function can be terminated and the compressor motor deenergized immediately by depressing the STOP button twice.
Chilled Water Recycle Mode — The chiller may cycle off and wait until the load increases to restart when the compressor is running in a lightly loaded condition. This cy- cling is normal and is known as “recycle.” A recycle shutdown is initiated when any of the following conditions are true:
•the chiller is in LCW control, the difference between the LEAVING CHILLED WATER temperature and ENTER- ING CHILLED WATER temperature is less than the RECYCLE SHUTDOWN DELTA T (found in the
SETUP1 table) the LEAVING CHILLED WATER tem- perature is 5° F (2.8° C) below the CONTROL POINT, the CONTROL POINT has not increased in the last 5 minutes and ICE BUILD is not active.
•the ECW CONTROL OPTION is enabled, the difference between the ENTERING CHILLED WATER temperature and the LEAVING CHILLED WATER temperature is less than the RECYCLE SHUTDOWN DELTA T (found in the
SETUP1 table), the ENTERING CHILLED WATER tem- perature is 5° F (2.8° C) below the CONTROL POINT, and the CONTROL POINT has not increased in the last 5 minutes.
•the LEAVING CHILLED WATER temperature is within 3° F (2° C) of the EVAP REFRIG TRIPPOINT.
When the chiller is in RECYCLE mode, the chilled water pump relay remains energized so the chilled water temperature can be monitored for increasing load. The recycle control uses RESTART DELTA T to check when the compressor should be restarted. This is an operator-configured function which de- faults to 5° F (3° C). This value can be viewed or modified on the SETUP1 table. The compressor will restart when the chiller is:
•in LCW CONTROL and the LEAVING CHILLED WATER temperature is greater than the CONTROL POINT plus the RECYCLE RESTART DELTA T.
•in ECW CONTROL and the ENTERING CHILLED WATER temperature is greater than the CONTROL POINT plus the RECYCLE RESTART DELTA T.
Once these conditions are met, the compressor initiates a start-up with a normal start-up sequence.
An alert condition may be generated if 5 or more recycle start-ups occur in less than 4 hours. Excessive recycling can reduce chiller life; therefore, compressor recycling due to ex- tremely low loads should be reduced.
To reduce compressor recycling, use the time schedule to shut the chiller down during known low load operation period, or increase the chiller load by running the fan systems. If the hot gas bypass is installed, adjust the values to ensure that hot gas is energized during light load conditions. Increase the RECYCLE RESTART DELTA T on the SETUP1 table to lengthen the time between restarts.
The chiller should not be operated below design minimum load without a hot gas bypass installed.
Safety Shutdown — A safety shutdown is identical to a manual shutdown with the exception that, during a safety shutdown, the CVC/ICVC displays the reason for the shut- down, the alarm light blinks continuously, and the spare alarm contacts are energized.
After a safety shutdown, the RESET softkey must be pressed to clear the alarm. If the alarm condition is still present, the alarm light continues to blink. Once the alarm is cleared, the operator must press the CCN or LOCAL softkeys to re- start the chiller.
