Specifications

47
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 Liquid
Recycle Mode section)
• the time schedule has gone into unoccupied mode
• the chiller protective limit has been exceeded 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 controls set TARGET VFD
SPEED to 0. This will cause the compressor to reduce speed to
the point where line amps equal the configured SOFT STOP
AMPS THRESHOLD. (In a recycle shut down, the compres-
sor will probably be at or below the soft stop threshold amps
when the stop signal is received.) At that point, or one minute
after the stop signal occurs (whichever is earlier), the VFD is
set to STOP. If the STOP key is depressed a second time during
the soft stop or within one minute of the stop signal occurring,
the compressor is immediately stopped.
When the VFD is set to STOP, the compressor is turned off.
The compressor shut down is confirmed by monitoring load
amps. When the compressor shut down is verified, the oil
pump is turned off and VFD STOP is complete. After one min-
ute, the chilled liquid pump is turned off, unless it is a recy-
cle shut down. At this point, the compressor on-time and ser-
vice on-time timers are turned off, and the stop-to-start timer is
turned on.
At this time the condenser liquid pump is also shut off, pro-
vided that the entering condenser liquid temperature is 115 F
(6.1 C) or greater, and the condenser refrigerant temperature is
greater than the condenser freeze point plus 5° F (3° C). Other-
wise, it remains under the control of the Condenser Pump
Control algorithm.
If the shut down is due to low evaporator refrigerant tem-
perature, the chilled liquid pump continues to run until the
leaving chilled liquid temperature is greater than the control
point, plus 5° F (3° C).
Automatic Soft Stop Amps Threshold — When
a non-recycle, non-alarm shutdown is called for, the soft stop
feature unloads the compressor by reducing speed to the point
where load amps equal the SOFT STOP AMPS
THRESHOLD. The compressor is then turned off (see the
above sequence).
If the chiller enters an alarm state or if the compressor enters
a RECYCLE mode, the compressor deenergizes immediately.
To modify the soft stop amps threshold feature, scroll to the
OPTIONS screen on the ICVC. Use the or
softkey to set the SOFTSTOP AMPS THRESH-
OLD parameter to the percent of amps at which the motor will
shut down. Setting SOFT STOP AMPS THRESHOLD to 100%
de-activates this feature. 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 ICVC.
The soft stop amps threshold function can be terminated and
the compressor motor deenergized immediately by depressing
the STOP button twice.
Chilled Liquid 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
cycling is normal and is known as “recycle.” A recycle
shutdown is initiated when any of the following conditions are
true:
1. ECL CONTROL OPTION is DISABLED (LCL
control):
The CONTROL POINT has not been increased by at
least 1° F in the last 5 min. AND LEAVING
CHILLED LIQUID temperature is less than the CON-
TROL POINT (MAINSTAT screen) minus 5° F.
OR LEAVING CHILLED LIQUID temperature is less
than the CONTROL POINT AND the difference
between ENTERING CHILLED LIQUID — LEAV-
ING CHILLED LIQUID is less than RECYCLE
SHUTDOWN DELTA T and ice build is not active.
Fig. 27 — Control Sequence
A—START INITIATED: Pre-start checks are made; chilled liquid pump
started
B—Condenser liquid pump started (5 seconds after A)
C—Liquid flows verified (30 sec to 5 minutes maximum after B)
D—Chilled liquid temperature checked against control point; tower fan
control enabled; oil pump on.
E—Oil pressure verified (oil pressure verified 45-300 sec after D.)
F—VFD starts; phase reversal conditions monitored; compressor
ontime and service ontime start; 15-minute inhibit timer starts (VFD
fault tests for 15 sec after “F”)
G—Verify average current >5% within 15 sec after VFD start, ramp to
VFD target speed.
H—Compressor reaches target speed, chiller set to running status
I—Ramp down until percent line current < soft stop amps threshold
(0-60 sec after I)
J—Shutdown initiated: Target VFD speed to 0%. All load currents <5%.
K—Oil pump relay off (1-20 sec after J)
L—Evaporator pump deenergized (60 sec after K); condenser pump
and tower fan control may continue to operate if condenser pres-
sure is high; evaporator pump may continue if in RECYCLE mode
or freeze protection alarm declared.
O/A — Restart permitted (both inhibit timers expired) (minimum of 15 min-
utes after F; minimum of 1 minute after L)
A23-1645
INCREASE
DECREASE