Specifications

52
Condenser Freeze Prevention — This control algo-
rithm helps prevent condenser tube freeze-up by energizing the
condenser pump relay. The PIC II controls the pump and, by
starting it, helps to prevent the water in the condenser from
freezing. The PIC II can perform this function whenever the
chiller is not running except when it is either actively in pump-
down or in pumpdown/lockout with the freeze prevention
disabled.
When the chiller is off and CONDENSER REFRIG TEMP
is less than the CONDENSER FREEZE POINT, the CON-
DENSER WATER PUMP will be energized (Alert State 154,
Potential Freeze Up) However, if the chiller is in pump down,
and when it entered pump down mode, the CONDENSING
REFRIG TEMP was more than 5° F (2.7° C) above the CON-
DENSER FREEZE POINT, the same low temperature condi-
tion will generate Alarm State 244 (Potential Freeze Up) and
the CONDENSER WATER PUMP will be energized. In either
case, the fault state will clear and the pump will turn off when
the CONDENSER REFRIG TEMP is more than 5° F (2.7° C)
above the CONDENSER FREEZE POINT and the entering
condenser water temperature is greater than the CONDENSER
FREEZE POINT. If the chiller is in Recycle Shutdown Mode
when the condition occurs, the controls will transition to a non-
recycle shutdown.
Evaporator Freeze Protection — When the EVAP-
ORATOR REFRIG TEMP is less than the EVAP REFRIG
TRIPPOINT plus the REFRIG OVERRIDE DELTA T (configu-
rable from 2° to 5° F or 1.1° to 2.8° C), Alert State 122 will be
displayed, and a capacity override will occur. (See Table 7.)
When the unit is running or in recycle, if the EVAPORATOR
REFRIG TEMP is equal to or less than the EVAP REFRIG
TRIPPOINT (33° F or 0.6° C for water, configurable for brine),
Protective Limit Alarm State 232 will be displayed, the unit
will shut down, and the CHILLED WATER PUMP will remain
on. The alarm will be clearable when the leaving chilled water
temperature rises 5°F (2.8°C) above the CONTROL POINT.
When the unit is off, if the EVAPORATOR REFRIG TEMP
is less than the EVAP REFRIG TRIPPOINT plus 1° F (0.6° C),
Alarm State 243 will be generated and the CHILLED WATER
PUMP will be turned on. The alarm can be reset when the
EVAPORATOR REFRIG TEMP rises 5° F (2.8° C) above the
EVAP REFRIG TRIPPOINT.
Tower Fan Relay Low and High — Low condens-
er water temperature can cause the chiller to shut down when
refrigerant temperature is low. The tower fan relays, located in
the starter, are controlled by the PIC II to energize and deener-
gize as the pressure differential between cooler and condenser
vessels changes. This prevents low condenser water tempera-
ture and maximizes chiller efficiency. The tower fan relay can
only accomplish this if the relay has been added to the cooling
tower temperature controller.
TOWER FAN RELAY LOW is turned on whenever the con-
denser water pump is running, and the difference between
EVAPORATOR PRESSURE and CONDENSER PRESSURE is
more than 30 psid (207 kPad) for ENTERING CONDENSER
WATER TEMPERATURE greater than 65 F (18.3 C).
TOWER FAN RELAY LOW is turned off when the condens-
er pump is off or the EVAP REFRIGERANT TEMP is less than
the EVAP SAT OVERRIDE TEMP for ENTERING CON-
DENSER WATER TEMPERATURE less than 62 F (16.7 C), or
the difference between the CONDENSER PRESSURE and
EVAPORATOR PRESSURE is less than 25 psid (172.4 kPad)
and ENTERING CONDENSER WATER TEMPERATURE is
less than 80 F (27 C).
TOWER FAN RELAY HIGH is turned on whenever the con-
denser water pump is running and the difference between
EVAPORATOR PRESSURE and CONDENSER PRESSURE is
more than 30 psid (206.8 kPad) and ENTERING COND WA-
TER temperature is greater than the TOWER FAN HIGH SET-
POINT (SETPOINT menu, default 75 F [23.9 C]).
The TOWER FAN RELAY HIGH is turned off when the
CONDENSER WATER PUMP is off or the EVAPORATOR
REFRIG TEMP is less than the EVAP REF OVERRIDE TEMP
and ENTERING CONDENSER WATER is less than 70 F
(21.1 C), or the difference between EVAPORATOR PRES-
SURE and CONDENSER PRESSURE is less than 28 Psid (193
kPa), and ENTERING CONDENSER WATER temperature is
less than TOWER FAN HIGH SETPOINT minus 3 F (5.4 C).
Auto. Restart After Power Failure — This option
may be enabled or disabled and may be viewed or modified on
the OPTIONS screen, which is accessed from the EQUIP-
MENT CONFIGURATION table. If the AUTO RESTART OP-
TION is enabled, the chiller will start up automatically after a
power failure has occurred, generating one of the following fault
alerts: single cycle dropout (if enabled), line current imbalance,
high line voltage, low line voltage, ISM power on reset, and
ICVC power on reset (Alerts 143-148). With this feature en-
abled, these faults are treated as alerts instead of alarms, so start-
up proceeds as soon as the condition is rectified. The 15-minute
start-to-start and 1-minute start inhibit timers are ignored during
this type of start-up, and the STARTS IN 12 HOURS counter is
not incremented.
When power is restored after the power failure and if the
compressor had been running, the oil pump will energize for
one minute before energizing the cooler pump. AUTO RE-
START will then continue like a normal start-up.
If power to the ICVC module has been off for more than 3
hours or the timeclock has been set for the first time, the com-
pressor starts with the slowest temperature-based ramp load
rate possible in order to minimize oil foaming.
The oil pump is energized occasionally during the time the
oil is being brought up to proper temperature in order to elimi-
nate refrigerant that has migrated to the oil sump during the
power failure. The pump turns on for 60 seconds at the end of
every 30-minute period until the chiller is started.
Fast Power Source Transfers — When the electri-
cal system is being prepared to transfer power from generator
power back to utility power or vice-versa, and the power trans-
fer is an open transition type, and time to transfer is less than 5
seconds, the chiller should be stopped before the transfer oc-
curs and restarted after the transfer has been completed. If the
chiller is not stopped before the transfer occurs, alarms on the
chiller can occur that must be manually reset, such as a circuit
breaker trip.
To accomplish shutdown and restart automatically, a set of
dry contacts should be opened 30 to 60 seconds before the
transfer occurs, then closed after the transfer is complete to re-
start the chiller. The contacts must be wired to the to the Re-
mote START/STOP contact in the starter or VFD (See the field
wiring diagrams) and the Remote Start contact configuration
must be enabled.
If power transfers take 5 seconds or longer, the chiller Auto
restart after Power Failure feature (if enabled) will automatical-
ly restart the chiller.
Water/Brine Reset — Chilled water capacity control is
based on achieving and maintaining a CONTROL POINT
temperature, which is the sum of the LCW SET POINT or ECW
IMPORTANT: A field-supplied water temperature control
system for condenser water should be installed. The system
should maintain the leaving condenser water temperature
at a temperature that is at least 20° F (11° C) above the
leaving chilled water temperature. While the tower fan
relay outputs described above are not a substitute for a
complete condenser water control system, they can serve as
useful inputs to such a system.