Condenser Freeze Prevention; Evaporator Freeze Protection; Tower Fan Relay Low And High; Auto. Restart After Power Failure - Carrier AquaEdge 19XR series Start-Up, Operation And Maintenance Instructions Manual

Condenser Freeze Prevention —
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 —
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 —
water temperature can cause the chiller to shut down when re-
frigerant 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
WATER temperature is greater than the TOWER FAN HIGH
This control algo-
SETPOINT (SETPOINT menu, default 75 F [23.9 C]).
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 tempera-
ture is less than TOWER FAN HIGH SETPOINT minus 3 F
(5.4 C).
Auto. Restart After Power Failure — ICVC
Software Version 14 —
abled/disabled in the OPTIONS screen.
NOTE: This section assumes that a chiller without Uninter-
When the EVAP-
ruptible Power supply has been installed.
abled: single cycle dropout (if enabled), line current imbalance,
high line voltage, low line voltage, and ISM power-on reset
(Alerts 143-148). With this feature enabled, these faults are
treated as alerts instead of alarms, so start-up proceeds as soon
as the condition has been 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 incre-
mented.
as long as the controls have been without power for 20 minutes
or less. If the power is off for less than 20 minutes, the timing
of the restart is now in an express mode. When enabled, at the
time of power up, if the chiller had been operating at the time
of shutdown, the controls will immediately energize the
CHILLED WATER PUMP output, wait 1 second, energize the
CONDENSER WATER PUMP output, then wait 1 second to
Low condenser
start to verify water flow. When flow is verified, and the
chilled water temperature is calling for cooling, the guide vane
is now checked for closure. If the unit is configured for VFD,
then the guide vanes have no closure requirement. If there is
no VFD configured, the vanes must be less than or equal to the
GUIDE VANE CLOSURE limit set in the OPTIONS table.
is started and when the oil pressure is confirmed the controls
wait 4 seconds to maintain pressure. At this point the compres-
sor is commanded to start.
timing of the restart will be standard timing for auto restart af-
ter power failure. When power is restored (after the longer
than 20-minute power failure) and if the compressor had been
running, the oil pump will energize for one minute before ener-
gizing the cooler pump. AUTO RESTART will then continue
like a normal start-up. If power to the ICVC module has been
off for more than 3 hours or the time clock has been set for the
first time, the compressor 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 eliminate
refrigerant that has migrated to the oil sump during the power
failure. The pump turns on for 30 seconds at the end of every
30-minute period until the chiller is started.
55
The TOWER FAN RELAY HIGH is turned off when the
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 con-
denser water control system, they can serve as useful inputs
to such a system.
The following faults will reset when Auto Restart is en-
This feature allows the controls to make an express restart
After guide vanes are checked and in position, the oil pump
If the power had been off for longer than 20 minutes, the
The Auto Restart feature is en-