Specifications

36
To give more precise information or warnings on the chill-
er’s operating condition, the operator can define alert limits on
various monitored inputs in the SETUP1 screen. Safety contact
and alert limits are defined in Table 5. Alarm and alert messag-
es are listed in the Troubleshooting Guide section, page 81.
Shunt Trip — The function of the shunt trip on the PIC III
is to act as a safety trip. The shunt trip is wired from the stan-
dard I/O board to a shunt trip equipped VFD circuit breaker. If
the PIC III tries to shut down the compressor using a normal
shutdown procedure but is unsuccessful for 20 seconds, the
shunt trip output is energized and causes the circuit breaker to
trip off. The ground fault trip also will energize the shunt trip to
trip the circuit breaker. Protective devices in the VFD can also
energize the shunt trip. The shunt trip feature can be tested
using the Control Test feature in the DISCRETE OUTPUTS
CONTROL TEST screen. Reset the circuit breaker immediate-
ly after performing this test.
Default Screen Freeze — When the chiller is in an
alarm state, the default ICVC display “freezes,” that is, it stops
updating. The first line of the ICVC default screen displays a
primary alarm message; the second line displays a secondary
alarm message.
The ICVC default screen freezes to enable the operator to
see the conditions of the chiller at the time of the alarm. If the
value in alarm is one normally displayed on the default screen,
the value flashes between normal and reverse contrast. The
ICVC default screen remains frozen until the condition that
caused the alarm is remedied by the operator.
Knowledge of the operating state of the chiller at the time an
alarm occurs is useful when troubleshooting. Additional chiller
information can be viewed on the status screens and the
VFD_HIST screen. Troubleshooting information is recorded in
the ALARM HISTORY table, which can be accessed from the
SERVICE menu.
To determine what caused the alarm, the operator should
read both the primary and secondary default screen messages,
as well as the alarm history. The primary message indicates the
most recent alarm condition. The secondary message gives
more detail on the alarm condition. Since there may be more
than one alarm condition, another alarm message may appear
after the first condition is cleared. Check the ALARM HISTO-
RY screen for additional help in determining the reasons for the
alarms. Once all existing alarms are cleared (by pressing the
softkey), the default ICVC display returns to normal
operation.
Ramp Loading — The ramp loading feature controls the
rate at which the compressor loads up. This control can prevent
the compressor from loading up too fast during the short period
of time when the chiller is started and the chilled liquid loop
has to be brought down to the CONTROL POINT. This helps
reduce electrical demand charges by slowly bringing the
chilled liquid to the CONTROL POINT.
There are two methods of ramp loading with the PIC III.
Ramp loading can be based on chilled liquid temperature or on
motor load. The method of ramp loading is selected from the
RAMP__DEM screen.
1. Temperature ramp loading
(TEMP PULLDOWN DEG/
MIN) limits the degrees per minute rate at which either
the leaving chilled liquid or the entering chilled liquid
temperature decreases. This rate is configured by the
operator on the TEMP_CTL screen. The lowest tem-
perature ramp rate will be used if chiller power has
been off for 3 hours or more (even if the motor kilo-
watts ramp loading is selected as the ramp loading
method).
2. Motor load ramp loading
(AMPS OR KW RAMP %/
MIN) limits the percent per minute rate at which the
compressor motor current or compressor motor load
increases. The AMPS OR KW RAMP %/MIN rate is
configured by the operator on the RAMP_DEM screen
in amps or kilowatts.
If kilowatts is selected for the DEMAND LIMIT SOURCE,
the MOTOR RATED LOAD KILOWATTS must be entered
(information found on the machine Electrical Data Nameplate)
in the VFD_CONF screen.
The TEMP PULLDOWN DEG/MIN may be viewed or
modified on the TEMP_CTL screen which is accessed from the
EQUIPMENT SERVICE screen. PULLDOWN RAMP TYPE,
DEMAND LIMIT SOURCE, and MOTOR KW RAMP %/MIN
may be viewed or modified on the RAMP_DEM screen.
Capacity Override (Table 6) — Adjustable capacity
overrides are available to prevent the chiller from exceeding
some limits and going into an alarm state. Alert messages 120
through 127 are displayed on the ICVC when capacity
overrides are in effect. Capacity overrides can prevent some
safety shutdowns caused by exceeding the refrigerant low
temperature safety limit, motor high temperature safety limit,
and condenser high pressure limit, high VFD inverter rectifier
temperature limit, and high VFD inverter temperature limit.
Compressor Minimum Speed Override — This
capacity override increases compressor speed if oil viscosity
falls below acceptable levels or if conditions exist that will
prevent sufficient refrigerant cooling to the VFD or motor. This
override is not configurable, it is the only override that will
increase chiller capacity to avoid a safety shutdown. Compres-
sor minimum speed override is most likely to happen at
evaporator temperatures of 50 degrees or more, combined with
low speed, low lift, and less than 25% tons.
The PIC III controls regulate the minimum allowable com-
pressor speed based on oil sump temperature and pressure and
on compressor head. The compressor bearings require higher
oil viscosity when operating at low speed than they do when
operating at high speeds. The controls increase compressor
speed when the oil viscosity is too low to operate the compres-
sor at the lower speed. The low compressor speed override is
also enabled at low loads with high condensing pressure.
Vaporizer Temperature Control COMPRES-
SOR ON —
The vaporizer temperature control is regulated
by the PIC III using the vaporizer heater relay and a flexible
surface heater that is attached to the bottom of the vaporizer.
The vaporizer heater relay is energized whenever the compres-
sor is at low loads and requires additional heat to maintain a
sufficient vaporizer temperature. The vaporizer heater is turned
off when the additional heat is no longer required. The vaporiz-
er heater is not energized when the chiller is not running.
Oil Sump Temperature Control COMPRES-
SOR OFF —
The OIL SUMP TEMP is regulated by the
PIC III using the oil heater relay and an immersion heater in the
oil sump. The oil heater relay is energized whenever the chiller
compressor is off, and the OIL SUMP TEMP is less than 140 F
(60 C) or whenever the OIL SUMP TEMP is less than the
CALC EVAP SAT TEMP plus 53 F (29.4 C). The oil heater is
then turned off when the OIL SUMP TEMP is:
1. More than 152 F (66.7 C) or
2. The OIL SUMP TEMP is more than 142 F (61.1 C) and
also warmer than the CALC EVAP SAT TEMP plus
55 F (30.6 C).
RESET