Specifications

35
The PIC III controls response to temperatures above the
control point is affected by the PROPORTIONAL INC BAND.
This parameter will slow or quicken the rate at which the com-
pressor speed is changed in response to chilled liquid/brine
temperatures above the control point plus
1
/
2
times the
CHILLED LIQUID DEADBAND. The PROPORTIONAL INC
BAND can be adjusted from a setting of 2 to 10; the default
setting is 6.5. A smaller value of PROPORTIONAL INC
BAND will increase the rate at which the compressor speed is
increased.
The response below the control point is called the PRO-
PORTIONAL DEC BAND, this parameter will slow or quicken
the rate at which the compressor speed is changed in response
to chilled liquid temperatures below the CONTROL POINT
minus
1
/
2
times the CHILLED LIQUID DEAD BAND. The
PROPORTIONAL DEC BAND can be adjusted on the ICVC
from a setting of 2 to 10. The default setting is 6.0. A smaller
value of PROPORTIONAL DEC BAND will increase the rate
at which the compressor speed is decreased.
The PROPORTIONAL ECL GAIN changes the amount the
compressor speed is changed each time the PIC III controls
command an adjustment. The PROPORTIONAL ECL GAIN
can be adjusted from 1 to 3. A larger value of PROPORTION-
AL ECL GAIN will increase the amount the compressor speed
changes each time the controls call for a change.
DEMAND LIMITING — The PIC III responds to the
ACTIVE DEMAND LIMIT set point by limiting the amps or
kilowatts consumed by the chiller. It compares the ACTIVE
DEMAND LIMIT set point to the DEMAND LIMIT SOURCE
(either the actual AVERAGE LINE CURRENT or the actual
MOTOR KW), depending on how the control is configured.
DEMAND LIMIT SOURCE is on the RAMP_DEM screen.
The default DEMAND LIMIT SOURCE is the compressor
motor amps.
CHILLER TIMERS — The PIC III maintains 2 runtime
clocks, known as COMPRESSOR ONTIME and SERVICE
ONTIME. COMPRESSOR ONTIME indicates the total
life-time compressor run hours. This timer can register up to
500,000 hours before the clock turns back to zero. The
SERVICE ONTIME is a resettable timer that can be used to
indicate the hours since the last service visit or any other event.
The time can be changed from the ICVC to whatever value is
desired. The SERVICE ONTIME timer can register up to
32,767 hours before it rolls over to zero.
The chiller also maintains a start-to-start timer and a stop-
to-start timer. These timers limit how soon the chiller can be
started. START INHIBIT TIMER is displayed on the MAIN-
STAT screen. See the Start-Up/Shutdown/Recycle Sequence
section, page 46, for more information on this topic.
OCCUPANCY SCHEDULE — The chiller schedule, de-
scribed in the Time Schedule Operation section (page 21),
determines when the chiller can run. Each schedule consists of
from 1 to 8 occupied or unoccupied time periods, set by the
operator. The chiller can be started and run during an occupied
time period (when YES is displayed next to OCCUPIED? on
the MAINSTAT display screen). It cannot be started or run
during an unoccupied time period (when NO is displayed next
to OCCUPIED? on the MAINSTAT display screen). These
time periods can be set for each day of the week and for holi-
days. The day begins with 0000 hours and ends with
2400 hours. When any occupancy schedule is in a time period
when the chiller is allowed to run, the parameter OCCUPIED?
is YES.
These schedules can be set up to follow a building’s occu-
pancy schedule, or can be set to be occupied 100% of the time,
if the operator wishes. In this case, the chiller is normally start-
ed and stopped manually using the CCN, LOCAL, and STOP
buttons. The schedules also can be bypassed by forcing the
CHILLER START/STOP parameter on the MAINSTAT screen
to START. For more information on forced starts, see Local
Start-Up, page 46.
The schedules also can be overridden to keep the chiller in
an occupied state for up to 4 hours, on a one time basis. See the
Time Schedule Operation section, page 21.
Figure 20 shows a schedule for a typical office building
with a 3-hour, off-peak, cool-down period from midnight to
3 a.m., following a weekend shutdown. Holiday periods are in
an unoccupied state 24 hours per day. The building operates
Monday through Friday, 7:00 a.m. to 6:00 p.m., and Saturdays
from 6:00 a.m. to 1:00 p.m. This schedule also includes the
Monday midnight to 3:00 a.m. weekend cool-down schedule.
NOTE: This schedule is for illustration only and is not
intended to be a recommended schedule for chiller operation.
Whenever the chiller is in the LOCAL mode, it uses Occu-
pancy Schedule 01 (OCCPC01S). The chiller uses Occupancy
Schedule 02 (OCCPCO2S) when it is in ICE BUILD mode.
When the chiller is in CCN mode, it uses Occupancy Schedule
03 (OCCPC03S).
The
CCN SCHEDULE NUMBER is configured on the
NET_OPT display screen, accessed from the EQUIPMENT
CONFIGURATION table. See Table 3, Example 16. SCHED-
ULE NUMBER can be changed to any value from 03 to 99. If
this number is changed on the NET_OPT screen, the operator
must go to the ATTACH TO NETWORK DEVICE screen to
upload the new number into the SCHEDULE screen. See
Fig. 19.
Safety Controls — The PIC III monitors all safety con-
trol inputs and, if required, shuts down the chiller or limits the
compressor speed to protect the chiller from possible damage
from any of the following conditions:
• high motor winding temperature
• high discharge temperature
• low oil pressure
• low evaporator refrigerant temperature
• condenser high pressure or low pressure
• inadequate liquid/brine cooler and condenser flow
• high, low, or loss of voltage
• ground fault
• voltage imbalance
• current imbalance
• excessive motor acceleration time
• lack of motor current signal
• excessive motor amps
• motor stall
• temperature sensor and transducer faults
• VFD power faults
• VFD over temperature
• humidity surrounding the VFD coldplate
• reverse compressor rotation
VFD faults or protective devices within the VFD can shut
down the chiller.
If the PIC III control initiates a safety shutdown, it displays
the reason for the shutdown (the fault code) on the ICVC dis-
play screen along with a primary and secondary message, and
blinks the alarm light on the control center. The alarm is stored
in memory and can be viewed on the ALARM HISTORY and
VFD_HIST screens on the ICVC, along with a message for
troubleshooting. If the safety shutdown was also initiated by a
fault detected in the VFD, the conditions at the time of the fault
will be stored in VFD_HIST.
CAUTION
If compressor motor overload or a motor ground fault
occurs, check the motor for grounded or open phases
before attempting a restart.