Pic System Functions; Capacity Control; Entering Chilled Water Control; Proportional Bands And Gain - Carrier 17 Start Up & Operation Manual

PIC System Functions

NOTE: Throughout this manual, words printed in capital let-
ters and italics are values that may be viewed on the LID.
See Table 2 for examples of LID screens. Point names are
listed in the Description column. An overview of LID op-
eration and menus is given in Fig. 14-20.
CAPACITY CONTROL — The PIC controls the machine
capacity by modulating the inlet guide vanes in response to
chilled water temperature changes away from the CON-
TROL POINT. The CONTROL POINT may be changed by
a CCN network device, or is determined by the PIC adding
any active chilled water reset to the chilled water SET POINT.
The PIC uses the PROPORTIONAL INC (Increase) BAND,
PROPORTIONAL DEC (Decrease) BAND, and the PRO-
PORTIONAL ECW (Entering Chilled Water) GAIN to de-
termine how fast or slow to respond. CONTROL POINT
may be viewed/overridden on the Status table, Status01
selection.
ENTERING CHILLED WATER CONTROL — If this op-
tion is enabled, the PIC uses ENTERING CHILLED WATER
temperature to modulate the vanes instead of LEAVING
CHILLED WATER temperature. ENTERING CHILLED WA-
TER control option may be viewed/modified on the Equip-
ment Configuration table, Config table.
DEADBAND — This is the tolerance on the chilled water/
brine temperature CONTROL POINT. If the water tempera-
ture goes outside of the DEADBAND, the PIC opens or closes
the guide vanes in response until it is within tolerance. The
PIC may be configured with a 0.5° to 2° F (0.3° to 1.1° C)
deadband. DEADBAND may be viewed or modified on the
Equipment Service1 table.
For example, a 1° F (0.6° C) deadband setting controls
the water temperature within ±0.5° F (0.3° C) of the control
point. This may cause frequent guide vane movement if the
chilled water load fluctuates frequently. A value of
1° F (0.6° C) is the default setting.
PROPORTIONAL BANDS AND GAIN — Proportional band
is the rate at which the guide vane position is corrected in
proportion to how far the chilled water/brine temperature is
from the control point. Proportional gain determines how
quickly the guide vanes react to how quickly the tempera-
ture is moving from CONTROL POINT.
The Proportional Band can be viewed/modified on the LID.
There are two response modes, one for temperature re-
sponse above the control point, the other for response below
the control point.
The first type is called PROPORTIONAL INC BAND, and
it can slow or quicken vane response to chilled water/brine
temperature above DEADBAND. It can be adjusted from a
setting of 2 to 10; the default setting is 6.5. PROPOR-
TIONAL DEC BAND can slow or quicken vane response to
chilled water temperature below deadband plus control point.
It can be adjusted on the LID from a setting of 2 to 10, and
the default setting is 6.0. Increasing either of these settings
will cause the vanes to respond slower than a lower setting.
The PROPORTIONAL ECW GAIN can be adjusted at the LID
display from a setting of 1.0 to 3.0, with a default setting of
2.0. Increase this setting to increase guide vane response to
a change in entering chilled water temperature. The propor-
tional bands and gain may be viewed/modified on the Equip-
ment Service3 table.
DEMAND LIMITING — The PIC will respond to the AC-
TIVE DEMAND LIMIT set point by limiting the opening of
the guide vanes. It will compare the set point to either COM-
PRESSOR MOTOR LOAD or COMPRESSOR MOTOR CUR-
RENT (percentage), depending on how the control is con-
figured for the DEMAND LIMIT SOURCE which is accessed
on the SERVICE1 table. The default setting is current
limiting.
MACHINE TIMERS — The PIC 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 SERV-
ICE ONTIME is a resettable timer that can be used to indi-
cate the hours since the last service visit or any other reason.
The time can be changed through the LID to whatever value
is desired. This 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 machine can
be started. See the Start-Up/Shutdown/Recycle Sequence sec-
tion, page 45, for operational information.
OCCUPANCY SCHEDULE — This schedule determines when
the chiller is either occupied or unoccupied.
Each schedule consists of from one to 8 occupied/unoccupied
time periods, set by the operator. These time periods can be
enabled to be in effect, or not in effect, on each day of the
week and for holidays. The day begins with 0000 hours and
ends with 2400 hours. The machine is in OCCUPIED mode
unless an unoccupied time period is in effect.
The machine will shut down when the schedule goes to
UNOCCUPIED. These schedules can be set up to follow the
building schedule or to be 100% OCCUPIED if the operator
wishes. The schedules also can be bypassed by forcing the
Start/Stop command on the PIC Status screen to start. The
schedules also can be overridden to keep the unit in an OC-
CUPIED mode for up to 4 hours, on a one-time basis.
Figure 19 shows a schedule for a typical office building
time schedule, with a 3-hour, off-peak cool down period from
midnight to 3 a.m., following a weekend shutdown. Ex-
ample: Holiday periods are unoccupied 24 hours per day.
The building operates Monday through Friday, 7:00 a.m. to
6:00 p.m., with a Saturday schedule of 6:00 a.m. to
1:00 p.m., and includes the Monday midnight to 3:00 a.m.
weekend cool-down schedule.
NOTE: This schedule is for illustration only, and is not in-
tended to be a recommended schedule for chiller operation.
Whenever the chiller is in the LOCAL mode, the machine
uses Occupancy Schedule 01.
The Ice Build Time Schedule is Schedule 02. When in the
CCN mode, Occupancy Schedule 03 is used.
The CCN schedule number is defined on the Config table
in the Equipment Configuration table on page 29. The sched-
ule number can change to any value from 03 to 99. If this
schedule number is changed on the Config table, the opera-
tor must use the Attach to Network Device table to upload
the new number into the Schedule screen. See Fig. 17.
Safety Controls —
inputs, and if required, shuts down the machine or limits the
guide vanes to protect the machine from possible damage
from any of the following conditions:
• high bearing temperature
• high motor winding temperature
• high discharge temperature
• low oil pressure
• low cooler refrigerant temperature/pressure
• condenser high pressure or low pressure
• inadequate water/brine cooler and condenser flow
• high, low, or loss of voltage
• excessive motor acceleration time
• excessive starter transition time
• lack of motor current signal
• excessive motor amps
• excessive compressor surge
• temperature and transducer faults
35
The PIC monitors all safety control