PIC II System Functions
NOTE: Words not part of paragraph headings and printed
in all capital letters can be viewed on the CVC (e.g., LO-
CAL, CCN, RUNNING, ALARM, etc.). Words printed in
both in all capital letters and italics can also be viewed on
the CVC and are parameters (CONTROL MODE, COOL-
ING SET POINT, TARGET GUIDE VANE POS, etc.) with
associated values (e.g., modes, temperatures, pressures, per-
centages, on, off, enable, disable, etc.). Works printed in all
capital letters and in a box represent softkeys on the CVC
(e.g., ENTER and EXIT ). See Table 2 for examples of
the type of information that can appear on the CVC screens.
Figures 12-18 give an overview of CVC operations and menus.
CAPACITY CONTROL — The PIC II controls the chiller
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 II adding
any active chilled water reset to the SET POINT. The PIC II
uses the PROPORTIONAL INC (Increase) BAND, PRO-
PORTIONAL DEC (Decrease) BAND, and the PROPOR-
TIONAL ECW (Entering Chilled Water) GAIN to determine
how fast or slow to respond. CONTROL POINT may be viewed
or overridden from the MAINSTAT screen.
ECW CONTROL OPTION — If this option is enabled, the
PIC II uses the ENTERING CHILLED WATER temperature
to modulate the vanes instead of the LEAVING CHILLED
WATER temperature. The ECW CONTROL OPTION may be
viewed on the TEMP_CTL screen, which is accessed from
the EQUIPMENT SERVICE screen.
CONTROL POINT DEADBAND — This is the tolerance
range on the chilled water/brine temperature control point.
If the water temperature goes outside the CHILLED WATER
DEADBAND, the PIC II opens or closes the guide vanes un-
til the temperature is within tolerance. The PIC II may be
configured with a 0.5 to 2 F (0.3 to 1.1 C) deadband. CHILLED
WATER DEADBAND may be viewed or modified on the
SETUP1 screen, which is accessed from the EQUIPMENT
SERVICE 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.
DIFFUSER CONTROL — On 19XR compressors equipped
with a variable discharge diffuser, the PIC II adjusts the dif-
fuser actuator position (DIFFUSER ACTUATOR on the COM-
PRESS screen) to correspond to the actual guide vane po-
sition (ACTUAL GUIDE VANE POS on the COMPRESS
screen).
The diffuser control can be enabled or disabled from the
SETUP2 screen. See Table 2, Example 18. In addition, the
diffuser and guide vane load points may be viewed and modi-
fied from this screen. These points must be correct for the
compressor size. The diffuser opening can be incremented
from fully open to completely closed. A 0% setting is fully
open; a 100% setting is completely closed. To obtain the proper
settings for Diffuser Control, contact a Carrier Engineering
representative.
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 the CONTROL POINT. The propor-
tional bands and gain may be viewed or modified from the
SETUP2 screen, which is accessed from the EQUIPMENT
SERVICE table.
The Proportional Band — There are two response modes,
one for temperature response above the control point, the
other for the response below the control point.
The temperature response above the control point is called
the PROPORTIONAL INC BAND, and it can slow or quicken
guide vane response to chilled water/brine temperatures above
the DEADBAND. The PROPORTIONAL INC BAND can be
adjusted from a setting of 2 to 10; the default setting is 6.5.
The response below the control point is called the
PROPORTIONAL DEC BAND, and it can slow or quicken
the guide vane response to chilled water temperature below
the deadband plus the control point. The PROPORTIONAL
DEC BAND can be adjusted on the CVC from a setting of
2 to 10. The default setting is 6.0.
NOTE: Increasing either of these settings causes the guide
vanes to respond more slowly than they would at a lower
setting.
The PROPORTIONAL ECW GAIN can be adjusted on the
CVC display for values of 1, 2, or 3; the default setting is 2.
Increase this setting to increase guide vane response to a change
in entering chilled water temperature.
DEMAND LIMITING — The PIC II responds to the
ACTIVE DEMAND LIMIT set point by limiting the opening
of the guide vanes. It compares the ACTIVE DEMAND LIMIT
set point to the DEMAND LIMIT SOURCE (either the
AVERAGE LINE CURRENT or the MOTOR KW). Depend-
ing on how the control is configured. DEMAND LIMIT
SOURCE is on the RAMP_DEM screen. The default source
is the compressor motor current.
CHILLER TIMERS — The PIC II maintains 2 runtime clocks,
known as COMPRESSOR ONTIME and SERVICE ON-
TIME. 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 reset table 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 CVC 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 chiller can be
started. START INHIBIT TIMER is displayed on the
MAINSTAT screen. See the Start-Up/Shutdown/Recycle Se-
quence section, page 44, for more information on this topic.
OCCUPANCY SCHEDULE — The chiller schedule, de-
scribed in the Time Schedule Operation section (page 19),
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 OCCUPIED ? is set to YES on
the MAINSTAT display screen). It cannot be started or run
during an unoccupied time period (when OCCUPIED ? is
set to NO on the MAINSTAT display screen). These time
periods can be set for each day of the week and for holidays.
The day begins with 0000 hours and ends with 2400 hours.
The default setting for OCCUPIED ? is YES, unless an un-
occupied time period is in effect.
These schedules can be set up to follow a building’s oc-
cupancy schedule, or the chiller can be set so to run 100%
of the time, if the operator wishes. 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 44.
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 19.
32
Summary of Contents for HERMETIC CENTRIFUGAL LIQUID CHILLERS 19XR
Page 13: ...Fig 10 Control Panel Fig 11 Power Panel 13 ...
Page 47: ...Fig 25 19XR Leak Test Procedures 47 ...
Page 102: ......
Page 103: ......