Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual page 34

The TARGET VFD SPEED, ACTUAL VFD SPEED and
the VFD GAIN can be viewed and modified in the CAPA-
CITY display screen. The TARGET VFD SPEED can be
manually overridden by the operator from the COMPRESS
screen. The VFD MINIMUM SPEED, VFD MAXIMUM
SPEED, VFD GAIN and VFD INCREASE STEP can be
selected and modified in the SETUP display screen.
TARGET and ACTUAL VFD SPEED can be viewed in
the COMPRESS screen.
5.1.2 - eCW control option
If this option is enabled, the PIC III 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 EQUIP-
MENT SERVICE screen.
5.1.3 - 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 III
opens or closes the guide vanes until the temperature is
within tolerance. The PIC III may be configured with a 0.3
to 1.1 K deadband. CHILLED WATER DEADBAND
may be viewed or modified on the SETUP1 screen, which
is accessed from the EQUIPMENT SERVICE table.
For example, a 0.6 K deadband setting controls the water
temperature within 0.3 K of the control point. This may cause
frequent guide vane movement if the chilled water load
fluctuates frequently. A value of 0.6 K is the default setting.
5.1.4 - Diffuser control
On all units with Frame 5 compressors and those Frame 4
compressors with the variable (split ring) diffuser option,
the PIC III adjusts the diffuser actuator position (DIFFU-
SER ACTUATOR on the COMPRESS screen) based on
the ACTUAL GUIDE VANE POSITION. This is done in
accordance with a compressor build-specific "schedule"
entered in the SETUP screen. The schedule consists of
guide vane and diffuser positions for three points (designated
as the 5%, 50%, and 75% Load Points). In order for the
schedule to be valid, the guide vane values must be ascending
and the diffuser values must be descending for the three
points. Diffuser actuator output is controlled by a 4 to 0 mA
output from CCM terminals J8-3(+) and J8-4(–). Fig. 10
shows the relationship between diffuser-related parameters
for a typical build.
Diffuser control output is enabled whenever the DIFFUSER
OPTION is enabled, whether the machine is running or
not. As shown in Fig. 10, 0% output corresponds to a full
open diffuser. The minimum closed position (5% Load
Point value) will be at less than 100% for most diffusers
(depending upon the model). This coordinated guide vane-
diffuser operation may be tested in the Control Test selec-
tion "IGV & SRD Actuator." Note that the diffuser actuator
should NOT be forced to a greater percent than the con-
figured 5% Load Point (maximum) value. The diffuser
opening can be incremented from fully open to completely
closed. A 0% setting is fully open; a 100% setting is com-
pletely closed. To obtain the proper settings for Diffuser
Control, contact a Carrier Engineering representative.
34
Fig. 10 - Diffuser Control
2 mA (0%)
4 mA (0.2%)
Fully open
Surge more likely
Rotating stall
less likely
Fully closed
25% load point
approx. 4 mA*
(100%)
0 %
* Diffuser full span mA
5.1.5 - proportional bands and gain
Proportional band is the rate at which capacity control
(including guide vane position and, if applicable, VFD
speed) is adjusted in proportion to how far the chilled
water/brine temperature is from the CONTROL POINT.
Proportional gain determines how quickly capacity control
reacts to how quickly the temperature is moving from the
CONTROL POINT. The proportional bands and gain may
be viewed or modified from the SETUP 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 capacity control response to chilled water/brine
temperatures above the CHILLED WATER DEADBAND.
The PROPORTIONAL INC BAND can be adjusted from
a setting of  to 10; the default setting is 6.5.
The response below the control point is called the PROPOR-
TIONAL DEC BAND, and it can slow or quicken the
capacity control response to chilled water temperature
below the deadband plus the control point. The PROPOR-
TIONAL DEC BAND can be adjusted on the ICVC from
a setting of  to 10. The default setting is 6.0.
NOTE: Increasing either of these settings causes the
capacity control to respond more slowly than at a lower
setting.
The PROPORTIONAL ECW GAIN can be adjusted on
the ICVC display for values of 1, , or 3; the default setting
is . Increase this setting to increase guide vane response
to a change in entering chilled water temperature.
75% load point
Surge less likely
50% load point
50 %
78 %
Guide vane opening (%)