Ecw Control Option; Control Point Deadband; Proportional Bands - Carrier AquaEdge 19XR series Start-Up, Operation And Maintenance Instructions Manual

Constant Flow Surge Prevention
Normal Capacity Control Mode occurs when ACTIVE
DELTA T> SURGE LINE DELTA T.
Surge Prevention Mode Level 1 occurs when ACTIVE
DELTA T  SURGE LINE DELTA T.
Surge Prevention Mode Level 2 occurs when ACTIVE
DELTA T + 1  SURGE LINE DELTA T.
Variable Primary Flow Surge Prevention
Normal Capacity Control Mode occurs when ACTIVE
DELTA TSAT> SURGE LINE DELTA TSAT.
Surge Prevention Mode Level 1 occurs when ACTIVE
DELTA TSAT  SURGE LINE DELTA TSAT.
Surge Prevention Mode Level 2 occurs when ACTIVE
DELTA TSAT + 1  SURGE LINE DELTA TSAT.
The VFD GAIN parameter allows for additional adjustment
of the VFD response. Increasing VFD GAIN will increase the
rate of speed change.
For chillers equipped with VFDs there is an additional over-
current feature which is similar to Demand Limit Control. The
ICVC computes a projected value for motor current (VFD out-
put current, which is not measured by the ISM). The computed
value is based on AVERAGE LINE CURRENT and TARGET
VFD SPEED. The control then compares it to VFD CURRENT
LIMIT. VFD CURRENT LIMIT is a configurable entry in the
SETUP2 screen, representing VFD output current when the
line side current equals RATED LOAD AMPS and VFD
SPEED is at its maximum. The VFD Control Configuration
Job sheet includes the recommended value for VFD CUR-
RENT LIMIT, and that value may be further adjusted as de-
scribed under the VFD Control Verification section. (See
page 78.)
If VFD LOAD FACTOR (the ratio of estimated VFD output
current to VFD CURRENT LIMIT) exceeds 0.98, then drive
speed is increased until VFD LOAD FACTOR goes below 0.96,
or until maximum speed is reached. If VFD LOAD FACTOR
exceeds 1.02 then the GUIDE VANE POSITION is made to de-
crease as well. This action ceases when the VFD LOAD FAC-
TOR subsequently drops below 1.0. VFD LOAD FACTOR is
displayed in the CONTROL ALGORITHM STATUS / CA-
PACITY screen.
NOTE: Increasing motor speed reduces motor amp draw. This
is the current between the VFD and the motor, NOT line cur-
rent. Generally for the case of LINE VOLTAGE equaling motor
voltage (460 volts), VFD output (motor) current is a few per-
cent higher than line current at full speed (60 Hz). As drive
speeds decrease from maximum, drive output voltage
decreases linearly with output frequency, and motor current
continues to increase relative to line current.
Table 5 — Guide Vane Delta Modes
NORMAL
CONTROL
GUIDE VANE
MODE
DELTA
IGV
POSITION
From +0.2 to Increase
+2.0 1st
Decrease
From –0.2 to when VFD
–2.0 speed =
min
The TARGET VFD SPEED, ACTUAL VFD SPEED and the
VFD GAIN can be viewed and modified in the CAPACITY
display screen. The TARGET VFD SPEED can be manually
overridden by the operator from the COMPRESS screen. The
VFD MINIMUM SPEED, MAXIMUM SPEED, VFD GAIN
SURGE
PREVENTION
MODE
VFD IGV VFD
SPEED POSITION SPEED
Increase
only if VFD
speed =
Increase
max and if Increase
when IGV
hot gas 1st
= max
bypass is
present
and open
Speed
Decrease decrease
Decrease
1st not
allowed
and VFD INCREASE STEP can be viewed and modified in the
SETUP2 display screen. TARGET and ACTUAL VFD SPEED
can be viewed in the COMPRESS 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 until
the temperature is within tolerance. The PIC II may be config-
ured with a 0.5 to 2 F (0.3 to 1.1 C) deadband. CHILLED
WATER DEADBAND may be viewed or modified on the SET-
UP1 screen, which is accessed from the EQUIPMENT SER-
VICE 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.
A deadband is a span of measurement in which a controller
takes no action. In the PIC controls it is a temperature range
centered on the CONTROL POINT. If the LEAVING
CHILLED WATER TEMP falls within the CHILLED WATER
DEADBAND, the guide vanes will not move.
The purpose of the deadband is to prevent slight fluctua-
tions in ENTERING CHILLED WATER TEMPERATURE
from keeping the guide vanes in constant movement.
Adjusting The Deadband — The default setting of the
CHILLED WATER DEADBAND, is 1°F, which is 0.5° F above
and below the CONTROL POINT. The CONTROL POINT set-
ting range is 0.5 to 2° F. If temperature control is satisfactory
and the guide vanes are stable, do not change the setting.
When very close temperature control is required, as for
some process applications, the deadband may be reduced.
When constant small load changes occur in a system and
the vanes will not stabilize, increase the size of the deadband.
The deadband must always be smaller than the allowable drift
in leaving water temperature.
PROPORTIONAL BANDS — The proportional bands con-
trol how far the guide vanes will move in response to a specific
change in leaving water temperature. Increasing the propor-
tional band increases the amount that the water temperature
must move away from the control point in order to move the
guide vanes a specific amount. Decreasing the proportional
band allows the vanes to move the same amount with a smaller
change in water temperature.
If the proportional band is too large, the leaving water tem-
perature will increase or decrease slowly enough that the tem-
perature moves away from the control point by an unaccept-
able amount. A proportional band set too low will cause the
leaving temperature to overshoot the control point and cause
the guide vanes to "hunt."
The PIC controls have separate proportional bands for in-
creasing and decreasing capacity. The PROPORTIONIONAL
INCREASE BAND should be set as described above. The PRO-
PORTIONIONAL DECREASE BAND should be set at a typi-
cally smaller value than the increasing band so that the guide
vanes can close quickly enough on a sudden drop in load to
prevent a low temperature safety trip.
Proportional Entering Chilled Water Gain — When Entering
Chilled Water Control is enabled the controls are resetting the
Leaving Chilled Water (LCW) control point every 10 seconds
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