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can be monitored for increasing load. The recycle control uses
Recycle Startup Offset to check when the compressor should
be restarted. In cooling mode, the compressor will restart when
the leaving chilled water temperature (or entering chilled water
temperature, if the EWT CONTROL OPTION is enabled) is
greater than the CONTROL POINT plus the Recycle Startup
Offset (default 5°F [2.8°C]) for 5 consecutive seconds.
CONTROL POINT TEMPERATURE
Capacity control is based on achieving and maintaining a control
point temperature, which is the sum of a valid set point (from the
SETPOINT screen) and a temperature reset value. The control
point temperature is equal to the set point plus temperature reset.
The control point can be viewed directly on the main screen in the
bottom left corner.
TEMPERATURE RESET
Three types of chilled water or brine reset are available and can be
enabled and modified on the Reset Configuration screen (Fig. 35).
Fig. 35 — Reset Configuration Screen
The default screen indicates when the chilled water reset is active.
The control point Reset on the General Parameters screen indi-
cates the amount of reset.
To activate a reset type, access the Reset Configuration
(RESETCFG) screen in the Configuration menu and input
all configuration information for that reset type.
Reset Type 1: 4 to 20 mA Temperature Reset
Reset Type 1 is an automatic reset utilizing a 4 to 20 mA analog
input signal provided from any external sensor, controller, or
other device which is appropriately configured. For this type,
Degrees Reset At 20 mA is configured in the RESETCFG table.
Reset Type 2: Remote Temperature Reset
Reset Type 2 is an automatic water temperature reset based on a
remote temperature sensor input signal. This function can be ac-
cessed by setting the following configurations:
1. Configure the remote temperature at which no reset occurs
(Remote Temp No Reset).
2. Configure the remote temperature at which full reset
occurs (Remote Temp Full Reset).
3. Enter the amount of reset (Deg Reset Water DT Full).
Reset Type 3: Controlled Water Temp Delta Reset
Reset Type 3 is an automatic controlled water temperature reset
based on chilled water temperature difference. This function can
be accessed by setting the following configurations:
1. Configure the controlled water temperature delta T at which
no reset occurs (Controlled DT No Reset).
2. Configure the controlled water temperature delta T at
which full reset occurs (Controlled DT No Reset).
3. Enter the amount of reset (Deg Reset Water DT Full).
CAPACITY CONTROL
From the compressor relay closed point to the end of ramp load-
ing, the VFD TARGET SPEED is the configured Motor Start
Speed. When the chiller is running normally, the capacity control
determines whether and how much to change VFD TARGET
SPEED. When the chiller is in the shut-down process, VFD TAR-
GET SPEED will be the minimum VFD speed.
RAMP LOADING
The ramp loading control slows the rate at which the compressor
loads up. This control can prevent the compressor from loading up
during the short period of time when the chiller is started and the
chilled water loop has to be brought down to CONTROL POINT.
Ramp loading helps reduce electrical demand charges by slowly
bringing the chilled water to CONTROL POINT.
Two methods of ramp loading are available: temperature ramp
loading and motor load ramp loading.
Temperature Ramp Loading
Temperature ramp loading limits the rate at which the controlled
water temperature decreases. The temperature ramp loading con-
figuration point is located in the General Configuration menu. It
is enabled by setting the Ramp Loading Type to "0 = Temp".
Motor Load Ramp Loading
Motor load ramp loading limits the rate at which either the load
current percentage or motor kilowatt percentage increases by in-
crementing the ramp demand limit at the configured rate. The
Ramp Loading type can be set for either 1=Amps or 2=KW in the
General Configuration Menu. The appropriate Ramp Rate per
minute for either Amps or KW will also need to be configured in
this menu.
HGBP CONTROL
This function is used to artificially load the chiller and keep it
running under low load conditions. Since this also reduces the
performance of the machine, HGBP Control is a user-select-
able option (Configuration MenuCir C Config Menu
Hot
Gas A Config). HGBP Control Option has to be enabled in
Factory Settings to become visible. See Fig. 36.
Fig. 36 — Hot Gas A Configuration Menu
The HGBP control valve is an on/off type solenoid control valve.
The 23XRV hot gas bypass operation has two different modes
when installed and enabled:
• Envelope (HGBP) low load operation. In this condition, the
valve will be opened to prevent a recycle shutdown from
occurring. The valve will open when the evaporator fluid
temp falls below the Control Point by Fluid Temp Offset.
The valve will close once the fluid temp rises above the
Control Point by the Fluid Temp Deadband.
• Low load operation controlled by compressor speed. This
HGBP control mode is the typical 23XRV setting. It acti-
vates the HGBP valve when the compressor speed falls be-
low the HGBP Enable Below Speed. This value is typically
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