Daikin WGZ030DW Installation, Operation And Maintenance Manual page 39

If the Unit mode is Cool:
When the Cool Leaving Water Temperature set point is more
than half the Control Band above 39.0° F the Stage Up
temperature is calculated as follows:
Stage Up Temperature = Cool LWT + (Control Band/2)
The Stage Down temperature is calculated as:
Stage Down Temperature = Cool LWT – (Control Band/2)
If the Cool Leaving Water Temperature set point is less
than half the Control Band above 39.0° F the Stage Down
temperature is calculated as:
Stage Down Temperature = Cool LWT – (Cool LWT - 39.0° F)
Stage Up temperature is calculated as:
Stage Up temperature = Cool LWT + Control Band – (Cool
LWT – 39.0°F)
In all other Unit modes the compressor staging temperatures
are calculated as shown below:
Stage Up Temperature = Cool LWT + (Control Band/2)
Stage Down Temperature = Cool LWT – (Control Band/2)
The Cool Start up and Shutdown temperatures are calculated
from the Control Band. The Start Up temperature determines
when the first compressor on the unit will start. The Start Up
temperature calculation is shown below:
Start Up Temperature = Stage Up Temperature + Start Up
Delta Temperature
The Shutdown temperature defines when the last running
compressor will shutdown. The Shutdown temperature
calculation is:
Shutdown Temperature = Stage Down Temperature –
Shutdown Delta Temperature
Leaving Water Temperature (LWT) Reset
The active leaving water set point is set to the current Leaving
Water Temperature (LWT) set point unless the unit is in either
cool or heat mode and any of the reset methods below are
selected. The type of reset in effect is determined by the LWT
Reset Type set point.
Reset Type = NONE
The Active Leaving Water Temperature set point is set equal to
the current LWT set point. IN cool mode, this will be Evap LWT
and in heat mode this will be Heat LWT.
Reset Type = 4-20 mA
The Active Leaving Water set point is adjusted by the 4 to 20
mA reset analog input.
Cooling Mode
The Active Leaving Water set point is adjusted by the 4 to 20
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mA reset analog input.
Parameters used:
1. Evaporator Leaving Water Temperature set point (Evap
LWT)
2. Cooling Maximum Reset set point (Clg MaxRes)
3. LWT Reset signal 4-20 mA
Reset is 0ºF and the active leaving water set point is equal to
the Evap LWT set point if the reset signal is less than or equal
to 4 mA. Reset is equal to the Max Reset set point and the
active leaving water set point is equal to the Evap LWT plus
Max Reset set points if the reset signal equals or exceeds 20
mA. The amount of reset will vary linearly between these
extremes if the reset signal is between 4 mA and 20 mA. An
example of the operation of 4-20 reset in Cool mode is shown
below.
Active LWT Set Point
The active LWT set point represents the current control set
point based on unit mode and reset. If unit mode is ice, then
the active set point is equal to the ice set point. If the unit mode
is cool, the active set point is the cool set point plus the leaving
water reset value. If the unit mode is heat, the active set point
is the heat set point minus the leaving water reset value.
LWT Error
LWT error compares the actual LWT to the active LWT set
point.
The equation for cool mode is:
LWT error = LWT – active LWT set point
The equation for heat mode is:
LWT error = active LWT set point – LWT
LWT Slope
LWT slope is calculated such that the slope represents a time
frame of one minute.
Every 12 seconds, the current LWT is subtracted from the
value 12 seconds back. This value is added to a buffer
containing values calculated at the last five intervals. The final
result is a slope value that is an average over the past 60
seconds.
39 IOM 1322-1 • WATER-COOLED SCROLL COMPRESSOR
Unit Controller