www.DaikinApplied.com 59 IOM 1322 • WATER-COOLED SCROLL COMPRESSOR
are moved down in the Event Log and the last entry is dropped
if 25 earlier event occurrences have been logged. Each Event
Log entry includes an event description and a time and date
stamp for the event occurrence.
Controller Operation
Calculations
The Control Band denes the temperatures around the
Controlling Leaving Water Temperature set point where
compressors will be staged on or o. In cool mode, the
controlling leaving water temperature set point will be Evap
LWT. In heat mode, the controlling leaving water temperature
set point will be Heat LWT.
In cooling mode, the Control Band is calculated as follows:
Control Band = Evap Delta Temperature Set Point * 0.3
Four compressor units
Control Band = Evap Delta Temperature Set Point * 0.2
Six compressor units
In heating mode, the Control Band is calculated as follows:
Control Band = Cond Delta Temperature Set Point * 0.3
Four compressor units
Control Band = Cond Delta Temperature Set Point * 0.2
Six compressor units
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 rst 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 denes when the last running
compressor will shutdown. The Shutdown temperature
calculation is:
Shutdown Temperature = Stage Down Temperature –
Shutdown Delta Temperature
If the Unit mode is Heat:
Stage Up temperature is calculated as follows:
Stage Up Temperature = Heat LWT - (Control Band/2)
The Stage Down temperature is calculated as:
Stage Down Temperature = Heat LWT + (Control Band/2)
The Heat Start up and Shutdown temperatures are calculated
from the Control Band. The Start Up temperature determines
when the rst 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 denes 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 eect is determined by the LWT
Reset Type set point.
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.
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