Unit Capacity Control; Leaving Water Temperature (Lwt) Reset/Target - Daikin AGZ 025D Operating & Maintenance Manual

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Leaving Water Temperature (LWT) Reset
The base LWT target may be reset if the unit is in Cool mode and LWT reset is enabled via the set
point.
The reset amount is adjusted based on the 4 to 20 mA reset input. Reset is 0° if the reset signal is less
than or equal to 4 mA. Reset is 5.56°C (10.0°F) 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.
When the reset amount increases, the Active LWT Target is changed at a rate of 0.1°C every 10
seconds. When the active reset decreases, the Active LWT Target is changed all at once.
After the reset is applied, the LWT target can never exceed a value of 15.56°C (60°F).

Unit Capacity Control

Unit capacity control will be performed as described in this section. All unit capacity limits described in
following sections must be applied as described.
Compressor Staging in Cool Mode
The first compressor on the unit should be started when evaporator LWT is higher than the Startup
Temperature.
Additional compressors can be started when Evaporator LWT is higher than the Stage Up Temperature and
the Stage Up Delay is not active.
When multiple compressors are running, one should shut down if evaporator LWT is lower than the Stage
Down Temperature and the Stage Down Delay is not active.
All running compressors should shut down when the evaporator LWT is lower than the Shut Down
Temperature.
Stage Up Delay
A minimum amount of time, defined by the Stage Up Delay set point, should pass between increases in the
capacity stage. This delay should only apply when at least one compressor is running. If the first compressor
starts and quickly shuts off for some reason, another compressor may start without this minimum time
passing.
Stage Down Delay
A minimum amount of time, defined by the Stage Down Delay set point, should pass between decreases in
the capacity stage. This delay should not apply when the LWT drops below the Shut Down Temperature
(unit should immediately shut down).
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OFF
ON
COOL
ICE
AGZ 025D through 190D
COOL/ICE Cool Set Point 1
w/Glycol
COOL/ICE Ice Set Point
w/Glycol
COOL/ICE BAS Cool Set Point
w/Glycol
COOL/ICE BAS Ice Set Point
w/Glycol
ICE w/Glycol Ice Set Point
ICE w/Glycol BAS Ice Set Point
OMM 1166-1