Daikin WGZ030DW Installation, Operation And Maintenance Manual page 65

Normal Operation – Staging Up
At startup, the first fan will start when the saturated condenser
temperature rises above the target. After this, the stage up
deadbands apply.
When the saturated condenser temperature is above the Target
+ the active deadband, a Stage Up error is accumulated.
Stage Up Error Step = Saturated Condenser Refrigerant
temperature – (Target + Stage Up dead band)
The Stage Up Error Step is added the Stage Up Accumulator
once every Stage Up Error Delay seconds. When Stage Up
Error Accumulator is greater than the Stage Up Error Set Point
another stage is started.
When a stage up occurs or the saturated condenser
temperature falls back within the Stage Up dead band the
Stage Up Accumulator is reset to zero.
Normal Operation – Staging Down
There are four Stage Down dead bands, one for each stage.
When the saturated condenser refrigerant temperature is
below the condenser saturated temperature target – the active
dead band, a Stage Down error is accumulated.
Stage Down Error Step = (Target – Stage Down dead band) –
Saturated Condenser Refrigerant temperature
The Stage Down Error Step is added to Stage Down
Accumulator once every Stage Down Error Delay seconds.
When the Stage Down Accumulator is greater than the Stage
Down Error Set Point another stage of condenser fans turn off.
The last stage on will not shut off until the circuit is in an off
state.
When stage down occurs or the saturated temperature rises
back within the Stage Down dead band the Stage Down Error
Accumulator is reset to zero.
Forced Fan Stage at Start
Fans may be started simultaneously with the compressor
based on outdoor ambient temperature. When the compressor
starts, and after compressor operation is verified by either a 1
psi drop in evaporator or 1 psi rise in condenser pressures, a
Fantrol stage is forced based on the following table.
OAT
>75°F
>90°F
>105°F
Up to four fans may be forced on when the compressor starts.
After forcing fans on, the saturated condenser temperature
may temporarily stay below the target by some amount. In
order to keep the fans from staging off, no stage down error
can be accumulated until either the OAT drops below 75°F or
the saturated condenser temperature goes above the target.
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Fantrol Stage At Start
Forced Fan 1 SP
Forced Fan 2 SP
Forced Fan 3 SP
65
Unit Controller Operation
Condenser Pump and Tower Control –
Water Cooled
Condenser pump and cooling tower control logic requires that
the unit be configured as water-cooled in order to be active.
Condenser Water Pump State Control
(Cond State)
If the unit is configured as water-cooled, then the state-
transition diagram shown below defines the condenser pump
control logic.
Figure 38: Condenser Pump State Diagram
Pump Selection
The pump output used will be determined by the Cond
Pump Control set point. The setting allows the following
configurations:
#1 only – Pump 1 will always be used.
#2 only – Pump 2 will always be used.
Auto – The primary pump is the one with the least run hours,
the other is used as a backup.
#1 Primary – Pump 1 is used normally, with pump 2 as a
backup.
#2 Primary – Pump 2 is used normally, with pump 1 as a
backup.
IOM 1322 • WATER-COOLED SCROLL COMPRESSOR