Unit Capacity Control; Unit Capacity Overrides; Demand Limit - Daikin AGZ030E Installation, Operation And Maintenance Manual

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).
Compressor Staging in Ice Mode
The first compressor on the unit should be started when
evaporator LWT is higher than the Startup Temperature.
All compressors should be operationg except during startup
or shut down. Additional compressors should be started as
quickly as possible with respect to the Stage Up Delay.
The unit should shut down when evaporator LWT is less than
the LWT target.
Stage Up Delay
A fixed stage up delay of one minute between compressor
starts should be used in this mode.
Staging Sequence
This section defines which compressor is the next one to
start or stop. In general, compressors with fewer starts will
normally start first, and compressors with more run hours will
normally stop first.
If possible circuits will be balanced in stage. If a circuit is
unavailable for any reason, the other circuit shall be allowed
to stage all compressors on. When staging down, one
IOM 1206-7 • TRAILBLAZER MODEL AGZ CHILLERS
™
compressor on each circuit shall be left on until each circuit has
only one compressor running.
Next To Start
If both circuits have an equal number of compressors running
or a circuit has no compressors available to start:
• the available compressor with the least starts will be next
to start
• if starts are equal, the one with the least run hours will be
next to start
• if run hours are equal, the lowest numbered one will be
next to start
If the circuits have an unequal number of compressors running,
the next compressor to start will be on the circuit with the least
compressors running if it has at least one compressor available
to start. Within that circuit:
• the available compressor with the least starts will be next
to start
• if starts are equal, the one with the least run hours will be
next to start
• if run hours are equal, the lowest numbered one will be
next to start
Next to Stop
If both circuits have an equal number of compressors running:
• the running compressor with the most run hours will be
next to stop
• if run hours are equal, the one with the least starts will be
next to stop
• if starts are equal, the lowest numbered one will be next
to stop
If the circuits have an unequal number of compressors running,
the next compressor to stop will be on the circuit with the most
compressors running. Within that circuit:
• the running compressor with the most run hours will be
next to stop
• if run hours are equal, the one with the least starts will be
next to stop
• if starts are equal, the lowest numbered one will be next
to stop

Unit Capacity Overrides

Unit capacity limits can be used to limit total unit capacity in
Cool or Cool with Glycol modes only. Multiple limits may be
active at any time, and the lowest limit is always used in the
unit capacity control.

Demand Limit

The maximum unit capacity can be limited by a 4 to 20 mA
signal on the Demand Limit analog input. This function is
only enabled if the Demand Limit set point is set to ON. The
maximum unit capacity stage is determined as shown in the
following tables:
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