Unit Capacity Control; Maximum Circuits Running; Cool Mode Operation; Staging Sequence - Daikin Pathfinder AWV Series Installation, Operation And Maintenance Manual

Unit Capacity Control

Unit capacity control will be performed as described in this
section. A combination of starting/stopping compressors and
loading/unloading compressors is used to control the overall
unit capacity.

Maximum Circuits Running

If the number of compressors running is equal to the Max
Circuits Running set point, no additional compressors should
be started. This applies in both Cool Mode and Ice Mode
operation.
When both circuits are running and the Max Circuits Running
set point is changed to one, a circuit should shut down.

Cool Mode Operation

In Cool Mode, unit capacity is adjusted via circuit staging
and capacity changes on each circuit. LWT error and
EWT pulldown rate are the primary factors in unit capacity
adjustments. This section details all the logic for unit capacity
control in Cool Mode.

Staging Sequence

This section defines which circuit is the next one to start or
stop if the logic does not call for simultaneous start or stop of
both circuits. In general, circuits with fewer starts will normally
start first, and circuits with more run hours will normally stop
first. Staging sequence can also be determined by an operator
defined sequence via set points.
The next circuit to start must meet the following requirements:
Lowest sequence number of those circuits available to start
• if sequence numbers are equal, it must have the least
starts
• if starts are equal, it must have least run hours
• if run hours are equal, it must be the lowest numbered
circuit
The next circuit to shut down must meet the following
requirements:
Lowest sequence number of the circuits that are running
• if sequence numbers are equal, it must have the most run
hours
• if run hours are equal, it must have the least starts
• if starts are equal, it must be the lowest numbered circuit
Load/Unload Sequence
This section defines which circuit is the next one to load or
unload if the logic does not call for simultaneous load or unload
of both circuits.
The next circuit to load must meet the following requirements:
Lowest capacity of the running circuits
• if capacities are equal, it must have the lowest sequence
number of the circuits that are running
• if the sequence numbers are equal, it must have the least
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starts
• if starts are equal, it must have the least run hours
• if run hours are equal, it must be the lowest numbered
circuit
The next compressor to unload must meet the following
requirements:
Highest capacity of the running compressors
• if capacities are equal, it must have the lowest sequence
number of the compressors that are running
• if sequence numbers are equal, it must have the most run
hours
• if run hours are equal, it must have the least starts
• if starts are equal, it must be the lowest numbered
compressor
Stage Up Delay
Any time the number of running circuits changes, the stage up
delay will start and run for a time equivalent to the Stage Up
Delay set point.
Any time there are no circuits running, the stage up delay will
be cleared.
For the purpose of this section, a "running" circuit is a circuit in
the Preopen, Start, or Run state.
Staging Circuits On
Unit capacity control will command at least one circuit to start if
all of the following are true:
• Unit State = Auto
• Evaporator Pump State = Run
• LWT error > Startup Delta T set point
• Pulldown Hold is not active
Both circuits are able to start at the same time if the following
conditions are true (in addition to the above conditions):
• Demand limit > 40% if Demand Limit = Enable
• Network limit set point > 40% if Control Source = Network
If one circuit is running, unit capacity control will command the
second circuit to start if all of the following are true:
• One circuit running at full capacity (see circuit details for
determination of full capacity)
• Stage Up Delay has completed
• LWT Error > Stage Up Delta T set point
• Capacity Increase command is active
• Max Number Circuits Running set point = 2
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