Daikin Pathfinder AWV Installation, Operation And Maintenance Manual page 59

Staging Circuits Off
Unit capacity control will command a single circuit to shut down
if both circuits are running and any of the following are true:
• LWT error < - (Stage Down Delta T set point)
• LWT error < Stage Up Delta T set point, both circuits
speed < Light Load Stage Down set point, and neither
circuit has an active capacity hold event
• A unit capacity limit is active, both circuits capacity < Light
Load Stage Down set point, and neither circuit has an
active capacity hold event
• Max Number Circuit Running set point changes to 1
If one circuit is running the capacity control logic will command
it to shut down if the following conditions are true for 15
minutes:
• Compressor running at 14 Hz
• LWT Error < -0.4°C
Unit capacity control will command all circuits to shut down if
LWT Error < - (Shut Down Delta T set point).
Circuit Capacity Change Commands
Load commands are issued when the following are true:
• LWT Error > Load Deadband
• Time > Load Delay has passed since the last unit
capacity increase
• EWT Pulldown Rate Hold is not active
Unload commands are issued when:
• Either LWT Error < - (Unload Deadband), or EWT
Pulldown Rate Unload is active
• Time > Load Delay has passed since the last unit
capacity decrease
Load Balancing
In Cool Mode, capacity of the circuits is controlled so that when
possible their capacities are balanced. Circuits will generally
maintain a capacity imbalance that does not exceed 15%.
If a capacity change has not occurred for at least one minute
and the difference in capacity between the two running circuits
is more than 15%, then the circuit capacities will be adjusted.
The circuit at the lower capacity will load and the circuit at the
higher capacity will unload simultaneously.
If either circuit is running in manual capacity control or running
with active capacity limiting events, then no load balancing
adjustments will be made.
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Ice Mode Operation
In Ice Mode, running circuits will load up simultaneously at the
maximum possible rate that allows for stable operation of the
individual circuits.
Staging Of Circuits
Both circuits should start when LWT error is greater than the
Startup Delta T set point and the Max Circuits Running set
point is set to 2. If only one circuit can start, the other circuit
should start as soon as possible after the stage up delay has
expired.
Both circuits should be staged off when LWT error is 0 or less.
Unit Capacity Limits
Unit capacity limits are used to limit total unit capacity in Cool
Mode only. Multiple limits may be active at any time, and the
lowest limit is always used in the unit capacity control.
Soft load, demand limit, and network limit use a deadband
around the actual limit value, such that unit capacity increase
is not allowed within this deadband. If unit capacity is above
the deadband, capacity is decreased until it is back within the
deadband, which is 8%.
The unit capacity will be adjusted as needed via circuit staging
and capacity changes to meet the lowest active limit, but the
last running compressor cannot be turned off to meet a limit
lower than the minimum unit capacity.
Demand Limit
The maximum unit capacity can be limited by a 4-20 mA signal
on the Demand Limit analog input at the unit controller. This
function is only enabled if the Demand Limit set point is set to
ON.
As the signal varies from 4 mA up to 20 mA, the maximum unit
capacity changes from 100% to 0%.
Network Limit
The maximum unit capacity can be limited by a network
command. This function is only enabled if the unit control
source is set to Network. The signal will be received through
the BAS interface on the unit controller.
This network limit command directly sets a maximum unit
capacity from 0% to 100%.
59 IOM 1242-8 • PATHFINDER
Unit Functions
MODEL AWV CHILLERS
®