Daikin McQuay AGZ-D 25, Operating And Maintenance Manual

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OMM 1087-1 AGZ 025D through 190D 27
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 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 mode 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:
Four Compressors:
Demand Limit Signal (%) Demand Limit (mA) Stage Limit
Limit ≥ 75% Limit ≥ 16 mA
1
75% > Limit ≥ 50% 16 mA > Limit ≥ 12 mA
2
50% > Limit ≥ 25%
12 mA > Li
mit ≥ 8 mA
3
25% > Limit 8 mA > Limit 4