Daikin AGZ065E - Page 80

IOM 1206-7 • TRAILBLAZER
™
MODEL AGZ CHILLERS 78 www.DaikinApplied.com
CIrCUIT fUnCTIons
Position Commands
In order to improve the reliability of the EXV positioning, the
position commands that are issued to the stepper driver are
limited in two ways:
1. Position commands are ltered so that the minimum change
in position is 0.3%. Changes of less than this are ignored. This
avoids unnecessary movement of the EXV and lowers the
chances of losing steps as a result.
2. The position commands are issued once per program cycle
with a maximum change of 0.7% each time. This allows the
stepper to move the valve to the commanded position before
the next position command is issued. Issuing commands in this
way may also lower the chances of losing steps.
EXV Position Range
The minimum EXV position while the circuit is running will
always be 8%. The maximum position will change as the
number of compressors running on the circuit changes. These
values are shown for each unit model in Table 78.
Table 78: Maximum Position Range
Model
# Compressors Running/Circuit
1 2 3
AGZ030E 50 100 n/a
AGZ035E 50 100 n/a
AGZ040E 50 100 n/a
AGZ045E 50 100 n/a
AGZ050E 50 100 n/a
AGZ055E 50 100 n/a
AGZ060E 50 100 n/a
AGZ065E 50 100 n/a
AGZ070E 50 100 n/a
AGZ075E 60 100 n/a
AGZ080E 60 100 n/a
AGZ090E 60 100 n/a
AGZ100E 60 100 n/a
AGZ110E 50 80 n/a
AGZ120E 50 80 n/a
AGZ130E 50 80 n/a
AGZ140E 70 100 n/a
AGZ150E 70 100 n/a
AGZ161E 80 100 n/a
AGZ170E 60 80 100
AGZ180E 60 80 100
AGZ190E 60 80 100
AGZ210E 60 80 100
AGZ225E 60 80 100
AGZ240E 60 80 100
Operation Considerations
For units equipped with shell and tube evaporators, when
staging down a compressor the maximum position is reduced
by 10% for one minute to prevent liquid refrigerant from
getting to the compressors. After this initial one minute delay,
the maximum valve position is allowed to return to its normal
value at a rate of 0.1% every six seconds. This offset to the
manximum position should not occur if the stage down is due
to a low pressure unload.
For all units - the expansion valve maximum position may
be increased if both the suction superheat is higher than the
target and the expansion valve has been within 1% of its
current maximum position for a minute. The maximum should
increase at a rate of 0.1% every six seconds up to a total of an
additional 10%. This addition to the maximum position should
be reset when the EXV is no longer in the Superheat Control
state, or a compressor on the circuit stages.
Manual Control
The EXV position can be set manually. Manual control can only
be selected when the circuit is in the run state. At any other
time, the EXV control set point is forced to auto.
When EXV control is set to manual, the EXV position is equal
to the manual EXV position setting. If set to manual when the
circuit state transitions from run to another state, the control
setting is automatically set back to auto. When in manual
control, the EXV control state displayed will be ‘Manual’.
Liquid Line Solenoid Valve
The liquid line solenoid output should be on when the circuit
state is either Pre-open or Run. This output should be off at all
other times.
Hot Gas Bypass Solenoid Valve
This output will be on when circuit state is Run for at least
30 seconds and one compressor on the unit is running. The
output should be off at all other times unless the unit is a model
190-240. For these models, the hot gas bypass will also be
activated for 10 minutes when a second or third compressor is
started on the circuit.
Capacity Overrides – Limits of
Operation
The following conditions shall override automatic capacity
control as described. These overrides keep the circuit from
entering a condition in which it is not designed to run.
Low Evaporator Pressure
If the Low Evaporator Pressure Hold or Low Evaporator
Pressure Unload alarms are triggered, the circuit capacity
may be limited or reduced. See the Circuit Events section for
details on triggering, reset, and actions taken.
High Condenser Pressure
If the High Condenser Pressure Unload alarm is triggered,
the circuit capacity may be limited or reduced. See the Circuit
Events section for details on triggering, reset, and actions
taken.