Daikin Navigator WWV Installation, Operation And Maintenance Manual page 34

Manual VR Control
VR can be controlled manually using settings on the variable
VR screen. VR control can be changed to Manual only when
the circuit state is Run. When VR Control is set to Manual,
the VR can be selected with choices of 1.6, 1.8, 2.4, 3.1. The
solenoid valve outputs will be set according to the table in the
previous section on automatic control. However, there will not
be any time delays or special operation for staging the VR
down as in automatic control.
Evaporator EXV Control
The Evaporator EXV is installed in the liquid line feeding the
evaporator and the chiller controls use specific logic to se the
position.
EXV will normally be positioned to control suction superheat
(SSH) with a PI loop. In some conditions, the evap EXV will
be positioned to control evaporator pressure to keep the
compressor within its operating envelope.
EXV States
The control of the EXV follows a sequence of states. The
transitions from one state to another is based on the running
conditions of the circuit. The states are as follows:
• Closed –EXV fully closed.
• Startup – The pressure target ramps up to bring the liquid
level up in the evaporator.
• Superheat – EXV controls to a calculated pressure target
in order to maintain evaporator liquid refrigerant level at
an optimal level.
Oil Return Solenoid Valve
The oil return solenoid valve output should be on whenever the
compressor is being commanded to run. This output activates
the oil return solenoid valve as well as the jet pump solenoid
valve.
IOM 1264-1 • NAVIGATOR
®
MODEL WWV CHILLERS
Circuit Capacity Overrides
The following conditions override automatic capacity control
as described. These overrides keep the circuit from entering a
condition in which it is not designed to run.
High Water Temperature Capacity Limit
If the evaporator LWT reaches 25°C (77°F) or higher, then high
evaporator loop temperature capacity limits will be in effect.
When high evaporator loop temperature capacity limits are
in effect and the capacity is 80% or higher, the circuit will not
increase in capacity.
When high evaporator loop temperature capacity limits are in
effect and the capacity is higher than 85%, the circuit capacity
will be reduced until it is at 85% or less.
High evaporator loop temperature capacity limits will no longer
be in effect when evaporator LWT is less than 25°C (77°F) for
at least a minute.
Low Discharge Superheat Capacity Limit
If DSH < Minimum DSH set point, unit mode is Cool, and the
compressor speed = 35 Hz, the compressor will not be allowed
to increase speed.
If DSH < Minimum DSH set point, unit mode is Cool, and the
compressor speed > 35 Hz the compressor speed will be
reduced until it is at 35 Hz or lower.
The above limits will no longer be in effect when DSH ≥
Minimum DSH set point for at least a minute or the unit mode
is no longer Cool.
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IrCuIT unCTIons
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