Daikin AWV024 - Operation - Closed State; Superheat Control State; Economizer EXV Control; MOP Control State

IOM 1242-2 • PATHFINDER
®
MODEL AWV CHILLERS 66 www.DaikinApplied.com
CIrCuIT funCTIons
MOP Control State
In MOP (Maximum Operating Pressure) Control, the EXV is
positioned to control the evaporator pressure to a target.
MOP Target
The MOP Target is Min {450, (Cond Pr + 101.325) / 1.7 –
101.325, Cond Pr – 180}.
Superheat Control State
In superheat control, the EXV is positioned to control suction
superheat (SSH) to the SSH Target.
SSH Target
The SSH target varies linearly based on discharge superheat
(DSH). This target is updated every 10 seconds and averaged
over a 100 second period (with sampling every 10 seconds).
Figure 67: Evaporator EXV Suction Superheat Target
When the EXV transitions to the superheat control state, the
target will ramp up or down until it meets the calculated SSH
target.
• If SSH Target Min ≤ current SSH ≤ SSH Target Max, the
target will start at the current SSH value and increase
or decrease by 0.1°C every 10 seconds until it meets
calculated SSH target.
• If current SSH > SSH Target Max, the target value will
start ramping from SSH Target Max. Then the target
will decrease by 0.1°C every 10 seconds until it meets
calculated SSH target.
• If current SSH < SSH Target Min, the target value will
start ramping from SSH Target Min. Then the target
will increase by 0.1°C every 10 seconds until it meets
calculated SSH target.
Economizer EXV Control
The economizer circuit is activated and modulated using an
EXV. This is an optional feature that will only be enabled if
the Economizer Conguration set point is set to Yes. If the
conguration set point is set to No, then the economizer
position should remain 0%.
Control Concept
• EXV will be positioned using control algorithm
• Maintain DSH above requirements for compressor
• Maximize circuit performance at the operating conditions
• Minimize vibration in economizer circuit piping
EXV States
There are three economizer EXV states:
• Closed: EXV is closing or closed
• Purge: EXV is opening to release condensed liquid in a
controlled manner
• Superheat: EXV is controlling economizer gas superheat
Operation – Closed State
The EXV position command should be 0% any time the EXV
is in the closed state. The 0% position command also causes
the EVD driver to reinitialize the valve to the zero position. After
one minute, the EXV position command should be set to 25%
open and remain there until the state changes.
Operation – Purge State
In the Purge state, the economizer EXV position is 0%.
Operation – Superheat Control State
In the Superheat control state, the EXV will be positioned to
control economizer gas superheat.
Liquid Injection Solenoid Valve
As an option, the chiller can be equipped with liquid injection
on the compressors. When congured with this option, the
Liquid Injection Conguration setting should be set to Yes and
the liquid injection solenoid valve outputs can be activated.
Liquid injection solenoid valve output is activated if both of the
following are true:
• Circuit state is Run
• Discharge Temperature > Liquid Injection Activation set
point
Liquid injection solenoid valve output will be turned off if either
of the following are true:
• Discharge Temperature < Liquid Injection Activation set
point - 15°C
• Circuit state is no longer Run
DSH (°C)
DSH Range Max
SSH Target Min
SSH target (°C)
DSH Range Min
SSH Target Max