Exv Control - Daikin AGZ030E Installation, Operation And Maintenance Manual

Once the condenser saturated temperature starts to exceed
that value, the fans will speed up beyond the speed limit as
needed to control the saturated temperature to that value.
High IPLV Mode
When the High IPLV Mode setting is 'On' and one compressor
is running on the unit, the condenser target setting for the
running circuit may be overridden. In this case, rather than use
the condenser target setting for 33% or 50% (depending on
number of compressors), the condenser target will be forced to
the value of the IPLV Condenser Target set point.
In addition, when high IPLV mode is active the calculation for
the minimum allowed condenser target (based on LWT) will
be changed. The minimum value will be changed from 23.9°C
(75°F) to the value of the IPLV Condenser Target set point.
No other changes to the operation are made when High IPLV
mode is on.
Additional Conditions For Microchannel
Coils
For units configured with microchannel condenser coils, the
fan staging is the same as for a tube and fin coil except there
are additional conditions which may cause the fan stage to
increase:
• If circuit has two compressors, the second compressor
on a circuit starts, the circuit is not already at the
maximum condenser stage, and the condenser saturated
temperature is higher than 37.78°C (100°F), then a
condenser stage will be added immediately.
• If the condenser stage is not already at the maximum,
the saturated condenser temperature exceeds 56.67°C
(134°F), it has been at least 5 seconds since adding
a condenser stage, and the saturated condenser
temperature is not dropping, then a condenser stage will
be added immediately.
In addition, if the circuit has 4 fans, or it has 6 fans and no
fan VFD's, then the first condenser stage may be skipped at
startup. This happens if the OAT is at least 21.11°C (70°F)
when the first condenser stage would normally be started, in
which case it will go directly to the second stage.
If the circuit has two fan VFDs and OAT is at least 10°C (50°F)
when the first condenser stage would normally be started.
Both of these additions are in place to deal with spikes in
condenser pressure resulting from the lower volume of the
microchannel coils.
Limiting Last Stage
For E vintage models with either 5 or 7 fans per circuit and two
fan VFD's per circuit, the last fan stage on those configurations
is a fixed speed fan. The last fan stage will be turned off and
will not be allowed to activate when noise reduction is active.
The last fan stage will also be turned off if OAT is less than
23.89°C (75°F) and it will not be allowed to activate if OAT is
less than 25.56°C (78°F).
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EXV Control

Control States
EXV control will always be in one of two states: Closed or
Superheat Control.
Transitions between these states are shown in
Figure 60: EXV Control Transitions
T1 – Closed to Superheat Control
• Circuit state is preopen
T2 – Superheat Control to Closed
• Circuit state is off or pumpdown
Closed State Operation
When the EXV is in the Closed state the position command will
be 0 and the EXV control state display will show 'Closed'.
Superheat Control State Operation
While in superheat control, the EXV controls suction superheat.
A PID loop will be used to control the suction superheat to
the target value. The EXV response is faster when the SSH
is lower than 1.67°C (3°F) or higher than the SSH Target +
1.67°C (3°F). Normally during superheat control the EXV
control state display will show 'Superheat'.
The EXV should also prevent the evaporator pressure from
exceeding the Maximum Evaporator Pressure set point. This
is done by using another PID function to control evaporator
pressure to the maximum evaporator pressure. The EXV
position should be the lesser position output from the two PID
functions. If the EXV position is being limited due to exceeding
the maximum evaporator pressure, then the EXV control state
display will show 'MaxEvapPr'.
Superheat Target
The suction superheat target is selected per the set points
depending on what capacity the circuit is running at.
• If the circuit has two compressors and one is running, the
value used is the SSH Target at 50% set point. If both
compressors are running the SSH Target at 100% set
point is used.
• If the circuit has three compressors and one is running,
the value used is the SSH Target at 33% set point. If
either two or three are running the SSH Target at
66/100% set point is used.
If no compressors are running the target is set to the set point
used when one compressor is running (this applies during EXV
preopen).
77 IOM 1206-7 • TRAILBLAZER
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IrCUIT UnCTIons
Figure 59.
MODEL AGZ CHILLERS
™