82
RT-SVX063E-EN
Configuration
Electronic Expansion Valves are always installed on DX
refrigeration circuits. Configuration is used to specify
the EXV selection on each refrigeration circuit. EXV
selection allows picking of a correlation between EXV
steps or EXV percent open, and the flow coefficient (C
v
)
at each EXV opening.
Functional Description
E
EX
XV
V C
Ca
alliib
brra
attiio
on
n
An EXV Calibration (also known as overdrive closed)
procedure will be initiated in the following
circumstances:
•
Whenever the unit controller is power cycled. This
is under the control of the unit controller software,
as part of the software startup procedure.
N
No
otte
e:: Under the most common scenario when both
the EXV electronic controller and unit
controller are power cycled, EXV Calibration
may occur twice.
•
When the circuit cycles off and the circuit has run
for at least EXV Recalibration Time since the
previous calibration.
N
No
otte
e:: EXV calibration time is used for both HGBP
and EXV valve calibration.
•
Whenever the EXV electronic controller is power
cycled. The EXV electronic controller does this
automatically.
E
EX
XV
V M
Ma
an
nu
ua
all O
Ov
ve
errrriid
de
e C
Co
on
nttrro
oll
See Programming Guide
EXV Control Sequence of Operation
The EXV control algorithm can be in one of the
following states:
Table 32.
EXV Control States
Control State
Description
Stopped
EXV closed. Overdrive closed (calibration) performed if criteria are
met.
Starting
EXV pre-position is calculated, and the valve arrives at the requested
opening before any compressors on the circuit start.
Stopping
EXV commanded to close. Remain in state until EXVs report that they
are closed.
Running
EXV operates in pre-start control, or in automatic control after the
pre-position hold time expires.
Running Mode Sub-States
Description
Running – Wait for Circuit Start
Time after valve arrives at pre-position value, but before a
compressor on the circuit starts.
Running – Pre-Position Hold Time
After a compressor on the circuit starts, but before automatic control
begins.
Running – Suction Superheat Control
Normal automatic superheat control
Running – Suction Pressure Control
Controlling suction pressure instead of suction superheat, to maintain
adequate compressor pressure ratio or to limit high suction saturated
temperature.
Running – Evaporator Dryout Control
Special version of suction pressure control, to dry out a flooded
evaporator and prepare to control suction superheat or suction
pressure again.
Operating Modes
C
Ca
alliib
brra
attiin
ng
g__E
EX
XV
V
Circuit submode displayed when EXV is going through
the calibration process. Most often active when circuit
top-level mode is Stopped, Run Inhibit, or Auto.
P
Prre
ep
po
ossiittiio
on
niin
ng
g__E
EX
XV
V
Circuit submode displayed when EXV(s) are moving
toward their commanded pre-position opening prior to
starting the first compressor on circuit startup.
M
Ma
an
nu
ua
all__O
Ov
ve
errrriid
de
e__E
Ev
va
ap
pX
XY
Y
Displayed when performing manual control override
on the EXV in the EvapXY position.
Economizing
Symbio 800 supports a common minimum outdoor air
and economizer damper (i.e. no separate minimum
outdoor air damper). Economizer high-limit decision
methods are defined as follows.
S
Se
eq
qu
ue
en
ncce
e o
off O
Op
pe
erra
attiio
on
n
