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Table 6-2
- Subcritical Parameters
Subcritical Parameter
Description
Default Value
HPV Mode Setpoint
Setpoint for Subcritical and Transcritical mode
31 DC
(87 DF)
HPV Mode Hysteresis
Control Temperature Hysteresis
3 DDC
(5 DDF)
HPV Subcool Setpoint
Subcool Setpoint in Subcritical Mode
2 DDC
(3 DDF)
HPV RS-Temp
Subcritical proportional band offset
0 DDC
HPV PB-Temp (P)
Subcritical proportional band
16.7 DC
(30DF)
HPV INC (I)
Integral sampling time
140 Sec
HPV DDER (D)
Derivative time
0 Sec
HPV Max Valve %
Maximum valve % opening
100%
Table 6-3
- Outputs
Outputs
Description
Type
Valve % Output
Valve Percentage Output
0-10VDC
Only or
LAN to
XEV20D
24 • High Pressure CO2 Controller Installation and Operation Manual
6.1.2
HPV Transcritical Mode
(Normal)
In a booster Transcritical system, when the tempera-
ture exceeds a certain value, there is no longer an accurate
temperature to pressure relation. Because of this, the con-
trol temperature of T1 or T2 (defined by digital CTS), will
be the deciding factor of when the application will
switches modes from subcritical to transcritical. If the con-
trol temperature is above the HPV Mode setpoint, the
application will be in transcritical mode. Once the control
temperature is below the HPV Mode setpoint minus HPV
Mode Hysteresis, the system reverts to subcritical mode.
In transcritical mode, the application will stop main-
taining a subcool setpoint and start maintaining a setpoint
value from an equation to achieve a virtual subcooling
using only the pressure input as a control point. The con-
trol temperature (T1 or T2) will still be used to as a refer-
ence to calculate the setpoint equation. Below is an
estimation of what the setpoint will be for the given con-
trol temperature readings.
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