Circuits For Control Of Co2 Gas Pressure - Danfoss AK-PC 781A User Manual

Circuits for control of CO2 gas pressure

Application
The function can be used in systems with transcritical and sub-
critical cooling control systems where CO2 is used as a refrigerant.
The controller regulates the pressure in the gas cooler (condenser)
so that the system achieves the optimal COP.
The controller will always optimise to a subcritical state.
The pressure in the gas cooler is controlled by the valve.
Instead of an ICMTS valve, a CCMT valve with stepper motor can
be used.
Regulation must have inputs from both a pressure transmitter Pgc
and a temperature sensor Sgc. Both must be fitted in the outlet
immediately after the gas cooler. If the gas can be routed outside
of the gas cooler, a Shp sensor must be installed. Should the Shp
sensor record too high a temperature, the gases will be routed
through the gas cooler once again.
The valve is an ICMTS valve, which has been specially developed
for the pressure conditions that exist in a transcritical CO2 system.
The motor section of the valve is an ICAD actuator and is control-
led by a 0-10 V signal from the controller.
The valve's degree of opening can be restricted both at the clos-
ing point and in the entire open point.
The settings OD Min. and OD max. are adjusted as % of the degree
of opening and will restrict the voltage signal for the valve.
Maximum COP control
During normal operation without override, the controller will
maintain the optimum pressure in the transcritical area.
AK-PC 781A Capacity controller RS8HE202 © Danfoss 2017-07
Overview
Reference curve
The controller is pre-programmed to follow the optimal COP
from the pressure/enthalpy chart. The top point is defined at 100
bar, 39°C. (Optimal theoretical COP is achieved at the curve that
passes through 100 bar and 39°C. The point of intersection can be
changed by setting a value other than the default).
Regulation will now follow the set reference curve, but will never
go above the set permitted max. pressure for the gas cooler.
The current reference can be read from the controller's overview
screen.
Subcooling
Subcooling can be used in the subcritical range.
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