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Cascade injection control
MT evaporator CO 2 flow
control
LT evaporator injection
control
Pressure control
6
In systems with cascade regulating and CO 2
as refrigerant on the low temperature circuit
EKC 313 can regulate liquid injection (by means
of an ETS stepper expansion valve) into the cas-
cade heat exchanger in one of two ways:
• Optimize superheat
• Regulate the condensation pressure at the low
temperature circuit while ensuring that the
superheat does not become too low.
If there are no evaporators on the high tempera-
ture circuit the cascade controller should be set
in control mode 1 to optimise superheat. In this
application the condensation pressure on the low
temperature circuit should be controlled by the
compressor capacity controller in the high tem-
perature circuit. Here the LT PC signal is received
at the HT P0 input.
The air temperature in the medium temperature
display cases or rooms is controlled by opening/
closing a solenoid valve/motor valve in the CO 2
supply to the evaporator. The actual temperature
control can take place in two ways: as ordinary
ON/OFF regulation with a differential, or as
modulating control (PWM) where the tempera-
ture variation will not be nearly as big as in ON/
OFF control.
In a system with several evaporators supplied by
the same CO 2 liquid pump, modulating tem-
perature control should be chosen as this also
provides a more constant flow of CO 2 to the CO 2
pump.
Injection control for the low temperature case
and cold room evaporators is an AK-CC 550A
utilizing pulse-width-modulating injection valves
AKVH and patented adaptive software algorithms
to optimise system performance and operation.
The Danfoss CO 2 controllers have more pressure
safety functions which prevents safety valves to
open and hereby loss of charge.
AK PC 740 pack controller
A max compressor discharge pressure safety
function will reduce compressor capacity
Application guide RA8AB102 © Danfoss 10/2010
Period time, n63
Cascade HC/HFC - CO 2 system
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