6
Application guide RA8AB102 © Danfoss 10/2010
Cascade HC/HFC - CO2 system
Cascade injection control
In systems with cascade regulating and CO2
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.
MT evaporator CO2 flow
control
The air temperature in the medium temperature
display cases or rooms is controlled by opening/
closing a solenoid valve/motor valve in the CO2
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 CO2 liquid pump, modulating tem-
perature control should be chosen as this also
provides a more constant flow of CO2 to the CO2
pump.
LT evaporator injection
control
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.
Period time, n63
Pressure control
The Danfoss CO2 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