4
User
Guide RS8KH202 © Danfoss 2019-03
AK-PC
572
Gas cooler
Fan control
The fans must be speed controlled by the controller's analog
output.
EC motors can receive the 0-10 V signal directly.
During night operation, the noise level of the fans can be kept
down. This is done by limiting the voltage and thus the speed.
The limitation is bypassed if safety function Sd max. start to
function.
Regulation
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 Vhp.
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.
The valve is an CCMT valve, which has been specially developed
for the pressure conditions that exist in a transcritical CO2 system.
The valve's degree of opening can be restricted both at the
closing point and in the entire open point.
Maximum COP control
During normal operation without override, the controller will
maintain the optimum pressure in the transcritical area.
Reference
It is controlled using variable references.
An outdoor temperature sensor, Sc3, must be installed.
The sensor must be positioned so that it registers the correct out-
door temperature. In other words, it must be shielded from direct
sunlight and located near the airway of the condenser.
Under normal operations it will be controlled using a fixed tempe-
rature reference of 3 k above the outdoor temperature.
The pressure reference will be the configured value for the sub-
cooling when adjusting in the sub-critical range, and will be ad-
justed based on optimal COP when adjusting in the trans-critical
range.
The reference value will be user-configured during heat recovery.
Important
This sensor must be placed
immediately at the gas
cooler outlet.
Liquid injection in the MT suction line
This function is possible only if there is an available DO output.
The function opens for liquid when:
• The suction temperature is too high
• The pressurised gas temperature is too high
• Liquid inlet to the compressor must be prevented.
De-super heater
This function is possible only if there is an available DO output.
This function activates a fan so that the pressurised gas tempera-
ture in the LT circuit can be lowered:
• The fan stops when the outdoor temperature is low
• The fan stops when the MT suction gas is too low
