Operation - Danfoss AK-CC 550 Manual

Operation

Liquid injection
Liquid injection in the evaporator is controlled by an electronic
injection valve of the type AKV. The valve functions as both expan-
sion valve and solenoid valve. The valve opens and closes using
signals from the controller.
The function contains an adaptive algorithm which independently
adjusts the valve's opening so that the evaporator constantly sup-
plies optimum refrigeration.
Superheat can be measured via one of the two following princi-
ples:
• Pressure sensor P0 and temperature sensor S2
For this use a correct measurement of superheat is achieved
under all conditions which ensures a very robust and precise
control.
The signal from one pressure transmitter can be used by several
controllers, but only if there is no significant pressure difference
between the evaporators in question.
• Two temperature sensors S1 and S2
Use of the S1 sensor means that location is particularly impor-
tant. The sensor must be located so as to read the evaporating
temperature during injection without the presence of too much
pressure drop. Danfoss recommends that the S1 sensor be
located on the first pipe bend on the evaporator.
Temperature control
The temperature in the appliance is registered by one or two
temperature sensors which are located in the air flow before the
evaporator (S3) or after the evaporator (S4) respectively. A setting
for the thermostat, alarm thermostat and display reading deter-
mines how much the two sensor values should influence each
individual function, e.g. 50% will produce an equal value from
both sensors.
The actual temperature control can take place in two ways: as an
ordinary ON/OFF regulation with a differential, or as a modulat-
ing control there the temperature variation will not be nearly as
great as in ON/OFF control. There is however a limit to the use of
a modulating control as it can only be used in central plant. In a
decentralised plant the thermostat function with ON/OFF control
should be selected.
In a central plant the thermostat function may either be selected
for ON/OFF control or modulating control.
Temperature monitoring
Just as is possible for the thermostat, the alarm monitoring can be
set with a weighting between S3 and S4 so that you can decide
how much the two sensor values should influence the alarm
monitoring. Minimum and maximum limits can be set for alarm
temperature and time delays. A longer time delay can be set for
high temperature alarms after defrosting, appliance cleaning or
start-up.
4 Manual RS8EN502 © Danfoss 02-2010
Placement of the S1 sensor is crucial for a safety signal
and with this a satisfactory control.
AK-CC 550