Danfoss AK-CC 550 - Operational Modes; Liquid Injection and Temperature Control; Temperature Monitoring

4 Manual RS8EN502 © Danfoss 02-2010 AK-CC550
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signicantpressuredierence
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rst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inuence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dierential,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inuence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.
PlacementoftheS1sensoriscrucialforasafetysignal
and with this a satisfactory control.