Danfoss AKA 245 Dokumentacja Pobierz pdf (Strona 4)

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.

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