Danfoss AKA 245 Specifications download pdf (Page 7)

AK-CC550 Manual RS8EN502 © Danfoss 02-2010 7

Coordinated defrost

There are two ways in which coordinated defrost can be arranged.

Eitherwithwireconnectionsbetweenthecontrollersorviadata

communication

Wireconnections

ThedigitalinputDI2isconnectedbetweenthecurrentcontrollers.

Whenonecontrollerstartsadefrostalltheothercontrollerswill

followsuitandlikewisestartadefrost.Afterthedefrosttheindi-

vidualcontrollerswillmoveintowaitingposition.Whenallarein

waitingpositiontherewillbeachange-overtorefrigeration.

Coordinationviadatacommunication

Herethesystemunithandlesthecoordination.

The controllers are gathered in defrosting groups and the system

unit ensures that defrosting is started in the group according to a

weeklyschedule.

Whenacontrollerhascompleteddefrosting,itsendsamessage

tothesystemunitandthengoesintoawaitingposition.When

everycontrollerinthegroupisinawaitingposition,refrigeration

isagainpermittedinalltheindividualcontrollers.

System manager

Defrost on demand

1Basedonrefrigerationtime

Whentheaggregaterefrigerationtimehaspassedaxedtime,

a defrost will be started.

2Adaptivedefrostingbasedonmonitoringofevaporatorper-

formance

This function is based on a registration of the air ﬂow through

theevaporator.ByusingtheAKVvalveasmassowmeterforthe

refrigerant ﬂow it is possible to compare the energy input on the

refrigerant side with the energy output on the air side. Via this

comparisontheairowthroughtheevaporatorcanbedeter-

minedandhencealsotheamountofice/frostbuild-uponthe

evaporatorsurface.Iftheice/frostbuild-upreducesthecapac-

ityoftheevaporatorthefunctionwillcarryoutanadditional

defrost.

Enterintheweeklydefrostschedulethenumberofdefrosts

correspondingtothebasicload.Iftheloadoftheevaporatoris

increased beyond this, defrost on demand will add the required

additional defrosts.

The function requires the following connections:

-ExpansionvalvetypeAKV

-TemperaturesignalfrombothS3andS4

-TemperaturesignalfromthecondensingpressurePcwhichisto

bedistributedviathenetworkfromthesystemmanager.

NOTE.TheS3andS4sensorsmustbeplacedintheairow/chan-

nelimmediatelybefore/aftertheevaporator.

Min. time between defrosts

There is a 2 hours minimum time between defrosts.

Thisavoidsthatplanneddefrostsinaccordancewiththeweekly

schedule are carried out immediately after a defrost on demand

has been carried out. The time applies from when a defrost on

demand has been completed to when a planned defrost is again

permitted. The defrost on demand will not start defrosting with a

shorterintervalthanthe2hourseither.

Reset

Iftheadaptivedefrostfunctionregistersproblemswiththe

defrost, it will show an error message and the function will no

longercarryoutextradefrosts.Inthiseventamanualresetofthe

functionviad22shouldbecarriedout.

Whentheresetfunctionisactivateditwillstartadefrostsothat

thesubsequenttuningwilltakeplaceonanevaporatorwithno

ice/frostbuild-up.

Note

Thefunction"Adaptivedefrost”shouldonlybeactivatedwhenthe

evaporatorrunsundernormaloperationalconditions.

Melting function

Thisfunctionwillstoptheairowintheevaporatorfrombeingre-

duced by frost created by uninterrupted operation for a long time.

Thefunctionisactivatedifthethermostattemperaturehas

remained in the range between -5°C and +10°C for a longer

periodthanthesetmeltinginterval.Therefrigerationwillthenbe

stopped during the set melting period. The frost will be melted

sothattheairowandhencetheevaporator’scapacitywillbe

greatlyimproved.

Real-time clock

Thecontrollerhasabuilt-inreal-timeclockwhichcanbeusedto

startdefrosts.Thisclockhasapowerreserveoffourhours.

Ifthecontrollerisequippedwithdatacommunication,theclock

will automatically be updated from the system unit.

Max. 10

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Danfoss AKA 245 Specifications Page 7

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