Riello NXC 021 - Defrost Function Operation; Master;Slave Unit System

PRO-DIALOG+
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runningforlessthanaminutethesystemautomaticallyre-
ducesthenumberofstart-upsbutinthiscasethecontrolon
the setpoint temperature is less effective.
Start-upscanbeinuencedbytheinterventionofotherfun-
ctions
suchasdefrost.
3.5.10 Night mode
Thisfunctionlimitsmachinecapacityoverasetperiodofti-
me. The period is set by accessing the GENUNIT menu and
simplysettingastartandnishtime.Usuallyitissetforthe
night time.
3.5.11 Control of optional electric heating elements
NXH units can manage up to four optional electric hea-
ting elements. Heating elements activate to compensate
the heat request to the machine in particular under these
conditions:
• When the unit is already at its full capacity or when
itscapacityisreducedduetothetriggeringofsomesafety
devices
• The outside temperature value is lower than the
setthresholdvalue(HCCONFIGmenu)
• The demand limit function has not been activated.
Incasemorethanoneheatingelementisused,thelastone
couldbeutilizedasbackup,whichcanbeactivatedincase
of machine fault, supporting the other heating elements.
3.5.12 Desuperheater option
In units equipped with desuperheater it is possi-
ble to recover the heat from the hot water. The op-
tion is activated from the SETPOINT menu by setting
the min_sct parameter. It is also possible to use the
drycontacts(seeinputsMENU,DSHTR_SWparameter).
3.5.13 Defrost function
It is a function present also in the NXH series machines.
It is activated when the unit is in heating mode to pre-
vent the formation of ice on the air side exchanger.
Thedefrostcycleisperformedononelineatatime(in
caseofmachineswithtwoormorelines);duringthedefrost
phasethefanofthelineundergoingthecyclewillstopand
thefour-wayvalvewillinvertthecycleforcingthemachine
to
operateincoolingmode.Defrostcycle
isautomaticanddoesnotrequireanysetting.
3.5.14 Control of an auxiliary boiler
 Thisfunction,aswellasthecontroloftheelectricheating
elements,isnotpossibleifthemachineisconguredas
Slave.
NXH units can manage an alternative source of heat such as a
boiler,bycontrollingitsstart-up.Whentheboilerisinope
-
rationtheunitisstopped.
Boilercanbeactivatedwhen:
• The unit is in heating mode but it is stopped due toan
error.
• Theunitisinheatingmodebuttheoutdoorairtempera
-
ture
istoolow.Usually,thesetthresholdvalueis-10_Kbut
itcanbeconguredfromtheHCCONFIGmenu.
3.5.15 Master/Slave unit
Two ProDialog+ can be connected together in a Master-
Slave unit system. The two controls communica-
te
 through the CCN bus. Conguration parameters are
accessible
 onlyfromthe SERVICE menu requiring the inter-
vention of the Technical Support Service.
The
Master-Slavesystemrequiresacascadingprobeforeach
machinetobeconnectedtothepipingcomingoutofthesystem.
The
systemcanmanagepumpswithxedandvariableow
rate;forunitswithvariableowratepump,eachunitcon-
trols
itspumpaccordingtotherequiredload.
Ifxedowratepumpsareusedinstead,thesearealways
runningevenwhenthesystemhasaloadrequest.Itispos-
sible
tohavetheMasterunittomanageonesystempump:in
thiscasetheSlavemachinepumpisnotused.
AllchecksandsettingswillbeperformedontheMasterma-
chine
thatwilltransmittheinformationtotheSlave.
TheMastercanbecontrolledfromtheunitpanel,remotepa-
nel
 or CCN system. If the Master is controlled from remote
panel,usedrycontactstoturnsystemonandoff.
One of the Master-Slave functions allows establishing
not only which one is the Master and which one is the
Slave unit, but also inverting the roles if the operating
hours of the two units are a lot different. The system, if
congured,
willtrytokeeptheoperatinghoursofbothma-
chines
identical.
Shouldthesystemnotbeconguredasdescribedabove,the
machinechosenasMasterwillalwaysremainthatway.The
Mastermachinealwaysstartsrst,untilitreachesitsfullca
-
pacity.

Now a countdown starts for the Slave machi-
ne
 that will be started once countdown is over.
The water setpoint used by the Slave machine is
the same of the Master machine.
During
 cascading operation, the Master will always
work to its full capacity if the Salve is running, other-
wise
 it can modulate its operation according to the
system
 request. In case of communication error
between
MasterandSlave,thetwounitswillcarryonwor-
king
asseparatemachines,usingtheprogrammingsetfrom
each control panel.
IftheMastershutsdownduetoanerror,thentheSlavewill
startregardlessoftheMasterenablingsignal.
 ForNXHmachinesinMaster-Slavecongurationorequip
-
pedwithatleastoneadditionalelectricheatingelement,
thecontrolmustbeontheenteringwatertemperature.