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3. TECHNICAL FEATURES
3.1 Main Components
Warm air heaters include:
• stainlesssteelheatexchanger
• frame and body
• centrifugal fan and electrical motor
• control panel and settings
• safetydevicesandcontrols
Stainless steel heat exchanger
The innovative design and large surface of the combustion
chamberandheatexchangerpipesensureoptimumefciency
and durability.
Combustionchamberanduegascollectorsarecompletely
made of AISI 441 stainless steel with low carbon content, as
wellasthesurfacesincontactwithuegases(tubebundle)in
order to ensure a high resistance to corrosion.
Tube bundle design is patented.
Characteristics of steel types used
Thefollowingtable shows naming correspondence ofthe steel
typesusedtomanufactureourexchangers:
USA-AISI EN-No. Composition
AISI441 1.4509 X2CrTiNb18
AISI310* 1,4845 X8CrNi25-21
AISI304* 1,4301 X5CrNi18-10
*Exchangersbuiltwithdifferentmaterials,suchasAISI310or
304, can be taken into account for special applications.
Heater’sheatexchangercanworkalsounderconditionsthatlead
tocondensation(ifequippedwiththenecessaryaccessories)
onlyiftherelevantburnerissuppliedwithgaseousfuel.
Frame and body
The frame consists of solid anodised aluminium bars. The
frameisassembledwithdemountablepartsallowing,inspecial
cases such as door crossing, to disassemble and reassemble
the heater completely.
Body panels are formed by:
-ontheexchanger side: riveted double-layered panels with
innergalvanizedsteelsheet,high-densityglassbreinsulation,
externalpaintedgalvanizedsteelsheet.
-onthefanside:paintedgalvanizedsteelsheetwithinnerlayer
forthermalandsoundisolation,securelyfastenedtosteelpanel.
Allpanelsfeatureagasketforaperfectsealingagainstairleaks.
Centrifugal Fan
Standardcentrifugalfansinstalledaremadeofgalvanisedsteel
sheetwithforwardcurvedbladesandlownoiseofoperation.
Fansarexedonhermeticballbearingswhichareself-aligned
and assembled inside rubber dampers. Three types of fan are
used:
• directdrivefan:themotorisdirectlycoupledtothefan.It
isusedonheaterswithsinglephaseelectricsupply(up
toPKA060-00A)
• fans for rectangular duct: driven by means of xed
diameterpulleys and belts, three-phase motor,(models
uptoPKA420-20A)
• fansforsquareduct:sameasprevious,theyareusedon
heatersfromPKA550-00Aupward.
Nolubricationisrequiredonstandardfans.Forspecialfans,
checkspecicrequirements.
Operating Temperatures:
A- directdrive -20°C +40°C
B- beltdrive -20°C +85°C
Thefollowingfansareavailableondemand:
• backwardcurvedblades
• plugfan,directlydrivenbythemotorandcontrolledthrough
inverter
• fansfortemperatureslowerthan-20°C
Electrical Motor
Allmotorsused,exceptthosewithdirectdrivetothefan,have
the following characteristics:
• Supply 400Vac-Three-phase-50Hz
• Structure B3-withterminalboardabove
• Protection degree IP55
• Isolationlevel cl.F
• Efciency IE3
Formoremodel-relatedinformationonmotors,seefurtherin
this Manual.
If required, motors with the following characteristics can be
supplied:
• varioussupplyvoltages,electricalfeaturesandphysical
shapes;
• motorsforlowtemperatures(below-30°C)
• motors with class H isolation
• tropicalised motors
• motors with internal heat protection, thermostat, or PT100
or PTC probe.
Control Panel and Settings
Standard control panel includes:
• oven-varnishedmetalbox
• quadripolar switch-disconnector, padlockable, with door
lock
• protectionfromoverheatandshortcircuitforeachmotor
• fuse-protectedwiringboardtocontrolheater,safetydevices
and burner.
• Formotorswithanoutputfrom5.5kWonward,asoftstarter
is built in. For motors with lower output, soft starters are
availableondemand.
The standard panel does not allow room temperature setting.
Thesettingtheusercanaskfordependsontheburnerinstalled.
Thefollowingtypesareavailable:
•ON/OFF,twostages,high/lowameormodulating.
Safety Devices and Controls
All heaters are supplied with the following thermostats:
-STB safetythermostatwithmanualreset.Itimmediately
stopstheburner.Theactivationissignalledbyaredlamplit
on the panel.
-TR fanstart-upthermostat.Itpostponesfanswitchonand
offasreferredtotheburner.Itpreventscoldairtobeblown
intotheroomatstartupandallowstheexchangertobecooled
down.
-TW burner'slimitthermostat.Itstopstheburneroperation
before STB safety thermostat triggers.