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Method 2: Primary/Secondary Piping - Boiler in Primary Loop
 Thismethodcanbeusedinheat-onlyapplicationsasshowninFigure8.8orwithanindirectwaterheaterasshownin
Figure8.9.LikeMethod1,thismethodreliesonprimary/secondarypumpingtoensurethattherequiredowisalways
maintainedthroughtheboiler.Inthissystem,theowratethroughtheboileriscompletelyindependentoftheowrate
throughtheheatingzones.Theboilerisinstalledintheheatingsystemprimaryloopasshown.
 Thissystemprovidesmoreaccuratecontrolofthewatertemperatureenteringtheheatingzonesasthenumberof
zonescallingforheatchanges.Whenthispipingmethodisused,theboilercontrolissettoprovidethehighestsupply
temperaturerequiredbyanyheatingzoneandsomeothermeans,suchas3-wayvalves,areusedtocontrolthewater
temperaturesrequiredbyanyzonesrequiringlowertemperaturewater.Thissystemisonlyrecommendedwhenthe
primaryloop(shownboldedinFigure8.10b)istobeconstructedaspartoftheboilerinstallationandcanbeconstructed
asshown.Also,iftheboileristoaccuratelycontrolthetemperatureenteringeachsecondaryloop,theowrateinthe
primaryloopmustbeatleastasgreatasthesumoftheowsthroughallsecondaryloops.
UsethefollowingguidelinestoensurethatboilerwillhavetherequiredowshowninTable8.1regardlessoftheowin
theheatingsystem.
1) HeatingSystemSecondaryLoopPiping-TheheatingsystemsecondarylooppipingisshowninFigure8.10a.Size
eachsecondaryzonecirculatorandpipingtoobtainthedesignowrateforthatzoneasyouwouldonanyotherheating
system.Whentheheatingzonerequiresawatertemperaturebelowthattobecontrolledbytheboiler,provideamixing
valveorblendingstationforthatzone.Inordertokeeptheowratesintheprimaryandsecondaryloopsindependentof
eachother,provideatleast8diametersofstraightpipeupstreamoftherstsecondaryteeand4diametersdownstreamof
thesecondsecondarytee.
2) HeatingSystemPrimaryLoop(“BoilerLoop”)–Theprimaryloop(“boilerloop”)pipingisshownboldedinFigure
8.10b.AllpipinginthisloopmustbethesizeshownfortheboilerinTable8.5,columna.Tosizethecirculator:
a) Startingattheboiler,traceapaththroughtheheatingsystemprimaryloopfromtheboilersupplyconnectiontothe
boilerreturnconnection,countingttingsandstraightpipeasyougo.Wheretheprimaryloopbreaks 
intoparallelpaths,followjustoneofthesepaths(itdoesn’tmatterwhichone).Donotcountthesecondary 
connectiontees,unions,orthettingssuppliedwiththeboiler(thesehavealreadybeenaccountedfor).
b) UsingTable8.7,ndtheequivalentlengthsofallttingscountedin(a).Totaltheseequivalentlengthsandaddthemto
thetotallengthofstraightpipemeasuredinstep(a).Theresultisthetotalequivalentlengthoftheprimaryloop.
c) UsingTable8.5,ndtheboilersizebeinginstalledandselectaboilerprimarycirculatorthatshowsa
“maximumequivalentlength”(columnd)inexcessofthetotalequivalentlengthcalculatedinStepb.
3) IndirectWaterHeaterLoopPiping(IfIndirectWaterHeaterisUsed)–AllpipingmustbethesizeshowninTable8.6,
column(a).Iftheindirectwaterheaterconnectionsaresmallerthanthepipesizecalledforincolumn(a),reducethepipe
sizeattheindirectwaterheaterconnections.Tosizethecirculator:
a) CountallttingsintheplannedIndirectWaterHeaterLoop(theindirectwaterheaterloopconsistsofthebolded
pipinginFigure8.10c).Indoingso,youwillbecountingsomepipingandttingswhicharecommontotheheating
systemprimarypiping(the“boilerloop”)andwhichwerecountedinStep2aabove.Donotcounttheelbowsor
ttingssuppliedwiththeboiler.
b) UsingTable8.7,ndtheequivalentlengthsofallttingsintheindirectwaterheaterloop.Totalthese
equivalentlengthsandaddthemtothetotallengthofplannedstraightpipeintheindirectwaterheaterloop. 
Theresultisthetotalequivalentlengthoffortheindirectwaterheaterloop.
c)UsingTable8.6,ndtheboilersizebeinginstalledandselectanindirectwaterheaterloopcirculatorthatshowsa
“maximumequivalentlength”(columnf)inexcessofthetotalequivalentlengthcalculatedinStepb.
Method 3: Direct Connection to Heating System (Generally NoT Recommended)
 TheCHGcanbeconnecteddirectlytotheheatingsystemasisdonewithconventionalboilers(Figure8.11).If
thisisdone,theowratethroughtheboilerwillequaltheowratethroughthesystem.Theowratethroughthe
systemmustthereforealwaysremainwithinthelimitsshowninTable8.1.Forthisreason,thepressuredropthroughthe
entiresystemmustbeknown,addedtotheboilerpressuredrop,andacirculatorselectedwhichwillprovidethe
requiredowatthetotalcalculatedpressuredrop.
 Thismethodisgenerallynotrecommendedbecauseitisoftenverydifculttoaccuratelycalculatethepressure
dropthroughthesystem.Inreplacementinstallations,itmaybeimpossibletogetanaccuratemeasurementofthe
amountofpipingandnumberofttingsinthesystem.Inaddition,ifthesystemiszoned,thesystemowmaydropwell
belowtheminimumrequiredwhenonlyonezoneiscallingforheat.
 Theoneadvantagetothismethodisitsinstallationsimplicity.Itmaymakesensetousethismethodwhenthe
boileristobeinstalledwithanewsinglezonesystemhavingalow-pressuredrop.Pressuredropcurvesforthe 
CHGSeriesboilersareshowninFigure8.12.Calculationofthesystempressuredrop,andselectionofthecirculator,must
beperformedbysomeonehavingfamiliaritywithpressuredropcalculations,suchasanHVACengineer.