User Guide

39
B. Near Boiler Piping Design
 ProperoperationofthisboilerrequiresthatthewaterowratethroughitremainwithinthelimitsshowninTable
9.1anytimetheboilerisring.Atowratesbelowtheminimumshown,theboiler’sowswitchand/ortemperature
riselimitfunctionmaypreventtheboilerfromring.Flowratesthroughtheboilerinexcessofthemaximumshownin
Table 9.1 can result in excessive noise or erosion damage to piping
Use of primary-secondary piping (described below) is strongly recommended for connection of the boiler to the
system. Additional information on hydronic system design can be found in the I=B=R Guide RHH published by the
Air-Conditioning, Heating and Refrigeration Institute (AHRI).
Table 9.1: Flow Limitations
Flow (GPM)
Model Minimum Maximum
80MBH 5.0 13.3
100MBH 5.1 13.3
120MBH 6.2 13.3
150MBH 7.7 13.3
180MBH 9.3 13.3
Primary-secondary piping can be used in heat-only applications as shown in Figure 9.2 or with an indirect water heater
asshowninFigure9.3AorFigure9.3B.Ineithersystem,theowratethroughtheboiler(“secondaryloop”or“boiler
loop”)iscompletelyindependentoftheowratethroughthesystem(“primaryloop”).Usethefollowingguidelinesto
ensurethattheboilerwillhavetherequiredowshowninTable9.1regardlessoftheowintheheatingsystem.
1)SystemLoopPiping-Sizethesystemcirculatorandpipingtoobtainthedesignowratethroughtheheatingsystem
as you would on any other heating system. All piping between the expansion tank and secondary connection tees must
beatleast1”.Inordertokeeptheowratesinthesystemandboilerloopsindependentofeachother,provideatleast
8diametersofstraightpipeupstreamoftherstteeand4diametersdownstreamofthesecondtee.Keepthedistance
betweentheexpansiontankandtherstsecondaryteeasshortaspractical.
2)BoilerLoopPiping–Theboilerloopcirculatorissuppliedbytheinstaller.ThecirculatorsinTable9.5willprovide
therequiredboilerloopowprovidedbothofthefollowingconditionsaremet:
• Allpipingintheboilerloophasanominalsizeofatleast1”
• Theequivalentlengthofallpipingintheboilerloopis60ftorless.
To verify that the 60ft, equivalent length is not exceeded, do the following:
a) Countallttingsintheplannedboilerloop(theshadedpipinginFigure9.6).Indoingso,donotcountthe
secondaryconnectiontees,unions,orthettingssuppliedwiththeboiler(thesehavealreadybeenaccountedfor).
b) UsingTable9.4,ndtheequivalentlengthsofallttingsintheboilerloop.Totaltheseequivalentlengthsandadd
them to the total length of planned straight pipe in the boiler loop.
c) The result is the total equivalent length of the planned boiler loop. If the equivalent length calculated in (b) is under
thelimitshowninTable9.5,theboilerpumpwillachieveaowrateandtemperatureriseapproximatelyequaltothat
shown in this table. Otherwise, the equivalent length must be reduced.