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Method 2: Direct Connection to Heating System (Generally NOT Recommended)
In some relatively rare cases it may be possible to connect this boiler directly to the heating system as is done with
conventionalboilers(Figure9.7).Ifthisisdone,theowratethroughtheboilerwillequaltheowratethroughthesystem.
TheowratethroughthesystemmustthereforealwaysremainwithinthelimitsshowninTable9.1.Forthisreason,the
pressure drop through the entire system must be known.
Thismethodisgenerallynotrecommendedbecauseitisoftenverydifculttoaccuratelycalculatethepressuredrop
through the system. In replacement installations, it may be impossible to get an accurate measurement of the amount of
pipingandnumberofttingsinthesystem.Inaddition,ifthesystemiszoned,thesystemowmaydropwellbelowthe
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.
Figure 9.8 shows the performance curve for the pump in each boiler model, taking into account the pressure drop through
theboiler’sheatexchangerandinternalpiping.Thesecurvesthereforeshowtheowthatcanbeachievedthroughtheboiler
as a function of the pressure drop through the connected piping. Calculation of the system pressure drop must be performed
by someone having familiarity with pressure drop calculations, such as an HVAC engineer.
FIGURE 9.7: PIPING METHOD #2 - DIRECT CONNECTION OF BOILER TO HEATING SYSTEM
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