Burnham K2WTC - Page 77

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Figure 9.6: Piping Method #2 - Direct Connection of Boiler to Heating System
NOTICE
Where it is not possible to install a separate boiler loop, the system circulator must be sized to ensure that
the ow through the boiler stays within the dened parameters to prevent overheating when the boiler is
red at it’s full rated input. Install a ow meter to measure the ow, or re the boiler at full rate and ensure
the boiler delta T does not exceed 35°F (19°C).
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
conventionalboilers(Figure9.6).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9.1.Forthisreason,the
pressure drop through the entire system must be known.
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.
Figure 9.7 shows the performance curve for the pump in each boiler model, taking into account the pressure drop through
theboiler’sheatexchangerandinternalpiping.Thesecurvesthereforeshowtheowthatcanbeachievedthroughtheboiler
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.
IX. System Piping (continued)