U.S. Boiler Company ASPEN ASPN-320, Installation, Operating And Service Instructions

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Figure 9.9: 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 flow through the boiler stays within the defined parameters to prevent overheating when the boiler is
fired at it’s full rated input. Install a flow meter to measure the flow, or fire the boiler at full rate and ensure
the boiler delta T does not exceed 35°F (19°C).
IX. System Piping
(continued)
Method 2: Direct Connection to Heating System (Generally NOT Recommended)
In some cases it may be possible to connect this boiler directly to the heating system as is done with conventional boilers
(Figure 9.9). If this is done, the flow rate through the boiler will equal the flow rate through the system. The flow rate through
the system must therefore always remain within the limits shown in Table 9.3. For this reason, the pressure drop through the
entire system must be known.
This method is generally not recommended because it is often very difficult 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 fittings in the system. In addition, if the system is zoned, the system flow 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.
Calculation of the system pressure drop must be performed by someone having familiarity with pressure drop calculations,
such as an HVAC engineer.