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PipingforSpecialSituations
Certain types of heating systems have additional requirements. Some of the more common variations
follow:
1) Indirect Water Heaters – Figure 18 shows typical indirect water heater piping. Boiler piping is
the same as for any two-zone system. Figure 18 shows circulator zoning, which is usually
preferred for indirect water heaters. Size the circulator and indirect water heater piping to obtain
the boiler water ow through the indirect water heater called for by the indirect water heater
manufacturer.
2) Gravity and “Large Water Volume” Systems – The piping shown in Figure 19 will minimize the
amount of time that the boiler operates with return temperatures below 120F on these systems.
A bypass is installed as shown to divert some supply water directly into the return water. The
bypass pipe should be the same size as the supply. The two throttling valves shown are
adjusted so that the return temperature rises above 120F during the rst few minutes of opera-
tion. A three-way valve can be substituted for the two throttling valves shown. If the circulator is
mounted on the supply, the bypass must be on the discharge side of the circulator.
3) Low Temperature Systems – Some systems, such as radiant tubing systems, require the system
water temperature to be limited to a value below the temperature of the water leaving the ODV.
These systems also typically have return temperatures well below the 120F minimum.
Figure 20 illustrates the use of a heat exchanger to connect an ODV boiler to this type of system.
The heat exchanger will permit the transfer of heat from the boiler water to the low temperature
system while holding the system supply and boiler return temperatures within their limits.
For this system to work properly the heat exchanger must be properly sized and the correct ow
rates are required on either side of the heat exchanger. Consult the heat exchanger manufacturer
for sizing information. The water in the boiler is completely isolated from the water in the
system. This means that separate ll and expansion tanks are required for the heating system
loop.
There are several other ways to connect low temperature systems to the non-condensing boilers like
the ODV such as four way mixing valve and variable speed injection pumping systems.