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FIGURE 13: ISOLATION OF BOILER FROM SYSTEM
WITH A HEAT EXCHANGER
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 TWZ. These systems also typically have return
temperatures well below the 120°F minimum.
Figure 13 illustrates the use of a heat exchanger to connect the TWZ 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 flow 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 fill 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 TWZ such as
four way mixing valves and variable speed injection pumping systems.
4)
Systems containing oxygen - Many hydronic systems contain enough dissolved oxygen to cause severe corrosion
damage to a cast iron boiler such as the TWZ. Some examples include:
• Radiant systems that employ tubing without an oxygen barrier.
• Systems with routine additions of fresh water.
• Systems which are open to the atmosphere.
If the boiler is to be used in such a system, it must be separated from the oxygenated water being heated with a heat
exchanger as shown in Figure 13.
Consult the heat exchanger manufacturer for proper heat exchanger sizing as well as flow and temperature requirements.
All components on the oxygenated side of the heat exchanger, such as the pump and expansion tank, must be designed
for use in oxygenated water.
5) Air Handlers - Where the boiler is connected to air handlers through which refrigerated air passes, use flow control
valves in the boiler piping or other automatic means to prevent gravity circulation during the cooling cycle.
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