building) and develop a common supply manifold to feed the pumps. Likewise, provide a common return manifold. DO NOT install manifold piping to produce a bull-headed tee condition. In a remote location, zone pumps may be mounted adjacent to the heating system PROVIDED: the total head loss (static and frictional) of the supply pipe is equal to or less than 3 feet; and the pump is mounted at least 6’ below the surface of the GARN® WHS water level. Again, this is necessary to prevent suction boiling at the pump inlet. (See previous section - Calculation of Net Positive Suction Head For Pumps) . DO NOT select a pump to operate near the top of its pump curve as “cycling flow” may occur with resultant damage to the pump and substandard system heating performance. See the figure below.
Area of good selection
In an existing system, the pump size must be confirmed as adequate for the modified system. Under-sizing a pump will significantly reduce the performance of the heating system and may allow system piping to freeze. When hooking into an existing system, use a primary-secondary setup.
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Hydronic System Design Manual ©DECTRA CORPORATION - March 2013
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