is connected to the end of the return pipe and the last unit supplied is connected to the beginning of the return pipe. By piping the system this way, the water flowing through each terminal unit has to travel approximately the same distance. As a result, the flow through each terminal unit is about the same. Multi-zoned two pipe system Similar to splitting series loop systems, splitting two pipe systems into separate zones provides better comfort and reduces energy consumption. For the best performance, rooms should be combined into zones based on similarities in usage. Figure 8. Primary secondary Primary-secondary piping arrangements provide better flow control and temperature control than other types of systems. They are very popular and common in residential systems because of the popularity of radiant heat. This piping system also helps to prevent flue gas condensation caused by low temperature return water. Primary/secondary piping also hydraulically isolates the loops from one another. There are two types of primary-secondary piping arrangements- one-pipe and two-pipe. One-pipe are the most common for residential applications. The piping is similar to a mono-flow system with each secondary circuit (zone) connected off a primary “loop”- BUT with standard tees instead of diverter tees. Figure 9. Each secondary circuit has its own circulator that must be piped to pump water away 18 National Oilheat Research Alliance Figure 7
NORA Advanced Hydronics
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