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