Onix Tubing Installation Manual

Near Boiler Piping
and Controls
The following schematics are provided
as a guide for common applications.
Other schematics are available from
the local Watts Radiant representative.
Primary/Secondary
Generally, the best way to pipe a
hydronic system is referred to as
Primary/Secondary.
Primary/Secondary piping allows for
better flow and temperature control
over the various components. Each
layout is broken down into two basic
sections: The Primary loop, or boiler
loop and the Secondary loop, or zone
loop.
The Primary loop provides boiler pro-
tection. Boilers must be operated
above their condensing point, unless
they are condensing boilers. If a boiler
operates in that condition, corrosion
will eventually lead to premature fail-
ure of the boiler.
In addition to condensation, boilers
must operate at a maximum tempera-
ture rise, typically 20¡ to 40¡F. The
primary pump is sized to ensure both
of these conditions are maintained
independent of the load or piping
requirements of the individual zones.
The Point of No Pressure
Change
The point of no pressure change is a
condition that has been discussed in
piping manuals for decades. The theo-
ry stems from how boiler pumps
respond to pressure differentials.
Circulators, in order to function prop-
erly, need to pump into the zone
(load). This condition will always cre-
ate a positive-to-positive rise across
the impeller. The placement of the
expansion tank will greatly affect how
the primary pump achieves this goal.
The expansion tank controls where the
pressure change in the system occurs.
Expansion tanks always see the same
pressure at their point of connection to
the system. Points on either side of of
the tank will either be higher or lower
depending on the primary pump loca-
tion. To prevent cavitation and maxi-
mize longevity and efficiency, the pri-
mary pump must be positioned so it
pumps away from the expansion
tank.
There are several books solely dedicat-
ed to this piping practice which offer a
very detailed explanation. For this
manual, we will assume the following
conditions:
1. The Air Remover, Expansion Tank
and automatic fill assembly are
located at roughly the same location.
2. The primary pump is positioned
after the expansion tank in a pump-
ing away position.
3. The primary pipe size is sized based
on the boiler load and flow require-
ments.
How to Size a Circulator
Circulators, or pumps, are sized based
on the required load and piping loss
for a given zone. The heat load dic-
Expansion Tank
FuseTron and RelayBox
Air Remover
Circulator
Isolation Flanges
Mix Valve
PRV Valve (AutoFill)
Backflow Preventer
Control
Sensor
Pressure and
Temperature Gauges
Ball Valve
Boiler Drain
Gravity Check Valve
Spring Check Valve
Zone Valve
Legend
Appendix
Watts Radiant: Onix Installation Manual page 69