Onix Tubing Installation Manual

Injection Pump Sizing
Injection systems incorporate a series
of sensors, some on the control piping
to measure fluid temperatures, while
other sensors are located outside to
measure outside air temperature. With
this information the injection control is
able to calculate the actual heat load
and required water temperature at any
given time.
Why is this important? Non-electrical
mix valves are set to provide a fixed
temperature all the time. This tempera-
ture is set to handle the heating load
on the coldest day of the year. This
temperature is only reached for a small
percentage of the time. For the rest of
the heating season, a mix valve is pro-
viding temperatures that will be higher
than required for the heat load at most
times.
Reset systems are continuously opti-
mizing the heating system by modulat-
ing the supply temperature. This helps
reduce the possibility of potential ther-
mal swings associated with mild fall
and spring days.
Injection pumps are sized the same
way zone pumps are sized.
Pure Water:
BTU/h = gpm
× 500 × ∆T
50% Glycol-50% Water:
BTU/h = gpm
× 455 × ∆T
As a rule, an injection pump will be
sized for a smaller flow rate than the
combined secondary zones.
Each zone is designed around a 20¡F
∆T. This is done for comfort and
response of the heating system. The
injection pump, on the other hand, is
only responsible for transferring
BTUs. This can be done with a higher
∆T value. As the ∆T increases, the
resulting gpm rate will decrease while
still providing the same BTU delivery.
For example, assume a zone supply
temperature of 120¡F, a zone return
temperature of 100¡F and a boiler sup-
ply temperature of 180¡F. The zone
flow rate is 10 gpm. What size does
the injection pump need to be?
The system load can be figured using
the equation for water:
BTUs = 10
× 500 × 20 = 100,000
Zone Pumps
Injection Pump
Primary Pump/
Boiler Loop
Zone Return Lines
Swing Check Valve
Balancing Valve
Supply From Boiler
Return To Boiler
Appendix
Watts Radiant: Onix Installation Manual page 73