Onix Tubing Installation Manual

page 70 Watts Radiant: Onix Installation Manual
tates the required flow rate (gpm) for
the zone. This can be calculated by
using the following equation:
Pure Water:
BTU = gpm
× 500 × ∆T
50% Glycol-50% Water:
BTU = gpm
× 455 × ∆T
For most heating systems using a 20¡F
temperature drop it can be assumed
1 gpm = 10,000 BTU/h
So, a system requiring 100,000 BTU/h
will need 10 gpm of flow.
The other performance factor in sizing
a circulator is the head pressure. Head
Pressure is the friction loss associated
with the water moving against the
inside surface of the tubing or pipe.
The circulator should be sized to over-
come this loss, while moving the
required volume of system fluid.
The zone head pressure is the pressure
drop seen through the Onix circuits in
a given zone. It is calculated using the
pressure drop charts and is added to
the pressure drop associated with the
supply and return piping.
Because the Onix circuits are always
plumbed in parallel, the pressure drop
for an individual circuit is the same as
the zone pressure drop.
Example:
Zone A calls for 20,000 BTU/h to
be delivered to a zone with 5’—200’
circuits of 3/8" Onix. The manifold is
located 20’ from the mechanical room.
Step 1:
Determine the zone flow rate.
The flow rate for the zone is
20,000/10,000 = 2 gpm.
Step 2:
Determine the circuit flow rate.
The flow rate through each circuit is
2 gpm/5 circuits = 0.40 gpm/circuit
Step 3:
Determine the zone pressure
drop
Using the pressure drop chart for
water, the pressure drop per foot of
tubing is 0.031 ft.-hd./ft. tubing. This
gives a zone pressure drop of
0.031
× 200 = 6.20 ft.-hd.
Step 4:
Determine the pressure drop of
the supply/return lines.
Assuming 3/4" supply lines are
installed, with a flow rate of 2 gpm.
0.02
× 40’ (supply and return dis-
tance) = 0.80 ft.-hd.
Step 5:
Determine complete pump spec.
The required pump load is 2 gpm at
(6.20 + 0.80) or 7.0 ft.-hd.
The actual pump required for this zone
is selected using the given manufactur-
er s guidelines. This is usually done
with the use of a pump curve chart.
The chart is set up showing the pumps
capacity at various pressure drops.
Choose the pump that best reflects the
needs of the system.
For this example, pump 2 is the best
choice.
This information is readily available
on a pump sizing chart. These charts
are created by the pump manufacturer
for each pump model and should be
consulted before selection of a pump
can be made.
Expansion Tank Sizing
Water will expand as its temperature
increases. Since a hydronic heating
system with an expansion tank is a
closed system, the internal fluid vol-
ume is fixed. A simple ratio of how the
volume, pressure and temperature of
the system interact can be modeled by
using a simplified version of the ideal
gas law.
1
2
3
2
4
6
8
2 4 6 8 10
10
Flow Rate (GPM)
Head Pressure (ft-hd)
Typical pump sizing chart. Make sure zone circulators are sized to include supply and return
piping in addition to the zone piping requirements.
Appendix