Onix Tubing Installation Manual

page 64 Watts Radiant: Onix Installation Manual
The diagonal lines illustrate the design
possibilities if the spacing of the Onix
tubing is adjusted.
Each diagonal line shows the heat out-
put of a different Onix spacing, under
the same design parameters. Changes
in the Onix size, supply water temper-
ature or the R value of the floor cover-
ing will make a difference in the heat
output of the radiant slab.
This nomograph shows five possible
Onix spacings, ranging from 6" to 18"
on center. Spacings greater than 12"
are usually limited to certain commer-
cial and industrial applications where
floor temperature variations between
circuits is not a design consideration.
Read the Nomograph from left to
right. A possible solution exists wher-
ever the horizontal line associated with
the heating intensity intersects the
diagonal line associated with a particu-
lar hose spacing, as long as the
required floor temperature is below the
maximum floor temperature. If this is
not the case, and the required floor
temperature is higher than the maxi-
mum 85¡F floor surface temperature,
auxiliary heat will be required.
Next, find the required mean water
temperature necessary to heat the
given conditions. Mark the point on
the nomograph where the horizontal
heat intensity line intercepts with a
hose spacing. From that point, move
directly down to the bottom axis. This
is the required mean temperature.
For our example, the kitchen slab
needs to radiate 17 BTU/h/sq.ft. and
we choose an Onix spacing of 12’’ on
center. The mean water temperature
where these two lines intersect is
about 92¡F, or 102¡F supply tempera-
ture (based on a 20¡ temperature
drop). If a 6’’ on center tube spacing is
used, a mean water temperature of
87¡F is required, or 97¡F supply tem-
perature.
This tool should be used with care, as
the Onix spacing necessary to meet the
load still may not satisfy the customer.
For example, an 18’’ o.c. radiant circuit
spacing in a home or office would
likely generate customer complaints
about uneven floor surface tempera-
tures. Also, care must also be taken
not to exceed the warranty temperature
limits of Watts Radiant products and
the installed flooring products.
Generally speaking, mean water
temperatures of 140¡F and below
should be used for slab heating and
mean water temperatures of 150¡F and
below should be used for frame
heating applications.
Pressure
Drop Charts
Watts Radiant s pressure drop charts
are available for all sizes of Onix, for
plain water, ethylene and propylene
glycol. Information regarding the heat
required by the circuit (Q
s
), pressure
drop in the hose (ft.-hd./ft.), flow rate
(gpm), and water velocity (ft./sec) can
all be calculated from these charts.
The charts are cataloged by average
water temperatures required to heat a
radiant zone, ranging from 100¡—
180¡F. The following pressure drop
charts are for an average water tem-
perature of 120¡F.
Example
The following example will demon-
strate the use of these charts.
Assume the total heat required for a
radiant zone is 16,000 BTU/h. Four,
200’ circuits of 3/8’’ Onix are used
with an average water temperature of
120¡F.
The pressure drop for a circuit in the
zone is calculated by following these
steps.
1. Determine the heat required for each
circuit in the zone.
(16,000/4 = 4,000 BTU/h/circuit)
2. Find this number on the Q
s
axis (left
side of the chart).
3. Draw a horizontal line until it
intersects the diagonal line for
3/8" Onix.
4. Drop a line vertically to read the
pressure drop per foot of hose
(0.03 ft.-hd/ft.)
5. Find the total length of the hose in
the circuit including the distance to
and from the manifold. In this exam-
ple the manifold is located in the
zone (total length 200’)
6. Find the total pressure drop by
multiplying the circuit length (in
this case, 200’) by the pressure drop
per foot of heat (in this case
0.03 ft.-hd./ft.)
Note: Follow steps 1—6 for other cir-
cuits if the heat output and/or lengths
are different. The pump head is chosen
according to the circuit having the
maximum pressure drop. The pump
gpm is the summation of the gpm for
all the circuits served by the pump.
There are many other uses for pressure
drop charts as well. Water velocity is
shown on the chart by the short diago-
nal lines that intersect the longer diag-
onal lines for each specific energy
transfer hose. If the flow rate or the
heat required is known, the water
velocity can be found by tracing hori-
zontally from either axis. In the above
example, the water velocity is approxi-
mately 1.25 ft./sec. It is a good prac-
tice to maintain water velocities above
1 ft./sec and below 5 ft./sec. For
instance, 3/8’’ Onix in 200’ lengths
should be designed to transfer at least
3,000 BTU/h, and 5/8’’ Onix in 200’
lengths should ordinarily be designed
to transfer at least 9,000 BTU/h.
Flow rate per circuit at 20¡F
∆T can
be found by continuing horizontally
from the heat required (Q
s
) per circuit
(on the left side of the chart) and
Appendix