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•
Installation ease - The smaller pipe is easier to
handle during installation than the larger diameters.
The 'memory' of the pipe can be especially
cumbersome when installing in cold conditions.
Smaller pipe takes less time to fuse and is easier to
cut etc.
When Should Series Loops Be Used?
In smaller loops of two tons or less, the reasons for
parallel listed above may be less obvious. In these cases,
series loops can have some additional advantages:
•
No header - fittings tend to be more expensive and
require extra labor and skill to install.
•
Simple design - no confusing piping arrangement
for easier installation by less experienced installers.
Loop Configuration - Determining the style of loop
primarily depends on lot size, and 'dirt' costs. For
instance, horizontal 1 pipe will have significantly (400%)
more trench than a horizontal 6 pipe. However the 6 pipe
will have about 75% more feet of pipe, therefore if
trenching costs are higher than the extra pipe costs the 6
pipe is the best choice. Remember that labor is also a
factor in loop costs. The 6 pipe could also be chosen
because a small lot as well. Generally a contractor will
know after a few installations which configuration is the
most cost effective for him. Then this information can be
applied to later installations for a more overall cost
effective installation for his particular area. Depth of the
Figure 11A - Typical Header through 15 tons
2" IPS PE Pipe
2" x 2" x
3/4" IPS PE Tee
3/4" IPS
PE Pipe
Circuit 9 - 15
Figure 11B - Typical Header through 5 tons
1 1/4" IPS PE Pipe
3/4" IPS
PE Pipe
2" x 1 1/4" x
3/4" IPS PE Tee
3/4" IPS
PE Pipe
Circuit 5 - 8
11/4" x 3/4"
1 1/4" x 1
x 3/4" IPS
1/4" x 3/4"
PE Tee
IPS PE Tee
Circuit 5
loop in horizontal systems generally does not exceed 5
feet because of trench safety issues and the sheer amount
of dirt required to move. In vertical systems economic
depth due to escalating drilling costs in rock can
sometimes require what is referred to as a parallel-series
loop. That is, a circuit will loop down and up through
two consecutive bores (series) to total the required circuit
length required.
Loop Circuiting - Loops should be designed with a
compromise between pressure drop and good turbulence
in the heat exchange pipe for heat transfer. Therefore the
following rules should be observed when designing a loop:
•
3 gpm per ton flow rate (2.25 gpm per ton minimum).
In larger systems 2.5 to 2.7 gpm per ton is adequate
in most cases. Overseeing the pumps to attain
exactly 3 gpm per ton is generally not cost effective
from an operating cost standpoint.
•
One circuit per nominal equipment ton with 3/4" IPS
and 1/2 circuit per ton with 1-1/4" IPS pipe. This
rule can be deviated by one circuit or so for different
loop configurations.
Header Design - Headers for parallel loops should be
designed with two factors in mind, the first is pressure
drop and the second is flushability. The header shown in
Figure 11A is a standard header design through 15 tons
for polyethylene pipe with 2" supply and return runouts.
1 1/4" IPS
PE Pipe
11/4" x 3/4"
x 3/4" IPS PE Tee
3/4" IPS
PE Pipe
Circuit
4
3/4" x 3/4"
x 3/4" IPS
PE Tee
3/4" IPS
3/4" IPS
PE Pipe
PE Pipe
Circuit 4
Circuit 3
13
3/4" x 3/4"
x 3/4" IPS
PE Tee
3/4" IPS
3/4" IPS
PE Pipe
PE Pipe
Circuit
Circuit
3
2
3/4" IPS
PE Pipe
Circuit 2
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