Bryant 50YEW Design Manual page 44

Water-to-Water System Design Guide
Part III: Source Side Design / Closed Loop Installation Guidelines
CLOSED LOOP DESIGN/INSTALLATION GUIDELINES
Closed Loop Basics*
Closed Loop Earth Coupled Heat Pump systems are commonly
installed in one of three confi gurations: horizontal, vertical and
pond loop. Each confi guration provides the benefi t of using the
moderate temperatures of the earth as a heat source/heat sink.
Piping confi gurations can be either series or parallel.
Series piping confi gurations typically use 1-1/4 inch, 1-1/2 inch or
2 inch pipe. Parallel piping confi gurations typically use 3/4 inch or
1 inch pipe for loops and 1-1/4 inch, 1-1/2 inch or 2 inch pipe for
headers and service lines. Parallel confi gurations require headers to
be either "closed-coupled" short headers or reverse return design.
Select the installation confi guration which provides you and your
customer the most cost effective method of installation after
considering all application constraints.
Loop design takes into account two basic factors. The fi rst is
an accurately engineered system to function properly with low
pumping requirements (low Watts) and adequate heat transfer to
handle the load of the structure. The second is to design a loop
with the lowest installed cost while still maintaining a high level of
quality. These factors have been taken into account in all of the
loop designs presented in this manual.
In general terms, all loop lengths have been sized by the
GeoDesigner loop sizing software so that every loop has
approximately the same operating costs. In other words, at the
end of the year the homeowner would have paid approximately
the same amount of money for heating, cooling, and hot water no
matter which loop type was installed. This leaves the installed cost
of the loop as the main factor for determining the system payback.
Therefore, the "best" loop is the most economical system possible
given the installation requirements.
Pipe Fusion Methods
Two basic types of pipe joining methods are available for earth
coupled applications. Polyethylene pipe can be socket fused or butt
fused. In both processes the pipe is actually melted together to
form a joint that is even stronger than the original pipe. Although
when either procedure is performed properly the joint will be
stronger than the pipe wall, socket fusion in the joining of 2" pipe
or less is preferred because of the following:
• Allowable tolerance of mating the pipe is much greater in
socket fusion. According to general fusion guidelines, a 3/4"
SDR11 butt fusion joint alignment can be off no more than
10% of the wall thickness (0.01 in. [2.54mm]). One hundredth
of an inch [2-1/2 mm] accuracy while fusing in a diffi cult
position can be almost impossible to attain in the fi eld.
• The actual socket fusion joint is 3 to 4 times the cross sectional
area of its butt fusion counterpart in sizes under 2" and
therefore tends to be more forgiving of operator skill.
* All Polyethylene pipe discussed in this manual is IPS (Iron Pipe
Size) in inches.
42
• Joints are frequently required in diffi cult trench connections
and the smaller socket fusion iron is more mobile. Operators
will have less of a tendency to cut corners during the fusion
procedure, which may happen during the facing and alignment
procedure of butt fusion.
In general socket fusion loses these advantages in fusion joints
larger than 2" and of course socket fi ttings become very expensive
and time consuming in these larger sizes. Therefore, butt fusion
is generally used in sizes larger than 2". In either joining method
proper technique is essential for long lasting joints. All pipe and
fi ttings in the residential price list are IGSHPA (International Ground
Source Heat Pump Association) approved. All fusion joints must be
performed by certifi ed fusion technicians. Table 3-2 illustrates the
proper fusion times for Geothermal PE 3408 ASTM Pipe.
Table 3-2: Fusion Times for Polyethylene 3408
ASTM Pipe
Pipe Size
3/4" IPS
1" IPS
1-1/4" IPS
1-1/2" IPS
2" IPS
Always use a timing device
Parallel vs Series Confi gurations
Initially, loops were all designed using series style fl ow due to the
lack of fusion fi ttings needed in parallel systems. This resulted in
large diameter pipe (>1-1/4") being used to reduce pumping
requirements due to the increased pressure drop of the pipe. Since
fusion fi ttings have become available, parallel fl ow using (3/4" IPS)
for loops 2 ton [7 kW] and above has become the standard for a
number of reasons.
• Cost of Pipe - The larger diameter (>1-1/4") pipe is twice the
cost of the smaller (3/4" IPS) pipe. However, the heat transfer
capability due to the reduced surface area of the smaller pipe
is only decreased by approximately 10-20%. In loop designs
using the smaller pipe, the pipe length is simply increased to
compensate for the small heat transfer reduction, although it
still results in around 50% savings in pipe costs over the larger
pipe in series. In some areas vertical bores using 1-1/4" pipe can
be more cost effective, where drilling costs are high.
• Pumping power - Parallel systems generally can have much
lower pressure drop and thus smaller pumps due to the
multiple fl ow paths of smaller pipes in parallel.
• Installation ease - The smaller pipe is easier to handle during
installation than the larger diameter pipe. 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, bend, etc.
Bryant: Whatever It Takes.
Butt Fusion
Socket
Fusion
Time Bead,
Time (Sec)
(sec.) in [mm]
8 - 10 8 1/16 [1.6]
10 - 14 12 1/16 [1.6]
1/16 - 1/8
12 - 15 15
[1.6 - 3.2]
1/16 - 1/8
15 - 18 15
[1.6 - 3.2]
18 - 22 18 1/8 [3.2]
Holding Curing
Time Time
60 Sec 20 min
60 Sec 20 min
60 Sec 20 min
60 Sec 20 min
60 Sec 20 min