Bosch Geothermal Heat Pumps, Руководство по применению

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4 8 | Bosch Geothermal Heat Pumps
Bosch Thermotechnology Corp. Data subject to change
Applications Manual
9 Closed-Loop Ground Heat
Exchanger Design
Considerations
9.1 Series or Parallel Con gurations
Typically, closed-loop ground heat exchangers are arranged
in either a series or parallel con guration (Fig. 33, 34).
Historically, closed-loop ground heat exchangers were all
designed using series ow due to the lack of fusion ttings
required for parallel con gurations. This typically resulted
in larger diameter pipe (>1-1/4”) being used in an effort
to reduce pumping requirements which were due to the
increased pressure drop apparent in the piping. As fusion
ttings have become available, parallel ow using 3/4” IPS
for loops for most geothermal heat pump equipment has
become typical.
For the most part, smaller diameter pipe is now used for
ground heat exchangers. Larger diameter (>1-1/4”) pipe
is typically 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 15%. In close-loop designs using the smaller
pipe, the pipe length is normally 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.
Parallel systems normally have lower pressure drop and
require smaller pumps due to the multiple ow paths of
smaller pipes in parallel.
Smaller diameter pipe is typically much easier to handle
during installation than larger diameter pipe as well. The
“pipe memory” can be problematic for larger pipe when
ground heat exchangers are installed during cold weather,
and are less apparent with smaller pipe. The smaller pipe
also takes less time to fuse and is much easier to prepare
for installation.
Series piping con gurations typically use 1-¼ inch or 2
inch HDPE pipe.
Parallel piping con gurations typically use ¾ inch or 1
inch HDPE pipe for loops and 1-¼ inch or 2 inch pipe for
headers and service lines.
Parallel con gurations require headers to be either
“closed-coupled” short headers or “reverse return header”
design.
Series Flow
Fig. 33 Series ow con guration
Courtesy of International Ground Source Heat Pump Association/Oklahoma
State University
Parallel Flow
Fig. 34 Parallel ow con guration
Courtesy of International Ground Source Heat Pump Association/
Oklahoma State University