Bosch Geothermal Heat Pumps Applications Manual page 79

Applications Manual
Two pipes in the same trench, one above the other,
separated by approximately 2 feet of earth requires a
trench typically 60% as long as a single pipe trench. The
total length of pipe would be approximately 120% as long
as a single pipe. This results due to the heat transfer effect
between the two pipes.
When laying a double layer of pipe, installers should be
careful to avoid kinks when making the return bend.
Two-pipe ground loops are more common with trenched
installations (Fig. 79). If a backhoe is available, more pipes
are typically added to the trench. Each two-pipe ground
loop is a circuit. If using ¾" pipe, there is usually one two-
pipe trench per ton of cooling capacity required. Typically,
the two pipes are spaced a minimum of 24 inches apart in
the trench at the average depth determined for the locale.
Fig. 79
Courtesy of International Ground Source Heat Pump Association/Oklahoma
State University
A four-pipe ground loop allows an installer to utilize 60 to
70% of the trench necessary for a two-pipe ground loop
as more pipes are located in the trench (Figure 80). If,
for example, 250 feet of a two-pipe trench (500 feet) is
necessary, only approximately 150 feet of four-pipe trench
(600 feet) is necessary for the four-pipe ground loop. This
arrangement allows installers to utilize smaller land areas.
A four-pipe ground loop typically has two (2) circuits per
trench, so if ¾" pipe is used, one trench can typically
handle a two (2) ton geothermal heat pump. Typically,
the four pipes are spaced a minimum of 24 inches apart
horizontally and vertically in the trench, with the upper
two pipes at the average depth determined for the locale.
As four-pipe ground loops have an even number of
circuits, there may be more or less circuits than tonnage,
depending on the geothermal heat pump equipment
capacity.
Bosch Thermotechnology Corp.
Bosch Geothermal Heat Pumps | 79
Fig. 80
Courtesy of International Ground Source Heat Pump Association/Oklahoma
State University
For example, a ve (5) ton geothermal heat pump could
use either two (2) trenches with four (4) circuits, or
three (3) trenches with six (6) circuits, depending on the
pressure drop and the Reynolds number.
A six-pipe ground loop uses more pipes in the trench so
there is less trench (Figure 81). This design allows the
installer to use about 90% of the trench necessary for a
typical four-pipe ground loop. For example, 250 feet of
trench is necessary for a two-pipe ground loop (500 feet
of pipe). 150 feet of trench is necessary for a four-pipe
ground loop (600 feet of pipe). A six-pipe ground loop
typically has three (3) ow paths of three (3) circuits and
only needs approximately 135 feet of trench (810 feet
of pipe). Subsequently, one trench could be used for a
three (3) ton cooling capacity system. This could limit the
amount of excavation necessary, especially for retro t
applications.
Fig. 81
Courtesy of International Ground Source Heat Pump Association/Oklahoma
State University
Data subject to change