Flow Controller 3
R e v. : F e b u r a r y 9 , 2 0 1 6
22
G e o t h e r m a l H e a t P u m p S y s t e m s
High and
Low Voltage
Knockouts
Vibration Isolation Pad
To Thermostat
Figure 15: Typical Ground-Loop
Application
Geothermal Closed Loop Design
Prior to installation, locate and mark all existing underground
utilities, piping, etc. Install loops for new construction before
sidewalks, patios, driveways and other construction has
begun. During construction, accurately mark all ground
loop piping on the plot plan as an aid in avoiding potential
future damage to the installation (see Site Survey Sheet).
This should be done before and after loop installation.
Final installation should be plotted from two fixed points to
triangulate the header/manifold location.
Loop Piping Installation
The typical closed loop ground source system is shown in
Figure 15. All earth loop piping materials should be limited to
only polyethylene fusion in below ground (buried) sections of
the loop. Galvanized or steel fittings should not be used at
any time due to the tendency to corrode by galvanic action.
All plastic to metal threaded fittings should be avoided as
well due to the potential to leak in earth coupled applications;
a flanged fitting should be substituted. P/T plugs should be
used so that flow can be measured using the pressure drop
of the unit heat exchanger in lieu of other flow measurement
means (e.g. flow meter, which adds additional fittings
and potential leaks). Earth loop temperatures can range
between 25-110°F [-4 to 43°C]. Flow rates of 2.25 to 3 gpm
per ton [2.41 to 3.23 l/m per kW] of cooling capacity are
recommended for all earth loop applications.
Horizontal Applications
For horizontal earth loops, dig trenches using either a
chain-type trenching machine or a backhoe. Dig trenches
approximately 8-10 feet [2.5 to 3 meters] apart (edge to
edge of next trench). Trenches must be at least 10 feet [3
meters] from existing utility lines, foundations and property
lines and at least 50 feet [15.2 meters] minimum from privies
and wells. Local codes and ordinances supersede any
recommendations in this manual. Trenches may be curved to
avoid obstructions and may be turned around corners. When
multiple pipes are laid in a trench, space pipes properly and
backfill carefully to avoid disturbing the spacing between the
pipes in the trench. Figure 16 details common loop cross-
sections used in horizontal loops. Actual number of circuits
used in each trench will vary depending upon property size.
Use GeoDesigner software to determine the best layout.
Vertical Applications
For vertical earth loops, drill boreholes using any size drilling
equipment. Regulations which govern water well installations also
apply to vertical ground loop installations. Vertical applications
typically require multiple boreholes. Space boreholes a minimum
of 10 feet [3 meters] apart. In southern or cooling dominated
climates 15 feet is required. Commercial installations may require
more distance between bores. This manual is not intended for
commercial loop design.
The minimum diameter bore hole for 3/4 inch or 1 inch U-bend
well bores is 4 inches [102 mm]. Larger diameter boreholes
may be drilled if convenient. Assemble each U-bend assembly,
fill with water and perform a hydrostatic pressure test prior to
insertion into the borehole.
To add weight and prevent the pipe from curving and digging
into the borehole wall during insertion, tape a length of conduit,
pipe or reinforcing bar to the U-bend end of the assembly. This
technique is particularly useful when inserting the assembly
into a borehole filled with water or drilling mud solutions, since
water filled pipe is buoyant under these circumstances.
Carefully backfill the boreholes with an IGSHPA approved
Bentonite grout (typically 20% silica sand soilds by weight)
from the bottom of the borehole to the surface. Follow IGSPHA
specifications for backfilling unless local codes mandate
otherwise. When all U-bends are installed, dig the header
trench 4 to 6 feet [1.2 to 1.8 meters] deep and as close to the
boreholes as possible. Use a spade to break through from
ground level to the bottom of the trench. At the top of the
hole, dig a relief to allow the pipe to bend for proper access to
the header. The “laydown” header mentioned earlier is a cost
effective method for connecting the bores. Figure 17 illustrates
common vertical bore heat exchangers.
Use an IGSHPA design based software such as GeoDesigner
for determining loop sizing and configurations.
Pond/Lake Applications
Pond loops are one of the most cost effective
applications of geothermal systems. Typically 1 coil of
300 ft of PE pipe per ton [26 meters per kW -- one 92
meter coil per 3.5 kW of capacity] is sunk in a pond
and headered back to the structure. Minimum pond
sizing is 1/2 acre [0.2 hectares] and minimum 8 to 10
feet [2.4 to 3 meters] deep for an average residential
