Installation for energy exchange between the ground and an energy exchanger

A heat exchanger is connected via an insulated flow pipe (26) to a pump (28) arranged in a borehole. The flow pipe and the pump are surrounded in the borehole by a protective tube (34) open at the bottom adjacent to a return region (38) which extends radially outward to the wall of the borehole. The return region communicates with the interior of the protective tube. A return line (42) from the energy exchanger contains at least one return pipe (40) which extends approximately to the bottom of the borehole and is subdivided along its length by a plurality of transverse plugs (44). At the transverse plugs, the return water flows through passages arranged on either side of the transverse plugs and penetrates the porous filling (48) surrounding the return pipe. After the transverse plugs, the return water flows out of the porous filling and back through the passages into the return pipe. This results in reliable guiding of the return water and optimal heat uptake by the water from the return region and from the wall of the drilled hole.

The invention relates to an installation for utilizing the earth's heat in 
accordance with the preamble of claim 1. 
Installations of the above-described type are known, for example, from 
Swiss Patent 650,069. In the installation described in this patent, the 
return line leads into the upper portion of the borehole underneath the 
earth's surface. The water then flows through the porous filling to the 
bottom of the borehole, the water is heated as a result and is again 
conducted to the heat pump through the flow lines by means of the pump. 
This has the disadvantage that the return water is conducted in an 
uncontrolled manner in the return region, so that, on the one hand, short 
circuit loads may occur which make a sufficient heating of the return 
water difficult On the other hand, there is the danger that the porous 
filling is clogged, so that the resistance to flow is increased and there 
is the danger that the return water flows off into the ground. It is then 
necessary to pump water by means of the pump from the surrounding ground 
which, however, poses problems because of the resistance to flow in the 
ground Moreover, silt material is picked up from the ground which, in 
turn, results in clogging of the intake region at the bottom of the 
borehole and causes the pump to become ineffective. 
It is the object of the invention to construct an installation of the 
above-described type in such a way that the described disadvantages are 
avoided. 
The above object is met in accordance with the invention by the 
characterizing features of claim 1. 
The arrangement of the return pipe with several transverse plugs 
distributed over the length of the return pipe and the passages arranged 
on both sides of the transverse plugs ensure a defined return flow of the 
return water. The transverse plugs force the return water radially 
outwardly through the passages into the porous filling and, thus, cause 
the water to come into contact with the wall of the borehole and to be 
heated. After passing the transverse plug, the return water can again flow 
through the passages into the return pipe and can flow to the next 
transverse plug where it is again forced to flow out. This guidance of the 
return water defines the return flow to the bottom of the borehole, on the 
one hand, and ensures, on the other hand, that the return water is always 
in contact with the filling and the borehole wall and, thus, can be 
heated. However, the distances are so short that the return water can 
again collect in the next section of the return pipe. The fact that the 
return water flows out radially also ensures that the flow paths are kept 
free along the porous filling. The defined guidance of the return water 
further prevents water losses to the surrounding area. This results in an 
excellent guidance of the return water to the bottom of the borehole and 
to the pump, so that an optimum heating of the return water and a 
sufficient amount of return water through the pump are ensured. The result 
is an installation having a high efficiency and a low susceptibility to 
trouble. 
Advantageous developments of the installation are described in claims 2 to 
7. 
A development of the installation in accordance with claim 2 is 
particularly advantageous because the longitudinal slots make it possible 
to distribute the water guidance over a greater area and the small width 
still makes possible a strong jet which is capable of penetrating the 
porous filling up to the borehole wall and simultaneously flushing out any 
silt material from the porous filling. It is a further advantage if the 
installation is constructed in accordance with claim 3, so that a uniform 
distribution of the water guidance over the entire length of the return 
pipe is ensured. By offsetting the passages of adjacent rows, flushing 
through the porous filling and flushing free the porous fillings are 
reinforced. 
Various materials may serve as filling, such as, slag, special components 
and the like. However, the feature according to claim 4 is preferred. 
It is essentially conceivable to arrange only one return pipe in the return 
region. However, substantially better results can be achieved by a 
construction according to claim 5 because it is then possible to uniformly 
reach and utilize all portions of the borehole. 
The development of the installation according to claim 6 is particularly 
advantageous for preventing corrosion. The pipes of plastic material have 
a long service life and prevent corrosion residues from depositing. As a 
result, the installation has a long service life and a low susceptibility 
to trouble and, moreover, the ground water surrounding the boreholes is 
not negatively influenced. 
In particular, the installation also makes possible the development of 
claim 7, whereby any clogging can be eliminated by means of return 
flushing water.

FIG. 1 shows an installation for utilizing the earth's heat, for example, 
for at least partially heating a house 2. For this purpose, the house has 
an energy exchanger which is constructed as a heat pump 4 which includes 
in a medium circulation system 6 an evaporator 8, a compressor 10, a 
condenser 12 and a throttle valve 14. Such heat pumps 4 are known. 
Connected to the condenser 12 is in the known manner a heating unit 16 with 
a heat flow line 18, a circulation pump 20 and a heat user 22. A heat 
return line 24 closes the connection from the heat user 22 to the 
condenser 12. 
A flow pipe 26 is connected to the evaporator 8. The flow line 26 is 
connected to a pump 28 which preferably is arranged at the bottom 30 of a 
borehole 32. The flow line 26 and the pump 28 are surrounded by a 
protective tube 34. A return region 38 extending radially outwardly to the 
borehole wall 36 is provided adjacent the protective tube 34. Several 
return pipes 40 are arranged in this return region 38. The return pipes 40 
are arranged distributed over the circumference and are combined in a 
common return line 42 which is connected to the evaporator 8. 
As can be seen in FIG. 2, each return pipe 40 extends almost to the bottom 
30 of the borehole 32 and includes several transverse plugs 44 which are 
distributed over the length of the return pipe 40. Passages 46 are 
arranged on both sides of the transverse plugs 44. The passages initially 
facilitate a discharge of the return water into the porous filling 48 
which surrounds the return pipe 40 and fills out the return region 38. The 
passages are preferably longitudinal slots which may have a width of 1 mm 
and a length of 150 mm. The return pipe has several rows 50.sub.1 to 4 of 
the passages 46. The rows are distributed over the length of the return 
pipe and, for example, four passages per row can be distributed over the 
circumference of the return pipe 40. The passages 46 of the adjacent rows 
are preferably arranged offset relative to each other in circumferential 
direction. 
The porous filling 48 filling out the return region 38 around the return 
pipe 40 advantageously is gravel having a granular size of 0.8 to 8 mm. In 
the region of the bottom 30 of the borehole 32, the return region 38 is in 
connection with the interior of the protective tube 34 through passages 52 
in the protective tube 34. A scavenging pump 54 is connected to the upper 
end of the protective tube 34. The scavenging pump 54 serves to introduce 
return flushing water into the protective tube 34 and through the passages 
52 into the return region 38 in order to eliminate any silt accumulation 
in the porous filling 48. 
A specific embodiment of the installation may have the following 
dimensions: 
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Diameter of borehole: 
500 to 1000 mm 
Depth of borehole: 
100 to 2000 m and deeper 
Diameter of flow pipe: 
50 to 90 mm 
Diameter of return pipe: 
40 to 50 mm 
Diameter of protective tube: 
120 to 160 mm 
Temperature of return water: 
greater than 6.degree. C. 
Quantity of circulating water: 
1.5 to 10 m.sup.3 /h 
Power: 30 KW at 250 m depth 
50 KW at 350 m depth 
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The insulating flow line and the return pipe are advantageously of plastic 
material, preferably polyvinylchloride. Depending on the geological 
conditions, the borehole itself may be lined at least over portions 
thereof by means of a steel pipe. 
The term energy exchanger used herein is to be understood in its most 
general sense and may include a direct user, such as, heating coils in 
floors, traffic routes (for example, bridges, ramps, etc.) or heating 
radiators and the like, but also heat exchangers and particularly heat 
pumps. As a rule, the energy exchanger will be constructed for the 
dissipation of energy, i.e. for heating purposes. However, the energy 
exchanger may also be used for absorbing heat, so that the installation 
can be used for cooling.