Note: Descriptions are shown in the official language in which they were submitted.
CA 02473369 2004-07-12
i 1
Heat source or heat sink system with thermal ground
cou Zing
The present invention relates to a heat source or heat
sink system with thermal ground coupling for near-surface
recovery of thermal energy from the ground or for near-
surface discharge of thermal energy into the ground,
wherein the system comprises at least one ground probe
arranged in the ground, wherein thermal energy can either
be withdrawn from or discharged into the ground by means
of a heat transfer fluid supplied through the ground
probe, wherein each ground probe comprises a metallic
probe shaft that is tight against the surrounding ground
and consists of several drive-pipe segments driven into
the ground, and wherein either an immersion pipe that is
open at its lower end or a U-shaped pipe loop is arranged
in the probe shaft for supplying or removing the heat
transfer fluid.
Systems for the aforementioned types of intended use
are known from practice in various executive forms. In
essence, these known solutions can be grouped in three
different groups.
A f first group of systems according to the known state-
of-the-art is operated with an open circuit, wherein
groundwater is collected from a groundwater conduit, is
cooled or heated in a heat pump or another unit and is
returned to the groundwater conduit. However, this heat
recovery from or heat discharge into the groundwater is
possible only if an appropriate groundwater conduit is
available and if the quality of the groundwater is
satisfactory. In addition, the collection and return of
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CA 02473369 2004-07-12
2
groundwater requires official approval which is granted
only under specific conditions.
Furthermore, panel collectors are already known, which
are usually designed as horizontally arranged tube-
s register heat exchangers and are placed in the ground at
a depth of approximately 1 m or slightly more. Such panel
collectors require extensive earthworks, thus causing
expensive installation; in addition, they can often not
be used owing to local conditions.
Finally, ground probes are known for the establishment
of heat source systems. These known ground probes consist
of a single or double pipe loop installed in a borehole
that is drilled vertically into the ground. In general,
the depth of the borehole is less than 100 m, but it may
also exceed this value. Where sandy soil is concerned,
the boreholes are usually drilled according to flush
drilling method. In solid ground, use is mostly made of
what is called the airlift drilling method with an in-
hole hammer. This drilling method requires provision of a
two-stage air compressor with a working pressure ranging
up to 24 bar and an operating energy input of 200 kW and
higher. Where unconsolidated rock is concerned, a
protective piping is used for drilling, said protective
piping being, in practice, for example typically 152 mm
in diameter. In hard.rock, a typical diameter of, for
example, 128 mm is used for continuing the drilling
process until the particular final depth required is
reached. The pipe loop assembly must be inserted. in the
finished ground borehole. Thereafter, the remaining space
between the pipe loop and the walls of the ground
borehole must be progressively filled with filling
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' CA 02473369 2004-07-12
3
material from bottom to 'top,~said filling material in
practice mostly being bentonite, i.e. a cement-clay
mixture. This ensures that water-bearing layers are
reliably and permanently sealed against each other and
that the thermal contact required between the pipe loop
and the ground is ensured. It is also obvious that the
establishment of such a system is very complicated and,
thus, expensive. In addition, such systems require
official approval, so that additional cost and time
ZO expenditures are caused by the appropriate application
for and processing of the approvals. What is more and as
practical observations have shown, the responsible
authorities often treat such applications in a
restrictive manner and with exaggerated care as regards
the potential contamination of groundwater in case of
leakages.
An apparatus for inserting rod-type heat exchangers
into the ground is known from DE 79 36 659 U1. It is,
preferably, provided that the heat exchangers used
therein have the form of drive core probes that are
composed of segments screwed to each other by means of
tapered threaded parts. This is to disadvantage in that
the screwed connections between the segments are
sensitive while the driving-in procedure is in progress,
and have a tendency to tears and leaks associated
therewith; this also applies to the welded or soldered
connections that are known from practice. The cutting of
threads, the welding or the soldering are to disadvantage
in that all of these processes result in local changes in
the structure and hardness of the material of the probe
shaft segments and, thus, in potential weak spots which
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" CA 02473369 2004-07-12
4
may, sooner or later, be the starting point of cracks or
breakages.
For that reason, the present invention aims at creating
a system of the aforementioned type which obviates the
drawbacks disclosed and which can, in particular, be
established in an economical mariner, which is
particularly safe with regard to potential environmental
impairments, which has a long service life, and which has
a first-rate efficiency.
This problem is solved by the invention by means of a
system of the aforementioned type that is characterized
in that
each drive-pipe segment consists of ductile cast
iron,
- the drive-pipe segments are formed such that they
can be fitted into each other at, their ends, and
- each drive-pipe segment comprises a tapered outer
perimeter at one of its ends and, at its other end,
a sleeve provided with a stop shoulder and having a
mating tapered inner perimeter, wherein _their
diameters and taper angles are dimensioned such that
the drive-pipe segments, on being driven in, can be
connected to each other in a force~closed and tight
manner.
Initially, it is provided according to the invention
that each drive-pipe segment consists of ductile cast
iron. In essence, ductile cast iron differs from
traditional gray cast iron in that the graphite is
contained in ductile cast iron in the form of nodular
graphite, so that the mechanical properties are changing;
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CA 02473369 2004-07-12
in particular, the strength and tenacity are increased.
As compared with gray cast iron, the chemical properties
of ductile cast iron are also improved, in particular the
corrosion resistance against pitting. The drive-pipe
5 segments can, for example, be produced according to the
centrifugal casting method, wherein it is practically
possible to use 100-percent recycling material, i.e.
steel scrap, this being both to economical and ecological
advantage. Since they are subjected to a special post-
casting process, the drive-pipe segments of ductile cast
iron have such a mechanical resistance that they can be
driven into the ground with considerable impact forces
without suffering any damage. To further facilitate the
formation of the probe shafts, the invention provides
that the drive-pipe segments are designed such that they
can be fitted into each other at their ends. Large-scale
screwed, soldered or welded connections which can be
established and tested on the construction site only
under the greatest d~.fficulties are not required between
the successive drive-pipe segments. This also facilitates
the mechanical treatment of the ends of the drive-pipe
segments during their production and also reduces the
amount of work and the risk of faults on the construction
site at the place where the drive-pipe segments are
driven into the ground. Therein, it is, furthermore,
provided according to the invention that each drive-pipe
segment comprises a tapered outer perimeter at one of its
ends and, at its other end, a sleeve having a mating
tapered inner perimeter, wherein their taper angles are
dimensioned such that the drive-pipe segments, solely by
being driven in, can be connected to each other in a
force-closed and tight manner. This embodiment of the
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6
drive-pipe segments ensures that the desired tightness
and force-closed connection of the various drive-pipe
segments to each other is obtained solely by the drive-in
process. Special sealants are not required. Each sleeve
is provided with a shoulder and, as regards the fitted
part of the respectively other segment, is designed such
that, after the sleeve has been expanded by a defined
amount, the fitted segment comes to rest on this shoulder
and then transfers the drive pulses, therein preventing
the sleeve from being subjected to the stress of a
further expansion to an impermissible extent. If the
pulses or drive blows for driving in the drive-pipe
segments are sufficiently strong, a friction weld
ensuring the desired tightness and force-locking
connection for very long operating times of the probe
shaft is obtained in the region where two drive-pipe
segments are connected to each other. Since it is not
necessary to ensure that the individual drive-pipe
segments are, at a later point, disconnected from each
other without being destroyed, this non-detachable
friction-welded connection is not of any technical
disadvantage whatsoever.
Since the probe shafts each consist of several drive-
pipe segments driven into the ground, a particularly
economical establishment of the system is ensured. This
high economical efficiency is, in particular, achieved
because the time and technical expenditures required for
driving in the drive-pipe segments in order to form the
probe shaft by means of appropriate devices, particularly
by means of a commercially available hydraulic hammer,
are less than those required for establishing a ground
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CA 02473369 2004-07-12
7
borehole; this applies, in' particular, to energy
expenditures which are, reduced by at least 80 percent. As
a matter of course, the drive-pipe segments are designed
such that, when being driven into the ground, they can
absorb the impact forces developing without suffering any
damage. The probe shaft is to advantage in that it is
tight against the surrounding ground solely by being
driven in, so that the heat transfer fluid is practically
prevented from being flowing out of the probe shaft and
into the ground, and this the more so since the drive
pipe segments forming the probe shaft have relatively
thick walls because of the mechanical stability required.
Therein, the tightness is maintained according to the
life expectancy of the probe shafts, even over long
periods of many decades.
The system according to the invention permits to
achieve a high efficiency because each probe shaft, after
having been driven into the ground, is in a firm and
close contact with the surrounding ground without special
filling or. contact materials having to be placed into the
region of the outer perimeter of the probe shaft. This
ensures a first-rate heat transfer from the ground into
the probe shaft and vice versa, without particular
measures being necessary. Since the probe shaft itself is
metallic, its thermal conductivity is very high so that
the resistance to the heat conduction out of the ground
and into the heat transfer fluid flowing in the inner
region of the probe shaft and vice versa is, altogether,
very-low.
The system can be used both as a heat source for
heating purposes and as a heat sink for cooling purposes.
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CA 02473369 2004-07-12
Therein, the system can, for 'cooling purposes, be used
either at the natural temperature level or with
interconnection of a reversely operated heat pump, i.e. a
refrigeration unit. If a reversible 'heat pump is used, it
is even possible to optionally and alternately select the
heating or cooling mode. This application is to
particular advantage, especially in southern hot climates
of the earth or in regions with typical continental
climate.
In a further embodiment, the invention preferably
proposes that the tapered outer perimeter of each drive-
pipe segment is provided at the latter' s forward end and
that the sleeve with the stop shoulder of each drive-pipe
segment is provided at the Tatter's backward end. This
embodiment permits to achieve as low a motional
resistance of the drive-pipe segments as possible when
they are driven into the ground.
A further contribution to a high economical efficiency
is obtained by the fact that only an immersion pipe that
is open at its lower end is requfired for supplying and
removing the heat transfer fluid, wherein, preferably,
the outer diameter of the immersion pipe is, furthermore,
smaller than the inner diameter of the probe shaft and
the length is slightly smaller than the length of the
probe shaft. The second half of the flow path of the heat
transfer fluid then extends through that part of the
interior region of the probe shaft that is not occupied
by the immersion pipe. This construction results in a
very low hydraulic resistance of the ground probe, this
being of decisive importance in practice. Herein, it is
not necessary to place a filling material.
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CA 02473369 2004-07-12
9
As an alternative, a U-shaped pipe loop is arranged in
the probe shaft in the stead of the immersion pipe for
supplying and removing the heat transfer fluid, wherein
it is, furthermore, preferably provided that the length
of said pipe Toop extending up to the latter' s U-bend is
slightly smaller than the length of the probe shaft and
that the part of the interior region of the probe shaft
that is not occupied by the pipe loop is filled with a
thermally conductive filling material. This embodiment of
the system according to the invention provides the
advantage of a particularly high protection against an
ingress of the heat transfer fluid into the ground in the
environment of the probe shaft since, here, both the pipe
loop and the probe shaft must become leaky before the
heat transfer fluid can penetrate into the ground. On the
other hand, this increased safety results in a slightly
lower efficiency because, here, the resistances to the
heat conduction from the ground into the heat transfer
fluid and vice versa are, altogether, slightly higher.
In order to achieve as great an advance as possible
with as low driving forces as possible when the drive-
pipe segments are driven into the ground, the first
advancing, drive-pipe segment of the probe shaft is, at
its forward end, appropriately provided with or tightly
connected to a probe tip. If the probe tip is tightly
connected to the -drive-pipe segment, this connection is
appropriately established in the manner described above
by tapered connection regions and their being friction-
welded by drive impacts.
It is, furthermore, provided according to the invention
that the last drive-pipe segment of the probe shaft is,
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CA 02473369 2004-07-12
at its backward end, tightly connected to a connection
cover attached after completion of the drive-in
procedure, with an inflow line connection and a return
flow line connection for the heat transfer fluid being
5 arranged on said connection cover. The connection -cover
provides the necessary connections for the inflow and the
return flow of the heat transfer fluid. Since it is to be
placed subsequently, the cover does not disturb when the
drive-pipe segments are driven in. Since, as a result,
10 the cover does not have to absorb any drive forces, it
can be of a light-weight design, and the usual connection
methods are appropriate for attaching the cover to the
last drive-pipe segment and for sealing the cover. In a
heat recovery system, it will be to advantage if the
inflow of the heat transfer fluid is passed through the
immersion pipe. The exit of the fluid out of the ground
probe will then be achieved through the cover where the
fluid, with regard to its temperature, has already
reliably exceeded the frost limit, so that a splitting
effect caused by the formation of ice, a problem that is
known from refrigeration engineering, is prevented on the
cover.
The fact that the immersion pipe or the pipe loop is
mounted only to or in the connection cover further
contributes to advantageously low production efforts.
Expensive and only di.fficultly accessible mounting means
in the course of the probe shaft itself are not necessary
here. Whether the immersion pipe or the pipe loop is
exactly centered while extending through the-probe shaft
or whether it approaches the walls of the probe shaft to
a higher or lesser degree is not of any noticeable
CA 02473369 2004-07-12
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importance either. Since the immersion pipe or the pipe
loop is mounted to or in the connection cover, it is not
yet positioned in the drive-pipe segments when these are
driven in, so that neither the immersion pipe nor the
pipe loop is disturbing or can be damaged in this step
either. The immersion pipe or the pipe loop is inserted
in the probe shaft only after the latter has been driven
into the ground over the complete length provided.
In order to prevent the heat transfer through the
ground probe and the remaining parts of the system from
being disturbed by air bubbles, it is provided that the
immersion pipe or the pipe loop comprises an air vent or
a vent valve at its upper end. The air vent or vent valve
permits air to exit out of the immersion pipe or the pipe
loop at the uppermost point of the probe shaft and to be
removed with the returning heat transfer fluid.
Thereafter, the air is, appropriately, finally separated
in the known manner by means of an automatic ventilation
device in the highest part of the system.
Preferably, the immersion pipe or the pipe loop
consists of plastic material, preferably of polyethylene
(PE) or polypropylene (PP). In this manner, the material
itself allows to achieve a first-rate thermal insulation
value which keeps any undesired heat exchange between the
inflowing and the returning heat transfer fluid inside
the probe shaft at a very low level. In this manner, the
immersion pipe is also relatively light so that it
practically does not cause any tensile forces to the
connection cover in connection with its buoyant lift in
the heat transfer fluid. In order to further reduce the
thermal short-circuit between the inflow and the return
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flow that is anyhow low, the immersion pipe can be
provided with an additional insulation, for example in
the form of a mounted corrugated plastic pipe, wherein
the intermediate space between the immersion pipe and the
corrugated pipe is, appropriately, also filled with the
fluid.
According to the invention, it is furthermore provided
that the probe shaft is driven into the ground either in.
vertical direction or in an inclined direction preferably
extending at an angle ranging from 15 to 75 degrees in
relation to the vertical direction. The particular drive-
in direction depends on local conditions. If the surface
area available is adequate, an inclined drive-in
direction should be preferred because this permits to
achieve a greater heat collection area on the surface of
the earth. In this manner, the amount of thermal energy
required, for example for heating a residential building,
can be obtained from the ground with a lesser number of
probe shafts. As has already been mentioned above, the
present invention relates, among others, to a system for
near-surface recovery of geothermal energy, wherein this
geothermal energy is generated by incoming solar
radiation. For that reason, it is to advantage if the
probe shaft extends at an inclined angle in relation to
the vertical direction because, in this case, the area of
the collection of the ground probe that is projected on
the surface of the earth becomes greater than when the
probe shaft only extends in vertical direction. An
inclined course of the probe shaft or of an arrangement
of probe shafts can be achieved by means of. the drive-in
method without any problems and, in particular, much more
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easier than the drilling of inclined boreholes, in
particular if the angle in relation to the vertical
direction is relatively large, for example more than 45
degrees.
If the ground is so solid that driving-in of the drive-
pipe segments is difficult, it can, exceptionally, be
provided that the probe shaft is driven into a borehole
that has been predrilled' into the ground, with the
maximum depth of the borehole being as great as the
length of the probe shaft and with the diameter of the
borehole being smaller than the outer diameter of the
probe shaft, this ensuring that the first-rate heat
conduction contact between the ground and the probe shaft
is achieved here as well. At the same time, driving-in is
facilitated to an essential degree.
To ensure that the individual drive-pipe segments of
the probe shaft can be driven into the ground without
suffering any damage and to achieve the stability
required to this end, it is preferably provided that the
wall thickness of each drive-pipe segment, with the
exception of the region at either of its ends, ranges
from 10 to 20 percent of the outer diameter of the drive-
pipe segment. Hence, the walls of the drive-pipe segments
are very thick in relation to their diameter; but, .owing
to the high thermal conductivity of the metal used to
make the drive-pipe segments, this is not to disadvantage
to the heat transfer from the ground into the heat
transfer fluid in the inner region of the probe shaft or
vice versa.
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In a more concrete embodiment that is well suitable for
most of the applications occurring in practice, each
drive-pipe segment, with the exception of the region at
either of its ends, comprises an outer diameter
approximately ranging from 80 to 200 mm and a wall
thickness approximately ranging from 7 to 12 mm. If
having the dimensions specified, the drive-pipe segments
can still be driven into the ground with relatively low
efforts and, thus, with accordingly relatively light-
weight machines, so that such drive-pipe segments can be
driven into the ground without any problems, even in
built-up areas, without causing any risk to buildings in
the environment.
In a concrete embodiment, it is, furthermore,
preferably provided that the length of each drive-pipe
segment approximately ranges from 4 to 6 m and is
preferably 5 m, and that the total length of the probe
shaft approximately ranges from 10 to 50 m and even more
if this is permitted by actual ground conditions. If
having these dimensions, the individual drive-pipe
segments can still be handled by two workers and the
current handling devices, this facilitating the work on
site at the place where the drive-pipe segments are to be
driven into the ground. Only two persons, that is an
operator for an excavator with a hydraulic hammer and a
person to hand over the pipe segments and to assist in
fitting the particular new pipe segment, are required as
personnel. If the preferred total length of the probe
shaft is as. specified, it can, in practice, be expected
in most of the cases that the drive-pipe segments of the
probe shaft can still be driven in without any problems
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CA 02473369 2004-07-12
and at a relatively high drive speed. As has already been
described above, driving-in of the ,drive-pipe segments is
usually facilitated by the drive-pipe segment s being
inserted in the ground not vertically, but at an inclined
5 angle.
For ecological reasons, the preferable heat transfer
fluid is pure water, in particular without any antifreeze
additive and in particular under a pressure of an order
of approximately 10 bar. As a matter of principle, this
10 excludes all groundwater and other environmental hazards;
that is the reason why it is much easier to obtain
official approvals and why these may even not be
applicable at all.
As an alternative, the heat transfer fluid may also be
15 carbon dioxide, in particular under a pressure of an
order of approximately 100 bar and more. This permits
operation of ground probes according to what is called
the "heat-pipe" methods, the more so since the probe
shafts, owing to their construction, are able to resist
such a high internal pressure without suffering any
damage. Moreover, an appropriately pressure-tight cover
can, without any difficulties, be provided at, in
particular welded to, the upper end .of the probe shafts .
It is also possible to optimize the "heat-pipe" method by
selecting a favorable drive angle of the probe shaft and
to distinctly improve said method as compared with the
presently usual vertical boreholes.
As mentioned above, the ductile cast iron preferably
used to make the drive-pipe segments is corrosion-
resistant to an essentially higher degree than the usual
CA 02473369 2004-07-12
16
gray cast iron. In order to protect the probe shaft even
more against leaks, even in case of long operating times
of several decades, each drive-pipe segment can, in
addition, be provided with an anticorrosive layer on its
external and/or internal surface. If saline water is
present in the ground, for example near coasts, the probe
shaft can be effectively protected against corrosion by
means of an impressed current anode. _
The anticorrosion layer can, for example, be formed by
galvanizing or by a plastic coating, preferably of
polyurethane (PU), wherein the material used should be
oxygen-diffusion-tight.
A further contribution to avoiding corrosion damages
consists in using pipes for the piping of the remaining
system and for its connection with a heating or cooling
device, which are oxygen-diffusion-tight. By this, an
introduction of oxygen into the heat transfer fluid,
which might promote corrosion of the drive-pipe segments,
is prevented.
Executive examples of the invention will be illustrated
below by means of a drawing, in which:
Figure 1 is a schematic vertical sectional view of
a heat recovery system with a single probe shaft
in a condition where it is driven into the
ground in vertical direction;
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Figure 2 is a longitudinah sectional view of a
section of a modified probe shaft; and
Figure 3 is a schematic vertical sectional view of
a heat recovery system with two probe shafts
driven into the ground at an inclined angle.
According to the executive example shown in Figure 1,
the ground probe 1 consists of a probe shaft 2 that is
composed of several drive-pipe segments 20. To form the
ground probe 1, the required number of drive-pipe
segments 20 are initially driven successively into the
ground 3 in a relatively small building pit 30 that has
been prepared beforehand, for example by means of a
hydraulic hammer mounted to an excavator arm or a
carriage. At first, the drive-pipe segment 20 that is the
bottommost in the drawing is provided with a probe tip 23
in order to ensure that said drive-pipe segments 20 can
be driven into the ground 3 with as low a resistance as
possible and as easily and quickly as possible. Herein,
the probe tip 23 is tightly connected to the forward end
21 of the lower drive-pipe segment 20. As soon as the
first drive-pipe segment 20 has been driven into the
ground 3 almost completely, a second drive-pipe segment
20 is fitted; thereafter, the first and second drive-pipe
segments 20 are further driven into the ground 3
together.
The drive blows executed by the hydraulic hammer cause
the drive-pipe segments 2O to connect to each other and
to the probe tip 23 in a force-closed and tight manner.
To achieve this, the forward end 21 of each drive-pipe
segment 20 is provided with a tapered outer perimeter
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CA 02473369 2004-07-12
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21'. The backward end of each drive-pipe segment 20 and
the rear side of the probe tip 23 are each provided with
a sleeve 22 with a mating tapered inner perimeter 22' or
23'. Therein, the taper angles of the outer perimeter 21'
S and the inner perimeter 22' or 23' are selected and
coordinated with each other such that the desired force-
closed and tight connection is achieved solely by the
drive blows or drive pulses executed while the drive-pipe
segments 20 are driven in, wherein these occurring blows
or pulses generate a friction-welded connection in the
connection area. At its lower part, each sleeve 22 is
provided with a shoulder 22" or 23" and, in connection
with the fitted forward end 21 of the particular other
segment 20, is designed such that the fitted end 21 of
the segment 20 comes to rest on this shoulder 22 " or
23" after the sleeve 22 has been expanded by a defined
amount and will then transfer the drive pulses without
subjecting the sleeve 22 to stress in expansion direction
to an impermissible extent.
Preferably, the drive-pipe segments 20 and the probe
tip 23 consist of ductile cast iron which has a
particularly high strength and tenacity so that it can
absorb the drive blows without suffering any damage and
facilitates the desired friction-welded connection in the
connection areas of the drive-pipe segments 20 when the
latter are driven in. Once the necessary total length of
the probe shaft 2, in practice for example approximately
ranging from 10 to 50 m, has been achieved, driving-in of
the drive-pipe segments 20 is completed. A connection
cover 24 is placed onto the upper end of the upper drive-
pipe segment 20 in a sealing manner and is secured with
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at least one locking screw 24'. The connection cover 24
comprises one inflow line connection 25 and one return
flow line connection 27 for a heat transfer fluid. In the
simplest case, the heat transfer fluid is water to which
an antifreeze agent, usually alcohol, is added as
required. An immersion pipe 26 that is only mounted to
the connection cover 24 and is, otherwise, extending
freely through the hollow inner region 28 of the probe
shaft 2 is connected to the inflow line connection 25.
Therein, the length of this immersion pipe 26 is only
slightly smaller than the length of the probe shaft 2.
When the ground probe 1 is operated as a part of a
heating device, cold heat transfer fluid flows through
the inflow line connection 25 into and through the
immersion pipe 26, until it reaches the lower end region
of the probe shaft 2. At the lower end 26' of the
immersion pipe 26, the heat transfer fluid exits out of
the immersion pipe 26 and is now flowing from bottom to
top through that part of the interior region 28 of the
probe shaft 2 that is not occupied by the immersion pipe
26. On its way along the wall of the probe shaft 2 from
bottom to top, the heat transfer fluid absorbs thermal
energy from the surrounding ground 3, wherein the heat
transfer fluid is heated as compared with its original
temperature. The heated heat transfer fluid exits the
probe shaft 2 through the return flow line connection 27
provided at the side of the connection cover 24. In the
case of the heat recovery system assumed here, the return
flow line connected to the connection 27 is usually
running to a heat pump in which the geothermal energy
contained and transported in the heat transfer fluid is
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CA 02473369 2004-07-12
withdrawn and is utilized for heating purposes, for
example for building or water heating purposes. The heat
transfer fluid which exits the heat pump and whose
temperature is now reduced is then supplied back to the
S inflow line connection 25 and through the immersion pipe
26 into the inner region 28 of the probe shaft 2. Hence,
this system represents a closed heat-transfer-fluid
circuit.
Intermittent operation of the associated heating device
10 and heat pump is to particular advantage because the heat
transfer fluid will, in this case, be able to absorb a
relatively great amount of thermal energy from the ground
while it is dwelling in the probe shaft 2, thus being
subjected to a relatively great increase in temperature,
15 this being favorable for the efficiency of the heat pump.
Here, the high fluid content of the ground probe, which
can, for ,example, be approximately 10 1/m in practice,
becomes positively apparent. This results in typical
times for a complete recirculation of the heat transfer
20 fluid approximately ranging from 30 to 60 minutes.
Owing to its relatively great material thickness which
it requires for being driven into the ground 3, the probe
shaft 2 is absolutely tight over very long operating
times ranging up to many decades, so that any exit of the
2S heat transfer fluid out of the probe shaft 2 and into the
ground 3 is practically excluded. After having been
driven into the ground 3, the probe shaft 2 is closely
embedded in said ground 3 so that, in connection with the
first-rate thermal conductivity of the metallic wall of
the probe shaft 2, a high efficiency is achieved on heat
transfer from the ground 3 into the heat transfer fluid
CA 02473369 2004-07-12
21
in the hollow inner region 28~of the probe shaft 2 and
vice versa.
Appropriately, the inflow and return flow lines for the
heat transfer fluid are also arranged in the ground 3,
wherein an arrangement below the frost limit, e.g. at a
depth of approximately 1 m or deeper if necessary, is to
reasonable advantage.
According to Figure 2, a pipe loop 29 that is
positioned in the probe shaft 2 in U-shaped form can
alternatively be used for routing the heat transfer
fluid. Therein, the U-bend 29' is, appropriately,
positioned near the lower end of the probe shaft 2.
Herein, the heat transfer fluid remains enclosed in the
pipe loop 29 along its entire path through the pipe shaft
2, being prevented from coming into an immediate contact
with the probe shaft 2. For reasons of heat conduction,
that part of the interior region 28 of the probe that is
arranged around the pipe loop 29 is, therefore, filled
with a thermally conducting filling material, for example
water, which is then an essentially still fluid.
Depending on the energy requirements, a heat recovery
system can comprise one or more probe shafts 2. If
several probe shafts 2 or ground probes 1 are used, as is
schematically represented in Figure 3, said shafts or
probes can be advantageously connected in series because
of their low hydraulic resistance, wherein the length of
the individual probe shafts 2 can be selected as desired.
As a result, installation becomes markedly less expensive
and a hydraulic calibration, which is always associated
with energy losses, is not applicable. If necessary,
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however, it is, of course, also possible to connect a
greater number of probe shafts 2 in parallel to each
other or in a mixed arrangement.
In a system with several ground probes I, the several
S ground probes 1 are spaced apart from each other
depending on the collection area of each individual
ground probe 1, wherein the size of the collection area
depends on the thermal conductivity of the ground 3 in
the particular case. It is also possible to drive the
probe shafts 2 into the ground 3 at an inclined angle, as
shown in Figure 3, instead of vertically as shown in
Figure 1 of the drawing. This is to advantage in many
application cases because, in this case, a larger
collection area for the thermal energy irradiated by the
sun across the surface of the earth and into the ground 3
can be achieved per probe shaft 2. With the direction of
the probe increasingly deviating from the vertical
direction, this will then allow an increasingly smaller
probe spacing. With a specified amount of energy
required, the upper ends of the probes 2 can then be
arranged on a smaller total area, this saving space and
installation cost.
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