U.S. patent application number 10/502070 was filed with the patent office on 2005-03-24 for heat source or heat sink unit with thermal ground coupling.
Invention is credited to Guynn, Kevin W., Waterkotte, Klemens.
Application Number | 20050061472 10/502070 |
Document ID | / |
Family ID | 7712738 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050061472 |
Kind Code |
A1 |
Guynn, Kevin W. ; et
al. |
March 24, 2005 |
Heat source or heat sink unit with thermal ground coupling
Abstract
The invention relates to a heat source or a heat sink unit with
thermal ground coupling, comprising at least one ground probe
arranged in the earth, whereby each earth probe is a probe tube
made from several pile tube segments. An open dip tube or a
U-shaped tube loop is arranged in the probe tube at the open lower
end thereof. Said unit is characterized in that each pile tub
segment is made from ductile cast iron, the pile tube segments re
embodied such as to plug into each other at the ends thereof and
each pile tube segment comprises, at the one end thereof, a conical
outer circumference and, at the other end thereof, a sleeve
embodied with a shoulder stop having a matching conical internal
circumference, whereby the diameter thereof and the cone angle are
such that on driving in the pile tube segments a positive and
sealed connection between the pile tube segments is generated.
Inventors: |
Guynn, Kevin W.; (Chicago,
IL) ; Waterkotte, Klemens; (Herne, DE) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL LLP
P.O. BOX 061080
WACKER DRIVE STATION, SEARS TOWER
CHICAGO
IL
60606-1080
US
|
Family ID: |
7712738 |
Appl. No.: |
10/502070 |
Filed: |
November 15, 2004 |
PCT Filed: |
January 18, 2003 |
PCT NO: |
PCT/EP03/00470 |
Current U.S.
Class: |
165/45 ;
165/104.11 |
Current CPC
Class: |
F24T 10/15 20180501;
F24T 10/17 20180501; Y02E 10/10 20130101 |
Class at
Publication: |
165/045 ;
165/104.11 |
International
Class: |
F28D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2002 |
DE |
102 02 261.5 |
Claims
1-18. CANCELLED.
19. 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ground, wherein thermal energy can either be withdrawn from or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 fight against the
surrounding ground and comprises 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, wherein
each drive-pipe segment is formed of ductile cast iron; and wherein
the drive-pipe segments are formed such that they can be fitted
into each other at their ends, wherein 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, and wherein a first advancing drive-pipe segment of
the probe shaft is, at its forward end, has a probe tip.
20. A system according to claim 1, wherein each tapered outer
perimeter of each drive-pipe segment is provided at a forward end
of said drive-pipe segment and wherein the sleeve of each
drive-pipe segment that is designed with the stop shoulder is
provided at a backward end of said drive-pipe segment.
21. A system according to claim 19, wherein an outer diameter of
the immersion pipe is smaller than an inner diameter of the probe
shaft and that a length of the immersion pipe is slightly smaller
than a length of the probe shaft.
22. A system according to claim 19, wherein a length of the
U-shaped pipe loop extending up to the latter's U-bend is slightly
smaller than a length of the probe shaft wherein a part of an
interior region of the probe shaft that is not occupied by the pipe
loop is filled with a thermally conductive filling material.
23. A system according to claim 19, wherein a last drive-pipe
segment of the probe shaft is, 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 arranged on
said connection cover.
24. A system according to claim 23, wherein the immersion pipe or
the pipe loop is solely mounted to or in the connection cover.
25. A system according to claim 19, wherein the immersion pipe or
the pipe loop comprises an air vent or a vent valve at its upper
end.
26. A system according to claim 19, wherein the immersion pipe or
the pipe loop is formed of a plastic material.
27. A system according to claim 19, wherein the probe shaft is
driven into the ground either in vertical direction or in an
inclined direction not exceeding 75.degree. in relation to the
vertical direction.
28. A system according to claim 19, wherein the probe shaft is
driven into a borehole that has been predrilled into the ground,
with a maximum depth of the borehole being as great as a length of
the probe shaft and with a diameter of the borehole being smaller
than an outer diameter of the probe shaft.
29. A system according to claim 19, wherein a wall thickness of
each drive-pipe segment, with the exception of a region at either
of its ends, ranges from 10 to 20 percent of an outer diameter of
the drive-pipe segment.
30. A system according to claim 19, wherein each drive-pipe
segment, with the exception of a 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.
31. A system according to claim 19, wherein a length of each
drive-pipe segment approximately ranges from 4 to 6 m and wherein a
total length of the probe shaft approximately ranges from 10 to 50
m.
32. A system according to claim 19, wherein the heat transfer fluid
is pure water under a pressure of an order approximately ranging up
to 10 bar.
33. A system according to claim 19, wherein the heat transfer fluid
is carbon dioxide under a pressure of an order of at least
approximately 100 bar.
34. A system according to claim 19, wherein each drive-pipe segment
is provided with an anticorrosive layer on at least one of its
external and internal surfaces.
35. A system according to claim 34, wherein the anticorrosive layer
is formed by one of galvanizing and plastic coating.
Description
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] A 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 groundwater requires official approval which is granted only
under specific conditions.
[0004] Furthermore, panel collectors are already known, which are
usually designed as horizontally arranged tube-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.
[0005] 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 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
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.
[0006] 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 may, sooner or later, be the starting
point of cracks or breakages.
[0007] 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 manner, which is particularly safe with regard to
potential environmental impairments, which has a long service life,
and which has a first-rate efficiency.
SUMMARY OF THE INVENTION
[0008] 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 is made 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.
[0009] Initially, it is provided according to the invention that
each drive-pipe segment is formed 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;
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 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 difficulties 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 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.
[0010] Since the probe shafts each comprise 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 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.
[0011] 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.
[0012] The system can be used both as a heat source for heating
purposes and as a heat sink for cooling purposes. 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.
[0013] 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
latter'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.
[0014] 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 required 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.
[0015] 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 loop 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.
[0016] 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.
[0017] It is, furthermore, provided according to the invention that
the last drive-pipe segment of the probe shaft is, 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 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, 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.
[0018] 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
difficultly 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 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.
[0019] 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.
[0020] 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 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.
[0021] 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 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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 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 segments being inserted in
the ground not vertically, but at an inclined angle.
[0026] 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 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.
[0027] As an alternative, the heat transfer fluid may also be
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.
[0028] 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 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.
[0029] 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.
[0030] 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.
BRIEF DESCRIPTION OF THE DRAWING
[0031] Executive examples of the invention will be illustrated
below by means of a drawing, in which:
[0032] FIG. 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;
[0033] FIG. 2 is a longitudinal sectional view of a section of a
modified probe shaft; and
[0034] FIG. 3 is a schematic vertical sectional view of a heat
recovery system with two probe shafts driven into the ground at an
inclined angle.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] According to the executive example shown in FIG. 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.
[0036] The drive blows executed by the hydraulic hammer cause the
drive-pipe segments 20 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 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' 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.
[0037] Preferably, the drive-pipe segments 20 and the probe tip 23
are formed 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 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.
[0038] 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 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 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.
[0039] Intermittent operation of the associated heating device 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, 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 I/m in practice,
becomes positively apparent. This results in typical times for a
complete recirculation of the heat transfer fluid approximately
ranging from 30 to 60 minutes.
[0040] 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 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 in the hollow inner region 28
of the probe shaft 2 and vice versa.
[0041] 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.
[0042] According to FIG. 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.
[0043] 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
FIG. 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, 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.
[0044] In a system with several ground probes 1, the several 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
FIG. 3, instead of vertically as shown in FIG. 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.
[0045] As is apparent from the foregoing specification the
invention is susceptible of being embodied with various alterations
and modifications which may differ particularly from those that
have been described in the preceding specification and description.
It should be understood that I wish to embody within the scope of
the patent warranted hereon all such modifications as reasonably
and properly come within the scope of my contribution to the
art.
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