Note: Descriptions are shown in the official language in which they were submitted.
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A BURIED VERTICAL SCREW-SUNK HEAT EXCHANGER FOR A HEATING
OR COOLING INSTALLATION
The field of the invention is shallow and medium-
depth geothermal engineering. Consequently, the
invention may also apply to laying foundations for
buildings.
In the field of shallow and medium-depth geothermal
engineering, air/soil or liquid/soil heat exchangers are
known that are used in heating or air-conditioning
installations and that are currently constituted either
by sheets of tubes made of plastics materials or of metal
and that are buried to depths of a few tens of
centimeters, or else by vertical tubes, or indeed, in
certain situations, by vertical pins.
Such heat exchangers pass a heat-transfer fluid.
The heat-transfer fluid can be water, or water to which
antifreeze and/or corrosion inhibitors has/have been
added, or indeed a refrigerant of the category
constituted by ammonia, by carbon dioxide, and by
fluorine-containing compounds.
Devices known as "Canadian wells" or "Provencal
wells" are also known, in which air is caused to pass
through underground pipes placed at depths generally
lying in the range 1 meter to 3 meters before the air, as
moderated in temperature by passing through the soil, is
fed into a building.
Implementing such prior art heat exchangers requires
considerable earthworking means and is thus particularly
costly. In addition, the performance of the heat
exchangers depends directly on the surface areas of tubes
in contact with the ground, that surface area being
limited, by construction, to the surface area of the
outside walls of the tubes, which walls are strictly
cylindrical. Under all circumstances, such heat
exchangers represent a pure extra cost, insofar as their
sole function is to contribute to operation of the
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heating and/or air-treatment systems equipping any given
building.
A main object of the invention is to improve the
performance of fluid/soil heat-exchangers used in making
heating or air-conditioning installations for buildings,
regardless of whether said buildings are individual or
collective residential buildings, service sector
buildings, or industrial or agricultural buildings, or
indeed lightweight buildings for residential leisure use.
A further object of the invention is to reduce the
prices of fluid/soil heat exchangers while also
increasing the life spans of such heat exchangers.
An additional object is to enable fluid/soil heat
exchangers to be implemented rapidly without requiring
the use of excessive earthworking means, and in
particular to enable such heat exchangers to be installed
in small plots of land or even directly under buildings
that are already built, or indeed, in plots of ground
areas that are fully occupied by buildings.
An additional object consists in facilitating
building of lightweight constructions while also
improving the thermal performance of such constructions.
In order to achieve these objects and others that
appear on reading the description of embodiments and uses
of the invention, the invention proposes to implement
heat exchangers by means of screw-sunk metal piles,
similar to those used for laying foundations for
lightweight constructions. Such an embodiment, which is
particularly inexpensive, makes it possible to increase
the working heat-exchange area and thus the effectiveness
of the heat exchangers. In a preferred embodiment, the
screw-sunk metal piles have two functions in that they
act both as building supports and also as heat exchangers
for feeding the heating/air-conditioning systems of the
buildings in question.
The invention is based on using hollow metal piles
that have bottom ends of conical shape, and that are
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provided with mainly horizontal fins of helical shape,
said fins having large surface areas and relatively small
pitch (typically and in a manner lying within the prior
art for laying foundations for lightweight constructions,
pitch of a few centimeters per turn, so as to make it
possible to put the piles into place by screw-sinking).
In the following description, it can be seen that
the objects of reducing cost are achieved by using tried
and tested installation and implementation methods that
are designed for laying foundations and/or while
combining the foundation function with the heat-exchanger
function. It can be observed that the objects of
improving efficiency are obtained by means of the action
of helical fins that contribute to increasing the area of
contact between each of the tubes and the soil, and
therefore to increasing the quality and effectiveness of
heat exchange, while also, when using the piles of the
invention both as heat exchangers and as foundation
elements, procuring a bed that is particularly resistant
both to pushing-in forces and to pulling-out forces. It
can also be observed that said helical fins offer not
only the advantage of enabling the piles of the invention
to be put into place rapidly and inexpensively since they
can be put into place by means of a simple screw-sinking
machine, but also the advantage of significantly
increasing the area of contact between each of the tubes
and the soil. In addition, it can be seen that the
specific features recommended by the invention make it
possible to increase the mass of materials involved in
the heat exchange between the fluid and the soil, by
putting materials into place, around the peripheries of
the piles, which materials are adapted to facilitate such
heat exchange, while also making it possible to
strengthen the anchoring of the vertical piles in the
soil.
In the invention, the mainly horizontal helical fins
have three functions:
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1) they enable the piles to be sunk by screw-sinking
whenever said piles are subjected to high rotary torque
by means suitable machines or tooling;
2) they constitute bearing surfaces suitable for
improving the resistance of the piles to being pushed
deeper and/or pulled out once said piles have been sunk
into the soil; and
3) they improve the area of heat exchange between
the outside wall of the pile, with which wall they are in
thermal contact, and the soil into which said pile has
been sunk by means of the screw-sinking operations made
possible by the presence of said fins.
Additionally, the piles of the invention are
provided with mainly vertical fins that serve to push
away the earth or the mineral matter making up the soil
to a distance corresponding to the width of said mainly
vertical fins relative to the outside walls of the piles.
Once a pile has been put into place by screw-sinking, the
resulting space generated as the piles are being sunk
into the soil may be filled with a suitable material,
e.g. lean cement, bentonite, or a substance that changes
state. This suitable material offers the advantage of
presenting conductivity that is greater than the
conductivity of earth. Advantageously, it may also
present high specific heat. In a variant offering
particularly good performance, this material is
constituted by a material chosen from paraffins, or from
substances having the property of storing and of
delivering large quantities of heat on going from their
solid states to their liquid states, or from their liquid
states to their solid states.
Putting the piles into place by using a suitable
machine that enables a first segment of tube provided
with a tapering and pointed or conical bottom end to be
subjected to thrust and rotation forces has the effect
firstly of causing said segment to penetrate into the
soil, under the effect of the mainly horizontal fin with
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which said segment is provided, and secondly of pushing
away the earth at the periphery of said tube under the
effect of the mainly vertical fins that compact the earth
that has been broken up by the mainly horizontal fin and
5 that form an empty cylindrical sheath between the outside
wall of the pile and the cylinder of compacted earth.
Once this first segment, which preferably has a length of
about 3 meters, has been sunk into the ground, it is
possible either to use it as it is by equipping it with
internal partitioning and with a flange plate at its top,
or to extend it with one or more additional segments,
each of which may also have one or more mainly horizontal
fins making it easier for them to penetrate into the soil
and one or more mainly vertical fins pushing away and
compacting the earth at the periphery of the tube. The
additional segments are assembled to the bottom segment
by crimping, by inter-fitting, by welding, or by screw-
fastening. In any event, said segments are assembled
together such that the resulting pile has the same shape
as a single tube provided with a pointed end and with a
plurality of mainly horizontal fins and, optionally, but
particularly advantageously for the performance of the
installation, with one or more mainly vertical fins. The
resulting pile is sunk until its top end comes flush with
the ground level, or indeed a little more deeply, in
which case the soil is dug out down to a depth of about
50 cm. The pile is then equipped with internal
partitioning, defining an axial compartment and an outer
compartment, and with a flange plate at its top, through
which flange plate the pipes pass that make it possible
to feed fluid to the inner and outer compartments. In
the particularly advantageous situation when the tubes
forming the piles are equipped with mainly vertical fins,
there exists a space having the shape of a hollow
cylinder between the outside wall of the tube and the
compacted earth that has been pushed away at the
periphery of the tube by the action of said mainly
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vertical fins. The space is mainly occupied by the
mainly vertical fin(s) and it can be understood that, in
this condition said mainly vertical fins cannot
effectively enable heat to be transmitted between the
soil and the fluid flowing through the internal
compartments of the piles. That is why the invention
recommends completely filling the empty space generated
by the mainly vertical fins moving in rotation. This
filling is performed with a material that, at the time it
is put in place by being cast, has viscosity sufficient
to fill the entire void lying between the outside wall of
the tube and the surface of the compacted earth. For
example, the filling may be performed with:
a lean mortar or cement;
= a resin preferably filled with conductive
particles (e.g. with iron filings or carbon fibers);
= a material of the bentonite type or of some
equivalent type; or
= a material having the property of changing state
at positive temperatures, preferably close to 20 C, so
that the quantities of heat stored and delivered are as
large as possible. In order to avoid any risk of the
material running away into the earth, it is
advantageously contained in reservoirs of elongate
cylindrical shape or of shape adapted to filling the
empty space generated by the mainly vertical fins moving
in rotation.
The invention can be understood more clearly with
reference to the accompanying figures, in which:
= Figure 1 is a view showing a dwelling standing on
four piles of the invention, which piles have two
functions since they act both as supports for the
dwelling and as heat exchangers for the primary circuit
of a reversible heat pump used for heating and for
cooling said dwelling;
= Figure 2 is an enlarged view of an element of
Figure 1;
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Figure 3 is a view showing a dwelling standing on
three piles of the invention, said piles feeding a
liquid/air heat exchanger for moderating the temperature
of replacement air for the dwelling;
= Figure 4 is a section view and shows
implementation details of a pile of the invention;
= Figures 5A and 5B are section views on section
lines AA and BB of Figure 4; and
= Figure 6 is an enlarged section view of a pile of
the invention in a preferred embodiment.
The figures show that the invention recommends using
at least one hollow pile 1 as a heat exchanger for
exchanging heat between the soil and a fluid, which pile
is preferably made of metal and is sunk substantially
vertically into the soil by screw-sinking. The pile has
an inside wall (1i), and outside wall (le) and a wall
thickness that is substantially constant. The pile 1 can
be made up of a plurality of segments connected together
end-to-end in leaktight manner.
The pile 1 has:
= at least one helical and substantially horizontal
fin 2 having a flattened shape and a small pitch, and
being suitable for causing the pile to sink by a few
centimeters per turn, when said pile is caused to move in
rotation, said helical fin 2 finding itself united
mechanically with and in thermal contact with the outside
wall le of the pile;
= internal partitioning 3 defining two distinct
compartments 11, 12 that communicate with each other at
the bottom 13 of the pile 1, namely an axial compartment
11, and an outer compartment 12, the outer compartment 12
advantageously having a flow section S2 that is
significantly smaller than the flow section'S1 of the
axial compartment 11;
a bottom portion 9 that is of conical shape; and
a top flange plate 8 having through openings for
pipes 4 communicating in leaktight manner with each of
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the two compartments defined by the internal
partitioning 3.
In a preferred embodiment that procures particularly
good performance, in addition to being provided with the
fin(s) 2, the pile 1 is provided with at least one mainly
vertical fin 22. This mainly vertical fin 22
advantageously has a length such that it does not extend
beyond the outer end of the mainly horizontal fin 2,
above which said mainly vertical fin is placed. Said
mainly vertical fin is connected to the outside wall of
the pile 1, preferably by welding. The fin 22 has a
rounded or beveled end so that, while it is moving in
rotation, it pushes away the earth that has previously
been broken up under the action of the mainly horizontal
fin 2. After all of the segments forming the fluid/soil
heat exchanger have been put into place by screw-sinking,
the void generated by the mainly vertical fin moving in
rotation 22 is advantageously filled with a material that
offers good performance as regards heat conduction and
storage, or, for certain uses, as regards strength.
Said material is lean mortar or cement, bentonite, or a
substance having the property of changing stage at a
temperature close to 20 C and, in any event, greater than
10 C.
The fact that each of the piles of the invention has
at least one vertical fin 22 of a width less than the
diameter of the mainly horizontal fin 2 thus makes it
possible to form an empty space that is coaxial with the
pile. This space that is formed by the vertical fin 22
moving in rotation being filled with a material 25 having
thermal inertia and conductivity greater than those of
the earth in which said pile is sunk. And the material
25 can be chosen from among substances that have the
feature of going from the solid state to the liquid state
at a temperature greater than 10 C, e.g. from among the
family of normal paraffins or of isoparaffins.
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Under these circumstances, it can be understood that
the fluid that is colder in winter or hotter in summer
relative to the soil exchanges heat firstly with the
outside wall of the pile 1, then with the horizontal
fin(s) 2 and with the vertical fin(s) 22, and,
simultaneously, with the mass of filler material 25 that
finds itself in thermal contact with the vertical fin(s)
22. Finally, the filler material 25 exchanges heat with
the compacted earth T that finds itself at its periphery,
as shown in Figure 6, the heat finally diffusing to the
rest of the soil that has not been affected by the
operations of putting the piles into place by screw-
sinking.
The piles of the invention are put into place in
successive segments. The bottom segment has an end 9 of
conical shape that is suitable for penetrating into the
soil, and that makes it possible to close off the
compartments in which the fluid flows. The segments are
assembled together in leaktight manner by welding, by
inter-fitting, or by screw-fastening, and each segment
has one or more helical fins 2 in thermal contact with
the outside wall 1 of said pile.
When the piles of the invention are used as
foundations for a building, and more specially for a
greenhouse or for a lightweight dwelling, each of them,
at its top, is provided with a link piece 10 having
fastening means suitable for being secured to the floor
17 or to the bottom structure of a building 7, and with a
side or top opening making it possible to pass feed and
discharge pipes for the fluid. Thus, each of the
vertical piles of the invention is provided with a top
flange plate 8 that is secured to the floor 17 or to the
bottom structure of a building 7 via a link piece
provided with orifices for passing the pipes 4.
The fluid that exchanges heat with the soil as it
passes through the compartments of the heat exchanger
constituted by one or more piles as described and
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connected together in series or in parallel via pipes 4
can be used to feed the primary circuit of a
thermodynamic machine 5 of the heat pump type.
In order to enable heat exchange to take place
5 between the fluid and the soil in which the piles of the
invention are sunk, the outer compartment 12 is connected
via pipes 4 to a liquid/air heat exchange unit 15, said
liquid/air heat exchange unit itself being connected via
pipes 4 to the axial compartment 11, which axial
10 compartment 11 co-operates with the outer compartment 12,
with the pipes 4, and with the liquid/air heat exchange
unit 15 to form a leaktight and sealed circuit that also
has at least one circulator 16.
In order to enable the replacement air for a
building to be pre-heated or to be cooled, the unit 15
passes the replacement air feeding the building, of which
said pile forms part of the foundations.
In this way, the use of at least one pile of the
invention makes it possible to implement heating or air-
conditioning installations, or air treatment or air pre-
treatment installations.
It is also possible, using at least one pile of the
invention, to lay foundations for an industrial or
agricultural building, an individual or collective
residential building, or a leisure building, thereby
enabling such buildings to benefit firstly from
foundations that are inexpensive and that offer
particularly good performance, and secondly from heating
and/or cooling installations that have very low energy
consumption.
In a simplified embodiment, each of the piles 1 is
provided with a single fin 2 at its bottom, thereby
enabling each pile to be implemented in a single segment.
In a preferred embodiment, each of the piles 1 is
provided with a plurality of fins 2, each fin being
situated at one end of a segment; the segments being
assembled together by welding, by inter-fitting, by
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force-fitting, or by screw-fastening. Thus, the machine
that exerts the screw-sinking torque and a vertical
pressure on the successive pile segments can put each
segment into place in succession, a leaktight mechanical
connection being formed, e.g. by welding, at the outside
walls of the piles. The operations of sinking the pile
into the soil are facilitated by the presence of a
conical piece 9 at the bottom of said pile.
Advantageously, said conical piece 9 is fastened to the
bottom end of a segment using the same means, e.g. screw-
fastening, crimping, or welding, as those used for
fastening one segment to the lower segment, so that the
segments are identical to one another and each of them
can then be connected equally well at its bottom to the
conical end-piece or to another segment, and at its top
either to a terminal flange plate or some other type of
plate, or to another segment.
Under all circumstances, each of the piles 1 is
equipped with means for causing a fluid to flow over all
or almost all of its length. Such means can, for
example, be internal partitioning 3 that opens out at its
bottom 13 such that the fluid flows vertically along the
length of the tube from top to bottom inside said
internal partitioning 3, at the bottom of which said
fluid flows out and back up along the inside wall through
an annular section lying between the outside wall of the
axial tube and the inside wall of the pile 1.
Advantageously, the outside diameter of the internal
partitioning 3 is close to the inside diameter of the
tube constituting the pile 1, in a manner such that the
residual annular section S2 lying between the two
cylindrical surfaces defined by said walls is
sufficiently small for the fluid to flow turbulently,
even for relatively low flow rates. Also advantageously,
and in accordance with an important characteristic of the
invention, the internal partitioning 3 is provided with a
section reducer that can be in the form of a projection
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or protuberance 31 that is placed at a height
corresponding to the presence of a helical fin in thermal
contact with the outside wall of the pile. This feature
makes it possible to accelerate the fluid passing between
the projection 31 and the outside wall of the tube
forming the pile, so that the zone equipped with a
helical fin constitutes a particularly effective heat
exchange zone for heat exchange between the earth in
which the pile is buried and the fluid flowing inside the
pile. This original feature makes it possible to reduce
the sinking depth and thus the cost of the fluid/soil
heat exchangers relative to known geothermal probes for
the same effectiveness. The combination firstly of the
action of a metal fin having a large surface area in
contact with the soil even at distances remote from the
axis of the pile, and secondly of the turbulent flow of
the fluid on either side of a metal wall makes it
possible to obtain very high performance as regards heat
exchange.
In Figure 4, the flow section reducer or projection
31 is in the form a sleeve engaged around the internal
partitioning 3 at the fin 2.
Figure 6 shows a preferred embodiment of the
invention, particularly as regards the internal
partitioning 3. Similarly to the partitioning in the
embodiment shown in Figure 4, this partitioning forms an
axial central compartment or passage 11 having a cross-
section Sl. The outer compartment is subdivided by the
partitioning 3 into a plurality of passages or cells 12a
running along the inside wall li of the pile 1. There
are seven of these passages 12a in the embodiment shown
in Figure 6. They are disposed in such a manner as to be
distributed around the central axial compartment 11.
Each passage 12a has a substantially half-moon shape. It
can be noted that the partitioning 3 has a wall thickness
that is considerable given that it extends from the axial
compartment 11 to the inside wall of the pile 1 between
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the passages 12a. The partitioning 3 thus occupies more
than one half of the section of the pile 1. It can be
thought of as a solid bar whose axial core has been
hollowed out to form the axial compartment 11, and whose
outside surface has been cut into to form the outer
passages 12a. Since the internal partitioning 3 comes
into contact with the inside wall of the pile 1, it is
centered automatically inside the pile 1.
Each passage 12a has a cross section s2. The sum of
the sections s2 of all of the passages 12a corresponds to
the total section S2. In the invention, the total
section S2 is less than the section S1 of the axial
compartment 11. In addition, as shown in Figure 6, the
two passages 12a situated at the helical fin 2 are
partially filled with a filler element that forms a
projection or protuberance 31 relative to the outside
wall of the partitioning 3. The projections 31 serve to
reduce the sections of the passages 12a so that there
remains only a reduced section s2' in each of them. The
fluid is thus forced to flow at high speed along the
inside wall of the pile 1 directly at the helical fin 2.
Said projections or protuberances 31 can be considered as
flow section reducers.
In practice, the partitioning 3 can be made by
extrusion so that it has a constant cross-section over
its entire length. The partitioning 3 can be made of
metal or of a plastics material. Preferably, the
partitioning 3 is made of a plastics material so as to
avoid heat exchange between the central compartment 11
and the outer compartment formed by seven passages 12a.
The flow section reducers or projections 31 can be in the
form of inserts mounted inside the passages 12a. In a
variant, the flow section reducers or projections 31 can
be formed directly by the partitioning or by the pile,
e.g. in the form of internal extensions of the fins.
The fluid thus exchanges heat with the soil in which
the piles 1 are sunk. This exchange is made more
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effective and faster by means of the action of the fins 2
that have a large surface area in contact with the soil
and are in thermal contact with the metal tube
constituting the pile. The fluid flowing in the piles 1
is then collected in pipes 4 that convey it to at least
one system 5 for heating or cooling premises 7, said
premises 7 preferably, but not necessarily, being built
on foundations formed by one or more piles of the
invention.
In a particularly advantageous embodiment shown in
Figures 1 and 2, the heating or cooling system 5 is
constituted by a water/water heat pump that is preferably
reversible and whose primary circuit exchanges heat with
one or more piles connected to the system 5 via a circuit
4, and whose secondary circuit exchanges heat with a
circuit 6, e.g. a low-temperature under-floor heating
circuit.
In a simplified embodiment shown in Figure 3, the
circuit 4 collecting the fluid flowing through the
pile(s) of the invention is connected to an air heat
exchanger unit 15, i.e. to an air/fluid heat exchanger,
the replacement air for the premises going through said
exchanger. Such a heating and cooling system, which is
described, in particular, in Patent Application WO
2006/109003, makes it possible to procure all of the
features of systems known as "Canadian wells" (or as
"Provencal wells" or indeed as "Californian wells") while
requiring earthworks that are inexpensive, and a small
footprint, and while facilitating maintenance operations.
In the simple example shown by Figure 3, three piles
1 of the invention are used. Each of these piles has
fins 2 and a conical bottom end 9 enabling it to be sunk
by screw-sinking and facilitating heat exchange with the
soil. The piles are provided with internal partitioning
3 inside which the fluid flows, the fluid in this example
being water, optionally with anti-freeze added. This
fluid is collected by a circuit 4 that is preferably
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buried at a depth of a few tens of centimeters below
ground level. The fluid flows continuously by means of
the action of a pump or circulator 16 so that, depending
the current climate conditions, it exchanges heat with
5 the new air fed into the premises under the action of a
fan (not shown) that causes said new air to flow through
an air heat exchanger unit 15 in which the fluid that
benefits from the heat exchange with the soil flows,
which heat exchange takes place due to said fluid flowing
10 in the piles and is made particularly effective by means
of the presence of the helical fins 2. In order to
improve heat-exchange capacities, and in order to make it
possible to optimize operation in day/night cycles, all
or some of the partitioning or of the zone at the
15 periphery of the tube that is vacated by the compacting
of the earth due to the mainly vertical fin 22 moving in
rotation can be filled with a substance having the
property of changing state at a temperature close to the
looked-for comfort temperature, e.g. 20 C and in all
cases greater than 10 C. For example, this substance is
chosen from among paraffins that offer the property of
storing and delivering about 50 kilocalories per gram,
when crossing their change-of-state thresholds. This
particularly advantageous embodiment makes it possible to
improve significantly the performance of liquid/soil heat
exchangers of the invention, without significantly
increasing their cost. In particular, this embodiment
makes it possible, during summer seasons, to extract
large quantities of heat during the day due the change of
state from solid to liquid. This is made possible by
previously freezing the paraffins during the night when
the outdoor temperature is at a temperature lower than
the melting point of the paraffins, such freezing
resulting from the paraffins that are contained in the
walls forming the partitioning 3 and/or filling the
hollow cylinder going from the liquid state to the solid
state.
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At the top of each of the piles of the invention, a
flange plate 8 is provided that serves as a cap and to
which the internal portioning can be fastened, thereby
defining an axial compartment and an outer compartment.
The diameter of the tube forming the internal
partitioning is chosen so that there remains only a flow
space of small section between the partitioning and the
outside wall of the pile, so that the fluid flows
turbulently in this portion of the pile. Preferably, the
partitioning wall has extra thickness or a protuberance
at the external fin(s), such that heat exchange between
the fluid and the wall of the pile is facilitated in this
zone that has the advantage of high potential for thermal
transmission to the surrounding environment constituted
by the soil.
In general, it is possible to use any type of
coupling with various systems for heating, air-
conditioning, pre-heating or cooling residential premises
or replacement air for residential premises, and in
particular the couplings with air-to-air, air-to-water,
water-to-water, water-to-air, refrigerant-to-water or
refrigerant-to-air heat pumps, without thereby going
beyond the ambit of the invention.
The invention is preferably used for building
lightweight leisure dwellings that require shallow or
medium-depth foundations and that need to be frost-
protected by heat exchange with the soil, even while they
are vacant. In this particular situation, the fluid can
be caused to flow between the soil and at least one air
heat exchanger unit by a pump powered by photovoltaic
solar collectors. The invention is also particularly
suitable for use in building agricultural or industrial
structures such as greenhouses or sheds or warehouses, it
being understood that these preferred uses are in no way
limiting.
Insofar as the piles of the invention are used for
both of their functions, i.e. both as heat exchangers and
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also as lightweight foundations, a link piece 10 is
provided between firstly the top of each of the piles 1,
which top is equipped with a flange plate 8, and secondly
the floor 17 or a bearing piece of the bottom structure
of the building 7.
