Patent Publication Number: US-2022228779-A1

Title: Ground heat exchanger

Description:
REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Patent Application No. 63/139,026 filed on Jan. 19, 2021 and Canadian Patent Application No. 3,121,345 filed Jun. 7, 2021, all of which are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     This disclosure relates to a geothermal system of heat exchange and more particularly to a geothermal pile that is disposed in the ground inside a contained volume of water or another liquid. 
     BACKGROUND 
     Geothermal energy is said to be the second most abundant source of heat on Earth. It is the heat energy that is stored in the Earth and contained in rocks and metallic alloys, just below the outer surface of the Earth. The temperature of these rocks and metal alloys is at or near their melting points. Geothermal piles are often used to capture and bring above ground this heat stored below the ground. U.S. Pat. No. 10,655,892 to Kong et al. describes a geothermal heat transfer pipe embedded in a prefabricated pipe pile, sealed by closing the bottom thereof. U.S. Pat. No. 9,611,611 to Klekotka et al. describes the process of driving piles and the installation of piles into the ground for geothermal applications. U.S. Pat. No. 9,708,885 to Loveday et al., entitled System and Method for Extracting Energy, describes ways in which to better couple a pile with the walls of a surrounding borehole by injecting water into an annulus between the pile and the soil, to have the soil form a better thermal coupling with the pile after mixing with the injected water. 
     Geothermal piles are typically made of concrete or steel, having a wellhead at an upper end and having a U-shaped conduit within the center thereof for carrying a liquid such as water, alcohol, refrigerant, or a combination thereof. Although piles of this type perform a function, their ability to capture heat from the surrounding soil is somewhat limited and depends to some degree on the type of soil in which the pile is installed. 
     The presence of a groundwater table can facilitate heat transfer to and from the ground because thermal conductivities of water and soil are orders of magnitude higher than that of air. Thus, water-saturated soil is a more efficient medium for heat transfer than dry soil. Furthermore, having a greater surface area in which to collect the heat energy, and a medium to augment the transfer is advantageous. 
     It would be beneficial to provide an improved geothermal system for extracting heat energy from the ground. 
     SUMMARY OF EMBODIMENTS 
     It is well known that energy transfer in a medium such as water has a convective and a conductive component. Although other liquids may be used, in at least some embodiments described hereinafter water is selected as a suitable medium to transfer heat from the ground to a geothermal pile rather than directly coupling the geothermal pile to the surrounding ground. Water has the significant advantage of being present in the environment under natural conditions and does not cause any environmental concerns. As such, using water as an intermediary coupling medium offers numerous advantages—it is abundant, safe in the instance of a leak in the vessel, and it has adequate conductive properties. 
     An embodiment includes an in-ground vessel containing a liquid such as water, which forms an artificial water table, for collecting heat from the surrounding ground. A geothermal pipe or pile is disposed generally coaxially within the vessel for collecting heat from the ground-heated water contained within the vessel. The vessel containing the geothermal pipe or pile may have crushed gravel or another solid medium disposed therein to assist in securing the geothermal pipe or pile. In some embodiments the in-ground vessel is a steel pipe or tube having a closed bottom end. Alternatively, the steel pipe or tube of the in-ground vessel has an open bottom end that butts up against an impermeable ground layer, such as a rock layer, or is set in a concrete plug that serves to seal and anchor the bottom end of the pipe or tube. Further alternatively, the in-ground vessel is fabricated from another suitable material such as for instance concrete or plastic, etc. 
     In some embodiments, a geothermal system includes a pipe or pile disposed substantially coaxially within a vessel located at a depth within the ground, the pipe or pile containing a conduit for transporting a liquid from an inlet port to an outlet port through at least a portion of the pipe or pile in two directions (i.e., initially downward and then back upward). The vessel contains a liquid such as water in a region around the outside of the pipe or pile so that the liquid surrounds and contacts the pipe or pile. The outer surface area of the vessel is significantly greater than the outer surface area of the pipe or pile at same height, by virtue of having a larger diameter, and therefore contacts a larger area of the surrounding ground for extracting energy therefrom than would be the case if the pipe or pile was in direct contact with the surrounding ground. 
     A method for installing a geothermal system according to an embodiment may include boring a hole in the ground having depth of at least 25 feet (i.e., up to at least 50 feet or more) and having a first diameter d 1  of at least 40 inches (i.e., generally at least in the range 36-60 inches in diameter or more). An outer vessel is positioned of formed in the bored hole and having a second diameter d 2  conforming to the first diameter d 1  of the bore hole (i.e., a steel pipe or tube is inserted into the bore hole or concrete is poured to form a tube-shaped concrete vessel within the bore hole). A bottom end of the vessel is either sealed prior to being inserted into the bore hole or is arranged adjacent to a naturally or artificially occurring impermeable layer at the bottom end of the bore hole (i.e., abuts an impermeable rock layer or is set into a poured concrete plug). The vessel forms a container suitable for containing a heat conducting first liquid, such as for instance water. A geothermal pile is then arranged within the vessel, having third diameter d 3  smaller than the second diameter d 2 . A region between the geothermal pile and inner wall of the vessel is filled with the heat conducting first liquid to a height so that at least a bottom portion of the geothermal pile is surrounded with the heat conducting first liquid. The geothermal pile has a conduit disposed therein for circulating a heat conducting second liquid into and out of the geothermal pile, the heat conducting first liquid being isolated from the heat conducting second liquid. In operation, heat is transferred between the ground surrounding the vessel and the heat conducting first liquid, and then subsequently between the heat conducting first liquid and the heat conducting second liquid through conduction. 
     In accordance with an aspect of at least one embodiment, there is provided a geothermal system for extracting heat energy from the ground, comprising: an outer vessel having a diameter d 2 , the outer vessel disposed within the ground and having a sidewall with an outer surface that is in contact with surrounding ground material when the geothermal system is in an installed condition, and the outer vessel having an inner surface defining an interior volume of the outer vessel; a geothermal pile having a diameter d 3  that is less than d 2  and being disposed within the interior volume when the geothermal system is in the installed condition; and a first heat conducting liquid at least partially filling a space between the inner surface of the sidewall of the outer vessel and an outer surface of the geothermal pile when the geothermal system is in the installed condition, wherein the geothermal pile comprises a conduit contained within an interior space thereof for conducting a second heat conducting liquid into the geothermal pile at a top end thereof and along a flow path within the geothermal pile toward a bottom end of the geothermal pile and then back to an outlet at the top end thereof, and wherein during operation heat is transferred from the surrounding ground to the second heat conducting liquid via the first heat conducting liquid within the space between the inner surface of the sidewall of the outer vessel and the outer surface of the geothermal pile. 
     In accordance with an aspect of at least one embodiment, there is provided a method of constructing a heat exchange system in the ground, comprising: providing a borehole in the ground having a first diameter d 1 ; providing an outer vessel, having a diameter d 2  less or equal to d 1 , within the borehole; arranging a geothermal pile having an internal conduit extending along a length thereof within the outer vessel; at least partially filling a space between an inner sidewall surface of the outer vessel and an outer surface of the geothermal pile with a first heat conducting liquid; and coupling an inlet port and an outlet port of the conduit to a liquid circuit for a second heat conducting liquid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments will be described in accordance with the drawings, which are not drawn to scale, and in which: 
         FIG. 1  is a simplified diagram of a prior art closed end geothermal heat exchange pile. 
         FIG. 2  is a simplified diagram of a prior art closed end geothermal heat exchange pile with helical flights. 
         FIG. 3  is a simplified diagram of a prior art geothermal heat exchange pile having a grout sealed closed end. 
         FIG. 4  is a simplified diagram of a co-axial geothermal heat exchanger in accordance with an embodiment. 
         FIG. 5  is a simplified diagram of another co-axial geothermal heat exchanger in accordance with an embodiment. 
         FIG. 6  is a simplified diagram of a geothermal heat exchanger in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 
       FIG. 1  is a simplified diagram showing a construction pile  100  adapted for use as a geothermal pile. The pile  100  has a closed end, e.g., a 25 mm base plate  102  is welded to the cylindrical sidewall of the pile  100 . The pile  100  has a length L and is driven into the ground in known fashion. For instance, the length of the pile  100  is a standard 50 ft. length. Alternatively, the pile  100  may be any suitable length required for a specific application. 
     Pile  100  is adapted to have an inlet port  104  and an outlet port  106  approximately at or above grade  108 . A continuous conduit  110  is disposed within the pile  100 , which extends longitudinally from a top end  112  to near the bottom end  114  along a substantial portion of the length L of the geothermal energy pile  100 . The conduit  110  may be coiled or U-shaped (as shown in  FIG. 1 ) and provides a path (indicated by the arrows within the conduit  110 ) for liquid to flow from the top end  112  to the bottom end  114  of the pile  100  and then back up to the top end  114  and out through the outlet port  106 . As the liquid moves along the path through the conduit  110  in the pile  100 , heat is transferred into or out of the liquid from outside the conduit  110 . In heating applications, this heat is collected from the surrounding ground  116 , which has a high water table  118  as shown in  FIG. 1 . An access cover  120  optionally is provided to allow access for servicing, etc. 
       FIG. 2  is a simplified diagram showing a helical construction pile  200  adapted for use as a geothermal pile. The pile  200  has a set of helical flights  202 , which are used to advance the pile  200  into the ground when the pile  200  is rotated about its longitudinal axis. The pile  200  has an angled, closed bottom-end, e.g., a 25 mm base plate  204  is welded to the cylindrical sidewalls of the pile  200 . The pile  200  has a length L and is screwed into the ground in known fashion. For instance, the length of the pile  200  is a standard 50 ft. length. Alternatively, the pile  200  may be any suitable length required for a specific application. 
     Pile  200  is adapted to have an inlet port  206  and an outlet port  208  approximately at or above grade  210 . A continuous conduit  212  is disposed within the pile  200 , which extends longitudinally from a top end  214  to near the bottom end  216  along a substantial portion of the length L of the geothermal energy pile  200 . The conduit  212  may be coiled or U-shaped (as shown in  FIG. 2 ) and provides a path (indicated by the arrows within the conduit  212 ) for liquid to flow from the top end  214  to the bottom end  216  of the pile  200  and then back up to the top end  214  and out through the outlet port  208 . As the liquid moves along the path through the conduit  212  in the pile  200 , heat is transferred into or out of the liquid from outside the conduit  212 . In heating applications, this heat is collected from the surrounding ground  218 , which has a high water table  220  as shown in  FIG. 2 . An access cover  222  optionally is provided to allow access for servicing, etc. 
       FIG. 3  is a simplified diagram showing a construction pile  300  adapted for use as a geothermal pile. The pile  300  has a non-shrink grout seal  302  closing a bottom end thereof. The pile  300  has a length L, for instance a standard 50 ft. length. Alternatively, the pile  300  may be any suitable length required for a specific application. 
     Pile  300  is adapted to have an inlet port  304  and an outlet port  306  approximately at or above grade  308 . A continuous conduit  310  is disposed within the pile  300 , which extends longitudinally from a top end  312  to near the bottom end  314  along a substantial portion of the length L of the geothermal energy pile  300 . The conduit  310  may be coiled or U-shaped (as shown in  FIG. 2 ) and provides a path (indicated by the arrows within the conduit  310 ) for liquid to flow from the top end  312  to the bottom end  314  of the pile  300  and then back up to the top end  312  and out through the outlet port  306 . As the liquid moves along the path through the conduit  310  in the pile  300 , heat is transferred into or out of the liquid from outside the conduit  300 . In heating applications, this heat is collected from the surrounding ground  316 , which has a high water table  318  as shown in  FIG. 3 . An access cover  320  optionally is provided to allow access for servicing, etc. 
     Referring now to  FIG. 4 , a geothermal pile  400  has a closed end, e.g., a 19 mm end cap  402  is welded to the cylindrical sidewalls of the pile  400 . Other means for closing the end of the geothermal pile  400  may be used. The geothermal pile  400  has a circular cross-section of e.g., diameter d 3  about 8 inches, but optionally the diameter d 3  may be greater than or less than 8 inches depending upon specific requirements. A conduit  404 , having an inlet port  406  and an outlet port  408  both disposed approximately at or above grade  410 , is arranged within the geothermal pile  400 . The conduit  404  extends along a substantial portion of a length L 1  of the geothermal pile. The length L 1  may be any suitable length depending on specific requirements, for instance between about 25 feet and 50 feet. Alternatively, the length L 1  is less than 25 feet or greater than 50 feet, depending on specific requirements. The conduit  404  is preferably fabricated from a heat conducting material such as for instance copper, although plastic tubing or other suitable materials may be used with less effectiveness in transferring heat to or from a liquid within the conduit  404 . 
     The description which follows refers to the capturing of heat from the ground  412  to the liquid within the conduit  404 , however it should be understood that the reverse may occur if the ground  412  is cooler than the liquid flowing into the conduit  404  via the inlet port  406 . Depending on the temperature difference, the geothermal system shown in  FIG. 4  may be used for heating or cooling. 
     Geothermal energy pile  400  is shown disposed within and being substantially coaxial with a larger energy transfer pile  418 , which is also referred to herein as an outer vessel, having circular cross-section with a diameter d 2  of e.g., 24 inches and a length L 2 . The energy transfer pile  418  may have a closed bottom end (not shown in  FIG. 4 ), or alternatively the energy transfer pile  418  may butt up against an impermeable subsurface layer, such as for instance a rock layer  420 . The energy transfer pile  418  is shown to have a diameter d 2  approximately three time greater than the diameter d 1  of the energy pile  400 , and the length L 2  in this example is less than the length L 1 . Of course, other pile sizes may be used, such as for instance a pile  400  having a 16-inch diameter d 3  and a pile  418  having a 48-inch diameter d 2 , etc. In addition, the lengths L 1  and L 2  may be substantially equal, or L 2  may be greater than L 1  etc. In general, both L 1  and L 2  are typically in the range of 25 feet to 50 feet, but lengths less than 25 feet or greater than 50 feet may be used depending on specific requirements. 
     A liquid, such as for instance water, is contained within an annular space  422  that is formed between an outer wall surface of the pile  400  and an inner wall surface of the energy transfer pile  418 . The liquid preferably fills the annular space  422  to a height H that is sufficient to cover less than 75% of the length L 1  of the pile  400 , however the liquid may fill the annular space  422  above this level and may even overflow the top of the energy transfer pile  418  into the surrounding ground  412 . Thus, pile  418  acts as an outer vessel containing water and also contains the geothermal pile  400  in a generally central region thereof. The pile  418  is made of any suitable material, such as for instance sections of steel pipe or tube that are joined together along joints  424  (such as for instance by welding) and having a predetermined thickness selected to provide a required strength and longevity to withstand forces upon it. As will be apparent, the larger diameter pile  418  has a much greater outer surface area than the outer surface area of the centrally disposed geothermal pile  400 . Since the surface area of a pile having a circular cross section is given by πr 2 h, the larger surface area of pile  418  is capable of collecting a significantly greater amount of energy from the soil  412  that is directly adjacent to it, compared to the amount of energy that could be collected by the smaller diameter pile  400  in the absence of the larger pile  418 , due to the squared term r 2 . For instance, a geothermal pile having a height of 10 feet and a radius of 1 foot has a surface area of 10π contacting the surrounding ground but a geothermal pile having the same height of 10 feet and a radius of 4 feet has a surface area of 160π contacting the surrounding ground. The water contained within the annular region  422  between the pile  418  and the geothermal pile  400 , which may be referred to as an artificial water table, is in contact with the large surface area (steel) wall of the pile  418 , and absorbs the ground heat from the soil  412  adjacent to the outer wall of the pile  418 . The heat that is absorbed by the contained water is transferred, though conduction and convection, to the inner geothermal pile  400 . The speed at which heat transfers by conduction and convection is considerably greater than the speed of heat transfer by conduction alone, and accordingly the efficiency of heat transfer between the surrounding ground and the inner geothermal pile  400  is improved in the system that is shown in  FIG. 4 . 
     As shown in  FIG. 4 , a material such as for instance one or more of sand, gravel or another solid medium may be placed within the annular space  422  between the geothermal pile  400  and the pile  418 , to assist in securing the geothermal pile  400 . In this embodiment, the liquid and the sand, gravel or other solid medium transfer the heat from the surrounding ground  412  to the conduit  404  within the geothermal pile  400 . An access cover  424  optionally is provided to allow access for servicing, etc. 
     Referring now to  FIG. 5 , shown is an alternative embodiment similar to the embodiment of  FIG. 4 , except a concrete plug  500  is formed at the bottom end of the outer vessel  418  and the bottom end of the geothermal pile  400  is embedded in the concrete plug  500 . The concrete plug  500  effectively seals the bottom of the outer vessel  418  to facilitate containing the first heat conducting liquid therein. 
     Various alternative and/or optional embodiments in addition to those described with reference to  FIGS. 4 and 5  may be envisaged. Some important variations are discussed in the following paragraphs, which apply equally to the embodiments shown in  FIGS. 4 and 5 . 
     In a not illustrated embodiment, an upper portion of the conduit  404  is insulated or double jacketed so that ground-heat that is collected at the lower portion of the pile  400  is not lost when the liquid in the conduit  404  travel upward toward the outlet port  408 . 
     In a further not illustrated embodiment, the conduit  404  is made of a first length of a highly conductive material at its bottom end, which is the end closest to where the bottom end  414  of the pile  400  is located within the borehole, and is made of a second length of an insulating material at its top end, which is the end closest to where the top end  416  of the pile  400  is located within the borehole. In this way, the heat that is collected by the liquid at the bottom end of the conduit  404  is not lost along the return path toward the outlet port  408 . 
     In another not illustrated embodiment, a circulating pump is provided to increase the turbulence and hence enhance the convective effect and speed of energy transfer through the water that is contained within the annular space  422  between the pile  418  and the pile  400 . 
     In yet another not illustrated embodiment, a small rotating hub with radiating blades (i.e., an impeller) is disposed within the water near the bottom of the pile  418  to provide additional circulation and increase turbulence, so as to increase the rate of heat transfer. 
     In yet another not illustrated embodiment, the larger diameter energy transfer pile  418  may be significantly shorter in length that the geothermal cell or pile  400  placed therewithin. What is important is that the larger pile  418  or outer vessel be located at a depth in the ground where the most energy transfer will take place. 
     One or more of the various embodiments described above may further include a means to ensure that the outer vessel  418  contains a suitable amount of water. A simple sump pump (not shown) can be provided, which fills the outer vessel  418  if the amount of water therewithin is less than a predetermined amount. 
     In a not illustrated embodiment the water fills the space  422  between the inner surface of the sidewall of the outer vessel  418  and the outer surface of the geothermal pile  400  only to a height that is sufficient to cover less than ¾ of the length L 1  of the geothermal pile  400 . What is important is that the water covers the geothermal pile at a depth in the ground where the most energy transfer will take place. In other embodiments the water may fill the space  422  between the inner surface of the sidewall of the outer vessel  418  and the outer surface of the geothermal pile  400  to a height that is sufficient to cover more than ¾ of the length L 1  of the geothermal pile  400 . In some embodiments, the water may cover the entire length L 1  of the geothermal pile  400  and may even overflow the space  422  into the surrounding ground material  412 . 
     In another embodiment, a flow control valve can be added to the bottom of the larger outer vessel  418  to allow pumped in water to flow into the outer vessel  418  slowly and/or in a controlled manner and/or to overflow over the annulus  422  to the surrounding soil  412  so as to have a better thermal contact between the surrounding soil  412  and the outer vessel  418 . This flow preferably adds turbulence to the water within the outer vessel  418  in the anulus  422  which is advantages for convective heat transfer between the surrounding soil and the geothermal pile. 
     Although the embodiments described heretofore have shown the liquid disposed between the inner geothermal cell and the outer pile to be water, other liquids can be used. In addition, although the embodiments described heretofore describe and illustrate providing a borehole, disposing a large diameter pile having a closed end (or an open end butted up against an impermeable layer) in the borehole, placing a geothermal pile within the large diameter pile, and filling the annulus between the two piles with an energy conducting liquid such as water, other embodiments may be envisaged. For example, a geothermal cell, which is not in the form of a pile, but is a conduit which directs a liquid into and out of the geothermal cell, may be disposed in the center of the large diameter pile. 
     The geothermal heat exchange systems described with reference to  FIGS. 4 and 5  may be constructed according to the following method. A bore borehole is formed in the ground having a first diameter d 1 . Known techniques, appropriate for the ground type within which the installation is occurring may be used to form the borehole. An outer vessel, having a diameter d 2  that is less than or substantially equal to d 1 , is inserted into the borehole. The outer vessel may be formed using a single length of pipe or tubing formed of a suitable metal or metal alloy, or by arranging a series of shorter lengths of pipe or tubing in a stacked arrangement with joints (sealed or unsealed) between adjacent lengths, or by pouring a concrete liner having a generally circular cross section with an internal diameter d 2 . A geothermal pile having an internal conduit extending along a length thereof is arranged generally centrally and coaxially within the outer vessel. The diameter d 3  of the geothermal pile is less than d 2 , preferably d 3  is about ⅓ d 2 . The generally annular space between an inner sidewall surface of the outer vessel and an outer surface of the geothermal pile is at least partially filled with a first heat conducting liquid, such as for instance water. An inlet port and an outlet port of the conduit within the geothermal pile is connected to a liquid circuit for a second heat conducting liquid. The liquid circuit e.g., collects the heated second heat conducting liquid from a plurality of geothermal piles, and provides the heated liquid to one or more points of use, such as for instance a building heating system. 
     Referring now to  FIG. 6 , shown is a geothermal heat exchanger similar to the ones that are shown in  FIGS. 4 and 5 , but without a separate outer vessel for containing a volume of water. The configuration that is shown in  FIG. 6  may be employed e.g., when the ground material  412  is stable and substantially impermeable to water, such that the inner wall  600  of the bore hole in the ground performs the roll of containing the volume of water. For instance, the bore hole may be formed into ground material  412  such as clay or rock, etc. to a depth L 2 , and geothermal pile  400  having length L 1  &lt;L 2  may be arranged substantially centrally within the borehole. A material  426  such as for instance sand and/or gravel or another suitable material may be added into the annular space  422  between the inner wall  600  and the outer surface of the geothermal pile  400 , to a height that is sufficient to cover at least the lower portion of the geothermal pile  400  so as to secure the geothermal pile  400  in its desired position within the borehole. The generally annular space  422  is also at least partially filled with a first heat conducting liquid, such as for instance water. An inlet port and an outlet port of the conduit within the geothermal pile  400  is connected to a liquid circuit for a second heat conducting liquid. The liquid circuit e.g., collects the heated second heat conducting liquid from a plurality of geothermal piles  400 , and provides the heated liquid to one or more points of use, such as for instance a building heating system. 
     Throughout the description and claims of this specification, the words “comprise”, “including”, “having” and “contain” and variations of the words, for example “comprising” and “comprises” etc., mean “including but not limited to”, and are not intended to, and do not exclude other components. 
     It will be appreciated that variations to the foregoing embodiments of the disclosure can be made while still falling within the scope of the disclosure. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the disclosure are applicable to all aspects of the disclosure and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).