US20220018577A1

US20220018577A1 - Groundwater enhanced geothermal heat pump

Info

Publication number: US20220018577A1
Application number: US17/299,363
Authority: US
Inventors: Jimmy Bryan Randolph; Scott Alexander; Martin Saar
Original assignee: University of Minnesota
Current assignee: University of Minnesota
Priority date: 2018-12-04
Filing date: 2019-12-04
Publication date: 2022-01-20
Also published as: WO2020117946A1; CA3121511A1; EP3891444A1

Abstract

A geothermal heat pump system includes a main heat exchanger, a borehole that penetrates an aquifer, and a ground loop. The main heat exchanger is configured to exchange heat between a ground loop flow and a heat distribution system. The ground loop includes a first and second groundwater heat exchangers, an input pipe and an output pipe. The groundwater heat exchangers are respectively contained in first and second zones within the borehole and are exposed to a groundwater flow within the aquifer. The input pipe is configured to deliver the ground loop flow from the main heat exchanger to the groundwater heat exchangers. The output pipe is configured to deliver the ground loop flow from the groundwater heat exchangers to the main heat exchanger. Heat exchange occurs between the ground loop flow within the groundwater heat exchangers and the groundwater flow.

Description

FIELD

Embodiments of the present disclosure relate to geothermal heat pump systems, geothermal heat pump system ground loops, geothermal boreholes and wells, and groundwater heat exchangers that are configured to utilize groundwater to provide and enhance heat exchange. Additional embodiments are directed to methods of using the systems, ground loops and heat exchangers.

BACKGROUND

Heat pumps generally move thermal energy from one location to another, such as moving thermal energy from a heat source to a heat sink (for example, a region of higher temperature to a region of lower temperature), or from a heat sink to a heat source (for example, a region of lower temperature to a region of higher temperature). Thus, a heat pump can provide cooling in the summer and heating in the winter. The heat pump performs a refrigeration cycle using a circulating refrigerant as the medium which moves the heat through evaporation (heat absorption) and condensation (heat rejection) phases. The evaporation and condensation phases of the refrigerant typically takes place in two different heat exchangers called the evaporator and condenser, respectively. In a heat pump, the evaporator is switched to be a condenser and vice versa depending on whether cooling or heating is required.
Geothermal or ground source heat pumps use the earth as a heat source or heat sink. A heat exchanger is positioned underground to provide cooling by using the earth as a heat sink, or to provide heating by using the earth as a heat source. The ground loops of most traditional geothermal heat pump systems focus on heat exchange with subsurface rocks and sediments, and do not systematically take advantage of heat exchange with flowing or stationary groundwater.

SUMMARY

Embodiments of the present disclosure are directed to geothermal heat pump systems having ground loops that utilize groundwater and groundwater flows to enhance heat exchange. One embodiment of a geothermal heat pump system includes a main heat exchanger; a borehole, well, pipe, or other device that penetrates an aquifer, and a ground loop. The main heat exchanger is configured to exchange heat between a ground loop flow and a heat distribution system. The ground loop includes a groundwater heat exchanger, an input pipe and an output pipe. The groundwater heat exchanger is contained within the borehole, well, or other device and exposed to groundwater within the aquifer. The input pipe is configured to deliver the ground loop flow from the main heat exchanger to the groundwater heat exchanger. The output pipe is configured to deliver the ground loop flow from the groundwater heat exchanger to the main heat exchanger. Heat exchange occurs between the ground loop flow within the groundwater heat exchanger and the groundwater flow.
In one embodiment, the borehole includes a sealed wall section that blocks the groundwater flow into the borehole, and a permeable wall section, through which the groundwater travels into the borehole. The permeable wall section of the borehole may include a screen.
In another embodiment, the borehole, well, pipe, drainage tile or other device has two permeable wall sections separated by an impermeable section or a section with lower permeability. The groundwater heat exchanger is positioned between the permeable sections or within permeable sections.
In another embodiment, the borehole has multiple permeable sections and multiple impermeable sections. One or more groundwater heat exchangers may be positioned between or within the permeable sections.
In one embodiment, the groundwater flow travels from a region of high hydraulic head to a region of low hydraulic head, and the groundwater heat exchanger is positioned in the borehole between the region of high hydraulic head and the region of low hydraulic head.
In one embodiment, the groundwater flow travels horizontally across the borehole and the groundwater heat exchanger.
One embodiment of the system includes one or more packers that are configured to support the groundwater heat exchanger within the borehole.
One embodiment of the system includes at least one packer in the borehole that divides a lower zone of the borehole containing the heat exchanger from an upper zone of the borehole, and restricts or blocks groundwater from flowing between the lower and upper zones.
One embodiment of the system includes a flow generator that is configured to circulate the groundwater flow over the groundwater heat exchanger. One embodiment of the flow generator comprises a pump.
In one embodiment, the groundwater heat exchanger is a first groundwater heat exchanger that is positioned in a first zone of the borehole, and the system includes a second groundwater heat exchanger that is positioned within a second zone of the borehole.
One embodiment of the groundwater heat exchanger includes a heat exchange coil, through which the ground loop flow travels between the input pipe and the output pipe. One embodiment of the heat exchange coil includes a first stacked coil and a second stacked coil. The first stacked coil includes a stack of a plurality of first coil sections, each first coil section is coiled around a central axis and has a first diameter. The second stacked coil is connected to the first stacked coil and includes a plurality of second coil sections, each second coil section is coiled around the central axis and has a second diameter that is greater than the first diameter. The ground loop flow travels through the first and second stacked coils. In another embodiment, the coils are initially and terminally connected to manifolds, and the manifolds are connected to the input and output lines.
Another embodiment of the borehole heat exchange coil includes a coil body that is spiraled around a central axis. The coil body includes an interior end proximate the central axis, an outer end that is radially displaced a greater distance from the central axis than the interior end, a divider wall that divides an interior cavity of the coil body into upper and lower fluid pathways, a first port at the interior end of the upper fluid pathway, a second port at the interior end of the lower fluid pathway, and a cap at the outer end of the coil body fluidically connecting the upper and lower fluid pathways. The ground loop flow travels through the upper and lower fluid pathways and the cap.
Another embodiment of the heat exchange coil includes a first conical spiral coil that extends along a central axis and includes a first end having a first port, and a second end having a second port. The first end is radially displaced a greater distance from the central axis than the second port. The first conical spiral coil includes a fluid pathway between the first and second ports. The ground loop flow travels through the fluid pathway of the first conical spiral coil. In one embodiment, the heat exchange coil includes a second conical spiral coil having a first end that includes a first port that is connected to a second port of the first conical spiral coil, and a second end having a second port. The first end of the second conical spiral coil is radially displaced a greater distance from the central axis than the second port of the second conical spiral coil. The second conical spiral coil includes a fluid pathway between the first and second ports of the second conical spiral coil. The ground loop flow travels through fluid pathways of the first and second conical spiral coils. In yet another embodiment, the heat exchange coil includes a third conical spiral coil that extends along the central axis and includes a first end having a first port that is connected to the second port of the second conical spiral coil, and a second end having a second port. The first end of the third conical spiral coil is radially displaced a greater distance from the central axis than the second port of the third conical spiral coil. The third conical spiral coil includes a fluid pathway between the first and second ports of the third conical spiral coil. The ground loop flow travels through the fluid pathways of the first, second and third conical spiral coils. In yet another embodiment, the conical spirals are initially and terminally connected to manifolds, with the manifolds connected to the input and output pipes, so that only a portion of the ground loop flow passes through any individual coil.
One embodiment of the groundwater heat exchanger includes an input manifold, an output manifold and a plurality of heat exchange tubes. The input manifold is connected to the input pipe and includes a plurality of input ports. The output manifold is connected to the output pipe and includes a plurality of output ports. Each of the plurality of heat exchange tubes extends into the groundwater flow and includes an input end coupled to one of the input ports and an output end coupled to one of the output ports. The input manifold distributes the ground loop flow from the input pipe to the plurality of heat exchange tubes through the input ports. The output manifold returns the ground loop flow from the plurality of heat exchange tubes to the output pipe through the output ports. The input and output manifolds may be supported by a manifold body. The input and output manifolds may also be displaced from each other along an axis of the borehole. In one embodiment, the plurality of heat exchange tubes each have a non-circular profile.
Another embodiment of the geothermal heat pump system includes at least one main heat exchanger, a plurality of boreholes, and a plurality of ground loops. The at least one main heat exchanger is configured to exchange heat between a ground loop flow and a heat distribution system. Each of the plurality of boreholes penetrates an aquifer and includes one of the plurality of ground loops. Each ground loop includes a groundwater heat exchanger, an input pipe and an output pipe. The groundwater heat exchanger is exposed to a groundwater flow within the aquifer. The input pipe is configured to deliver a portion of the ground loop flow from the main heat exchanger to the groundwater heat exchanger. The output pipe is configured to deliver the portion of the ground loop flow from the groundwater heat exchanger to the main heat exchanger. Heat exchange occurs between the portion of the ground loop flow within the groundwater heat exchanger and the groundwater flow.
In one embodiment, each borehole includes an open surface end at a ground surface and an underground closed distal end. The distal ends of the boreholes are displaced from each other a greater distance than the surface ends are displaced from each other.
In one embodiment, each of the groundwater heat exchangers includes a heat exchange coil, through which the ground loop flow travels between the input pipe and the output pipe. In one embodiment, the heat exchange coil includes a first stacked coil and a second stacked coil. The first stacked coil includes a stack of a plurality of first coil sections, each coil section coiled around a central axis and having a first diameter. The second stacked coil is connected to the first stacked coil and includes a plurality of second coil sections, each second coil section coiled around the central axis and having a second diameter that is greater than the first diameter. A portion of the ground loop flow travels through the first and second stacked coils.
Another embodiment of the heat exchange coil includes a coil body spiraled around a central axis. The coil body includes an interior end proximate the central axis, an outer end radially displaced a greater distance from the central axis than the interior end, a divider wall dividing an interior cavity of the coil body into upper and lower fluid pathways, a first port at the interior end of the upper fluid pathway, a second port at the interior end of the lower fluid pathway, and a cap at the outer end of the coil body fluidically connecting the upper and lower fluid pathways. The portion of the ground loop flow travels through the upper and lower fluid pathways and a cap.
In one embodiment, each of the groundwater heat exchangers includes an input manifold connected to the input pipe and including a plurality of input ports, an output manifold connected to the output pipe and including a plurality of output ports, and a plurality of heat exchange tubes. Each heat exchange tube extending into the groundwater flow and including an input and coupled to one of the input ports and an output coupled to one of the output ports. The input manifold distributes the portion of the ground loop flow from the input pipe to the plurality of heat exchange tubes through the input ports. The output manifold returns the portion of the ground loop flow from the plurality of heat exchange tubes to the output pipe through the output ports.
Additional embodiments of the present disclosure are directed to a ground water heat exchanger formed in accordance with one or more embodiments described herein.
Still further embodiments of the present disclosure are directed to a heat exchange coil formed in accordance with one or more embodiments described herein.
Another embodiment of the present disclosure is directed to a method of exchanging heat using a geothermal heat pump system. In the method, a ground loop fluid flow is delivered through an input pipe of a ground loop to a groundwater heat exchanger installed in a borehole. Heat is exchanged between the ground loop fluid flow and a groundwater flow at the groundwater heat exchanger. The ground loop fluid flow is then delivered from the groundwater heat exchanger to a main heat exchanger, and heat is exchanged between the ground loop fluid flow and a heat distribution system at the main heat exchanger.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the Background.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 are simplified cross-sectional views of geothermal heat pump systems each having an exemplary ground loop installed in a vertical well or borehole, in accordance with embodiments of the present disclosure.

FIG. 5 is a simplified cross-sectional view of a geothermal heat pump system having an exemplary ground loop installed in a horizontal well or borehole, in accordance with embodiments of the present disclosure.

FIG. 6 is a simplified cross-sectional view of a geothermal heat pump system having exemplary ground loops installed in multiple wells or boreholes, in accordance with embodiments of the present disclosure.

FIGS. 7A and 7B are top and side cross-sectional views of an example of a heat exchange coil, in accordance with embodiments of the present disclosure.

FIGS. 8A-8D illustrate an example of a heat exchange coil, in accordance with embodiments of the present disclosure.

FIG. 9 is an isometric view of an example of a heat exchange coil, in accordance with embodiments of the present disclosure.

FIG. 10 is a side view of an example of a nested group of heat exchange coils, in accordance with embodiments of the present disclosure.

FIGS. 11A and 11B are simplified top and side views of an example of a groundwater heat exchanger, in accordance with embodiments of the present disclosure.

FIGS. 12 and 13 are simplified side views of additional examples of heat exchangers, in accordance with embodiments of the present disclosure.

FIGS. 14A and 14B are simplified isometric cross-sectional views of examples of heat exchange tubes, in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements that are identified using the same or similar reference characters refer to the same or similar elements. The various embodiments of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.
Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it is understood by those of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, conventional pumps, fluid circuitry, compressors, expanders, evaporators, heat exchangers, controllers, circuits, processors, and other conventional geothermal heat pump system components may not be shown, or may be shown in block diagram form in order to not obscure the embodiments in unnecessary detail.
Embodiments of the present disclosure relate to geothermal heat pump systems, geothermal heat pump system ground loops, and groundwater heat exchangers that are configured to utilize groundwater to provide and enhance heat exchange, such as through convective and advective heat exchange with a groundwater flow. Additional embodiments are directed to methods of using the systems, ground loops and heat exchangers. While embodiments describe the use of a groundwater flow, it is understood that embodiments of the present disclosure may generally be used to exchange heat with stagnant groundwater, naturally flowing groundwater, or a groundwater flow that is generated or supplemented by one or more devices, such as a pump, for example. As discussed below in greater detail, the ground loops may be configured for a vertical well installation or for a horizontal installation or for any variants in between.
FIGS. 1-4 are simplified diagrams of geothermal heat pump systems 100 formed in accordance with one or more embodiments of the present disclosure. FIG. 5 is a simplified diagram of a geothermal heat pump system 100 having an example of a ground loop 102E installed in a horizontal configuration, in accordance with embodiments of the present disclosure.
Each of the systems 100 of FIGS. 1-4 includes a ground loop 102. Each of the ground loops 102, such as ground loop 102A (FIG. 1), ground loop 102B (FIG. 2), ground loop 102C (FIG. 3) and ground loop 102D (FIG. 4) are installed in a vertical borehole or well 104 that extends vertically below the ground 106 and penetrates one or more aquifers or aquifer or groundwater zones 110 (hereinafter “aquifer”). When a borehole is used, it may have a diameter of approximately 3-24 inches, such as 4, 6 or 8 inches, for example. If a well is used, it may be formed much larger than the borehole.
The well, pipe, drainage tile, borehole or other device 104 (hereinafter “borehole”) may include sealed wall sections, such as a sealed upper section 112 (FIG. 1), to prevent groundwater from entering the section, which may increase a flow rate of the groundwater flow through selected sections of the borehole 104 where the groundwater flow is desired for heat transfer purposes. For example, the upper section 112 may be formed as a sealed wall section by encasing the section in grout 114 or other suitable material to prevent groundwater from entering the section and provide support for the wall 116 of the borehole 104.
Each ground loop 102 includes at least one groundwater heat exchanger 120 within the borehole 104 that is configured to exchange heat between a fluid flow 122 (e.g., refrigerant) that may be driven by a pump 124 through piping 126 of the ground loop 102, such as pipes 126A and 126B, and one or more groundwater flows 132, each of which may be associated with an aquifer zone. For example, the system 100 may include one or more groundwater heat exchangers 120 within the borehole 104, such as the groundwater heat exchanger 120A within the aquifer zone 110A and groundwater heat exchanger 120B within the aquifer zone 110B, of the system 100, as shown in FIG. 1.
Additionally, each aquifer zone that is penetrated by the borehole may include one or more groundwater heat exchangers. For example, the borehole 104 of the system 100 of FIG. 1 penetrates aquifer zones 110A and 110B, and the system 100 may include the groundwater heat exchanger 120A and the groundwater heat exchanger 120C (phantom lines) in the aquifer zone 110A, which are configured to exchange heat with the associated groundwater flow 132 within the aquifer zone 110A, and a groundwater heat exchanger 120B in the aquifer zone 110B, which is configured to exchange heat with the associated groundwater flow 132 within the aquifer zone 110B.
In one embodiment, the piping 126 of each ground loop 120 forms a closed loop of piping, and does not extract groundwater or carry groundwater to the surface. In another embodiment, the piping may be configured to capture subsurface groundwater into a separate pipe (not shown in the figure) , and optionally return a portion of the groundwater to the surface for use (e.g., consumption).
The pipes 126A and 126B that extend below the surface 106 may be thermally insulated to reduce heat exchange with their surroundings and isolating the heat exchange with the fluid flow 122 to the one or more groundwater heat exchangers 120. Thus, rather than providing heat exchange along nearly the entire length of the borehole 104, embodiments of the system 100 provides heat exchange with the groundwater flow(s) 132 at the one or more groundwater heat exchangers 120 that are generally located within an aquifer 110 at the distal end of the borehole 104.
Each geothermal heat pump system 100 may include a heat pump 138 that includes a main heat exchanger 140 that is configured to exchange heat between a fluid flow 142 of a heat distribution system 144 and the ground loop flow 122, as indicated in FIG. 1, using any suitable technique. The heat distribution system 144 may use the fluid flow 142 to provide heating or cooling for a water heater, an HVAC, a chiller, a heat recovery chiller, or another device in accordance with conventional techniques.
The heat pump 138 may also include conventional heat pump components, such as a compressor 146, an expander 148, and/or other conventional components, to perform a desired heat pump cycle, as shown in FIG. 1. While the compressor 146 and the expander 148 are illustrated as performing a heating cycle based on the direction of the fluid flow 142, it is understood that the direction of the fluid flow 142 may be reversed to perform a cooling cycle.
The ground loops 102A-D may include packers 150 that support the one or more heat exchangers 120 within the borehole 104, but allow groundwater flow 132 to flow through the one or more heat exchangers 120. Packers 150 may also be utilized to ensure separation of aquifer zones 110 and their associated groundwater flows 132 to prevent commingling of groundwater flows 132, and to allow one or more heat exchangers 120 to be placed in a single aquifer zone 110. For example, as shown in the system of FIG. 1, packers 150 may be used to isolate the aquifer zones 110A and 110B, and their associated groundwater flows 132 from each other. This configuration can also isolate the groundwater heat exchangers 120A and 120C within the zone 110A from the groundwater heat exchanger 120B in the zone 110B. Thus, with this configuration, the groundwater heat exchangers 120A and 120C exchange heat with the groundwater flow 132 within the aquifer zone 110A, and the groundwater heat exchanger 120B exchanges heat with the groundwater flow 132 within the aquifer zone 110B.
Alternatively, it may be desirable to place the heat exchangers 120 such that there is interaction between the heat exchangers 120. For example, the heat exchangers 120A and 120B of the system 100 of FIG. 1 may be placed such that heated groundwater 132 travels from the heat exchanger 120B, which has added heat to the groundwater 132, to the next heat exchanger 120A so that this heat exchanger 120 can extract the extra heat when heating is needed, or vice versa. In this case, the system 100 does not include the aquifer isolating packers 150 described above. This design is a form of aquifer thermal energy storage.
The heat exchangers 120 may take on any suitable form. In some embodiments, each heat exchanger 120 includes heat exchange piping, tubing or one or more coils 152 (hereinafter “heat exchange coil”), as shown in FIGS. 2-5. The heat exchange coil 152 receives the fluid flow 122 from the input pipe 126A (e.g., tube, conduit, etc.). The coil 152 may be formed of copper, stainless steel, or other suitable thermally conductive material. Heat between the surrounding environment in the well 104 including the groundwater flow 132 is exchanged with the fluid flow 122 within the coil 152 before discharging the flow 122 to the output pipe 126B (e.g., tube, conduit, etc.) where it is delivered to the main heat exchanger 140 (FIG. 1) of the heat pump 138.
In the system 100 shown in FIG. 2, the ground loop 102B is configured to take advantage of a groundwater flow 132 from a region 154 of high hydraulic head to a region 142 of low hydraulic head 156. Such groundwater flow behavior commonly occurs, for example, in the Ironton-Galesville, St. Peter, and Platteville aquifers in Minnesota. Here, the heat exchanger 120 may be positioned between the regions 154 and 156 to take advantage of the groundwater flow 132 between the regions.
In some embodiments, the wall 116 of the borehole 104 is made more permeable to groundwater flow 132 adjacent the aquifer zones 110A and 110B to enhance the groundwater flow 132 into and out of the borehole 104, and through the corresponding heat exchangers 120. This may be accomplished by forming the wall 116 in the regions or zones 110A and 110B of a high permeability backfill, perforating the wall 116 in the zones 110A and 110B, and/or installing a screen 158 in the wall 116 in the zones 110A and 110B, for example.
Other techniques may also be used to enhance the groundwater flow 132 into and out of the borehole 104 and through the groundwater heat exchangers 120. In one embodiment, the wall 116 of the borehole 104 is sealed from the surface 106 to the bottom of the borehole 104 using grout or other suitable material as discussed above, and the zones 110 where groundwater flow is desired, such as zones 110A and 1110B of the system 100 of FIG. 2, are made relatively permeable using one or more of the techniques described above.
In the example of the system 100 shown in FIG. 3, the ground loop 102C may be configured to take advantage of a groundwater flow 132 that moves laterally across the borehole 104. Such groundwater flow behavior occurs in surficial aquifers in Minnesota. Here, the heat exchanger 120 is positioned within the groundwater flow 132 for heat exchange. As discussed above, sections of the wall 116 of the borehole 104 may be sealed and/or made more permeable to enhance the groundwater flow 132 into and out of the borehole 104 and through the heat exchanger 120 (i.e., over and around heat exchange coils), using a low permeable encasing (e.g., grout 114), a high permeability backfill, perforations or a screen 158 (shown), and/or through the use of other techniques.
When the vertical (FIG. 2) or lateral (FIG. 3) groundwater flow 132 is insufficient in a given aquifer for the desired heat exchange with the heat exchanger 120, a flow generator 160 may be installed above, below or adjacent the heat exchanger 120 to drive the groundwater flow 132 through the heat exchanger 120 (i.e., across, over and around heat exchange coils 152), such as shown in the exemplary ground loop 102D of the system 100 shown in FIG. 4, which is configured similarly to the ground loop 102B of FIG. 2. This increases circulation of the groundwater flow or flows 132 through the one or more heat exchangers 120, and increases convective and/or advective heat transfer between the groundwater flow 132 and the ground loop flow 122 through the one or more coils 152 of the heat exchanger 120. This circulation of the groundwater flow 132 by the flow generator 160 is distinct from the flow 122 through the ground loop piping (e.g., pipes 126A and 126B) and the coils 152 of the heat exchanger 120, which may be driven by the pump 124 that is separate from the flow generator 160. Thus, the primary purpose of the flow generator 160 is to improve heat transfer between the groundwater flow 132 and the ground loop flow 122, rather than driving groundwater to the surface 106, for example or circulating flow through the ground loop piping.
The flow generator 160 may comprise any suitable device to increase the circulation of the groundwater flow 132 through a corresponding groundwater heat exchanger 120. The flow generator 160 may comprise low energy devices, because the heat exchanger 120 needs a relatively low flow rate of groundwater to achieve several tons of heating or cooling capacity. When used with a small-diameter borehole 104 (e.g., 3-8 inches) the flow generator 160 allows the heat exchanger 120 to access a large volume of the local groundwater flow 132 for the purpose of heat exchange. With the aid of the flow generator 160, the circulated fluid flow 122 is able to exchange heat with a volume of groundwater flow 132 that could be far greater than what would naturally be allowed within the narrow space of the borehole 104.
The flow generator 160 may comprise any suitable device or mechanism that may induce or increase convective or advective heat transfer between the groundwater flow 132 and the ground loop flow 122 within the heat exchanger 120. In some embodiments, the flow generator 160 includes a submersible pump (e.g., dipole pump), or a pump or pump motor located on the surface that drives circulation of the groundwater flow 132 through the heat exchanger 120 through a mechanical, hydraulic or other connection to the zone 110 containing the heat exchanger 120. One embodiment of the flow generator 160 may comprise a heating device that heats the groundwater below the heat exchanger 120 to generate a temperature difference within the aquifer 110 that drives the flow of the groundwater 132 through the heat exchanger 120.
In the example of the system 100 shown in FIG. 5, the ground loop 102E is in a horizontal configuration, such as through the use of a trench, drainage tile, or a horizontal borehole (hereinafter “trench”) 170. As with the heat exchangers 120 of the ground loops 102A-D, the heat exchanger 120 of the ground loop 102E is submerged, fully or partially, in groundwater 132. In some embodiments, the trench 170 may be filled with a high permeability material 172 to increase the groundwater flow 132 into the trench 170, through the heat exchanger 120 (i.e., over and around heat exchange coils), and out of the trench 170.
This horizontal installation scenario could be combined, for instance, with drain tiles in fields. Such drain tiles operate to concentrate the groundwater flow 132 through the heat exchanger 120. For example, the heat exchanger 120 could be plowed into the ground using drain tile installation equipment, resulting in very cost-effective and minimally disruptive installations. Alternatively, a drain tile zone could also be accessed using directional drilling, rather than conventional methods of plowing in drain tile. In some embodiments, a flow generator 160 may be used to drive the groundwater flow 132 through the heat exchanger 120, as indicated shown in FIG. 5.
The system 100 may comprise multiple boreholes 104, such as boreholes 104A-C, each penetrating an aquifer 110 and having one or more groundwater heat exchangers 120, as shown in the simplified diagram of FIG. 6. The groundwater heat exchangers 120 may each be connected to one or more main heat exchangers 140 (FIG. 1) of the heat pump 138 through ground loops 102 that may be interconnected with each other or formed as separate closed loop pipes.
The boreholes 104 each have an open surface end 180A-C at the ground surface 106 and an underground closed distal end 182A-C. In one embodiment, some of the boreholes 104 are formed at a non-perpendicular angle to the surface 106 and are oriented such that the open surface ends 180A-C of the boreholes 104 are located closer to each other than the closed distal ends 182A-C, as shown in FIG. 6. This allows the piping 126 of the system to extend from the ground surface 106 in close proximity to the main heat exchanger(s) 140 (FIG. 1) of the heat pump 138 and other surface components of the system 100, while providing a desired separation of the groundwater heat exchangers 120 and/or access to desired aquifers 110. This design allows the borehole drilling equipment to be located at or near a single point on the surface 106, resulting in less disturbance to the surface 106, and reduced installation and labor costs due to the time saved from having to significantly move the drilling equipment. Additionally, the angled boreholes 104 may provide access to parts of aquifers at depth that may not otherwise be accessible, for example, because they are under roads, buildings or other surface structures. Furthermore, having all boreholes 104 terminate at or near the same point on the surface 106 reduces the complexity of the pipes 126 needed to connect the heat exchangers 120 together and to the heat pump equipment, such as the one or more compressors 146 and expanders 148, for example.
The angled boreholes 104 of the system 100 are not suitable for conventional geothermal heat pump systems, which are optimized for heat transfer along the total length of the borehole, rather than only or primarily at a distally located heat exchanger 120. Additionally, conventional geothermal heat pump systems utilize vertical or orthogonal boreholes relative to the surface 106, rather than the angled boreholes shown in FIG. 6, to maximize the number of boreholes in a given land area.
In some embodiments, one or more flow generators 160 (FIG. 4) may be used to pump groundwater between the multiple boreholes 104 (FIG. 6), when there is low or no natural groundwater flow. In such a case, groundwater may be pumped using the one or more flow generators to circulate the groundwater through the heat exchanger within the borehole 104, then the groundwater could be pumped to an adjacent borehole where it is circulated through the corresponding heat exchanger, and so on. It would not be necessary for the groundwater to leave the borehole system in this scenario, or be exposed to the atmosphere. Thus, there would be no net extraction of water from the ground. Additionally, the boreholes could be designed such that the water never passes above the ground surface.
Embodiments of the present disclosure include the use of multiple semi-vertical or angled boreholes 104 to accomplish aquifer thermal energy storage. Here, the boreholes may be formed such that the natural groundwater flow in the aquifer system would move heat from one borehole to another borehole of the system over a period of approximately six months, or contra-seasonally, or over some other time period that is useful for a particular application. In such a system, heat that is added to the aquifer in one, upgradient borehole during the cooling season can be extracted from the aquifer from a second borehole during the heating season.
Embodiments of the present disclosure also can provide for thermal energy storage by moving groundwater and heat between vertically separated sections of one or more aquifers within a single or multiple boreholes, then reversing the flow contra-seasonally or when energy is needed.
Embodiments of the present disclosure also include the use of hybrid systems, such as solar thermal—geothermal systems. In this case, the non-geothermal heat energy sources or sinks can add or remove heat to the geothermal system to enhance the performance of the overall heating and cooling system and to balance heating and cooling loads.
The vertical boreholes 104 may be formed using an old water supply well or a dual-purpose well. Old water supply wells (or any other type of bore into/through a groundwater bearing unit) could be repurposed to include a ground loop 102 and, therefore, used for heat exchange rather than water supply (or fluid injection/disposal). Old wells may pass through several distinct aquifers, each of which could be used for heat exchange (as could be done with wells drilled exclusively for the ground loops 102). Sections of the wells 104 may be isolated using suitable packers 150 (FIG. 2) to ensure that groundwater is not exchanged between separate aquifer zones. In this way, embodiments of the ground loops 102 could help improve local water quality and eliminate one of the big issues facing local water authorities—interaquifer exchange.
Dual-purpose wells may be used to provide both potable and/or process water and the heat exchange capacity for heating/cooling. In such a well, a potable water pump may be installed in the water column, such as above the location of the heat exchanger 120 or another location. The pipes 126 of the ground loop 102 of the system 100 may extend to the surface past the potable water pump. Such a borehole 104 may utilize a secondary, flow generator 160 associated with the heat exchanger to induce and/or enhance flow through the reservoir and across the exchanger, as described above.
Borehole convection wells having any significant diameter (e.g., greater than 5 cm diameter) will experience natural convection within the borehole. This natural convection can be enhanced with two heat exchangers 120, such as the heat exchangers 120A and 120C shown in FIG. 1. For heating demand, the fluid flow 122 returning from the heat exchanger 120C is colder and can be transferred to the second exchanger 120A toward the top of the water table within the borehole 104. The cooler water will mix downward, driving convection and drawing in heat from the length of the borehole. For cooling demand, the heat exchanger 120B at the bottom of the borehole will allow heated water to mix upwards. In some embodiments, this system is used in a short open-hole or screened interval and a large saturated, but cased borehole. Heat exchange could occur along the full length of the saturated thickness. Alternatively, the open hole could be enlarged by blasting and bailing to produce a larger diameter chamber with a single heat exchanger 120 driving convective heat exchange across the entire surface area of the open interval.
The ground loops 102 described above provide several advantages over traditional geothermal heat pump ground loops. For example, because the ground loops 102 require fewer wells/boreholes 104 than traditional systems due to the high heat transfer between the groundwater flow 132 and the heat exchanger(s) 120, the amount of space needed for the ground loops 102 is far less than traditional ground loops. Thus, the systems 100 can be installed at sites that wouldn't otherwise have sufficient space, and larger systems 100 (e.g., multiple borehole systems) can be installed in a given space than would be possible with traditional geothermal heat pumps.
Additionally, embodiments of the heat exchanger 120 allow it to be serviced, removed, and/or replaced after the initial installation. In comparison, the subsurface exchange loops in traditional ground loops are installed such that they can never be serviced. When they break or degrade, entirely new loops must be installed, which is a costly endeavor. At the end of the lifespan of traditional ground loops subsurface equipment, new loops may need to be installed, or the ground system may have been over or under thermally saturated. However, in the disclosed embodiments, maintenance or replacement of the groundwater heat exchanger is a straightforward operation, requiring no new drilling or trenching, thus significantly decreasing operation, maintenance, and replacement costs.
The disclosed embodiments also reduce pumping energy requirements. For example, some embodiments of the disclosed ground loops use a small fraction of the length of piping and associated volume of fluid that is required with traditional ground loops to achieve a given amount of heat exchange. Thus, the power needed to circulate the ground loop flow is reduced, as is wear on the pumps themselves. With lower pumping power, the overall coefficient of performance of the system 100 is better than traditional geothermal heat pump systems. Moreover, with lower frictional losses from pipe length, smaller diameter pipes can be used, decreasing overall system cost, while improving heat transfer properties.
The disclosed embodiments also may not need an antifreeze, such as a glycol mixture, in the ground loop flow 122, something required in traditional geothermal systems, because groundwater generally always exceeds freezing temperature. Rather than antifreeze, water can be used in the ground loop piping. Water is less expensive, less toxic, and less energy intensive to pump than antifreeze. If water is used in the ground loop piping, certain additives may need to be added to the water, such as to prevent biological activity.
FIGS. 7-13 illustrate examples of heat exchange coils 152 of a heat exchanger 120, in accordance with embodiments of the present disclosure. Each of the coils 152 includes an interior fluid pathway and ends 184 and 186 that connect to the pipes and allow for the fluid flow to travel through the interior fluid pathway of the coil 152. The coils 152 may be formed of a thermally conductive material, such as a metal, such as copper, stainless steel, or other suitable material, to facilitate heat transfer from the ground loop flow 122 to the groundwater flow 132 within the borehole 104.
FIGS. 7A and 7B are top and side cross-sectional views of a heat exchange coil 152A, in accordance with embodiments of the present disclosure. The coil 152A includes a plurality of nested stacked coils 188, such as stacked coils 188A-C. Other configurations of the coil 152A include a pair of stacked coils and more than three stacked coils. Each of the stacked coils 188 includes a coil section 190 that surrounds or is coiled around a central axis 192 and has a different diameter 194 than the other stacked coils 188. In one embodiment, each coil section 190 is substantially concentric to the central axis 192.
In the example shown in FIGS. 7A and 7B, the coil 152A includes an outer stacked coil 188A having a coil section 190A that is coiled around and substantially concentric to the axis 192 and has a diameter 194A, an inner stacked coil 188B having a coil section 190B that is coiled around and substantially concentric to the axis 192 and has a diameter 194B, and a middle stacked coil 188C having a coil section 190C that is coiled around and substantially concentric to the axis 192 and has a diameter 194C, which is between the diameters 194A and 194B. Gaps 196 may be formed between the stacked coils 188 to allow for the passage of the groundwater flow 132 and improved heat transfer therewith.
The diameter of the outer stacked coil 188A may be set to allow the coil 152A to be inserted into the borehole 104 in which it is to be used. In some embodiments, the outer diameter 194A of the outer stacked coil 188A is less than 4 inches to allow it to be inserted within a 4-inch borehole. However, in some embodiments, the coil 152A may be radially compressible relative to the axis 192. This allows the coil 152A to have an expanded state, in which the diameter 194A of the outer stacked coil 188A is greater than the diameter of the borehole in which it is to be used, and a compressed state that allows the coil 152A to be installed within the borehole 104. The coils can be designed to be recompressed downhole for later removal if required.
FIGS. 8A-8D illustrate a heat exchange coil 152B, in accordance with embodiments of the present disclosure. FIG. 8A is a simplified isometric view of the coil 152B, and FIGS. 8B-D are simplified cross-sectional views of portions of the coil 152B. The coil 152B includes a coil body 200 formed of a thermally conductive material (e.g., copper, stainless steel, etc.) that is spiraled around a central axis 202. An interior end 204 of the coil body 200 is proximate the central axis 202, and an outer end 206 of the coil body 200 is radially displaced from the central axis 202 a greater distance than the interior end 204. The interior end 204 of the coil body 200 may be connected to a central hub 208 having a port 210 and a port 212, which may be respectively connected to the pipes 126A and 126B for receiving the ground loop flow 122. The coil body 200 may be flattened such that a dimension along the central axis 202 is substantially greater (e.g., more than 50% greater) than a dimension along an axis that is perpendicular to the central axis 202.
The coil body 200 may include a divider wall 214 that divides an interior cavity 216 of the coil body 200 into an upper fluid pathway 218 and a lower fluid pathway 220, as shown in FIGS. 8B-D. The interior end 204 of the upper pathway 218 is connected to the port 210 and the interior end 204 of the lower pathway 220 is connected to the port 212, as shown in FIG. 8B. The outer end 206 of the coil body 200 includes a cap 222 that fluidically connects the upper and lower fluid pathways 218 and 220, as shown in FIG. 8D. Thus, the ground loop flow 122 in the pipe 126A is received by the upper fluid pathway 218 through the port 210, and the flow 122 travels through the upper fluid pathway 218 to the outer end 206 where it is passed to the lower fluid pathway 220 through the cap 222, as illustrated in FIGS. 8B-D. The flow 122 is then returned to the interior end 204 through the lower fluid pathway 220 where it is discharged through the port 212 to the pipe 126B, as indicated in FIG. 8B.
Gaps 224 between spirals of the coil body 200, allow the groundwater flow 132 to travel along the central axis 202 and over the surfaces of the coil body 200. Heat energy is exchanged between the ground loop flow 122 traveling through the upper and lower fluid pathways 218 and 220 and the groundwater flow 132. The flattened shape of the coil body 200 enhances this heat transfer by exposing a large surface area of the coil body 200 to the groundwater flow 132, while reducing resistance to the groundwater flow.
FIG. 9 is an isometric view of exemplary heat exchange coil 152C, in accordance with embodiments of the present disclosure. The coil 152C is in the form of a conical spiral coil having ends 230 and 232 that may connect to the pipes 126A and 126B (FIG. 1) of the system 100 . A fluid pathway within the coil 152C allows the ground loop flow 122 to travel between the ends 230 and 232. The end 230 is radially displaced a greater distance from a central axis 234 than the end 232. Additionally, the ends 230 and 232 are displaced from each other along the axis 234. This design forces the groundwater flow 132 across the extent of the conical spiral coil 152C, while reducing the interference from one loop of the coil 152C to the next.
Each of the heat exchange coils 152 described above may be nested to provide a desired heat exchange rate for the heat exchanger 120. For example, the conical coils 152C may be nested together, such as shown in FIG. 10 for increased heat exchange.
FIGS. 11A and 11B are simplified top and side views of an example of a groundwater heat exchanger 120, in accordance with embodiments of the present disclosure. The groundwater heat exchanger 120 includes an input manifold 240 and an output manifold 242, which are respectively configured to connect to the input and output pipes 126A and 126B. The input and output manifolds 240 and 242 may be separate components, or integrated into a manifold body 244, as shown in FIG. 11A. The manifold body 244 may be sized to be received within the borehole 104, in which it is to operate, as shown in FIG. 11B. In one example, the manifold body 244 may have an outside diameter of 5.5 inches or less.
The input manifold 240 includes a plurality of input ports 246, such as input ports 246A-D, and the output manifold 242 includes a plurality of output ports 248, such as output ports 248A-D. In some embodiments, the input and output manifolds 240 and 242 accommodate two or more pairs of input and output ports, such as four pairs of input and output ports, as shown in FIG. 11A.
Heat exchange tubes 250 connect the input ports to corresponding output ports, as shown in FIG. 11B. For example, a tube 250A may connect the input port 246A to the output port 248A, and a tube 250B may connect the input port 246B to the output port 248B. Each tube 250 may be formed of a thermally conductive material (e.g., copper, stainless steel, etc.) and may be configured in any desirable shape, such as a coil.
During operation, the ground loop flow 122 is received by the input manifold 240 from the pipe 126A and delivered to each of the input ports 246. Each tube 250 delivers a portion of the ground loop flow 122 to the corresponding output ports 248 of the output manifold 242, from which the flow 122 is transferred to the output pipe 126B. The groundwater fluid flow 132 is configured to travel over and around the tubes 250 during which heat energy is transferred from the portions of the ground loop flow 122 traveling through the tubes 250 to the groundwater flow 132.
FIGS. 12 and 13 are simplified side views of additional examples of heat exchangers 120, in accordance with embodiments of the present disclosure. The illustrated heat exchangers 120 include similar features to the heat exchanger 120 of FIGS. 11A-B, including input and output manifolds 240 and 242 that may be connected to the input and output pipes 126A and 126B of the system 100. Each input manifold 240 includes a plurality of input ports 246, and each output manifold 242 includes a plurality of output ports 248. Heat exchange tubes 250 connect pairs of the input and output ports together.
In operation, the input manifolds 240 of the heat exchangers 120 of FIGS. 12 and 13 receive the ground loop flow 122 from the input pipe 126A and deliver portions of the ground loop flow 122 to the heat exchange tubes 250 through the input ports 246. The output manifolds 242 receive the portions of the flow 122 from the tubes 250 through the output ports 248 and deliver the flow 122 to the output pipe 126B. Heat exchange occurs between the portions of the groundwater flows 132 traveling over and around the tubes 250 and the ground loop flow 122 in the tubes 250.
The input and output manifolds 240 and 242 of the heat exchangers 120 may be located adjacent each other, as shown in FIG. 12, or displaced from each other along an axis 252 of the borehole 104 such that the input manifold 240 is at a higher elevation than the output manifold 242. However, it is understood that the ground loop flow 122 may be reversed from that indicated by the arrows in FIG. 13, effectively changing the locations of the input and output manifolds 240 and 242. The input and output manifolds 240 and 242 may also be joined together using a suitable manifold body 244, which is shown in phantom lines in FIG. 12.
The heat exchange tubes 250 may take on various forms. In some embodiments, the heat exchange tubes 250 have a cross-sectional shape and/or features that facilitate efficient heat exchange between the ground loop flow 122, or portion thereof, flowing through the tubes 250 and the groundwater flow 132, in which the heat exchanger 120 is placed. In some embodiments, the heat exchange tubes 250 have non-circular cross-sectional shapes.
Examples of non-circular tubes 250 are shown in the cross-sectional views provided in FIGS. 14A and 14B. In one embodiment, the heat exchange tubes 250 have a flattened or oval cross-section, as shown in FIG. 14A, which may be used to increase the surface area of the tubing that may be exposed to the groundwater flow 132. In one embodiment, the heat exchange tubes 250 include one or more heat-conducting fins 254 that extend from an exterior surface 256 of the tubing, as shown in FIG. 14B. Additional options for the tubes include a combination of the features shown in FIGS. 14A-B, such as internal and external enhancements to the tubes. These enhancements include external fins, external surface area enhancement, internal surface area enhancement, and turbulators.
The length of each heat exchange tube 250 may be chosen to provide the desired rate of heat transfer between the portions of the ground loop fluid flow 122 traveling through the tube 250 and the groundwater flow 132, in which the tube 250 is placed. In some embodiments, the tubes 250 may have a length of 2-10 feet, such as six feet, for example. The heat exchange tubes 250 may also be coiled, as shown in FIG. 13 to pack a greater length of the tubes 250 per unit length along the axis of the borehole 104. The length of each heat exchange tube 250 may also be chosen to provide the desired ground loop fluid pressure drop through the tube and overall ground loop. The widths of each tube 250 may also vary.
Although the embodiments of the present disclosure have been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the present disclosure.

Claims

1. A geothermal heat pump system comprising:

a main heat exchanger configured to exchange heat between a ground loop flow and a heat distribution system;

a borehole that penetrates an aquifer; and

a ground loop comprising:

a first groundwater heat exchanger contained within a first zone of the borehole and exposed to a groundwater flow within the aquifer;

a second groundwater heat exchanger contained within a second zone of the borehole and exposed to the groundwater flow, wherein the second zone is displaced from the first zone;

an input pipe configured to deliver the ground loop flow from the main heat exchanger to the first and second groundwater heat exchangers; and

an output pipe configured to deliver the ground loop flow from the first and second groundwater heat exchangers to the main heat exchanger;

wherein heat exchange occurs between the ground loop flow within the first and second groundwater heat exchangers and the groundwater flow.

2. The system of claim 1, wherein the borehole comprises:

a sealed wall section that blocks the groundwater flow into the borehole; and

a permeable wall section through which the groundwater flow travels into the borehole.

3. The system of claim 2, wherein the permeable wall section includes a screen.

4. The system of claim 1, wherein:

the groundwater flow travels from a region of high hydraulic head to a region of low hydraulic head; and

the first and second groundwater heat exchangers are positioned in the borehole between the region of high hydraulic head and the region of low hydraulic head.

5. The system of claim 1, wherein the groundwater flow travels horizontally across the borehole and the first and second groundwater heat exchangers.

6. The system of claim 1, further comprising packers configured to support the first and second groundwater heat exchangers within the borehole.

7. The system of claim 1, further comprising at least one packer in the borehole that divides a lower zone of the borehole containing the first groundwater heat exchanger from an upper zone of the borehole, and blocks water from flowing between the lower and upper zones.

8. The system of claim 1, further comprising a flow generator configured to circulate the groundwater flow over at least one of the first and second groundwater heat exchangers.

9. The system of claim 8, wherein the flow generator comprises a pump.

10. (canceled)

11. (canceled)

12. The system of claim 1, wherein the first groundwater heat exchanger comprises:

an input manifold connected to the input pipe and including a plurality of input ports;

an output manifold connected to the output pipe and including a plurality of output ports; and

a plurality of heat exchange tubes each extending into the groundwater flow and including an input end coupled to one of the input ports and an output end coupled to one of the output ports,

wherein:

the input manifold distributes the ground loop flow from the input pipe to the plurality of heat exchange tubes through the input ports; and

the output manifold returns the ground loop flow from the plurality of heat exchange tubes to the output pipe through the output ports.

13. The system of claim 12, wherein the input and output manifolds are supported by a manifold body.

14. The system of claim 12, wherein the input and output manifolds are displaced from each other along an axis of the borehole.

15. The system of claim 12, wherein the plurality of heat exchange tubes each have a non-circular profile.

16. A geothermal heat pump system comprising:

at least one main heat exchanger configured to exchange heat between a ground loop flow and a heat distribution system;

a plurality of boreholes, each borehole penetrating an aquifer;

each borehole containing one of a plurality of ground loops, each ground loop comprising:

a groundwater heat exchanger exposed to a groundwater flow within the aquifer;

an input pipe configured to deliver a portion of the ground loop flow from the main heat exchanger to the groundwater heat exchanger; and

an output pipe configured to deliver the portion of the ground loop flow from the groundwater heat exchanger to the main heat exchanger,

wherein:

heat exchange occurs between the portion of the ground loop flow within the groundwater heat exchanger and the groundwater flow;

each borehole includes an open surface end at a ground surface and an underground closed distal end; and

the distal ends of the boreholes are displaced from each other a greater distance than the surface ends are displaced from each other.

17. (canceled)

18. (canceled)

19. The system of claim 16, wherein each groundwater heat exchanger comprises:

a plurality of heat exchange tubes each extending into the groundwater flow and including an input end coupled to one of the input ports and an output end coupled to one of the output ports;

wherein:

the input manifold distributes the portion of the ground loop flow from the input pipe to the plurality of heat exchange tubes through the input ports; and

the output manifold returns the portion of the ground loop flow from the plurality of heat exchange tubes to the output pipe through the output ports.

20. (canceled)

21. The geothermal heat pump system of claim 1, wherein:

the first and second zones are separated a packers;

the groundwater flow includes a first groundwater flow through the first zone, and a second groundwater flow through the second zone that is isolated from the first groundwater flow;

heat exchange occurs between the first groundwater heat exchanger and the first groundwater flow; and

heat exchange occurs between the second groundwater heat exchanger and the second groundwater flow.

22. A groundwater heat exchanger configured for use within a borehole comprising:

an input manifold including a plurality of input ports;

an output manifold including a plurality of output ports; and

a plurality of exposed heat exchange tubes each including an input end coupled to one of the input ports and an output end coupled to one of the output ports,

wherein:

the input manifold is configured receive a ground loop flow and distribute the ground loop flow to the plurality of heat exchange tubes through the input ports; and

the output manifold is configured to discharge the ground loop flow received through the output ports from the plurality of heat exchange tubes to the main heat exchanger.

23. The groundwater heat exchanger of claim 22, wherein the input and output manifolds are supported by a manifold body.

24. The groundwater heat exchanger of claim 22, wherein the input and output manifolds are displaced from each other along an axis of the borehole.

25. The groundwater heat exchanger of claim 22, wherein the plurality of heat exchange tubes each have a non-circular profile.