Closed-loop geothermal and heat pump systems

Abstract

This method includes the step of determining a specified demand as a function of time of thermal energy from a heat pump's heat exchanger. The heat pump is configured to transfer thermal energy from a geothermal working fluid circulating within a closed-loop geothermal well to a heat exchanger. The closed-loop geothermal well includes a first surface well extending from the surface to the geothermal subsurface zone, a second surface well extending from the surface to the geothermal subsurface zone, and a number of connecting wells connecting the first surface well to the second surface well. The thermal output from the heat exchanger is controlled to meet the specified demand by adjusting at least one of the flow rate or inlet temperature of the geothermal working fluid within the closed-loop geothermal well.

Description

[Technical Field]

[0001] This disclosure relates to geothermal systems and methods. [Background technology]

[0002] Geothermal systems utilize heat from the Earth's interior for surface heat distribution, power generation, or other purposes. Some geothermal systems use geothermal working fluid. This working fluid is injected into a closed-loop well drilled into the underground zone. After absorbing heat from the underground zone, the working fluid can be recovered.

[0003] A heat pump system uses a refrigerant fluid to transfer heat from one place to another. A typical mechanical heat pump system consists of, for example, an evaporator, a compressor, a condenser, and an expansion valve. The refrigerant absorbs heat in the evaporator, is compressed by the compressor, releases heat in the condenser, and is depressurized through the expansion valve. This allows the heat pump to efficiently heat or cool by transferring heat rather than generating it (for example). [Overview of the project] [Means for solving the problem]

[0004] This disclosure relates to geothermal energy generation.

[0005] Certain aspects of the subject matter herein can be implemented as a method. This method includes the step of determining a specified demand as a function of time of thermal energy from a heat exchanger of a heat pump. The heat pump is configured to transfer thermal energy from a geothermal working fluid circulating within a closed-loop geothermal well to a heat exchanger. The closed-loop geothermal well includes a first surface well extending from the surface to a geothermal subsurface zone, a second surface well extending from the surface to a geothermal subsurface zone, and a plurality of connecting wells connecting the first surface well to the second surface well. This method further includes the step of controlling the thermal output from the heat exchanger to meet a specified demand. The control is performed at least in part by adjusting at least one of the flow rate or inlet temperature of the geothermal working fluid within the closed-loop geothermal well.

[0006] Embodiments that can be combined with any of the other embodiments may include the following features: Thermal energy from a heat exchanger can supply a first portion of thermal energy to be supplied to a heat distribution system. The method may further include the step of supplying a second portion of thermal energy to a heat distribution system, wherein the thermal energy is extracted directly from a geothermal working fluid without going through a heat pump.

[0007] Embodiments that can be combined with any of the other embodiments may include the following features: The thermal energy from the geothermal working fluid transmitted by the heat pump may include a first portion of the thermal energy from the geothermal working fluid, and the method further includes the step of using a second portion of the thermal energy from the geothermal working fluid to generate electricity.

[0008] Embodiments that can be combined with any of the other embodiments may include the following features: The flow of the working fluid in the closed-loop geothermal system can be generated via a thermal siphon.

[0009] Embodiments that can be combined with any of the other embodiments may include the following features: The flow of geothermal working fluid in a closed-loop geothermal system can be driven at least partially by a circulation pump.

[0010] Embodiments that can be combined with any of the other embodiments may include the following features: The heat pump may be a mechanical heat pump.

[0011] Embodiments that can be combined with any of the other embodiments may include the following features: The heat pump may be an absorption heat pump or an adsorption heat pump.

[0012] Embodiments that can be combined with any of the other embodiments may include the following features: The specified demand is the annual peak demand and is greater than 1 megawatt.

[0013] Certain aspects of the subject matter herein can be implemented as a method comprising the step of determining a designated target heat output to a district thermal network based at least in part on predicted electricity or heat rates. This method further comprises the step of satisfying the target heat output by controlling the operation of a closed-loop geothermal well to control the heat output from a heat exchanger of a heat pump. The closed-loop geothermal well includes a first surface well extending from the surface to a geothermal underground zone, a second surface well extending from the surface to a geothermal underground zone, and a plurality of connecting wells connecting the first surface well to the second surface well. The heat pump is configured to transfer thermal energy from a geothermal working fluid circulating within the closed-loop geothermal well to a heat exchanger. The control of the heat pump is at least in part by adjusting the flow rate and / or inlet temperature of the geothermal working fluid within the closed-loop geothermal well.

[0014] Embodiments that can be combined with any of the other embodiments may include the following features: The target thermal output may be partially based on net cash flow and at least one of predicted heat charges and electricity charges as a function of time.

[0015] Embodiments that can be combined with any of the other embodiments may include the following features: The flow of the working fluid in the closed-loop geothermal system can be generated via a thermal siphon.

[0016] Embodiments that can be combined with any of the other embodiments may include the following features: The flow of geothermal working fluid in a closed-loop geothermal system can be partially assisted by a circulating pump.

[0017] Embodiments that can be combined with any of the other embodiments may include the following features: Thermal energy from a heat exchanger can supply a first portion of thermal energy to be supplied to a heat distribution system. The method may further include the step of supplying a second portion of thermal energy to a heat distribution system, wherein the thermal energy is extracted directly from a geothermal working fluid without going through a heat pump.

[0018] Embodiments that can be combined with any of the other embodiments may include the following features: The heat pump may be a mechanical heat pump.

[0019] Embodiments that can be combined with any of the other embodiments may include the following features: The heat pump may be an absorption heat pump or an adsorption heat pump.

[0020] Embodiments that can be combined with any of the other embodiments may include the following features: Thermal energy from an electric resistance heater can supply a portion of the thermal energy to a heat distribution system. The method further includes the step of supplying a second portion of the thermal energy to a heat distribution system, wherein the thermal energy is extracted directly from the geothermal working fluid of a closed-loop geothermal system and transferred by a heat pump, and the distribution of the thermal energy supplied between these systems can be determined in part on predicted electricity and heat charges.

[0021] An aspect combinable with any of the other aspects can include the following features. The prediction period may be less than 72 hours.

[0022] An aspect combinable with any of the other aspects can include the following features. Operation of the closed-loop geothermal system can be performed with adjustable output using a charge-discharge cycle.

[0023] An aspect combinable with any of the other aspects can include the following features. The thermal energy from the geothermal working fluid transferred by the heat pump can include a first portion of the thermal energy from the geothermal working fluid. The method can further include generating electric power using a second portion of the thermal energy from the geothermal working fluid.

[0024] An aspect combinable with any of the other aspects can include the following features. The specified demand is an annual peak demand that exceeds 1 megawatt. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] [Figure 1] FIG. 1 is an explanatory diagram of city-wide heat demand over one year in accordance with the concepts of the present specification. [Figure 2A] FIG. 2 is a schematic side cross-sectional view of an exemplary closed-loop geothermal system in accordance with the concepts of the present specification. [Figure 2B] FIG. 3 is a schematic side cross-sectional view of another exemplary closed-loop geothermal system in accordance with the concepts of the present specification. [Figure 2C] FIG. 4 is a schematic side cross-sectional view of another exemplary closed-loop geothermal system in accordance with the concepts of the present specification. [Figure 3] FIG. 5 is a schematic diagram of a heat pump system supplied by a geothermal working fluid circulating in a closed-loop geothermal system in accordance with the concepts of the present specification. [Figure 4] FIG. 6 is an explanatory diagram of a coefficient of performance as a function of a desired heat temperature in accordance with the concepts of the present specification. [Figure 5]This diagram illustrates the thermal output as a function of the flow rate of the geothermal working fluid circulating within a closed-loop geothermal system according to the concept of this specification. [Figure 6] This diagram illustrates the coefficient of performance as a function of the desired thermal temperature, according to the concepts of this specification. [Figure 7] This diagram illustrates the optimal closed-loop geothermal system and heat pump system capacities for three different electricity rates and a fixed heat rate. [Figure 8] This diagram illustrates the coefficient of performance as a function of thermal output in condensers of different systems according to the concepts described herein. [Figure 9] This is an explanatory diagram of heat demand accompanied by variable daily electricity rates. [Figure 10] This is a schematic diagram of an electric resistance heater, as well as a combined heat pump system and a closed-loop geothermal system operating in parallel. [Figure 11] This diagram shows a "cascade configuration" in which the heat distribution fluid is preheated before the geothermal working fluid of a closed-loop geothermal system enters the heat pump evaporator. [Figure 12] This figure shows a cascade configuration similar to Figure 11, but inverted. [Figure 13] This is a schematic diagram of a combined closed-loop geothermal system and heat pump system that includes combined thermal and power modes, can be configured to prioritize heat sales, and redirect residual heat to an organic Rankine cycle plant to generate electricity. [Figure 14] Figure 10 is an example diagram illustrating how heat from the geothermal working fluid can be distributed within the configuration shown. [Modes for carrying out the invention]

[0026] The generation of medium-temperature grade heat and steam (considered herein to be between 100°C and 400°C) can pose a challenge to decarbonization. Low theoretical maximum thermal efficiency and existing technical challenges in heat pump systems may limit the generation of this grade of heat in heat pump systems using ambient temperature heat sources.

[0027] In a closed-loop geothermal system, geothermal working fluid circulates within a closed loop that includes a subsurface well and a surface facility. The geothermal working fluid is heated by the soil surrounding the well and then circulated to the surface, where the surface facility extracts heat from it. In certain examples, this facility includes a heat exchanger to extract the heat and transfer it to a Rankine cycle (e.g., an organic Rankine cycle) or a related process such as power generation, a district heating plant, a steam generation process, or another thermal cycle that produces another process. In certain examples, the process directly uses the heated geothermal working fluid, such as by passing it through an expander (e.g., a turbine) that drives a generator, or by directly using the heat of the geothermal working fluid in industrial, agricultural, or domestic processes. In a closed-loop system, primary heat transfer occurs between the geothermal working fluid and the soil (bedrock) surrounding the well. Therefore, the well is sealed to prevent (completely or substantially) contact between the geothermal working fluid and natural fluids within the structure (e.g., groundwater).

[0028] In some cases, heat generation within a closed-loop geothermal system can be limited by the subsurface temperature. If the rock temperature exceeds the desired process temperature, methods to transfer these high temperatures to the surface include increasing the inlet temperature and / or decreasing the circulation rate of the geothermal working fluid. The drawback of both of these methods is that they reduce the thermal output of the closed loop and, therefore, the potential revenue from heat sales for a given closed-loop system. In other words, using the same capital expenditure, it may be possible to construct a loop with reduced thermal output and high temperature generation. For example, if the desired process heating is in the form of steam (rather than pressurized water), a high outlet temperature may be required to supply the latent heat energy needed to convert liquid water to steam (further reducing the system's thermal output).

[0029] Beyond supplying baseload heat, there is a need for flexible / adjustable heat generation to address the daily and seasonal fluctuations of annual heat demand. Closed-loop geothermal systems may not be able to economically store thermal energy below the surface on a seasonal timescale, and adjustable operation may only be efficient on a diurnal cycle. A large portion of the cost of a closed-loop geothermal system can be capital expenditure, and marginal power generation costs are low, so the system may need to operate at nearly 100% capacity to be economical.

[0030] In contrast to closed-loop geothermal systems, heat pump systems may have a large portion of their total cost attributable primarily to electricity expenditures. For example, if the electricity rate is €100 / MWhe (electricity per hour) and the heat pump COP is 2.5, the heat cost (after accounting for the heat pump's capital cost and other operating expenses) is approximately €100 / MWhe / 2.5 = €40 / MWhth (thermal energy per hour). Therefore, the unit economics of using heat pumps are highly susceptible to electricity rates. Due to their high marginal generation costs, heat pumps can be utilized at low capacity utilization rates (often less than 50%), resulting in flexible / adjustable heat generation.

[0031] In addition to efficiency challenges, heat pump system design can have technical limitations, primarily centered on the compressor. Some commercially available heat pumps are limited to a temperature lift of <100°C. Generally, increasing the temperature lift requires a higher compression ratio, and due to extreme conditions (high compressor pressure ratios), multi-stage compressor designs are used, leading to increased technical complexity and cost. Therefore, heat pumps capable of supplying heat >120°C (when using an ambient temperature heat source) are rare. Achieving higher temperatures (required for industrial applications and / or steam generation) requires a higher-temperature heat source (which is often unavailable or inaccessible).

[0032] Heat distribution networks (such as district heating networks) have demand profiles that can be correlated with ambient temperature. The time of year with the lowest ambient temperature corresponds to the time of year with the highest heat demand. Most networks have several baseload thermal requirements necessary for hot water heating and other uses. Figure 1 illustrates the district heating demand (30 MWth baseload demand and 210 MWth peak demand) for an exemplary medium-sized European city. Meeting annual heat demand with flexible / output-adjustable heat generation may be challenging.

[0033] In contrast to applications using small-scale heat pumps used in individual homes / businesses (for example, small ground source heat pumps may be used), larger heat distribution networks designed to supply regional-scale or industrial heat (typically >1 megawatt(heat) (MWth) annual peak demand) may require substantially higher input temperatures when ambient temperatures are at their lowest (highest heat demand matches the highest lift temperature). If the heat pump is supplied from a heat source affected by ambient conditions (water, air, etc.), this can result in lowest system efficiency during peak demand.

[0034] Figure 2A shows an exemplary closed-loop geothermal system 100 in a schematic side section view according to the concept herein. In a particular example, a closed-loop geothermal well system can be a system like the one developed by Eavor Technologies Inc. of Calgary, Alberta, which includes, for example, a network of sealed lateral wells that exchange heat with the subsurface zone. A closed-loop system like the one shown in Figures 2A–2C includes multiple lateral wells connecting an inlet surface well and an outlet surface well, and can provide a larger surface area for transferring heat from the geothermal zone 204 than other closed-loop systems (e.g., pipe-in-pipe systems). The multilateral closed-loop system design can improve the capital efficiency of the closed-loop system because it does not require casing, liners, and / or cement for most of the wells, and thus eliminates substantial consumption in the well construction process. When a multilateral closed-loop system is combined with a heat pump system, the thermal siphon effect is enhanced, and the parasitic load on the circulating pump is significantly reduced or, in some cases, eliminated compared to other closed-loop systems, allowing for a wider range of inlet temperature and flow rate selection. In addition, the multilateral closed-loop system allows for a larger subsurface volume of geothermal working fluid and a longer residence time, thereby increasing the system's energy storage capacity, which is beneficial for power-adjustable operation.

[0035] System 200 includes geothermal wells 202 drilled into the soil through a geothermal subsurface zone 204 of interest. In certain examples, the subsurface zone is a structure, part of such a structure, or multiple such structures that have little or no naturally occurring fluids. In certain examples, this structure can be impermeable or substantially impermeable (e.g., less than 0.1 millidarcy). In certain examples, the subsurface zone is located in a bedrock layer. In certain examples, the bedrock of the subsurface zone is granite. In the illustrated example, well 202 includes an inlet surface well 220 and an outlet surface well 230 that are close to each other, and each of these wells extends between the surface and the subsurface zone 204. The inlet surface well 220 and the outlet surface well 230 are connected within the subsurface zone 204 by one or more connecting wells 240. In the illustrated example, the connecting well 240 defines a multilateral well pattern including multiple sets of lateral wells 250, a subset of which begins at the inlet well 220 and another subset of which begins at the outlet well 230. Each set of lateral wells 250 intersects at its respective confluence point, either at or near its toe. Thus, the inlet well 220, the outlet well 230, and the connecting well 240 define a closed loop.

[0036] The inlet well 220 and the outlet well 230 can be drilled from the same drilling pad and / or be located at the same well site. In certain examples, wells 220 and 230 are drilled within 10m, 25m, 50m, or 100m of each other. In other examples, the inlet surface well 220 and the outlet surface well 230 can be separated by a longer distance. For example, Figure 2B shows a configuration in which surface wells 220, 230 and a connecting well 240 define a U-shape, which will be discussed in more detail below. In certain examples, the inlet surface well 220 and the outlet surface well 230 are drilled more than 3000m apart from each other when the geothermal well 202 is configured in a U-shape.

[0037] In the illustrated example, the inlet surface well 220 and outlet surface well 230 are vertical wells, drilled substantially in a straight line (i.e., without the use of inclined drilling methods or equipment). In other examples, one or both of the surface wells may be non-vertical (e.g., oblique) and / or drilled using inclined drilling techniques. The connecting well 240 is drilled using inclined drilling techniques through the surface wells 220, 230, and includes a curve in its trajectory starting from tip 248 in the surface wells 220, 230. Although shown as downward inclined, in some examples some or all of the connecting wells are horizontal. In some examples, the connecting well 240 follows the geological inclination of the structure within the subsurface zone. In some examples, the lateral well 250 is of any length from 2000m to over 10000m and of any depth from the surface from 1000m to over 8000m. Typical wells can exceed 3000m in depth.

[0038] Figure 2A shows pairs of lateral wells 250 that are parallel to each other and extend in the same direction (azimuth) from their respective surface wells 220 and 230. The lateral wells 250 extending from the inlet surface well 220 are shown above the lateral wells 250 extending from the outlet surface well 230. In some examples, the upper lateral wells 250 are directly above them, and in some examples, they are directly above each of the lateral wells of the lower lateral wells 250. In Figure 2A, each upper lateral well 250 changes direction and intersects with an adjacent pair of lower lateral wells 250 at confluence 254, connecting the surface wells 220 and 230. In other examples, one or more of the lower lateral wells 250 may intersect with the upper lateral wells 250. Nevertheless, the configuration of the connecting wells 240, i.e., the configuration in which one set lies above the other set, defines a layered well pattern, with one subpattern of wells located above and one subpattern of wells located below. In certain examples, one or more additional sets of the layered pattern can be drilled from surface wells 220, 230, each at different depths (i.e., each by a different tip 248). In Figure 2A, the lower lateral well 250 extends downward beyond the confluence 254 to define a sump 252. The sump 252 forms a place where debris is deposited outside the flow channel through the well. In other examples, one or more of the upper lateral wells 250 can extend beyond the confluence to define a sump 252.

[0039] The connecting well 240 in Figure 2A is inclined downward, i.e., has a slope of 270 from the vertical. In some examples, some or all of the connecting wells can be horizontal (i.e., the slope 270 is approximately 90 degrees) or substantially horizontal. In some examples, as shown in Figure 2B, the connecting well 240 can have a steeper slope, i.e., the slope 270 can be less than the slope shown in Figure 1B, or it can be vertical (slope 270 is zero) or substantially vertical. In some examples, the connecting well 240 follows the geological slope of the structure within the subsurface zone. In some examples, the lateral well 150 can have a length of 2000m to over 10000m and can reach a depth of 1000m to over 8000m.

[0040] Figure 2C shows another embodiment of the geothermal well system 200, each having lateral wells 250 extending toward each other from an inlet surface well 220 and an outlet surface well 230. The set of lateral wells 250, after intersecting, define a roughly U-shape together with the inlet well 220 and the outlet well 230. The configuration of connecting wells 240 defines a pattern of wells in the same plane in certain examples. In certain examples, one or more additional patterns of connecting wells can be drilled between the surface wells 220, 230, each at different depths (i.e., each by a different tip 248).

[0041] Referring together to Figures 2A, 2B, and 2C, in some examples, surface wells 220, 230 are (at least partially or entirely) cased, and the connecting well 240, which includes the confluence point at tip 248, is open (i.e., without casing or liner or confluence liner). In some examples, the connecting well 240 may be reinforced at least partially (e.g., including liner or casing in parts where the subsurface zone 204 is fractured, fragile, unconsolidated, or otherwise requires liner). The connecting well 240 includes the confluence point to the inlet surface well 220 and the outlet surface well 230 and is (all or substantially) sealed with sealant to prevent fluid exchange with the surrounding subsurface zone 204. In some examples, the sealant may be in the form of a liquid sealant (such as an alkali-silicate fluid) that flows within the well. The sealant ensures that all or substantially all of the geothermal working fluid circulating through the well 202 during operation is recovered to the surface, while little or no fluid naturally occurring from the subsurface zone 204 is recovered. In other words, the resulting well 202 is a closed-loop system. In certain examples, the sealant can be applied to the well while drilling the connecting well 240, and can be supplied, for example, by being included in the drilling fluid and / or by being included in a fluid slag separate from the drilling fluid. Alternatively, or in addition, the sealant can be applied after drilling and / or during the operation of the well. In certain examples, the sealant can be supplied by being included in the geothermal working fluid and / or by being included in a fluid slag separate from the geothermal working fluid.

[0042] In the illustrated example, system 200 further includes facility 210 located between an inlet surface well 220 and an outlet surface well 230. The well 202 can be sealed, and geothermal working fluid can be added to the system in a closed loop and circulated therethrough, thereby allowing the geothermal working fluid to absorb heat from the underground zone 204. In a particular example, facility 210 includes valves and pumps for controlling the flow of geothermal working fluid through the well 202, as well as a heat exchanger for extracting heat from the geothermal working fluid and transferring it to a related process such as a Rankine cycle (e.g., an organic Rankine cycle) or another heat cycle that generates electricity, an industrial, agricultural, or household steam generation process, or another process. In a particular example, facility 210 uses the heated geothermal working fluid directly, either by passing it through an expander (e.g., a turbine) that drives a generator, or by directly using the heat of the geothermal working fluid in an industrial, agricultural, or household process, instead of, or in addition to, a heat exchanger. In some examples, the facility 210 may be located on or near the soil surface, while in other examples, it may be located partially or completely below the surface. The facility 210 does not need to be housed in a single location. For example, in some examples, the facility 210 may be divided between one or more different locations connected by piping.

[0043] In the illustrated example, facility 210 includes a heat pump system 260, which is configured to extract heat from the geothermal working fluid as the working fluid circulates through a closed-loop system. As shown in Figure 3, the heat pump system 260 may include an evaporator 302, a compressor 304, a condenser 306 (operated by mechanical energy from, for example, a power source), and an expansion valve 308, through which the working fluid circulates. The heat pump system includes a heat exchanger 310 that enables heat exchange from the geothermal working fluid to the working fluid, and a heat exchanger 312 that enables heat exchange from the working fluid to a heat distribution system (such as a district heating network). As will be understood by those skilled in the art, a closed-loop geothermal system is powered by mechanical energy to meet heat demand (Q condenser It supplies thermal energy that can be raised to the desired temperature required. In other words, the heat pump is the interface between the heat demand and the closed-loop geothermal system. This configuration has the advantage of improving system output by maximizing flexibility and optimization opportunities by eliminating the interaction (and the temperature limitations resulting from this interaction) between the closed-loop geothermal system and the heat demand.

[0044] The efficiency of the heat pump system 260 can be expressed as a coefficient of performance (COP), which is defined by the following formula:

[0045]

number

[0046] In the above equation, Q condenser Q is the heat output of the heat pump. electric This is the power input to the compressor. The system's energy balance can be expressed as follows: Q condenser= Q electric+ Q evaporator (2)

[0047] In the above equation, Qevaporator is the heat absorbed by the evaporator. The COP of a heat pump exceeds 1, which means that more thermal energy is exchanged than the electrical energy supplied to the system. The second law of thermodynamics limits the maximum COP of a heat pump according to the following formula:

[0048]

Formula

[0049] Using a method based on the Lorentz method, COP can also be evaluated with temperature glide. The COP achieved by commercially available heat pump systems is typically up to 50% to 60% of the maximum Lorentz / Carnot COP. T hot -T cold is referred to as the lift temperature required by the system; the higher the lift temperature, the lower the efficiency of the heat pump.

[0050] Figure 4 is an explanatory diagram of COP as a function of desired heat demand in a heat pump system according to the concept of the present specification. More specifically, Figure 4 shows an example of how COP varies with different desired heat temperature glides when assuming 55% of the Carnot COP. When generating heat at 80°C from a constant 10°C heat source, the maximum COP is 2.8, while when generating heat at 120°C, the COP is less than 2. Many heat distribution networks, particularly older, less efficient district heating networks, have peak demand temperature requirements of ≧120°C. This change in COP depending on the desired temperature also affects the carbon intensity of these systems depending on the configuration of the power grid that supplies power to the heat pump.

[0051] Figure 5 illustrates the thermal output as a function of the flow rate of the geothermal working fluid circulating within a closed-loop geothermal system according to the concept herein. Two principal variables, the geothermal working fluid circulation velocity and the inlet temperature, can be manipulated. Each variable corresponds to the thermal output (plotted on the y-axis) and the outlet temperature (not shown). Increasing the circulation velocity and decreasing the inlet temperature can maximize the temperature difference between the geothermal working fluid and the rock mass (and thus the thermal output), but can also decrease the outlet temperature.

[0052] This independence of flow rate and inlet temperature from outlet temperature is generally unique to closed-loop systems, and there may be little to no cost increase in changing the operating point of the loop (except for using a circulation pump at a flow rate greater than the maximum thermal siphon flow rate). Figure 5 shows that the thermal output of the loop can be increased by more than 2x simply by changing the operating point (for example, an inlet temperature of 60°C and a flow rate of 60 kg / s corresponds to a thermal output of 14 MWth, compared to an inlet temperature of 20°C and a flow rate of 150 kg / s corresponding to a thermal output of 28 MWth). In systems with only closed-loop geothermal systems, the operating point of the loop can be fixed based on the required heat distribution system temperature (i.e., the inlet temperature is set by the heat distribution system return temperature (plus a small amount), and the outlet temperature is set by the required heat distribution system inlet temperature (plus a small amount)). This limitation does not apply to combined closed-loop geothermal systems and heat pump systems, which improve system flexibility and provide additional optimization opportunities. In many cases, using a circulating pump to maximize heat extraction can be optimal for combined systems, as it allows the lower temperature heat generated by a closed-loop geothermal system to be raised to the desired temperature by the heat pump.

[0053] Figure 6 is an illustrative diagram of the coefficient of performance as a function of a desired thermal temperature according to the concepts herein, illustrating the COP advantages when using a closed-loop geothermal system. A “heat pump alone” system dependent on ambient temperature heat is plotted in blue, and there are two simplified closed-loop geothermal scenarios (modeled as isothermal heat sources), namely, one scenario generating heat at 60°C and the other generating heat at 100°C. The higher the heat source temperature, the more efficient the system becomes and the lower the power consumption. Closed-loop geothermal operation and heat pump design can be optimized in cooperation based on the desired heat demand, the capital cost of the loop / heat pump, and the electricity rate (opex). For a given desired temperature, a closed-loop geothermal system and a heat pump system can have a COP of more than twice that of an equivalent heat pump alone system (thus, CO2 emissions are halved and power consumption is halved). The three operating temperatures shown in Figure 6 (120°C, 150°C, and 200°C) represent the peak heat distribution network temperature, lower temperature / pressure steam generation, and higher temperature / pressure steam generation, respectively. Optimal capacity and system design are influenced, in part, by projected electricity and heat costs.

[0054] Figure 7 presents the optimal closed-loop geothermal system and heat pump system capacities for three different electricity rates and a constant heat rate. The closed-loop geothermal system and its geometry are identical in all cases, and the thermal output of the closed-loop geothermal system is adjusted by changing the inlet temperature and flow rate. Each operating point of the closed-loop geothermal system corresponds to a specific heat input and temperature input to the heat pump evaporator, which also determines the system's total thermal output and COP. The dashed vertical line represents the optimal system capacity that maximizes the project cash flow after expenditure on electricity. This simplified example demonstrates that under lower electricity rates ($50 / MWh), the optimal system capacity increases to 48 MWth, while under higher electricity rate scenarios ($150 / MWh), the optimal system capacity decreases to 23 MWth. Reducing the power consumption of a heat pump system by adjusting the operating point (closed-loop geothermal inlet temperature and circulation rate) for a given system design is generally unique to closed-loop systems and provides system flexibility for implementation in areas where different heat and electricity rates exist.

[0055] The ability to control the outlet temperature and thermal output of closed-loop geothermal systems, as shown in Figures 2A and 2B, can affect the power-adjustable capability using a heat pump system compared to conventional geothermal systems and conventional geothermal energy boosting systems (EGS). Such systems may be less effective (or unable to be controlled) to control the outlet temperature and flow rate to the same extent as the systems shown in Figures 2A and 2B. Systems and methods disclosed herein, designed according to specifications for maximum heat demand, can improve system efficiency in off-design scenarios using cooperative control of the heat pump and the geothermal working fluid circulation operating point. The temperature of the geothermal working fluid at the surface can be adjusted to match the heat demand and increase system efficiency. Reducing thermal output (by lowering the circulation rate or increasing the inlet temperature) can increase the working fluid outlet temperature, thus lowering the temperature lift, improving the COP, and reducing power consumption.

[0056] Figure 8 illustrates the coefficient of performance as a function of thermal output in the condensers of different systems, according to the concepts of this specification. When matched to the temperature profile of the heat source, a closed-loop geothermal system can supply up to (for example) 15 MWth. For heat generation exceeding this nominal capacity, the operating point of the geothermal working fluid is adjusted (to increase the circulation rate and / or to decrease the temperature of the geothermal working fluid at the loop inlet), increasing the thermal output of the geothermal system but decreasing the outlet temperature. The heat generated from the closed-loop geothermal system is amplified using a heat pump to meet the temperature requirements of the heat demand. The maximum design capacity of the closed-loop geothermal system and heat pump system shown in Figure 8 is 36 MWth (Q condenser) and require maximum temperature lift. This flexible operation may be most useful in applications where heat demand fluctuates within a seasonal timeframe. For example, in a district heating network, the system may supply 36 MWth in winter and a base load of ~15 MWth in summer from the closed-loop geothermal system alone, and the system may efficiently generate heat when demand is between those two endpoints. A typical standalone heat pump system does not have the ability to adjust the temperature of the heat source (in response to demand fluctuations), and therefore its COP is flat (negating the inefficiency of off-design compressors and heat exchangers). Furthermore, a closed-loop geothermal system can operate with adjustable output to generate higher temperatures for demands that vary in a particular batch process or diurnal cycle, thereby reducing the temperature lift requirement of the heat pump. This may be desirable in reducing power consumption when predicted electricity rates are high. Many industrial processes have large fluctuations in heat demand within a diurnal period, and according to the concepts disclosed herein, thermal energy can be stored below the surface to reduce the power consumption of the heat pump at peak times.

[0057] In the example provided in Figure 9, the heat demand is flat (20 MWth) and is met by the system shown in Figures 2A-2C, with fluctuating daily electricity rates. Note that combined closed-loop geothermal systems and heat pump systems can be configured to supply heat across a wide range of daily fluctuations in electricity rates, heat rates, and heat demand. Heat demand refers to the heat pump thermal output in the condenser, and closed-loop geothermal system thermal output refers to the heat pump evaporator input. According to the energy balance in Equation (2), residual energy is supplied to the heat pump via the power input. Often characterized by the term "duck curve," fluctuations in electricity rates due to a significant imbalance between power supply and demand trends can result in substantial daily fluctuations in electricity rates, particularly with increased penetration of intermittent renewable power production. The output-adjustable nature of closed-loop geothermal systems allows for reduced power expenditures of the system and leverages daily electricity rate fluctuations. Closed-loop geothermal systems achieve adjustable output operation by storing energy below the surface, and by controlling the circulation of the geothermal working fluid via automated surface valve control, the fluid residence time is extended, heat intake is increased, and the system is essentially charged. If necessary, this energy is released by increasing the circulation rate and rapidly transferring this preheated fluid to the surface. When electricity rates are low, the closed-loop geothermal system can be recharged, and the increased portion of the total heat output is comprised of electricity. During periods when electricity rates are high, the charged fluid can be transferred to the surface, thereby reducing the electricity required to meet a particular heat demand.

[0058] In a specific example, as shown in Figure 10, the heat demand can be met using a system 1000 that combines an electric resistance heater 1002 and a heat pump system 260 operating in parallel. The electric resistance heater 1002 converts electricity to power with a maximum COP of 1, while the COP of the combined heat pump system and closed-loop geothermal system is greater than 1. During periods of low electricity rates, the closed-loop geothermal system can be "switched off" or its heat output reduced to charge the system using a substantial portion or all of the heat demand provided by the electric resistance heater. When electricity rates rise, the closed-loop geothermal system can be discharged, and the heat output of the resistance heater can be reduced or completely eliminated.

[0059] Figure 11 shows the "cascade configuration" 1100. In the "cascade configuration" 1100, the geothermal working fluid of the closed-loop geothermal system preheats the heat pump fluid (refrigerant) in a preheating heat exchanger 1102 before the heat pump fluid (refrigerant) enters the heat pump evaporator. The evaporator lowers the inlet temperature of the geothermal working fluid, and this energy is used to raise the inlet temperature of the heat distribution network. This configuration has the advantage of lowering the geothermal working fluid inlet temperature, improving the temperature difference between the rock mass and the geothermal working fluid, and increasing the thermal output of the closed-loop geothermal system. It should be noted that this configuration may result in a decrease in COP due to a larger temperature lift between the geothermal working fluid inlet temperature and the heat demand temperature requirements.

[0060] Figure 12 shows a cascade configuration 1200 that is similar to configuration 1100 in Figure 11, but inverted. The heat pump COP is improved because the temperature of the geothermal working fluid outlet used in the heat pump system rises first, and the temperature lift decreases. The heat pump return fluid is preheated in the preheater 1202 using residual heat. This configuration has a higher heat pump COP but a lower system thermal output compared to the configuration in Figure 8.

[0061] As shown in Figure 13, the combined closed-loop geothermal configuration, heat pump configuration, and organic Rankine cycle (ORC) configuration 1300 include combined thermal and power modes, and generate power using a simple ORC and heat distribution heat exchanger system 1302, prioritizing heat sales from residual heat directed to the ORC plant. In this embodiment, the ORC includes one or more turbines, evaporators, reheaters, pumps, and air coolers, and generates power from a closed-loop geothermal heat source when heat demand is less than the base load capacity of the closed-loop geothermal system. The ORC may include a Rankine cycle or other thermal cycle that generates power. The heat exchanger in 1302 transfers heat from the closed-loop geothermal working fluid to the heat distribution network without using a heat pump. In some examples, heat for the heat distribution network can be drawn from the ORC working fluid rather than directly from the closed-loop geothermal working fluid. The cooled geothermal working fluid is returned to the closed-loop geothermal well. The advantage of this operating mode is that it prioritizes heat sales, which can be extremely economical due to little to no conversion losses. In scenarios where the nominal capacity of the geothermal working fluid loop (without a heat pump) exceeds the nominal capacity of the annual baseload heat demand or minimum heat demand, the ORC can be used to fully utilize the available heat from the geothermal working fluid and convert it into electricity.

[0062] Figure 14 is a process flow diagram of an exemplary method 1400 of how heat from a geothermal working fluid can be distributed in the configuration shown in Figure 10. For example, we can assume a 10 MW base-load geothermal working fluid output that can produce the temperature profile required by the heat demand. The method begins in step 1402, where it is determined whether the heat demand of the heat distribution system is above or below the base load (e.g., 10 MW). If the demand is above the base load of 10 MW, in step 1404, the heat pump (and the operating point of the tuned geothermal working fluid) can be started, thereby directing all the heat flow from the geothermal working fluid to the heat pump. If it is determined in step 1402 that the demand is not above the base load, and then in step 1406 that the demand is exactly equal to the base load (e.g., 10 MW), then in step 1408, all the heat flow from the geothermal working fluid can be directed to the heat distribution exchanger. In step 1406, if it is determined that the demand is below the base load (e.g., less than 10 MW), then in step 1410, a portion of the heat flow can be converted from the geothermal working fluid to the heat distribution exchanger, allowing the residual heat to flow to the ORC for power production. (Note that if the heat demand is below the base load (e.g., ≤10 MW), the heat pump can be shut down.) In some examples with this configuration, there may be no scenario in which both the heat pump and the ORC operate simultaneously. This configuration with a heat pump and an ORC may only be suitable when the base load heat demand is below the nominal capacity of the closed-loop geothermal loop; otherwise, the geothermal working fluid loop alone or the geothermal working fluid loop and the heat pump can be used economically.

[0063] In some cases, absorption / adsorption cycle heat pumps can be used instead of conventional heat pumps with compressors as shown in Figures 2A–2C, 3, and 8–10. Essentially, an absorption / adsorption heat pump takes in moderate heat supplied by a geothermal working fluid and splits it into two flows, one high-temperature and the other low-temperature. The absence of mechanical compression in such systems means that while the operating / electricity costs of these cycles are substantially lower, the system efficiency may be lower. The COP for these cycles can be defined as (useful heat output (high temperature)) / (heat input (moderate temperature)). The COP for these systems may be around 50%, meaning that for every 1 MW of geothermal working fluid heat input, 0.5 MW of high-temperature heat is generated. Due to this low thermal efficiency, the advantages of these systems are marginal in some cases and may be technically less mature than conventional heat pumps. The combination of absorption / adsorption systems and closed-loop geothermal systems can also be inverted to generate a cooling flow that can be used in district cooling networks, with the geothermal working fluid acting as a heat sink. [Explanation of symbols]

[0064] 100 Closed-loop geothermal systems 200 Systems 202 Geothermal wells 204 Underground Zone 210 facilities 220 Inlet surface well 230 outlet surface well 240 connecting wells 248 Tip 250 Side well 252 Sump 254 Confluence 260 Heat Pump System 270 Slope 302 Evaporator 304 Compressor 306 Condenser 308 Expansion valve 310 heat exchanger 312 Heat exchanger 1000 System 1002 Electrical Resistance Heater 1100 Cascade Configuration 1102 Preheating heat exchanger 1200 Cascade Configuration 1300 Organic Rankine Cycle (ORC) Composition 1302 ORC and Heat Distribution Heat Exchanger System

Claims

1. A step of determining a specified demand as a function of time of thermal energy from a heat exchanger of a heat pump, wherein the heat pump is configured to transfer thermal energy from a geothermal working fluid circulating within a closed-loop geothermal well to the heat exchanger, and the closed-loop geothermal well is The first surface well extends from the surface to the geothermal underground zone, A second surface well extending from the ground surface to the geothermal underground zone, A step comprising: a plurality of connecting wells that connect the first surface well to the second surface well; A step of controlling the heat output from the heat exchanger to meet the specified demand, wherein the control is at least partially performed by adjusting at least one of the flow rate or inlet temperature of the geothermal working fluid in the closed-loop geothermal well. A method that includes this.

2. The method according to claim 1, wherein the thermal energy from the heat exchanger supplies a first portion of thermal energy to be supplied to a heat distribution system, and the method further comprises the step of supplying a second portion of thermal energy to the heat distribution system, wherein the thermal energy is extracted directly from the geothermal working fluid without going through the heat pump.

3. The method according to claim 1 or 2, wherein the thermal energy from the geothermal working fluid transmitted by the heat pump includes a first portion of the thermal energy from the geothermal working fluid, and the method further includes the step of generating electricity using a second portion of the thermal energy from the geothermal working fluid.

4. The method according to any one of claims 1 to 3, wherein the flow of the working fluid in the closed-loop geothermal system is generated via a thermal siphon.

5. The method according to any one of claims 1 to 4, wherein the flow of the geothermal working fluid in the closed-loop geothermal system is at least partially driven by a circulation pump.

6. The method according to any one of claims 1 to 5, wherein the heat pump is a mechanical heat pump.

7. The method according to any one of claims 1 to 6, wherein the heat pump is an absorption heat pump or an adsorption heat pump.

8. The method according to any one of claims 1 to 7, wherein the specified demand is an annual peak demand and is at least 1 megawatt thermal.

9. The steps include determining a designated target heat output to a heat distribution system based at least in part on predicted electricity or heat charges, A step of satisfying the target heat output by controlling the operation of a closed-loop geothermal well and controlling the heat output from the heat exchanger of a heat pump, wherein the heat pump is configured to transfer thermal energy from a geothermal working fluid circulating within the closed-loop geothermal well to the heat exchanger, and the closed-loop geothermal well is The first surface well extends from the surface to the geothermal underground zone, A second surface well extending from the ground surface to the geothermal underground zone, The system comprises a plurality of connecting wells that connect the first surface well to the second surface well, wherein the control of the thermal output is at least partially performed by adjusting the flow rate and / or inlet temperature of the geothermal working fluid in the closed-loop geothermal well, A method that includes this.

10. The method according to claim 9, wherein the target thermal output is partially based on at least one of net cash flow and predicted heat charges and electricity charges as a function of time.

11. The method according to claim 9 or 10, wherein the flow of the working fluid in the closed-loop geothermal system is generated via a thermal siphon.

12. The method according to any one of claims 9 to 11, wherein the flow of the geothermal working fluid in the closed-loop geothermal system is partially supported by a circulating pump.

13. The method according to any one of claims 9 to 12, wherein the thermal energy from the heat exchanger supplies a first portion of thermal energy to be supplied to a heat distribution system, and the method further comprises the step of supplying a second portion of thermal energy to the heat distribution system, wherein the thermal energy is extracted directly from the geothermal working fluid without going through the heat pump.

14. The method according to any one of claims 9 to 13, wherein the heat pump is a mechanical heat pump.

15. The method according to any one of claims 9 to 14, wherein the heat pump is an absorption heat pump or an adsorption heat pump.

16. The method according to any one of claims 9 to 15, wherein the thermal energy from an electric resistance heater supplies a portion of the thermal energy to a heat distribution system, the method further comprising the step of supplying a second portion of the thermal energy to the heat distribution system, the thermal energy being directly extracted from the geothermal working fluid of the closed-loop geothermal system and transmitted by the heat pump, and the distribution of the thermal energy supplied between these systems is determined in part on predicted electricity and heat charges.

17. The method according to claim 16, wherein the prediction period is less than 72 hours.

18. The method according to claim 17, further comprising the step of operating the closed-loop geothermal system in an output-adjustable manner using a charge-discharge cycle.

19. The method according to any one of claims 9 to 15, wherein the thermal energy from the geothermal working fluid transmitted by the heat pump includes a first portion of the thermal energy from the geothermal working fluid, and the method further includes the step of generating electricity using a second portion of the thermal energy from the geothermal working fluid.

20. The method according to any one of claims 9 to 15, wherein the specified demand is an annual peak demand and is at least 1 megawatt thermal.

Images