Geothermal heat utilization system, control device, control method, and program

Abstract

A geothermal heat utilization system (1) according to the present disclosure includes: a pumping well (21); a water injection well (22); piping (3) extending from the pumping well (21) to the water injection well (22); a pump (31) capable of feeding groundwater from the pumping well (21) to the water injection well (21) via the piping (3); a heat exchanger (4) provided at the piping (3); a control valve (72) that is provided at the piping (3) and is capable of adjusting the flow rate of groundwater within the piping (3); and a control device (80) that, if the operation frequency of inverter control of the pump (31) has reached the minimum frequency, adjusts the flow rate of groundwater injected into the water injection well (22) by controlling the control valve (72) to reduce the flow rate within the piping (3). (FIG. 3)

Description

Geothermal energy utilization system, control device, control method, and program

[0001] This disclosure relates to a geothermal energy utilization system, a control device, a control method, and a program. This application claims priority to Japanese Patent Application No. 2021-078700, filed on May 6, 2021, the contents of which are incorporated herein by reference.

[0002] BACKGROUND ART In recent years, geothermal energy utilization systems that utilize groundwater as a heat or cold source have been proposed.

[0003] For example, Patent Document 1 proposes a geothermal energy utilization system that includes a pumping well and a water injection well, pumps groundwater from the pumping well, and exchanges heat with the load side using a heat exchanger. This type of geothermal energy utilization system stores heat by injecting the groundwater that has passed through the heat exchanger into the water injection well.

[0004] Japanese Patent Application Laid-Open No. 2018-173256

[0005] In the geothermal energy utilization system disclosed in Patent Document 1, in order to maintain a constant temperature of water injected into the water injection well, it is necessary to reduce the water injection flow rate during low loads. However, when inverter control is used with the pump disclosed in Patent Document 1, it can be difficult to control the water injection temperature during low loads when the water injection flow rate is smaller than the water injection flow rate at the lowest frequency of the inverter control.

[0006] The present disclosure has been made to solve the above-mentioned problem, and aims to provide a geothermal energy utilization system, a control device, a control method, and a program that make it easy to control the temperature of injected water during low load periods.

[0007] In order to solve the above problems, the geothermal energy utilization system of the present disclosure comprises a pumping well, an injection well, a pipe extending from the pumping well to the injection well, a pump capable of transporting groundwater from the pumping well to the injection well via the pipe, a heat exchanger provided in the pipe, a control valve provided in the pipe and capable of adjusting the flow rate of the groundwater in the pipe, and a control device that adjusts the flow rate of the groundwater injected into the injection well by controlling the control valve to throttle the flow rate in the pipe when the operating frequency of the inverter control of the pump reaches the lowest frequency.

[0008] The control device of the present disclosure includes a pump operation control unit that adjusts the operating frequency of the inverter control of a pump that transports groundwater from a pumping well to an injection well, depending on the temperature of the groundwater that is pumped up from the pumping well and injected into the injection well through a heat exchanger, and a control valve opening / closing control unit that adjusts the opening of a control valve installed in a pipe that transports the groundwater to the injection well, depending on the temperature of the groundwater that is injected into the injection well, when the operating frequency reaches its lowest frequency.

[0009] The control method disclosed herein adjusts the operating frequency of the inverter control of a pump that transports groundwater from a pumping well to an injection well in accordance with the temperature of the groundwater that is pumped up from the pumping well and injected into the injection well after passing through a heat exchanger, and when the operating frequency reaches its lowest frequency, adjusts the opening of a control valve installed in a pipe that transports the groundwater to the injection well in accordance with the temperature of the groundwater that is injected into the injection well.

[0010] The program disclosed herein causes a computer to execute a method of adjusting the operating frequency of the inverter control of a pump that transports groundwater from a pumping well to an injection well in accordance with the temperature of the groundwater pumped from the pumping well and injected into the injection well through a heat exchanger, and when the operating frequency reaches its lowest frequency, adjusting the opening of a control valve installed in a pipe that transports the groundwater to the injection well in accordance with the temperature of the groundwater injected into the injection well.

[0011] According to the geothermal energy utilization system, control device, control method, and program disclosed herein, it is easy to control the temperature of injected water during low load periods.

[0012] 1 is a diagram showing a schematic configuration of a geothermal utilization system according to an embodiment of the present disclosure; FIG. 2 is a diagram showing a schematic configuration of a geothermal utilization system and a load equipment side according to an embodiment of the present disclosure; FIG. 3 is a system diagram of a geothermal utilization system according to an embodiment of the present disclosure; FIG. 4 is a diagram showing the flows of groundwater and a medium when a cooling mode is performed on the load equipment side in a geothermal utilization system according to an embodiment of the present disclosure; FIG. 5 is a diagram showing the flows of groundwater and a medium when a heating mode is performed on the load equipment side in a geothermal utilization system according to an embodiment of the present disclosure; FIG. 6 is a block diagram of a control device according to an embodiment of the present disclosure; FIG. 7 is a diagram showing the flows of groundwater and a medium when a cooling tower mode is performed on the load equipment side in a geothermal utilization system according to an embodiment of the present disclosure; FIG. 8 is a diagram showing the flows of groundwater and a medium when a chiller mode is performed on the load equipment side in a geothermal utilization system according to an embodiment of the present disclosure;

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In all drawings, the same or corresponding components are denoted by the same reference numerals, and common descriptions will be omitted.

[0014] [Embodiment] An embodiment of a geothermal energy utilization system according to the present disclosure will be described with reference to Figures 1 to 9. (Configuration of geothermal energy utilization system) As shown in Figures 1 to 3, a geothermal energy utilization system 1 mainly includes a plurality of wells 2, piping 3, a heat exchanger 4, a temperature adjustment system 7 (see Figure 3), and a pump 31.

[0015] (Well Configuration) As shown in FIG. 1 , multiple wells 2 extend from the ground OG into the aquifer LY. For example, the multiple wells 2 include a first well 2A and a second well 2B. The geothermal heat utilization system 1 pumps groundwater from one of the first well 2A and the second well 2B, exchanges heat in a heat exchanger 4, and then injects the heat-exchanged groundwater into the other of the first well 2A and the second well 2B. In other words, the geothermal heat utilization system 1 has two operating modes: one in which groundwater is pumped from the first well 2A and injected into the second well 2B, and one in which groundwater is pumped from the second well 2B and injected into the first well 2A. In the following description, the first well 2A or the second well 2B that pumps groundwater will be referred to as a pumping well 21, and the first well 2A or the second well 2B that injects groundwater will be referred to as an injection well 22. That is, the first well 2A and the second well 2B may function as a pumping well 21 or as a water injection well 22. However, in the following, for the sake of simplicity, the explanation will be centered on the case where the first well 2A is used as the pumping well 21 and the second well 2B is used as the water injection well 22, and heat exchange is performed in the heat exchanger 4.

[0016] Each well 2 includes a casing 2a embedded in a borehole HOL drilled underground from the surface OG to the aquifer LY. The casing 2a is cylindrical and extends in the vertical direction.

[0017] Each well 2 has an opening 2c at its top. For example, the opening 2c may be an opening at the top of the casing 2a.

[0018] The casing 2a has a strainer 2b consisting of, for example, a plurality of slits. The strainer 2b allows the well 2 to take groundwater from the aquifer LY into the casing 2a and return groundwater from the inside of the casing 2a to the aquifer LY. For example, as shown in Figure 3, a well cover 6 that closes the opening at the top of the casing 2a may be provided.

[0019] 1 and 3 , the piping 3 extends inside the well 2. For example, the piping 3 may be immersed at both ends in the groundwater of the pumping well 21 and the water injection well 22 so as to connect the pumping well 21 and the water injection well 22. For example, one end of the piping 3 may be provided in the pumping well 21 and the other end of the piping 3 may be provided in the water injection well 22 so that groundwater pumped up by the pump 31 can flow from the pumping well 21 to the water injection well 22.

[0020] A pump 31 is provided in the pipe 3. The pump 31 pumps water from the well 2 to the pipe 3. For example, when the well 2 functions as a pumping well 21, the pump 31 pumps water from the well 2 to the pipe 3. For example, the pump 31 may pump groundwater in the well 2 into the pipe 3. For example, the pump 31 may be provided at both ends of the pipe 3 and immersed in the groundwater in each well 2. For example, the pump 31 may be able to change its output by inverter control.

[0021] The pipe 3 is provided with a water injection valve 32. The water injection valve 32 is provided at each end of the pipe 3. The water injection valve 32 may be disposed between the pump 31 at each end of the pipe 3 and the heat exchanger 4. For example, the water injection valve 32 may be immersed in the groundwater in each well 2. The water injection valve 32 injects the groundwater in the pipe 3. For example, when the well 2 functions as a water injection well 22, the water injection valve 32 injects the groundwater in the pipe 3 into the well 2 (water injection well 22). The water injection valve 32 opens when the pressure in the pipe 3 exceeds a set pressure, and the groundwater in the pipe 3 is injected into the water injection well 22.

[0022] 3, the piping 3 is provided with check valves 35a to 35d between the heat exchanger 4 and the pumping well 21 and the water injection well 22. The check valves 35a to 35d control the flow of groundwater in the piping 3 so that the groundwater flows in the same direction toward the heat exchanger 4, whether the groundwater is pumped from the pumping well 21 or the water injection well 22.

[0023] For example, when groundwater is pumped from the first well 2A, the groundwater in the pipe 3 passes from the first well 2A through the check valve 35a, the heat exchanger 4, and the check valve 35b, in that order, before being poured into the second well 2B. At this time, the pressure in the pipe 3 is higher upstream of the heat exchanger 4 (the first well 2A side) than downstream, so water does not flow through the check valves 35c and 35d. Similarly, when groundwater is pumped from the second well 2B, the groundwater in the pipe 3 passes from the second well 2B through the check valve 35c, the heat exchanger 4, and the check valve 35d, in that order, before being poured into the first well 2A. At this time, the pressure in the pipe 3 is higher upstream of the heat exchanger 4 (the first well 2A side) than downstream, so water does not flow through the check valves 35a and 35b.

[0024] (Configuration of heat exchanger) The heat exchanger 4 exchanges heat between the groundwater in the pipe 3 and the medium on the load equipment 100 side. For example, the heat exchanger 4 exchanges heat between the groundwater pumped up from the well 2 and flowing in the pipe 3 and the medium on the load equipment 100 side. After the heat exchange, the groundwater flows from the heat exchanger 4 through the pipe 3 and is injected into the well 2. For example, the heat exchanger 4 may be provided midway along the pipe 3 above ground OG.

[0025] If the water that has passed through the heat exchanger 4 is hot water, the geothermal energy utilization system 1 stores hot water heat by injecting hot water into the well 2. If the water that has passed through the heat exchanger 4 is cold water, the geothermal energy utilization system 1 stores cold water heat by injecting cold water into the well 2. Here, "hot water" refers to water with a temperature higher than the initial underground temperature of the groundwater in the aquifer, and "cold water" refers to water with a temperature lower than the initial underground temperature of the groundwater in the aquifer. For example, the initial underground temperature of the groundwater in the aquifer is 18°C.

[0026] (Configuration of Load Equipment) As shown in FIG. 2 , the load equipment 100 uses a medium that has undergone heat exchange with groundwater in a pipe 3 in a heat exchanger 4. The load equipment 100 is, for example, an air conditioning system including a heat source unit 110 and an air conditioner 120. For example, the heat source unit 110 may be a heat pump including a condenser, an evaporator, a compressor, etc. The air conditioner 120 performs air conditioning of the space in which the air conditioner 120 is installed by exchanging heat with the medium supplied from the heat source unit 110. For example, the load equipment 100, as an air conditioning system, is capable of switching its operating mode between a cooling mode and a heating mode. The load equipment 100 has a piping system 101 for forming a flow of medium corresponding to each operating mode between the heat exchanger 4, the heat source unit 110, and the air conditioner 120. The piping system 101 is appropriately provided with on-off valves, etc. (not shown), and the medium is circulated between the heat exchanger 4, the heat source unit 110, and the air conditioner 120 via a predetermined route depending on each operating mode of the air conditioning system.

[0027] In this embodiment, the load equipment 100 may further include a cooling tower 130 and a second heat exchanger 140.

[0028] The cooling tower 130 cools the cooling water by the heat of vaporization generated when the cooling water comes into contact with the atmosphere and vaporizes. The cooling tower 130 circulates the cooling water between the cooling tower 130 and the second heat exchanger 140. The second heat exchanger 140 exchanges heat between the medium in the piping system 101 on the air conditioning system side and the cooling water on the cooling tower 130 side. The second heat exchanger 140 cools the medium in the piping system 101 on the air conditioning system side by exchanging heat with the cooling water cooled in the cooling tower 130. The configuration and use of the load equipment 100 are not limited to those described above and can be changed as appropriate.

[0029] As shown in FIG. 4 , when cooling operation is performed on the load equipment 100 side and hot water thermal storage is performed in the water injection well 22, the second well 2B serves as the pumping well 21 and the first well 2A serves as the water injection well 22. A pump 31 in the second well 2B, which serves as the pumping well 21, pumps groundwater and sends it to the heat exchanger 4. In the heat exchanger 4, heat exchange occurs between the groundwater in the pipe 3 and the medium flowing through the piping system 101 on the load equipment 100 side. On the load equipment 100 side, the medium cooled by heat exchange in the heat exchanger 4 is sent to the heat source unit 110 and undergoes heat exchange there. This allows the air conditioner 120 connected to the heat source unit 110 to cool the room. Meanwhile, the medium heated by heat exchange in the heat source unit 110 is sent back to the heat exchanger 4 and circulated. In the heat exchanger 4, heat exchange occurs between the heated medium and the groundwater flowing through the pipe 3, heating the groundwater. The geothermal energy utilization system 1 stores hot water heat by injecting heated groundwater into a water injection well 22 through a pipe 3.

[0030] As shown in FIG. 5 , when heating operation is performed on the load equipment 100 side and cold water thermal storage is performed in the water injection well 22, the first well 2A serves as the pumping well 21 and the second well 2B serves as the water injection well 22. A pump 31 in the first well 2A, which serves as the pumping well 21, pumps groundwater and sends it to the heat exchanger 4. In the heat exchanger 4, heat exchange occurs between the groundwater in the pipe 3 and the medium flowing through the piping system 101 on the load equipment 100 side. On the load equipment 100 side, the medium heated by heat exchange in the heat exchanger 4 is sent to the heat source unit 110 and undergoes heat exchange there. This allows the air conditioner 120 connected to the heat source unit 110 to heat the room. Meanwhile, the medium cooled by heat exchange in the heat source unit 110 is sent back to the heat exchanger 4 and circulated. In the heat exchanger 4, heat exchange occurs between the cooled medium and the groundwater flowing through the pipe 3, thereby cooling the groundwater. The geothermal energy utilization system 1 stores cold water heat by injecting cooled groundwater into a water injection well 22 through a pipe 3.

[0031] 3 , the temperature adjustment system 7 includes a pump controller 71, a control valve 72, and a control device 80. The temperature adjustment system 7 adjusts the temperature of the water injected into the water injection well 22 by adjusting the flow rate of groundwater injected into the water injection well 22.

[0032] The pump controller 71 controls the operation of the pump 31. For example, the pump controller 71 may be provided in association with the pump 31 of each well 2. For example, the pump controller 71 has an inverter circuit (not shown) and performs inverter control of the pump 31. The pump controller 71 adjusts the rotation speed of the pump 31 by varying the operating frequency of the inverter control by the inverter circuit under the control of a control device 80 described below. The pump controller 71 adjusts the rotation speed of the pump 31 by varying the operating frequency of the inverter control by the inverter circuit, and adjusts the flow rate of groundwater injected from the pipe 3 into the water injection well 22 via the heat exchanger 4. Hereinafter, the operating frequency of the inverter control of the pump 31 will also be referred to as the "operating frequency of the pump 31."

[0033] The control valve 72 is provided in the pipe 3. For example, the control valve 72 may be provided between each well 2 and the heat exchanger 4. For example, in the present embodiment, the control valve 72 may be provided closer to the water injection well 22 than the heat exchanger 4. The control valve 72 can adjust the flow rate of groundwater in the pipe 3. The control valve 72 adjusts the flow rate of groundwater in the pipe 3 by opening and closing a flow path in the pipe 3. The control valve 72 adjusts the flow rate of groundwater in the pipe 3 by adjusting its opening degree. The control valve 72 adjusts the flow rate of groundwater in the pipe 3 under the control of the control device 80. The control valve 72 adjusts its opening degree when the operating frequency of the pump 31 drops to the minimum frequency. For example, the minimum frequency is determined by the type of pump and may differ depending on the pump manufacturer.

[0034] (Configuration of the Control Device) The control device 80 adjusts the flow rate of groundwater injected into the water injection well 22. The control device 80 adjusts the operating frequency of the pump 31 and the aperture of the control valve 72 so that the temperature of the groundwater injected into the water injection well 22 is constant. The control device 80 adjusts the flow rate of groundwater injected into the water injection well 22 by adjusting only the operating frequency of the pump 31 when the operating frequency of the pump 31 is equal to or higher than the minimum frequency. For example, the control device 80 may be controllably connected to each pump controller 71. For example, the control device 80 may be controllably connected to each control valve 72. For example, when the operating frequency of the pump 31 drops to the minimum frequency, the control device 80 adjusts the flow rate of groundwater injected into the water injection well 22 by adjusting the aperture of the control valve 72. When the operating frequency of the pump 31 drops to the minimum frequency, the control device 80 reduces the flow rate of groundwater injected into the water injection well 22 by throttling (reducing) the aperture of the control valve 72. For example, when the operating frequency of the pump 31 drops to the minimum frequency and the flow rate of groundwater injected into the water injection well 22 is being adjusted by adjusting the aperture of the control valve 72, the control device 80 may maintain the operating frequency of the pump 31 at the minimum frequency. Furthermore, when the aperture of the control valve 72 is narrowed to a preset minimum aperture, the control device 80 adjusts the flow rate of groundwater injected from the pipe 3 into the water injection well 22 by exchanging heat with the medium on the load equipment 100 side cooled by the cooling tower 130 in the heat exchanger 4.

[0035] As shown in FIG. 6 , the control device 80 includes a pump operation control unit 81 , a control valve opening / closing control unit 82 , and a load-side flow path control unit 83 .

[0036] The pump operation control unit 81 adjusts the rotation speed of the pump 31 by varying the operating frequency of the inverter control by the inverter circuit of the pump controller 71. The pump operation control unit 81 adjusts the operating frequency of the pump 31, which pumps groundwater from the pumping well 21, depending on the temperature of the groundwater injected into the water injection well 22. The pump operation control unit 81 adjusts the flow rate of groundwater injected from the pipe 3 into the water injection well 22 by varying the operating frequency of the pump 31 based on a pre-stored map or the like. For example, when cooling operation is performed on the load equipment 100 side and hot water thermal storage is performed in the water injection well 22, the pump operation control unit 81 controls the operating frequency of the pump 31 based on the difference between the actual injection temperature of the groundwater injected from the pipe 3 into the water injection well 22 and the set temperature. For example, when heating operation is performed on the load equipment 100 side and cold water thermal storage is performed in the water injection well 22, the pump operation control unit 81 controls the operating frequency of the pump 31 based on the difference between the actual injection temperature of the groundwater injected from the pipe 3 into the water injection well 22 and the set temperature. The pump operation control unit 81 controls the pump controller 71 to adjust the operating frequency (output) of the pump 31 according to the required temperature of injected water based on a pre-stored map or the like. The pump operation control unit 81 stores, for example, the lower limit of the operating frequency at which the pump 31 can operate stably as the minimum frequency. The pump operation control unit 81 controls the pump controller 71 to adjust the operation of the pump 31 in a frequency range equal to or higher than the preset minimum frequency.

[0037] The control valve on / off control unit 82 adjusts the flow rate of groundwater in the pipe 3 by opening and closing the control valve 72. The control valve on / off control unit 82 adjusts the opening degree of the control valve 72 to adjust the flow rate of groundwater in the pipe 3. The control valve on / off control unit 82 adjusts the opening degree of the control valve 72 when the operating frequency of the pump 31 drops to the minimum frequency. When the operating frequency of the pump 31 becomes the minimum frequency, the control valve on / off control unit 82 adjusts the opening degree of the control valve 72 in accordance with the temperature of the groundwater injected into the water injection well 22.

[0038] The load-side flow path control unit 83 controls the flow of the medium in the load equipment 100 by switching valves and the like provided in the piping system 101 on the load equipment 100 side. The load-side flow path control unit 83 controls the flow of the medium in the piping system 101 according to each operation mode, such as cooling mode or heating mode. When the opening degree of the control valve 72 reaches a preset minimum opening degree and the injection water temperature does not reach a set temperature, the load-side flow path control unit 83 switches the operation mode on the load equipment 100 side to a cooling tower mode, which will be described later. When the opening degree of the control valve 72 reaches a preset minimum opening degree while the operating frequency of the pump 31 is reduced to the minimum frequency, the load-side flow path control unit 83 switches the operation mode on the load equipment 100 side to a cooling tower mode. In the cooling tower mode, the medium cooled by the cooling water in the cooling tower 130 and the groundwater that has undergone heat exchange in the heat exchanger 4 are injected into the water injection well 22. Furthermore, the load-side flow path control unit 83 may switch the operation mode of the load equipment 100 to a chiller mode, which will be described later.

[0039] As shown in Figure 7, a cooling tower mode may be used to cool groundwater and perform cold water thermal storage. In the cooling tower mode, the load equipment 100 sends the cooling water, which has been cooled by the heat of vaporization when the cooling water is vaporized by contacting the cooling water with the atmosphere in the cooling tower 130, to the second heat exchanger 140. In the second heat exchanger 140, heat exchange occurs between the cooling water and the medium in the piping system 101. That is, in the second heat exchanger 140, the medium in the piping system 101 is cooled by the cooling water cooled in the cooling tower 130. The cooled medium is sent to the heat exchanger 4 and exchanges heat with the groundwater in the pipe 3. As a result, the groundwater in the pipe 3 is cooled and injected into the water injection well 22, thereby performing cold water thermal storage.

[0040] As shown in FIG. 8 , a chiller mode may be used to cool groundwater and store cold water heat. In the chiller mode, the load equipment 100 uses the cooling tower 130 and the heat source unit 110 as chillers. In this case, the pump 31 of the first well 2A, which serves as the pumping well 21, pumps groundwater and sends it to the heat exchanger 4. The heat exchanger 4 exchanges heat between the groundwater in the piping 3 and the medium flowing through the piping system 101 on the load equipment 100 side, thereby cooling the groundwater. On the load equipment 100 side, the medium heated by heat exchange in the heat exchanger 4 is sent to the heat source unit 110. The heat source unit 110, connected to the cooling tower 130 via the second heat exchanger 140, cools the heated medium by heat exchange. The medium cooled by heat exchange in the heat source unit 110 is sent back to the heat exchanger 4 and circulated. In the heat exchanger 4, the groundwater is cooled by heat exchange between the cooled medium and the groundwater flowing in the pipe 3. The geothermal energy utilization system 1 injects the cooled groundwater into the water injection well 22 through the pipe 3, thereby storing cold water heat.

[0041] The operation of the control device 80 of this embodiment will be described. The operation of the control device 80 corresponds to an embodiment of a control method. The control device 80 performs each step shown in FIG. 9.

[0042] First, when the load equipment 100 is operating in cooling mode or heating mode, the pump operation control unit 81 adjusts the operating frequency of the inverter control of the pump 31 that sends groundwater from the pumping well 21 to the water injection well 22, in accordance with the set temperature of the groundwater injected into the water injection well 22 via the heat exchanger 4 (ST01: step of adjusting the operating frequency of the pump). This adjusts the flow rate of water injected from the pumping well 21 to the water injection well 22 by the pump 31.

[0043] Following execution of ST01, the pump operation control unit 81 determines whether the operating frequency of the inverter control of the pump 31 has dropped to the minimum frequency (ST02: step of determining whether the operating frequency of the pump has dropped to the minimum frequency).

[0044] If the determination in ST02 indicates that the operating frequency of the inverter control of the pump 31 has not dropped to the minimum frequency, the process returns to ST01, where the pump operation control unit 81 continues adjusting the flow rate of water injected by the pump 31 from the pumping well 21 to the water injection well 22. If the determination in ST02 indicates that the operating frequency of the inverter control of the pump 31 has dropped to the minimum frequency, the control valve opening / closing control unit 82 adjusts the aperture of the control valve 72 in a direction toward closure, depending on the set temperature of the groundwater to be injected into the water injection well 22 (ST03: step of adjusting the aperture of the control valve). The control valve opening / closing control unit 82 adjusts the flow rate of water to be injected into the water injection well 22 by adjusting the aperture of the control valve 72. At this time, the operating frequency of the inverter control of the pump 31 is maintained at the minimum frequency. In other words, by closing the control valve 72 while the operating frequency of the inverter control of the pump 31 is at the minimum frequency, the control device 80 further reduces the flow rate of groundwater to be injected into the water injection well 22.

[0045] Following execution of ST03, the control valve control unit 82 determines whether the opening of the control valve 72 is at a preset minimum opening (ST04: step of determining whether the opening of the control valve is at the minimum opening). If the determination in ST04 shows that the opening of the control valve 72 is not at the minimum opening, the process returns to ST03, and the control valve control unit 82 continues processing. If the determination in ST04 shows that the opening of the control valve 72 is at the minimum opening, the load-side flow path control unit 83 switches the operation mode of the load equipment 100 to the cooling tower mode (ST05: step of switching the operation mode of the load equipment to the cooling tower mode). In the cooling tower mode, the geothermal utilization system 1 injects into the water injection well 22 the groundwater that has undergone heat exchange in the heat exchanger 4 with the medium cooled by the cooling water in the cooling tower 130. As a result, the groundwater in the pipe 3 is cooled and injected into the water injection well 22, thereby performing cold water thermal storage. For example, when cold water thermal storage in the cooling tower mode cannot be performed due to high atmospheric temperature, the control device 80 may switch to the chiller mode and perform cold water thermal storage in the chiller mode.

[0046] (Operations and Effects) According to this embodiment, the geothermal utilization system 1 pumps groundwater from the pumping well 21 using the pump 31 and sends it to the heat exchanger 4 through the pipe 3. The heat exchanger 4 exchanges heat between the groundwater and a medium on the load equipment 100 side, thereby utilizing geothermal energy. The groundwater that has passed through the heat exchanger 4 is injected into the water injection well 22 through the pipe 3. The pump 31 adjusts the flow rate of the groundwater pumped through the pipe 3 using inverter control. When the operating frequency of the inverter control of the pump 31 reaches a preset minimum frequency, the geothermal utilization system 1 throttles the flow rate in the pipe 3 using the control valve 72, thereby enabling groundwater to be injected into the water injection well 22 at a flow rate lower than the flow rate at the minimum frequency of the pump 31. This makes it easier for the geothermal utilization system 1 to control the temperature of the injected water under low load conditions.

[0047] According to one example of this embodiment, the control valve 72 is provided closer to the water injection well 22 than the heat exchanger 4. This allows the geothermal energy utilization system 1 to control the water injection flow rate near the water injection well 22. Therefore, the geothermal energy utilization system 1 can easily control the temperature of the water injected into the water injection well 22.

[0048] Furthermore, according to one example of this embodiment, when the control device 80 adjusts the flow rate of groundwater in the pipe 3 by throttling the control valve 72, the operating frequency of the inverter control of the pump 31 is kept at the minimum frequency. In this way, when the control valve 72 is being throttled to adjust the flow rate of groundwater, the operating frequency of the inverter control of the pump 31 is kept at the minimum frequency, so that the geothermal energy utilization system 1 can efficiently adjust the flow rate using the control valve 72.

[0049] According to one example of this embodiment, when the opening degree of the control valve 72 reaches the minimum setting, the control device 80 performs heat exchange in the heat exchanger 4 between the medium cooled by the cooling water in the cooling tower 130 and the groundwater in the pipe 3, and injects the cooled groundwater into the water injection well 22. When the opening degree of the control valve 72 reaches the minimum setting, the flow rate of the groundwater injected into the water injection well 22 cannot be further reduced. In such a case, by using the cooling tower 130, the geothermal energy utilization system 1 can further adjust the temperature of the groundwater injected into the water injection well 22. This allows the geothermal energy utilization system 1 to control the temperature of the injected water over a wider range during low load conditions.

[0050] According to one example of the present embodiment, the control device 80 includes a pump operation control unit 81 and a control valve on / off control unit 82. According to this control device 80, the pump operation control unit 81 adjusts the operating frequency of the inverter control of the pump 31 in accordance with the temperature of the groundwater injected into the water injection well 22. By adjusting the flow rate of the groundwater injected into the water injection well 22, the control device 80 can adjust the temperature of the groundwater injected into the water injection well 22. When the operating frequency of the inverter control of the pump 31 reaches a preset minimum frequency, the control valve on / off control unit 82 adjusts the aperture of the control valve 72 to throttle the flow rate in the piping 3, thereby enabling groundwater to be injected into the water injection well 22 at a flow rate lower than the flow rate at the pump 31's minimum frequency. This makes it easier for the control device 80 to control the temperature of the injected water under low load conditions.

[0051] [Modification] In the above-described embodiment, a program for realizing the various functions of the control device 80 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system such as a microcomputer and executed to perform various processes. Here, the various processes of the CPU of the computer system are stored in the form of a program on a computer-readable recording medium, and the computer reads and executes the program to perform the various processes. Examples of computer-readable recording media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories. Alternatively, the computer program may be distributed to a computer via a communication line, and the computer that receives the program may execute the program.

[0052] In the above-described embodiment, an example of the hardware configuration of the computer 190 that executes the programs for realizing the various functions of the control device 80 will be described.

[0053] As shown in FIG. 10 , the computer 190 provided in the control device 80 includes a processor 195, a memory 196, a storage / playback device 197, an input output interface (hereinafter referred to as “IO I / F”) 198, and a communication interface (hereinafter referred to as “communication I / F”) 199.

[0054] For example, the processor 195 may be a CPU. For example, the memory 196 may be a medium such as random access memory (hereinafter referred to as "RAM") that temporarily stores data and the like used by programs executed by the control device 80. For example, the storage / playback device 197 may be a device for storing data and the like in external media such as CD-ROMs, DVDs, and flash memories, or for playing back data and the like from external media. For example, the IO I / F 198 may be an interface for inputting and outputting information and the like between the control device 80 and other devices. For example, the communication I / F 199 may be an interface for communicating between the control device 80 and other devices via a communication line such as the Internet or a dedicated communication line.

[0055] [Other Embodiments] Although the embodiments of the present disclosure have been described above, these embodiments are provided by way of example only and are not intended to limit the scope of the present disclosure. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the present disclosure. These embodiments and their modifications are considered to be within the scope and spirit of the present disclosure, as well as within the scope of the present disclosure and its equivalents.

[0056] [Additional Notes] The geothermal energy utilization system 1, the control device 80, the control method, and the program described in the embodiment can be understood, for example, as follows.

[0057] (1) The geothermal energy utilization system 1 of the first aspect comprises a pumping well 21, a water injection well 22, a pipe 3 extending from the pumping well 21 to the water injection well 22, a pump 31 capable of transporting groundwater from the pumping well 21 to the water injection well 22 via the pipe 3, a heat exchanger 4 provided in the pipe 3, a control valve 72 provided in the pipe 3 and capable of adjusting the flow rate of the groundwater in the pipe 3, and a control device 80 that adjusts the flow rate of the groundwater injected into the water injection well 22 by controlling the control valve 72 to throttle the flow rate in the pipe 3 when the operating frequency of the inverter control of the pump 31 becomes the lowest frequency.

[0058] In this geothermal energy utilization system 1, groundwater pumped from a pumping well 21 by a pump 31 is sent to a heat exchanger 4 through a pipe 3. Geothermal energy is utilized by exchanging heat between the groundwater and a medium on the load equipment 100 side in the heat exchanger 4. The groundwater that passes through the heat exchanger 4 is injected into the water injection well 22 through the pipe 3. The pump 31 adjusts the flow rate of the groundwater pumped through the pipe 3 using inverter control. When the operating frequency of the inverter control of the pump 31 reaches a preset minimum frequency, the geothermal energy utilization system 1 throttles the flow rate in the pipe 3 using a control valve 72, thereby enabling groundwater to be injected into the water injection well 22 at a flow rate lower than the flow rate at the minimum frequency of the pump 31. This makes it easier for the geothermal energy utilization system 1 to control the temperature of the injected water under low load conditions.

[0059] (2) The geothermal energy utilization system 1 according to the second aspect may be the geothermal energy utilization system 1 of (1), in which the control valve 72 is provided closer to the water injection well 22 than the heat exchanger 4.

[0060] This allows the geothermal energy utilization system 1 to control the flow rate of water injection near the water injection well 22. Therefore, the geothermal energy utilization system 1 can easily control the temperature of the water injected into the water injection well 22.

[0061] (3) The geothermal energy utilization system 1 according to the third aspect is the geothermal energy utilization system 1 of (1) or (2), and when the control device 80 adjusts the flow rate of the groundwater in the pipe 3 by throttling the control valve 72, the operating frequency may be maintained at the minimum frequency.

[0062] In this way, when the control valve 72 is throttled to adjust the groundwater flow rate, the geothermal energy utilization system 1 can efficiently adjust the flow rate using the control valve 72 by maintaining the operating frequency of the inverter control of the pump 31 at the lowest frequency.

[0063] (4) The geothermal energy utilization system 1 relating to the fourth aspect is any one of the geothermal energy utilization systems 1 of (1) to (3), and is provided with a cooling tower 130 on the side of the load equipment 100 that uses a medium that exchanges heat with the groundwater in the piping 3 in the heat exchanger 4, and when the opening of the control valve 72 reaches the minimum set opening, the control device 80 may inject the medium cooled by the cooling tower 130 and the groundwater that has exchanged heat in the heat exchanger 4 into the water injection well 22.

[0064] When the opening degree of the control valve 72 reaches the minimum setting, it becomes impossible to further reduce the flow rate of the groundwater injected into the water injection well 22. In such a case, by using the cooling tower 130, the geothermal energy utilization system 1 can further adjust the temperature of the groundwater injected into the water injection well 22. This allows the geothermal energy utilization system 1 to control the temperature of the injected water over a wider range during low load periods.

[0065] (5) The control device 80 relating to the fifth aspect includes a pump operation control unit 81 that adjusts the operating frequency of the inverter control of the pump 31 that transports groundwater from the pumping well 21 to the injection well 22, depending on the temperature of the groundwater pumped from the pumping well 21 and injected into the injection well 22 via the heat exchanger 4, and a control valve opening / closing control unit 82 that adjusts the opening degree of the control valve 72 provided in the piping 3 that sends the groundwater to the injection well 22, depending on the temperature of the groundwater injected into the injection well 22, when the operating frequency reaches the lowest frequency.

[0066] According to this control device 80, the pump operation control unit 81 adjusts the operating frequency of the inverter control of the pump 31 in accordance with the temperature of the groundwater injected into the water injection well 22. By adjusting the flow rate of the groundwater injected into the water injection well 22, the control device 80 can adjust the temperature of the groundwater injected into the water injection well 22. When the operating frequency of the inverter control of the pump 31 reaches a preset minimum frequency, the control valve opening / closing control unit 82 adjusts the aperture of the control valve 72 to throttle the flow rate in the piping 3, thereby making it possible to inject groundwater into the water injection well 22 at a flow rate smaller than the flow rate at the minimum frequency of the pump 31. This makes it easier for the control device 80 to control the temperature of the injected water under low load conditions.

[0067] (6) The control method of the sixth aspect adjusts the operating frequency of the inverter control of the pump 31 that transports groundwater from the pumping well 21 to the injection well 22 in accordance with the temperature of the groundwater pumped from the pumping well 21 and injected into the injection well 22 via the heat exchanger 4, and when the operating frequency reaches its minimum frequency, adjusts the opening of the control valve 72 provided in the pipe 3 that transports the groundwater to the injection well 22 in accordance with the temperature of the groundwater injected into the injection well 22.

[0068] This control method adjusts the operating frequency of the inverter control of the pump 31 in accordance with the temperature of the groundwater injected into the water injection well 22. This makes it possible to adjust the temperature of the groundwater injected into the water injection well 22 by adjusting the flow rate of the groundwater. When the operating frequency of the inverter control of the pump 31 reaches a preset minimum frequency, the control method adjusts the aperture of the control valve 72 to throttle the flow rate in the piping 3, making it possible to inject groundwater into the water injection well 22 at a flow rate smaller than the flow rate at the minimum frequency of the pump 31. This makes it easy for the control method to control the temperature of the injected water during low load times.

[0069] (7) The program relating to the seventh aspect causes the computer 190 to execute a method of adjusting the operating frequency of the inverter control of the pump 31 that transports groundwater from the pumping well 21 to the injection well 22 in accordance with the temperature of the groundwater pumped from the pumping well 21 and injected into the injection well 22 via the heat exchanger 4, and when the operating frequency reaches its minimum frequency, adjusting the opening of the control valve 72 provided in the piping 3 that transports the groundwater to the injection well 22 in accordance with the temperature of the groundwater injected into the injection well 22.

[0070] According to this program, the computer 190 adjusts the operating frequency of the inverter control of the pump 31 in accordance with the temperature of the groundwater injected into the water injection well 22. This makes it possible to adjust the temperature of the groundwater injected into the water injection well 22 by adjusting the flow rate of the groundwater. When the operating frequency of the inverter control of the pump 31 reaches a preset minimum frequency, the computer 190 adjusts the aperture of the control valve 72 to throttle the flow rate in the piping 3, thereby enabling the computer 190 to inject groundwater into the water injection well 22 at a flow rate lower than the flow rate at the minimum frequency of the pump 31. This makes it easier for the program to control the temperature of the injected water during low load times.

[0071] According to the present disclosure, it is possible to provide a geothermal energy utilization system, a control device, a control method, and a program that make it easy to control the temperature of injected water during low load periods.

[0072] DESCRIPTION OF SYMBOLS 1...Geothermal heat utilization system 2...Well 2A...First well 2B...Second well 2a...Casing 2b...Strainer 2c...Opening 3...Piping 4...Heat exchanger 6...Well cover 7...Temperature adjustment system 21...Pumping well 22...Water injection well 31...Pump 32...Water injection valve 35a-35d...Check valve 71...Pump controller 72...Control valve 80...Control device 81...Pump operation control unit 82...Control valve opening / closing control unit 83...Load side flow path control unit 100...Load equipment 101...Piping system 110...Heat source unit 120...Air conditioner 130...Cooling tower 140...Second heat exchanger 190...Computer 195...Processor 196...Memory 197...Storage / playback device 198...IO I / F 199...Communication I / F HOL...Drill hole LY... Aquifer OG... Ground ST01... Step of adjusting the operating frequency of the pump ST02... Step of determining whether the operating frequency of the pump has dropped to the minimum frequency ST03... Step of adjusting the opening of the control valve ST04... Step of determining whether the opening of the control valve is the minimum set opening ST05... Step of switching the operation mode of the load equipment side to the cooling tower mode

Claims

1. A geothermal energy utilization system comprising: a pumping well; an injection well; a pipe extending from the pumping well to the injection well; a pump capable of transporting groundwater from the pumping well to the injection well via the pipe; a heat exchanger provided in the pipe; a control valve provided in the pipe and capable of adjusting the flow rate of the groundwater in the pipe; and a control device that adjusts the flow rate of the groundwater injected into the injection well by controlling the control valve to throttle the flow rate in the pipe when the operating frequency of the inverter control of the pump reaches its lowest frequency.

2. A geothermal energy utilization system according to claim 1, wherein the control valve is provided closer to the water injection well than the heat exchanger.

3. A geothermal energy utilization system as described in claim 1 or 2, wherein the control device maintains the operating frequency at the minimum frequency when adjusting the flow rate of the groundwater in the pipe by throttling the control valve.

4. A geothermal energy utilization system as described in any one of claims 1 to 3, further comprising a cooling tower on the load equipment side that uses a medium that exchanges heat with the groundwater in the piping in the heat exchanger, and when the opening of the control valve reaches the minimum set opening, the control device injects the medium cooled by the cooling tower and the groundwater that has exchanged heat in the heat exchanger into the water injection well.

5. A control device comprising: a pump operation control unit that adjusts the operating frequency of the inverter control of a pump that transports groundwater from a pumping well to an injection well, depending on the temperature of the groundwater that is pumped up from the pumping well and injected into the injection well through a heat exchanger; and a control valve opening / closing control unit that adjusts the opening of a control valve installed in a pipe that sends the groundwater to the injection well, depending on the temperature of the groundwater that is injected into the injection well, when the operating frequency reaches its lowest frequency.

6. A control method comprising: adjusting the operating frequency of an inverter control pump that transports groundwater from a pumping well to an injection well according to the temperature of the groundwater that is pumped up from a pumping well and injected into the injection well after passing through a heat exchanger; and, when the operating frequency reaches its minimum frequency, adjusting the opening of a control valve installed in a pipe that transports the groundwater to the injection well according to the temperature of the groundwater that is injected into the injection well.

7. A program for causing a computer to execute a method of adjusting the operating frequency of the inverter control of a pump that transports groundwater from a pumping well to an injection well in accordance with the temperature of the groundwater that is pumped up from a pumping well, passed through a heat exchanger, and injected into an injection well, and when the operating frequency reaches its minimum frequency, adjusting the opening of a control valve installed in a pipe that transports the groundwater to the injection well in accordance with the temperature of the groundwater that is injected into the injection well.