Ground thawing method and ground thawing device

Abstract

To provide a ground thawing method and a ground thawing device that can thaw frozen ground in an energy-saving manner.SOLUTION: A ground thawing method includes a step S18 of gasifying a refrigerant supplied from a refrigerant tank 10, and a step S18 of supplying the gasified refrigerant to a ground freezing pipe 200 and thawing the ground 5 using latent heat of the refrigerant.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a ground thawing method and a ground thawing device. [Background technology]

[0002] BACKGROUND ART A construction method has been known in the past in which excavation work is carried out on the ground while the surrounding ground is frozen, and the ground is thawed after the excavation work is completed.

[0003] For example, Patent Document 1 describes a method in which a refrigerant is supplied to a double pipe (ground freezing pipe) buried in the ground to freeze the ground, and then excavation work is carried out, and after the excavation work is completed, a warm medium (warm brine) is supplied to the double pipe to thaw the ground. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-363987 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method described in Patent Document 1 uses the sensible heat of a hot medium (hot brine) to heat the ground, and a large amount of hot medium needs to be supplied to the double pipe to provide the heat required to thaw the ground, which requires a lot of energy to circulate the hot medium through the double pipe.

[0006] In view of the above circumstances, at least some embodiments of the present invention aim to provide a ground thawing method and a ground thawing device that can thaw frozen ground in an energy-saving manner. [Means for solving the problem]

[0007] According to some embodiments, a method for thawing ground comprises: gasifying the refrigerant supplied from the refrigerant tank; supplying the gasified refrigerant to a ground freezing pipe and thawing the ground using the latent heat of the refrigerant; Equipped with.

[0008] In some embodiments, the ground thawing device comprises: a refrigerant tank that stores a refrigerant; a refrigerant supply line for guiding the refrigerant from the refrigerant tank to a ground freezing pipe; a refrigerant supply pump provided in the refrigerant supply line for supplying the refrigerant from the refrigerant tank to the ground freezing pipe; a gasification device that is provided in the refrigerant supply line downstream of the refrigerant supply pump and that gasifies the refrigerant; Equipped with The refrigerant gasified by the gasification device is supplied to the ground freezing pipe, and the ground is thawed using the latent heat of the refrigerant. [Effects of the Invention]

[0009] According to at least some embodiments of the present invention, the latent heat of the refrigerant is utilized to thaw the ground, which allows the ground to be thawed using a relatively small amount of refrigerant. This reduces the energy required to circulate the heat medium (a collective term for the refrigerant described above and warm brine in conventional ground thawing methods) through the freezing pipes, thereby achieving energy savings in ground freezing. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing the overall configuration of a ground freezing device according to one embodiment. FIG. [Figure 2A] FIG. 2 is a diagram showing a cross-sectional view of a ground freezing pipe according to one embodiment. [Figure 2B] FIG. 10 is a cross-sectional view of a ground freezing pipe according to another embodiment. [Figure 3A] 1 is a diagram showing the overall configuration of a ground thawing device according to one embodiment. [Figure 3B] FIG. 10 is a diagram showing the overall configuration of a ground thawing device according to another embodiment. [Figure 3C] FIG. 10 is a diagram showing the overall configuration of a ground thawing device according to another embodiment. [Figure 4A] 1 is a diagram showing a specific configuration of an area A around a heat pump device in a ground thawing device according to one embodiment. FIG. [Figure 4B] FIG. 10 is a diagram showing a specific configuration of an area A around a heat pump device in a ground thawing device according to another embodiment. [Figure 5] 10 is a diagram showing a specific configuration of an area B around a ground thawing circuit in a ground thawing device according to one embodiment. FIG. [Figure 6] 10 is a flowchart illustrating a procedure for thawing ground using a ground thawing device according to one embodiment. [Figure 7] 1 is a flowchart illustrating an example of a procedure for intermittent ground thawing and refrigerant recovery according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0012] Hereinafter, a ground thawing method and a ground thawing device according to several embodiments will be described with reference to the drawings.

[0013] Prior to describing the ground thawing device 1 according to some embodiments, a ground freezing pipe 200 and a ground freezing device 300 according to some embodiments will be described with reference to Figures 1 to 2B. Note that the ground freezing pipe 200 and the ground freezing device 300 may be installed inside a mine to freeze the ground 5 inside the mine. FIG. 1 is a diagram showing the overall configuration of a ground freezing pipe and a ground freezing device according to one embodiment. 2A and 2B are cross-sectional views of a ground freezing pipe according to one embodiment and another embodiment, respectively;

[0014] 1, multiple ground freezing pipes 200 are buried in the ground 5. A secondary refrigerant cooled in a ground freezing device 300 is supplied to the ground freezing pipes 200. The secondary refrigerant supplied to the ground freezing pipes 200 freezes the ground 5 as it passes through the ground freezing pipes 200. The secondary refrigerant may be, for example, a CO2 refrigerant.

[0015] A feed pipe 210 is connected to the ground freezing pipe 200 for guiding the secondary refrigerant from the ground freezing device 300 to the ground freezing pipe 200. The feed pipe 210 connected to the ground freezing pipe 200 is connected to a feed header 220 at the end opposite the end connected to the ground freezing pipe 200. The feed header 220 includes a pipe 222 having a connection portion 224 connected to the ground freezing device 300. By connecting the feed header 220 to the ground freezing device 300 at the connection portion 224 of the pipe 222, the secondary refrigerant supplied from the ground freezing device 300 is supplied to multiple ground freezing pipes 200 via multiple feed pipes 210. A return pipe 230 is further connected to the ground freezing pipe 200 to guide the secondary refrigerant that has passed through the ground freezing pipe 200 to the ground freezing device 300. The return pipe 230, connected to the ground freezing pipe 200, is connected to a return header 240 at an end opposite to the end connected to the ground freezing pipe 200. The return header 240 includes a pipe 242 having a connection 244 that is connected to the ground freezing device 300. By connecting the return header 240 to the ground freezing device 300 at the connection 244 of the piping 242, the secondary refrigerant that has passed through the multiple ground freezing pipes 200 is returned to the ground freezing device 300 via the multiple return pipes 230 and the return header 240.

[0016] In some embodiments, as shown in FIGS. 2A and 2B, the ground freezing pipe 200 (200A, 200B) includes an outer cylinder 202 and refrigerant piping 204 (204A, 204B) provided inside the outer cylinder 202. One end of refrigerant pipes 204 (204A, 204B) is connected to feed pipe 210, and the other end is connected to return pipe 230. Refrigerant pipes 204 (204A, 204B) are formed so as to be folded back inside outer cylinder 202. An internal flow path 206 is provided inside refrigerant pipes 204 (204A, 204B) for circulating the secondary refrigerant. Furthermore, the ground freezing pipe 200 (200A, 200B) has a space 208 between the outer cylinder 202 and the refrigerant pipe 204 (204A, 204B). The space 208 may be filled with a fluid (e.g., water) that has a higher thermal conductivity than air. When water is used as the fluid filling the space 208, the water filling the space 208 freezes when a secondary refrigerant is supplied to the refrigerant pipe 204 (204A, 204B), and absorbs heat from the ground 5 via the outer cylinder 202, thereby allowing the ground 5 to be frozen by the ground freezing circuit 7.

[0017] In the exemplary embodiment shown in FIG. 2A, the refrigerant piping 204A has a flattened exterior profile and includes multiple internal flow passages 206. In the exemplary embodiment shown in FIG. 2B, the refrigerant pipe 204B has a circular outer shape, and an internal flow passage 206 is formed inside the hollow refrigerant pipe 204B.

[0018] The ground freezing pipe 200 configured as described above is connected to a ground freezing device 300 via a feed pipe 210 and a feed header 220, and the ground freezing pipe 200 receives a supply of secondary refrigerant from the ground freezing device 300. As shown in Figure 1, the ground freezing device 300 includes a refrigerator 310 that cools a secondary refrigerant, a receiver 320 connected to the refrigerator 310 via a secondary refrigerant reliquefaction line 322, and a secondary refrigerant line 330 provided between the receiver 320 and the ground freezing pipe 200.

[0019] The refrigerator 310 includes a primary refrigerant line 312 that circulates a primary refrigerant that exchanges heat with a secondary refrigerant, and a compressor 314, a condenser 315, an expansion valve 316, and an evaporator 317 that are provided in the primary refrigerant line 312. The compressor 314 compresses the primary refrigerant and discharges it to a primary refrigerant line 312. The discharged primary refrigerant is cooled in a condenser 315. The primary refrigerant that passes through the condenser 315 is reduced in pressure in an expansion valve 316. The evaporator 317 exchanges heat between the reduced-pressure primary refrigerant and the secondary refrigerant guided from a receiver 320 via a secondary refrigerant reliquefaction line 322. The heat exchange in the evaporator 317 cools the secondary refrigerant and evaporates the primary refrigerant.

[0020] The secondary refrigerant cooled by the refrigerator 310 is stored in the receiver 320 via a secondary refrigerant re-liquefaction line 322 .

[0021] In addition to the secondary refrigerant reliquefaction line 322, a secondary refrigerant line 330 is also connected to the receiver 320. The secondary refrigerant line 330 includes a connection part 332 and a connection part 334, and a secondary refrigerant supply pump 336 provided on the secondary refrigerant line 330. Connections 332 and 334 are connected to connection 224 of feed header 220 and connection 244 of return header 240, respectively. Secondary refrigerant line 330 communicates with the feed header 220 and feed piping 210, as well as return piping 230 and return header 240, via connection 332 and connection 334, and forms ground freezing circuit 7 together with ground freezing pipe 200. Secondary refrigerant supply pump 336 is provided between receiver 320 and connection 332. Secondary refrigerant supply pump 336 supplies the secondary refrigerant from receiver 320 to ground freezing pipe 200.

[0022] As described above, the ground freezing device 300 can be used to send a secondary refrigerant to the ground freezing pipe 200 to perform ground freezing.

[0023] Next, with reference to Figs. 3A to 4B, a ground thawing device 1 (1A, 1B, 1C) used to thaw the ground 5 after the ground has been frozen will be described. Fig. 3A is a diagram showing the overall configuration of a ground thawing device according to one embodiment, Fig. 3B and Fig. 3C are diagrams showing the overall configuration of a ground thawing device according to another embodiment. Fig. 4A is a diagram showing a specific configuration of an area A around a heat pump device in a ground thawing device according to one embodiment. Fig. 4B is a diagram showing a specific configuration of an area A around a heat pump device in a ground thawing device according to another embodiment. Hereinafter, among the ground freezing pipe 200 and its peripheral configuration, the description of the parts common to the configuration described above with reference to FIGS. 1 to 2B will be simplified or omitted.

[0024] In some embodiments, as shown in Figures 3A to 3C, the ground thawing apparatus 1 (1A to 1C) is connected to a feed header 220 and a return header 240 that are disconnected from the ground freezing apparatus 300. In this case, the ground thawing apparatus 1 (1A to 1C) may include connection portions 24, 52, which will be described later, for connection to the feed header 220 and the return header 240.

[0025] In some embodiments, as shown in Figures 3A to 3C, the ground thawing device 1 (1A to 1C) includes a refrigerant tank 10, a refrigerant supply line 20 for guiding the refrigerant to the ground freezing pipe 200, a refrigerant supply pump 30 provided in the refrigerant supply line 20, and a gasification device 40 for gasifying the refrigerant. The refrigerant used to thaw the ground 5 is not particularly limited, but may be, for example, an HFO (Hydrofluoroolefin) refrigerant.

[0026] The refrigerant tank 10 stores the refrigerant in a liquid state. A refrigerant supply line 20 is connected to the liquid phase portion of the refrigerant tank 10.

[0027] The refrigerant supply line 20 has an upstream end forming a connection 22 connected to the refrigerant tank 10, and a downstream end forming a connection 24 connected to a connection 224 of the feed header 220. When the connection 24 of the refrigerant supply line 20 is connected to the connection 224 of the feed header 220, the refrigerant supply line 20 communicates with the above-mentioned feed piping 210 and forms the ground thawing circuit 3 together with the ground freezing pipe 200. In this way, the refrigerant from the refrigerant tank 10 is guided to the refrigerant piping 204 via the refrigerant supply line 20, the feed header 220, and the feed piping 210.

[0028] The refrigerant supply pump 30 is provided between the refrigerant tank 10 and the gasification device 40. The refrigerant supply pump 30 supplies the refrigerant in a liquid state from the refrigerant tank 10 to the gasification device 40.

[0029] The gasifier 40 heats the refrigerant that has passed through the refrigerant supply pump 30, changing its state from a liquid state to a gas state. In the exemplary embodiment shown in Figures 3A to 3C, the gasifier 40 is a heat exchanger that gasifies the refrigerant by exchanging heat with a heat medium. The heat medium that serves as the heat source for the gasifier 40 is not particularly limited, and may be hot water generated by a heat pump device 100 (described later) and stored in a hot water storage tank 80. The refrigerant that has passed through the gasification device 40 branches in the feed header 220 toward multiple ground freezing pipes 200, and as it passes through the internal flow paths 206 of the refrigerant pipes 204, it heats the fluid that fills the space 208 of the ground freezing pipes 200. When water is used as the fluid that fills the space 208, the water is frozen by the ground freezing device 300. When the refrigerant is supplied to the internal flow paths 206 of the refrigerant pipes 204, the ice that fills the space 208 thaws and transfers heat to the ground 5 via the outer cylinder 202, so that the ground 5 can be thawed by the ground thawing circuit 300. A temperature measuring pipe 70 having a temperature sensor 72 is buried in the ground 5, making it possible to monitor the progress of thawing of the ground 5.

[0030] The refrigerant used to thaw the ground 5 loses heat in the space 208 of the ground freezing pipe 200 and condenses. At this time, all of the refrigerant flowing out of the ground freezing pipe 200 may be in the form of a liquefied liquid-phase flow, or a portion of the refrigerant may be in the form of a gaseous two-phase flow. The refrigerant that has passed through the internal flow path 206 is discharged as a liquid-phase flow or a two-phase flow via the return header 240 to the ground thawing device 1 (1A-1C).

[0031] Return header 240 may have a pressure relief valve 246. Pressure relief valve 246 of return header 240 is configured to release the refrigerant to the outside of ground freezing pipe 200 when the internal pressure of ground freezing pipe 200 exceeds a specified value. Pressure relief valve 246 is not particularly limited, but may have a mechanism that automatically releases the refrigerant when the internal pressure of ground freezing pipe 200 exceeds a specified value, for example.

[0032] In some embodiments, as shown in Figures 3A to 3C, the ground thawing device 1 (1A to 1C) includes a refrigerant recovery line 50 for recovering refrigerant from the ground freezing pipe 200 to the refrigerant tank 10, and a re-liquefaction device 60 provided in the refrigerant recovery line 50.

[0033] Refrigerant recovery line 50 has an upstream end forming connection 52 connected to connection 244 of return header 240, and a downstream end forming connection 54 connected to refrigerant tank 10. When connection 52 of refrigerant recovery line 50 is connected to connection 244 of return header 240, refrigerant recovery line 50 communicates with the above-mentioned return piping 230 and forms ground thawing circuit 3 together with ground freezing pipe 200. In this way, refrigerant from refrigerant piping 204 is guided to refrigerant tank 10 via return piping 230, return header 240, and refrigerant recovery line 50.

[0034] The re-liquefaction device 60 liquefies the two-phase refrigerant that has passed through the refrigerant pipe 204 of the ground freezing pipe 200. The liquid refrigerant thus obtained in the re-liquefaction device 60 is collected in the refrigerant tank 10. The reliquefaction device 60 may be a heat exchanger that liquefies the refrigerant by heat exchange with a heat medium. The heat medium as a cold heat source of the reliquefaction device 60 is not particularly limited, but may be cold water generated in a heat pump device 100 described below and supplied to the reliquefaction device 60 via a cold water line 122.

[0035] In one embodiment, as shown in FIG. 3A, the ground thawing device 1A circulates the refrigerant in the ground thawing circuit 3 by a refrigerant supply pump 30.

[0036] In another embodiment, as shown in Figures 3B and 3C, the ground thawing device 1 (1B, 1C) includes a vacuum pump (56, 12) for recovering the refrigerant from the ground freezing pipe 200 to the refrigerant tank 10 during ground thawing in case the refrigerant circulation by the refrigerant supply pump 30 becomes insufficient. If the amount of refrigerant in the refrigerant tank 10 decreases excessively during ground thawing, it is determined that the refrigerant circulation in the ground thawing circuit 3 is insufficient, and the vacuum pump (56, 12) is used to recover the refrigerant from the ground freezing pipe 200 into the refrigerant tank 10. Note that, from the viewpoint of improving the efficiency of refrigerant recovery, refrigerant recovery using the vacuum pump (56, 12) during ground thawing may be performed with the refrigerant supply pump 30 temporarily stopped. In this case, to resume ground freezing after refrigerant recovery, the vacuum pump (56, 12) is stopped and the refrigerant supply pump 30 is operated.

[0037] As shown in FIG. 3B, the vacuum pump 56 of the ground thawing device 1 (1B) is provided in the refrigerant recovery line 50. The refrigerant remaining in the internal flow path 206 of the ground freezing pipe 200 is discharged from the return header 240 to the refrigerant recovery line 50 by the vacuum pump 56. The refrigerant discharged from the ground freezing pipe 200 reaches the refrigerant tank 10 via the refrigerant recovery line 50. In this way, the vacuum pump 56 sucks the refrigerant from the ground freezing pipe 200 and guides the refrigerant to the refrigerant tank 10.

[0038] In the exemplary embodiment shown in FIG. 3B, the refrigerant recovery line 50 includes a re-liquefaction line 50A in which a re-liquefaction device 60 is provided, and a bypass line 50B that bypasses the re-liquefaction device 60, and a vacuum pump 56 is provided in the bypass line 50B of the refrigerant recovery line 50.

[0039] The refrigerant recovery line 50 may be provided with valves 57 and 58 for recovering the refrigerant using a vacuum pump 56. 3B, refrigerant recovery line 50 branches into reliquefaction line 50A and bypass line 50B at branch point 50C, and reliquefaction line 50A and bypass line 50B join at junction 50D. Valve 57 is located in reliquefaction line 50A between reliquefaction device 60 and branch point 50C to block refrigerant flow to reliquefaction device 60. Valve 58 is located in bypass line 50B between vacuum pump 56 and branch point 50C to allow refrigerant suction by vacuum pump 56.

[0040] As shown in FIG. 3C, the ground thawing device 1 (1C) includes a vacuum pump 12 and an exhaust pipe 14 that connects the vacuum pump 12 to the gas phase part of the refrigerant tank 10. When the vacuum pump 12 is started, the gas inside the refrigerant tank 10 is discharged outside the refrigerant tank 10. As the pressure inside the refrigerant tank 10 decreases, the internal pressure of the refrigerant recovery line 50 and the internal pressure of the return header 240 also decrease. Therefore, the refrigerant remaining in the internal flow path 206 of the ground freezing pipe 200 is discharged from the return header 240 to the refrigerant recovery line 50. The refrigerant discharged from the ground freezing pipe 200 flows through the refrigerant recovery line 50 and reaches the refrigerant tank 10. In this way, the vacuum pump 12 sucks the refrigerant from the ground freezing pipe 200 and recovers the refrigerant in the refrigerant tank 10.

[0041] The feed header 220 may be provided with a valve 226 for recovering the refrigerant using the vacuum pump (56, 12). 3B and 3C, a valve 226 is provided in the pipe 222 of the feed header 220. The valve 226 is a valve for preventing the inflow of refrigerant from the refrigerant supply line 20, and may be, for example, a valve that can be opened and closed manually.

[0042] In some embodiments, as shown in Figures 3A to 4B, the ground thawing device 1 includes a heat pump device 100 for generating hot water and a hot water storage tank 80 for storing the hot water generated by the heat pump device 100.

[0043] 4A and 4B, the heat pump device 100 includes at least one evaporator 120 (120A, 120B) that evaporates a CO2 refrigerant and a gas cooler 130 that exchanges heat between the CO2 refrigerant and hot water. The evaporator 120 and the gas cooler 130 are provided on a CO2 refrigerant circulation path 140 together with a compressor 150 and an expansion valve 160 as other heat pump cycle components. The CO2 refrigerant circulates through the CO2 refrigerant circuit 140, passing through the compressor 150, gas cooler 130, expansion valve 160, and evaporator 120 in that order. The CO2 refrigerant circulating through the CO2 refrigerant circuit 140 is pressurized by the compressor 150 and then flows into the gas cooler 130. In the gas cooler 130, the CO2 refrigerant is cooled by heat exchange with hot water. The CO2 refrigerant that leaves the gas cooler 130 is depressurized by the expansion valve 160 and then evaporated in the evaporator 120. The gaseous CO2 refrigerant that leaves the evaporator 120 is returned to the compressor 150.

[0044] The evaporator 120 (120A, 120B) as a component of the heat pump cycle is located downstream of the expansion valve 160 and is a heat exchanger that evaporates the CO 2 refrigerant that has passed through the expansion valve 160. The heat source for the evaporator 120 is not particularly limited, and air or water can be used as the heat source. In one embodiment, the evaporator 120 is an air heat source evaporator 120A that evaporates CO2 refrigerant using air as a heat source. In another embodiment, the evaporator 120 is a cold water heat source evaporator 120B that evaporates CO2 refrigerant using water (hereinafter referred to as "cold water" to distinguish it from hot water stored in the hot water storage tank 80) as a heat source.

[0045] In the embodiment shown in Figures 4A and 4B, the heat pump device 100 includes both an air heat source evaporator 120A and a cold water heat source evaporator 120B as the evaporator 120, and one of these two types of evaporators 120A, 120B can be selected by an evaporator switching means 170. The evaporator switching means 170 (170A, 170B) circulates the CO2 refrigerant through either the air heat source evaporator 120A or the chilled water heat source evaporator 120B. In the exemplary embodiment shown in FIGS. 4A and 4B, the heat pump apparatus 100 includes a first valve 170A and a second valve 170B as the evaporator switching means 170. The CO2 refrigerant circulation path 140 includes a first branch path 140A in which the air heat source evaporator 120A and the first valve 170A are provided, and a second branch path 140B in which the chilled water heat source evaporator 120B and the second valve 170B are provided. The CO2 refrigerant circulation path 140 branches into the first branch path 140A and the second branch path 140B at a branch point 140C, and the first branch path 140A and the second branch path 140B join at a joining point 140D. The first valve 170A is located on the first branched passage 140A upstream of the air heat source evaporator 120A. The second valve 170B is located on the second branched passage 140B upstream of the chilled water heat source evaporator 120B. In another embodiment, the heat pump apparatus 100 includes, as the evaporator 120, only one of the air heat source evaporator 120A or the chilled water heat source evaporator 120B.

[0046] In some embodiments, the heat pump device 100 includes, as components associated with the chilled water heat source evaporator 120B, a chilled water line 122 for conducting chilled water as a heat source to the chilled water heat source evaporator 120B, and a chilled water pump 124 provided on the chilled water line 122, as shown in Figures 4A and 4B. A cold water line 122 is provided between the cold water heat source evaporator 120B and the re-liquefaction device 60, and a cold water pump 124 moves cold water back and forth between the cold water heat source evaporator 120B and the re-liquefaction device 60. In this way, the cold water generated by the heat pump device 100 functions as a cold heat source in the re-liquefaction device 60.

[0047] The gas cooler 130, which is a component of the heat pump cycle, is located downstream of the compressor 150 and is a heat exchanger that exchanges heat between the CO2 refrigerant and hot water. 4A and 4B, the gas cooler 130 is connected to the hot water storage tank 80 via a hot water supply line 132. The hot water supply line 132 includes an outward path 132A and a return path 132B. The hot water in the hot water storage tank 80 flows into the gas cooler 130 via the outward path 132A of the hot water supply line 132, and is heated by heat exchange with the CO2 refrigerant in the gas cooler 130. The high-temperature hot water that leaves the gas cooler 130 returns to the hot water storage tank 80 via the return path 132B of the hot water supply line 132. As described above, the hot water stored in the hot water storage tank 80 is used as a heat source for the gasification apparatus 40. At this time, the hot water storage tank 80 is connected to the gasification apparatus 40 via a hot water line 82. A hot water pump 84 is provided in the hot water line 82 to supply the hot water from the hot water storage tank 80 to the gasification apparatus 40.

[0048] Here, switching of the operation mode of the heat pump unit 100 using the above-mentioned evaporator switching means 170 (170A, 170B) will be described. 4A, the evaporator switching means 170 (170A, 170B) selects the air heat source evaporator 120A. The heat pump device 100 operates in an air heat source mode in which the CO refrigerant is circulated through the gas cooler 130 and the air heat source evaporator 120A, and only hot water is generated for gasifying the refrigerant. 4A, in the air heat source mode, the first valve 170A is opened and the second valve 170B is closed, and the CO refrigerant flows from the branch point 140C through the first branch path 140A and passes through the junction 140D.

[0049] 4B, the evaporator switching means 170 (170A, 170B) selects the chilled water heat source evaporator 120B. The heat pump device 100 operates in a water heat source mode in which the CO refrigerant is circulated through the gas cooler 130 and the chilled water heat source evaporator 120B to generate both hot water used to gasify the refrigerant and chilled water used to liquefy the refrigerant. 4, in the water heat source mode, the first valve 170A is closed and the second valve 170B is open, and the CO refrigerant flows from the branch point 140C through the second branch path 140B and passes through the junction 140D.

[0050] After the ground 5 has been thawed by the ground thawing device 1 having the above configuration, the refrigerant may remain in the ground freezing pipe 200, just as it did while the ground 5 was thawing. Therefore, the ground thawing device 1 may have the configuration described below with reference to FIG. 5 in order to recover the refrigerant remaining in the ground freezing pipe 200 (residual refrigerant). FIG. 5 is a diagram showing a specific configuration of an area B around the ground thawing circuit in the ground thawing device according to one embodiment.

[0051] 5, the ground thawing device 1 includes a residual refrigerant recovery means 90 (92) for recovering the refrigerant remaining in the ground freezing pipe 200. In one embodiment, the residual refrigerant recovery means 90 is a nitrogen gas cylinder 92 that supplies nitrogen gas to the ground freezing pipe 200. In other embodiments, the residual refrigerant recovery means 90 may be the vacuum pump (56, 12) described above.

[0052] In the embodiment shown in Figure 5, the ground thawing device 1 includes a nitrogen gas pipe 94 connecting a nitrogen gas cylinder 92 as a residual refrigerant recovery means 90 to the feed header 220, and a nitrogen gas valve 96 provided on the nitrogen gas pipe 94. Nitrogen gas from nitrogen gas cylinder 92 is supplied to feed header 220 by opening nitrogen gas valve 96. Nitrogen gas that has passed through feed header 220 discharges the refrigerant remaining in internal flow path 206 from return header 240 to refrigerant recovery line 50. The refrigerant discharged from ground freezing pipe 200 flows through refrigerant recovery line 50 and reaches refrigerant tank 10. In this way, the refrigerant remaining in ground freezing pipe 200 can be pushed out by nitrogen gas using nitrogen gas cylinder 92, thereby recovering the refrigerant in refrigerant tank 10.

[0053] The refrigerant recovery line 50 and the feed header 220 may be provided with valves (59, 226) for recovering the refrigerant using a nitrogen gas cylinder 92. 5 includes a nitrogen purge valve 59 provided in the refrigerant recovery line 50 to release nitrogen gas from the refrigerant recovery line 50, and a valve 226 provided in the piping 222 of the feed header 220 to prevent nitrogen gas from flowing into the refrigerant supply line 20. The valve 226 is a valve for preventing nitrogen gas from flowing into the refrigerant supply line 20, and may be, for example, a valve that can be manually opened and closed, or a check valve that allows only fluid flowing from the gasifier 40 to the feed header 220 to pass.

[0054] Next, with reference to FIG. 6, a ground thawing method using the ground thawing device 1 according to some embodiments will be described. FIG. 6 is a flowchart illustrating a procedure for thawing ground using a ground thawing device according to one embodiment.

[0055] The ground thawing device 1 is connected to the ground freezing pipe 200 that has been disconnected from the ground freezing device 300 (step S10). Specifically, connection 24 of refrigerant supply line 20 is connected to connection 224 of feed header 220. Similarly, connection 54 of refrigerant recovery line 50 is connected to connection 244 of return header 240. This process connects refrigerant supply line 20, ground freezing pipe 200, and refrigerant recovery line 50, forming ground thawing circuit 3.

[0056] Thereafter, the heat pump device 100 is operated in the air heat source mode (step S12). Specifically, CO2 refrigerant is circulated through the gas cooler 130 and the air heat source evaporator 120A to generate only hot water to be used for gasifying the refrigerant. In the air heat source mode, the evaporator switching means 170 (170A, 170B) selects the CO2 refrigerant circulation path 140 (140A) so that the CO2 refrigerant is circulated through the air heat source evaporator 120A. In the heat pump unit 100, the CO2 refrigerant and hot water are circulated through the gas cooler 130 as described above to heat the hot water. The hot water generated by the heat pump unit 100 is stored in the hot water storage tank 80 via the return line 132B of the hot water supply line 132.

[0057] During execution of step S12, the timing to end hot water storage is determined based on the temperature of the hot water in the hot water storage tank 80 (step S14). Specifically, the temperature of the hot water in the hot water storage tank 80 is measured by a temperature sensor 86 provided in the hot water storage tank 80. If the temperature of the hot water in the hot water storage tank 80 is lower than the specified temperature T_th1, the heat pump device 100 continues to operate in the air heat source mode (No in step S14).

[0058] If the temperature of the hot water in the hot water storage tank 80 is equal to or higher than the specified temperature T_th1 (Yes in step S14), the operation mode of the heat pump unit 100 is switched from the air heat source mode to the water heat source mode, and the water heat source mode is executed (step S16). The switching from the air heat source mode to the water heat source mode is performed by the evaporator switching means 170 (170A, 170B). Specifically, the evaporator switching means 170 (170A, 170B) is operated to cause the CO refrigerant that had been circulating through the air heat source evaporator 120A to circulate through the chilled water heat source evaporator 120B. In the water heat source mode, CO2 refrigerant is circulated through the gas cooler 130 and the cold water heat source evaporator 120B to generate both hot water used to gasify the refrigerant and cold water used to liquefy the refrigerant. In the water heat source mode, as in the air heat source mode, the CO2 refrigerant and hot water are circulated through the gas cooler 130 to heat the hot water. The hot water produced by the heat pump unit 100 is stored in the hot water storage tank 80. At the same time, the cold water that has undergone heat exchange with the CO2 refrigerant in the cold water heat source evaporator 120B loses heat to the CO2 refrigerant and is cooled, as described above. The cold water produced by the heat pump unit 100 in this manner is supplied to the re-liquefaction unit 60.

[0059] After the heat pump device 100 starts operating in the water heat source mode, the ground 5 is thawed (step S18). The order of steps S16 and S18 is not limited to the example in FIG. 6, and steps S16 and S18 may be performed substantially simultaneously, or steps S18 and S16 may be performed in that order. Specifically, the refrigerant supply pump 30 is started to gasify the refrigerant supplied from the refrigerant tank 10 to the gasification device 40. The refrigerant in the refrigerant tank 10 is supplied to the gasification device 40 via the refrigerant supply line 20, and heat exchange occurs between the refrigerant and hot water supplied from the hot water storage tank 80 via the hot water line 82. The hot water after the heat exchange is returned to the hot water storage tank 80. The gasified refrigerant is then supplied to ground freezing pipe 200, and the latent heat of the refrigerant is used to thaw ground 5. Specifically, as described above, the gasified refrigerant provides heat to ground 5 through heat exchange with the ice filling space 208 of ground freezing pipe 200, causing ground 5 to thaw. The refrigerant that has passed through the internal flow path 206 of the ground freezing pipe 200 is guided via the return header 240 to the refrigerant recovery line 50 of the ground thawing device 1. Using a re-liquefaction device 60 provided in the refrigerant recovery line 50, heat exchange is carried out between the cold water cooled in the cold water heat source evaporator 120B and the refrigerant that has passed through the internal flow path 206, and the two-phase refrigerant is liquefied. Meanwhile, the cold water heated by the heat exchange is guided via the cold water line 122 to the cold water heat source evaporator 120B. The refrigerant liquefied in the re-liquefaction device 60 is returned to the refrigerant tank 10.

[0060] After the thawing of the ground 5 starts, the temperature of the ground 5 is measured by the temperature measuring pipe 70, and the timing for completing the thawing of the ground is determined based on the temperature of the ground 5 (step S20). If the temperature of the ground 5 is lower than the specified temperature T_th2 (No in step S20), it is determined that the ground freezing is not complete, and the refrigerant supply pump 30 continues to operate to continue supplying refrigerant to the ground freezing pipe 200, thereby continuing to thaw the ground 5.

[0061] On the other hand, if the temperature of the ground 5 is equal to or higher than the specified temperature T_th2 (Yes in step S20), it is determined that the ground thawing is complete, and the refrigerant supply pump 30 is stopped (step S22). By stopping the refrigerant supply pump 30, the supply of refrigerant to the ground freezing pipe 200 is stopped.

[0062] After the refrigerant supply pump 30 is stopped, the refrigerant remaining in the ground freezing pipe 200 is collected into the refrigerant tank 10 (step S24). In one embodiment, the refrigerant remaining in the ground freezing pipe 200 is pushed out with nitrogen gas, and the refrigerant is recovered in the refrigerant tank 10. Specifically, a nitrogen gas cylinder 92 is used as the residual refrigerant recovery means 90. A nitrogen gas pipe 94 is connected to the feed header 220 of the ground freezing pipe 200. A valve 226 provided on the pipe 222 of the feed header 220 is closed, and the nitrogen gas valve 96 is opened. As described above, the nitrogen gas from the nitrogen gas cylinder 92 pushes out the refrigerant remaining in the ground freezing pipe 200 from the ground freezing pipe 200, and the refrigerant is guided to the refrigerant tank 10 via the refrigerant recovery line 50. In another embodiment, a vacuum pump 56 is used as residual refrigerant recovery means 90 provided in the refrigerant recovery line 50 to guide the refrigerant from the ground freezing pipe 200 to the refrigerant tank 10. Specifically, the valve 226 provided in the pipe 222 of the feed header 220 is closed, and the vacuum pump 56 is started. If the refrigerant recovery line 50 has a bypass line 50B, the valve 226 provided in the feed header 220 and the valve 57 provided in the refrigerant recovery line 50 are closed. After the vacuum pump 56 is started, the valve 58 provided in the bypass line 50B is opened. The refrigerant remaining in the ground freezing pipe 200 is recovered into the refrigerant tank 10 via the refrigerant recovery line 50, as described above. In yet another embodiment, a vacuum pump 12 serving as residual refrigerant recovery means 90 is connected to the refrigerant tank 10, and the refrigerant is sucked from the ground freezing pipe 200. Specifically, the exhaust pipe 14 of the vacuum pump 12 is connected to the gas phase part of the refrigerant tank 10. The valve 226 provided on the piping 222 of the feed header 220 is closed, and the vacuum pump 12 is started. As described above, the refrigerant remaining in the ground freezing pipe 200 is sucked by the refrigerant tank 10, the internal pressure of which has been reduced, and is recovered into the refrigerant tank 10 via the refrigerant recovery line 50.

[0063] After the recovery of the residual refrigerant is started, the liquid level of the refrigerant in the refrigerant tank 10 is measured, and the timing to finish the refrigerant recovery is determined based on the liquid level of the refrigerant (step S26). Specifically, the liquid level of the refrigerant in the refrigerant tank 10 is measured by the liquid level sensor 16 provided in the refrigerant tank 10. If the liquid level of the refrigerant in the refrigerant tank 10 is lower than the specified value H_th1, it is determined that the amount of recovered residual refrigerant is insufficient, and the recovery of the residual refrigerant from the ground freezing pipe 200 by the residual refrigerant recovery means 90 (92, 56, 12) continues (No in step S26). On the other hand, if the liquid level in the refrigerant tank 10 is equal to or higher than the specified value H_th1, the recovery of the residual refrigerant from the ground freezing pipe 200 by the residual refrigerant recovery means 90 (92, 56, 12) is terminated (Yes in step S26).

[0064] In some embodiments, the thawing of the ground 5 (step S18) in the ground thawing method described with reference to FIG. 6 is performed intermittently, and the refrigerant is recovered from the ground freezing pipe 200 into the refrigerant tank 10 while the ground 5 is thawing. FIG. 7 is a flowchart showing an example of a procedure for intermittent ground thawing and refrigerant recovery.

[0065] After the thawing of the ground 5 starts (step S18), the timing to start collecting the refrigerant is determined based on the liquid level of the refrigerant in the refrigerant tank 10 (step S30). If the liquid level of the refrigerant in the refrigerant tank 10 is equal to or higher than the specified value H_th2, it is determined that the refrigerant circulation in the ground thawing circuit 3 is good, and the thawing of the ground 5 is continued (Yes in step S30). Thereafter, as described above, the timing to end the ground thawing is determined based on the temperature of the ground 5 (step S20).

[0066] On the other hand, if the liquid level of the refrigerant in the refrigerant tank 10 is lower than the specified value H_th2 (No in step S30), it is determined that the refrigerant circulation in the ground thawing circuit 3 is insufficient, and recovery of the remaining refrigerant is started (step S32). Specifically, after the refrigerant supply pump 30 and the heat pump device 100 are stopped, the refrigerant remaining in the ground freezing pipe 200 is collected into the refrigerant tank 10. In one embodiment, as described above, the vacuum pump 56 provided in the refrigerant recovery line 50 is activated to guide the refrigerant from the ground freezing pipe 200 to the refrigerant tank 10. In another embodiment, as described above, the vacuum pump 12 connected to the refrigerant tank 10 is activated to suck the refrigerant from the ground freezing pipe 200 into the refrigerant tank 10.

[0067] After the recovery of the residual refrigerant starts, the liquid level in the refrigerant tank 10 is measured, and the timing to end the refrigerant recovery is determined based on the liquid level of the refrigerant (step S34). If the liquid level of the refrigerant in the refrigerant tank 10 is lower than the specified value H_th3, the vacuum pump (56, 12) continues to collect the remaining refrigerant from the ground freezing pipe 200 (No in step S34).

[0068] On the other hand, if the liquid level of the refrigerant in the refrigerant tank 10 is equal to or higher than the specified value H_th3, the recovery of the residual refrigerant from the ground freezing pipe 200 using the vacuum pump (56, 12) is terminated, and the refrigerant supply pump 30 and the heat pump device 100 are started to resume thawing the ground 5 (Yes in step S34).

[0069] The characteristic configurations of the ground thawing method and ground thawing device according to the above-mentioned several embodiments can be summarized as follows.

[0070] [1] Some embodiments of a ground thawing method include: a step (S18) of gasifying the refrigerant supplied from the refrigerant tank (10); A step (S18) of supplying a gasified refrigerant to the ground freezing pipe (200) and thawing the ground (5) using the latent heat of the refrigerant; Equipped with.

[0071] According to the method [1], the latent heat of the refrigerant is used to thaw the ground (5), so that the ground can be thawed with a smaller amount of refrigerant than the flow rate of warm brine in the ground thawing method using sensible heat. Therefore, it is possible to reduce the energy required to circulate the heat medium (a collective term for the refrigerant in the method [1] and the warm brine in the conventional ground thawing method) used for thawing the ground through the ground freezing pipe (200), and energy saving in the ground thawing can be realized.

[0072] [2] In some embodiments, in the method of [1] above, The method includes steps (S12, S16) of operating a heat pump device (100) having an evaporator (120 (120A, 120B)) that evaporates a CO2 refrigerant and a gas cooler (130) that performs heat exchange between the CO2 refrigerant and hot water, In the gasifying step (S18), the refrigerant is gasified by heat exchange between the refrigerant and hot water heated by the gas cooler (130).

[0073] According to the method [2], the heat pump device (100) that is excellent in energy saving can generate hot water for gasifying the refrigerant, thereby achieving further energy saving in the ground thawing method.

[0074] [3] In some embodiments, in the method of [1] or [2] above, A step (S18) of liquefying the refrigerant that has passed through the ground freezing pipe (200); a step (S18) of returning the liquefied refrigerant to the refrigerant tank (10); Equipped with.

[0075] According to the method [3] above, the refrigerant returned to the refrigerant tank (10) can be reused in the gasification step (S18).

[0076] [4] In some embodiments, in the method of [3] above, a step (S16) of operating a heat pump device (100) having a cold water heat source evaporator (120B) that evaporates a CO2 refrigerant using cold water as a heat source and a gas cooler (130) that exchanges heat between the CO2 refrigerant and hot water; In the gasifying step (S18), the refrigerant is gasified by heat exchange between the refrigerant and hot water heated by the gas cooler (130); In the liquefying step (S18), the refrigerant is liquefied by heat exchange between the refrigerant and the cold water cooled by the cold water heat source evaporator (120B).

[0077] According to the method [4] above, the heat pump device (100) can simultaneously generate hot water for gasifying the refrigerant and cold water for liquefying the refrigerant, thereby achieving further energy savings in the ground thawing method.

[0078] [5] In some embodiments, in the method of [4] above, The heat pump device (100) further includes an air heat source evaporator (120A) that evaporates a CO2 refrigerant using air as a heat source, The method includes switching the operation mode of the heat pump device (100) from an air heat source mode in which only hot water for gasifying the refrigerant is generated using an air heat source evaporator (120A) to a water heat source mode in which both hot water for gasifying the refrigerant and cold water for liquefying the refrigerant are generated using a cold water heat source evaporator (120B).

[0079] According to the method [5] above, it is possible to selectively generate only hot water or both hot water and cold water by switching the operation mode of the heat pump unit (100). Therefore, it is possible to use one type of heat pump unit (100) to meet the demand for both hot water and cold water that fluctuates depending on the progress of ground thawing, thereby achieving further energy savings in ground thawing.

[0080] [6] In some embodiments, in any of the methods [1] to [5] above, a step (S20) of measuring the temperature of the ground (5) using a temperature measuring pipe (70) buried in the ground (5); A step (S20) of determining the timing of completion of ground thawing based on the temperature of the ground (5); Equipped with.

[0081] According to the method [6] above, the progress of ground thawing can be determined from the temperature of the ground (5), so that the ground thawing can be completed reliably, and the thawing work can be completed quickly after the ground thawing is completed.

[0082] [7] In some embodiments, in any of the methods [1] to [6] above, The method includes a step (S24) of recovering the refrigerant remaining in the ground freezing pipe (200) into the refrigerant tank (10) after the thawing of the ground (5) is completed.

[0083] According to the method [7] above, the amount of refrigerant released into the environment can be reduced and the amount of refrigerant that can be reused can be increased, thereby reducing the environmental impact of the ground thawing method.

[0084] [8] In some embodiments, in the method of [7] above, In the step (S24) of recovering the refrigerant, the refrigerant remaining in the ground freezing pipe (200) is pushed out by nitrogen gas, and the refrigerant is recovered into the refrigerant tank (10).

[0085] According to the method [8], the reliability of refrigerant recovery from the ground freezing pipe (200) is improved, and the environmental load of the ground thawing method can be further reduced.

[0086] [9] In some embodiments, in the method of [7] above, In the step (S24) of recovering the refrigerant, the pressure in the refrigerant tank (10) is reduced using the vacuum pump (12), and the refrigerant is sucked into the refrigerant tank (10) by the pressure difference between the ground freezing pipe (200) and the refrigerant tank (10).

[0087] According to the method [9], it is only necessary to prepare a vacuum pump (12) as an additional facility required for refrigerant recovery, and the refrigerant can be recovered with a simple device configuration.

[0088]

[10] In some embodiments, in any of the methods [7] to [9] above, a step (S26) of measuring the liquid level of the refrigerant in the refrigerant tank (10); a step (S26) of determining the timing to end refrigerant recovery based on the liquid level; Equipped with.

[0089] According to the method

[10] above, the timing to finish refrigerant recovery can be appropriately determined, and it is possible to achieve both reliable refrigerant recovery and a reduction in the time required for refrigerant recovery work.

[0090]

[11] In some embodiments, in any of the methods [1] to

[10] above, The refrigerant is an HFO refrigerant.

[0091] From the viewpoint of reducing the cost of ground thawing, it is desirable to continue using the ground freezing pipe (200) used for ground freezing for ground thawing without reinforcing or replacing it. In this case, the specifications of a general ground freezing pipe (200) are not compatible with high-pressure refrigerants, so there is a limit to the refrigerant pressure during ground thawing. In this regard, according to the method

[11] above, by using an HFO refrigerant with a saturation pressure of approximately 0.2 MPaG under refrigerant temperature conditions suitable for ground thawing (for example, 50 to 60°C), the ground freezing pipe (200) used for ground freezing can be continuously used for ground thawing, thereby reducing the cost of the ground thawing method.

[0092]

[12] In some embodiments, the ground thawing device (1) includes: a refrigerant tank (10) for storing a refrigerant; a refrigerant supply line (20) for guiding the refrigerant from the refrigerant tank (10) to the ground freezing pipe (200); a refrigerant supply pump (30) provided in the refrigerant supply line (20) for supplying the refrigerant from the refrigerant tank (10) to the ground freezing pipe (210); a gasification device (40) that is provided downstream of the refrigerant supply pump (30) in the refrigerant supply line (20) and gasifies the refrigerant; Equipped with The refrigerant gasified by the gasification device (40) is supplied to the ground freezing pipe (200), and the ground (5) is thawed using the latent heat of the refrigerant.

[0093] According to the configuration

[12] , the latent heat of the refrigerant is used to thaw the ground (5), so that the ground can be thawed with a smaller amount of refrigerant than the flow rate of warm brine in a ground thawing device that uses sensible heat. Therefore, it is possible to reduce the energy required to circulate the heat medium (a collective term for the refrigerant in the configuration

[12] and the warm brine in the conventional ground thawing method) used for thawing the ground through the ground freezing pipe (200), thereby realizing energy saving in thawing the ground.

[0094]

[13] In some embodiments, in the configuration of

[12] above, The heat pump device (100) includes an evaporator (120 (120A, 120B)) that evaporates a CO2 refrigerant and a gas cooler (130) that exchanges heat between the CO2 refrigerant and hot water, The gasifier (40) is configured to gasify the refrigerant by heat exchange between the refrigerant and hot water heated by the gas cooler (130).

[0095] According to the configuration

[13] , the heat pump device (100) having excellent energy saving properties can generate hot water for gasifying the refrigerant, thereby achieving further energy saving in the ground thawing device (1).

[0096]

[14] In some embodiments, in the configuration of

[12] or

[13] above, a refrigerant recovery line (50) for recovering refrigerant from the ground freezing pipe (200) to the refrigerant tank (10); a re-liquefaction device (60) provided in the refrigerant recovery line (50) for liquefying the refrigerant that has passed through the ground freezing pipe (200); Equipped with.

[0097] According to the above configuration

[14] , the refrigerant returned to the refrigerant tank (10) can be supplied again to the gasification device (40).

[0098]

[15] In some embodiments, in the configuration of

[14] above, The heat pump device (100) includes a cold water heat source evaporator (120B) that uses cold water as a heat source to evaporate a CO2 refrigerant, and a gas cooler (130) that performs heat exchange between the CO2 refrigerant and hot water, The gasification device (40) is configured to gasify a refrigerant by heat exchange between the refrigerant and hot water heated by a gas cooler (130), The re-liquefaction device (60) is configured to liquefy the refrigerant by heat exchange between the refrigerant and the cold water from the cold water heat source evaporator (130B).

[0099] According to the configuration

[15] above, the heat pump device (100) can simultaneously generate hot water for gasifying the refrigerant and cold water for liquefying the refrigerant, thereby further reducing the energy consumption of the ground thawing device (1).

[0100]

[16] In some embodiments, in the configuration of

[15] above, The heat pump device (100) further includes an air heat source evaporator (120A) that evaporates a CO2 refrigerant using air as a heat source, an evaporator switching means (170 (170A, 170B)) for switching the evaporator (120 (120A, 120B)) through which the CO2 refrigerant flows, out of the air heat source evaporator (120A) or the chilled water heat source evaporator (120B); The evaporator switching means (170 (170A, 170B)) is configured to switch the operation mode of the heat pump device (100) from an air heat source mode in which only hot water for gasifying the refrigerant is generated using the air heat source evaporator (120A) to a water heat source mode in which both hot water for gasifying the refrigerant and cold water for liquefying the refrigerant are generated using the cold water heat source evaporator (120B).

[0101] According to the configuration

[16] above, by switching the operation mode of the heat pump unit (100), it is possible to selectively generate only hot water or both hot water and cold water. Therefore, it is possible to use one type of heat pump unit (100) to meet the demand for hot water and cold water that varies depending on the progress of ground thawing, thereby achieving further energy savings in ground thawing.

[0102]

[17] In some embodiments, in any of the configurations

[12] to

[16] above, The refrigerant is an HFO refrigerant.

[0103] From the viewpoint of reducing the cost of ground thawing, it is desirable to continue using the ground freezing pipe (200) used for ground freezing for ground thawing without reinforcing or replacing it. In this case, the specifications of a general ground freezing pipe (200) are not compatible with high-pressure refrigerants, so there is a limit to the refrigerant pressure during ground thawing. In this regard, according to the configuration of

[17] above, by using an HFO refrigerant with a saturation pressure of approximately 0.2 MPaG at refrigerant temperature conditions suitable for ground thawing (for example, 50 to 60°C) for ground thawing, the ground freezing pipe (200) used for ground freezing can be continuously used for ground thawing, thereby reducing the cost of the ground thawing device (1).

[0104] Although several embodiments of the present invention have been described above, it is of course possible to add modifications to the above-described embodiments without departing from the spirit of the present invention.

[0105] In this specification, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent rectangular shapes or cylindrical shapes in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components. [Explanation of symbols]

[0106] 1: Ground thawing device 5: Ground 10: Refrigerant tank 20: Refrigerant supply line 30: Refrigerant supply pump 40: Gasifier 50: Refrigerant recovery line 60:Reliquefaction equipment 70: Temperature measuring tube 100: Heat pump device 120: Evaporator 120A: Air heat source evaporator 120B: Chilled water heat source evaporator 130: Gas cooler 170: Evaporator switching means 200: Ground freezing pipe

Claims

1. gasifying the refrigerant supplied from the refrigerant tank; supplying the gasified refrigerant to a ground freezing pipe and thawing the ground using the latent heat of the refrigerant; Equipped with Ground thawing method.

2. CO ２ an evaporator for evaporating a refrigerant, and ２ The method includes a step of operating a heat pump device having a gas cooler that performs heat exchange between a refrigerant and hot water, In the gasifying step, the refrigerant is gasified by heat exchange between the hot water heated by the gas cooler and the refrigerant. The method for thawing ground according to claim 1.

3. liquefying the refrigerant that has passed through the ground freezing pipe; returning the liquefied refrigerant to the refrigerant tank; Equipped with The method for thawing ground according to claim 1 or 2.

4. Using cold water as a heat source, CO ２ a cold water heat source evaporator for evaporating a refrigerant; and ２ The method includes a step of operating a heat pump device having a gas cooler that performs heat exchange between a refrigerant and hot water, In the gasifying step, the refrigerant is gasified by heat exchange between the hot water heated by the gas cooler and the refrigerant, In the liquefying step, the refrigerant is liquefied by heat exchange between the refrigerant and the cold water cooled by the cold water heat source evaporator. The method for thawing ground according to claim 3.

5. The heat pump device uses air as a heat source to ２ The system further includes an air-heat source evaporator that evaporates the refrigerant; a step of switching the operation mode of the heat pump device from an air heat source mode in which only the hot water for gasifying the refrigerant is generated using the air heat source evaporator to a water heat source mode in which both the hot water for gasifying the refrigerant and the cold water for liquefying the refrigerant are generated using the cold water heat source evaporator. The method for thawing ground according to claim 4.

6. measuring the temperature of the ground using a temperature measuring pipe buried in the ground; determining a ground thawing completion timing based on the temperature of the ground; Equipped with The method for thawing ground according to claim 1 or 2.

7. The refrigerant is an HFO refrigerant The method for thawing ground according to claim 1 or 2.

8. a refrigerant tank that stores a refrigerant; a refrigerant supply line for guiding the refrigerant from the refrigerant tank to a ground freezing pipe; a refrigerant supply pump provided in the refrigerant supply line for supplying the refrigerant from the refrigerant tank to the ground freezing pipe; a gasification device that is provided in the refrigerant supply line downstream of the refrigerant supply pump and that gasifies the refrigerant; Equipped with The refrigerant gasified by the gasification device is supplied to the ground freezing pipe, and the ground is thawed using the latent heat of the refrigerant. Ground thawing equipment.

9. CO ２ an evaporator for evaporating a refrigerant, and ２ a heat pump device having a gas cooler that exchanges heat between a refrigerant and hot water; The gasification device is configured to gasify the refrigerant by heat exchange between the hot water heated by the gas cooler and the refrigerant. The ground thawing device according to claim 8.

10. a refrigerant recovery line for recovering the refrigerant from the ground freezing pipe to the refrigerant tank; a re-liquefaction device provided in the refrigerant recovery line for liquefying the refrigerant that has passed through the ground freezing pipe; Equipped with The ground thawing device according to claim 8 or 9.

11. Using cold water as a heat source, CO ２ a cold water heat source evaporator for evaporating a refrigerant; and ２ a heat pump device having a gas cooler that exchanges heat between a refrigerant and hot water; the gasification device is configured to gasify the refrigerant by heat exchange between the hot water heated by the gas cooler and the refrigerant, The re-liquefaction device is configured to liquefy the refrigerant by heat exchange between the cold water from the cold water heat source evaporator and the refrigerant. The ground thawing device according to claim 10.

12. The heat pump device uses air as a heat source to ２ The system further includes an air-heat source evaporator that evaporates the refrigerant; The CO ２ an evaporator switching means for switching an evaporator through which a refrigerant flows; The evaporator switching means is configured to switch the operation mode of the heat pump device from an air heat source mode in which only the hot water for gasifying the refrigerant is generated using the air heat source evaporator to a water heat source mode in which both the hot water for gasifying the refrigerant and the cold water for liquefying the refrigerant are generated using the cold water heat source evaporator. The ground thawing device according to claim 11.

13. The refrigerant is an HFO refrigerant The ground thawing device according to claim 8 or 9.

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