JP2010145022A - Underground heat exchanger and air conditioning system including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a configuration capable of reducing installation cost without largely lowering heat exchange efficiency, in an underground heat exchanger having a heat transfer pipe where fluid subject to heat exchange is made to flow and which is inserted to inside of an outer pipe and having a heating medium filled in the outer pipe. <P>SOLUTION: The underground heat exchanger (10) is embedded in the ground so that the outer pipe (11) to which the heat transfer pipe (12) where a refrigerant is made to flow is inserted and in which carbon dioxide is filled is not exposed to the ground surface and the entire outer surface is covered with soil. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a ground heat exchanger that performs heat exchange between a heat exchange fluid and soil in the ground.

  2. Description of the Related Art Conventionally, underground heat exchangers configured to perform heat exchange between a heat exchange fluid and underground soil are known. As such a ground heat exchanger, a configuration is known in which heat is exchanged between a heat exchange fluid and soil via a heat medium that changes phase.

  Specifically, as disclosed in, for example, Patent Document 1, a pipe in which a heat medium is accommodated is buried in the ground, and heat is exchanged with a heat medium in a pipe that is evaporated by geothermal heat. A heat exchanger through which the heat exchange fluid flows is provided. Thereby, the heat of the heat medium evaporated in the pipe embedded in the ground is transmitted to the heat exchange fluid by the heat exchanger, and is used as a heat source for heating in a circuit through which the heat exchange fluid flows.

In addition to the above-described configuration, as a configuration of the underground heat exchanger, a tube method for exchanging heat with the soil in the ground by flowing a heat exchange fluid into a tube buried vertically in the deep underground, A horizontal method in which a tube is embedded in a loop shape near the ground surface is considered.
International Publication No. WO2004 / 111559 Pamphlet

  By the way, in the structure disclosed by the said patent document 1, the upper part of the pipe embed | buried under the ground is exposed from the ground surface, and it is comprised so that it may heat-exchange with the heat exchange fluid which flows through the inside of a heat exchanger in this upper part. Therefore, it is necessary to embed the pipe in a relatively shallow portion of the ground, and it is easily affected by changes in temperature and temperature on the ground surface. Therefore, in the summer when the ground heat exchanger dissipates heat to the soil in the ground during cooling operation, the temperature of the soil near the ground surface increases, while in the winter when heat is absorbed from the soil in the ground by the ground heat exchanger during heating operation. The temperature of the soil near the surface of the earth may be lowered, and heat exchange may not be performed efficiently.

  In addition, in the above-mentioned tube method using a long and narrow tube, it is necessary to increase the length of the tube in order to ensure heat exchange performance. Usually, excavation of about 100 m in the ground is required, which increases the installation cost. As in the configuration of Patent Document 1, the horizontal method has a configuration in which the tube is embedded near the ground surface and is greatly affected by the temperature and the temperature of the ground surface, so that the heat exchange efficiency is not so good.

  The present invention has been made in view of the above points, and an object of the present invention is an underground heat exchanger in which a heat transfer tube through which a heat exchange fluid flows is inserted and a heat medium is enclosed in an outer tube. An object of the present invention is to obtain a configuration capable of reducing the installation cost without greatly reducing the heat exchange efficiency.

  In order to achieve the above object, in the underground heat exchanger (10) according to the present invention, the outer cylinder (11) into which the heat transfer tube (12) is inserted and the heat medium is enclosed is exposed to the ground surface. Instead, it was placed in the ground so that the entire outer surface was covered with soil.

  Specifically, in the first invention, the outer pipe (11) buried vertically in the ground and the heat transfer pipe (12) inserted into the outer pipe (11) and through which the heat exchange fluid flows. ) And a heat medium (13) enclosed in the outer tube (11), and is configured to exchange heat with soil using the phase change of the heat medium (13). Intended for exchangers. The outer pipe (11) is embedded in the ground so as not to be exposed on the ground surface, and the entire outer surface is covered with soil.

  With the above configuration, the outer pipe (11) is buried vertically in the ground, and the heat exchange fluid flowing in the heat transfer pipe (12) inserted into the outer pipe (11) is transferred into the outer pipe (11). In the underground heat exchanger (10) configured to exchange heat with the soil using the phase change of the heat medium sealed in the outer wall, the outer pipe (11) is not exposed to the ground surface. Since the surface is covered with soil, heat exchange can be reliably performed between the heat exchange fluid in the heat transfer tube (12) and the soil.

  Moreover, in the underground heat exchanger (10) having the above-described configuration, heat exchange is performed using the phase change of the heat medium, so that the heat exchange efficiency is better than the conventional tube type, and the tube type Since it is not necessary to embed a long tube deep in the ground like this, the installation cost can be greatly reduced.

  In addition, since the underground heat exchanger (10) is buried vertically in the ground, it exchanges heat with soil with a stable temperature compared to the horizontal type in which tubes are placed in a loop near the ground surface. It can be performed and is not easily affected by changes in temperature or the temperature of the ground surface.

  In the above-described configuration, it is preferable that the outer tube (11) is embedded at a predetermined depth so as to exhibit a capability required as a heat exchanger (second invention). As a result, it is possible to obtain an underground heat exchanger (10) that is not easily affected by a change in temperature or a change in temperature on the ground surface, and that can exchange heat with the soil in the ground to exhibit a predetermined ability.

  3rd invention is equipped with the underground heat exchanger (10) as described in the said 1st or 2nd invention, and targets air-conditioning system which performs a refrigerating cycle. A plurality of the underground heat exchangers (10) are provided, and the plurality of underground heat exchangers (10) are connected in parallel.

  With this configuration, it is possible to obtain the required heat exchange performance with multiple underground heat exchangers (10), so the length of the underground heat exchanger is shortened compared to conventional underground heat exchangers. Is possible. Therefore, unlike the prior art, it is not necessary to excavate deeply into the ground in order to embed the underground heat exchanger in the ground, so that the installation cost can be reduced.

  As described above, in the underground heat exchanger (10) according to the first invention, the outer pipe (11) into which the heat transfer pipe (12) through which the heat exchange fluid flows is inserted and the heat medium is sealed is formed on the ground surface. Since the outer surface is covered with the soil without being exposed, the heat exchange between the heat exchange fluid and the soil can be reliably performed. Therefore, it is possible to realize the underground heat exchanger (10) having a configuration capable of reducing the installation cost as compared with the conventional configuration without greatly reducing the heat exchange performance.

  In addition, according to the second invention, the outer tube (11) is disposed at a predetermined depth so as to exhibit the ability required as a heat exchanger, so that the performance as a heat exchanger is stabilized. An underground heat exchanger (10) can be obtained that can be exhibited.

  According to the air conditioning system according to the third aspect of the invention, a plurality of the underground heat exchangers (10) according to the first or second aspect of the invention are provided, and the underground heat exchangers (10) are arranged in parallel. Therefore, the installation cost can be reduced while ensuring the required heat exchange capacity.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the present invention, its application, or its use.

  An underground heat exchanger according to an embodiment of the present invention is used in an air conditioning system capable of heating operation and cooling operation, and functions as an evaporator during heating operation to recover heat from soil in the ground, while cooling operation It is sometimes configured to function as a condenser and dissipate heat to the soil in the ground.

<Overall configuration of air conditioning system>
Drawing 1 is a schematic structure figure of an air-conditioning system (1) provided with a geothermal heat exchanger (10) concerning an embodiment of the present invention. The air conditioning system (1) includes a compressor (3), a four-way switching valve (4), an indoor heat exchanger (5), an expansion valve (6), and a plurality of underground heat exchangers embedded in the ground. (10) is provided with a refrigerant circuit (2) connected in order by refrigerant piping. The refrigerant circuit (2) contains a refrigerant (heat exchange fluid), and the refrigerant circulates in the refrigerant circuit (2), so that the indoor heat exchanger (5) is heated during heating operation. Becomes the condenser and the underground heat exchanger (10) becomes the evaporator, while the indoor heat exchanger (5) becomes the evaporator and the underground heat exchanger (10) condenses during the cooling operation. A vapor compression refrigeration cycle is performed. In the present embodiment, the plurality of underground heat exchangers (10) are connected in parallel to the refrigerant circuit (2), and in each of the heat exchangers (10), the soil and heat in the ground are heated. Configured to replace.

  The compressor (3) is composed of, for example, a scroll compressor, and is configured to suck and compress the refrigerant from the suction port and discharge the compressed refrigerant from the discharge port. In the refrigerant circuit (2), the discharge port of the compressor (3) is connected to the second port (P2) of the four-way switching valve (4), and the suction port of the compressor (3) is connected to the four-way Connected to the fourth port (P4) of the switch valve (4).

  The four-way switching valve (4) has a first port (P1) connected to the indoor heat exchanger (5), a second port (P2) connected to the discharge port of the compressor (3), Three ports (P3) are connected to the underground heat exchanger (10), and a fourth port (P4) is connected to the suction port of the compressor (3). The four-way selector valve (4) is in a first state in which the first port (P1) and the second port (P2) communicate with each other and the third port (P3) and the fourth port (P4) communicate with each other. (The state indicated by the solid line in FIG. 1), the second port (P1) and the fourth port (P4) communicate with each other, and the second port (P2) and the third port (P3) communicate with each other. The state (state indicated by a broken line in FIG. 1) can be switched.

  The indoor heat exchanger (5) is, for example, a cross fin type fin-and-tube heat exchanger, and is an air heat exchanger for exchanging heat between the refrigerant and room air. In the air conditioning system (1), the indoor heat exchanger (5) is incorporated in an indoor unit disposed in a room that performs air conditioning. In the refrigerant circuit (2), one end of the indoor heat exchanger (5) is connected to the expansion valve (6), and the other end is the first port (P1) of the four-way switching valve (4). )It is connected to the. Furthermore, an indoor fan (7) is provided in the vicinity of the indoor heat exchanger (5) for flowing air exchanged with the indoor heat exchanger (5) into the room.

  The expansion valve (6) is an electronic expansion valve with a variable opening. By changing the opening of the expansion valve (6), the refrigerant flowing from the indoor heat exchanger (5) or the underground heat exchanger (10) can be expanded and depressurized to a predetermined pressure. .

  The above-mentioned underground heat exchanger (10) has a substantially cylindrical outer shape, and heat is exchanged between the refrigerant embedded in the ground so as to extend in the vertical direction (vertical direction) and the soil flowing inside. It is configured as follows. As will be described in detail later, the underground heat exchanger (10) includes a bottomed cylindrical outer tube (11), and a heat transfer tube (12) that is housed in the outer tube (11) and through which the refrigerant flows. And a heat medium (13) enclosed in the outer tube (11). The underground heat exchanger (10) is configured to exchange heat between the refrigerant flowing in the heat transfer tube (12) and the soil outside the outer tube (11) via the heat medium (13). .

  In the air conditioning system (1) having the above-described configuration, the heating operation is performed when the four-way switching valve (4) is in the first state, and the cooling operation is performed when the four-way switching valve (4) is in the second state. Is done. That is, in the heating operation, a vapor compression refrigeration cycle in which the underground heat exchanger (10) functions as an evaporator and the indoor heat exchanger (5) functions as a condenser is performed in the refrigerant circuit (2). On the other hand, in the cooling operation, in the refrigerant circuit (2), a vapor compression refrigeration cycle is performed in which the underground heat exchanger (10) functions as a condenser and the indoor heat exchanger (5) functions as an evaporator.

<Configuration of underground heat exchanger>
Below, the structure of a underground heat exchanger (10) is demonstrated in detail based on FIG.

  As described above, the underground heat exchanger (10) includes the outer pipe (11), the heat transfer pipe (12) accommodated therein, and the heat medium (13) enclosed in the outer pipe (11). ). The underground heat exchanger (10) is embedded in the ground so that the outer pipe (11) is not exposed to the ground surface, and the entire outer surface of the outer pipe (11) is covered with soil. Yes. Specifically, the underground heat exchanger (10) is embedded in a range of about 5 m to 10 m from the ground surface. For example, as shown in FIG. 6, this depth is hardly affected by the temperature change of the ground surface even when the temperature on the ground surface (the depth of the ground in the figure is 0 m) greatly fluctuates. It is a depth (predetermined depth) that can exhibit the ability required as. Therefore, by burying the underground heat exchanger (10) at the depth, heat exchange between the refrigerant flowing through the internal heat transfer tube (12) and the soil in the ground can be performed stably and efficiently. it can. And since the depth which excavates becomes shallow compared with the conventional structure (tube system), installation cost can be reduced. In addition, the said FIG. 6 shows the example which calculated | required the temperature change of the soil in the ground by the calculation formula, and the state of the soil (solid line) in summer (right side of the figure) and winter (left side of the figure) : Soil with average moisture, broken line: damp soil, alternate long and short dash line: slightly dry soil).

The outer tube (11) is one in which both ends of a metallic cylindrical member are closed by a metallic plate member, and a space (S) is formed inside thereof. The outer pipe (11) has a sealed structure capable of enclosing a predetermined amount of carbon dioxide (CO ₂ ) as the heat medium (13) in the space (S). Further, the heat transfer pipe (12) through which the refrigerant flows is housed in the space (S) of the outer pipe (11). The heat transfer pipe (12) passes through a plate member constituting one end face (the end face on the ground surface side) of the outer pipe (11) and is connected to the refrigerant pipe of the refrigerant circuit (2). Here, the outer pipe (11) is embedded vertically in the ground so that the cylinder axis direction is substantially vertical. Although it is ideal to embed the outer pipe (11) substantially vertically in the ground, a certain degree of inclination is allowed.

  The heat transfer tube (12) is made of copper and is made of a tubular member through which the refrigerant flows so as to constitute a part of the flow path of the refrigerant circuit (2). In this embodiment, the heat transfer tube (12) is formed so as to extend from the top of the outer tube (11) to the bottom, bend at the bottom, and return to the top. 11) is accommodated in the outer pipe (11) so as to penetrate the plate member constituting one end face and project outside. Specifically, the heat transfer tube (12) includes a first connection part (12a) connected to the expansion valve (6) on one end side, and a main body connected to the other end side of the first connection part (12a). And a second connection portion (12b) connected to the main body portion (12c) on one end side and connected to the third port (P3) of the four-way switching valve (4) on the other end side. ing. These connecting portions (12a, 12b) are provided so as to penetrate through a plate member constituting one end surface (end surface on the ground surface side) of the outer pipe (11), while the main body portion (12c) These are arranged along the inner surface of the outer tube (11).

  The main body (12c) includes a linear first main body (12d) connected to the other end of the first connecting portion (12a) and extending to the bottom of the outer tube (11), and the first main body It comprises a spiral second main body portion (12e) connected to the portion (12d) and extending to the top of the outer tube (11). Thus, by forming the second main body portion (12e) in a spiral shape, the carbon dioxide (13) in which the refrigerant flowing in the second main body portion (12e) is sealed in the outer pipe (11). The surface area of the portion that exchanges heat with can be increased, and heat exchange can be performed efficiently between the refrigerant and carbon dioxide (13).

  The spiral second main body portion (12e) is disposed so as to come into contact with the inner peripheral surface of the outer tube (11), and the second inner body portion (12e) is inward of the second main body portion (12e). The first main body portion (12d) is disposed so as to be in contact with the main body portion (12e). In this way, by bringing the second main body portion (12e) into contact with the inner peripheral surface of the outer tube (11), as described later, the outer peripheral surface of the second main body portion (12e) or the outer tube (11). The carbon dioxide (13) condensed on the inner peripheral surface of the gas can move to the inner peripheral surface of the outer pipe (11) or the outer peripheral surface of the second main body (12e), and carbon dioxide (13) Can be evaporated.

  That is, as shown in FIG. 4, during the heating operation of the air conditioning system (1), the inside of the heat transfer pipe (12) of the underground heat exchanger (10) is a low pressure whose saturation temperature is lower than the temperature of the soil in the ground. Since the refrigerant flows, carbon dioxide (13) in the outer pipe (11) having a saturation temperature lower than that of the soil and higher than that of the low-pressure refrigerant condenses on the outer surface of the heat transfer pipe (12). . At this time, the refrigerant flowing in the second main body (12e) of the heat transfer tube (12) evaporates due to the heat of condensation of the carbon dioxide (13) and is sucked from the suction port of the compressor (3).

  As described above, since the second main body portion (12e) and the inner peripheral surface of the outer pipe (11) are in contact with each other, the condensed carbon dioxide (13) is absorbed by the second main body portion (12e). It moves from the outer peripheral surface onto the inner peripheral surface of the outer pipe (11), and evaporates (vaporizes) on the inner peripheral surface by the heat of the soil in the ground. The vaporized carbon dioxide (13) condenses again when cooled by the second main body (12e) of the heat transfer tube (12).

  On the other hand, as shown in FIG. 5, during the cooling operation of the air conditioning system (1), the inside of the heat transfer pipe (12) of the underground heat exchanger (10) is a high pressure whose saturation temperature is higher than the temperature of the soil in the ground. The refrigerant flows. Since the carbon dioxide (13) in the outer pipe (11) has a saturation temperature higher than the temperature of the soil and lower than the temperature of the high-pressure refrigerant, it vaporizes on the outer surface of the heat transfer pipe (12). On the other hand, it condenses on the inner peripheral surface of the outer pipe (11).

  That is, as described above, since the second main body portion (12e) and the inner peripheral surface of the outer tube (11) are in contact with each other, carbon dioxide condensed on the inner peripheral surface of the outer tube (11) ( 13) moves to the outer peripheral surface of the second main body portion (12e) and is vaporized by the heat of the refrigerant on the outer peripheral surface. The vaporized carbon dioxide (13) is condensed again when cooled by the inner peripheral surface of the outer pipe (11). When carbon dioxide (13) is vaporized on the outer surface of the second main body (12e) of the heat transfer tube (12), the refrigerant flowing in the second main body (12e) is evaporated of carbon dioxide (13). Deprived of heat and condensed, and flows to the expansion valve (6).

  In the present embodiment, as shown in FIG. 3, a plurality of grooves (11a) extending horizontally in the circumferential direction of the outer tube (11) are arranged in the longitudinal direction on the inner circumferential surface of the outer tube (11). Is formed. Further, the heat transfer tube (12) is parallel to the outer peripheral surface of the second main body portion (12e) of the heat transfer tube (12) with respect to the groove (11a) of the inner peripheral surface of the outer tube (11). ), A plurality of grooves (12f) extending horizontally in the circumferential direction are formed side by side in the longitudinal direction.

  Thus, by forming the grooves (11a, 12f) on the inner peripheral surface of the outer tube (11) and the outer peripheral surface of the second main body (12e) of the heat transfer tube (12), respectively, during heating operation Carbon dioxide (13) condensed on the outer peripheral surface of the second main body (12e) and carbon dioxide (13) condensed on the inner peripheral surface of the outer pipe (11) during cooling operation are respectively It can hold | maintain in a groove | channel (11a, 12f), and it can prevent flowing down to the lower part of an outer tube | pipe (11). Moreover, as described above, the grooves (11a, 12f) extend in the circumferential direction and in the horizontal direction on the inner peripheral surface of the outer tube (11) and the outer peripheral surface of the second main body portion (12e) of the heat transfer tube (12). Therefore, the carbon dioxide (13) condensed on the outer peripheral surface of the second main body portion (12e) of the heat transfer tube (12) and the inner peripheral surface of the outer tube (11) is removed from the outer tube. (11) can be expanded in the circumferential direction (horizontal direction) (see FIGS. 4 and 5), and heat exchange between the refrigerant and the soil and the carbon dioxide (13) can be performed efficiently. Therefore, by providing the groove (11a, 12f), heat exchange between the refrigerant in the heat transfer tube (12) and the soil outside the outer tube (11) can be efficiently performed via carbon dioxide (13). Can do.

  In this embodiment, the groove (11a) formed on the inner peripheral surface of the outer tube (11) and the groove (12f) formed on the outer peripheral surface of the heat transfer tube (12) are substantially parallel. However, the present invention is not limited to this, and the grooves (11a, 12f) may intersect with each other, and the grooves (11a, 12f) may be slightly inclined up and down with respect to the horizontal direction.

-Driving action-
Next, operation | movement of the air conditioning system (1) which has the above structures is demonstrated based on FIG.1, FIG4 and FIG.5.

(Heating operation)
As shown in FIG. 1, when the heating operation is started, first, the four-way switching valve (4) is switched to the first state. When the compressor (3) is in an operating state, the compressed high-pressure refrigerant (gas refrigerant) is discharged from the discharge port of the compressor (3), and indoor heat exchange is performed via the four-way switching valve (4). Flows into the vessel (5). In the indoor heat exchanger (5), the high-pressure refrigerant dissipates heat to the indoor air and condenses. The indoor air is warmed by this condensation heat, and the room is heated. The refrigerant condensed in the indoor heat exchanger (5) flows out of the indoor heat exchanger (5), is decompressed by the expansion valve (6), and is introduced into the underground heat exchanger (10) (see FIG. (Solid arrow in 1). In the expansion valve (6), the refrigerant is decompressed so that the saturation temperature is lower than the temperature of the soil in the ground.

  The low-pressure refrigerant flowing into the underground heat exchanger (10) absorbs underground heat through the carbon dioxide (13) in the outer pipe (11) and evaporates. At this time, the underground heat exchanger (10) has the entire outer surface of the outer pipe (11) covered with soil and is buried at a stable depth in the surrounding soil. Heat exchange with other soils. The refrigerant evaporated in the underground heat exchanger (10) flows out of the underground heat exchanger (10), and is sucked again into the compressor (3) through the four-way switching valve (4). Until compressed.

  As described above, the refrigerant circulates in the refrigerant circuit (2) and performs a vapor compression refrigeration cycle, thereby heating the room.

  Next, the state change of the refrigerant and carbon dioxide (13) in the underground heat exchanger (10) will be described.

  As mentioned above, the low-pressure refrigerant whose saturation temperature is lower than the temperature of the soil in the ground is in the body (12c) of the heat transfer tube (12) in the underground heat exchanger (10) buried in the ground. 4, as shown in FIG. 4, carbon dioxide (13) enclosed in the outer pipe (11) of the underground heat exchanger (10) and having a saturation temperature higher than that of the refrigerant is transferred to the heat transfer pipe ( 12) Condensate on the body (12c). Due to the heat of condensation of the carbon dioxide (13), the refrigerant in the heat transfer tube (12) evaporates and flows out of the underground heat exchanger (10), and is then sucked into the compressor (3).

  On the other hand, in the outer pipe (11) of the underground heat exchanger (10), condensed carbon dioxide (13) is formed on the outer peripheral surface of the spiral second main body (12e) of the heat transfer pipe (12). It moves to the inner peripheral surface of the outer tube (11) that comes into contact with the second main body (12e) through the groove (12f). On the inner peripheral surface of the outer tube (11), the carbon dioxide (13) is held in a groove (11a) formed on the inner peripheral surface of the outer tube (11), and the soil in the ground Carbon dioxide (13) is vaporized by the heat of the gas, and the vaporized carbon dioxide (13) is condensed again by the refrigerant flowing through the second main body portion (12e) of the heat transfer tube (12).

(Cooling operation)
At the start of the cooling operation, first, the four-way switching valve (4) is switched to the second state. When the compressor (3) is in an operating state, the compressed high-pressure refrigerant is discharged from the discharge port of the compressor (3), and the underground heat exchanger (10) is passed through the four-way switching valve (4). (Broken arrows in FIG. 1). The high-pressure refrigerant that has flowed into the underground heat exchanger (10) dissipates heat to the underground soil via the carbon dioxide (13) in the outer pipe (11) and condenses. At this time, the underground heat exchanger (10), in which the entire outer surface of the outer pipe (11) is covered with soil and buried at a stable depth of the surrounding soil, Heat can be efficiently exchanged between the two. The refrigerant condensed in the underground heat exchanger (10) flows out of the underground heat exchanger (10), is decompressed by the expansion valve (6), and is introduced into the indoor heat exchanger (5). In the expansion valve (6), the refrigerant is decompressed so that the saturation temperature is lower than the indoor temperature.

  The low-pressure refrigerant that has flowed into the indoor heat exchanger (4) absorbs the heat of indoor air and evaporates. The evaporated refrigerant flows out of the indoor heat exchanger (4), is again sucked into the compressor (3) through the four-way switching valve (4), is compressed to a predetermined pressure, and is discharged.

  As described above, the refrigerant circulates in the refrigerant circuit (2) to perform the vapor compression refrigeration cycle, thereby cooling the room.

  Next, the state change of the refrigerant and carbon dioxide (13) in the underground heat exchanger (10) will be described.

  As shown in FIG. 5, in the cooling operation as described above, it is enclosed in the outer pipe (11) of the underground heat exchanger (10), has a saturation temperature lower than the temperature of the refrigerant, and underground soil. Carbon dioxide (13), whose saturation temperature is higher than the temperature of, is condensed by geothermal heat on the inner peripheral surface of the outer pipe (11). The condensed carbon dioxide (13) passes through the groove (11a) formed on the inner peripheral surface of the outer tube (11), and then contacts the inner peripheral surface of the outer tube (11). It moves to the outer peripheral surface of the second main body (12e) and is held by a groove (12f) formed on the surface. Since a high-pressure refrigerant having a temperature higher than the saturation temperature of the carbon dioxide (13) flows in the heat transfer tube (12), the heat transfer tube (12) has an outer peripheral surface on the second main body portion (12e). Carbon dioxide (13) vaporizes. At this time, the refrigerant in the heat transfer tube (12) is deprived of heat by the carbon dioxide (13), condenses, and flows out from the underground heat exchanger (10) to the expansion valve (6).

  On the other hand, the carbon dioxide (13) evaporated on the outer peripheral surface of the second main body portion (12e) of the heat transfer tube (12) is condensed again on the inner peripheral surface of the outer tube (11).

-Effect of the embodiment-
As described above, according to this embodiment, the heat transfer pipe (12) through which the refrigerant flows is inserted into the outer pipe (11) buried vertically in the ground, and carbon dioxide ( 13) In the underground heat exchanger (10) in which the outer tube (11) is enclosed, the underground heat exchanger (10) is placed outside the outer tube (11) without exposing the outer tube (11) to the ground surface. Since the entire surface is buried in the ground so as to cover with soil, the soil is in contact with the entire outer surface of the outer pipe (11), and carbon dioxide (13) enclosed in the outer pipe (11) and the outer pipe Heat exchange can be performed efficiently with the surrounding soil of (11).

  Moreover, since the entire underground heat exchanger (10) is covered with soil on the entire outer surface of the outer pipe (11), the ground heat exchanger (10) can be compared to the case where a part of the heat exchanger is exposed to the ground. It is difficult to be affected by the temperature of the surface and can exhibit a higher ability as a heat exchanger.

  Further, the underground heat exchanger (10) is required to be buried in a predetermined underground depth so as to exhibit the capability required as a heat exchanger. The air-conditioning system (1) using geothermal heat can be realized more reliably.

<< Other Embodiments >>
About the said embodiment, it is good also as the following structures.

  In the above embodiment, the devices (3,4,6) constituting the refrigerant circuit (2) are installed on the ground with respect to the underground heat exchanger (10) buried in the ground. Not limited to this, these devices (3,4,6) may be installed in the basement of the house. That is, as shown in FIG. 7, in the basement (22) of a building such as a house (21), the devices (3,4,6) constituting the refrigerant circuit (2) are arranged and the basement (22 The above-mentioned underground heat exchanger (10) may be embedded at a position deeper than that. In this case, as shown in FIG. 7, the upper portion of the underground heat exchanger (10) is connected to the devices (3,4, 6) via the refrigerant pipe. Is preferably exposed in the underground space (23).

  Moreover, in the said embodiment, although the carbon dioxide (13) is used as a thermal medium in an outer tube | pipe (11), it is not this limitation, If it is a medium which changes a phase between -10 degree | times and 40 degree | times, Any thing is acceptable.

  Moreover, in the said embodiment, although only the 2nd main-body part (12e) of the heat exchanger tube (12) is formed in a helix, and the groove | channel (12f) is formed in the outer surface, it is not restricted to this, 1st The main body portion (12d) may also be formed in a spiral shape and grooves may be formed on the outer peripheral surface thereof. In this case, the spiral first main body portion (12d) is also arranged so as to contact the inner peripheral surface of the outer tube (11). Moreover, you may form a part of said 1st main-body part (12d) and 2nd main-body part (12e) helically. Further, the heat transfer tube (12) is in contact with the inner peripheral surface of the outer tube (11), and the heat transfer tube (12) is in contact with the inner peripheral surface of the outer tube (11). You may form a groove | channel on the outer peripheral surface. Furthermore, the structure which does not provide a groove | channel in the inner peripheral surface of an outer tube | pipe (11) and the outer peripheral surface of a heat exchanger tube (12) may be sufficient.

  Moreover, in the said embodiment, although the 2nd main-body part (12e) of the heat exchanger tube (12) is formed helically, it is not this limitation, Between the inlet side and outlet side of this heat exchanger tube (12) Any shape may be used as long as the pressure loss does not affect the heat exchange efficiency.

  Moreover, in the said embodiment, although the underground heat exchanger (10) is comprised by accommodating one heat exchanger tube (12) in one outer tube (11), it is not restricted to this, The outer tube may be divided in the length direction, the heat transfer tube may be divided in accordance with the outer tube, and the two may be combined. Moreover, although the several underground heat exchanger (10) is connected in parallel in the said embodiment, you may connect a part or all in series.

  Moreover, in the said embodiment, although the heat exchanger tube (12) inserted in an outer tube (11) is made from copper, it is not restricted to this, Thermal conductivity and corrosion resistance, such as aluminum, aluminum alloy, iron, or a composite material Any material may be used as long as it is excellent in material.

  Moreover, in the said embodiment, although it is comprised so that the flow direction of the refrigerant | coolant in the refrigerant circuit (2) in an air-conditioning system (1) may be switched using a four-way switching valve (4), it is not restricted to this. Any configuration may be used as long as the flow direction can be switched.

  The present invention is particularly useful for an underground heat exchanger that performs heat exchange between a refrigerant and underground soil.

Drawing 1 is a schematic structure figure of an air-conditioning system provided with the underground heat exchanger concerning the embodiment of the present invention. FIG. 2 is a longitudinal sectional view showing a schematic configuration of the underground heat exchanger. FIG. 3 is a partially enlarged perspective view of the schematic configuration of the outer tube and the heat transfer tube of the underground heat exchanger. FIG. 4 is a partial enlarged cross-sectional view showing the phase change of carbon dioxide inside the underground heat exchanger during heating operation. FIG. 5 is a diagram corresponding to FIG. 4 showing the phase change of carbon dioxide inside the underground heat exchanger during cooling operation. FIG. 6 is a diagram illustrating an example of a relationship between soil temperature and underground depth. Drawing 7 is a mimetic diagram showing the example of installation of the underground heat exchanger concerning other embodiments.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air conditioning system 2 Refrigerant circuit 3 Compressor 4 Four-way switching valve 5 Indoor heat exchanger 6 Expansion valve 7 Indoor fan 10 Ground heat exchanger 11 Outer pipe 11a Groove 12 Heat transfer pipe 12a First connection part 12b Second connection part 12c Main body 12d First main body 12e Second main body 12f Groove 13 Carbon dioxide (heat medium)
21 house 22 basement 23 basement space S space

Claims (3)

An outer pipe (11) buried vertically in the ground, a heat transfer pipe (12) inserted into the outer pipe (11) and through which the heat exchange fluid flows, and the outer pipe (11) An underground heat exchanger configured to perform heat exchange with soil using a phase change of the heat medium (13),
The outer pipe (11) is embedded in the ground so as not to be exposed to the ground surface, and the entire outer surface is covered with soil. The underground heat exchanger according to claim 1,
The underground heat exchanger is characterized in that the outer pipe (11) is buried at a predetermined depth so as to exhibit the ability required as a heat exchanger. An air conditioning system comprising the underground heat exchanger (10) according to claim 1 or 2 and performing a refrigeration cycle,
A plurality of the above-mentioned underground heat exchangers (10),
The air conditioner characterized in that the plurality of underground heat exchangers (10) are connected in parallel.

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