JP2008128494A - Geothermal utilization system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a geothermal utilization system capable of acquiring sufficient geothermal heat at low cost. <P>SOLUTION: This geothermal utilization system is composed of a geothermal acquiring portion composed of surface soil, a heat barrier buried under the surface soil, and having heat conductivity of 0.10 W/m*K or less and a thickness of 20-500 mm, and a bore hole formed under the heat barrier, a heat exchange pipe passing through the bore hole of the geothermal acquiring portion, and circulating the water or an antifreeze liquid inside over the outside of the geothermal acquiring portion, and a pump unit portion connected to the heat exchange pipe and circulating the water or the antifreeze liquid into the heat exchange pipe. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a geothermal utilization system capable of acquiring sufficient geothermal heat at a low cost.

Conventionally, non-sprinkling snow melting systems that remove snow by circulating hot water heated by kerosene boilers, gas water heaters, heat pumps, etc., or antifreeze liquid to the roadbed, etc. have high snow melting performance and can be controlled automatically without human intervention. As a system, it has been well received and constructed throughout the country.
In recent years, in order to reduce the running cost while enjoying the convenience of such a non-sprinkling snow melting system, various methods for acquiring the heat source have been studied.

For example, Patent Document 1 discloses a method of using waste hot water as a heat source for a snow melting system. According to this method, the consumption of fossil fuels such as oil can be suppressed by effectively utilizing the thermal energy of the waste water that has been discarded without being used.

However, when using the heat of the waste water, for example, the heat energy of the waste water itself may be insufficient. Also, especially from dawn to early morning, the problem of freezing due to snow, etc. is likely to occur. However, it is difficult to secure enough hot water because there is no human activity during this time. There is a problem that the necessary amount of heat cannot be secured when necessary.

On the other hand, a method of keeping the temperature of a tank in which waste hot water is stored using a water heater has been studied. However, in such a method, there is a problem that fossil fuel such as oil must be consumed after all, and impurities In some cases, there is a problem that the piping is clogged.

Further, for example, Patent Document 2 discloses a method of using geothermal heat as a heat source for a snow melting system. According to this method, use of an artificial heat source can be suppressed, and consumption of fossil fuels such as oil can be suppressed.

However, when simply excavating the ground to obtain geothermal heat, if the ground is excavated shallowly, it is necessary to use it directly for melting snow, etc. due to the influence of surface temperature and solar radiation. The geothermal heat cannot be acquired stably, and an auxiliary heat source must be installed after all.
On the other hand, in order to stably acquire sufficient geothermal energy, when the ground is deeply excavated until it reaches a stratum of 12-18 ° C throughout the year, there is a problem that the initial cost for excavation becomes extremely high. It was.
JP 2004-137727 A JP 2001-107307 A

An object of this invention is to provide the geothermal utilization system which can acquire sufficient geothermal at low cost in view of the above.

The present invention provides a surface soil, a heat shielding layer embedded under the surface soil with a thermal conductivity of 0.10 W / m · K or less and a thickness of 20 mm to 500 mm, and the heat shielding layer. A geothermal acquisition unit composed of a borehole formed below, a heat exchange pipe that passes through the borehole of the geothermal acquisition unit, circulates outside the geothermal acquisition unit, and circulates water or antifreeze liquid therein, and the heat exchange pipe And a geothermal heat utilization system comprising a pump unit that circulates water or antifreeze in the heat exchange pipe.
Hereinafter, the present invention will be described in detail.

As a result of intensive studies, the inventors of the present invention have embedded a heat shield layer having a predetermined thermal conductivity and thickness under the surface soil as a geothermal acquisition unit, and further formed a bore hole below the borehole. By acquiring geothermal heat through a heat exchange pipe, it is possible to stably acquire geothermal heat even when the borehole is formed by excavating the ground shallowly by about 5 to 10 m compared to the conventional case. As a result, the present invention has been completed.

FIG. 1 is a schematic diagram showing an example of a geothermal utilization system of the present invention. As shown in FIG. 1, the geothermal utilization system 1 has a geothermal acquisition including a surface soil 21, a heat shielding layer 22 buried below the surface soil 21, and a bore hole 23 formed below the heat shielding layer 22. A heat exchange pipe 30 that circulates water or an antifreeze liquid inside the part 20 and the bore hole 23 and circulates outside the geothermal acquisition part 20, and is connected to the heat exchange pipe 30. And a pump unit 40 for circulating the gas.
The heat exchange pipe 30 is used as the snow melting pipe portion 31 by being buried indoors or in a roadbed, for example. The water or antifreeze circulating inside the heat exchange pipe 30 passes through the borehole 23 in the geothermal acquisition unit 20 to acquire geothermal heat, and releases the acquired geothermal heat in the snow melting pipe unit 31 embedded in the roadbed.

The geothermal acquisition unit includes a surface soil, a heat insulating layer embedded under the surface soil with a thermal conductivity of 0.10 W / m · K or less and a thickness of 20 mm to 500 mm, and the heat insulating layer. A borehole formed below the layer.
In general, when excavating the ground, it varies depending on the climate of the area, the groundwater level, the presence or absence of hot springs, etc., but when the excavation depth reaches about 7 to 10 m, the underground temperature is stable throughout the year. It becomes about -18 degreeC. Even when the excavation depth is about 10 to 50 m, the temperature of the surface soil is stably about 12 ° C. to 18 ° C. throughout the year. Furthermore, when the excavation depth reaches about 100 m, the underground temperature may further increase.

The surface soil generally has a thermal conductivity of about 1.5 W / m · K, and conducts the influence of the ground surface temperature, solar radiation, wind, and the like to the ground. By blocking such influence, even when the ground is excavated shallowly, sufficient heat can be secured stably.

The surface soil is not particularly limited, and may be general soil distributed throughout the country, for example. The thermal conductivity of the surface soil varies depending on the components constituting the soil, but is preferably low.
Although it does not specifically limit as the soil which has the low heat conductivity which comprises the said surface soil, For example, you may replace with the sand etc. with a comparatively low heat conductivity and a large particle size.

The surface soil may constitute a ground surface usually used in daily life by laminating concrete, asphalt, cobblestone, or the like on the soil constituting the surface soil.
The surface soil is preferably waterproofed by using a waterproof sheet or the like. When water such as rainwater enters the soil and the porosity of the soil decreases, it is possible to prevent the thermal conductivity from increasing and easily transmitting the influence of the ground surface temperature and the like to the ground.

The heat shield layer is embedded below the topsoil layer.
By being buried in this way, it can be made less susceptible to the influence of the ground surface temperature, etc., and the heat exchange pipe passing through the borehole formed below the heat shield layer can efficiently acquire geothermal heat. Is possible.
The above heat-shielding layer has a preferable upper limit of thermal conductivity of 0.10 W / m · K. If it exceeds 0.10 W / m · K, a sufficient heat shielding effect may not be obtained. A more preferable upper limit is 0.04 W / m · K.

The heat insulation layer has a preferable lower limit of the thickness of 20 mm and an upper limit of 500 mm. If it is less than 20 mm, a sufficient heat shielding effect may not be obtained. If it exceeds 500 mm, construction may become difficult due to an increase in excavation volume or residual soil treatment. A more preferable lower limit is 50 mm, and a more preferable upper limit is 200 mm.

For example, in order to secure a temperature difference of 15 ° C., the above heat-shielding layer having a thermal conductivity of 0.03 W / m · K and a thickness of 200 mm can be used. When using 1.5 W / m · K soil, a thickness of about 5 m is required.
When such a heat shield layer is buried below the topsoil layer and a bore hole is formed below the buried heat shield layer to form a geothermal acquisition part, even if the ground is excavated shallowly Since the same geothermal heat as when deeply excavating the ground can be obtained, the depth of excavation can be reduced.

The said heat insulation layer has the preferable minimum of a closed cell rate of 85%. If it is less than 85%, thermal conductivity may be reduced by absorbing underground water. A more preferred lower limit is 90%.

In the heat shield layer, a preferable upper limit of water absorption is 1.0 g / 100 cm ³ . If it exceeds 1.0 g / 100 cm ³ , the thermal conductivity may be reduced by absorbing underground water. A more preferable upper limit is 0.1 g / 100 cm ³ .

The heat insulation layer has a preferable lower limit of compressive strength of 3.0 N / cm ² . If it is less than 3.0 N / cm ² , it may be buried in the ground and the thickness may be damaged by the weight of the soil. A more preferred lower limit is 10.0 N / cm ² .

It does not specifically limit as a raw material which comprises the said heat-shielding layer, For example, foamed polyethylene, a phenol foam, a phenol urethane foam, a urethane foam, a polystyrene foam, a foamed polycarbonate, a foamed polypropylene, a polyisocyanate foam etc. are used.

The bore hole is formed below the heat shield layer. By being formed in this way, it becomes possible for the heat exchange pipe passing through the borehole to efficiently acquire geothermal heat.
The end of the bore hole is preferably in contact with the heat shield layer. By contacting in this way, the heat exchange pipe passing through the borehole can efficiently acquire geothermal heat.
In the present specification, the borehole means a borehole, that is, a hole dug in the ground for obtaining geothermal heat.

The depth of the borehole is preferably 5 m and preferably 30 m from the viewpoint of ensuring stable and sufficient geothermal heat and cost for excavation. If it is less than 5 m, sufficient geothermal heat may not be obtained stably. If it exceeds 30 m, the cost for excavation may increase dramatically.

Although the hole diameter of the bore hole varies depending on the outer diameter of the heat exchange pipe to be inserted, the size of the tip member, and the like, the preferable lower limit is 50 mm and the preferable upper limit is 300 mm. If it is less than 50 mm, it may be difficult to insert the heat exchange pipe, or the diameter of the heat exchange pipe to be relatively inserted becomes thin, and a sufficient heat exchange effect cannot be obtained. is there. If it exceeds 300 mm, the borehole excavation cost may become extremely expensive.

A preferable lower limit of the interval between the bore holes is 1.5 m. If it is less than 1.5 m, the bore holes may interfere with each other and a desired amount of heat may not be obtained. A more preferred lower limit is 2.5 m.

The outer diameter of the end portion of the bore hole is preferably at least 3 m smaller than the outer diameter of the end portion of the heat shield layer. By having such a size, the heat shielding performance of the heat shielding layer is exhibited, and the heat exchange pipe passing through the bore hole can efficiently acquire geothermal heat.

The method for forming the bore hole is not particularly limited, and examples thereof include a boring method.

The heat exchange pipe passes through the bore hole of the geothermal acquisition unit, circulates outside the geothermal acquisition unit, and circulates water or antifreeze liquid therein.
By having such a structure, for example, in winter, the water or antifreeze liquid circulating inside the heat exchange pipe acquires geothermal heat when passing through the borehole, and acquired when passing outside the geothermal acquisition unit. Release geothermal heat. Also, for example, in summer, water or antifreeze circulating inside the heat exchange pipe acquires heat when passing outside the geothermal acquisition unit, and releases the acquired heat into the ground.

The space between the heat exchange pipe and the bore hole is preferably buried. By burying in this way, it becomes possible to quickly exchange heat between the heat exchange pipe and the surrounding underground.

The material used for burying the space between the bore hole and the heat exchange pipe is not particularly limited, and examples thereof include grout materials and excavated soil. Of these, a grout material is preferable because of its high thermal conductivity.

The antifreeze is not particularly limited, and examples thereof include those obtained by diluting ethylene glycol, propylene glycol or the like as a main component with water and adding a rust inhibitor or the like.

The heat exchange pipe includes a synthetic resin composition layer provided in an outermost layer having a thermal emissivity of 0.85 or more and a thermal conductivity of 0.80 W / m · K or more, and the synthetic resin composition layer. It is preferable that the metal composite pipe is composed of a metal layer provided on the inner surface side and a polyolefin synthetic resin layer containing at least one kind of antioxidant provided on the inner surface side of the metal layer.

Conventionally, as a heat exchange pipe utilized in a geothermal utilization system, for example, a resin tube made of plastic or a metal tube made of metal has been used. However, since the resin pipe has low thermal conductivity, it may not be possible to acquire sufficient geothermal heat, or the acquired thermal energy may not be used for melting snow or the like. In addition, depending on the resin used, it may be deteriorated by heat, soil microorganisms, water, antifreeze from which the copper of the equipment is eluted. Furthermore, the resin pipe has poor self-supporting property, and in order to embed it in asphalt, concrete or the like on the road surface, a shape maintaining means such as a metal net is required.

On the other hand, metal pipes have high thermal conductivity, but there is a possibility that corrosion will occur due to water or the like, particularly at joints. Moreover, since the weight is large and flexibility is low, workability | operativity may be inferior. As described above, neither a resin tube nor a metal tube is an optimum material for a heat exchange pipe used in a geothermal utilization system from the viewpoint of thermal performance, corrosion resistance, flexibility, self-supporting property, weight, and the like.
Therefore, it has excellent thermal conductivity, corrosion resistance, light weight, excellent workability, flexibility that enables bending, etc., and self-supporting ability to hold the shape until concrete is cured. There has been a demand for a heat exchange pipe that can be easily embedded inside.

As a result of intensive studies, the present inventors can efficiently exchange heat by using the above metal composite tube, and can obtain excellent corrosion resistance, bending workability, shape retention, and the like. I found out.
In FIG. 2, the schematic diagram which shows an example of the cross section of a metal composite pipe was shown. In FIG. 2, 51 is a synthetic resin composition layer, 52 is a metal layer, and 53 is a polyolefin synthetic resin layer.

In the metal composite tube, the synthetic resin composition layer constitutes an outermost layer.
Examples of the resin composition constituting the synthetic resin composition layer include those composed of heat-resistant polyethylene, crosslinked polyethylene, polypropylene, polybutene, polyphenylene sulfide (PPS), polyethylene terephthalate, vinyl chloride, and the like.
Especially, since heat conductivity and heat emissivity are favorable, it is preferable to use heat-resistant polyethylene and crosslinked polyethylene.

The synthetic resin composition layer preferably contains an inorganic material 1 such as metal or carbon. Thus, by containing the inorganic material 1, desired high heat conductivity can be obtained.

The inorganic material 1 is not particularly limited, and examples thereof include iron, tin, zinc, gold, copper, silver, chromium, titanium, magnesium, alumina, silicon nitride, carbon graphite, and oxides thereof.

In the synthetic resin composition layer, the blending amount of the inorganic material 1 varies depending on the particle surface state, specific gravity and the like of the inorganic material to be used, but a preferred lower limit is 10% by weight and a preferred upper limit is 100% by weight. If it is less than 10% by weight, the desired thermal conductivity may not be obtained. If it exceeds 100% by weight, moldability and the like may deteriorate. A more preferred upper limit is 50% by weight.

The synthetic resin composition layer preferably contains an inorganic material 2 such as silicon oxide, titanium oxide, manganese oxide, sodium silicate, silicon carbide, carbon black, or natural serpentine. Thus, by containing the inorganic material 2, it becomes possible to obtain desired thermal radiation.

The shape of the inorganic material 2 is not particularly limited, and may be granular, needle-like, or the like. For example, it is preferable to adjust the particle size so that a close-packed structure is obtained.

In the synthetic resin composition layer, the blending amount of the inorganic material 2 varies depending on the particle surface state, specific gravity and the like of the inorganic material 2 to be used, but the preferred lower limit is 3% by weight and the preferred upper limit is 33% by weight. If it is less than 3% by weight, the desired thermal radiation may not be obtained. If it exceeds 33% by weight, moldability and the like may be deteriorated.
The synthetic resin composition layer may further contain various additives such as a viscosity modifier and a surfactant.

The preferable lower limit of the thickness of the synthetic resin composition layer is 0.01 mm, and the preferable upper limit is 5 mm. If the thickness is less than 0.01 mm, the synthetic resin composition layer may be broken when the metal composite tube is bent. When it exceeds 5 mm, thermal conductivity may deteriorate, rigidity may increase, and flexibility may decrease. A more preferable lower limit is 0.2 mm, and a more preferable upper limit is 2.0 mm.

In the metal composite tube, the metal layer constitutes an intermediate layer.
The metal constituting such a metal layer usually has an excellent thermal conductivity of several hundred times more than that of a resin and the like, and has an excellent strength, so that the thermal conductivity of the metal composite tube as a whole is improved. Is possible.

The metal constituting the metal layer is not particularly limited as long as it is a metal having excellent thermal conductivity, and examples thereof include iron, brass, copper, stainless steel, aluminum, titanium, and a silver alloy.

If necessary, the metal constituting the metal layer may be subjected to blast treatment, degreasing treatment with alkali, treatment with acid such as hydrochloric acid, nitric acid, sulfuric acid, or the like. Thus, deterioration of the adhesiveness between the metal layer and the synthetic resin composition layer or the adhesiveness between the metal layer and the polyolefin synthetic resin layer can be prevented.

In the metal composite pipe, the polyolefin synthetic resin layer constitutes the innermost layer of the metal composite pipe.
It does not specifically limit as polyolefin-type resin which comprises the said polyolefin synthetic resin layer, For example, polyethylene, crosslinked polyethylene, a polypropylene, polybutylene etc. are mentioned.

Considering that the temperature of water circulating inside the heat exchange pipe may be about 90 ° C. at the maximum as the polyolefin resin, a preferable lower limit of the Vicat softening temperature is 115 ° C. A more preferred lower limit is 120 ° C.

As the polyolefin-based resin, for example, short chain branching is introduced by copolymerizing with α-olefin such as propylene, butene, hexene, octene, 4-methylpentene, and the number average molecular weight is 15,000 to 50000, weight average A polyethylene resin composition having a molecular weight of 80,000 to 150,000 is preferred. By using such a polyethylene-based resin composition, it is possible to further improve the stability and durability at high temperatures while suppressing the material cost.

The polyolefin synthetic resin layer contains at least one kind of antioxidant. By containing an antioxidant, it is possible to prevent deterioration due to an oxidation reaction caused by the action of light, heat, transition metal ions, and the like.

The antioxidant is not particularly limited, and examples thereof include phenolic antioxidants such as 3,5-di-t-butyl-4-hydroxybenzylbenzene and 4-methyl-6-t-butylphenol, and triphenyl phosphite. And phosphorus-based antioxidants such as trinonylphenyl phosphite, and ionic antioxidants such as dilauryl thiodipropionic acid ester and distearyl thiodipropionic acid ester.
These antioxidants may be used alone or in combination of two or more.

As the antioxidant, for example, it is preferable to use a phenol-based antioxidant and a phosphorus-based antioxidant in combination, or to use a phenol-based antioxidant and a sulfur-based antioxidant in combination. By using together in this way, the antioxidant effect and the yellowing prevention effect by the production | generation of quinones are acquired.

The amount of the antioxidant added is preferably 0.001 part by weight and preferably 5 parts by weight with respect to 100 parts by weight of the polyolefin resin. If it is less than 0.001 part by weight, a sufficient antioxidant effect may not be obtained. When the amount exceeds 5 parts by weight, deterioration of physical properties of the resin or deterioration of water quality due to elution into water may occur.

The polyolefin synthetic resin layer may further contain various additives such as a viscosity modifier, a surfactant, an antistatic agent, a flame retardant, a dew condensation inhibitor, and these master batches. For example, the moldability can be improved by containing a viscosity modifier.

The polyolefin synthetic resin layer has a preferable lower limit of thickness of 0.3 mm and a preferable upper limit of 5.0 mm. If it is less than 0.3 mm, water or the like may reach the metal layer and cause corrosion due to deterioration caused by movement of water or the like, or generation of microcracks when bent. If it exceeds 5.0 mm, the thermal conductivity may decrease, or the rigidity may increase and the flexibility may decrease. A more preferable lower limit is 1 mm, and a more preferable upper limit is 3 mm.

A preferable lower limit of the diameter of the metal composite tube is 3 mm, and a preferable upper limit is 50 mm. If it is less than 3 mm, clogging may occur when foreign matter or the like is mixed. If it exceeds 50 mm, the handleability deteriorates, and the weight of water or the like that is held increases, so the installation part in the house may be damaged.

In the above-mentioned metal composite tube, in order to improve the adhesion between the synthetic resin composition layer, the metal layer, and the polyolefin synthetic resin layer, an adhesive may be applied between the layers as necessary. Good.

The upper limit of the thickness of the adhesive layer formed by applying the adhesive is preferably 0.5 mm. If it exceeds 0.5 mm, the thermal conductivity between the layers may be impaired.

The said heat exchange pipe can comprise a snow melting pipe part by laying in a house or a roadbed. With such a snowmelt pipe section, it is possible to release the geothermal heat acquired in the geothermal acquisition section and remove snow on the house or roadbed.
The shape of the heat exchange pipe constituting the snow melting pipe portion is not particularly limited as long as it has a conventionally known shape.

The said heat exchange pipe can comprise an air-conditioning piping part by laying in a house. By using such an air conditioning piping unit, for example, water or antifreeze liquid is circulated through the air conditioning piping unit in summer, high indoor heat is acquired, the acquired heat is discharged into the ground, and used as air conditioning for cooling the house. Can do. Thus, the geothermal utilization system that has been used only in the winter can be used in the summer, and the consumption of fossil fuels such as oil can be suppressed using geothermal heat throughout the year.

It does not specifically limit as a shape of the heat exchange pipe which comprises the said air-conditioning piping part, What is necessary is just to have a conventionally well-known shape.
Depending on the shape of the air-conditioning piping section, a heat radiating pipe having fins may be used, or a fan may be used in combination.

FIG. 3 is an exploded perspective view schematically showing a radiant cooling / heating panel as an example of an air conditioning piping section. As shown in FIG. 3, when the heat exchange pipe 60 is attached to the header 61 to form a panel, the heat exchange pipe 60 is disposed between the pair of headers.
That is, the pair of headers 61 are arranged so that the surfaces provided with the openings 62 face each other, and the openings 62 of each header 61 and the ends of the heat exchange pipes 60 arranged in parallel according to the number of the openings 62 are arranged. It is attached via the connection fitting 63. As shown in FIG. 3, the connection fitting 63 attached to one end of the heat exchange pipe 60 is preferably attached to the opening 62 of the header 61 via a flow rate adjusting valve 64.

As shown in FIG. 3, when using a radiation cooling / heating panel in which the heat exchange pipe 60 is attached to the header 61, the cooling / heating medium passes from the flow path 65 of one header 61 to each opening 62, and the heat exchange pipe Supplied inside 60, circulates from the opening 62 of the other header 61 to the flow path 65.

The pump unit is connected to the heat exchange pipe and circulates water or antifreeze liquid in the heat exchange pipe. By having such a structure, water etc. can be circulated to the geothermal utilization system of the present invention through the heat exchange pipe.

The pump unit is not particularly limited as long as it has a structure capable of circulating water or antifreeze, and a conventionally known pump or the like can be used.
The pump unit section preferably has a throttle valve, inverter control, and the like. By having such a throttle valve or the like, it becomes possible to adjust the flow rate of water or the like according to a load such as snow melting.

The pump unit section preferably has a valve mechanism for switching a circulation path of water or antifreeze. By having such a valve mechanism, the circulation path of the water or antifreeze liquid circulating inside the heat exchange pipe can be switched and changed. Thus, for example, in winter, by circulating water or antifreeze liquid in the snow melting pipe part, high geothermal heat in the ground can be acquired, and the acquired heat can be released on the road and used for snow melting. In addition, in summer, water or antifreeze can be circulated through the air conditioning piping section to acquire high indoor heat, release the acquired heat into the ground, and use the air conditioning to cool the room. Thus, since the geothermal utilization system that has been used only in the winter can be used in the summer, geothermal heat can be used throughout the year and consumption of fossil fuels such as oil can be suppressed.
The valve mechanism is not particularly limited, and examples thereof include conventionally known valve mechanisms such as a three-way valve and a four-way valve.

FIG. 4 is a schematic diagram showing an example of the geothermal utilization system of the present invention having the valve mechanism and the air conditioning piping section. As shown in FIG. 4, the geothermal utilization system of the present invention includes a three-way valve 7 and an air conditioning piping section 32 as a valve mechanism. By using the three-way valve 7 and switching the circulation path of the water or antifreeze liquid circulating inside the heat exchange pipe, it becomes possible to circulate the water or the like circulating through the snow melting pipe section to the air conditioning piping section 32. .

ADVANTAGE OF THE INVENTION According to this invention, the geothermal utilization system which can acquire sufficient geothermal at low cost can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
After excavating 50 cm of the ground in our laboratory, a borehole (depth 10 m, diameter 88 mm) was excavated, and a heat exchange pipe made of cross-linked polyethylene having an inner diameter of 20 mm was inserted. Furthermore, a borehole for heat measurement (depth 10 m, diameter 88 mm) was excavated at a position 50 cm away from it, a position 100 cm further away, and a position 500 cm further away, and a thermocouple was inserted.
Polystyrene foam (thickness 20 cm, 3600 cm square, thermal conductivity 0.028 W / m · K, compressive strength) prepared by extruding each borehole with mountain sand (thermal conductivity 1.34 W / m · K) 17.3 N / cm ² ) is laid around the bore hole with the heat exchange pipe inserted above, and the excavation residual soil generated by excavating the ground is placed thereon, and the ground surface is returned to the original state. The geothermal utilization system was made.

(Example 2)
A polyethylene resin composition (Vicat softening temperature 123 ° C.) having a number average molecular weight of about 30,000 and a weight average molecular weight of about 120,000 by copolymerizing octene as an α-olefin to introduce short chain branching, and 4 as a phenolic antioxidant. -0.1 parts by weight of methyl-6-t-butylphenolphenol and 0.05 parts by weight of trinonylphenyl phosphite as a phosphorus antioxidant, and after molding a polyolefin synthetic resin layer using an extruder, An aluminum plate having a thickness of 0.28 mm is wound from the outside on the extension line in the traveling direction to obtain a tubular molded body having an inner diameter of 20 mm comprising a polyolefin synthetic resin layer and a metal layer formed on the outer periphery of the polyolefin synthetic resin layer. It was.
Next, a master batch obtained by kneading and extruding high-density polyethylene (P9820, manufactured by Maruzen Petrochemical Co., Ltd.), 10% by weight of 50 μm silicon oxide, and 5% by weight of carbon black having a particle size of 10 μm is described above. A synthetic resin composition layer is formed from the outside with an extruder on the outer periphery of the metal layer of the tubular molded article, a polyolefin synthetic resin layer, a metal layer formed on the outer periphery of the polyolefin synthetic resin layer, and the metal layer The metal composite pipe | tube which consists of a synthetic resin composition layer formed in the outer periphery of this was produced.
A geothermal utilization system was produced by the same method as in Example 1 except that the obtained heat exchange pipe was used instead of using the heat exchange pipe made of crosslinked polyethylene.
In addition, when the thermal emissivity and thermal conductivity of the obtained synthetic resin composition layer were measured using an emissivity measuring device (manufactured by D & A), the thermal conductivity was 1.02 W / m · K, thermal radiation. The rate was 0.94. Moreover, the thickness of the polyolefin synthetic resin layer of the obtained metal composite pipe was 1.2 mm, and the thickness of the synthetic resin composition layer was 0.3 mm.

(Comparative Example 1)
A geothermal utilization system was produced in the same manner as in Example 1 except that polystyrene foam was not used.

(Evaluation)
The following evaluation was performed about the geothermal utilization system obtained in Examples 1 and 2 and Comparative Example 1. The results are shown in Table 1.

(1) Cold water 5 ° C. was used as the acquired heat quantity snow melting load, and water was circulated through the heat exchange pipe at a flow rate of 0.5 L / s. The return temperature warmed by geothermal heat was measured, and the amount of heat acquired per hour (W) was determined from the temperature difference and flow rate one week after the start of water flow.

(2) Warm water was circulated through the heat exchange pipe at a flow rate of 0.5 L / s, with the hot water at 32 ° C. as the outgoing temperature as the heating load of the released heat. The temperature of the cooling water that released heat underground was measured, and the amount of heat released per hour (W) was determined from the temperature difference and flow rate one week after the start of water flow.

ADVANTAGE OF THE INVENTION According to this invention, the geothermal utilization system which can acquire sufficient geothermal at low cost can be provided.

It is a schematic diagram which shows an example of the geothermal utilization system of this invention. It is a schematic diagram which shows an example of the cross section of a metal composite pipe. It is a disassembled perspective view which shows typically the panel for radiation cooling / heating as an example of an air-conditioning piping part. It is a schematic diagram which shows an example of the geothermal utilization system of this invention which has a valve mechanism and an air-conditioning piping part.

Explanation of symbols

1 Geothermal utilization system 20 Geothermal acquisition unit
21 Surface soil 22 Heat insulation layer 23 Bore hole 30 Heat exchange pipe 31 Snow melting pipe part 32 Air conditioning piping part 40 Pump unit part 41 Snowfall sensor
51 Synthetic resin composition layer 52 Metal layer 53 Synthetic resin composition layer 60 Heat exchange pipe 61 Header 62 Opening 63 Connection fitting 64 Flow rate adjusting valve 65 Flow path 7 Three-way valve

Claims (2)

A surface soil, a heat shielding layer buried under the surface soil with a thermal conductivity of 0.10 W / m · K or less and a thickness of 20 mm to 500 mm, and formed below the heat shielding layer. A geothermal acquisition unit consisting of a borehole,
A heat exchange pipe that passes through the borehole of the geothermal acquisition unit, circulates outside the geothermal acquisition unit, and circulates water or antifreeze liquid therein;
A geothermal heat utilization system comprising a pump unit connected to the heat exchange pipe and circulating water or antifreeze liquid in the heat exchange pipe. The heat exchange pipe has a thermal conductivity of 0.80 W / m · K or more provided in the outermost layer and a thermal emissivity of 0.85 or more, and the synthetic resin composition layer. 2. A metal composite pipe comprising a metal layer provided on the inner surface side and a polyolefin synthetic resin layer containing at least one kind of antioxidant provided on the inner surface side of the metal layer. The geothermal utilization system described.

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