JP7124263B2 - Sampling heat pipe and geothermal heat pump using it - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat collecting pipe and a geothermal heat pump using the same, and more particularly to a heat collecting pipe used in a direct expansion type geothermal heat pump and a geothermal heat pump using the same.

There are two types of geothermal heat pumps: indirect type and direct expansion type. In the indirect method, a heat exchanger is installed in the outdoor unit of the heat pump between a refrigerant such as a CFC alternative and water or antifreeze (called brine), and the heat of the refrigerant is given to the brine. The brine is introduced into a resin or metal pipe provided inside, and heat is taken out and released from the ground indirectly through this brine. (Patent Documents 1 and 2)

On the other hand, in the direct expansion method, a copper circular pipe is buried in the ground shallower than the indirect method (about 30m deep) to act as an underground heat exchanger. In this method, heat is extracted from the ground by introducing it into an exchanger. For this reason, CFC substitute refrigerants are used as refrigerants.

In the direct expansion method, the refrigerant is introduced directly into the underground heat exchanger, so the underground heat exchanger becomes an evaporator during heating operation and a condenser during cooling operation. It becomes a flow that accompanies change.

In geothermal heat pumps, various measures have been taken to increase the efficiency of heat extraction. For example, as shown in Patent Documents 1 and 2, a method for preventing unnecessary heat exchange by using a heat insulating material in a heat collecting pipe or the like is shown.

In addition, in the direct expansion type geothermal heat pump, it is necessary to deal with the phase change of the refrigerant. For this reason, as in Non-Patent Document 1, for example, a radiation extraction tube having a configuration in which a portion of a U-shaped radiation extraction tube is wrapped with a heat insulating material has been proposed.

JP 2014-005981 A JP 2014-084857 A

Norihiko Muramatsu et al., The Japan Society of Mechanical Engineers 2016 Annual Meeting, Exchange Performance of Direct Expansion Geothermal Heat Pump - Performance of Geothermal Heat Exchanger -, 9/11-14, 2016

There is a demand for measures to increase the efficiency of heat collection and heat collection in direct expansion type geothermal heat pumps, which cause phase changes in the refrigerant.

The heat collection pipe of the present invention is a heat collection pipe for a direct expansion geothermal heat pump that is housed in a casing pipe buried in the ground, and the heat collection pipe comprises a main pipe and a part of the main pipe. The main pipe has first and second inlets and outlets through which the refrigerant flows in and out, a first pipe from the first inlet to an end, and a second outlet. a second pipe from the inlet to the end, the first pipe and the second pipe being connected to each other at the end so as to communicate with each other, the first and second inlets being on the ground surface side of the casing pipe and the end is located at the deepest position in the sampling and radiation pipe when the casing pipe is buried, the first pipe is covered with a heat insulating material, and the heat insulating material covers the first pipe up to at least the end It is characterized by being configured as follows.

The ground source heat pump of the present invention includes the heat collection tube.

It is possible to increase the efficiency of the heat sampling/radiating pipe of the direct expansion type geothermal heat pump.

It is a figure which shows the 1st example of the heat collection tube of this invention. It is a figure which shows an example of the geothermal heat pump using the heat collection tube of this invention. FIG. 10 is a diagram showing a second example of the heat-collecting/radiating tube of the present invention; FIG. 10 is a diagram showing a third example of the heat-collecting/radiating tube of the present invention;

(Example 1)
(Constitution)
A first example of the heat collecting pipe of the present invention is shown in FIG. 1, and an example of a geothermal heat pump using the heat collecting pipe 11 of the present invention is shown in FIG.

As shown in FIG. 1, the heat collection tube 11 has a main tube 4 and a heat insulating material 5 covering a portion of the main tube 4 . The main pipe 4 is a U-shaped pipe provided with inlets and outlets 1 and 2 for the refrigerant, and is the main body of the pipe through which the refrigerant flows. The inlets 1 and 2 are refrigerant inlets or outlets depending on the operation mode of the geothermal heat pump. Further, the main pipe 4 includes a first pipe 41 from the first inlet 1 to the end 3 and a second pipe 42 from the second inlet 2 to the end 3. The tube 41 and the second tube 42 are communicatively connected to each other at the end 3 . Also, the first pipe 41 is covered with a heat insulating material (heat insulating material) 5 and configured to cover at least the end portion 3 of the heat insulating material 5 . Here, the end portion 3 is the portion corresponding to the deepest position when the main pipe 4 is installed in the ground as shown in FIG. The end (or end point) 3 is thus the deepest or lowest point of the main pipe 4 .

In the example of FIG. 1, the first pipe 41 has a linear portion 41a extending linearly from the first inlet/outlet 1 toward the end portion 3, and a curved portion 41b formed by bending the pipe 41 to form a U-shaped bottom. and Straight portion 41a and curved portion 41b are configured such that the tubes communicate with each other at point B where tube 41 begins to bend. Similarly, the second pipe 42 has a straight portion 42a extending straight from the second inlet/outlet 2 toward the end portion 3, and a curved portion 42b formed by bending the pipe 42 to form a U-shaped bottom. ing. Straight portion 42a and curved portion 42b are configured such that the tubes communicate with each other at point C where tube 42 begins to bend. Note that the points B and C may be configured to be parallel to the horizontal plane when the geothermal heat pump using the radiation sampling pipe 11 is installed in the ground.

A copper pipe, for example, can be used for the main pipe 4 . Also, a diameter of about 3/8 inch, for example, can be used.

In the example shown in FIG. 1 , the heat insulating material 5 is composed of a heat insulating material 51 covering the straight portion 41 a of the first pipe 41 and a heat insulating material 52 covering the curved portion 41 b of the first pipe 41 . In addition, the heat insulating material 5 may cover up to including the first flow inlet 1 . Alternatively, the main pipe 4 may cover up to the water surface portion of the water 7 filled in the casing pipe 6 . Preferably, the entire piping from the first inlet/outlet to the air conditioner should be covered with the heat insulating material 5 . Also, if the performance is good, the part slightly submerged in water 7 may be used as shown in FIG.

In the geothermal heat pump of this example, a casing pipe 6 is placed in a borehole 9 formed in the ground, and the casing pipe 6 is filled with water 7 and the above-described sampling and radiation pipe 11 is installed in the casing pipe 6 . Here, it is preferable to fill the space between the casing pipe 6 and the borehole 9 with silica sand 8 .

As the refrigerant, for example, a CFC substitute such as R410A or R32 can be used.

In this example, the heat collecting pipe 11 for a direct expansion type geothermal heat pump is housed in a casing pipe 6 buried in the ground. 5, the main pipe 4 includes first and second inlets (1, 2) through which the refrigerant flows in or out, and a first pipe 41 from the first inlet 1 to the end 3. , and a second pipe 42 from the second inlet/outlet 2 to the end 3, the first pipe 41 and the second pipe 42 being connected to each other at the end 3 so as to communicate with each other. The inlet and outlet of 2 are provided on the ground surface side of the casing pipe, the end 3 is located deepest in the heat collection pipe when the casing pipe is buried, and the first pipe 41 is a heat insulating material (heat insulating material) 5 , and the heat-insulating material 5 covers the first tube 41 up to at least the end 3 .

(motion)
In the heating operation, the liquid refrigerant is allowed to flow in from the inlet/outlet 1 (first inlet/outlet) of the main pipe 4 of the heat sampling/radiating pipe 11 . Here, the first pipe 41 of the main pipe 4 is covered with the heat insulating material 5 up to the end (lowermost part) 3 . Therefore, when the liquid refrigerant flows from the ground through the first pipe 41 of the main pipe 4, it receives heat from the ground and does not evaporate (vaporize).

In other words, the portion where the flow of the refrigerant in the main pipe 4 reverses from downward flow to upward flow (at least up to the portion including the end portion 3) is covered with the heat insulating material (heat insulating material) 5 to cut off the underground heat. there is As a result, while the liquid refrigerant in the main pipe 4 is flowing down, bubbles due to evaporation are not generated, and the generation of bubbles is eliminated until the liquid refrigerant reverses its upward flow. In other words, the second pipe 42 without heat insulating material 5 acts as an evaporator, and the first pipe 41 covered with heat insulating material 5 can be regarded as a bubble eliminator. The refrigerant that has passed through the end portion 3 flows upward through the second pipe 42 of the main pipe 4, where it receives heat from the ground and evaporates (vaporizes). The evaporated (vaporized) warm refrigerant flows out from the outlet 2 (second outlet) of the main pipe 4 and is used for heating.

On the other hand, in the cooling operation, the gaseous refrigerant is allowed to flow in from the inlet/outlet 2 (second inlet/outlet) of the main pipe 4 of the heat sampling/radiating pipe 11 . Here, the first pipe 41 of the main pipe 4 is covered with the heat insulating material 5 up to the end (lowermost part) 3 . For this reason, while the gaseous refrigerant flows down the second pipe 42 of the main pipe 4 from the ground, it radiates heat into the ground and condenses to become a liquid refrigerant. , while rising to the ground through the first pipe 41 of the main pipe 4, the liquid refrigerant receives heat from the ground and does not evaporate (vaporize) again. In other words, the second tube 42 without insulation 5 acts as a condenser and the first tube 41 covered with insulation 5 can be regarded as a bubble eliminator. The refrigerant that has passed through the end 3 flows upward through the first pipe 41 of the main pipe 4, where it is taken out as a liquid-cooled refrigerant from the inlet/outlet 1 of the main pipe 4 without evaporating (vaporizing) again, Used for cooling.

(Example 2)
FIG. 3 shows a second example of the invention. FIG. 3 shows an example in which the radiation sampling tube 11 of FIG. 1 is replaced with a radiation sampling tube 11'. Specifically, FIG. 3 is a diagram showing a case where the curved portion 42b of the second pipe 42 of the main pipe 4 of the heat sampling/radiating pipe 11' beyond the end portion 3 is covered with the heat insulating material 5. 1 is the same as the example shown in FIG. The heat insulating material 5 is composed of a heat insulating material 51 covering the straight portion 41 a of the first pipe 41 and a heat insulating material 52 ′ covering the curved portion 41 b of the first pipe 41 and the curved portion 42 b of the second pipe 42 . and the insulation 52 ′ is configured to completely contain the end 3 . By constructing in this manner, even the portion where the direction of flow of the refrigerant is completely switched is covered. In other words, the second pipe 42 is further covered with the heat insulating material 5 from the end 3 to the portion where the second pipe 42 is formed perpendicular to the ground surface. As a result, it is possible to more completely prevent the generation of air bubbles in the first pipe 41 and the backflow of the generated air bubbles during cooling and heating, and to improve the efficiency. In this example, the portion of the second pipe 42 without the heat insulating material 5 functions as an evaporator (during heating operation) or a condenser (during cooling operation).

In addition, when the geothermal heat pump using the radiation sampling pipe 11 ′ is installed in the ground, the point B and the point C are configured to be parallel to the horizontal surface, beyond the end 3 and point It is preferable to cover up to C with the heat insulating material 5 . More preferably, the second pipe 42 of the main pipe 4 of the heat collection pipe 11' is covered with the heat insulating material 52' from the end 3 to a position higher than 100 mm.

(Example 3)
FIG. 4 shows a third example of the invention. FIG. 4 shows an example in which the radiation sampling tube 11 in FIG. 1 is replaced with a radiation sampling tube 11''. Specifically, FIG. 4 is obtained by replacing the second tube 42 of the main tube 4 of the heat sampling/radiating tube 11 in FIG. 1 with a second tube 42' provided with a plurality of parallel tubes. Alternatively, the second pipe 42 is configured to include a plurality of pipes connected via branch pipe portions (branch portions) 10 and arranged in parallel with each other. In FIG. 4, the heat insulating material covers the first pipe 41 up to the end 3 as in the example of FIG. Alternatively, as in the example of FIG. 3 , the heat insulating material 5 may cover the curved portion 42 b of the second tube 42 of the radiation sampling tube 4 beyond the end 3 . Alternatively, even the branch pipe section 10 to a plurality of parallel pipes may be covered.

By adopting such a configuration, the heat transfer area can be increased in a portion of the second pipe 42 which is not wrapped with the heat insulating material 5 and serves as a condenser during cooling operation, and efficiency can be improved. be done. Furthermore, it is effective to use a plurality of circular copper tubes each having a diameter smaller than that of the first tube to configure the condensation section. For the reasons described later, it is preferable that the number of parallel pipes is an odd number (excluding one), and more preferably three.

(Experiment/Consideration)
During heating operation, the heat collection pipe acts as an evaporator, so when the liquid refrigerant collects heat from the ground and evaporates at the part where the liquid refrigerant flows down from the inlet of the heat collection pipe to the inside of the pipe, the liquid refrigerant flows down. Evaporation bubbles may be generated from the surface of the collecting heat tube. For this reason, buoyancy is generated in the refrigerant flowing down through evaporation due to the generation of bubbles, and the flow resistance of the refrigerant flow increases, increasing the load on the compressor, resulting in an increase in power consumption. On the other hand, during cooling operation, when the vapor-phase refrigerant flows down the intake/radiating pipe, it radiates heat into the ground and condenses, and the liquid-phase refrigerant reverses at the bottom of the heat exchanger and rises. Part of the heat released during condensation from the collecting and radiating pipes where the water and gaseous refrigerant flows down is transmitted to the collecting and radiating pipes where the liquefied refrigerant rises, and when the refrigerant evaporates due to the heat again, it goes underground. The total heat dissipation from the heat exchanger is reduced, which reduces the coefficient of performance and reduces performance.

In order to prevent performance deterioration due to these, a heat insulating material with a minute air layer, which is used for heat insulation of the connecting copper pipe between the outdoor unit and the indoor unit of a commercially available air heat pump, was used to cut the portion corresponding to the pipe 41a in FIG. By covering it, it is possible to suppress the evaporation of the liquid-phase refrigerant in the sampling/radiating pipe, which is the part where the refrigerant flows down during heating operation, and the re-evaporation of the liquid-phase refrigerant in the sampling/radiating pipe, which is the part where the refrigerant rises during cooling operation. Performance has improved.

However, it was visually confirmed that the heat insulating material was crushed by the water pressure inside the casing pipe filled with water at a depth of 10 m or more underground. From this, it is considered that the insulation performance is declining, and although the performance has improved to some extent, the following construction is essential for the optimum design.

First, it is necessary to prevent condensation and evaporation of the refrigerant as much as possible in the portion of the U-shaped intake/radiator pipe that functions as a condenser and an evaporator. Especially in heating or hot water supply operation, in the part where the liquid refrigerant flows down in the U-shaped heat collecting and radiating pipe, the heat received from the wall of the collecting and radiating pipe causes evaporation bubbles in the flow of the liquid refrigerant, which increases the load on the compressor. The coefficient of performance may drop significantly as power consumption increases. For this reason, as in the first embodiment, it is necessary to cover at least the end portion 3 of the heat collection tube 11 with the heat insulating material 5 . Preferably, even the curved portion 42a of the second tube 42 of the main tube 4 of the radiation sampling tube 11' is covered with the heat insulating material 52' as in the second embodiment. Furthermore, in Example 2, it is more preferable that the second tube 42 of the heat-collecting/radiating tube 4 insulates a section from the end 3 to a position higher than 100 mm.

In addition, it is necessary to confirm that the flow is turbulent from the Reynolds number when the diameter of the circular pipe is D as liquid refrigerant. A distance of about 20D or more is required as the straight pipe section distance.

As a result, it is possible to reliably prevent the mixture of the vapor-phase refrigerant that has evaporated while the liquid refrigerant is flowing down. can be prevented and energy saving performance can be maintained.

During the cooling operation, part of the heat-collecting/radiating pipes (11, 11', 11'') functions as a condenser. When the vapor-phase refrigerant flows down through the collecting and radiating pipes (11, 11', 11''), it radiates heat into the ground and condenses. 11''), the second pipe 42 of the main pipe 4 of the heat-collecting/radiating pipe is made of a plurality of circular copper pipes with a small diameter so as to increase the heat transfer area. Then, the plurality of copper circular tubes were configured to serve as the condensation section.

At this time, in the results of experiments conducted with multiple pipes of two or four, vibrations were observed in the refrigerant flow in the multiple circular pipe flow paths, especially when functioning as an evaporator, which is a heating operation, and the flow was stable. It was confirmed that the refrigerant could not evaporate. Furthermore, in the case of parallel boreholes with two boreholes containing heat exchangers, it was confirmed that the performance during heating operation was not stable. I found out. Therefore, an odd number (1, 3 or 5) of copper circular tubes is preferable for the part corresponding to the condensing part in the second tube 42 of the main tube 4 of the heat sampling tube. In particular, the optimum number of multiple tubes is three. This is due to the fact that the equilateral triangular arrangement in manufacturing the branch pipes (branching parts) makes it possible to equalize the distances of the respective circular pipes, thereby facilitating equal distribution of flow rates. By adopting this configuration as shown in the third embodiment, it is possible to further suppress the increase in the power consumption of the compressor and improve the efficiency.

In addition to this, by applying a material with low thermal conductivity, such as polyethylene pipe or VP pipe, to the outside of the copper pipe, insulation performance is maintained while preventing deformation of the insulation due to water pressure. It is possible to prevent the deterioration of energy-saving performance by maintaining

It has been confirmed from consideration of the temperature change in the borehole that the condensation process during cooling operation will be completed if the distance of the multiple pipe sections housed in the borehole is 20m at the minimum and 30m at the maximum. If the heat is insulated from the second pipe 42 of the main pipe 4 of the heat-sampling/radiating pipe located at a position higher than 100 mm to the above-ground pipe, the power consumption of the compressor can be suppressed and the efficiency can be improved.

For the convenience of explanation, the heat-collecting/radiating tube is U-shaped in the embodiment, but the present invention can be applied to other shapes. For example, the second tube may be a spiral tube. Further, the cross section of the tube is not limited to circular, and may be elliptical, rectangular, or the like.

Reference Signs List 1, 2 inlet/outlet 3 end 4 main pipe 5 heat insulating material 6 casing pipe 7 water 8 silica sand 9 borehole 10 branch pipe portions 11, 11', 11'' sampling heat pipe

Claims (10)

A sampling and radiating pipe for a direct expansion geothermal heat pump to be housed in a casing pipe buried underground,
The heat sampling/radiating pipe comprises a main pipe and a heat insulating material covering a part of the main pipe,
Said main is
a first pipe having a first inlet/outlet through which a liquid refrigerant flows in or out and extending from the first inlet/outlet to an end;
a second pipe having a second inlet/outlet for inflow or outflow of a gaseous refrigerant and extending from the second inlet/outlet to the end,
the first tube and the second tube are connected at the ends so as to communicate with each other;
The first and second inlets and outlets are provided on the ground surface side of the casing pipe,
the end is located at the deepest point in the radiation sampling tube when the casing tube is buried;
the first tube is covered with the insulating material, and the insulating material covers the first tube at least up to the end;
The second pipe has a plurality of pipes connected via branch pipe portions and arranged in parallel with each other, and the diameter of each of the plurality of pipes is smaller than the diameter of the first pipe. collection tube. 2. The radiation sampling tube according to claim 1, wherein said second tube is further covered with said heat insulating material from said end portion to a portion where said second tube is formed perpendicularly to said ground surface. 3. The heat collection tube according to claim 1, wherein said second tube is further covered with said heat insulating material to a position higher than said end by 100 mm or more. 2. The heat collection tube according to claim 1 , wherein the second tube is covered with the heat insulating material from the end portion to the branch tube portion. 2. The heat collection tube according to claim 1 , wherein said plurality of tubes is an odd number excluding one. 2. The heat collection tube according to claim 1 , wherein said plurality of tubes is three. 7. The heat collecting/radiating tube according to any one of claims 1 to 6 , wherein when the liquid refrigerant flows from the first inlet/outlet, the refrigerant starts to evaporate from a portion not covered with the heat insulating material. . When the gaseous refrigerant flows from the second inlet/outlet, the refrigerant condenses and becomes the liquid refrigerant by the time it reaches the location covered with the heat insulating material, and the first pipe. 8. The heat collecting/radiating pipe according to any one of claims 1 to 7, wherein the refrigerant does not evaporate again when flowing through the heat collecting/radiating pipe covered with the heat insulating material. 9. The heat collection tube according to claim 1 , wherein said heat insulating material is a member that does not deform under water pressure. A geothermal heat pump comprising the radiation collection pipe according to any one of claims 1 to 9 .

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