CN114893929A - Underground pipe heat exchange enhancement system and method based on combined backfill - Google Patents
Underground pipe heat exchange enhancement system and method based on combined backfill Download PDFInfo
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- CN114893929A CN114893929A CN202210415660.0A CN202210415660A CN114893929A CN 114893929 A CN114893929 A CN 114893929A CN 202210415660 A CN202210415660 A CN 202210415660A CN 114893929 A CN114893929 A CN 114893929A
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- 238000000034 method Methods 0.000 title claims abstract description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 147
- 239000000463 material Substances 0.000 claims abstract description 57
- 239000004576 sand Substances 0.000 claims abstract description 28
- 239000000440 bentonite Substances 0.000 claims abstract description 26
- 229910000278 bentonite Inorganic materials 0.000 claims abstract description 26
- SVPXDRXYRYOSEX-UHFFFAOYSA-N bentoquatam Chemical compound O.O=[Si]=O.O=[Al]O[Al]=O SVPXDRXYRYOSEX-UHFFFAOYSA-N 0.000 claims abstract description 26
- 239000000203 mixture Substances 0.000 claims abstract description 18
- 238000005516 engineering process Methods 0.000 claims abstract description 16
- 239000003673 groundwater Substances 0.000 claims abstract description 15
- 239000002689 soil Substances 0.000 claims abstract description 15
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- 238000012546 transfer Methods 0.000 claims abstract description 13
- 239000012530 fluid Substances 0.000 claims abstract description 11
- 230000008859 change Effects 0.000 claims abstract description 10
- 238000010276 construction Methods 0.000 claims description 17
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- 238000012806 monitoring device Methods 0.000 claims description 8
- 230000000694 effects Effects 0.000 claims description 7
- 238000002844 melting Methods 0.000 claims description 6
- 230000008018 melting Effects 0.000 claims description 6
- 239000002352 surface water Substances 0.000 claims description 5
- 230000002708 enhancing effect Effects 0.000 claims description 4
- 238000011156 evaluation Methods 0.000 claims description 3
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- 239000002245 particle Substances 0.000 claims description 2
- 230000003014 reinforcing effect Effects 0.000 claims 1
- 238000009825 accumulation Methods 0.000 abstract description 5
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B30/00—Heat pumps
- F25B30/06—Heat pumps characterised by the source of low potential heat
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24T—GEOTHERMAL COLLECTORS; GEOTHERMAL SYSTEMS
- F24T10/00—Geothermal collectors
- F24T10/10—Geothermal collectors with circulation of working fluids through underground channels, the working fluids not coming into direct contact with the ground
- F24T10/13—Geothermal collectors with circulation of working fluids through underground channels, the working fluids not coming into direct contact with the ground using tube assemblies suitable for insertion into boreholes in the ground, e.g. geothermal probes
- F24T10/15—Geothermal collectors with circulation of working fluids through underground channels, the working fluids not coming into direct contact with the ground using tube assemblies suitable for insertion into boreholes in the ground, e.g. geothermal probes using bent tubes; using tubes assembled with connectors or with return headers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/10—Geothermal energy
Abstract
The invention provides a ground pipe heat exchange enhancement system and method based on composite backfill. Backfilling with a permeable material below the ground water level. The temperature change generated by heat exchange between the water body in the pipeline and the surrounding underground water enables the energy difference between the underground water molecules around the heat exchange tube and the distant water molecules to drive the fluid to flow, the phenomenon that the heat drives the underground water to flow is formed, the heat or the cold energy emitted by the heat exchange tube is taken away by the flowing underground water to form a heat flow channel, the heat transfer resistance is greatly reduced, and the heat accumulation phenomenon is reduced. Above the ground water level, the bentonite and fine sand mixture backfill can enable the space between the pipeline and the rock-soil body to be filled compactly and isolate air, and ensure good thermal conductivity. Under the water-containing geological condition, the application of the technology can more effectively utilize the shallow geothermal energy of the region and greatly improve the heat exchange efficiency of the system.
Description
Technical Field
The invention relates to the technical field of ground source heat pumps, in particular to a system and a method for enhancing heat exchange of a buried pipe based on combined backfilling.
Background
The shallow geothermal energy is a clean renewable energy source, is widely distributed, has huge resource potential, and has great significance in safely and efficiently developing shallow geothermal resources. In the aspect of shallow geothermal energy utilization, the ground source heat pump technology is the main mode for developing shallow geothermal energy resources at present, and is favored by the world due to the characteristics of economy, environmental friendliness and the like.
A vertical buried pipe ground source heat pump system is one of ground source heat pump technologies, specifically, an underground rock-soil body is used as a heat/cold source, heat exchange is carried out between the underground rock-soil body and a heat exchanger embedded in a drill hole, and a heat pump technology is utilized to input a small amount of high-level electric energy to carry out indoor refrigeration/heat supply circulation or provide domestic hot water. The water-saving device has small floor area, is not limited by underground water and surface water resources, is suitable for the current national conditions of China, and has very wide application.
In the construction process of the buried pipe heat exchanger, backfill is an important link, namely, a drill hole backfill material is injected into a hole after a U-shaped pipe is drilled and laid. The backfill is arranged between the buried pipe and the hole wall, and aims to enhance the heat exchange capacity between the buried pipe and the surrounding rock-soil body, prevent surface water from permeating into the underground through the drill hole, pollute the underground water and avoid cross contamination between the underground water of different aquifers. When the system operates, the water in the pipeline can exchange heat with the rock-soil body only through a plurality of layers of section thermal resistances such as a pipe wall, backfill materials and the like, so that the selection of a backfill technology is one of suitable means for reducing investment and improving system operation economy of most buried pipe ground source heat pump projects on the premise that the existing pipeline material and rock-soil body conditions cannot be changed. The selection of the backfill technology and the correct backfill construction have important significance for ensuring the performance of the ground heat exchanger. If a drill hole backfill material with poor heat conduction performance is adopted, the thermal resistance in the drill hole is obviously increased, the total length of the required drill hole is increased under the same condition, and the initial investment and the operation cost of the system are increased.
In the prior art, in the construction of buried pipes, the backfill material of the drilled holes mostly adopts mixed slurry of bentonite and fine sand (or cement), or cement base material is adopted for backfilling in compact and hard rock-soil bodies; and most grouting pumps and the bound grouting pipes are used in the backfilling process, the grouting speed is controlled, and the uplifting of the grouting pipes is promoted to ensure that the backfilling is compact. In summary, the backfill material in the backfill technology has a low heat conductivity coefficient, isolates underground water, and completely transfers heat by heat conduction, so that the heat exchange efficiency is low, heat accumulation is easy to cause, and the heat exchange performance is continuously reduced; in addition, the quality, compactness, etc. of the backfill are difficult to control during the field construction.
The existing backfill technology enables the heat exchange efficiency between the buried pipe and the rock-soil mass to be continuously low, influences the working efficiency of the ground source heat pump under long-term operation, reduces the energy efficiency ratio of the system, and is an important reason that the performance of the buried pipe ground source heat pump system is difficult to improve. Therefore, the backfill technology needs to be innovated to solve the problem of low heat exchange efficiency of the buried pipe ground source heat pump system.
The materials, backfill equipment and the like of the existing backfill materials are still in essence dependent on heat conduction for heat transfer, the improvement of the heat transfer effect is limited, the advantages of geological conditions are not utilized, the economy is not high, the field operation of material preparation is difficult, and the backfill materials can not be used on a large scale in construction.
Disclosure of Invention
In order to solve the problems, the invention considers the groundwater seepage factor in the geological condition, uses the permeable material, bentonite and fine sand mixture to backfill layer by layer to be used as the backfill technology of the buried pipe drilling hole under the geological condition with water, so that the groundwater can freely flow in the drilling hole, the heat transfer is carried out by using the groundwater thermal convection caused by thermal excitation, the heat transfer mode is changed from the heat transfer into the thermal convection, a new thought is provided for the ground source heat pump system of the buried pipe on the backfill technology, a buried pipe heat exchange enhancement system based on the composite backfill is provided, and the buried pipe heat exchange enhancement system is applied to the backfill aspect of the drilling hole of the buried pipe construction in the ground source heat pump system, and comprises the following components: the system comprises a drill hole backfill material, a ground heat exchanger and an operation monitoring device;
the ground heat exchanger is positioned in a drill hole backfill material in the ground pipe construction, and the operation monitoring device is connected to the top end of the ground heat exchanger;
the drill hole backfill material is used for densely filling the anhydrous space in the drill hole, improving the heat transfer performance and preventing surface water from permeating into the drill hole;
the ground heat exchanger is used for realizing the heat exchange between fluid in the ground heat exchanger and underground rock-soil bodies;
the operation monitoring device is used for controlling the flow rate of the fluid in the water inlet and outlet pipeline and monitoring the temperature of the water in the water inlet and outlet pipeline and the flow change of the fluid in the pipeline in real time.
Furthermore, the drill hole backfill material mainly comprises a permeable material and a bentonite and fine sand mixture, wherein the bentonite and fine sand mixture is positioned above the permeable material, and the permeable material is used for backfilling the drill hole, so that the backfill height is flush with the ground water level surface, and the free flow of the ground water in the drill hole is realized.
Further, the bentonite and fine sand mixed material is prepared by mixing 10% of bentonite and 90% of fine sand.
Further, the particle size of the fine sand is 0.25-0.35 mm.
Further, the ground heat exchanger comprises a PE pipeline and a bottom U-shaped connector, and the top end of the bottom U-shaped connector is connected with the PE pipeline.
Furthermore, the interior of the ground heat exchanger is connected in a hot melting or electric melting mode, so that firm connection and no water leakage are ensured.
Further, the operation monitoring device comprises a water inlet and outlet pipeline valve, a water inlet and outlet temperature sensor and a flowmeter, the water inlet and outlet pipeline valve comprises a water inlet pipeline valve and a water outlet pipeline valve, the water inlet and outlet temperature sensor comprises a water inlet temperature sensor and a water outlet temperature sensor, the water inlet pipeline valve, the water inlet temperature sensor and the flowmeter are sequentially connected onto the water inlet pipeline, the water outlet pipeline valve and the water outlet temperature sensor are sequentially connected onto the water outlet pipeline, the water inlet and outlet pipeline valve is used for controlling the flow rate of fluid in the water inlet and outlet pipeline, the water inlet and outlet temperature sensor is used for monitoring the temperature of inlet and outlet water in the pipeline in real time, and the flowmeter is used for monitoring the flow change of water in the water inlet pipeline in real time.
A method for enhancing heat exchange of a buried pipe based on composite backfill comprises the following steps:
s1: actually surveying the construction site of the ground source heat pump system, wherein the main indexes of the survey comprise the soil quality and the underground water condition of the construction site, and measuring the underground water level in the rich water season and the low water season according to the underground water level change condition recorded in the past year to determine the lowest underground water level value as a top plate of the permeable backfill;
s2: determining the lowest value of the underground water level in one year, and taking the value as the specified height required by the backfill permeable material;
s3: calculating the volume of the required permeable material and the mixture of the bentonite and the fine sand according to the bore diameter of the drilled hole and the volume of the buried pipe;
s4: adopting a casing running mode to carry out U-shaped pipe laying and backfilling, lifting the casing pipe when the unit casing pipe height is backfilled, then continuing backfilling, filling the permeable material to a specified height, and backfilling the hole opening by using a mixture of bentonite and fine sand;
s5: tamping the hole opening after the backfilling is finished, if the backfill material sinks, continuously backfilling until a gap between the PE heat exchange tube and the drill hole is filled, ensuring the heat exchange effect, and checking for many times after the backfilling for the first time is finished;
s6: when the system operates, the monitoring and evaluation of the heat exchange performance of the ground heat exchanger after the backfill technology is improved are realized through the water inlet and outlet temperature sensor and the flowmeter.
The technical scheme provided by the invention has the following beneficial effects:
1. the permeable material is adopted for backfilling, the rapid movement of water molecules under thermal excitation is fully utilized, and the thermal transmission resistance is reduced by means of thermal excitation convection, so that the heat exchange is carried out more fully, and the working performance of the system is greatly improved;
2. under the condition of high-load operation of the system, the phenomenon of thermally exciting groundwater flow is more obvious, the phenomenon of long-term heat accumulation of the vertical buried pipe ground source heat pump system is effectively reduced, and the operation effect and the durability of the system are improved.
3. The adopted drilling backfill material is economical and convenient, has strong operability in construction, and effectively improves the working performance of the system on the premise of not increasing the early investment of the ground source heat pump system of the buried pipe.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
fig. 1 is a structural diagram of a ground heat exchange enhancement system based on composite backfill in an embodiment of the invention.
1. A pipeline water inlet; 2. water inlet and outlet pipeline valves; 21. a water inlet pipe valve; 22. a water outlet pipeline valve; 3. a flow meter; 4. a pipeline water outlet; 5. a water inlet and outlet temperature sensor; 51. a water inlet temperature sensor; 52. a water outlet temperature sensor; 6. a mixture of bentonite and fine sand; 7. a water-tight formation; 8. an underground water line; 9. an aqueous layer; 10. a permeable material; PE heat exchange tubes; 12. a bottom U-shaped connector.
Detailed Description
For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
The embodiment of the invention provides a buried pipe heat exchange enhancement system based on composite backfill.
Referring to fig. 1, fig. 1 is a structural diagram of a ground heat exchange enhancement system based on a composite backfill, specifically including: the water inlet and outlet pipeline comprises a pipeline water inlet 1, a water inlet and outlet pipeline valve 2, a flow meter 3, a pipeline water outlet 4, a water inlet and outlet temperature sensor 5, a bentonite and fine sand mixture 6, a water-proof stratum 7, an underground water line 8, a aquifer 9, a permeable material 10, a PE heat exchange pipe 11 and a bottom U-shaped connector 12, wherein the water inlet and outlet pipeline valve 2 comprises a water inlet pipeline valve 21 and a water outlet pipeline valve 22, and the water inlet and outlet temperature sensor 5 comprises a water inlet temperature sensor 51 and a water outlet temperature sensor 52. The underground water level line 8 is provided with a water-resistant stratum 7, a water-containing layer 9 is arranged below the underground water level line 8, a permeable material 10 is located in the water-containing layer 9, a bentonite and fine sand mixed material 6 is located in the water-resistant stratum 7, the bentonite and fine sand mixed material 6 is located above the permeable material 10, a bottom U-shaped connector is located in the permeable material 10, the top ends of U-shaped connectors 12 are connected with PE heat exchange tubes 11, the PE heat exchange tubes 11 penetrate into the permeable material 10 and penetrate through the bentonite and fine sand mixed material 6, the top ends of the PE heat exchange tubes 11 are respectively connected with a water inlet pipeline and a water outlet pipeline, the water inlet pipeline is provided with a pipeline water inlet 1, the water outlet pipeline is provided with a pipeline water outlet 4, the water inlet pipeline is sequentially connected with a water inlet pipeline valve 21, a water inlet temperature sensor 51 and a flow meter 3, and the water outlet pipeline is sequentially connected with a water outlet pipeline valve 22 and a water outlet temperature sensor 52. The water inlet and outlet pipeline valve 2 is arranged on the water inlet and outlet pipeline and used for controlling the flow rate of fluid in the water inlet and outlet pipeline, the water inlet and outlet temperature sensor 5 and the flowmeter 3 are connected to the water inlet and outlet pipeline, the water inlet and outlet temperature sensor 5 is used for monitoring the temperature of inlet and outlet water in the pipeline in real time, and the flowmeter is used for monitoring the flow change of water in the water inlet pipeline in real time.
The permeability material 10 has good sorting property and rounding property, and during construction, the permeability material 10 is firstly adopted for backfilling, the backfilling height is flush with the ground water level surface, so that the ground water can freely flow in the drill hole, the characteristics of large heat capacity and good fluidity of the ground water are fully utilized, a convection heat dissipation (absorption) channel is formed, and the generated heat or cold is taken away.
The bentonite and fine sand mixture 6 is prepared by mixing 10 percent of bentonite and 90 percent of fine sand (the grain diameter is 0.25-0.35mm), and is used for densely filling the anhydrous space in the drill hole, ensuring good heat transfer and preventing surface water from permeating into the drill hole.
The PE heat exchange tube has the characteristics of good heat conductivity coefficient, high strength, corrosion resistance and the like, and when the system operates, the water body realizes heat exchange with the underground rock-soil body through the ground heat exchanger. The PE heat exchange tubes 11 and the bottom U-shaped connector 12 are connected in a hot melting or electric melting mode to prepare the ground heat exchanger, so that the ground heat exchanger is firmly connected and does not leak water.
According to the ground heat exchange enhancement system based on the combined backfill, the specific implementation mode is as follows:
s1: actually surveying the construction site of the ground source heat pump system, wherein the main indexes of the survey comprise the soil quality and the underground water condition of the construction site, and measuring the underground water level in the rich water season and the low water season according to the underground water level change condition recorded in the past year to determine the lowest underground water level value as a top plate of the permeable backfill;
s2: determining the lowest value of the underground water level in one year, and taking the value as the specified height required by the backfill permeable material;
s3: calculating the volume of the required permeable material 10 and the volume of the bentonite and fine sand mixture 6 according to the bore diameter of the drill hole and the volume of the buried pipe;
s4: according to the calculation result, a bottom U-shaped connector 12 is used for pipe descending and backfilling in a casing pipe descending mode, after a permeable material 10 is filled to a specified height, the hole opening is backfilled with a mixture 6 of bentonite and fine sand;
s5: tamping the hole opening after the backfilling is finished, if the backfilling material sinks, continuously backfilling until a gap between the PE heat exchange tube 11 and the drilled hole is filled, ensuring the heat exchange effect, and checking for many times after the backfilling for the first time is finished;
s6: when the system is operated, the monitoring and the evaluation of the heat exchange performance of the ground heat exchanger after the improved backfilling technology are realized through the water inlet and outlet temperature sensor 5 and the flowmeter 3.
The application takes the layered backfilling of the permeable material 10 and the mixture 6 of the bentonite and the fine sand as the backfilling technology of the buried pipe drilling under the water-containing geological condition. This technique is backfilled below the ground level 8 with a permeable material 10, the greater porosity giving the ground water free flowing conditions. When the system operates, the water body in the pipeline exchanges heat with the surrounding underground water, the change of the temperature enables the underground water molecules around the heat exchange pipe and the distant water molecules to generate energy difference, the fluid is driven to flow, the phenomenon of the flow of the heat-driven underground water is formed, and the larger the temperature difference is, the more remarkable the heat-driven phenomenon is. The heat or cold dissipated by the heat exchange tube is taken away by the flowing underground water to form a heat flow channel, thereby greatly reducing the heat transfer resistance and reducing the heat accumulation phenomenon. Above the underground water level surface 8, the bentonite and fine sand mixture 6 is backfilled, so that dense and isolated air can be filled between the pipeline and the rock-soil body, and good thermal conductivity is guaranteed. Under the water-containing geological condition, the application of the technology can more effectively utilize the shallow geothermal energy of the region and greatly improve the heat exchange efficiency of the system.
The invention has the beneficial effects that:
1. the permeable material is adopted for backfilling, the rapid movement of water molecules under thermal excitation is fully utilized, and the thermal transmission resistance is reduced by means of thermal excitation convection, so that the heat exchange is carried out more fully, and the working performance of the system is greatly improved;
2. under the condition of high-load operation of the system, the phenomenon of thermally exciting groundwater flow is more obvious, the phenomenon of long-term heat accumulation of the vertical buried pipe ground source heat pump system is effectively reduced, and the operation effect and the durability of the system are improved.
3. The adopted drilling backfill material is economical and convenient, has strong operability in construction, and effectively improves the working performance of the system on the premise of not increasing the early investment of the ground source heat pump system of the buried pipe.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. The utility model provides a ground buried pipe heat transfer reinforcing system based on combined type is backfilled which characterized in that: this ground pipe heat transfer enhancement system includes: the system comprises a drill hole backfill material, a ground heat exchanger and an operation monitoring device;
the ground heat exchanger is positioned in a drill hole backfill material in the ground pipe construction, and the operation monitoring device is connected to the top end of the ground heat exchanger;
the drill hole backfill material is arranged between the buried pipe in the drill hole and the hole wall and used for improving the heat transfer performance of the buried pipe and preventing surface water from permeating into the drill hole;
the ground heat exchanger is used for realizing the heat exchange between fluid in the ground heat exchanger and underground rock-soil mass;
the operation monitoring device is used for controlling the flow rate of the fluid in the water inlet and outlet pipeline and monitoring the temperature of the water in the water inlet and outlet pipeline and the flow change of the fluid in the pipeline in real time.
2. The composite backfill-based ground heat exchange enhancement system of claim 1, wherein: the drill hole backfill material mainly comprises a permeable material and a bentonite and fine sand mixture, wherein the bentonite and fine sand mixture is positioned above the permeable material, and the permeable material is used for backfilling the drill hole, so that the backfill height is flush with the ground water level surface, and the free flow of the ground water in the drill hole is realized.
3. The composite backfill-based ground buried pipe heat exchange enhancement system of claim 2, wherein: the bentonite and fine sand mixture is prepared by mixing 10% of bentonite and 90% of fine sand.
4. The composite backfill-based ground heat exchange enhancement system according to claim 3, wherein: the particle size of the fine sand is 0.25-0.35 mm.
5. The composite backfill-based ground buried pipe heat exchange enhancement system of claim 1, wherein: the ground heat exchanger comprises a PE pipeline and a bottom U-shaped connector, and the top ends of the bottom U-shaped connectors are connected with the PE pipeline.
6. The composite backfill-based ground buried pipe heat exchange enhancement system of claim 1, wherein: the interior of the ground heat exchanger is connected in a hot melting or electric melting mode, and the ground heat exchanger is used for ensuring firm connection and no water leakage.
7. The composite backfill-based ground buried pipe heat exchange enhancement system of claim 1, wherein: the operation monitoring device comprises a water inlet and outlet pipeline valve, a water inlet and outlet temperature sensor and a flowmeter, wherein the water inlet and outlet pipeline valve comprises a water inlet pipeline valve and a water outlet pipeline valve, the water inlet and outlet temperature sensor comprises a water inlet temperature sensor and a water outlet temperature sensor, the water inlet pipeline valve, the water inlet temperature sensor and the flowmeter are sequentially connected onto the water inlet pipeline, the water outlet pipeline valve and the water outlet temperature sensor are sequentially connected onto the water outlet pipeline, the water inlet and outlet pipeline valve is used for controlling the flow of fluid in the water inlet and outlet pipeline, the water inlet and outlet temperature sensor is used for monitoring the temperature of inlet and outlet water in the pipeline in real time, and the flowmeter is used for monitoring the flow change of water in the water inlet pipeline in real time.
8. A method for enhancing heat exchange of a buried pipe based on composite backfilling is realized by the system for enhancing heat exchange of the buried pipe based on the composite backfilling as claimed in any one of claims 1 to 7, and is characterized in that: the method comprises the following steps:
s1: actually surveying the construction site of the ground source heat pump system, wherein the main indexes of the survey comprise the soil quality and the underground water condition of the construction site, and measuring the underground water level in the rich water season and the low water season according to the underground water level change condition recorded in the past year to determine the lowest underground water level value as a top plate of the permeable backfill;
s2: determining the lowest value of the underground water level in one year, and taking the value as the specified height required by the backfill permeable material;
s3: calculating the volume of the required permeable material and the mixture of the bentonite and the fine sand according to the bore diameter of the drilled hole and the volume of the buried pipe;
s4: adopting a casing running mode to carry out U-shaped pipe laying and backfilling, lifting the casing pipe when the unit casing pipe height is backfilled, then continuing backfilling, filling the permeable material to a specified height, and backfilling the hole opening by using a mixture of bentonite and fine sand;
s5: tamping the hole opening after the backfilling is finished, if the backfill material sinks, continuously backfilling until a gap between the PE heat exchange tube and the drill hole is filled, ensuring the heat exchange effect, and checking for many times after the backfilling for the first time is finished;
s6: when the system is operated, the monitoring and the evaluation of the heat exchange performance of the buried pipe heat exchanger after the backfilling technology is improved are realized through the water inlet and outlet temperature sensor and the flowmeter.
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