Spiral energy pile structure capable of improving heat transfer efficiency

Abstract

According to the spiral energy pile structure capable of improving the heat transfer efficiency, an energy pile well is arranged in a soil body layer, the energy pile well is in a cone frustum shape, and the diameter of the upper bottom face of an energy pile is larger than that of the lower bottom face of the energy pile; a heat exchange pipe is arranged in an energy pile well and fixed, and the heat exchange pipe is composed of a heat exchange pipe inlet pipe section, a heat exchange pipe spiral pipe section and a heat exchange pipe outlet pipe section which are sequentially connected. And the energy pile well is backfilled with energy pile backfill materials. The spiral heat exchange pipe sections are arranged at a certain taper, the spiral pipes are staggered in the radial direction, the heat interference strength of the adjacent spiral pipes in the axial direction is weakened, and the heat transfer capacity of the spiral pipes in the axial direction is improved; heat exchange fluid with a large heat exchange temperature difference with a soil body flows in from the upper bottom surface of the circular truncated cone with a large radius, so that the thermal short circuit phenomenon of a backfill area at the upper part of the energy pile is weakened to a certain extent, and the heat transfer efficiency of the energy pile is improved; the corrosion resistance is obviously improved, and the service life is greatly prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of buried pipes of a ground source heat pump system, and in particular to a spiral energy pile structure capable of improving heat transfer efficiency, and is mainly applicable to the technical field of ground source heat pumps for heating and cooling buildings. Background Art

[0002] The ground source heat pump system uses underground soil as a low-grade cold and heat source. Since the temperature of the underground soil is relatively constant and the temperature range is very suitable for the efficient operation of the heat pump unit, it can effectively reduce the energy consumption of the unit and make positive contributions to the cause of building energy conservation and emission reduction. The buried pipe heat exchanger is the most critical component of the ground source heat pump system, and its heat exchange efficiency has an important impact on the design capacity and operation effect of the buried pipe system. Single U-type and double U-type vertical buried pipe heat exchangers are widely used, but their drilling holes are deep, generally in the range of 50m to 120m. For rocky geological areas in southern regions such as Chongqing and Chengdu, drilling is difficult, the construction period is long, and the drilling cost is expensive. Its economic efficiency restricts the promotion and application of vertical U-type buried pipes. In addition, the vertical U-type buried pipe has a more serious thermal short circuit phenomenon in the borehole, and its heat exchange efficiency is low. In recent years, an energy pile technology has been widely used. Since the energy pile can rely on the building foundation to bury the heat exchange pipe, it greatly reduces the drilling cost and has good economic efficiency. The energy pile heat exchange tube adopts parallel double U-type, series double U-type and spiral arrangement to improve the heat transfer efficiency, especially the spiral energy pile, which greatly increases the contact area between the heat exchange fluid and the surrounding soil, and its heat transfer efficiency is greatly improved. Related research has shown that the pitch is an important factor affecting the heat transfer efficiency of the spiral energy pile. Due to the small pitch of the spiral heat exchange tube, there is a more obvious thermal interference phenomenon between the axially adjacent spiral tubes, which restricts the improvement of the heat transfer efficiency of the spiral energy pile. Therefore, how to reduce the degree of thermal interference between the axially adjacent spiral tubes is important to improve the heat transfer efficiency of the spiral energy pile.

[0003] Prior to the present invention, the Chinese invention patent "Heat transfer method of geothermal heat exchanger of pile-buried spiral tube ground source heat pump system" (patent number: ZL200810159583.7) disclosed a technical solution for tying and burying spiral heat exchange tubes on the steel cage of cast-in-place piles of building pile foundation. This technical solution can reduce the cost of special drilling and pipe burial, greatly reducing the initial investment of the system. The tying and burying of heat exchange tubes is carried out simultaneously with the construction of building pile foundation, which reduces the construction period. However, in this technical solution, the heat exchange tubes are arranged in a spiral form, the spiral spacing is small, the thermal interference intensity between axially adjacent spiral tubes is large, and the heat exchange efficiency is limited. The Chinese invention patent "Construction method of a prefabricated energy pile" (patent number: ZL201310441978.7) discloses a technical solution for energy pile construction in which heat exchange tubes are buried in hollow steel pipes, and the hollow steel pipes replace traditional solid steel pipes as the main reinforcement of the prefabricated piles. This technical solution solves the technical problems of mutual interference caused by the binding and burying of heat exchange pipes and main reinforcement, concrete density, steel corrosion, etc., and has the advantages of high survival rate of buried pipes, short construction period, and saving of underground space and engineering cost. However, its buried pipe layout is a vertical U-shape, the contact area between the heat exchange fluid and the soil is small, and the heat exchange amount and heat exchange efficiency are not as good as the spiral energy pile. Summary of the invention

[0004] The patent of this invention aims at the current development status and existing problems of ground source heat pump technology. On the basis of facilitating construction operation, reducing initial investment and not changing the contact heat exchange area between the heat exchange fluid and the soil, it reduces the axial thermal interference of the spiral energy pile and improves the heat exchange efficiency of the energy pile, thereby providing a hollow truncated cone spiral energy pile that can improve heat transfer efficiency.

[0005] The technical solution of the patent of the present invention: a spiral energy pile structure for improving heat transfer efficiency, an energy pile well is arranged in the soil layer, characterized in that: the energy pile well is in the shape of a truncated cone, and the energy pile upper bottom surface, the energy pile lower bottom surface, the energy pile side curved surface and the energy pile inner wall surface constitute a truncated cone-shaped energy pile well with a cylindrical middle part, and the diameter of the energy pile upper bottom surface is greater than the diameter of the energy pile lower bottom surface;

[0006] A heat exchange pipe is arranged and fixed in the energy pile well, and the heat exchange pipe consists of three parts connected in sequence: an inlet pipe section of the heat exchange pipe, a spiral pipe section of the heat exchange pipe, and an outlet pipe section of the heat exchange pipe; the spiral heat exchange pipe section is arranged and fixed along the side curved surface of the energy pile, the inlet pipe section of the heat exchange pipe enters vertically from the edge of the upper bottom surface of the energy pile, and the outlet pipe section of the heat exchange pipe is led vertically upward along the inner wall surface of the energy pile;

[0007] After the heat exchange tube is arranged in the hollow energy pile well, the energy pile well is backfilled with energy pile backfill material to obtain an energy pile backfill material layer.

[0008] Further features are: the spiral section 8 of the heat exchange tube is arranged in the form of a truncated cone spiral with a pitch of 100 to 300 mm; fixing nails are driven vertically into the side curved surface of the energy pile every 1.5 to 3 m along the spiral direction, and the fixing nails extend out of the side curved surface by 30 to 40 mm. The spacing of the fixing nails gradually increases in the spiral direction from the lower bottom surface to the upper bottom surface, and the spiral section of the heat exchange tube is tied to the fixing nails in sequence to form a spiral section of the heat exchange tube.

[0009] The heat exchange tube is a polyethylene plastic tube or a polybutylene tube.

[0010] A method for manufacturing a spiral energy pile structure for improving heat transfer efficiency, characterized by comprising the following steps:

[0011] (1) Determine the parameters of the truncated cone-shaped energy pile well according to the process requirements;

[0012] (2) Excavation and shaping of the energy pile well: According to the parameters determined above, construction work is carried out at the project site to excavate the soil layer to obtain a truncated cone-shaped energy pile well with a cylindrical middle part formed by the upper bottom surface of the energy pile, the lower bottom surface of the energy pile, the side curved surface of the energy pile and the inner wall surface of the energy pile;

[0013] (3) Arrange heat exchange tubes in the energy pile well: Determine the pitch of the spirally arranged heat exchange tubes according to the process requirements. According to the determined pitch, drive fixing nails into the truncated cone side curved surface of the energy pile well every 1.5 to 3 m along the spiral direction. The fixing nails extend out of the side curved surface by 30 to 40 mm. The spacing of the fixing nails gradually increases from the lower bottom surface to the upper bottom surface in the spiral direction. Tie the heat exchange tubes to the fixing nails in sequence to form a spiral tube section of the heat exchange tube;

[0014] (4) Fixing of the outlet pipe section of the heat exchanger: drive fixing nails vertically into the inner wall of the energy pile every 0.5 to 1 m in the vertical direction. The fixing nails extend 30 to 40 mm from the outer wall of the cylinder. Tie the insulated outlet pipe section of the heat exchanger to the fixing nails.

[0015] (5) Backfilling of the energy pile well: The energy pile well is backfilled with energy pile well backfill material after binding to obtain the hollow truncated cone spiral energy pile structure.

[0016] The outlet pipe section is insulated with foam rubber and plastic insulation material. The insulation material is wrapped around a certain length of the outlet pipe section, and the thickness of the insulation layer is 20 to 30 mm.

[0017] Compared with the prior art, the patent of this invention has the following characteristics:

[0018] Under the condition of ensuring the consistency of the effective heat exchange tube length, compared with the traditional spiral energy pile arranged on the cylindrical surface, the spiral heat exchange tube section of the patent of the present invention is arranged with a certain taper, and the spiral tubes are staggered with each other in the radial direction, and the thermal interference intensity of adjacent spiral tubes in the axial direction is weakened, which increases the heat transfer capacity of the spiral tube in the axial direction; the heat exchange fluid with a large temperature difference with the soil flows in from the bottom surface of the circular platform with a larger radius, which to a certain extent weakens the thermal short circuit phenomenon in the backfill area on the upper part of the energy pile. In summary, the patent of the present invention effectively improves the heat transfer efficiency of the energy pile. Compared with the traditional spiral energy pile arranged on the cylindrical surface, the patent of the present invention reduces the amount of earth excavation and the amount of backfill material used for the energy pile, thereby saving the initial investment of the energy pile. Compared with the traditional cylindrical energy pile, the well wall of the patent of the present invention has a certain taper, which reduces the risk of well wall collapse during excavation. Moreover, the heat exchange tube is a polyethylene plastic tube or a polybutylene tube, which significantly improves the corrosion resistance and greatly increases the service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a longitudinal schematic diagram of the hollow truncated cone energy pile well of the present invention.

[0020] Figure 2 It is a plan view schematic diagram of the hollow truncated cone spiral energy pile structure layout of the present invention.

[0021] Figure 3 It is a longitudinal schematic diagram of the pile body arrangement of the hollow truncated cone spiral energy pile structure of the present invention.

[0022] Figure 4 Comparison of heat transfer resistance per unit tube length under different design parameters (the height of the frustum is 1.5m)

[0023] In the figure: 1-soil layer; 2-energy pile well; 3-upper bottom surface of energy pile; 4-lower bottom surface of energy pile; 5-side curved surface of energy pile; 6-inner wall surface of energy pile; 7-soil surface; 8-spiral section of heat exchange tube; 9-inlet section of heat exchange tube; 10-outlet section of heat exchange tube; 11-backfill material layer of energy pile; 12-soil layer covering the upper bottom surface of energy pile. DETAILED DESCRIPTION

[0024] The following is a detailed description of the specific implementation of the present invention in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1The structure of the hollow truncated cone energy pile well of the present invention is shown, and an energy pile well 2 is arranged in a soil layer 1, and the energy pile well 2 is in the shape of a truncated cone, an inverted cone; or a truncated cone with a cylindrical middle part, and the diameter of the upper bottom surface 3 of the energy pile is greater than the diameter of the lower bottom surface 4 of the energy pile; to ensure that the energy pile has a certain taper, thereby reducing the risk of well wall collapse. The side curved surface 5 of the energy pile is an inclined surface, and the inner wall surface 6 of the energy pile is vertical or inclined; the upper bottom surface 3 of the energy pile, the lower bottom surface 4 of the energy pile, the side curved surface 5 of the energy pile and the inner wall surface 6 of the energy pile constitute a truncated cone-shaped energy pile well 2 with a cylindrical middle part, and its cross section is a trapezoidal structure, a right-angled trapezoid or a non-right-angled trapezoid.

[0026] Excavation and shaping of energy pile well 2: According to the construction site conditions, the covering layer 12 on the upper bottom surface of the energy pile is removed, and the thickness of the covering layer is not less than 1.5m. The upper bottom surface 3 of the hollow truncated cone energy pile is used as the reference surface for excavation. According to the design size of the hollow truncated cone, the hollow truncated cone energy pile well 2 is shaped by a semi-mechanical hole digging method. During excavation, 10-20mm thick concrete mortar is applied to the side curved surface 5 of the energy pile to ensure the flatness and smoothness of the side curved surface 5 of the energy pile. The diameter of the lower bottom surface 4 of the hollow truncated cone energy pile is not less than 0.3mm, the diameter of the upper bottom surface 3 of the hollow truncated cone energy pile is not more than 2.5m, and the height of the hollow truncated cone energy pile well 7 is 1.0-2.0m.

[0027] A heat exchange tube is arranged and fixed in the energy pile well 2. The heat exchange tube consists of three parts connected in sequence: a heat exchange tube inlet pipe section 9, a heat exchange tube spiral pipe section 8, and a heat exchange tube outlet pipe section 10. During installation, the heat exchange tube is spirally arranged in the energy pile well 2. The spiral heat exchange tube section 8 is arranged and fixed along the side curved surface 5 of the energy pile. The spiral heat exchange tube section 8 is arranged in the form of a truncated cone spiral with a pitch of 100 to 300 mm. Every 1.5 to 3 m along the spiral direction, a fixing nail is vertically driven into the side curved surface 5 of the truncated cone. The fixing nail extends 30 to 40 mm from the side curved surface. The spacing of the fixing nails gradually increases in the spiral direction from the lower bottom surface 4 to the upper bottom surface 3. The heat exchange tube spiral pipe section 8 is tied to the fixing nails in sequence to form a spiral pipe section of the heat exchange tube. The heat exchange tube is specifically selected from polyethylene tubes or polybutylene tubes. The heat exchange tube inlet pipe section 9 enters vertically from the edge of the upper bottom surface 3 of the hollow truncated cone energy pile. The outlet pipe section 10 of the heat exchange tube is insulated, and the insulation material is foam rubber and plastic insulation material, and the thickness of the insulation layer is 20 to 30 mm. The outlet pipe section 10 of the heat exchange tube is led vertically upward along the inner wall surface 6 of the energy pile. Every 0.5 to 1 m along the direction of the outlet pipe section, a fixing nail is vertically driven into the outer wall surface of the hollow cylinder. The fixing nail extends 30 to 40 mm from the outer wall surface of the cylinder. The number of fixing nails is not less than 3, and the insulated outlet pipe section is tied to the fixing nail. The inlet pipe section and the outlet pipe section are both 100 to 200 mm higher than the bottom surface of the hollow truss to facilitate connection with the system horizontal header.

[0028] After the heat exchange tube is arranged in the hollow energy pile well 2, the energy pile well 2 needs to be backfilled; the energy pile backfill material of the present invention can be made of a variety of materials: such as existing concrete, a mixed slurry of bentonite and fine sand (cement), or other backfill materials with good thermal conductivity, and the energy pile backfill material is used for backfilling to obtain an energy pile backfill material layer 11. When using concrete for backfilling, because the energy pile of the present invention does not need to bear a large load (such as a building foundation, etc.), the concrete can use C15 concrete with lower strength, and use a concrete delivery pump to inject the stirred concrete into each energy pile well that needs to be backfilled through a delivery pipeline, and the backfilling is completed in one pouring. When using a mixed slurry of bentonite and fine sand (cement) for backfilling, the proportion of bentonite is preferably 4%-6% to improve the heat transfer coefficient of the backfill material. During the backfilling process, a compacting device should be used for vibration compaction. At least 20 to 30 days after the energy pile is backfilled, after the backfill material solidifies, combined with the construction of the horizontal header, the original soil is used to backfill and compact the top soil layer 12 of the energy pile.

[0029] By arranging effective heat exchange tubes in a truncated cone spiral, the heat transfer efficiency of the energy pile is effectively improved and the heat transfer thermal resistance per unit tube length is reduced while ensuring the same length of the heat exchange tubes. Figure 4 The heat transfer resistance per unit length of hollow truncated cone spiral energy piles with different design parameters is given. The result is calculated using CFD numerical simulation software. R1 is the radius of the lower bottom surface of the truncated cone energy pile, and R2 is the radius of the upper bottom surface of the truncated cone energy pile. It can be seen that compared with the spiral energy pile with a traditional cylindrical surface, the heat transfer resistance per unit length of the hollow truncated cone spiral energy pile is reduced by 3% to 14%; increasing the difference between the lower bottom surface radius and the upper bottom surface radius, the heat transfer resistance per unit length of the pipe is reduced more, and the heat transfer effect is better.

[0030] The present invention provides a method for manufacturing a spiral energy pile structure for improving heat transfer efficiency, comprising the following technical steps:

[0031] (1) Determine the parameters of the truncated cone-shaped energy pile well according to the process requirements;

[0032] (2) Excavation and shaping of energy pile wells: According to the parameters determined above, construction work is carried out at the project site, and the soil layer is excavated manually, semi-mechanically or fully mechanically to obtain a truncated cone-shaped energy pile well with a cylindrical middle part formed by the upper bottom surface of the energy pile, the lower bottom surface of the energy pile, the side curved surface of the energy pile and the inner wall surface of the energy pile;

[0033] (3) Heat exchange tubes are arranged in the energy pile well: according to the process requirements, the pitch of the spirally arranged heat exchange tubes is determined. According to the determined pitch, fixing nails are vertically driven into the truncated cone side curved surface of the energy pile well every 1.5 to 3 m along the spiral direction. The fixing nails extend out of the side curved surface by 30 to 40 mm. The spacing of the fixing nails gradually increases from the lower bottom surface to the upper bottom surface in the spiral direction. The polyethylene plastic pipes (heat exchange tubes) are arranged on the truncated cone side curved surface of the energy pile well in sequence and fixed (tied) on the fixing nails to form a spiral pipe section of the heat exchange tube.

[0034] Insulation of the outlet pipe section of the heat exchange tube: After the spiral pipe section is fixed in the energy pile well, in order to obtain a better insulation effect, the outlet pipe section is insulated. The insulation material is foam rubber and plastic insulation material. The insulation material is wrapped on the surface of a certain length of the outlet pipe section, and the thickness of the insulation layer is 20 to 30 mm.

[0035] (4) Fixing of the outlet pipe section of the heat exchanger: Fixing nails are driven vertically into the inner wall of the energy pile every 0.5 to 1 m in the vertical direction. The fixing nails extend 30 to 40 mm from the outer wall of the cylinder. The number of fixing nails should be no less than 3. The insulated outlet pipe section of the heat exchanger is tied to the fixing nails.

[0036] (5) Backfilling of the energy pile well: Use a mixture of existing concrete, bentonite and fine sand (cement), or other backfill materials with good thermal conductivity to backfill the energy pile well after binding.

[0037] The inlet and outlet of the heat exchange tube should be 100 to 200 mm higher than the bottom surface of the energy pile to facilitate connection with the system horizontal header.

[0038] The heat exchange fluid flows into the inlet section of the heat exchange tube and flows out from the outlet section.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Although the applicant has described the present invention in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that those modifications or equivalent substitutions of the technical solution of the present invention without departing from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A spiral energy pile structure for improving heat transfer efficiency, wherein an energy pile well (2) is arranged in a soil layer (1), characterized in that: The energy pile well (2) is in the shape of a truncated cone, and is composed of an energy pile upper bottom surface (3), an energy pile lower bottom surface (4), an energy pile side curved surface (5) and an energy pile inner wall surface (6) to form a truncated cone-shaped energy pile well (2) with a cylindrical middle portion, and the diameter of the energy pile upper bottom surface (3) is greater than the diameter of the energy pile lower bottom surface (4).

2. A spiral energy pile structure for improving heat transfer efficiency according to claim 1, characterized in that: A heat exchange pipe is arranged and fixed in the energy pile well (2), wherein the heat exchange pipe is composed of three parts connected in sequence: a heat exchange pipe inlet pipe section (9), a heat exchange pipe spiral pipe section (8), and a heat exchange pipe outlet pipe section (10); the spiral heat exchange pipe section (8) is arranged and fixed along the side curved surface (5) of the energy pile, the heat exchange pipe inlet pipe section (9) vertically enters from the edge of the upper bottom surface (3) of the energy pile, and the heat exchange pipe outlet pipe section (10) is vertically led out along the inner wall surface (6) of the energy pile.

3. A spiral energy pile structure for improving heat transfer efficiency according to claim 2, characterized in that: After the heat exchange tube is arranged in the hollow energy pile well (2), the energy pile well (2) is backfilled with energy pile backfill material to obtain an energy pile backfill material layer (11).

4. A spiral energy pile structure for improving heat transfer efficiency according to claim 3, characterized in that: The spiral sections (8) of the heat exchange pipe are arranged in the form of a truncated cone spiral with a pitch of 100 to 300 mm. Fixing nails are vertically driven into the side curved surface (5) of the energy pile every 1.5 to 3 m along the spiral direction. The fixing nails extend out of the side curved surface by 30 to 40 mm. The spacing of the fixing nails gradually increases in the spiral direction from the lower bottom surface (4) to the upper bottom surface (3). The spiral sections (8) of the heat exchange pipe are sequentially tied to the fixing nails to form the spiral sections of the heat exchange pipe.

5. A spiral energy pile structure for improving heat transfer efficiency according to claim 4, characterized in that: The heat exchange tube is a polyethylene plastic tube or a polybutylene tube.

6. A method for manufacturing a spiral energy pile structure for improving heat transfer efficiency, characterized in that The steps include: (1) Determine the parameters of the truncated cone-shaped energy pile well according to the process requirements; (2) Excavation and shaping of the energy pile well: According to the parameters determined above, construction work is carried out at the project site to excavate the soil layer to obtain a truncated cone-shaped energy pile well with a cylindrical middle part formed by the upper bottom surface of the energy pile, the lower bottom surface of the energy pile, the side curved surface of the energy pile and the inner wall surface of the energy pile; (3) Arrange heat exchange tubes in the energy pile well: Determine the pitch of the spirally arranged heat exchange tubes according to the process requirements. According to the determined pitch, drive fixing nails into the truncated cone side curved surface of the energy pile well every 1.5 to 3 m along the spiral direction. The fixing nails extend out of the side curved surface by 30 to 40 mm. The spacing of the fixing nails gradually increases from the lower bottom surface to the upper bottom surface in the spiral direction. Tie the heat exchange tubes to the fixing nails in sequence to form a spiral tube section of the heat exchange tube; (4) Fixing of the outlet pipe section of the heat exchanger: drive fixing nails vertically into the inner wall of the energy pile every 0.5 to 1 m in the vertical direction. The fixing nails extend 30 to 40 mm from the outer wall of the cylinder. Tie the insulated outlet pipe section of the heat exchanger to the fixing nails. (5) Backfilling of the energy pile well: The energy pile well is backfilled with energy pile well backfill material after binding to obtain the hollow truncated cone spiral energy pile structure.

7. A method for manufacturing a spiral energy pile structure for improving heat transfer efficiency according to claim 6, characterized in that: The outlet pipe section is insulated with foam rubber and plastic insulation material. The insulation material is wrapped around a certain length of the outlet pipe section, and the thickness of the insulation layer is 20 to 30 mm.

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