Layered gradual change spiral ground heat exchanger and using method

Abstract

The invention relates to the technical field of ground heat exchangers, and discloses a layered gradient spiral ground heat exchanger and a using method. The deep pipeline comprises a second inlet spiral pipeline, a second steering connecting pipe and a second outlet pipeline which are connected in sequence; the second inlet spiral pipeline and the second outlet pipeline are vertically arranged; the pipeline radius of the second inlet spiral pipeline is gradually increased from top to bottom; the spiral radius of the second inlet spiral pipeline is gradually increased from top to bottom; and the spiral axis of the second inlet spiral pipeline is parallel to the second outlet pipeline. The invention aims to adapt to the soil vertical thermal gradient by optimizing the pipe group layout, the heat exchange efficiency is improved compared with the traditional uniform pipe group, the layered spiral design reduces the shallow soil thermal accumulation risk, and the system energy efficiency attenuation caused by the soil thermal imbalance is delayed. The technology is especially suitable for high-load and long-period operation energy intensive scenes, and has long-term sustainable benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of underground pipe heat exchangers, and in particular to a layered gradient spiral underground pipe heat exchanger and a use method thereof. Background Art

[0002] Traditional ground-mounted heat exchangers operate based on the fundamental principle of heat conduction. A series of tubes are meticulously buried in the soil, forming a large and complex heat exchange network. During system operation, heat is exchanged between the circulating medium (usually water or antifreeze) within the buried tubes and the surrounding soil.

[0003] However, under current technological conditions, traditional buried pipe designs and structures have numerous limitations. Currently, most buried pipes utilize a straight pipe structure with a single depth or uniform distribution. While this structure offers fundamental advantages such as relatively simple construction and low cost, and can, to a certain extent, meet the basic heat exchange requirements of ground-source heat pump systems, it has, however, exposed a series of significant issues during long-term operation.

[0004] Among them, the problem of soil thermal imbalance is particularly significant. Because the cooling and heating load demands of buildings vary significantly in different seasons, for example, when cooling demand is higher in the summer, the heat released into the soil by the buried pipes far exceeds the heat absorbed from the soil in the winter, and vice versa. The straight pipe structure with a single depth or uniform distribution cannot flexibly adjust to this dynamic load change, resulting in local areas of the soil being in an unbalanced state of heat absorption or heat release for a long time. Over time, this thermal imbalance will continue to intensify, causing the soil temperature to gradually deviate from its initial equilibrium temperature. When the soil temperature is too high or too low, the heat exchange efficiency between the buried pipes and the soil will be greatly reduced, which will in turn affect the performance and stability of the entire ground-source heat pump system, increase the system's operating energy consumption, and may even cause the system to fail to operate normally.

[0005] Furthermore, traditional buried pipes have significant shortcomings in utilizing vertical thermal gradients. Soil has a vertical temperature gradient: as depth increases, soil temperature becomes relatively stable and differs from the surface temperature. However, straight pipe structures with a single depth or uniform distribution fail to fully exploit this vertical thermal gradient. They typically only exchange heat within a relatively narrow depth range, ignoring the potential heat transfer benefits offered by soil temperature differences at different depths. Summary of the Invention

[0006] To address existing issues, this invention aims to provide a layered, gradient spiral underground heat exchanger and its use method. By optimizing the tube layout to adapt to the vertical thermal gradient of the soil, its heat exchange efficiency is improved compared to traditional uniform tube groups. The layered spiral design reduces the risk of heat accumulation in shallow soil layers and slows the system's energy efficiency degradation caused by soil thermal imbalance. This technology is particularly suitable for energy-intensive scenarios with high loads and long operating cycles, offering long-term sustainable benefits.

[0007] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0008] The present invention provides a layered gradient spiral buried pipe heat exchanger, comprising a deep pipeline; the deep pipeline comprises a second inlet spiral pipeline, a second turning connecting pipe and a second outlet pipeline connected in sequence; the second inlet spiral pipeline and the second outlet pipeline are both arranged vertically; the pipeline radius of the second inlet spiral pipeline gradually increases from top to bottom; the spiral radius of the second inlet spiral pipeline gradually increases from top to bottom; the spiral axis of the second inlet spiral pipeline is parallel to the second outlet pipeline.

[0009] As a further improvement of the present invention, the pitch of the second inlet spiral pipe gradually decreases from top to bottom.

[0010] As a further improvement of the present invention, the pitch s(z) of the second inlet spiral pipe is s0-(k·G(z) / G0)·z, where s0 is the initial pitch of the uppermost layer, k is the attenuation coefficient, z is the vertical depth from the ground surface, s(z) is the actual pitch at depth z, G(z) is the geothermal gradient at depth z, and G0 is the reference geothermal gradient.

[0011] As a further improvement of the present invention, the radius of the second inlet spiral pipe is 12.5 mm-20 mm.

[0012] As a further improvement of the present invention, the spiral radius of the second inlet spiral pipe is 100 mm-600 mm.

[0013] As a further improvement of the present invention, the distance between the spiral axis of the second inlet spiral pipe and the outlet pipe is 1000 mm-3000 mm.

[0014] As a further improvement of the present invention, the wall thickness of the second outlet pipe is 5 mm-30 mm.

[0015] As a further improvement of the present invention, it also includes a shallow pipeline; the shallow pipeline includes a first inlet spiral pipeline, the pipeline radius or spiral radius of the first inlet spiral pipeline gradually increases from top to bottom; the first spiral pipeline is connected to the second spiral pipeline.

[0016] The present invention also provides a method for using a layered gradient spiral buried pipe heat exchanger, comprising the following steps: surveying the underground conditions and selecting an underground space that avoids obstacles as a drilling area; when the soil quality of the stratum in the drilling area is good, adopting open hole drilling; if it is a sand layer or easily collapsed soil, using casing to fill the hole and grouting for support; and splicing the shallow pipeline and the deep pipeline above ground or splicing them underground in sections and constructing the pipes.

[0017] As a further improvement of the present invention, the deep pipeline is spliced ​​above ground or laid down in sections, including covering the outer surface of the second outlet pipeline with a thermal insulation material.

[0018] The present invention has the following beneficial effects: The gradient spiral structure design of the local buried heat exchanger enables the deep pipeline to better adapt to the heat exchange characteristics of soil at different depths. The second inlet spiral pipe and the second outlet pipe are set vertically to facilitate construction and fluid flow; the pipe radius and spiral radius gradually increase from top to bottom, which can increase the contact area between the lower layer and the soil and improve the heat exchange efficiency; the spiral axis is parallel to the second outlet pipe, which is conducive to the smooth flow of fluid in the pipeline, reduces flow resistance, and makes the heat exchange process more efficient and stable.

[0019] Preferably, the pitch of the second inlet spiral pipe decreases gradually from top to bottom. This design further optimizes heat exchange. As soil temperature changes with depth and heat exchange requirements vary, the gradually decreasing pitch allows the pipe to make closer contact with the soil at different depths, increasing the heat exchange area. It also guides the fluid to produce a more complex flow within the pipe, enhancing heat exchange between the fluid and the soil and improving heat exchange efficiency.

[0020] Optimally, the pitch calculation formula takes into account the effect of geothermal gradients on heat transfer, allowing the pitch to be dynamically adjusted based on the geothermal gradient at different depths. By incorporating parameters such as the attenuation coefficient, initial pitch, depth, geothermal gradient, and reference geothermal gradient, the actual pitch at different depths can be accurately calculated, enabling the heat exchanger to achieve optimal heat transfer at all depths, improving the energy efficiency of the entire system.

[0021] Preferably, the pipe radius range of the second inlet spiral pipe is specified to be 12.5mm-20mm, which not only ensures that the pipe has sufficient internal space for fluid flow to meet the flow requirements required for heat exchange, but also makes the pipe size reasonable, facilitates construction and installation, and reduces material costs and construction difficulty.

[0022] Preferably, the spiral radius of the second inlet spiral pipe is set within the range of 100mm-600mm, so that the pipe can be reasonably laid out in the underground space, which can not only ensure that the pipe has sufficient contact area with the soil and improve the heat exchange efficiency, but also avoid the increase in construction difficulty and cost due to the spiral radius being too large, or the impact on the heat exchange effect due to the spiral radius being too small.

[0023] Preferably, the distance between the spiral axis of the second inlet spiral conduit and the outlet conduit is 1000mm-3000mm. This distance helps to rationally allocate pipeline space and facilitates installation and maintenance. Furthermore, the appropriate distance can reduce thermal interference between pipelines, ensuring fluid flow stability and heat exchange efficiency within the pipelines, making the entire heat exchange system more reliable.

[0024] The second outlet pipe preferably has a wall thickness of 5mm-30mm, minimizing material usage while ensuring pipe strength. This appropriate wall thickness can withstand underground and fluid pressure, preventing pipe rupture or leakage. It also reduces material costs and construction weight, improving construction efficiency and system economics.

[0025] Preferably, the shallow-layer first inlet spiral pipe also features a design with gradually increasing pipe and spiral radius from top to bottom, mirroring the deeper pipes. This optimizes the heat exchange performance in the shallow layer based on the heat exchange characteristics of the shallow soil. The interconnection of the first and second spiral pipes creates an organic integration of the shallow and deep pipes, enabling the entire heat exchanger to fully utilize soil heat at varying depths, improving the system's overall heat exchange performance.

[0026] The method of using the present invention selects an underground space avoiding obstacles as the drilling area, which can avoid encountering obstacles such as underground pipelines and rocks during the construction process, reduce the construction difficulty and risk, improve the construction efficiency, and at the same time ensure the installation quality and safety of the heat exchanger; in strata with good soil quality, open hole drilling is used, which is simple to construct and low in cost; in sand layers or soils prone to collapse, casing is used to fill the hole and grouting is used for support, which can ensure the stability of the drill hole, prevent the drill hole from collapsing, ensure that the pipeline can be installed smoothly, and ensure the normal operation of the heat exchanger; the ground splicing or step-by-step underground splicing pipe construction method is flexible and diverse, and the most suitable construction method can be selected according to actual conditions to improve construction efficiency and quality, and at the same time reduce the impact of construction on the surrounding environment.

[0027] Preferably, coating the outer surface of the second outlet pipe with insulation material can effectively reduce heat loss during pipe transportation. During the heat exchange process, the fluid absorbs heat from the deep or shallow pipes and is transported out through the second outlet pipe. The insulation coating maintains the fluid's temperature, improving energy efficiency and reducing energy waste, making the entire heat exchange system more energy-efficient and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the components in the drawings are merely schematic and are used to facilitate understanding of the present invention. They are not intended to limit the shapes and proportional dimensions of the components of the present invention. In the drawings: Figure 1 This is a schematic diagram of a layered gradient spiral underground heat exchanger in Example 1; Figure 2 This is a graph showing the variation of the buried pipe pitch with depth in Example 1; Figure 3 Schematic diagram of equal spiral radii of the second inlet spiral pipe in Example 2; Figure 4 This is a schematic diagram of the first inlet spiral pipeline in Example 3.

[0029] Among them, 1. the second inlet spiral pipe; 2. the second steering connecting pipe; 3. the second outlet pipe; 4. the first inlet spiral pipe. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0031] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be an element centered thereon. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an element centered thereon. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] Example 1 like Figure 1As shown in the figure, this embodiment provides a hierarchical gradient spiral buried tube heat exchanger, including a deep pipeline; the deep pipeline includes a second inlet spiral pipeline 1, a second turning connection pipe 2 and a second outlet pipeline 3 connected in sequence; both the second inlet spiral pipeline 1 and the second outlet pipeline 3 are vertically arranged; the pipe radius of the second inlet spiral pipeline 1 gradually increases from top to bottom; the spiral radius of the second inlet spiral pipeline 1 gradually increases from top to bottom; the spiral axis of the second inlet spiral pipeline 1 is parallel to the second outlet pipeline 3. Specifically, the radius of the inlet spiral pipeline can be selected as D(z) = D0 + α(G(z) - G0), where D0 is the initial spiral radius of the uppermost layer of the inlet spiral pipeline, α is the proportionality coefficient, D(z) is the actual pitch at depth z, G(z) is the geothermal gradient at depth z, and G0 is the reference geothermal gradient. Taking the geothermal gradient G(z) at depth z as the independent variable, the pipe radius is dynamically adjusted according to the change of the geothermal gradient. When G(z) > G0 (critical gradient threshold), it indicates that the geothermal temperature increase rate is relatively fast. At this time, the radius should be linearly increased to increase the contact area between the pipeline and the soil, that is, to increase the heat exchange area. When G(z) < G0, a smaller radius is advisable to reduce the total pipeline area and control costs.

[0034] Table 1 Pipe Radius, Spiral Radius and Heat Exchange Efficiency (Proportionality Coefficient α = 0.015 m·km / ℃)

[0035] As shown in Table 1 above, at the surface layer, the spiral radius is 0.3 m and the heat exchange efficiency is slightly low, mainly because the surface temperature is greatly affected by the environment, the geothermal gradient is low (about 0.015 m·km / ℃), and the thermal energy stability is poor, resulting in a lower heat exchange efficiency; at the shallow layer, the spiral radius is 0.39 m and the heat exchange efficiency is slightly low, mainly because the depth increase is limited, the geothermal temperature has not increased significantly (the proportionality coefficient is still 0.015 m·km / ℃), and the potential for thermal energy extraction is still limited; at the bottom of the middle and deep layers, the spiral radius is 0.525 m and the heat exchange efficiency is relatively high, mainly because the depth further increases and the geothermal gradient effect is more significant (for example, the local geothermal temperature can reach above 150°C); the larger spiral radius further optimizes the fluid flow path, reduces the flow resistance, and enhances the heat exchange ability; at the shallow layer, the spiral radius is 0.39 m and the heat exchange efficiency is slightly low, mainly because the depth increase is limited, the geothermal temperature has not increased significantly (the proportionality coefficient is still 0.015 m·km / ℃), and the potential for thermal energy extraction is still limited. Among them, the proportionality coefficient is constantly 0.015 m·km / ℃, indicating that the geothermal gradient is a constant in this model and does not change with depth.

[0036] It can be seen that as the vertical depth increases from 0m to 2500m, the ground temperature increases, the heat storage conditions improve, and the thermal energy stability increases; at the same time, as the spiral radius increases from 0m to 2500m, the radius promotes fluid turbulence, expands the heat exchange area, reduces flow resistance, and increases the heat transfer coefficient; the heat transfer efficiency increases from slightly low to high, and the geothermal gradient and the spiral structure work synergistically: the depth contributes to the thermal energy potential, and the spiral radius optimizes the heat transfer process.

[0037] like Figure 2 As shown, the pitch of the second inlet spiral pipe 1 gradually decreases from top to bottom. Specifically, the pitch s(z) of the second inlet spiral pipe 1 is s0-(k·G(z) / G0)·z, where s0 is the initial pitch of the uppermost layer, k is the attenuation coefficient, z is the vertical depth from the ground surface, s(z) is the actual pitch at depth z, G(z) is the geothermal gradient at depth z, and G0 is the reference geothermal gradient.

[0038] Table 2 Vertical depth z and pitch s0 and heat transfer efficiency

[0039] As shown in Table 2 above, vertical depth z‌ increases significantly from the surface (0 m) to the bottom of the mid-depth layer (2500 m). The screw pitch s decreases from 1400 mm to 802 mm, a 42.7% decrease, showing a negative correlation with increasing depth. Heat transfer efficiency gradually increases from "slightly low" to "high," directly related to depth and screw pitch adjustment. The attenuation coefficient (k) remains constant at 0.5 mm / m, indicating that the heat loss rate in the vertical direction does not vary with depth.

[0040] It can be seen that at the surface and shallow layers (0-100m), the pitch is larger (1370-1400mm), the fluid flow path is long, the heat exchange contact time is insufficient, and the efficiency is slightly low; in the medium-deep layer (1500m), the pitch is reduced to 1202mm, the turbulence effect is enhanced, the heat exchange area is optimized, and the efficiency is improved to a moderate level; at the bottom of the medium-deep layer (2500m), the pitch is further reduced to 802mm. Combined with the deep high temperature environment (geothermal gradient effect), the fluid mixing is more sufficient and the efficiency is significantly improved.

[0041] Specifically, the radius of the second inlet spiral pipe 1 is 12.5 mm to 20 mm.

[0042] Specifically, the distance between the spiral axis of the second inlet spiral pipe 1 and the outlet pipe is 1000 mm to 3000 mm. The length of the second steering connecting pipe 2 should be set accordingly to the distance.

[0043] The wall thickness of the second outlet pipe 3 is 5 mm to 30 mm.

[0044] Example 2 like Figure 2 As shown, the main differences between this embodiment and embodiment 1 are: 1) The spiral radius of the second inlet spiral pipe 1 remains consistent from top to bottom; The spiral radius of the second inlet spiral pipe 1 remains constant from top to bottom, and is suitable for formations where the gradient of geothermal heat variation with depth is not obvious.

[0045] Example 3 The main difference between this embodiment and embodiment 1 is: 1) Also includes a shallow pipeline; the shallow pipeline includes a first inlet spiral pipeline, the pipeline radius or spiral radius of the first inlet spiral pipeline gradually increases from top to bottom; the first spiral pipeline is connected to the second spiral pipeline.

[0046] Shallow pipelines are buried at depths between 0 and 1000 meters. Compared to deep pipelines, which are buried at depths of 1000 to 2000 meters, shallow pipelines can utilize heat or cold stored in shallower soil layers. Specifically, the shape (pipe radius and spiral radius) of the first inlet spiral pipeline is identical to that of the second inlet spiral pipeline 1, also designed to optimize heat exchange with depth. Both the shallow (first inlet spiral pipeline) and the deep (second inlet spiral pipeline 1) layers utilize a design where the pipe and spiral radius increase from top to bottom, creating a continuously gradient flow path and reducing sudden changes in fluid resistance. The deep pipeline's pitch is dynamically reduced according to the formula s(z) = s0 - (k·G(z) / G0)·z to adapt to changing geothermal gradients; the shallow pipeline's pitch can be reduced simultaneously to maintain flow continuity.

[0047] The advantages of this solution are that shallow pipelines (within 100m) use low-temperature surface heat sources to pre-cool / preheat the fluid, reducing heat load fluctuations in deeper pipelines. Deep pipelines (1500-2500m) use a large spiral radius (100-600mm) and optimized pitch to enhance turbulent heat transfer and match high-temperature geothermal resources. The first and second spiral pipelines are directly connected to form a series loop, unifying flow distribution and avoiding hydraulic imbalances in parallel systems. The shallow pipeline radius (12.5-20mm) and the deep pipeline thickness (5-30mm) match the pressure requirements to ensure structural stability.

[0048] In addition, this embodiment provides a method for using a layered gradient spiral buried pipe heat exchanger, comprising the following steps: Survey underground conditions and select underground spaces that avoid obstacles as drilling areas; When the soil quality of the drilling area is good, open hole drilling is adopted; if it is a sand layer or soil prone to collapse, casing is used to fill the hole and grouting is used for support; The shallow pipeline and the deep pipeline are spliced ​​on the ground or section by section underground for pipe laying; The outer surface of the second outlet pipe 3 is covered with a heat-insulating material.

[0049] The above-mentioned usage method selects an underground space away from obstacles as the drilling area, which can avoid encountering obstacles such as underground pipelines and rocks during the construction process, reduce the difficulty and risk of construction, improve construction efficiency, and at the same time ensure the installation quality and safety of the heat exchanger; in strata with good soil quality, open hole drilling is used, which is simple to construct and low in cost; in sand layers or soils prone to collapse, casing is used to fill the hole and grouting is used for support, which can ensure the stability of the borehole, prevent the borehole from collapsing, ensure that the pipeline can be installed smoothly, and ensure the normal operation of the heat exchanger; the ground splicing or underground splicing construction method is flexible and diverse, and the most suitable construction method can be selected according to the actual situation to improve construction efficiency and quality, and at the same time reduce the impact of construction on the surrounding environment.

[0050] Coating the outer surface of the second outlet pipe 3 with insulation material effectively reduces heat loss during pipe transportation. During the heat exchange process, the fluid absorbs heat from the deeper or shallower pipes and is then transported out through the second outlet pipe 3. The insulation coating maintains the fluid's temperature, improving energy efficiency and reducing energy waste, making the entire heat exchange system more energy-efficient and efficient.

[0051] The above embodiment is only one of the implementation methods that can realize the technical solution of the present invention. The scope of protection claimed by the present invention is not limited only to this embodiment, but also includes changes, replacements and other implementation methods that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention.

Claims

1. A layered gradient spiral underground heat exchanger, characterized in that: It includes a deep pipeline; the deep pipeline includes a second inlet spiral pipeline, a second steering connecting pipe and a second outlet pipeline connected in sequence; the second inlet spiral pipeline and the second outlet pipeline are both vertically arranged; the pipeline radius of the second inlet spiral pipeline gradually increases from top to bottom; the spiral radius of the second inlet spiral pipeline gradually increases from top to bottom; the spiral axis of the second inlet spiral pipeline is parallel to the second outlet pipeline.

2. The layered gradient spiral buried pipe heat exchanger according to claim 1, characterized in that: The pitch of the second inlet spiral pipe gradually decreases from top to bottom.

3. The layered gradient spiral buried pipe heat exchanger according to claim 2, characterized in that: The pitch s(z) of the second inlet spiral pipe is s0-(k·G(z) / G0)·z, where s0 is the initial pitch of the uppermost layer, k is the attenuation coefficient, z is the vertical depth from the ground surface, s(z) is the actual pitch at depth z, G(z) is the geothermal gradient at depth z, and G0 is the reference geothermal gradient.

4. The layered gradient spiral buried pipe heat exchanger according to claim 1, characterized in that: The radius of the second inlet spiral pipe is 12.5 mm to 20 mm.

5. The layered gradient spiral buried pipe heat exchanger according to claim 1, characterized in that: The spiral radius of the second inlet spiral pipe is 100mm-600mm.

6. The layered gradient spiral buried pipe heat exchanger according to claim 1, characterized in that: The distance between the spiral axis of the second inlet spiral pipe and the outlet pipe is 1000mm-3000mm.

7. The layered gradient spiral buried pipe heat exchanger according to claim 1, characterized in that: The wall thickness of the second outlet pipe is 5 mm to 30 mm.

8. The layered gradient spiral buried pipe heat exchanger according to claim 1, characterized in that: It also includes a shallow pipeline; the shallow pipeline includes a first inlet spiral pipeline, the pipeline radius or spiral radius of the first inlet spiral pipeline gradually increases from top to bottom; the first spiral pipeline is connected to the second spiral pipeline.

9. A method for using a layered gradient spiral buried pipe heat exchanger according to any one of claims 1 to 8, characterized in that: The following steps are involved: Survey underground conditions and select underground spaces that avoid obstacles as drilling areas; When the soil quality of the drilling area is good, open hole drilling is adopted; if it is a sand layer or soil prone to collapse, casing is used to fill the hole and grouting is used for support; The shallow pipeline and the deep pipeline are spliced ​​above ground or section by section underground for pipe laying.

10. The method for using the layered gradient spiral underground heat exchanger according to claim 9, characterized in that: The deep pipelines are spliced ​​above ground or laid down in sections, including covering the outer surface of the second outlet pipeline with insulation material.

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