Solar mid-deep ground source heat pump flexible heat supply system and design and calculation method

Abstract

The invention provides a solar middle-deep layer ground source heat pump flexible heat supply system and a design calculation method. The system comprises a solar heat collector, a middle-deep layer sleeve type buried pipe heat exchanger, a heat pump unit and a heat exchanger. The solar heat collector is connected with the heat exchanger; the heat exchanger is connected with the middle-deep layer sleeve type buried pipe heat exchanger and a user side through a three-way adjusting valve group; the middle-deep layer sleeve type ground heat exchanger is connected with the heat pump unit through the valve group, and the heat pump unit is connected with the user side through the valve group; the solar heat collector collects low-grade heat energy, and part of the low-grade heat energy is stored underground through the middle-deep layer sleeve type buried pipe heat exchanger and used for flexible regression of an underground temperature field deviating from an initial value under the influence of heat extraction. The ground source heat pump unit converts low-grade heat energy into high-grade heat energy. The invention further provides a design calculation method based on the system. On the basis of the heat transfer model, the quantitative regulation operation method of the heat supply system is provided to guide flexible and efficient operation of the composite system.

Description

Technical Field

[0001] This application relates to the technical field of composite energy heating, and particularly relates to a flexible heating system for solar medium-deep geothermal heat pumps and a design calculation method. Background Art

[0002] Building heating and air-conditioning energy consumption, as the main part of building energy consumption, has always attracted much attention for its green and low-carbon development. Solar energy and geothermal energy have received more and more attention and applications due to their wide energy distribution characteristics, low-cost and low-carbon operation characteristics, and the advantages of green and sustainable development. Their application contributions and development potentials in promoting the development of clean energy and ensuring energy security are beyond doubt. Therefore, the development of building heating technologies that combine solar energy and geothermal energy is of great significance for optimizing the energy structure and saving energy and reducing emissions. The main geothermal heat pump heating / air-conditioning technologies include: shallow buried pipe geothermal heat pump technology, medium-deep casing / U-shaped pipe buried pipe geothermal heat pump technology, surface water source heat pump technology, medium-deep hydrothermal geothermal heat pump technology, and deep enhanced geothermal heating technology (hot dry rock technology). Among them, the deep enhanced geothermal heating technology (hot dry rock technology) has very high mining technical difficulties, high costs, and the risk of secondary disasters, and it is currently impossible to achieve commercial development; although the medium-deep hydrothermal geothermal heat pump technology has a large single-well heat extraction capacity, its application involves mining rights and groundwater development, is greatly restricted by resource endowments, and has a great impact on the environment; the application of surface water source heat pump technology is restricted by natural geographical conditions, and the system operation efficiency is greatly affected by natural climate conditions. Therefore, the buried pipe geothermal heat pump technology is currently the most widely used geothermal heat pump heating / air-conditioning technology. Compared with the shallow buried pipe geothermal heat pump technology, the medium-deep buried pipe geothermal heat pump technology is a building heating technology that has emerged in recent years. The application and development of this technology have solved the problems of large floor area of traditional shallow buried pipe heat exchangers, inflexible drilling layout, and small single-hole heat exchange capacity, and at the same time improved the operation efficiency of the units and systems of buried pipe geothermal heat pumps. In medium-deep buried pipe geothermal heat pumps, the casing buried pipe heat exchanger is more popular and has a wider application because it has less construction difficulty, lower construction cost, and more flexible layout form than the U-shaped buried pipe heat exchanger.

[0003] Although the medium - deep buried - pipe ground - source heat pump technology has many advantages compared with the shallow buried - pipe ground - source heat pump technology, medium - deep ground - source heat pump heating operates in a single heat - extraction mode. After long - term operation, it will inevitably lead to underground cold accumulation, resulting in the deviation of the underground temperature field from the original value, the decline in the heat - extraction capacity of the heat exchanger, and the gradual reduction of the operating efficiency of the heat pump unit and the system. The most applicable and effective method to solve the above problems is to develop a composite medium - deep ground - source heat pump heating system and provide scientific and practical design calculations and operation guidance for the composite medium - deep ground - source heat pump heating system. However, due to the extremely long spatial span and long - term operation span of the medium - deep buried - pipe heat exchanger, the complexity and calculation difficulty of its underground heat - transfer model are inherently very high, and its underground heat - transfer calculation itself faces problems such as high requirements for computing hardware and slow calculation speed.

[0004] How to develop a composite medium - deep ground - source heat pump heating system and how to establish a heat - transfer model for the composite medium - deep ground - source heat pump heating system are technical problems that need to be solved. Summary of the Invention

[0005] The purpose of the embodiments of this application is to provide a solar - energy medium - deep ground - source heat pump flexible heating system and a design calculation method, which can give full play to the technical advantages of solar energy and geothermal energy, and realize the flexible operation of the composite system by taking advantage of the complementary advantages of the two renewable energy sources.

[0006] In the first aspect, a system is provided, including: a solar collector 1, a medium - deep casing - type buried - pipe heat exchanger 2, a heat pump unit 3, and a heat exchanger 4;

[0007] The solar collector 1 is connected to the heat exchanger 4; the heat exchanger 4, the medium - deep casing - type buried - pipe heat exchanger 2, and the user side are connected through a first three - way regulating valve group 9 and a second three - way regulating valve group 10; the medium - deep casing - type buried - pipe heat exchanger 2 is connected to the heat pump unit 3 through a valve group 11, and the heat pump unit 3 is connected to the heat user side through a valve group 12;

[0008] The solar collector 1 is used to collect low - grade heat energy, and store a part of the low - grade heat energy underground through the medium - deep casing - type buried - pipe heat exchanger 2 for the flexible regression of the underground temperature field deviated from the initial value due to heat extraction;

[0009] The ground - source heat pump unit 3 is used to convert the low - grade heat energy at the solar collector 1 and the low - grade heat energy at the medium - deep casing - type buried - pipe heat exchanger 2 into high - grade heat energy.

[0010] In the second aspect, a design calculation method is provided, including:

[0011] A heat transfer model of any borehole in each stratum of a medium - deep - layer casing - type cluster ground heat exchanger is established based on the thermal diffusivity, thermal conductivity, and volumetric specific heat capacity of the rock and soil in each geological stratum, and the boundary conditions of the heat transfer domain of any borehole in each stratum are determined; a heat transfer model of the medium - deep - layer casing - type cluster ground heat exchanger in the entire underground heat transfer domain is established according to the superposition principle of heat response of any borehole in each stratum; according to the heat transfer model, a temperature response function of any point at any time is defined.

[0012] The heat transfer model is solved by using the discrete mathematics method to obtain the distribution of the underground temperature field affected by the hourly dynamic load; to achieve the quantitative control of the flexible regression of the underground temperature field, the solar energy recharge temperature that meets the balance adjustment requirements of heat extraction from the underground rock and soil and heat energy recharge is determined.

[0013] The effects provided in the invention content are only the effects of the embodiments, rather than all the effects of the invention. One of the above - mentioned technical solutions has the following advantages or beneficial effects:

[0014] In the embodiment of the present application, a system is first provided, including: a solar collector, a medium - deep - layer casing - type ground heat exchanger, a heat pump unit, and a heat exchanger; the solar collector is connected to the heat exchanger; the heat exchanger, the medium - deep - layer casing - type ground heat exchanger, and the user side are connected through a first three - way regulating valve group and a second three - way regulating valve group; the medium - deep - layer casing - type ground heat exchanger is connected to the heat pump unit through a valve group, and the heat pump unit is connected to the heat user side through a valve group; the solar collector is used to collect low - grade heat energy, and store a part of the low - grade heat energy underground through the medium - deep - layer casing - type ground heat exchanger for the flexible regression of the underground temperature field deviated from the initial value due to heat extraction; the ground - source heat pump unit is used to convert the low - grade heat energy at the solar collector and the low - grade heat energy at the medium - deep - layer ground heat exchanger into high - grade heat energy. Based on this system, a design calculation method is also proposed. The present invention takes the given heat transfer model as the theoretical basis, and proposes a quantitative adjustment operation method for the solar medium - deep - layer ground - source heat pump composite flexible heating system to guide the flexible, efficient, and stable operation of the composite system.

[0015] The present invention can give full play to the technical advantages of solar energy and geothermal energy, and utilize the complementary advantages of the two renewable energy sources to achieve the flexible operation of the composite system, with significant energy - saving and emission - reduction advantages. At the same time, the underground heat transfer model of the composite system given by the present invention not only conforms to the actual heat transfer and operation conditions of the system, but also has the advantages of accurate calculation, high efficiency, and low requirements, and can meet the complex calculation needs of quantitatively adjusting the ground temperature field regression of the composite system. Brief Description of the Drawings

[0016] The accompanying drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0017] Figure 1 It is a schematic connection diagram of a flexible heating system of a solar medium and deep geothermal heat pump proposed in Embodiment 1 of the present invention;

[0018] Figure 2 It is a schematic diagram of the formation stratification of an underground heat transfer model proposed in Embodiment 2 of the present invention;

[0019] Figure 3 It is a flowchart of a design calculation method for a flexible heating system of a solar medium and deep geothermal heat pump proposed in Embodiment 2 of the present invention;

[0020] Figure 4 It is a calculation process diagram of the solar thermal energy reinjection temperature proposed in Embodiment 2 of the present invention;

[0021] Figure 5 It is the temperature field at 1000 m underground with solar reinjected thermal energy proposed in Embodiment 2 of the present invention;

[0022] Figure 6 It is the temperature field at 1000 m underground without solar reinjected thermal energy proposed in Embodiment 2 of the present invention; Marking description:

[0023] 1 - Solar collector, 2 - Medium and deep casing type buried pipe heat exchanger, 3 - Heat pump unit, 4 - Heat exchanger; 5 - Solar heat source side heat collection circulating water pump, 6 - Medium and deep buried pipe heat exchanger heating circulating water pump, 7 - Solar user side heating circulating water pump, 8 - Heat pump unit heating circulating water pump; 9 - First three-way regulating valve group; 10 - Second three-way regulating valve group; 11 - First valve group; 12 - Second valve group. Detailed implementation manners

[0024] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application. The drawing numbers in the present application are only used to distinguish each step in the solution and do not limit the execution order of each step. The specific execution order shall be subject to the description in the specification.

[0025] Embodiment 1

[0026] Embodiment 1 of the present application proposes a flexible heating system for solar medium-deep geothermal heat pumps, which is used to solve the technical problem of how to develop a composite medium-deep geothermal heat pump heating system in the prior art.

[0027] Figure 1 It is a schematic connection diagram of a flexible heating system for solar medium-deep geothermal heat pumps proposed in Embodiment 1 of the present invention; the system includes: a solar collector 1, a medium-deep casing type ground heat exchanger 2, a heat pump unit 3, and a plate heat exchanger 4;

[0028] The solar collector 1 is connected to the heat exchanger 4; the heat exchanger 4, the medium-deep casing type ground heat exchanger 2, and the user side are connected through a first three-way regulating valve group 9 and a second three-way regulating valve group 10; the medium-deep casing type ground heat exchanger 2 is connected to the heat pump unit 3 through a valve group 11, and the heat pump unit 3 is connected to the heat user side through a valve group 12;

[0029] The solar collector 1 is used to collect low-grade heat energy. On the one hand, the low-grade heat energy is flexibly used for direct or indirect heating in each season. On the other hand, in summer and the transition season, it is stored underground through the medium-deep ground heat exchanger, acting on the flexible regression of the underground temperature field that deviates from the initial value due to heat extraction.

[0030] The ground source heat pump unit 3 is used to convert the low-grade heat energy at the solar collector 1 and the low-grade heat energy at the medium-deep casing type ground heat exchanger 2 into high-grade heat energy.

[0031] The first three-way regulating valve group 9 and the second three-way regulating valve group 10 are used to connect or disconnect the connection between the heat exchanger 4, the user side, and the medium-deep casing type ground heat exchanger 2, and to adjust the flow ratio between the medium-deep casing type ground heat exchanger 2 and the user side. The valve group 11 is used to disconnect the connection between the medium-deep casing type ground heat exchanger 2 and the heat pump unit 3. The valve group 12 is used to disconnect the connection between the heat pump unit 3 and the heat user.

[0032] A flexible heating system for solar medium-deep geothermal heat pumps in the present application can realize flexible switching and operation adjustment of 5 operation modes. The 5 operation modes are: the first working mode: the medium-deep casing type ground source heat pump heating operation mode; the second working mode: the solar medium-deep casing type ground source heat pump combined heating operation mode; the third working mode: the solar heating operation mode; the fourth working mode: the solar heating-energy storage combined operation mode; the fifth working mode: the solar energy storage operation mode.

[0033] The first working mode is as follows: both the first three-way regulating valve group 9 and the second three-way regulating valve group 10 are closed, the first valve group 11 located between the medium-deep casing buried tube heat exchanger 2 and the heat pump unit 3 and the second valve group 12 located between the heat pump unit 3 and the user side are both opened, so that the heat pump unit 3 supplies heat alone;

[0034] The second working mode is as follows: the inlet a and the outlet b connected to the user side of the first three-way regulating valve group 9 are both opened, and the outlet c connected to the medium-deep casing buried tube heat exchanger 2 is closed; the outlet a and the inlet b connected to the user side of the three-way regulating valve group 10 are both opened, and the outlet c connected to the medium-deep casing buried tube heat exchanger 2 is closed; the first valve group 11 and the second valve group 12 are both opened; the solar collector 1 and the heat pump unit 3 supply heat jointly;

[0035] The third working mode is as follows: the inlet a and the outlet b connected to the user side of the first three-way regulating valve group 9 are both opened, and the outlet c connected to the medium-deep casing buried tube heat exchanger 2 is closed; the outlet a and the inlet b connected to the user side of the second three-way regulating valve group 10 are both opened, and the outlet c connected to the medium-deep casing buried tube heat exchanger 2 is closed; the first valve group 11 and the second valve group 12 are both closed; the solar collector 1 supplies heat alone;

[0036] The fourth working mode is as follows: the inlet a, the outlet b and the outlet c of the first three-way regulating valve group 9 are all opened; the inlet b, the inlet c and the outlet a of the second three-way regulating valve group 10 are all opened; the first valve group 11 and the second valve group 12 are both closed; the solar collector 1 realizes the combined operation of heat supply and energy storage; by adjusting the opening degrees of the outlet c connected to the medium-deep buried tube heat exchanger 2 and the outlet b connected to the user side of the first three-way regulating valve group 9; adjusting the opening degrees of the inlet c connected to the medium-deep buried tube heat exchanger 2 and the inlet b connected to the user side of the second three-way regulating valve group 10, the proportion of the heat supply amount and the energy storage amount is adjusted;

[0037] The fifth working mode is as follows: the inlet a and the outlet c connected to the medium-deep casing buried tube heat exchanger 2 of the first three-way regulating valve group 9 are opened, and the outlet b connected to the user side is closed; the outlet a and the inlet c connected to the medium-deep casing buried tube heat exchanger 2 of the second three-way regulating valve group 10 are opened, and the inlet b connected to the user side is closed; the first valve group 11 and the second valve group 12 are both closed; the solar collector 1 realizes the energy storage operation mode.

[0038] Among them, the solar heat source side heat collection circulation pump 5 is located on the pipeline in the middle of the solar collector 1 and the plate heat exchanger 4; the medium-deep buried tube heat exchanger heating circulation pump 6 is located on the pipeline between the medium-deep casing type buried tube heat exchanger 2 and the heat pump unit 3; the solar user side heating circulation pump 7 is located between the first three-way regulating valve group 9 and the user side, and the heat pump unit heating circulation pump 8 is located on the user side, and is connected or disconnected respectively according to corresponding requirements.

[0039] The solar medium-deep geothermal heat pump flexible heating system proposed in Embodiment 1 of the present invention is an optimal green energy-saving heating solution for northern heating users with dual demands for hot water and heating, and is suitable for heat users with significantly smaller hot water loads than heating loads. Among them, the basic design principle of the medium-deep casing type buried tube ground source heat pump is to be responsible for the main heating demand during the winter heating period; the design principle of the solar heating module is to meet the hot water demand of heat users, store surplus heat underground in summer and transition seasons, and meet the heat requirement for the flexible return of the soil temperature field. At the same time, the solar heating module also has the application of auxiliary heating in winter. It has the characteristics of high comprehensive energy utilization efficiency, flexible and stable system operation, sustainable development, and adaptation to market application requirements.

[0040] Embodiment 2

[0041] Based on the solar medium-deep geothermal heat pump flexible heating system proposed in Embodiment 1 of the present invention, Embodiment 2 of the present invention also proposes a design calculation method for the solar medium-deep geothermal heat pump flexible heating system. Embodiment 2 of the present invention gives an underground heat transfer model that takes into account complex heat transfer conditions such as complex geological stratification, non-uniform hole wall heat flux, and cluster buried tube arrangement of the medium-deep casing type buried tube heat exchanger, and is more in line with the actual underground heat transfer process and actual engineering situation. Figure 3 It is a flowchart of the design calculation method for the solar medium-deep geothermal heat pump flexible heating system proposed in Embodiment 2 of the present invention.

[0042] In step S300, according to the rock and soil thermal diffusivity, rock and soil thermal conductivity, and rock and soil volume specific heat capacity in each layer of the geology, establish the heat transfer model of any borehole in the medium-deep casing type cluster buried tube heat exchanger in each geological layer, and determine the boundary conditions of the heat transfer domain of any borehole in each geological layer; establish the heat transfer model of the medium-deep casing type cluster buried tube heat exchanger in the entire underground heat transfer domain according to the heat response superposition principle of any borehole in each geological layer; according to the heat transfer model, define the temperature response function of any point at any time.

[0043] In step S310, use the discrete mathematics method to solve the heat transfer model to obtain the distribution of the underground temperature field affected by the hourly dynamic load; to realize the quantitative control of the flexible return of the underground temperature field, determine the solar return temperature that meets the balance adjustment requirements of heat extraction and heat energy reinjection of the underground rock and soil.

[0044] Figure 2 It is a schematic diagram of formation stratification of the underground heat transfer model proposed in Embodiment 2 of the present invention; before establishing the underground heat transfer model, first, the domain of definition of the three-dimensional heat transfer model of the medium-deep casing-type clustered ground heat exchangers is given as -∞ < x < +∞, -∞ < y < +∞, 0 ≤ z ≤ Z nn , Z nn → +∞ ≥ H. x is the abscissa of the horizontal plane within the drilling area; y is the ordinate of the horizontal plane within the drilling area; z is the direction coordinate perpendicular to the horizontal plane within the drilling area; nn is the total number of formations, and z nn is the depth of nn formations; since the spatial geometric domain involved in the heat transfer calculation of the medium-deep ground heat exchangers is very large, the heat transfer model of the medium-deep casing-type clustered ground heat exchangers must consider the influence of the non-uniform physical properties of the rock and soil brought by different formations, and must also consider the problem of non-uniform temperature of the borehole wall brought by the ultra-long heat exchangers.

[0045] To ensure that the established model has a solution and the solution is unique, and at the same time facilitate the solution, the following assumptions are adopted within the domain of definition of the model:

[0046] 1. Within the rock and soil body of the domain of definition, the heat transfer mode outside the boreholes of the clustered medium-deep ground heat exchangers is mainly conduction, and the groundwater seepage within the rock and soil body is ignored.

[0047] 2. Assume that there are nn formations (any formation j = 1, 2,... n... nn) within the rock and soil body of the domain of definition, from the ground surface downwards are the 1st formation, the 2nd formation... the jth formation... the nth formation (the formation where the bottom of the borehole is located)... the nnth formation (far enough below the bottom of the borehole and the last formation within the domain of definition), and each formation is a medium with constant and uniform physical properties.

[0048] 3. The terrestrial heat flux (Q d ) within the entire rock and soil body of the domain of definition is uniform and stable.

[0049] 4. At the initial moment, there is no other thermal disturbance within the entire rock and soil body of the domain of definition, and the temperature of the rock and soil body is a steady-state temperature field maintaining the initial temperature gradient.

[0050] 5. Assume that there are m boreholes (any borehole i = 1, 2,... m) within the domain of definition. The area in the depth direction corresponding to the bottom cross-section of each borehole below the bottom of the borehole (H < z < +∞) is regarded as a hollow cylinder, and the heat capacity within this cylindrical domain is ignored.

[0051] 6. At the outer boundary of the horizontal plane, that is, in the drilling area far from the clustered buried pipes, it is an adiabatic boundary.

[0052] 7. The upper boundary of the rock and soil body of the domain of definition is the ground surface position. The influence of the ground surface temperature on the heat transfer of the medium-deep ground heat exchangers with a depth of several kilometers is very small. Therefore, the ground surface boundary is an isothermal boundary.

[0053] 8. The horizontal position of the borehole wall is another boundary, which connects the inner and outer regions of the borehole. This interface is a boundary where temperature and heat flux are continuous.

[0054] 9. The medium and deep - layer casing - type cluster buried - pipe stratified model established according to the geological stratification. The interfaces between different strata are the axial boundaries of each stratified model. At the stratified boundaries, temperature is continuous and heat flux is continuous.

[0055] To fully illustrate the heat transfer models of any borehole i in different strata in Embodiment 1 of the present invention, this application lists in total the heat transfer model of any borehole i in the first stratum, the heat transfer model of any borehole i in any intermediate j - th stratum, the heat transfer model of any borehole i in the n - th stratum at the bottom of the borehole, and the heat transfer model of any borehole i in the last stratum nn within the defined domain.

[0056] Among them, according to the soil thermal diffusivity, soil thermal conductivity, and soil volume specific heat capacity in the first stratum, the heat transfer model of any borehole in the medium and deep - layer casing - type cluster ground - source heat exchanger in the first stratum is established, and the boundary conditions of the first stratum are determined, including:

[0057] The heat transfer model of any borehole i in the first stratum is:

[0058]

[0059] In the above formula:

[0060]

[0061] Among them, a1 is the soil thermal diffusivity in the first stratum, m 2 / s; λ1 is the soil thermal conductivity in the first stratum, W / (m·K); c v1 is the soil volume specific heat capacity in the first stratum, J / (m 3 ·K); T i,1 is the heat transfer temperature of the i - th borehole in the first stratum; x is the abscissa of the horizontal plane in the borehole area; y is the ordinate of the horizontal plane in the borehole area; z is the direction coordinate perpendicular to the horizontal plane in the borehole area; τ is the change of temperature with time;

[0062] The top boundary of the heat transfer domain of the first stratum is the ground surface (z = Z0 = 0), and the ground surface is the first - type boundary condition (assuming the ground surface maintains a constant temperature t c , K).

[0063] The top boundary of the heat transfer domain of the first stratum is the ground surface. If the ground surface maintains a constant temperature t c ; then here:

[0064] T i,1 = tc , -∞ < x < +∞, -∞ < y < +∞, z = 0, τ ≥ 0; (3)

[0065] The bottom boundary of the first formation heat transfer region is z = Z1, which is the interface between the first formation and the second formation; since the temperature and heat flux are continuous at the formation interface, the boundary conditions here are expressed as:

[0066]

[0067] Among them, is the geotechnical temperature at z = Z1, K; T i,2 is the heat transfer temperature of the i-th borehole in the second formation, K; λ2 is the geotechnical thermal conductivity in the second formation, W / (m·K);

[0068] The outer boundary of the horizontal plane of the first formation underground heat transfer region is set far enough away from the borehole area, and an adiabatic boundary is adopted:

[0069]

[0070] In the cluster of buried tube heat exchangers, the boundary condition of the borehole wall of any borehole i in the first formation is that the heat flux is continuous on the borehole wall, that is, the heat transferred from the fluid in the borehole to the borehole wall is equal to the heat conducted through the borehole wall into the geotechnical. The wall boundary of any borehole i in the cluster of buried tubes in the first formation is:

[0071] T i,1 = T b,i,1 , x, y ∈ Γ i , 0 ≤ z ≤ Z1, τ ≥ 0; (8)

[0072]

[0073] Among them, θ i,1 +(t c + zQ d / λ1) = T i,1 ; T b,i,1 is the borehole wall temperature of any borehole i in the first formation within the borehole group; Γ i is the circular perimeter boundary of the axial projection of the borehole wall on the cross-section, m; θ i，1 is the excess temperature response affected by the i-th borehole and the first formation within the domain; r i is the radial radius representing borehole i, m; r represents the radial coordinate of the horizontal plane; T f1,i,1 is the outer tube fluid temperature of any borehole i in the first formation within the borehole group, K; R 1,i,1 is the thermal resistance between the outer tube fluid and the borehole wall of any borehole i in the first formation within the borehole group, m·K / W; θ ii,jjTo calculate the excess temperature response of borehole (here borehole i) affected by the ii-th borehole and the jj-th formation within the domain; Z1 is the bottom depth of the first formation.

[0074] When it is assumed that the underground consists of nn horizontal formations and the physical properties of the medium within each formation are uniform; when it is assumed that the terrestrial heat flow underground is uniform and stable, the initial temperature distribution within the first formation can be expressed as:

[0075]

[0076] Among them, Q d is the terrestrial heat flow within the rock and soil of the entire domain.

[0077] The heat transfer model of any borehole i within any middle j-th formation is expressed as:

[0078]

[0079] Among them, a j is the thermal diffusivity of the rock and soil within the j-th formation, m 2 / s; λ j is the thermal conductivity of the rock and soil within the j-th formation, W / (m·K); c vj is the volumetric specific heat capacity of the rock and soil within the j-th formation, J / (m 3 ·K); T i,j is the heat transfer temperature of the i-th borehole within the j-th formation; Z j-1 represents the bottom depth of the j-1-th formation; Z j represents the bottom depth of the j-th formation.

[0080] The upper boundary of the heat transfer domain of the j-th formation is the interface between the j-1-th layer and the j-th layer (i.e., at z = Z j-1 ), where the temperature is continuous and the heat flux is continuous: The upper boundary of the heat transfer domain of the j-th formation is expressed as:

[0081]

[0082] Among them, is the rock and soil temperature at z = Z j-1 ;

[0083] The bottom boundary of the heat transfer domain of the j-th formation is the interface between the j-th layer and the j + 1-th layer (i.e., at z = Z j ), where the temperature is also continuous and the heat flux is continuous: The bottom boundary of the heat transfer domain of the j-th formation is expressed as:

[0084]

[0085] λ j-1 is the thermal conductivity of the rock and soil within the j-1-th formation, W / (m·K); λ j+1is the thermal conductivity of the rock and soil in the (j + 1)-th layer, W / (m·K); T Zj is the rock and soil temperature at z = Z j ; T i,j-1 is the heat transfer temperature in the (j - 1)-th layer of the arbitrary borehole i; T i,j+1 is the heat transfer temperature in the (j + 1)-th layer of the arbitrary borehole i, K;

[0086] The outer boundary of the horizontal plane of the underground heat transfer domain is set far enough away from the borehole area and an adiabatic boundary is adopted. The horizontal outer boundary of any intermediate layer j is expressed as:

[0087]

[0088]

[0089] In the cluster of ground heat exchangers, the boundary condition of the hole wall of the i-th borehole in the j-th layer is still the continuity of heat flux on the borehole wall. That is, the heat transferred from the fluid in the borehole to the borehole wall is equal to the heat conducted by the hole wall into the rock and soil. For the wall boundary of any borehole i in the j-th layer in the cluster of ground heat exchangers:

[0090] T i,j = T b,i,j , x,y∈Γ i ,Z j-1 ≤z≤Z j ,τ≥0; (19)

[0091]

[0092] where, θ i，j is the excess temperature response affected by the i-th hole and the j-th layer within the defined domain; T b,i,j is the borehole wall temperature of the arbitrary borehole i in the j-th layer within the borehole group; Γ i is the circular peripheral boundary of the axial projection of the borehole wall on the cross-section, m; r i represents the radial radius of the borehole i, m; T f1,i,j is the outer tube fluid temperature of the arbitrary borehole i in the j-th layer within the borehole group, K; R 1,i,j is the thermal resistance between the outer tube fluid and the borehole wall of the arbitrary borehole i in the j-th layer within the borehole group, m·K / W; θ ii,jj is the excess temperature response of the calculation hole (here it is the borehole i) affected by the ii-th hole and the jj-th layer within the defined domain; Z j is the bottom depth of the j-th layer; then the initial temperature distribution in the j-th layer can be expressed as:

[0093]

[0094] where, λk is the thermal conductivity of the rock and soil in the k-th formation.

[0095] Based on the thermal diffusivity, thermal conductivity, and volumetric specific heat capacity of the rock and soil in the n-th formation at the bottom of the borehole, establish the heat transfer model of any borehole in the middle and deep layer casing type cluster ground heat exchanger in the n-th formation at the bottom of the borehole, and determine the boundary conditions of the n-th formation at the bottom of the borehole, including:

[0096] The heat transfer model of any borehole i in the n-th formation at the bottom of the borehole is:

[0097]

[0098]

[0099] Among them, a n is the thermal diffusivity of the rock and soil in the n-th formation, m 2 / s; λ n is the thermal conductivity of the rock and soil in the n-th formation, W / (m·K); c vn is the volumetric specific heat capacity of the rock and soil in the n-th formation, J / (m 3 ·K); T i,n is the heat transfer temperature of the i-th borehole in the n-th formation; Z n-1 represents the bottom depth of the (n - 1)-th formation; Z n represents the bottom depth of the n-th formation;

[0100] The upper boundary of the heat transfer domain of the n-th formation is the interface between the (n - 1)-th layer and the n-th layer (i.e., z = Z n-1 ), where the temperature is continuous and the heat flux is continuous: The upper boundary of the heat transfer domain of the (n - 1)-th formation is expressed as:

[0101]

[0102] Among them, is the rock and soil temperature at z = Z n-1 ;

[0103] The bottom boundary of the heat transfer domain of the n-th formation is the interface between the n-th layer and the (n + 1)-th layer (i.e., z = Z n ), where the temperature is also continuous and the heat flux is continuous: The bottom boundary of the heat transfer domain of the n-th formation is expressed as:

[0104]

[0105] λ n-1 is the thermal conductivity of the rock and soil in the (n - 1)-th formation, W / (m·K); λ n+1 is the thermal conductivity of the rock and soil in the (n + 1)-th formation, W / (m·K); is the value at z = Z nThe geotechnical temperature at [location]; T i,n-1 is the heat transfer temperature in the n-1th layer of any borehole i; T i,n+1 is the heat transfer temperature in the n+1th layer of any borehole i, K;

[0106] The outer boundary of the horizontal plane of the underground heat transfer domain is set far enough away from the borehole area and an adiabatic boundary is adopted. The horizontal outer boundary of the nth layer of the formation at the bottom of the borehole is expressed as:

[0107]

[0108] Then, it is determined whether the adiabatic boundary is not set for the wall boundary of the nth layer according to whether the bottom of the borehole is on the formation boundary. The heat transfer model of any borehole i in the formation (the nth layer) where the bottom of the borehole is located is divided into two cases: 1. The bottom of the borehole is located within the nth layer, that is, the borehole depth H < Z n ; 2. The bottom of the borehole is located on the formation interface, that is, the borehole depth H = Z n . The heat transfer expressions of the heat transfer model at the borehole wall boundary are different in these two cases.

[0109] When the bottom of the borehole is located in the nth layer of the formation, that is, the borehole depth H < Z n : Then, on the borehole wall within the borehole depth, the heat transferred from the fluid in the borehole to the borehole wall is equal to the heat conducted through the borehole wall into the geotechnical, and the heat flow is continuous. An adiabatic boundary is adopted at the borehole wall below the borehole depth. The specific boundary conditions are as follows:

[0110] T i,n = T b,i,n , x,y∈Γ i , Z n-1 ≤ z ≤ H, τ≥0; (30)

[0111]

[0112] When the bottom of the borehole is located on the formation interface, that is, the borehole depth H = Z n : Then, the heat flow is kept continuous at the borehole wall. The specific boundary conditions are as follows:

[0113] T i,n = T b,i,n , x,y∈Γ i , Z n-1 ≤ z ≤ Z n , τ≥0; (33)

[0114]

[0115] Among them, T b,i,n is the borehole wall temperature of any borehole i in the nth formation within the borehole group; θ i，nis the excess temperature response affected by the i-th hole and the n-th formation within the defined domain; T f1,i,n is the outer tube fluid temperature of any borehole i in the n-th formation within the borehole group; R 1,i,n is the thermal resistance between the outer tube fluid and the borehole wall of any borehole i in the n-th formation within the borehole group, m·K / W.

[0116] When it is assumed that the underground consists of nn horizontal formations and the physical properties of the medium within each formation are uniform and consistent; when it is assumed that the terrestrial heat flow underground is uniform and stable, the initial temperature distribution within the n-th formation can be expressed as:

[0117]

[0118] where, λ k is the geotechnical thermal conductivity within the k-th formation.

[0119] The heat transfer model of any borehole i within the last formation nn (below the bottom of the borehole and far enough from the bottom of the borehole) within the defined domain is:

[0120]

[0121] where,

[0122] where, a nn is the geotechnical thermal diffusivity within the nn-th formation, m 2 / s; λ nn is the geotechnical thermal conductivity within the nn-th formation, W / (m·K); c vnn is the volumetric specific heat capacity of the geotechnical material within the nn-th formation, J / (m 3 ·K);

[0123] The upper boundary of the nn-th layer is the interface between the nn-1-th layer and the nn-th layer (i.e., at z = Z nn-1 ). At the formation interface, the temperature is continuous and the heat flux is continuous:

[0124]

[0125] The lower boundary of the nn-th layer is the bottom boundary of the underground heat transfer domain, set far from the bottom of the hole (i.e., z = Z nn >>H)

[0126] The second type of boundary condition is adopted:

[0127]

[0128] The outer boundary of the horizontal plane of the underground heat transfer domain is set far enough from the borehole area, and an adiabatic boundary is adopted:

[0129]

[0130] In the cluster of buried pipe heat exchangers, the boundary condition of the hole wall of any borehole i in the nnth stratum is the adiabatic condition:

[0131]

[0132] Assuming that the underground in the borehole area consists of nn horizontal strata, the initial temperature distribution in the nnth stratum below the borehole depth can be expressed as:

[0133]

[0134] According to the heat transfer model outside the borehole of the stratified medium-depth casing type cluster buried pipe heat exchanger given above, the calculation formula for the temperature response T(x, y, z, τ) of any point (x, y, z) in the domain space at any time τ is:

[0135]

[0136] Among them, θ i,j (x, y, z, τ) is the excess temperature response affected by the ith hole and the jth stratum in the domain; T i,j (x, y, z, τ) is the temperature response affected by the ith hole and the jth stratum in the domain.

[0137] Based on the established underground heat transfer model of the stratified medium-depth cluster buried pipe heat exchanger, combined with the heat transfer model inside the borehole of the casing type buried pipe heat exchanger, and solved by numerical calculation methods such as finite difference, finite volume or finite element, the distribution of the underground temperature field affected by the hourly dynamic load can be obtained. The above hourly dynamic load can be obtained by reading the hourly building heat load and solar collector heat load data calculated by software such as EnergyPlus, TRNSYS, and DeST.

[0138] Since the solar medium-depth ground source heat pump flexible heating system given in the present invention stores the heat collected by the solar module underground through the medium-depth casing type buried pipe heat exchanger in summer and transition seasons, therefore, the underground temperature field after heat extraction in the heating season of the heating system will inevitably undergo a certain degree of flexible regression. To achieve quantitative control of the flexible regression of the underground temperature field and give full play to the heating capacity of the buried pipe heat exchanger as much as possible, the following will give the calculation method of the solar energy energy storage and reinjection temperature (T s ) for the flexible regression of the underground temperature field after heat extraction based on the above model.

[0139] First, assume that the calculation range of the solar energy energy storage and reinjection temperature (T s ) is (T1, T2), and any temperature T is randomly selected within the above range s预设, while reading the hourly building heat load and solar collector heat load data calculated by software such as EnergyPlus, TRNSYS, and DeST. The heat transfer model in the borehole of the double-pipe ground heat exchanger is used to calculate according to the constant inlet temperature T sj Perform heat energy reinjection, supply heat according to the read hourly building heat load and solar collector heat load, and the change of the circulating fluid temperature in each borehole of the deep ground heat exchanger in the cluster.

[0140] Substitute the calculated circulating fluid temperature in the borehole into the borehole wall boundary conditions of the borehole external heat transfer model established by the present invention, that is, substitute into formulas (9), (20), (31) and (34), and use numerical calculation methods such as finite difference, finite volume or finite element to solve the borehole external heat transfer model established by the present invention, whereby the porous superposition temperature response at any point in any layer of the rock and soil can be solved. Therefore, the borehole wall temperature response of any borehole affected by the superposition of other boreholes in any layer can be calculated by formula (46). This borehole wall superposition temperature response is the calculation basis for the circulating fluid temperature at the next moment and will participate in the calculation of the circulating fluid temperature at the next moment. By analogy, the heat transfer calculation of the circulating fluid temperature in each underground borehole and the temperature of the rock and soil outside the borehole for the entire operation cycle is completed hour by hour.

[0141] Figure 4 It is the calculation process diagram of the solar energy reinjection temperature proposed in Embodiment 2 of the present invention; in the above underground heat transfer model calculation, at the same time, according to the hourly building heat load and solar collector heat load data calculated by software such as EnergyPlus, TRNSYS, and DeST, the hourly cumulative heat extraction amount borne by the deep double-pipe cluster ground heat exchanger can be calculated according to the following formula.

[0142]

[0143] Among them, Q L is the hourly cumulative heat extraction amount; COP is the heating performance coefficient of the heat pump unit; Q τ is the hourly heating load; Q s is the hourly heating load shared by the solar collector;

[0144] The outlet temperature of the circulating fluid during solar energy reinjection obtained according to the preset solar energy reinjection temperature and the numerical solution of the underground heat transfer model:

[0145]

[0146] Among them, C τ is the specific heat capacity of the circulating fluid in the deep double-pipe ground heat exchanger at time τ, J / (kg·K); M τ is the total mass flow rate of the circulating fluid at time τ, kg / s; T τis the hourly cycle liquid outlet temperature when the medium and deep casing - type cluster ground heat exchanger returns the recovered heat energy in the underground heat transfer calculation, K; Q R is the total recovered heat energy;

[0147] In formulas (47) and (48),

[0148]

[0149] where, Δτ is the calculation time step set in the numerical model calculation; τ g is the total heat supply duration, s; τ x is the total recovered heat energy duration; p is the number of time segments into which the total heat supply duration is evenly divided according to Δτ; q is the number of time segments into which the total recovered heat energy duration is evenly divided according to Δτ.

[0150] To achieve the quantitative control of the flexible regression of the underground temperature field, determine the solar energy injection temperature that meets the balance adjustment requirements of heat extraction from the underground rock and soil and heat energy injection; including:

[0151] Set the balance adjustment requirements for heat extraction from the underground rock and soil and heat energy injection; set Q according to the given balance adjustment requirements L and Q R ratio, and determine the calculation termination condition of T L / Q R . If Q s预设 / Q L / Q R meets the calculation termination condition, then the assumed T s预设 meets the calculation requirements, that is, the heat extraction amount and the recovered heat energy amount underground meet the set balance requirements, and the underground soil temperature field can flexibly return, or even balance, which can ensure the long - term heat extraction capacity and operation efficiency of the medium - deep ground heat exchanger. If it does not meet the calculation termination condition, then use the bisection method to find the root and reset T s预设 , and recalculate until the solar energy injection temperature that can meet the set balance adjustment requirements is found. At this time, T s = T s预设 , and the solar energy injection temperature is solved.

[0152] Assume that the underground consists of nn horizontal strata (nn = 4), and the physical properties of the medium within each stratum are uniform. The borehole depth H = 2000m, and the lower limit of the 4th stratum is 3000m, that is, H < Z n . The following Table 1 is the stratum parameter table; the following Table 2 is the design parameters inside the borehole of the casing; the following Table 3 is the other design parameters.

[0153] Table 1: Stratum Parameter Table

[0154]

[0155]

[0156] Table 2: Design Parameters inside the Borehole of the Casing

[0157] parameter outer pipe inner pipe backfill material outer diameter (mm) 193.7 110 —— wall thickness (mm) 8.33 10 —— thermal conductivity (W / (m·K)) 45.00 0.40 1.5 <![CDATA[Volume heat capacity (J / (m 3 ·K))]]> <![CDATA[3.4×10 6 > <![CDATA[1.2×10 6 > <![CDATA[2.2×10 6 >

[0158] Table 3: Other Design Parameters

[0159]

[0160] According to Figure 4 the calculation process of the solar thermal energy reinjection temperature shown below, Table 4 gives the calculation results of Q L、 Q R and T s as follows.

[0161] Table 4: Calculation Results of Q L、 Q R and T s as follows

[0162] <![CDATA[Q L Calculation result (kJ)]]> <![CDATA[Q R Calculation result (kJ)]]> <![CDATA[T s Calculation result (°C)]]> <![CDATA[7.98×10 10 > <![CDATA[7.96×10 10 > 67.33

[0163] After operating at this solar reinjection temperature for 30 years, Figure 5 this is the temperature field at 1000 m underground with solar reinjected thermal energy proposed in Embodiment 2 of the present invention; Figure 6 this is the temperature field at 1000 m underground without solar reinjected thermal energy proposed in Embodiment 2 of the present invention. Figure 5 It shows that by performing thermal energy reinjection according to T calculated by the solar reinjection temperature calculation method given in the present invention s the underground soil temperature field can return to the initial soil temperature (52.4 °C) after the long-term operation of the solar medium-deep geothermal heat pump composite system, which provides a reliable guarantee for the efficient and stable operation of the composite system.

[0164] A design calculation method for a solar medium-deep geothermal heat pump flexible heating system proposed in Embodiment 2 of the present invention, based on the given heat transfer model as the theoretical basis, proposes a quantitative adjustment operation method for the solar medium-deep geothermal heat pump composite flexible heating system to guide the flexible and efficient operation of the composite system.

[0165] The above are only embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A solar mid-deep ground source heat pump flexible heating system, characterized in that: include: A solar thermal collector (1), a medium-deep casing-type underground pipe heat exchanger (2), a heat pump unit (3) and a heat exchanger (4); The solar thermal collector (1) is connected to a heat exchanger (4); the heat exchanger (4), the medium-deep layer casing-type underground pipe heat exchanger (2) and the user side are connected via a first three-way regulating valve group (9) and a second three-way regulating valve group (10); the medium-deep layer casing-type underground pipe heat exchanger (2) is connected to a heat pump unit (3) via a valve group (11), and the heat pump unit (3) is connected to a heat user side via a valve group (12); The solar thermal collector (1) is used to collect low-grade thermal energy, and a portion of the low-grade thermal energy is stored underground through a medium-deep casing-type buried pipe heat exchanger (2) for flexible return of the underground temperature field that deviates from the initial value due to the influence of heat extraction; The ground source heat pump unit (3) is used to convert low-grade heat energy at the solar collector (1) and low-grade heat energy at the medium-deep casing-type buried pipe heat exchanger 2 into high-grade heat energy.

2. The system according to claim 1, characterized in that The system includes five working modes; The first working mode is: the first three-way regulating valve group (9) and the second three-way regulating valve group (10) are both closed, and the first valve group (11) located between the medium-deep layer casing-type underground pipe heat exchanger (2) and the heat pump unit (3) and the second valve group (12) located between the heat pump unit (3) and the user side are both opened, so that the heat pump unit (3) alone provides heat; The second working mode is: the inlet a of the first three-way regulating valve group (9) and the outlet b connected to the user side are both opened, and the outlet c connected to the medium-deep casing-type ground pipe heat exchanger (2) is closed; the outlet a of the second three-way regulating valve group (10) and the inlet b connected to the user side are both opened, and the outlet c connected to the medium-deep casing-type ground pipe heat exchanger (2) is closed; the first valve group (11) and the second valve group (12) are both opened; the solar collector (1) and the heat pump unit (3) are combined to provide heat; The third working mode is: the inlet a of the first three-way regulating valve group (9) and the outlet b connected to the user side are both opened, and the outlet c connected to the medium-deep casing-type ground pipe heat exchanger (2) is closed; the outlet a of the second three-way regulating valve group (10) and the inlet b connected to the user side are both opened, and the outlet c connected to the medium-deep casing-type ground pipe heat exchanger (2) is closed; the first valve group (11) and the second valve group (12) are both closed; the solar thermal collector (1) provides heat alone; The fourth working mode is: the inlet a and outlets b and c of the first three-way regulating valve group (9) are all open; the inlet b, c and outlet a of the second three-way regulating valve group (10) are all open; the first valve group (11) and the second valve group (12) are all closed; the solar thermal collector (1) realizes the combined operation of heat supply and energy storage; by adjusting the opening of the outlet c connected to the medium-deep underground heat exchanger (2) of the first three-way regulating valve group (9) and the outlet b connected to the user side; by adjusting the opening of the inlet c connected to the medium-deep underground heat exchanger (2) of the second three-way regulating valve group (10) and the inlet b connected to the user side, the ratio of heat supply and heat storage can be adjusted; The fifth working mode is: the inlet a of the first three-way regulating valve group (9) and the outlet c connected to the medium-deep layer casing-type ground pipe heat exchanger (2) are opened, and the outlet b connected to the user side is closed; the outlet a of the second three-way regulating valve group (10) and the inlet c connected to the medium-deep layer casing-type ground pipe heat exchanger (2) are opened, and the inlet b connected to the user side is closed; the first valve group (11) and the second valve group (12) are both closed; and the solar thermal collector (1) realizes the energy storage operation mode.

3. A design and calculation method for a solar mid-deep geothermal heat pump flexible heating system is implemented based on a solar mid-deep geothermal heat pump flexible heating system according to any one of claims 1 to 2, characterized in that: The following steps are involved: According to the thermal diffusivity, thermal conductivity and volumetric heat capacity of the rock and soil in each geological layer, a heat transfer model of any borehole in the medium-deep casing cluster underground heat exchanger in each stratum is established, and the boundary conditions of the heat transfer domain of any borehole in each stratum are determined; according to the thermal response superposition principle of any borehole in each stratum, a heat transfer model of the medium-deep casing cluster underground heat exchanger in the entire underground heat transfer domain is established; according to the heat transfer model, the temperature response function of any point in the underground heat transfer domain of the medium-deep casing cluster underground heat exchanger at any time is defined; The discrete mathematical method is used to solve the heat transfer model to obtain the underground temperature field distribution affected by the hourly dynamic load. In order to achieve quantitative control of the flexible regression of the underground temperature field, the solar energy reinjection temperature that meets the balance adjustment requirements of underground rock and soil heat extraction and heat energy reinjection is determined.

4. The design calculation method according to claim 3, characterized in that: According to the thermal diffusivity, thermal conductivity and volumetric heat capacity of the rock and soil in the first stratum, a heat transfer model of any borehole in the medium-deep casing cluster buried pipe heat exchanger in the first stratum is established to determine the boundary conditions of the first stratum, including: The heat transfer model of any borehole i in the first stratum is: In the above formula: Where a1 is the thermal diffusivity of the rock and soil in the first stratum; λ1 is the thermal conductivity of the rock and soil in the first stratum; c v1 is the volume specific heat capacity of the rock and soil in the first stratum; T i,1 is the heat transfer temperature of the ith borehole in the first stratum; x is the horizontal coordinate of the horizontal plane in the borehole area; y is the vertical coordinate of the horizontal plane in the borehole area; z is the direction coordinate of the vertical horizontal plane in the borehole area; τ is the change of temperature with time; The top boundary of the first layer heat transfer domain is the ground surface. If the ground surface maintains a constant temperature t c ; Then here: T i,1 =t c ,-∞<x<+∞,-∞<y<+∞,z=0,τ≥0; (3) The bottom boundary of the heat transfer domain of the first layer is z=Z1, which is the interface between the first layer and the second layer. The boundary condition here is expressed as: in, is the rock and soil temperature at z = Z1; T i,2 is the heat transfer temperature of the ith borehole in the second stratum; λ2 is the thermal conductivity of the rock and soil in the second stratum; The outer boundary of the horizontal plane of the underground heat transfer domain in the first layer adopts an adiabatic boundary: The wall boundary of any borehole i in the cluster buried pipe in the first stratum is: T i,1 =T b,i,1 ,x,y∈Γ i ,0≤z≤Z1,τ≥0; (8) Among them, θ i,1 +(t c +zQ d / λ1=T i,1 );θ i，1 is the excess temperature response affected by the ith hole and the first formation in the definition domain; T b,i,1 is the borehole wall temperature of any borehole i in the borehole group in the first stratum; Γ i is the circumferential boundary of the axial projection of the borehole wall on the cross section; r i represents the radial radius of borehole i; r represents the radial coordinate of the horizontal plane; T f1,i,1 is the outer tube fluid temperature of any borehole i in the borehole group in the first stratum; R 1,i,1 is the thermal resistance between the inner and outer pipe fluid and the borehole wall of any borehole i in the borehole group; θ ii,jj To calculate the excess temperature response of the hole (here, borehole i) affected by the ii-th hole and the jj-th formation in the definition domain; Z1 is the bottom depth of the 1st formation; The initial temperature distribution in the first layer is expressed as: Among them, Q d is the geothermal heat flow in the rock and soil of the entire definition domain.

5. The design calculation method according to claim 3, characterized in that: According to the thermal diffusivity, thermal conductivity and volume specific heat capacity of the rock and soil in the jth stratum, a heat transfer model of any borehole in the medium-deep casing cluster buried pipe heat exchanger in the jth stratum is established to determine the boundary conditions of the jth stratum, including: The heat transfer model of any borehole i in any j-th stratum in the middle is: In the above formula, Among them, a j is the thermal diffusivity of rock and soil in the jth stratum; j is the thermal conductivity of rock and soil in the jth stratum; c vj is the volume specific heat capacity of rock and soil in the jth stratum; T i,j is the heat transfer temperature of the ith borehole in the jth formation; Z j-1 represents the bottom depth of the j-1st stratum; Z j represents the bottom depth of the jth stratum; The upper boundary of the heat transfer domain of the jth formation is expressed as: in, z=Z j-1 The rock and soil temperature at The bottom boundary of the j-th formation heat transfer domain is expressed as: λ j-1 is the thermal conductivity of rock and soil in the j-1th layer; j+1 is the thermal conductivity of rock and soil in the j+1th stratum; z=Z j The rock and soil temperature at i,j-1 is the heat transfer temperature in the j-1th layer of any borehole i; T i,j+1 is the heat transfer temperature in the j+1th layer of any borehole i; The horizontal outer boundary of any intermediate layer j is expressed as: The wall boundary of any borehole i in the jth stratum is expressed as: T i,j =T b,i,j , x,y∈Γ i ,Z j-1 ≤z≤Z j ,τ≥0; (19) Among them, T b,i,j is the borehole wall temperature of any borehole i in the jth stratum within the borehole group; θ i，j is the excess temperature response affected by the i-th hole and the j-th formation in the definition domain; T f1,i,j R is the outer tube fluid temperature of any borehole i in the jth formation in the borehole group; 1,i,j is the thermal resistance between the inner and outer pipe fluid and the borehole wall in the jth formation of any borehole i in the borehole group; The initial temperature distribution in the jth layer is expressed as: Among them, λ k is the thermal conductivity of rock and soil in the kth stratum.

6. The design calculation method according to claim 3, characterized in that: According to the thermal diffusivity, thermal conductivity and volume specific heat capacity of the rock and soil in the nth stratum at the bottom of the borehole, a heat transfer model of any borehole in the medium-deep casing cluster buried pipe heat exchanger in the nth stratum at the bottom of the borehole is established, and the boundary conditions of the nth stratum at the bottom of the borehole are determined, including: The heat transfer model of any borehole i in the formation n where the bottom of the borehole is located is: Among them, a n is the thermal diffusivity of rock and soil in the nth stratum; n is the thermal conductivity of rock and soil in the nth stratum; c vn is the volume specific heat capacity of rock and soil in the nth stratum; T i,n is the heat transfer temperature of the ith borehole in the nth stratum; Z n-1 Represents the bottom depth of the n-1th stratum; Z n represents the bottom depth of the nth stratum; The upper boundary of the heat transfer domain of the nth layer is expressed as: in, z=Z n-1 The rock and soil temperature at The bottom boundary of the heat transfer domain of the nth layer is expressed as: λ n-1 is the thermal conductivity of rock and soil in the n-1th layer; n+1 is the thermal conductivity of rock and soil in the n+1th layer; z=Z n The rock and soil temperature at i,n-1 is the heat transfer temperature in the n-1th layer of any borehole i; T i,n+1 is the heat transfer temperature in the n+1th layer of any borehole i; The horizontal outer boundary of the nth stratum at the bottom of the borehole is expressed as: Then, it is determined whether the wall boundary of the nth layer is not provided with an insulating boundary according to whether the bottom of the borehole is located on the boundary of the stratum.

7. The design calculation method according to claim 6, characterized in that: Determine the wall boundary based on the formation position of the bottom of the borehole; including: When the bottom of the borehole is located in the nth layer, that is, the borehole depth H<Z n hour: T i,n =T b,i,n ,x,y∈Γ i ,Z n-1 ≤z≤H,τ≥0;(30) When the bottom of the borehole is located on the stratum interface, that is, the borehole depth H = Z n hour: T i,n =T b,i,n ,x,y∈Γ i ,Z n-1 ≤z≤Z n ,τ≥0; (33) Among them, T b,i,n is the borehole wall temperature of any borehole i in the nth stratum within the borehole group; θ i，n is the excess temperature response affected by the ith hole and the nth formation in the definition domain; T f1,i,n R is the outer tube fluid temperature in the nth formation of any borehole i in the borehole group; 1,i,n is the thermal resistance between the inner and outer pipe fluid and the borehole wall in the nth formation of any borehole i in the borehole group; The initial temperature distribution in the nth layer is expressed as: Z n-1 ≤z≤Z n ,-∞<x<+∞,-∞<y<+∞,τ=0,k=1,...n-1 Among them, λ k is the thermal conductivity of rock and soil in the kth stratum.

8. The design calculation method according to claim 3, characterized in that: According to the thermal diffusivity, thermal conductivity and volume specific heat capacity of the rock and soil in the nth stratum, a heat transfer model of any borehole in the medium-deep casing cluster buried pipe heat exchanger in the nth stratum is established to determine the boundary conditions of the nth stratum, including: The heat transfer model of any borehole i in the last formation nn in the definition domain is: in, Among them, a nn is the thermal diffusivity of rock and soil in the nth stratum; nn is the thermal conductivity of rock and soil in the nth stratum; c vnn is the volume specific heat capacity of rock and soil in the nth stratum; T i,nn is the heat transfer temperature of the ith borehole in the nth formation; Z nn-1 Represents the bottom depth of the nn-1st stratum; Z nn represents the bottom depth of the nnth stratum; The upper boundary of the nnth layer is expressed as: The lower boundary of the nth layer adopts the second type of boundary condition: The outer boundary of the horizontal surface of the underground heat transfer domain adopts an adiabatic boundary: In the cluster ground heat exchanger, the boundary condition of the hole wall of any borehole i in the nth stratum is adiabatic condition: The initial temperature distribution in the nnth formation below the borehole depth can be expressed as:

9. The design calculation method according to any one of claims 3 to 8, characterized in that: The method further includes defining a temperature response function of any point in the underground heat transfer domain of the mid-depth casing cluster underground heat exchanger at any time in the heat transfer model; including: The calculation formula for the temperature response T(x,y,z,τ) of any point (x,y,z) in the domain space at any time τ is: Among them, θ i,j (x, y, z, τ) is the excess temperature response affected by the i-th hole and the j-th formation in the definition domain; T i,j (x, y, z, τ) is the temperature response affected by the i-th hole and j-th formation in the definition domain.

10. The design calculation method according to claim 9, characterized in that: The heat transfer model is solved by discrete mathematical methods to obtain the underground temperature field distribution affected by hourly dynamic loads; in order to achieve quantitative control of the underground temperature field flexible regression, the solar energy reinjection temperature that meets the balance adjustment requirements of underground rock and soil heat extraction and heat energy reinjection is determined; including: Calculate the hourly cumulative heat intake of the deep-layer cluster underground heat exchanger: Among them, Q L is the cumulative heat taken hourly; COP is the heating performance coefficient of the heat pump unit; Q τ is the hourly heating load; Q s Hourly heating load shared by solar thermal collectors; The circulating fluid outlet temperature during solar recharge is obtained based on the preset solar recharge temperature and the numerical solution of the underground heat transfer model: Among them, C τ M is the specific heat capacity of the circulating fluid in the deep-layer casing-type underground heat exchanger at time τ; τ is the total mass flow rate of the circulating fluid at time τ; T τ is the hourly circulating fluid outlet temperature of the deep-layer cluster underground heat exchanger when recharging heat energy, obtained from underground heat transfer calculation; Q R is the total heat energy reinjection amount; Among them, Δτ is the calculation time step set in the numerical model calculation; τ g is the total heating time; τ x is the total heat energy recharge time; p is the number of time periods divided equally by the total heating time according to Δτ; q is the number of time periods divided equally by the total heat energy recharge time according to Δτ; Set the balance adjustment requirements for underground rock and soil heat extraction and heat energy reinjection; determine Q L / Q R Whether T is satisfied s The calculation termination condition of ; if it is satisfied, then T s预设 Meet the calculation requirements; if not, use the binary search method to reset T s预设 Until the solar energy recharging temperature that can meet the set balance adjustment requirements is found, at this time T s =T s预设 .

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