Design method of ground heat exchanger suitable for geothermal energy storage and utilization system

Abstract

The invention discloses a ground heat exchanger design method suitable for a geothermal energy storage and utilization system, the geothermal energy storage and utilization system is used for supplying heat and cold to a building and comprises a heat pump unit, a heat source tower and ground heat exchangers, and the ground heat exchangers are respectively arranged in energy storage units of a geothermal energy storage area; the design method of the ground heat exchanger comprises the following steps that S1, the soil average volumetric specific heat capacity CV of the geothermal energy storage area is measured and calculated through a coring method; s2, calculating the total energy storage energy Q storage of the single energy storage unit; and S3, according to the annual cold load Q cold and heat load Q heat of the building, the maximum heat absorption quantity Q heat absorption and the maximum heat release quantity Q heat release of the buried pipe heat exchangers in the geothermal energy storage area are calculated, the number n of energy storage units is calculated, and the number of the buried pipe heat exchangers is determined. According to the method, the relation between the energy storage capacity of the soil and the annual cooling and heating load of the building can be reflected more truly, the number of the buried pipe holes can be reduced, and the construction investment is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal energy development and utilization, and in particular to a design method for a buried pipe heat exchanger suitable for a geothermal energy storage and utilization system. Background Art

[0002] As a green, low-carbon, recyclable and renewable energy source, the development and utilization of geothermal energy is of great significance. Unlike traditional fossil energy, the utilization of shallow geothermal energy produces almost no greenhouse gas emissions such as carbon dioxide. Taking the ground source heat pump system as an example, it achieves heating and cooling by extracting shallow geothermal energy. Compared with gas boiler heating, the energy saving rate can reach more than 30%, greatly reducing the carbon emissions generated by burning fossil fuels, and playing a significant role in alleviating global warming. However, in the implementation of specific ground source heat pump projects, the following problems are often encountered: First, the data required for existing geothermal heat pump system design is obtained through geotechnical heat release testing. During these tests, two test holes are typically excavated. Ground pipes are installed in these test holes and connected to heating lines. After a specified heating period, as required by regulations, the heat exchange between the ground pipes and the geotechnical system is considered to have reached a steady state. The collected data is then input into specialized geothermal heat pump geotechnical testing software to infer thermal properties such as heat transfer per linear meter, geotechnical thermal conductivity, and volumetric specific heat capacity. This geotechnical heat transfer per linear meter data is closely related to the spacing of the test holes. Because the test holes are spaced far apart, heat dissipation is essentially directed to an infinite surface. However, actual construction adheres to the design specification of 3-6 meter spacing between ground pipes. Consequently, the design scheme suffers from a mismatch between the basic parameters and actual conditions. This leads to decreased system energy efficiency and long-term degradation of heating / cooling performance after project operation, diminishing the credibility of the technology and hindering project promotion.

[0003] Second, due to the disparity between heat release and heat absorption in traditional geothermal heat pump systems, the soil's inherent thermal balance is disrupted, leading to heat or cold accumulation in the soil. This, in turn, causes the soil's constant temperature layer to rise or fall, causing the system to operate unstably. This ultimately impacts the system's heating or cooling performance, significantly reducing the system's energy efficiency. Therefore, when designing a geothermal heat pump system, to achieve soil thermal equilibrium, if the soil releases more heat than it absorbs, a chiller combined with a cooling tower is required to dissipate the excess heat directly into the air. However, due to high outdoor temperatures in summer, the chiller's workload increases, increasing energy consumption. If the soil absorbs more heat than it releases, additional heat sources (such as air-source heat pumps or gas boilers) are required to supplement the heat. Due to lower outdoor temperatures in winter, the air-source heat pump's energy consumption increases. Therefore, whether using a chiller combined with a cooling tower or other heat sources for heat dissipation increases energy consumption, further reducing system efficiency. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a design method for a buried pipe heat exchanger suitable for a geothermal energy storage and utilization system, which is simple to implement and has good project implementation effects. Specifically, the following technical solutions can be adopted: The present invention relates to a method for designing a ground heat exchanger suitable for a geothermal energy storage and utilization system. The ground heat storage and utilization system is used to provide heating and cooling to a building and includes a heat pump unit, a heat source tower, and a ground heat exchanger. The ground heat exchangers are respectively arranged in each energy storage unit in the geothermal energy storage area. The design method of the buried pipe heat exchanger comprises the following steps: S1, calculate the average volumetric specific heat capacity C of the soil in the geothermal energy storage area by coring method V ,J / (m 3 ℃); S2, calculate the total energy storage energy Q of a single energy storage unit 储 =C v ×V×ΔT, Where V is the volume of a single energy storage unit, m 3 ; ΔT—the difference between the average design supply and return water temperature of the buried pipe heat exchanger and the initial temperature of the soil constant temperature layer, °C; S3, based on the building's annual cooling load Q 冷 and heat load Q 热 , calculate the maximum heat absorption Q of the buried heat exchanger in the geothermal energy storage area 吸 and maximum heat release Q 放 , Q 放 = Q 冷 × (1 + 1 / EER) + Q 输耗 + Q 泵耗 Q 吸 = Q 热 × (1-1 / COP) + Q 输耗 -Q 泵耗 Among them, EER—ratio of cooling / heating to input power, COP—the ratio of cooling capacity to cooling power, Q 输耗 —Heat loss in the transmission pipeline, kW·h; Q 泵耗 —Heat loss during operation of the heat pump unit, kW·h; If Q 吸 >Q 放 , calculate the number of energy storage units n=Q 吸 / Q 储 ; If Q 放 >Q 吸, calculate the number of energy storage units n=Q 放 / Q 储 ; The number of ground heat exchangers is determined according to the number n of energy storage units.

[0005] Furthermore, the coring method is used to determine and calculate the average volumetric specific heat capacity C of the soil in the area where the buried heat exchanger is located. V When the geothermal energy storage area is used, a drilling position is randomly selected in the drilling area, and then the cores are taken from top to bottom in batches, with one group taken each time. The volume specific heat capacity C of each group of core samples is then measured by differential scanning calorimetry. i (i=1, 2, 3, ...), and then according to the moisture content P of each group of core samples i (i=1, 2, 3, ...), the weighted average is used to obtain the average volumetric specific heat capacity Cv of the soil in the sampling area, Among them, V i —Volume of each core sample, m 3 ; C 水 —Volume specific heat capacity of water, J / (m 3 ·℃).

[0006] The specific structure of the geothermal energy storage and utilization system described in the present invention is as follows: The ground source side of the heat pump unit is provided with a geothermal water supply pipe and a geothermal return pipe, and the user side of the heat pump unit is provided with a heating and cooling water supply pipe and a heating and cooling return pipe; a first valve is provided on the geothermal water supply pipe, a second valve is provided on the geothermal return pipe, a third valve is provided on the heating and cooling water supply pipe, and a first water pump and a fourth valve are provided on the heating and cooling return pipe; The energy storage units are distributed in a grid pattern within the geothermal energy storage area. The buried heat exchangers within each energy storage unit are provided with a geothermal water supply branch pipe and a geothermal water return branch pipe. The geothermal water supply branch pipes are arranged in parallel on the geothermal water supply connecting main pipe, and the geothermal water return branch pipes are arranged in parallel on the geothermal water return connecting main pipe. The geothermal water supply connecting main pipe is connected to the geothermal water supply pipe, and the geothermal water return connecting main pipe is connected to the geothermal water return pipe. A second water pump is provided on the geothermal water return connecting main pipe. The heat source tower is provided with an energy replenishment water supply pipe and an energy replenishment return pipe; the energy replenishment water supply pipe is connected to the geothermal water supply connecting main pipe, and a third water pump and a fifth valve are provided on the energy replenishment water supply pipe. A heat replenishment water supply branch pipe connected to the heating and cooling water supply pipe is also provided between the third water pump and the fifth valve, and a sixth valve is provided on the heat replenishment water supply branch pipe; the energy replenishment return pipe is connected to the geothermal return water connecting main pipe, and a seventh valve is provided on the energy replenishment return pipe. A heat replenishment return water branch pipe connected to the heating and cooling return water pipe is provided behind the seventh valve, and an eighth valve is provided on the heat replenishment return water branch pipe.

[0007] The present invention provides a design method for a buried pipe heat exchanger suitable for a geothermal energy storage and utilization system. The method divides the geothermal energy storage area where the buried pipe heat exchanger is installed into energy storage units. The energy storage capacity of the energy storage units is calculated based on the soil's thermophysical properties. The required number of energy storage units is then calculated based on the building's annual cooling and heating loads, thereby determining the number of buried pipe heat exchangers. This method can more realistically reflect the relationship between the soil's energy storage capacity and the building's annual cooling and heating loads, while also reducing the number of buried pipe holes and effectively lowering construction investment. Furthermore, the geothermal energy storage and utilization system described in the present invention utilizes a closed heat source tower system instead of a chiller + cooling tower to achieve intelligent regulation of thermal energy in different seasons. This system releases stored heat in winter and absorbs excess heat in summer, maintaining a dynamic balance between heat release and heat absorption in the soil layer during different operating cycles. This thermal balance mechanism not only ensures the stability of cooling / heating in the building space but also significantly improves the system's energy efficiency by eliminating the soil's heat and cold accumulation effect, saving energy investment while ensuring the long-term stable and safe operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a structural schematic diagram of the novel geothermal energy storage and utilization system described in the present invention.

[0009] Figure 2 It is a structural schematic diagram of a single energy storage unit in the present invention.

[0010] Figure 3 It is a schematic diagram of the distribution of energy storage units in the geothermal energy storage area in the present invention. DETAILED DESCRIPTION

[0011] The following describes an embodiment of the present invention in detail with reference to the accompanying drawings. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific implementation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0012] like Figure 1-3 As shown, the design method of a buried heat exchanger suitable for a geothermal energy storage and utilization system according to the present invention includes the following steps: S1, calculate the average volumetric specific heat capacity C of the soil in the geothermal energy storage area by coring method V ,J / (m 3 ℃); Specifically, firstly, a drilling position is randomly selected in the geothermal energy storage area, and then cores are taken from top to bottom in batches, with one group taken each time. Then, the volume specific heat capacity C of each group of core samples is measured by differential scanning calorimetry (DSC). i (i=1, 2, 3, ...), and then according to the moisture content P of each group of core samples i(i=1, 2, 3, ...), the weighted average is used to obtain the average volumetric specific heat capacity Cv of the soil in the sampling area, Among them, V i —Volume of each core sample, m 3 ; C 水 —Volume specific heat capacity of water, J / (m 3 ·℃).

[0013] In this embodiment, the depth of the core hole is 150 m, and a group of core samples are taken every 10 m, for a total of 15 groups of core samples.

[0014] S2, calculate the total energy storage energy Q of a single energy storage unit 储 =C v ×V×ΔT, Where V is the volume of a single energy storage unit, m 3 ; ΔT—the difference between the average design supply and return water temperature of the buried pipe heat exchanger and the initial temperature of the soil constant temperature layer, °C; The energy storage unit M is a cubic structure formed by dividing the geothermal energy storage area into a grid. Its volume V is calculated as "length × width × depth". Typically, the length and width of the energy storage unit M are both 7 meters, and the depth is calculated as 150 meters. The average design supply and return water temperatures of the buried heat exchanger are calculated from design data, and the initial temperature of the soil isothermal layer is obtained from field measurements.

[0015] S3, based on the building's annual cooling load Q 冷 and heat load Q 热 , calculate the maximum heat absorption Q of the buried heat exchanger in the geothermal energy storage area 吸 and maximum heat release Q 放 , Q 放 = Q 冷 × (1 + 1 / EER) + Q 输耗 + Q 泵耗 Q 吸 = Q 热 × (1-1 / COP) + Q 输耗 -Q 泵耗 Among them, EER—ratio of cooling / heating to input power, COP—the ratio of cooling capacity to cooling power, Q 输耗 —Heat loss in the transmission pipeline, kW·h; Q 泵耗 —Heat loss during operation of the heat pump unit, kW·h; If Q 吸 >Q 放 , calculate the number of energy storage units n=Q 吸 / Q 储 ; Under this condition, the ground source heat pump system operates in normal mode in winter and summer. In the transition season, the heat in the air can be heated by the heat source tower II through the heat pump unit I and then supplemented to the energy storage unit through the buried pipe heat exchanger III. The supplementary heat is Q 吸 -Q 放 ; If Q 放 >Q 吸 , calculate the number of energy storage units n=Q 放 / Q 储 ; In this case, the ground source heat pump system operates in normal mode in winter and summer. In the transition season, the heat in the energy storage unit can be released into the air through the heat source tower II. The released heat is Q 放 -Q 吸 , thus ensuring the soil's hot and cold balance throughout the year; Since each energy storage unit M corresponds to a buried ground heat exchanger III, once the number n of energy storage units M is determined, the number of ground heat exchangers III can be determined. The buried depth of ground heat exchangers III should be compatible with the depth of the energy storage units M. If the site for the ground heat exchangers is small, resulting in insufficient storage space and insufficient energy storage requirements, adjust the depth of the energy storage units M and repeat steps 2 and 3 until the required depth is achieved.

[0016] Since Q 储 This calculation is based on a configuration close to the actual layout of the ground heat exchanger III. Compared to the heat transfer rate per unit hole depth of the ground heat exchanger derived from traditional geothermal response exothermic tests, it more accurately reflects the energy storage capacity of soil as an energy storage medium. Furthermore, this invention can also reduce construction investment by adjusting the effective design depth of the energy storage unit to change the number of ground heat exchangers III.

[0017] The geothermal energy storage and utilization system described in the present invention is used to provide heating and cooling to buildings, and includes a heat pump unit I, a heat source tower II, and a buried pipe heat exchanger III.

[0018] Among them, the ground source side of the heat pump unit I is provided with a geothermal water supply pipe 11 and a geothermal return pipe 12, and the user side of the heat pump unit I is provided with a heating and cooling water supply pipe 13 and a heating and cooling return pipe 14; a first valve K1 is provided on the geothermal water supply pipe 11, a second valve K2 is provided on the geothermal return pipe 12, a third valve K3 is provided on the heating and cooling water supply pipe 13, and a first water pump Q1 and a fourth valve K4 are provided on the heating and cooling return pipe 14.

[0019] The energy storage unit M is a cubic structure, and its volume V is calculated as "length × width × depth." In this embodiment, multiple energy storage units M are provided within the geothermal energy storage area, arranged closely together in a grid pattern. A buried well N is excavated at the center of each energy storage unit M for installing a ground heat exchanger III. Each ground heat exchanger III within each buried well N is equipped with a geothermal water supply branch pipe 21 and a geothermal water return branch pipe 22. The geothermal water supply branch pipe 21 is arranged in parallel on the geothermal water supply connecting main pipe 23, and the geothermal water return branch pipe 22 is arranged in parallel on the geothermal water return connecting main pipe 24. The geothermal water supply connecting main pipe 23 is connected to the geothermal water supply pipe 11, and the geothermal water return connecting main pipe 24 is connected to the geothermal water return pipe 12. A second water pump Q2 is provided on the geothermal water return connecting main pipe 24.

[0020] Heat source tower II is provided with an energy replenishment water supply pipe 31 and an energy replenishment return water pipe 32; the energy replenishment water supply pipe 31 is connected to the geothermal water supply connecting main pipe 23, and a third water pump Q3 and a fifth valve K5 are provided on the energy replenishment water supply pipe 31. A heat replenishment water supply branch pipe 33 connected to the heating and cooling water supply pipe 13 is also provided between the third water pump Q3 and the fifth valve K5, and a sixth valve K6 is provided on the heat replenishment water supply branch pipe 33; the energy replenishment return water pipe 32 is connected to the geothermal return water connecting main pipe 24, and a seventh valve K7 is provided on the energy replenishment return water pipe 32. A heat replenishment return water branch pipe 34 connected to the heating and cooling return water pipe 14 is provided behind the seventh valve K7, and an eighth valve K8 is provided on the heat replenishment return water branch pipe 34.

[0021] The specific operation mode of the above-mentioned geothermal energy storage and utilization system is as follows: 1) Summer Operation: The summer operation mode is the same as that of existing ground-source heat pump systems. Open valves K1, K2, K3, and K4, close valves K5, K6, K7, and K8, and then start pumps Q1 and Q2. Heat from the building's interior is transferred through heat pump unit I and ground heat exchanger III via the user-side supply and return pipes and then stored in the soil. This means that the cooling energy in the soil is transferred through ground heat exchanger III and heat pump unit I to cool the building.

[0022] 2) The transition season is divided into two modes: Mode 1: The soil absorbs more heat than it releases When the heat absorption of the soil is greater than the heat release, that is, the heat absorption in winter is greater than the heat release in summer, after the summer air-conditioning season ends, the first valve K1, the second valve K2, the sixth valve K6, and the eighth valve K8 can be opened, and the third valve K3, the fourth valve K4, the fifth valve K5, and the seventh valve K7 can be closed. Then the second water pump Q2 can be turned on. At this time, the external heat is absorbed by the heat source tower II, and after being heated by the heat pump unit I, the soil is continuously heated through the buried pipe heat exchanger III. The heating amount is recorded by the energy meter, and the soil temperature is monitored. The heating amount is the difference between the heat released and absorbed by the building to the soil, ensuring that the heat absorption and heat release of the soil are balanced throughout the year.

[0023] Mode 2: The soil absorbs less heat than it releases When the heat absorbed by the soil is less than the heat released, that is, the heat intake in winter is less than the heat released in summer, before the start of the winter heating season, the fifth valve K5 and the seventh valve K7 can be opened, the third water pump Q3 can be turned on, the first valve K1, the second valve K2, the third valve K3, the fourth valve K4, the sixth valve K6, and the eighth valve K8 can be closed, and the second water pump Q2 can be turned on. At this time, since the outdoor temperature is lower than the soil temperature, the excess heat in the soil can be released into the air through the heat source tower, and the heat release can be recorded by the energy meter, and the soil temperature is monitored. The heat release is the difference between the heat released and absorbed by the building to the soil, ensuring that the heat absorption and heat release of the soil are balanced throughout the year.

[0024] 3) Winter Operation: The winter operation mode is the same as that of existing ground-source heat pump systems. Open valves K3, K4, K1, and K2, close valves K8, K6, K5, and K7, and start pumps Q1 and Q2. Heat from the building's interior is transferred through heat pump unit I and ground heat exchanger III via the user-side supply and return pipes and then stored in the soil. This transfers the cooling energy from the soil through ground heat exchanger III and heat pump unit I to cool the building.

[0025] It should be noted that, in the description of the present invention, terms indicating orientation or positional relationships such as “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “inside”, and “outside” are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

Claims

1. A design method for a buried heat exchanger suitable for a geothermal energy storage and utilization system, characterized by: The geothermal energy storage and utilization system is used to provide heating and cooling to buildings, and includes a heat pump unit, a heat source tower and a buried pipe heat exchanger, wherein the buried pipe heat exchanger is respectively arranged in each energy storage unit of the geothermal energy storage area; The design method of the buried pipe heat exchanger comprises the following steps: S1, calculate the average volumetric specific heat capacity C of the soil in the geothermal energy storage area by coring method V ,J / (m 3 ℃); S2, calculate the total energy storage energy Q of a single energy storage unit 储 =C v ×V×ΔT, Where V is the volume of a single energy storage unit, m 3 ; ΔT—the difference between the average design supply and return water temperature of the buried pipe heat exchanger and the initial temperature of the soil constant temperature layer, °C; S3, based on the building's annual cooling load Q 冷 and heat load Q 热 , calculate the maximum heat absorption Q of the buried heat exchanger in the geothermal energy storage area 吸 and maximum heat release Q 放 , Q 放 = Q 冷 ×(1+1 / EER)+ Q 输耗 + Q 泵耗 Q 吸 = Q 热 ×(1-1 / COP)+ Q 输耗 - Q 泵耗 Among them, EER—ratio of cooling / heating to input power, COP—the ratio of cooling capacity to cooling power, Q 输耗 —Heat loss in the transmission pipeline, kW·h; Q 泵耗 —Heat loss during operation of the heat pump unit, kW·h; If Q 吸 >Q 放 , calculate the number of energy storage units n=Q 吸 / Q 储 ; If Q 放 >Q 吸 , calculate the number of energy storage units n=Q 放 / Q 储 ; The number of ground heat exchangers is determined according to the number n of energy storage units.

2. The method for designing a buried heat exchanger suitable for a geothermal energy storage and utilization system according to claim 1, characterized in that: The coring method is used to determine and calculate the average volumetric specific heat capacity C of the soil in the area where the buried heat exchanger is located. V When the geothermal energy storage area is used, a drilling position is randomly selected in the drilling area, and then the cores are taken from top to bottom in batches, with one group taken each time. The volume specific heat capacity C of each group of core samples is then measured by differential scanning calorimetry. i (i=1, 2, 3, ...), and then according to the moisture content P of each group of core samples i (i=1, 2, 3, ...), the weighted average is used to obtain the average volumetric specific heat capacity Cv of the soil in the sampling area, Among them, V i —Volume of each core sample, m 3 ; C 水 —Volume specific heat capacity of water, J / (m 3 ·℃).

3. The method for designing a buried heat exchanger suitable for a geothermal energy storage and utilization system according to claim 1, characterized in that: The ground source side of the heat pump unit is provided with a geothermal water supply pipe and a geothermal return pipe, and the user side of the heat pump unit is provided with a heating and cooling water supply pipe and a heating and cooling return pipe; a first valve is provided on the geothermal water supply pipe, a second valve is provided on the geothermal return pipe, a third valve is provided on the heating and cooling water supply pipe, and a first water pump and a fourth valve are provided on the heating and cooling return pipe; The energy storage units are distributed in a grid pattern within the geothermal energy storage area. The buried heat exchangers within each energy storage unit are provided with a geothermal water supply branch pipe and a geothermal water return branch pipe. The geothermal water supply branch pipes are arranged in parallel on the geothermal water supply connecting main pipe, and the geothermal water return branch pipes are arranged in parallel on the geothermal water return connecting main pipe. The geothermal water supply connecting main pipe is connected to the geothermal water supply pipe, and the geothermal water return connecting main pipe is connected to the geothermal water return pipe. A second water pump is provided on the geothermal water return connecting main pipe. The heat source tower is provided with an energy replenishment water supply pipe and an energy replenishment return pipe; the energy replenishment water supply pipe is connected to the geothermal water supply connecting main pipe, and a third water pump and a fifth valve are provided on the energy replenishment water supply pipe. A heat replenishment water supply branch pipe connected to the heating and cooling water supply pipe is also provided between the third water pump and the fifth valve, and a sixth valve is provided on the heat replenishment water supply branch pipe; the energy replenishment return pipe is connected to the geothermal return water connecting main pipe, and a seventh valve is provided on the energy replenishment return pipe. A heat replenishment return water branch pipe connected to the heating and cooling return water pipe is provided behind the seventh valve, and an eighth valve is provided on the heat replenishment return water branch pipe.

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