A method for analyzing geothermal heat pump buried pipe rock-soil thermal response test

Abstract

The application discloses a kind of ground source heat pump buried pipe rock-soil thermal response test analysis methods, it is related to buried pipe rock-soil thermal response test analysis field, comprising: the present application is divided into multiple rock-soil layer section by borehole, and its temperature data sequence is collected, the temperature rise rate and stable temperature value of each layer section are calculated, and then the layer section that temperature rise rate and stable temperature value exist difference is identified, longitudinal thermal resistance mutation interface is identified;Based on the position tracking heat transfer path along the depth of borehole of longitudinal thermal resistance mutation interface, the temperature delay and attenuation amplitude generated when heat is conducted in rock-soil layer section are analyzed;According to the temperature delay and attenuation amplitude of each layer section, longitudinal thermal interference is removed and corrected to original temperature data sequence, and respectively inversion calculation of thermal physical property parameter is carried out, and the rock-soil comprehensive thermal conductivity coefficient of each layer section and the borehole inner thermal resistance value are output, the identification and removal of longitudinal thermal interference in heterogeneous formation are realized, and the analysis precision of rock-soil thermal response test is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of thermal response test analysis of buried pipes in soil and rock, and relates to a method for thermal response test analysis of buried pipes in soil and rock of ground source heat pumps. Background Technology

[0002] Ground source heat pump systems are an energy-saving and environmentally friendly HVAC technology that exchanges heat with the ground through buried pipe heat exchangers to provide heating and cooling for buildings. The geothermal thermal response test of buried pipes is a key method for obtaining thermophysical parameters such as the overall thermal conductivity of the soil and the thermal resistance within the borehole.

[0003] Currently, due to geological sedimentation, actual rock and soil masses exhibit significant stratification and heterogeneity along the depth direction. The thermal conductivity of different rock and soil layers can differ by several times. This heterogeneity drives the redistribution of heat in the vertical direction, i.e., generates vertical thermal interference. This causes heat to accumulate quickly and the temperature to rise in the layers with poor thermal conductivity, while heat to diffuse quickly and the temperature to rise slowly in the layers with good thermal conductivity. The resulting temperature gradient along the depth direction drives the longitudinal conduction of heat from high-temperature zones to low-temperature zones.

[0004] If existing technologies are used to directly invert the average temperature data across the entire depth, the resulting comprehensive thermal conductivity is essentially an apparent value obtained by mixing the thermal conductivity of each layer with unknown weights. This leads to a systematic underestimation of the heat accumulation risk in layers with poor thermal conductivity, which is diluted by surrounding layers with good thermal conductivity. Furthermore, the heat dissipation potential of layers with excellent thermal conductivity is obscured by longitudinal heat inflow from adjacent layers, making accurate identification impossible. Simultaneously, the hindering effect of abrupt changes in interlayer thermal resistance on longitudinal heat transfer is completely ignored, ultimately resulting in misjudgments of the actual underground heat exchange capacity and heat migration paths. Summary of the Invention

[0005] In view of this, in order to solve the problems mentioned in the background art, the present invention provides a method for testing and analyzing the thermal response of ground source heat pump buried pipes in soil and rock.

[0006] The objective of this invention can be achieved through the following technical solution: a method for testing and analyzing the thermal response of a ground source heat pump buried pipe in soil and rock, comprising: S1, obtaining geological information of the borehole of the ground source heat pump buried pipe, dividing the borehole into multiple soil and rock layers, and collecting temperature data sequences within each layer.

[0007] S2. Based on the temperature data sequence of each soil and rock layer, calculate the temperature rise rate and stable temperature value of each layer after applying heating power.

[0008] S3. Compare the temperature rise rate and stable temperature value of each soil and rock layer, identify the layers with differences in temperature rise rate and stable temperature value, and identify the longitudinal thermal resistance abrupt change interface by combining the proportion of each layer in the total borehole heating.

[0009] S4. Based on the location of each longitudinal thermal resistance abrupt change interface, trace the heat transfer path along the borehole depth during the heating process, and analyze the temperature delay and attenuation magnitude generated when heat is conducted from the soil and rock layer to the adjacent layer.

[0010] S5. Based on the temperature delay and attenuation amplitude of each layer, the original temperature data sequence of each layer is corrected by longitudinal thermal interference removal, and the thermal property parameters are inverted and calculated respectively, and the comprehensive thermal conductivity of the soil and rock and the thermal resistance value inside the borehole are output for each layer.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention divides the borehole into multiple soil and rock layers and collects their temperature data sequence, calculates the temperature rise rate and stable temperature value of each layer, and then identifies the layers with different temperature rise rates and stable temperature values, identifies the vertical thermal resistance abrupt change interface, realizes the positioning of the key control point of vertical thermal interference in the heterogeneous layer, overcomes the misjudgment caused by the traditional method of simplifying the heterogeneous layer into a homogeneous whole and ignoring the differences in thermal properties between layers, and provides a basis for the identification of the subsequent interlayer thermal coupling effect.

[0012] (2) Based on the location of the longitudinal thermal resistance abrupt change interface, the present invention tracks the heat transfer path along the borehole depth and analyzes the temperature delay and attenuation amplitude generated when the heat is conducted in the soil and rock layers. This overcomes the physical defects of traditional methods, which dilute the risk of heat accumulation in layers with poor thermal conductivity and interfere with the heat dissipation potential of layers with excellent thermal conductivity. This allows the true heat load and heat diffusion capacity of each layer to be identified.

[0013] (3) The present invention performs longitudinal thermal interference removal and correction on the original temperature data sequence based on the temperature delay and attenuation amplitude of each layer, and performs inversion calculation of thermal property parameters respectively, outputting the comprehensive thermal conductivity of soil and rock and the thermal resistance value inside the borehole of each layer. This overcomes the problem that the traditional method of using a single lumped model for overall fitting leads to the complete neglect of the blocking effect of the interlayer thermal resistance abrupt interface on longitudinal heat transfer. It realizes the matching of inversion parameters with the actual thermal diffusion capacity of the stratum, so that the analysis results can truly reflect the underground heat exchange capacity and heat migration path. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a diagram illustrating the implementation steps of the method of the present invention; Figure 2 This is a flowchart of the longitudinal thermal resistance abrupt change interface identification process of the present invention; Figure 3 This is a flowchart illustrating the heat transfer path tracking process of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Please see Figure 1 As shown, the present invention provides a method for testing and analyzing the thermal response of soil and rock in a ground source heat pump buried pipe, including: S100, obtaining geological information of the borehole of the ground source heat pump buried pipe.

[0018] As a specific implementation method, the above-mentioned acquisition of geological stratification information of the ground source heat pump buried pipe borehole can be achieved in the following way: First, after the completion of the buried pipe borehole construction, core image data of the entire borehole depth is acquired using a borehole camera system; then, based on the acquired core image data, a depth distribution curve of soil and rock characteristic parameters is established along the depth direction. The soil and rock characteristic parameters include, but are not limited to, the gray value, texture features, fracture density or color components of the core image, and the lithology is recorded to form geological information.

[0019] S101. Divide the borehole into multiple soil and rock layers and collect temperature data sequences within each layer.

[0020] Because the rock and soil mass is a continuous medium, but its thermal properties are non-uniformly distributed along the depth direction, this non-uniformity originates from lithological changes during geological sedimentation or diagenesis. If the entire borehole is regarded as a single homogeneous body, it is impossible to characterize the distribution pattern of heat between different lithological strata.

[0021] Based on this, the process of dividing the borehole into multiple soil and rock layers and collecting temperature data sequences within each layer includes: during the process of applying constant heating power to the buried pipe heat exchanger, using distributed optical fibers continuously arranged along the borehole depth to collect temperature data at the full depth, thereby obtaining depth, time, and temperature datasets.

[0022] It should be noted that distributed optical fiber is based on the principles of Raman scattering or Brillouin scattering, which can realize continuous monitoring of the temperature field at full depth, thereby obtaining a three-dimensional dataset of depth, time and temperature, which can meet the needs of soil and rock layer analysis.

[0023] Based on the depth, time, and temperature datasets, the temperature rise response feature values ​​of each depth point over time are extracted to form a depth and temperature rise response feature sequence.

[0024] The heating response characteristic value refers to an index characterizing the temperature response characteristics of a certain depth point during the heating process; rock and soil layers with good thermal conductivity heat up more slowly, while those with poor thermal conductivity heat up more quickly. By extracting the heating response characteristic value, subsequent cluster analysis of depth points can be based on characteristic indicators that reflect the thermophysical nature of the rock and soil, avoiding the uncertainty of artificially stratifying based solely on depth location.

[0025] In this embodiment, the preferred temperature response characteristic value is the average temperature rise rate of the depth point during the initial heating stage, i.e., the average temperature increase per unit time. For each depth point, the temperature time series of that depth point during the entire heating process is extracted from the depth, time, and temperature dataset; the linear regression slope of this time series within a preset time window is calculated. The preset time window is determined based on the total heating duration of the thermal response test, specifically the first to sixth hours after the start of heating. This slope value is used as the temperature response characteristic value of that depth point.

[0026] Then, the position coordinates of each depth point and their corresponding heating response characteristic values ​​are arranged in ascending order of depth, thus forming a depth and heating response characteristic sequence.

[0027] Cluster analysis was performed on the depth and temperature response characteristic sequences to group consecutive depth points with similar temperature response characteristic values ​​into the same soil and rock layer segment, and the cluster boundary was used as the interface between each soil and rock layer segment.

[0028] Specifically, by calculating the Euclidean distance between the feature values ​​of adjacent depth points, the adjacent points or point groups with the smallest Euclidean distance are successively merged to generate a hierarchical tree structure. When the variance of the internal feature values ​​of the merged new class exceeds the preset variance threshold, the merging is stopped.

[0029] The preset variance threshold is determined in the following way: First, the overall standard deviation σ of the temperature response characteristic values ​​of all depth points is calculated, and the preset variance threshold is set to 0.3σ. 0.3 is an empirical value, which aims to balance the layering accuracy and noise resistance. In practical applications, it can be adjusted in the range of 0.2σ to 0.4σ according to the formation complexity determined by the core image.

[0030] During clustering, only adjacent sample points at depth are allowed to be merged into the same class. For isolated points caused by data noise, they are assigned to the adjacent class with the closest feature values. The boundary depth point between two adjacent classes in the clustering results is determined as the interface of the soil and rock layer.

[0031] For each segment of soil and rock, temperature monitoring data of all depth points within that segment during the heating process are extracted from the depth, time, and temperature datasets to form a temperature data sequence for that segment of soil and rock.

[0032] S200. Based on the temperature data sequence of each soil and rock layer, calculate the temperature rise rate and stable temperature value of each layer after applying heating power.

[0033] Because heat diffuses rapidly and temperatures rise gradually in sections with good thermal conductivity, while heat accumulates significantly and temperatures rise more drastically in sections with poor thermal conductivity, and because the stable temperatures at thermal equilibrium vary among sections due to differences in depth and surrounding thermal environment, the calculated temperature rise rate of each soil and rock section during heating reflects the section's sensitivity to heat and its heat diffusion capacity, while the stable temperature reflects the thermal equilibrium state of the section under continuous heating conditions.

[0034] Therefore, the calculation process of the temperature rise rate is as follows: extract the temperature values ​​of all depth points in each soil and rock layer during the entire heating process from the temperature data sequence of each layer, and calculate the average temperature of all depth points in the layer at each moment.

[0035] Starting from the moment heating begins, select an initial time window, calculate the total change in average temperature within that time window, and divide it by the length of the time window to obtain the temperature rise rate of each layer.

[0036] It should be added that the initial phase time window is determined based on the total heating time of the thermal response test, specifically from hour t1 to hour t2 after the start of heating. Specifically, t1 ranges from 0.5 to 2 hours to exclude interference from temperature fluctuations in the circulating fluid and equipment instability during the initial heating start-up; t2 ranges from 4 to 8 hours to ensure that the window contains sufficient data points and that temperature changes have not yet been significantly affected by the borehole's far-end boundary conditions.

[0037] The calculation process for the stable temperature value is as follows: Select a time window for the final stage from the end of heating, and calculate the arithmetic mean of the average temperature within the time window as the stable temperature value for each layer.

[0038] The time window for the final stage is selected based on the total heating time T of the thermal response test, choosing a continuous time period backward from the end of heating. The start time of this time window is T-t3, the end time is T, and the window length is t3. The value of t3 ranges from 10% to 20% of the total heating time, and is no less than 4 hours, to ensure that the window contains sufficient data points for calculating a stable average value.

[0039] S300. Compare the temperature rise rate and stable temperature value of each soil and rock layer to identify the layers where the temperature rise rate and stable temperature value differ.

[0040] Considering that when the lithology of adjacent strata changes, their thermal properties can change abruptly. This abrupt change will inevitably manifest in strata where there are differences in the rate of temperature rise and the stable temperature value.

[0041] Based on this, the identification of segments with differences in temperature rise rate and stable temperature value includes: normalizing the temperature rise rate and stable temperature value of each soil and rock segment to form a feature vector of that segment; eliminating the imbalance caused by differences in dimensions and orders of magnitude between the temperature rise rate and stable temperature value, so that the thermal response characteristics of each segment can be compared on the same scale.

[0042] Arrange the soil and rock layers in descending order of depth, calculate the Euclidean distance between the feature vectors of each pair of adjacent soil and rock layers, and obtain the sequence of differences between adjacent layers.

[0043] Sort all values ​​in the adjacent segment difference sequence in descending order, and mark the two adjacent soil segments corresponding to the preset number of adjacent segment differences at the top of the sort as difference segment pairs.

[0044] In actual geological formations, only a few interfaces truly control the vertical transfer of heat; differences between most interfaces have little impact on heat transfer. Ranking the top few adjacent soil and rock layers based on their differences is to identify the truly effective interfaces and avoid being overwhelmed by a large amount of irrelevant information.

[0045] The preset quantity is determined in the following ways: calculate the mean μ and standard deviation σ of the difference sequence of all adjacent segments, and take the preset quantity as the number of adjacent segments with a difference greater than μ+σ; or sort all differences from largest to smallest and draw a scree map, and take the index corresponding to the inflection point of the scree map as the preset quantity.

[0046] Traverse all soil and rock strata. If the feature vector of a certain soil and rock strata is simultaneously greater than the feature vector magnitude of its upper and lower adjacent strata, or simultaneously less than the feature vector magnitude of its upper and lower adjacent strata, then mark the soil and rock strata as an extreme value difference strata.

[0047] In a geological profile of continuous sedimentation, when the modulus of the characteristic vector formed by the temperature rise rate and the stable temperature value of a certain layer is simultaneously greater than or simultaneously less than the adjacent layers above and below, it indicates that the layer has formed an abnormal peak or valley value of thermophysical properties in the local stratigraphic sequence. Such anomalies often correspond to special geological sedimentary events or subsequent alteration.

[0048] S301. Identify the longitudinal thermal resistance abrupt change interface by combining the proportion of each layer in the total borehole heating.

[0049] Given two adjacent layers with significantly different rates of temperature rise and stable temperatures, abrupt changes in longitudinal thermal resistance are inevitable at their interface. This interface is the critical location for the longitudinal redistribution of heat; if the upper layer has poor thermal conductivity and the lower layer has good thermal conductivity, the heat accumulated in the upper layer will preferentially conduct to the lower layer with better thermal conductivity. Identifying these interfaces with abrupt changes in thermal resistance is equivalent to locating the control points for the longitudinal redistribution of heat.

[0050] refer to Figure 2 As shown, the identification of the longitudinal thermal resistance abrupt change interface includes: obtaining the interface in the difference segment pair and the interface between the extreme difference segment and the adjacent segment as candidate interfaces.

[0051] The interfaces between differential stratigraphic segments and between extreme differential stratigraphic segments and adjacent stratigraphic segments are selected as candidate interfaces because vertical thermal resistance abrupt changes either occur at the boundary between two stratigraphic segments with significant thermal property differences, or at the boundary between a stratigraphic segment with abnormal thermal properties and the normal stratigraphic segments above and below it. These two types of interfaces completely cover all locations of thermal resistance abrupt changes that heat may encounter during vertical conduction.

[0052] Obtain the absolute value of the temperature rise rate difference between adjacent soil and rock layers on both sides of each candidate interface, as well as the minimum heating ratio of adjacent soil and rock layers on both sides. Multiply the absolute value of the temperature rise rate difference by the minimum heating ratio as the abrupt change intensity value of each candidate interface.

[0053] The absolute value of the temperature rise rate difference reflects the degree of difference in thermal resistance characteristics between the rock and soil on both sides of the interface. The larger the difference, the more drastic the change in thermal resistance.

[0054] The heating percentage represents the share of the total heating amount in the soil and rock layer. For the layers on both sides of the interface, the limiting effect of the interface on heat conduction actually depends on the side with weaker heat absorption capacity, i.e., the layer with a smaller heating percentage. The smaller the heating percentage, the more limited the heat carrying capacity of that side, and the easier it is to trigger the thermal resistance effect at the interface. Therefore, multiplying the absolute value of the temperature rise rate difference by the minimum heating percentage on both sides not only reflects the severity of the thermal resistance abrupt change but also captures the limiting link in the interface's control over heat transfer, thus obtaining the actual thermal resistance intensity of each candidate interface for longitudinal heat conduction.

[0055] Sort all candidate interface mutation intensity values ​​in descending order, and sum the sorted mutation intensity values ​​sequentially to obtain a cumulative sum sequence.

[0056] Calculate the second-order difference sequence of the cumulative sum sequence, and use the mutation intensity value corresponding to the maximum value in the second-order difference sequence as the boundary value.

[0057] All candidate interfaces with mutation intensity values ​​greater than or equal to the threshold value are identified as longitudinal thermal resistance mutation interfaces.

[0058] In real strata, the abrupt change intensity of vertical thermal resistance interfaces is higher than that of ordinary interfaces caused by lithological gradation or measurement noise. When the abrupt change intensity values ​​are sorted from largest to smallest and accumulated, the intensity values ​​of the earlier real interfaces are larger, leading to rapid accumulation and growth. The intensity values ​​of the later non-abrupt interfaces are smaller and more evenly distributed, resulting in slower accumulation and growth. The inflection point where the accumulation slows down, i.e., the location of the maximum value of the second-order difference, is the natural boundary between the real abrupt change interface and the ordinary interface. Using this method, the abrupt change interfaces that truly impede heat conduction can be screened out.

[0059] S400: Based on the location of each longitudinal thermal resistance abrupt change interface, it tracks the heat transfer path along the borehole depth during the heating process.

[0060] refer to Figure 3 As shown, the tracking of heat transfer path along the borehole depth during the heating process includes: dividing the entire borehole into several heat transfer sections according to the position of each longitudinal thermal resistance abrupt change interface at the borehole depth.

[0061] Two adjacent soil and rock layers are obtained on both sides of each longitudinal thermal resistance abrupt change interface, and the average temperature time series of the two soil and rock layers during the entire heating process is extracted.

[0062] The average temperature values ​​of the two soil and rock layers are compared at each time step. The cumulative duration of the side with the higher average temperature value during the entire heating process is counted. The side with the longer cumulative duration is determined as the main heat-generating side at the interface, and the other side is the main heat-receiving side.

[0063] Throughout the heating process, heat is spontaneously transferred from the high-temperature object to the low-temperature object; that is, the side with the higher temperature is the main heat-emitting side, and the side with the lower temperature is the main heat-receiving side. However, since temperature fluctuations may cause the direction to reverse in a short period of time, the primary and secondary relationship cannot be determined based on a single moment. Therefore, by statistically analyzing the cumulative duration of the side with the higher temperature throughout the entire heating process, the side with the longer duration is identified as the primary heat-emitting side, which can stably reflect the dominant direction of heat transfer at the interface.

[0064] Based on the main heat-generating side and the main heat-receiving side of each longitudinal thermal resistance abrupt change interface, the overall path sequence of heat transfer from the high-temperature section to the low-temperature section is determined throughout the entire borehole depth.

[0065] S401. Analyze the temperature delay and attenuation magnitude that occur when heat is conducted from the soil layer to the adjacent layer.

[0066] The analysis of the temperature delay and attenuation caused by heat conduction from the soil and rock layer to the adjacent layer includes: obtaining two adjacent soil and rock layers on both sides of each longitudinal thermal resistance abrupt change interface, and extracting the average temperature time series of the two soil and rock layers during the entire heating process.

[0067] Calculate the cross-correlation function of two average temperature time series to obtain the sequence of cross-correlation function values ​​as a function of lag time.

[0068] Specifically, the cross-correlation function is achieved through the following formula: ; where x(t) and y(t) represent the average temperature values ​​of the two soil and rock layers on both sides of the interface at time t, and t is the discrete sampling time point. , , are the arithmetic mean of x(t) and y(t) over the entire heating period, respectively, used to zero-mean normalize the original sequence and eliminate the influence of absolute temperature on correlation. N is the total length of the time series, i.e., the total number of sampling points. τ represents the lag time, in integer multiples of the sampling interval, representing the time offset of the y sequence relative to the x sequence. This represents the cross-correlation function value at a lag time of τ, reflecting the similarity between two sequences after the shift τ. When |τ| is close to N, the number of effective data points N-|τ| may be too small, which may lead to unstable cross-correlation estimation. In actual calculations, it is recommended to only consider the lag range of |τ|≤N / 2 to ensure the reliability of the results.

[0069] The lag time corresponding to the maximum value of the cross-correlation function is determined as the temperature delay at the interface.

[0070] It's important to note that the cross-correlation function essentially measures the similarity between two signals at different time offsets. For the soil and rock layers on either side of an interface, heat transfer from one side to the other takes time, causing the temperature change on the receiving side to lag behind that on the transmitting side. When comparing two temperature time series with different lag times, the fluctuation patterns of the two series are most similar at the point where the lag time exactly equals the actual heat transfer time, reaching the maximum similarity. Therefore, the cross-correlation function reaches its maximum value at this lag time, which is the temperature delay.

[0071] The ratio of the maximum value of the cross-correlation function to the geometric mean of the autocorrelation function of the average temperature time series of the two soil and rock layers at zero hysteresis is used as the temperature decay rate at the interface.

[0072] The maximum value of the cross-correlation function is affected by the amplitudes of the two sequences themselves; the larger the amplitude, the larger the cross-correlation value, but this does not necessarily mean that the attenuation during heat transfer is smaller. The autocorrelation function at zero lag reflects the energy level of the sequence itself. Dividing the maximum cross-correlation value by the geometric mean of the zero lag autocorrelation values ​​of the two sequences can eliminate the influence of amplitude differences, yielding a dimensionless normalized cross-correlation coefficient. This coefficient reflects the waveform similarity of the two temperature sequences at the optimal delay time; the closer the value is to 1, the smaller the attenuation during temperature signal transmission.

[0073] Repeat the above steps for all interfaces with abrupt changes in longitudinal thermal resistance to obtain the temperature delay and attenuation magnitude at each interface.

[0074] S500: Based on the temperature delay and attenuation amplitude of each segment, perform longitudinal thermal interference removal and correction on the original temperature data sequence of each segment.

[0075] Since the thermal interference between different sections is coupled with each other, directly using the original uncorrected data to correct all sections at the same time will result in a computational circular dependency.

[0076] Therefore, the longitudinal thermal interference removal correction of the original temperature data sequence of each layer includes: obtaining multiple heat transfer sections divided based on the longitudinal thermal resistance abrupt change interface, and constructing an inter-segment thermal interference coefficient matrix according to the temperature delay time and temperature attenuation amplitude at each longitudinal thermal resistance abrupt change interface.

[0077] As a specific implementation method, the inter-segment thermal interference coefficient matrix is ​​constructed as follows: Assuming the entire borehole is divided into N heat transfer segments based on the longitudinal thermal resistance abrupt change interface, and numbered sequentially from top to bottom as S1, S2, ..., S... N .

[0078] For any two different heat transfer sections S i and S j， That is, i≠j, if S j Located in S i If there is one or more vertical thermal resistance abrupt changes between the two, then S is defined. j For S i The thermal interference coefficient is β. This coefficient characterizes the thermal interference of the lower segment S. j The temperature rise on the upper section S i The intensity of the influence of temperature measurements.

[0079] The method for determining β is as follows: identifying from S j To S i Let M be the number of all longitudinal thermal resistance abruptly changed interfaces along the longitudinal heat transfer path. For the k-th interface on the path, its temperature decay is α. k That is, 0 < α k <1. Therefore, the total thermal interference coefficient β is equal to the product of the temperature attenuation magnitudes of all interfaces along the path, i.e.: .

[0080] At the same time, records from S j To S i Total temperature delay time The temperature signal experiences a time lag each time it passes through an interface. The total delay time is the sum of the delay times of each interface, which is equal to the temperature delay time η of all interfaces along the path.k The sum is: .

[0081] If S j Located in S i Above that, S is defined. j For S i The thermal interference coefficient β can be obtained similarly. For the same segment itself, i.e., i=j, β=0 is defined, that is, the interference between itself and itself is not considered.

[0082] Therefore, an N×N inter-segment thermal interference coefficient matrix B is constructed, where the element in the i-th row and j-th column is β when i≠j, or 0 when i=j. Simultaneously, a delay time matrix of the same dimension is constructed, whose elements are the corresponding... .

[0083] Extract the average temperature time series of each heat transfer section throughout the entire heating process.

[0084] The corrected temperature time series for each heat transfer section is obtained by subtracting the average temperature time series of other sections from the average temperature time series of each section after shifting by the corresponding delay time and multiplying by the corresponding thermal interference coefficient.

[0085] Because the measured temperature time series of each segment contains thermal interference components from other segments that have been delayed and attenuated, if these components are not removed, the thermal conductivity calculated through inversion will be affected by interlayer thermal coupling effects and will not accurately reflect the thermal properties of each segment itself. Therefore, the components from other segments that have been delayed, shifted, and multiplied by the interference coefficient are subtracted from the original sequence to recover a corrected sequence that only reflects the thermal response of that segment.

[0086] The corrected temperature time series is used as the corrected temperature data series for each soil and rock layer in this section.

[0087] In practical engineering, due to differences in geological stratification and borehole backfill materials, longitudinal heat transfer often occurs along the borehole depth, violating the fundamental assumption of the line heat source model that heat is transferred only radially. By eliminating and correcting longitudinal thermal interference, the remaining temperature response mainly reflects the radial thermal diffusion characteristics of the line heat source corresponding to that stratum, thus maximally satisfying the physical assumption of the line heat source model regarding pure radial heat transfer. If the corrected temperature is lower than the initial ground temperature, the initial ground temperature is taken as the lower limit. If the corrected temperature sequence exhibits severe oscillations, a smoothing filter is applied before inversion calculation.

[0088] S501. Perform inversion calculations of thermal property parameters respectively, and output the comprehensive thermal conductivity of soil and rock and the thermal resistance value inside the borehole for each layer.

[0089] The output of the comprehensive thermal conductivity of soil and rock in each layer and the thermal resistance value inside the borehole includes: based on the infinite long linear heat source model, using the natural logarithm of time as the independent variable and the corrected temperature data sequence as the dependent variable, performing linear regression to obtain the slope and intercept of the regression line.

[0090] Specifically, based on the infinitely long line heat source model, under constant heating power conditions, the borehole wall temperature at heating time t is... With initial temperature The relationship can be approximated as: Where q is the heating power per unit hole depth, which is equal to the applied constant heating power divided by the total drilling depth; λ is the overall thermal conductivity of the soil and rock; and a is the thermal diffusivity of the soil and rock, which can be obtained by a=λ / ρ c The estimated volumetric heat capacity ρ of the rock and soil mass c Rock and soil samples collected during the detailed site investigation phase can be directly measured using indoor thermophysical tests according to engineering rock mass testing method standards; b R is the borehole radius, and γ is a known borehole geometry parameter; γ is the Euler constant, approximately equal to 0.5772; b This represents the thermal resistance inside the borehole.

[0091] The above formula can be simplified to Among them, slope ;intercept .

[0092] Calculate the overall thermal conductivity of the soil and rock layer based on the slope and the applied constant heating power.

[0093] Based on the above infinitely long linear heat source model, the overall thermal conductivity of the soil and rock layer can be calculated by reverse calculation: .

[0094] Calculate the borehole thermal resistance value of this soil and rock layer based on the intercept, borehole geometry parameters, and soil thermal diffusivity.

[0095] Specifically, the thermal resistance inside the borehole is calculated in reverse: The above inversion calculation assumes that the corrected temperature data basically satisfies the radial heat transfer assumptions of the line heat source model. If a significant longitudinal temperature gradient still exists after correction, it is recommended to further verify the reliability of the inversion results using numerical simulation methods.

[0096] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0097] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0098] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0099] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0100] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing and analyzing the thermal response of buried pipes for ground source heat pumps in soil and rock, characterized in that: include: Geological information of the ground source heat pump buried pipe borehole is obtained, the borehole is divided into multiple soil and rock layers, and temperature data sequences are collected in each layer. Based on the temperature data sequence of each soil and rock layer, the temperature rise rate and steady-state temperature value of each layer after applying heating power were calculated. By comparing the temperature rise rate and stable temperature value of each soil and rock layer, the layers with differences in temperature rise rate and stable temperature value are identified. In combination with the proportion of each layer in the total borehole heating, the longitudinal thermal resistance abrupt change interface is identified. Based on the location of each longitudinal thermal resistance abrupt change interface, the heat transfer path along the borehole depth during the heating process is traced, and the temperature delay and attenuation magnitude generated when heat is conducted from the soil and rock layer to the adjacent layer are analyzed. Based on the temperature delay and attenuation amplitude of each layer, the original temperature data sequence of each layer is corrected by longitudinal thermal interference removal, and the thermal property parameters are inverted and calculated respectively to output the comprehensive thermal conductivity of the soil and rock and the thermal resistance value inside the borehole for each layer.

2. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 1, characterized in that: The process of dividing the borehole into multiple soil and rock layers and collecting temperature data sequences within each layer includes: During the process of applying constant heating power to the buried pipe heat exchanger, temperature data of the entire depth is collected by distributed optical fibers continuously arranged along the borehole depth to obtain depth, time and temperature datasets. Based on the depth, time, and temperature datasets, the temperature rise response feature values ​​of each depth point over time are extracted to form a depth and temperature rise response feature sequence. Cluster analysis was performed on the depth and temperature response characteristic sequences to group consecutive depth points with similar temperature response characteristic values ​​into the same soil and rock layer segment, and the cluster boundary was used as the interface between each soil and rock layer segment. For each segment of soil and rock, temperature monitoring data of all depth points within that segment during the heating process are extracted from the depth, time, and temperature datasets to form a temperature data sequence for that segment of soil and rock.

3. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 1, characterized in that: The calculation process for the temperature rise rate is as follows: Extract the temperature values ​​of all depth points within each soil and rock layer during the entire heating process from the temperature data sequence of that layer, and calculate the average temperature of all depth points in that layer at each time point. Starting from the moment heating begins, select an initial time window, calculate the total change in average temperature within that time window, and divide it by the length of the time window to obtain the temperature rise rate of each layer.

4. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 3, characterized in that: The calculation process for the stable temperature value is as follows: Select a time window for the final stage preceding the end of heating, and calculate the arithmetic mean of the average temperature within this time window as the stable temperature value for each layer.

5. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 1, characterized in that: The segments identified as having differences between the rate of temperature rise and the stable temperature value include: The temperature rise rate and stable temperature value of each soil and rock layer are normalized to form the feature vector of that layer. Arrange the soil and rock layers in order of depth from top to bottom, calculate the Euclidean distance between the feature vectors of each pair of adjacent soil and rock layers, and obtain the sequence of differences between adjacent layers. Sort all values ​​in the adjacent segment difference sequence in descending order, and mark the two adjacent soil segments corresponding to the preset number of adjacent segment differences at the top of the sort as difference segment pairs; Traverse all soil and rock strata. If the feature vector of a certain soil and rock strata is simultaneously greater than the feature vector magnitude of its upper and lower adjacent strata, or simultaneously less than the feature vector magnitude of its upper and lower adjacent strata, then mark the soil and rock strata as an extreme value difference strata.

6. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 5, characterized in that: The identification of the interface with a sudden change in longitudinal thermal resistance includes: Obtain the interfaces in the difference segment pairs and the interfaces between the extreme value difference segment and the adjacent segment as candidate interfaces; Obtain the absolute value of the temperature rise rate difference between adjacent soil and rock layers on both sides of each candidate interface, as well as the minimum heating ratio of adjacent soil and rock layers on both sides. Multiply the absolute value of the temperature rise rate difference by the minimum heating ratio as the abrupt change intensity value of each candidate interface. Sort all candidate interface mutation intensity values ​​in descending order, and sum the sorted mutation intensity values ​​sequentially to obtain a cumulative sum sequence; Calculate the second-order difference sequence of the cumulative sum sequence, and use the mutation intensity value corresponding to the maximum value in the second-order difference sequence as the boundary value; All candidate interfaces with mutation intensity values ​​greater than or equal to the threshold value are identified as longitudinal thermal resistance mutation interfaces.

7. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 1, characterized in that: The tracking of heat transfer along the borehole depth during the heating process includes: Based on the location of each longitudinal thermal resistance abrupt change interface at the borehole depth, the entire borehole is divided into several heat transfer sections. Obtain the two adjacent soil and rock layers on both sides of each longitudinal thermal resistance abrupt change interface, and extract the average temperature time series of the two soil and rock layers during the entire heating process; The average temperature values ​​of the two soil and rock layers are compared at each time step. The cumulative duration of the side with the higher average temperature value during the entire heating process is counted. The side with the longer cumulative duration is determined as the main heat-emitting side at the interface, and the other side is the main heat-receiving side. Based on the main heat-generating side and the main heat-receiving side of each longitudinal thermal resistance abrupt change interface, the overall path sequence of heat transfer from the high-temperature section to the low-temperature section is determined throughout the entire borehole depth.

8. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 1, characterized in that: The temperature delay and attenuation caused by the conduction of heat from the soil layer to the adjacent layer include: Obtain the two adjacent soil and rock layers on both sides of each longitudinal thermal resistance abrupt change interface, and extract the average temperature time series of the two soil and rock layers during the entire heating process; Calculate the cross-correlation function of two average temperature time series to obtain the sequence of cross-correlation function values ​​as a function of lag time; The lag time corresponding to the maximum value of the cross-correlation function is determined as the temperature delay at the interface; The ratio of the maximum value of the cross-correlation function to the geometric mean of the autocorrelation function of the average temperature time series of the two soil and rock sections at zero hysteresis is used as the temperature decay rate at the interface. Repeat the above steps for all interfaces with abrupt changes in longitudinal thermal resistance to obtain the temperature delay and attenuation magnitude at each interface.

9. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 1, characterized in that: The longitudinal thermal interference removal and correction of the original temperature data sequence of each layer includes: Multiple heat transfer sections are obtained based on the longitudinal thermal resistance abrupt change interface, and the inter-segment thermal interference coefficient matrix is ​​constructed according to the temperature delay time and temperature decay amplitude at each longitudinal thermal resistance abrupt change interface. Extract the average temperature time series of each heat transfer section during the entire heating process; The corrected temperature time series for a given heat transfer section is obtained by subtracting the average temperature time series of other sections from the average temperature time series of each heat transfer section after shifting by the corresponding delay time and multiplying by the corresponding thermal interference coefficient. The corrected temperature time series is used as the corrected temperature data series for each soil and rock layer in this section.

10. The method for testing and analyzing the thermal response of buried pipes for ground source heat pumps according to claim 1, characterized in that: The output of the overall thermal conductivity of the soil and rock in each layer and the thermal resistance value inside the borehole includes: Based on the infinite long-line heat source model, a linear regression was performed with the natural logarithm of time as the independent variable and the corrected temperature data series as the dependent variable to obtain the slope and intercept of the regression line. Calculate the overall thermal conductivity of the soil and rock layer based on the slope and the applied constant heating power. Calculate the borehole thermal resistance value of this soil and rock layer based on the intercept, borehole geometry parameters, and soil thermal diffusivity.

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