Buried Pipe System Research Articles

Experimental investigation on dynamic thermal storage and extraction performance of seasonal thermal storage

The initial investment for a buried pipe system using soil as a seasonal thermal storage medium is costly and not suitable for small rural buildings. To promote the cost-effective heating in rural areas, this study proposes a novel seasonal thermal storage system utilizing water and soil as thermal storage medium with copper rods to enhance thermal transfer between water tank and the surrounding soil. An experimental platform was established to discuss the temperature variation characteristics and investigate the thermal performance under different operating modes and experimental parameters. The results show that the temperature of the soil without copper rods is linearly related to the depth, while the highest temperature at the end of the copper rods occurs at the middle depth. The soil with short copper rods exhibits the most rapid thermal storage response and a relatively shorter thermal extraction response time. Intermittent operation can significantly enhance the thermal extraction rate and outlet temperature of the thermal storage unit, whereas the energy storage efficiency decreases with the extension of the downtime. The soil contribution rate of the thermal storage unit is influenced by the operational duration, initial temperature of the water tank and outdoor ambient temperature.

Modification of Risers in Buried Pipe Irrigation System to Improve their Performance

This study identified the problems associated with the design, construction, operation, and maintenance of risers in buried pipe irrigation systems and proposed a modified design. The problems of buried pipe irrigation systems were assessed by inspecting three deep tube wells (DTWs) supplying water through buried pipes with twenty-five outlets. One DTW of the Bangladesh Agricultural Development Corporation (BADC) with five outlets in Netrokona, and one with fifteen outlets in Bara Kailati village and one with five outlets in Bali Bazar, both in Netrokona Sadar, were selected. Data were collected from farmers, field staff, and management authorities by employing pretested questionnaires and field investigations. Site visits revealed that the primary problems were the water leakage through outlets and cracks in the riser structure around the outlet. These problems were due to unsuitable outlet design of the buried pipe system. To overcome these problems, the riser design has been modified structurally, that may lead the buried pipe to suitable and durable performance of buried pipe irrigation system and reduce water losses. J Bangladesh Agril Univ 22(2):225-230, 2024

Heating performance analysis of solar energy-medium deep buried pipe

In order to promote the vigorous development of renewable energy. Regarding the thermal load of buildings in Yulin mining area. Establish a solar deep buried pipe system using TRNSYS software. The feasibility of the components is verified by experiments. After comparing three different operating systems, it is concluded that the solar-medium and deep buried pipe system has more advantages. By simulating the solar energy - deep buried pipe system, it is concluded that: (1) The water supply temperature is relatively stable and can be maintained at 48 °C. (2) The COP can be up to 6.2, and the heat supply can also meet the building demand. (3) The cost is also low after long - term operation. Therefore, it is feasible to use solar energy-deep buried pipe system in mining area.

Heat Transfer Mechanism of Heat–Cold Alternate Extraction in a Shallow Geothermal Buried Pipe System under Multiple Heat Exchanger Groups

Shallow geothermal energy usually uses underground buried pipes to achieve the purpose of extracting heat while storing cold in winter and extracting cold while storing heat in summer. However, the heat transfer mechanism under the alternate operation of heat–cold extraction in winter and summer under multiple heat exchanger groups is still worth studying. Based on the constructed flow and heat transfer model in pipelines and reservoirs, this study first analyzes the temperature field evolution of a shallow buried pipe system (SBPS) under the alternate operation of heat–cold extraction, and then discusses the heat transfer performance under different pipeline flow rates, pipeline wall thermal conductivity, heat injection durations, numbers of heat exchanger groups, and flows of underground fluid. The results show that the continuous alternating process of heat–cold extraction has a promoting effect on the temperature increase or decrease in the next operating cycle due to the low- or high-temperature zone produced in the previous operating cycle. As the number of multiple heat exchanger groups increases, the heat transfer efficiency of the SBPS significantly improves. With a rise in the groundwater flow velocity, the heat transfer efficiency first decreases and then increases.

Experimental validation of the dynamic thermal network approach in modeling buried pipes

The transient behavior of buried pipe systems plays a significant role in many heating and cooling systems, particularly in thermal energy networks and ground heat exchangers. In this study, the dynamic thermal network (DTN) approach’s validity as a response factor method in modeling dynamic conduction heat transfer in a buried pipe system is experimentally validated. A lab-scale representation of a buried pipe system has been excited by step changes in boundary temperatures and heat fluxes measured up to times approaching steady-state conditions. This data is used to derive weighting factors and also evaluate the validity of numerical representations of the buried pipe and to verify that the DTN method can reproduce the heat flux responses. It is demonstrated that the weighting factors required in this method can be derived from both numerical and experimental step-response time series data. The DTN method is found to be both accurate in reproducing the heat fluxes in the validation experiments but also significantly more computationally efficient than a conventional numerical model when simulating long timescale responses in buried pipe systems.

Experimental and numerical simulation research on heat transfer performance of coaxial casing heat exchanger in 3500m-deep geothermal well in Weihe Basin

The deep coaxial borehole heat exchanger (DCBHE), as an important part of the deep-seated ground heat exchanger system, undertakes the important task of heat exchange with the underground geotechnical body to provide heating for the building. In this paper, through field test, numerical simulation and sensitivity analysis, the influence of thermal insulation performance of inner tube, heat preservation method of inner tube and diameter ratio of inner tube to outer tube on heat extraction capacity of deep coaxial borehole heat exchanger is studied. Field tests in intermittent operation mode (9.5 h operation and 14.5 h shutdown) show that the short-term single-well heat extraction capacity of the deep coaxial borehole heat exchanger using the vacuum gel steel tube with a thermal conductivity of 0.002 W/(m·K) as the inner tube is 574.96 W/m. The simulation results show that the diameter ratio of the inner and outer tubes has little effect on the heat extraction capacity, and the diameter ratio of the inner and outer tubes of 0.65 has the smallest resistance loss along the way. For heat exchanger with depth of 3500 m, the location of severe thermal interference between the inner and outer tubes is mainly located in the upper part of the heat exchanger near the surface, especially in the 1400 m to 2100 m section. The research results can provide a reference for the optimization design of medium-deep coaxial heat exchange buried pipe system and the promotion of medium-deep geothermal energy utilization.

A data-driven approach to low-enthalpy shallow geothermal energy extraction: A case study on indoor heating for precision agriculture applications

Shallow geothermal energy systems utilize the upper layers of the ground to provide space heating and cooling, with a relatively high efficiency. The research presented aims to assess the potential harnessing of this source and applying it for indoor conditioning of a precision agriculture facility. An experimental phase was conducted to measure the temperature of the ground at 0.75 m, 1.5 m, 2.25 m, and 3.0 m. Field testing was performed employing two probes; one uncovered and a second insulated with a polyethylene sheet, to evaluate the effect soil water content variations exert over the soil temperature. It was found that, given the high permeability and good drainage of the soil material, water content is not statistically significant, ruling out the presence of microconvective phenomena within the interstices of the undisturbed earth. Based on the temperature profile obtained, achievable heat extraction capacity was computed by modelling a buried pipe system. A parametrization was conducted showing that, of all the involved factors, pipe depth, pitch and their interaction, are the ones that contribute the most to the heat output variability. The computed available heat flow was used to simulate the performance of a geothermal heat pumping system for greenhouse heating based on real operation data, provided by the owners. The results show that, shallower layers of the ground, can provide adequate solutions for immediate thermal needs; a 5-pipe, 100m-length ground loop at 0.75 m, could provide 90% of the total thermal demand, whilst an 11-pipe, 200m-length loop, at 1.5 m depth, reaches 84% of the same demand, with a variability reduction in availability of 10% to 20% depending on the severity of surface conditions. However, for deeper layers, i.e., 2.25 m and 3.0 m, respective maximum heat output amounts to 43% and 49% of the total thermal demand. Nonetheless, these configurations yield the most stable and constant heat flow of the lot, making them particularly suitable for preheating/subcooling processes or even long-term thermal storage. Despite not fulfilling the total thermal demand of the greenhouse, these setups are more than capable of providing support to on-site conditioning devices; requiring a lower upkeep and yielding a higher efficiency, which would reduce overall production costs. Furthermore, from the conducted data analysis, it was found that controlling the agronomic values, associated to indoor agriculture, facilitates the physical aspect of greenhouse energy management, paving the way to more optimized thermal solutions, tailored to different sets of operation conditions.

A coupled hydro-mechanical model for subsurface erosion with analyses of soil piping and void formation

A coupled hydro-mechanical erosion model is presented that is used for studying soil piping and erosion void formation under practical, in-situ conditions. The continuum model treats the soil as a two-phase porous medium composed of a solid phase and a liquid phase, and accounts for its elasto-plastic deformation behaviour caused by frictional sliding and granular compaction. The kinetic law characterizing the erosion process is assumed to have a similar form as the type of threshold law typically used in interfacial erosion models. The numerical implementation of the coupled hydro-mechanical model is based on an incremental-iterative, staggered update scheme. A one-dimensional poro-elastic benchmark problem is used to study the basic features of the hydro-mechanical erosion model and validate its numerical implementation. This problem is further used to reveal the interplay between soil erosion and soil consolidation processes that occur under transient hydro-mechanical conditions, thereby identifying characteristic time scales of these processes for a sandy material. Subsequently, two practical case studies are considered that relate to a sewer system embedded in a sandy soil structure. The first case study treats soil piping caused by suffusion near a sewer system subjected to natural ground water flow, and the second case study considers the formation of a suffosion erosion void under strong ground water flow near a defect sewer pipe. The effects on the erosion profile and the soil deformation behaviour by plasticity phenomena are elucidated by comparing the computational results to those obtained by modelling the constitutive behaviour of the granular material as elastic. The results of this comparison study point out the importance of including an advanced elasto-plastic soil model in the numerical simulation of erosion-driven ground surface deformations and the consequent failure behaviour. The numerical analyses further illustrate that the model realistically predicts the size, location, and characteristic time scale of the generated soil piping and void erosion profiles. Hence, the modelling results may support the early detection of in-situ subsurface erosion phenomena from recorded ground surface deformations. Additionally, the computed erosion profiles may serve as input for a detailed analysis of the local, residual bearing capacity and stress redistribution of buried concrete pipe systems.

Simulation Experiment on Energy Tower Coupled with Buried Pipe System of Ground-source Heat Pump for Cross-season Heat Storage

It is proposed to use energy tower instead of solar collector system to store heat for buried pipe system of ground-source heat pump in summer, so as to solve the problem that soil temperature is too low due to unbalanced cold and heat load of GSHP in cold and severe cold area. The simulation results show that the thermal storage power of energy tower is affected by soil temperature and environmental temperature. The lower the soil temperature, the better the thermal storage effect of energy tower system for soil. The thermal storage power and environmental temperature change in a positive relationship. It is proved that the application of cross-season heat storage is feasible for energy tower coupled with buried pipe system of ground-source heat pump in cold and severe cold area.

VERIFICATION AND RESULTS FROM MODEL INVESTIGATION OF DYNAMIC BEHAVIOR OF BURIED PIPES-PART 2

The operating conditions of the buried pipe system require consideration of three main elements of a deterministic limit states analysis carried out by experimental or analytical techniques (Eurocode). In the prognosis analyses (reliable and workable), the complex of external and internal impacts for the system is a first step of limit states estimation (A-EN1990). The second element (M-material parameters)-investigation of the material properties of the system inextricably related to the model. The third element (R-resistance) of deterministic analysis is the most delicate part of the study of any limit state. It poses a significant challenge to creative thinking and requires a reasonable combination of the first two elements to formulate a system model. The investigation focuses on the composition of three-dimensional discrete models based on the bearing capacity of the ground strata. Here, the bearing capacity factors are determined in the general context of geometrical and material characteristics as a function of both changes of soil mass strains and as a result of the degradation of the entire system’s stiffness. This allows models to be used in conditions developed in slow movements conditions, such as landslides. These model interpretations have been compared with well-known solutions and are evaluated in example solutions in a frame and solid model using both modal analysis and time-dependent displacement surface functions.

Mathematical Modelling and Operational Analysis of Combined Vertical–Horizontal Heat Exchanger for Shallow Geothermal Energy Application in Cooling Mode

Geothermal heat exchangers (GHEs) represent a buried pipe system, which can be utilised to harness renewable thermal energy stored in the ground to improve the efficiency of heating and cooling systems. Two basic arrangements of GHEs have been widely used: vertical and horizontal. Vertical GHEs generally have a better performance in comparison with the horizontal arrangement, and these systems are particularly suitable for confined spaces. Nevertheless, the main technical challenge associated with GHEs, for either the vertical or the horizontal arrangement, is the performance deterioration associated with an increase in the operation times during summer or winter seasons. In this paper, a combined horizontal-vertical GHE arrangement is proposed to address the current challenges. The combined GHE arrangement can be operated in five different modes, corresponding to different thermal loading conditions. These five operation modes of the combined GHE are analysed based on the transient finite difference models previously developed for the horizontal and vertical arrangements. The simulation results reveal that for the single operation mode (horizontal or vertical only), the vertical GHE performs better than the horizontal GHE due to relatively stable ground temperature deep down. While, for the combined operation mode, the series operations (horizontal to vertical or vertical to horizontal) of the GHE are superior to the split mode. It is found that the effect of the fluid mass flow rate ratio is trivial on the heat dissipation of the split mode GHE. The highest heat transfer rate in the split flow operational mode is rendered by the ratio of the mass flow rate of 40% horizontal and 60% vertical. In addition, the climate condition has more effect on GHE’s performance and the increase of the fluid flow rate it can enhance the amount of energy released by the GHE.

A Comprehensive Review of Acoustic Methods for Locating Underground Pipelines

Underground pipelines are vital means of transporting fluid resources like water, oil and gas. The process of locating buried pipelines of interest is an essential prerequisite for pipeline maintenance and repair. Acoustic pipe localization methods, as effective trenchless detection techniques, have been implemented in locating underground utilities and shown to be very promising in plastic pipeline localization. This paper presents a comprehensive review of current acoustic methods and recent advances in the localization of buried pipelines. Investigations are conducted from multiple perspectives including the wave propagation mechanism in buried pipe systems, the principles behind each method along with advantages and limitations, representative acoustic locators in commercial markets, the condition of buried pipes, as well as selection of preferred methods for locating pipelines based on the applicability of existing localization techniques. In addition, the key features of each method are summarized and suggestions for future work are proposed. Acoustic methods for locating underground pipelines have proven to be useful and effective supplements to existing localization techniques. It has been highlighted that the ability of acoustic methods to locate non-metallic objects should be of particular practical value. While this paper focuses on a specific application associated with pipeline localization, many acoustic methods are feasible across a wide range of underground infrastructures.

Numerical study on the heat transfer, extraction, and storage in a deep-buried pipe

Aiming at the thermal attenuation problem of ground temperature field in unidirectional heat extraction and supply in buildings of deep-buried geothermal energy, we propose supplementing heat to the ground using some heat source such as solar energy that is stored during the non-heating period, thus enabling long-term operation of a buried pipe system. With the study conducted on a buried U-bend pipe project with a depth of 2505 m, a three-dimensional (3D) full-scale model was established based on the numerical modeling method which obtained by the author’s research team in the early stage. The heat extracted from the buried pipe or the heat storage capacity of ground for a constant inlet water temperature and given initial ground temperature field was analyzed and predicted. Meanwhile, the heat storage capacity after heat was taken from the buried pipe was calculated and analyzed. Finally, heat flux through the wall of the buried pipe was analyzed, and heat transfer to ground at different buried depths during the heat storage period was discussed.

Combining EPS geofoam with geocell to reduce buried pipe loads and trench surface rutting

This paper reports full scale experiments, under simulated heavy traffic, of geocell and EPS (expanded polystyrene) geofoam block inclusions to mitigate the pressure on, and deformation of, shallow buried, high density polyethylene (HDPE) flexible pipes while limiting surface settlement of the backfilled trench. Geocell of two pocket sizes and EPS of different widths and thickness are used. Soil surface settlement, pipe deformation and transferred pressure onto the pipe are evaluated under repeated loading. The results show that using EPS may sometimes lead to larger surface settlements but can alleviate pressure onto the pipe and, consequentially, result in lower pipe deformations. This benefit is enhanced by the use of geocell reinforcement, which not only significantly opposes any EPS-induced increase in soil surface settlement, but further reduces the pressure on the pipe and its deformation to within allowable limits. For example, by using EPS geofoam with width 0.3 times, and thickness 1.5 times, pipe diameter simultaneously with geocell reinforcement with a pocket size 110 × 110 mm2 soil surface settlement, pipe deformation and transferred pressure around a shallow pipe were respectively, 0.60, 0.52 and 0.46 times those obtained in the fully unreinforced buried pipe system. This would represent a desirable and allowable arrangement.

Experimental Analysis of Effect of Soil Moisture on Thermal Performance of Earth Air Heat Exchanger

Earth Air Heat Exchanger (EAHX) systems are renewable energy systems based on the use of the high energy potential of the soil. Although it has a simple structure, there are multiple parameters that affect thermal performance. These parameters should be taken into consideration when installing the EAHX, which consists of a buried pipe system and a fan. In this study, the effect of humidification of the soil on which EAHX is placed by placing an irrigation line on thermal performance was investigated. In this study, two EAHX with the different material piping systems are discussed. In the study carried out at different airspeeds, inlet-outlet air temperatures, water temperature and air humidity were measured. It was determined that the decrease in the outlet temperatures of the systems using PVC and metal pipes was 10% compared to the dry condition. As a result of the study, it has been observed that moistening the soil increases EAHX efficiency. When the increase in cooling capacity and the additional cost caused by the irrigation system are compared, it is seen that the installation of soil humidification system is applicable in terms of energy efficiency.

Effect of inner pipe type on the heat transfer performance of deep-buried coaxial double-pipe heat exchangers

In the present study, based on the currently used deep-buried coaxial double-pipe heat exchange systems for closed loop heat extraction, the influence of several inner pipe types on the heat transfer performance of buried pipe systems is analyzed. The deep-buried coaxial double-pipe with a smooth inner pipe used in current practice was taken as an example, and a full-scale three-dimensional (3D) numerical model coupling the heat transfer processes inside and outside the pipe was established by using a depth of 50 m and taking into account the modeling workload. Based on this model, full-scale 3D numerical models of coaxial double-pipes with spiral and corrugated pipes as the inner pipe types were established, and numerical analysis of heat transfer was performed. The results indicated that the heat transfer capacity of the buried pipe system can be improved by changing the shape of the inner pipe. However, the influence of the inner pipe type on heat transfer was far lower than that of the water flow rate circulating inside the buried pipe system and the initial ground temperature.

THE USAGE OF GROUND-COUPLED HEAT EXCHANGERS IN SUBTROPICAL CLIMATES

This study aims to identify the feasibility of using a ground-coupled heat exchanger system for air conditioning in subtropical regions. Geothermal systems are used effectively in cold climates, but little explored in hot and humid climate regions, although they show potential for passive air-conditioning environments. The tubes were installed in Southern Brazil, in Foz do Iguaçu, Paraná, which has temperatures of 0ºC in the winter and 40ºC in the summer. The methodology for the research was organized as follows: bibliographic research and geological characterization of the site, system sizing, installation of 22 meters of a 300mm PVC tube, 4 meters depth, and subsequently measurement and data collection on temperatures with use HOBO U10-001 Data Logger. The research was held from March to October 2016. The results showed that at external temperatures of 30ºC, the system was able to cool on average 6ºC, reaching peaks of 7ºC in the temperature of air exit to the environment. At temperatures below 6ºC, the system was able to heat on average 10ºC, with peaks of up to 11ºC. Based on the results, it is concluded that a buried pipe system is a viable alternative for passive climate control in subtropical climates

깊이 인자를 고려한 매설배관의 사고피해영향 비교 분석에 관한 연구

매설배관은 내부 또는 외부의 결함으로 인하여 leak나 rupture가 발생 할 수 있으며, 가스가 누출 시 큰 사고가 발생할 수 있기 때문에 정량적 위험성평가를 통한 분석이 필요하다. 하지만 현재 매설배관에 대한 위험성 평가시 매설을 고려하지 않거나, 매설 깊이를 고려하지 않고 무조건 배관압력의 1/10으로 가정하는 OGP기준을 사용하고 있는 실정이다. 이에 본 연구에서는 여러 기관의 매설배관 ETA분석자료를 통하여 발생가능 사고 중 Jet fire의 사고피해영향을 분석하였으며, Jet fire의 복사열 계산에 있어서 배관의 매설깊이 인자를 고려한 매설모델을 수립하였다. 사례연구는 New Jersey의 Edison지역에서 발생한 사고를 이용하여 본 모델과 OGP모델을 비교 분석하였다. 연구결과 화염원으로부터 10m거리를 기준으로 매설모델의 복사열 값이 OGP모델에 비해 실제 사례와 비슷한 값을 얻을 수 있었다. Buried pipe system is subject to leak or rupture due to internal and external defects with age. Especially, if the pipeline is designed for pressurized gas, the leak can wreak a devastating on its surrounding area. The current method of setting up underground gas pipeline is based on OGP criteria of applying one tenth of the inner pipe pressure. The criteria is applied irrespective of their burial depth or pipe's properties. At times, even the whole safety measures are totally ignored. Considering the magnitude of possible damage from a gas leakage, a precise analytical tool for the risk assessment is urgently needed. The study was conducted to assess possible scenarios of gas accidents and to develop a computer model to minimize the damage. The data from ETA was analyzed intensively, and the model was developed. The model is capable of predicting jet fire influence area with comprehensive input parameters, such as burial depth. The model was calibrated and verified by the historic accident data from Edison Township, New Jersey, the United States. The statistical model was also developed to compare the results of the model in this study and the existing OGP model. They were in good agreement with respect to damage predictions, such as radiation heat coming from 10 meters away from the heat source of gas flame.

Monitoring buried pipe deformation using acoustic emission: quantification of attenuation

Deformation of soil bodies and soil-structure systems generates acoustic emission (AE), which are high-frequency stress waves. Listening to this AE by coupling sensors to structural elements can provide information on asset condition and early warning of accelerating deformation behaviour. There is a need for experimentation to model the propagation of AE in buried pipe systems to enhance understanding of real behaviour. Analytical solutions are often based on many assumptions (e.g. homogeneity, isotropy, boundary conditions and material properties) and cannot exactly represent the behaviour of the in situ system. This paper details a series of experiments conducted on buried pipes to investigate AE attenuation in pipes due to couplings and soil surround. The attenuation coefficients reported provide guidance to engineers for designing sensor spacing along buried pipes for monitoring ground deformations, and active waveguide installation depths for slope deformation monitoring. Attenuation coefficients have been quantified for both air–pipe–air and air–pipe–soil trilayer systems for the frequency range of 20–30 kHz.

Air–soil heat exchangers for heating and cooling of buildings: Design guidelines, potentials and constraints, system integration and global energy balance

Air–soil heat exchangers for heating and cooling of buildings are analyzed under various aspects. Based on the analytically resolved case of a constant airflow subject to sinusoidal temperature input, we start by deriving climate independent design guidelines, for dampening of the daily and/or the yearly temperature oscillation. In a second step, constraints and potential of buried pipe systems are analyzed for the case of a typical Central European climate, for which the constraint between climate and comfort threshold induces a fundamental asymmetry between preheating and cooling potential. Finally, it is shown that the net yield of an air–soil heat exchanger has to take into account more than the mere input–output temperature differential.