Groundwater heat pump (GWHP) systems have gained attention for space heating and cooling due to their efficiency and low installation costs. Their number is growing in many countries, and therefore ...in some areas, dense installations are expected. This might lead to thermal interferences between neighbouring groundwater wells and a decrease in efficiency. In the presented study, three analytical formulations are inspected for the prediction of the thermal plume around such open-loop systems under various hydrogeological conditions. A thermal radial transport scenario without background groundwater flow and two advective scenarios with moderate to significant ambient flow velocities (1 and 10 m d−1) are analytically simulated and compared with numerical simulations. Two-dimensional (2D) numerical models are used to estimate the validity of analytical results for a homogeneous confined aquifer, without considering heat transfer in upper and lower layers of the aquifer. In order to represent more realistic aquifer conditions of limited vertical extension, an additional three-dimensional numerical model (3D) is deployed to account for vertical heat losses. The estimated relative errors indicate that the analytical solution of the radial heat transport is in good agreement with both numerical model results. For the advective scenarios, the suitability of the linear and planar advective heat transport models strongly depend on ambient groundwater flow velocity and well injection rate. For low groundwater velocities (1 m d−1), the planar model fits both numerical model results better than the linear advective model. However, the planar model's ability to estimate thermal plumes considerably decreases for high injection rates (>0.6 l s−1). In contrast, the linear advective model shows a good agreement with the two-dimensional numerical results for high groundwater flow conditions (≥10 m d−1). The comparison with the three-dimensional numerical models indicates that the vertical heat transfer is challenging for all of the selected analytical solutions. Despite this, there is a wide range of applicability for the provided analytical solutions in studying the thermal impact of GWHP systems. Hence, the inspected solutions prove to be useful candidates for first-tier impact assessment in crowded areas with potential thermal interferences.
•Three analytical models for thermal impact assessment of GWHP systems are evaluated.•Their validity is evaluated for common hydrogeological conditions.•Analytical predictions are compared with 2D and 3D numerical model results.•For each examined scenario, an analytical model satisfactorily estimates the impact.•The analytical models are suitable for prior assessment of GWHP systems' thermal impact.
Thermophysical properties of rock and soil are important parameters that affect the efficiency of shallow geothermal energy utilization. This paper analyzes the thermophysical parameters (specific ...heat capacity and thermal conductivity) and their influencing factors based on 6467 sample data in 24 provincial capitals, China. The statistical distributions of thermophysical properties are analyzed based on histogram plots. Linear regression analysis is conducted to investigate the correlation between thermophysical properties and lithology (classified as metamorphic rocks, igneous rocks, chemical sedimentary rocks, clastic sedimentary rocks, and loose sediments in this study)), density, and water content. The results show that the thermophysical properties are influenced predominantly by lithology. The measured values of thermophysical properties generally show normal distribution characteristics. The specific heat capacity of loose sediments is relatively high, the thermal conductivity of other four types are relatively high. The specific heat capacity is negatively correlated with density, positively correlated with water content, whereas thermal conductivity is positively correlated with density, and negatively correlated with water content. The findings obtained in this study provide evidence and guidelines for the investigation, evaluation, and development of shallow geothermal resources.
Renewable thermal energy from seabed sediment is used for heating and cooling houses in Suvilahti, Vaasa, Finland. Innovative coaxial polyethylene pipes (Refla) filled with heat collection fluid are ...laid horizontally in the sediment layer. This study aims to evaluate the adequacy and possible overuse of this shallow geothermal energy. This entailed a numerical analysis of the heat relations of a “coaxial closed-loop geothermal system (CCGS)" to investigate the thermal behavior of the sediment. The numerical model was developed in Midas GTS NX software with a thermal analysis module. The objective was to understand temperature fluctuation in the sediment, which is influenced not only by geothermal energy exploitation, but also by seasonal weather. The numerical model, due to its design, provided information mainly about changes in sediment temperature due to the geothermal energy exploitation during the different seasons. The results show that in the first third of the total length of the Refla pipes, the sediment environment is significantly affected by energy exploitation's temperature loading. It is advisable to exclude the first third from an analysis of total geothermal energy reserves. The remaining two-thirds of the length shows potential to provide sustainable, long-term geothermal energy (GE) exploitation at the current rate.
This paper summarizes the development of the Ground Source Heat Pump (GSHP) system in China during the period from 1989 to 2021. A statistical analysis shows the Ground-Coupled Heat Pump (GCHP) ...system is the major type of GSHP, accounting for 95.09% of the collected 2754 systems. The most likely building types of GSHP are residential and commercial buildings. The development of GSHP can be divided into three stages including the initial stage, the accelerating stage and the steady growing stage. The analysis of distribution density displays the GSHP is majorly located at the Yangtze River Area (YRA) and North China Plain (NCP) area. This matches very well with the potential density of GSHP estimated by considering air pollution, the thermal load of buildings, people density and GDP. Technical measures aiming at the reduction of the costs and the improvement of thermal efficiency of GSHP are the dominated internal factors, policy incentives and energy price are considered the major external factors determining the development of GSHP system.
•The finite element method can reliably capture heat exchange between embedded walls and the ground given sufficient attention is paid to mesh refinement and the assessment of key parameters.•For ...experimental case studies careful consideration should be given to the characterisation of such geostructures, their constituent materials and surrounding environment to ensure the heat transfer processes are understood.•The thermal properties of the wall elements are at least as important as, and in some cases more so than, those of the ground in determining the heat transfer potential.•Wall geometry in terms of the height of wall exposed to any internal space relative to the height of the wall panel height and the wall thickness have been revealed to have an important influence on heat exchange potential.
A number of operational cases exist where embedded retaining walls, used in the construction of underground spaces such as basements and shallow tunnels, have also been utilised as ground-heat exchangers in shallow geothermal energy systems. These are complex structures in terms of their geometry, the surrounding temperature field and boundary conditions, and there are currently no methods to assess their heat exchange capacity in a simple and expedient manner. This contribution uses the finite element method to validate the use of the method in predicting heat flow for this application and then, to assess the influence of wall and excavation geometry in the heat exchange process. The influence of the soil and wall thermal conductivity is shown to be quasi-linear with the latter showing the greatest influence on peak heat exchange. The work identifies a geometric parameter - the ratio of excavation depth to total wall panel depth, H/L which in combination with the wall thickness (D), provide a consistent and simple means by which the heat exchange potential can be estimated, for a given set of wall and soil thermal properties and boundary conditions.
The extraction of shallow geothermal energy using borehole heat exchangers (BHEs) is a promising approach for decarbonisation of the heating sector. However, a dense deployment of BHEs may lead to ...thermal interference between neighboring boreholes and thereby to over-exploitation of the heat capacity of the ground. Here we propose a novel method to estimate the technical potential of BHEs which takes into account potential thermal interference as well as the available area for BHE installations. The method combines simulation of the long-term heat extraction through BHEs for a range of borehole spacings and depths and includes an optimisation step to maximise the heat extraction. Application of the method to a case study in western Switzerland, from an available area of 284km2, yields an annual technical potential of 4.65TWh and a maximum energy density of 15.5kWh/m2. The results also suggest that, for a minimum borehole spacing of 5m and a maximum borehole depth of 200m, the cumulative installed borehole depth should not exceed 2km/ha. The estimated technical potential can be used by urban planners for the techno-economic analysis of BHE systems and by policy makers to develop strategies that encourage the use of shallow geothermal energy.
Display omitted
•Technical potential for densely deployed vertical borehole heat exchangers (BHEs).•Estimation of the potentially available area for the installation of BHEs.•Model of thermal interference between BHEs for various borehole spacings and depths.•Trade-off between optimal operation and minimal interference of neighboring BHEs.•Case study in Western Switzerland: potential of 4.65 TWh on 284 km2 available area.
The design and operation of Shallow Geothermal Energy (SGE) systems have been continuously increasing in scientific research over the past years. What hinders the wide penetration of SGE systems in ...most countries are issues mostly related to high installation costs, administration, stakeholders' awareness, and marketing. On top of this, SGE systems lack an in-depth economic evaluation, which is often limited to the financial inputs, and thus omitting the non-market monetized environmental benefits. This paper consists of a primer for conceptually improving understanding in regions with low levels of SGE penetration. It provides guidance to project evaluation and discusses the social and institutional strategies to assist SGE systems penetration.
•Economic principles for shallow geothermal energy are discussed.•Social barriers and stakeholders' awareness issues are elicited.•Institutional aspects that hinder penetration of shallow geothermal energy are presented.•A communication plan among stakeholders is recommended.
•Field tests of super-long flexible thermosyphons (SFTSs) for shallow geothermal systems.•Effects of evaporator dimension and corrugated-pipe shape.•A better thermal performance of SFTS with helical ...corrugated-pipe.•The maximum heat extraction rate achieved by SFTSs is approximately 25 W/m.•Insights into the heat-transfer mechanism of geothermal thermosyphons.
This study investigates the thermal performance of three super-long flexible thermosyphons (SFTSs) fabricated using metal corrugated-pipe under shallow geothermal conditions, aiming to uncover enhanced heat-transfer methods applicable to this innovative design. Field tests are conducted for SFTSs, each with a length of 52.5 m, under various cooling conditions in a drilling environment. The effects of evaporator dimensions and corrugated-pipe shape on the start-up and steady-state thermal performance of SFTSs are also discussed. The results indicate that the whole liquid pool of all SFTSs boils during start-up, even with an initial liquid column height of 15 m. The SFTS with the lower-diameter evaporator demonstrates better thermal performance during both start-up and steady-state operations, with an increase of approximately 31.8% in the heat transfer power under optimal conditions within the test parameters. Moreover, the helicon-shaped corrugated-pipe evaporator provides better thermal performance for SFTSs than the U-shaped corrugated-pipe evaporator, thus resulting in an increase in the heat transfer power by approximately 5.5% under optimal conditions. The maximum heat transfer power achieved in this study is approximately 1227 W when the inlet temperature of cooling water is 3 °C and the flow rate of cooling water is 4500 mL/min, demonstrating the potential of super-long flexible thermosyphon in extracting shallow geothermal energy. These results provide valuable insights into the heat-transfer and enhancement mechanisms of geothermal thermosyphons.
PDF
