ERE2.7 | Shallow geothermal energy: geoscience and engineering approaches at different scales
EDI
Shallow geothermal energy: geoscience and engineering approaches at different scales
Convener: Giorgia Dalla Santa | Co-conveners: Rotman A. Criollo Manjarrez, Alberto Previati, Cornelia Steiner, Francesco Cecinato, Lazaros Aresti
Orals
| Wed, 17 Apr, 08:30–12:30 (CEST)
 
Room D3
Posters on site
| Attendance Wed, 17 Apr, 16:15–18:00 (CEST) | Display Wed, 17 Apr, 14:00–18:00
 
Hall X4
Orals |
Wed, 08:30
Wed, 16:15
The session welcomes contributions about shallow geothermal energy applications, including traditional closed- and open-loop borehole heat exchangers as well as so-called energy geostructures.
Different types of analysis and approaches are relevant to this session aiming to engage discussions on successful and less successful experiences at different scales:
Small scale (system): spanning from the evaluation of ground thermal properties to the mapping of shallow geothermal potential or local thermal interferences, from energy storage and innovative materials to sustainability issues and consequences of the geothermal energy use, from the design of new heat exchangers and installation techniques to the energy and thermo-(hydro-) mechanical performance of energy geostructures (e.g. thermo-active foundations, walls, tunnels).
Large scale (city or larger): the sustainability of subsurface water and energy resources may be jeopardized by human activities as well as by climate change. Relevant studies in densely urbanized areas unraveling the impact on/by groundwater characteristics may include: 1) monitoring evidence of physical-chemical-biological changes associated with subsurface warming, 2) elucidate interactions between shallow geothermal systems (and other heating sources), 3) assessment of the potential and sustainability of shallow geothermal energy at the city scale.
Contributions based on experimental, analytical, numerical modelling and artificial intelligence techniques are welcome as well as interventions about legislative and social-economic aspects.

Session assets

Orals: Wed, 17 Apr | Room D3

Chairpersons: Giorgia Dalla Santa, Francesco Cecinato, Lazaros Aresti
08:30–08:40
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EGU24-14738
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ECS
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On-site presentation
Anna Albers, Fabien Koch, Kathrin Menberg, Hagen Steger, Christina Fliegauf, Linda Schindler, Sascha Wilke, Roman Zorn, and Philipp Blum

The sandstones of the Middle and Upper Buntsandstein are suitable host rocks for the installation of shallow geothermal systems due to their high thermal conductivities typically ranging between 1.9 to 4.6 W m-1 K-1 (Verein Deutscher Ingenieure 2010). Knowledge of the effective thermal conductivity is crucial to efficiently dimension borehole heat exchanger (BHE) systems. The standard method for determining effective thermal conductivities at a site is the thermal response test (TRT). However, thermal conductivity can also be analysed in the laboratory from core samples. In addition, various prediction models for the estimation of thermal conductivity based on lithological properties, such as porosity, exist. In this study, depth-specific thermal conductivities of sandstone samples of the Upper and Middle Buntsandstein are comprehensively analysed by applying different methods. First, thermal conductivities of about 140 core samples are analysed in the laboratory, and relations between material properties, such as porosity and mineralogy, and thermal conductivity are investigated. Furthermore, common prediction models are applied, and in addition, the measured and estimated thermal conductivities are compared to the effective thermal conductivities evaluated with an enhanced thermal response test (ETRT). The average effective thermal conductivity analysed with the ETRT is 4.7 W m-1 K-1, while the thermal conductivities analysed in the laboratory on saturated core samples range between 2.7 to 6.4 W m-1 K-1 with an average value of 4.6 W m-1 K-1. The best estimate from the prediction models is achieved by the Voigt-Reuss-Hill model with an average error of 13 % and a maximum error of 26 %. Overall, prediction models that assume a random distribution of solid and fluid components can achieve reliable estimates of the thermal conductivity of the sandstone. Thus, the results demonstrate that laboratory analyses can provide representative values of the effective thermal conductivities at a site with negligible or low groundwater flow. However, we also show that in order to achieve a representative value a sufficient number of samples has to be analysed, which entails high expenses for laboratory analyses.

Verein Deutscher Ingeniere. VDI 4640, part 1: Thermal use of the underground, fundamentals, approvals, environmental aspects, 2010.

How to cite: Albers, A., Koch, F., Menberg, K., Steger, H., Fliegauf, C., Schindler, L., Wilke, S., Zorn, R., and Blum, P.: Measuring the thermal conductivity of sandstones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14738, https://doi.org/10.5194/egusphere-egu24-14738, 2024.

08:40–08:50
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EGU24-5378
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ECS
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On-site presentation
Hesam Soltan Mohammadi, Lisa Maria Ringel, Christoph Bott, and Peter Bayer

Most shallow geothermal systems harness renewable energy from the ground by circulating a heat-carrier fluid through borehole heat exchangers (BHEs). While these systems have emerged as promising contributors to the ongoing energy transition, open questions regarding their durability and performance in practical applications remain. Critical factors are the uncertainty in the long-term heating/cooling demand as well as the uncertainty in the evolution of the ground thermal conditions. To enhance the environmental and economic appeal of such systems that should be operated for decades, optimal control procedures that adjust the heat extraction during the course of operation have been proposed. In this study, we introduce an improved sequential simulation-optimization procedure to tune the efficiency of BHEs exposed to transient groundwater flow conditions. The variability of groundwater flow not only perturbs subsurface heat transfer but also impairs the predictability through standard BHE modeling tools. For example, the well-established moving finite line source (MFLS) formulation offers no capabilities to represent transient trends in advective heat transport associated with groundwater flow. We restructure the MFLS by a time-varying groundwater flow term that ensures compliance with thermal equilibrium assumptions. This modified variant is validated with a numerical model and then interfaced with a linear programming algorithm to optimize the operation of the BHE array. To examine the efficacy of the proposed procedure, a synthetic field containing ten BHEs operating in the heating mode is implemented. Three distinct groundwater fluctuation scenarios, with monthly resolutions over a ten-year operational lifespan, are considered. The groundwater flow dynamic exhibits variations in an increasing, decreasing, and periodic manner. As the objective, local cooling is to be minimized. This is achieved by determining the monthly optimal load pattern for individual BHEs. The proposed methodology employs a cost function to minimize the maximum temperature change over two distinct temporal terms. The first term considers the entire operational lifetime, while the second term focuses on a forthcoming 12-month horizon.
The proposed methodology does not only achieve optimal BHE operation, but it also facilitates calibrating unknown or transient model parameters. This is demonstrated for the groundwater flow velocity that is estimated by solving a nonlinear least-squares problem using the trust-region-reflective algorithm. The benefit of sequential learning is compared with results obtained by optimization without any model calibration. This calibration-optimization routine, informed by transient temperature changes in the simulated ground, outperforms sequential optimization that relies on non-tunable model parameters.

How to cite: Soltan Mohammadi, H., Ringel, L. M., Bott, C., and Bayer, P.: Tuning the performance of a borehole heat exchanger array in response to transient hydrogeological conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5378, https://doi.org/10.5194/egusphere-egu24-5378, 2024.

08:50–09:00
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EGU24-21884
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ECS
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On-site presentation
Sriparna Roy, Tanusree Chakraborty, and Jagdish Telangrao Shahu

Introduction: Geothermal heat pump systems GSHPs use the Earth’s subsurface as a heat source in winter and heat sink in summer. A GSHP system integrated with vertical HDPE U-loops for transferring the heat to and from the ground is called a closed-loop ground heat exchanger (CLGHE) system placed by drilling the boreholes. In this study, the relationship between borehole diameter, thermal resistance, and the optimum loop length of CLGHE
systems is investigated.
Methods: Utilizing the standard thermal line source equation, analysis of borehole thermal resistivity bR variations across a spectrum of borehole diameter d sizes (ranging from 80-180 mm) has been performed. The soil thermal properties like conductivity λ are considered as 1.5 W/mK , initial ground temperature is considered to be 25⁰C. The analysis is extended to evaluate the influence of borehole diameter sizes on the optimal length of geothermal single U-loops using Ground Loop Design (GLD) software. This comprehensive assessment incorporated critical factors such as soil thermal properties, heat transfer fluid characteristics, and U-loop pipe attributes which has been replicated from the analytical study for a heat load of 10MWh.
Results: The outcomes of our simulations revealed notable correlations: larger boreholes consistently demonstrated increased thermal resistance analytically. It has also been observed through the GLD simulations that the loop length increases as the borehole diameter increases for example: when the diameter increases from 80mm to 100mm the loop length increases from 57.6 to 56.5m for a geothermal grid of 2x2 rectangular configuration for the same soil properties and thermal loading conditions. The observed relationship holds implications for optimizing system design and performance, particularly in diverse soil conditions. In conclusion, our study contributes valuable insights into the thermal efficiency of GSHP systems, emphasizing the importance of borehole diameter in influencing overall energy transfer capabilities. These findings provide a foundation for further research and practical applications for the CLGHE systems.

How to cite: Roy, S., Chakraborty, T., and Shahu, J. T.: The Impact of Borehole Diameter on Loop Length and ThermalResistivity in Closed-Loop Ground Heat Exchanger System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21884, https://doi.org/10.5194/egusphere-egu24-21884, 2024.

09:00–09:10
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EGU24-16828
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ECS
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On-site presentation
Nikolas Makasis, Monika Kreitmair, Chaoqun Zhuang, Kathrin Menberg, Wonjun Choi, and Ruchi Choudhary

Shallow geothermal energy technologies have seen significant development over past decades and the number of ground-source heat pump (GSHP) installations has seen an increasing trend worldwide. Importantly, a plethora of scientific research has explored performance, mechanical stability, optimisation, and innovative approaches to utilise the ground as a source or sink of thermal energy. Despite this, however, there is often a gap between the designed performance of a system and the realised in-situ operation. Such a gap can result from a lack of information, such as imprecise ground profile/thermal properties, changes in the environment and conditions, such as in building usage due to changes in behavioural patterns, as well as the fact that GSHP design is typically undertaken in isolation of other system elements, e.g., by using only estimates of the heating and cooling demands.

Real-time monitoring and appropriate smart control methods can help bridge this discrepancy, alleviating potential issues. Heat pumps and building management systems typically record useful data, such as the temperature of the fluid in the ground loop, constituting valuable sources of information on the current system performance at a given moment. However, using these data to predict how the system will perform in the future, and thus inform system operation, is not trivial. A field that can help tackle this problem is data science, which uses data-driven artificial intelligence (AI) approaches to provide useful insights from data and has had tremendous advancements in recent years. It is therefore expected that statistical AI approaches can be used with data from GSHP systems meaningfully, to inform the efficient operation of the system.

This research focuses on a case study in Cambridge, UK, where a GSHP system, with capacity of 320 kW and a ground loop with 24 160-m deep boreholes, provides heating and cooling for a recently constructed university building. The data recorded from this system is utilised together with a combination of AI methods, such as gradient boosting and deep neural network predictive models, and finite element modelling to assess how well the ground loop performance can be predicted in real time and the implications this can have on the performance of the system. Thus, this work demonstrates how GSHP data can be leveraged to make useful decisions based on updated information and thereby ensure that a GSHP system performs efficiently throughout its lifetime.

How to cite: Makasis, N., Kreitmair, M., Zhuang, C., Menberg, K., Choi, W., and Choudhary, R.: A case study on the use of AI methods towards bridging the gap between design and operation of ground-source heat pump systems., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16828, https://doi.org/10.5194/egusphere-egu24-16828, 2024.

09:10–09:20
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EGU24-11181
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ECS
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On-site presentation
Marco Gerola, Francesco Cecinato, Jacco K. Haasnoot, and Philip J. Vardon

In recent decades, there has been a notable rise in the utilization of the subsurface as a source for heating and cooling through shallow geothermal installations. This trend is exemplified by the emergence of Energy Geostructures (EGs), an innovative technology that not only provides structural support to the ground or buildings but also facilitates the exchange of heat with the subsurface. EGs offer versatile applications for various energy needs, including their integration with ground source heat pumps for space heating, cooling, and domestic hot water provision.

Energy Quay Walls (EQWs) represent a promising type of energy Geostructures that demonstrate a unique ability to exchange heat with both the surrounding soil and open water. Despite the considerable potential for energy efficiency that EQWs hold, their limited implementation underscores the need for extensive research to comprehend their thermal behavior.

This study conducts an in-depth examination of EQWs, employing two Finite Element numerical models to reconstruct the undisturbed temperature profile within the soil and conduct a detailed 3D analysis of heat exchange processes in an EQW application. These models are validated using real data obtained from a full-scale test in Delft, The Netherlands. The results emphasize the significance of transitioning from laminar to turbulent flow regimes within the heat exchanger pipes, showcasing improved energy extraction efficiency, particularly from the open water layer.

Moreover, the study underscores the critical role of open water movement in the energy extraction process. This finding emphasizes the dynamic nature of open water in contributing to the overall effectiveness of EQWs as an EG. The study's outcomes provide important considerations for optimizing the design and implementation of EQWs, pointing towards the benefits of promoting turbulent flow regimes within the heat exchanger pipes and emphasizing the advantages of harnessing energy from actively moving open water layers. As the implementation of EQWs continues to expand, these insights contribute to advancing our understanding and enhancing the energy efficiency of this innovative technology. 

How to cite: Gerola, M., Cecinato, F., Haasnoot, J. K., and Vardon, P. J.: Optimizing Energy Quay Walls: Insights from Comprehensive Thermal Analysis and Turbulent Flow Enhancement, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11181, https://doi.org/10.5194/egusphere-egu24-11181, 2024.

09:20–09:30
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EGU24-7965
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ECS
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On-site presentation
Mouadh Rafai, Diana salciarini, and Philip J Vardon2

Displacement cast in situ Fundex (DCSF) energy piles are a new type of energy pile with the advantages of convenient construction, simple manufacturing, low vibration, and low noise and cost. This work focuses on the response of a stand-alone DCSF energy pile under different mechanical loads simultaneously with the operation of a ground source heat pump through a series of full-scale field tests. After applying an axial load on the pile head (60% of the bearing capacity), the pile was subjected to ten thermal cycles. The effects of mechanical load and the impact of temperature on the mechanical capacity of the DCSF energy pile were investigated. 

The results indicate that the cyclic thermal loadings induce a progressive increase in the compressive stress of piles. Furthermore, a residual compressive stress was observed and attributed to the drag-down effects of the surrounding soil.

During cooling phase, the tensile stress induced by thermal load decreased drastically due to the shrinkage of the near soils, leading to an insignificant effect on the energy pile during cooling. The maximum thermo-mechanical axial compressive stress in the foundations was approximately 1.55 MPa, well within structural limits and not expected to affect the building.

Progressive pile head displacement was observed indicating that thermal creep can affect pile head displacement at higher working loads.

How to cite: Rafai, M., salciarini, D., and Vardon2, P. J.: Thermo-mechanical response of a cast in situ displacement energy pile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7965, https://doi.org/10.5194/egusphere-egu24-7965, 2024.

09:30–09:40
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EGU24-20924
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ECS
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On-site presentation
Gabrielle Beaudry, Philippe Pasquier, Jasmin Faucher, Giulio Tonellato, and Michaël Kummert

Standing column wells (SCW) are ground heat exchangers that recirculate groundwater in a deep uncased borehole and “bleed” only a fraction of the pumped water during peak demand periods to boost advective heat transfer. While operational feedback collected from numerous systems in the northeastern United States is available and provides general design guidelines (Orio et al., 2005; 2006), practitioners have been slow to embrace SCWs outside their area of emergence. This reluctance can be explained in part by a lack of awareness, as well as lingering concerns about groundwater chemistry and the reliability of these systems in diverse climatic and geological settings. In this context, the present work presents a case study of a demonstration SCW system that was retrofitted in a school near Montreal, Québec, Canada, with the aim of sharing the knowledge gained during the design and commissioning phases.

The demonstration system’s design relied on an early exploratory phase, which included an exploratory drilling, a thermal response test, a pumping test, and groundwater analyses. These field operations first uncovered the presence of a highly productive sandstone aquifer, which 1) halted drilling early at 133 m due to the elevated water pressure, and 2) had a strong influence on the thermal response test’s results due to the high efficiency of advective heat transfer, even in the absence of bleed. Accordingly, the development and calibration of an advanced coupled thermo-hydrogeological numerical model was deemed necessary to evaluate the proper sizing of the ground heat exchanger.

Following design and construction, a review of the available data was conducted to evaluate the SCW system’s general performance metrics. This exercise first demonstrated its overall efficiency, which reduced drilling lengths by approximately 73%, construction time by 52%, and initial costs by 37% compared to conventional closed-loop boreholes. It was also found that the SCWs were able to sustain building loads over 200 W/m and to reduce peak electrical power demand by 71% compared to electric resistance heating, this on the coldest winter day when the air temperature was -26 °C. Monitoring of the pressure losses through the plate heat exchanger and step-drawdown tests did not indicate any immediate groundwater quality concerns. On the other hand, the elevated energy consumption of the pumping equipment affected the system’s seasonal performance factor, and a few operational issues related to corroded probes and inefficient control sequences compromised energy and financial savings and had to be resolved.

In conclusion, the results of this case study demonstrate the strong potential of SCWs for reducing the environmental and economic costs of heating operations in cold climates. The importance of conducting an early exploratory phase was emphasized, as well as the potentially significant impact of productive aquifers and groundwater flow on field testing, design studies and overall performance metrics. Lastly, it also became evident that careful selection of the pumping equipment and control sequences, as well as post-commissioning efforts, were necessary to ensure the optimal operation of this innovative technology.

How to cite: Beaudry, G., Pasquier, P., Faucher, J., Tonellato, G., and Kummert, M.: Standing column wells in cold climates: a case study in a highly productive aquifer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20924, https://doi.org/10.5194/egusphere-egu24-20924, 2024.

09:40–09:50
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EGU24-2003
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ECS
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On-site presentation
Gabriel Dion and Philippe Pasquier

Ground-coupled heat pump systems exchange heat between a building and the surrounding ground. To simulate a ground heat exchanger (GHE), a transfer function is commonly used. This function represents the ground's capacity to exchange energy. Its use allows for the simulation of the ground's response to different heat load patterns. The heat transfer process is affected by key factors such as the ground's thermal properties and the groundwater flow. Accurate evaluation is critical for designing the GHE field to meet the thermal needs of a building for heating and cooling.

The transfer function of the GHE represents its heat transfer over a time range from seconds to years of operation. The long-term component is usually defined by an analytical model, while the short-term component requires a more complex model to be evaluated. Indeed, analytical models do not accurately represent the transient heat transfer effects that occur in the borehole materials and heat transfer fluid. To avoid using thermal transfer models, the data from a thermal response test (TRT) can be used to retrieve an experimental transfer function. This study aims to outline the different applications of a deconvolution algorithm to retrieve a short-term transfer function from experimental TRT data.

Applying a deconvolution algorithm to the outlet temperature signal of a TRT allows for estimation of the short-term response of the GHE without the need for a defined thermal model. The algorithm can iterate on the transfer function form, enabling accurate reconstruction of experimental temperature. One advantage of this method is that it only requires experimental data from a TRT to construct the transfer function.

The methodology is applied to tests with constant and varying operating conditions, allowing to obtain one or more transfer functions depending on the number of operating conditions. Additionally, a deconvolution algorithm can be utilized to interpret distributed thermal response tests, helping in the identification of geological layers with the best thermal properties. This can assist system designers to reduce drilling costs for systems with multiple boreholes. Results present transfer functions that are smooth and close to ones obtained from a more advanced numerical model. Additionally, they can reconstruct experimental temperature precisely. It is worth noting that the transfer function curve is affected by groundwater flow, with larger flows resulting in a decrease in the curve for similar operating conditions.

In conclusion, this research demonstrates the diverse applications of a deconvolution algorithm in interpreting a thermal response test across various geological settings, groundwater flow rates, operating conditions, and types of GHE. This leads to the estimation of a short-term transfer function, which can be used either to compute thermal parameters or validate various heating loads on the GHE through implementation in a simulation algorithm.

How to cite: Dion, G. and Pasquier, P.: Experimental transfer function of ground heat exchanger from thermal response tests using a deconvolution approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2003, https://doi.org/10.5194/egusphere-egu24-2003, 2024.

09:50–10:00
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EGU24-11234
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On-site presentation
Laurence Champagne-Péladeau and Philippe Pasquier

Due to their potential for reducing energy consumption and greenhouse gas emissions, ground heat exchangers (GHE) coupled with heat pumps are now more commonplace. In urban areas, interference between neighboring GHEs can be a cause for concern, as it can affect average ground temperature and the long-term efficiency of heat pumps. Standing column wells, which use groundwater as a heat transfer fluid, are particularly suited to urban contexts as they do not require a productive aquifer or large areas of land. Unlike open-loop systems, groundwater is mainly recirculated in SCWs. However, to improve their performance, a fraction of the recirculation flow can be diverted to an injection well (IW), enabling the development of a thermal plume around the SCW and IW. Therefore, the delineation of the thermal plume for SCW systems is important to prevent environmental disturbances and maintain their thermal efficiency. A case study is conducted on a real system consisting of five SCWs and one IW installed in a productive fractured aquifer in the city of Mirabel, Canada. Using a 25-day hydraulic tomography, geophysical logs, drilling reports and thermal profiles, a 3D numerical model coupling heat transfer and groundwater flow was developed and calibrated. Using this calibrated model, numerical simulations were used to generate a 3D thermal plume and assess the environmental impact of the SCW system. The results indicate that the impact of SCW on this particular aquifer is limited, and that the system alone can be operated for 10 years without significant loss of efficiency or environmental impact.

How to cite: Champagne-Péladeau, L. and Pasquier, P.: Delineation of the thermal plume associated with a standing column well system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11234, https://doi.org/10.5194/egusphere-egu24-11234, 2024.

10:00–10:10
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EGU24-18386
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ECS
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On-site presentation
Felix Schumann, Nikolai Konenenko, and Tomás Fernandez-Steeger

A rapid decarbonisation of the heating and cooling sector requires accelerated retrofitting of buildings, increased use of renewable energy and waste heat utilisation (European Commission, 2016). From 2023, the German Heat Planning Act will legally mandate this development for cities and municipalities, with a special obligation to utilise unavoidable waste heat (BMWSB, 2023). In the transformation of future heating and cooling networks, a synergy of different energy sources is crucial, whose complementary strengths and weaknesses must be coordinated. A holistic concept for the future heating and cooling supply at campus level has been developed in cooperation with various disciplines from the fields of energy technology, building energy technology and engineering geology at the TU Berlin, using the university campus in Berlin-Charlottenburg as a example. Key components of the concept include load shifting between buildings, heat recovery from data centres and process cooling, expansion of a cooling network and the use of chillers as heat pumps during the heating season (Stanica et al, 2022).

The project also investigated the use of a seasonal geothermal energy storage system. The hydrogeological and urban planning parameters support the use of a borehole thermal energy storage (BTES). The subsurface is characterised by glacial fluvial sands and clays from the last ice ages, which have high thermal conductivity and capacity. The groundwater temperature is approximately 12°C and the subsurface has a very low groundwater flow velocity, which favours a high efficiency of the BTES. On the North Campus there is a 12,900 m² open space that can accommodate about 130 heat exchangers and has a heat storage capacity of about 1.2 GWh/a.

The cooling demand for the North Campus is approximately 4.7 GWh/a. The cooling systems are to be supported by free cooling at outdoor temperatures below 0°C and by the BTES at temperatures above 0°C. The special point here is that the so-called regeneration of the storage in summer is realised by the existing waste heat on the campus and not by solar thermal energy. This allows the available roof space for photovoltaic systems to be used to generate additional electricity for the operation of the individual systems. To operate sustainably and efficiently, the chillers require an inlet temperature between 6 and 12°C.

The dynamic interaction between the BTES and the associated heating and cooling system has a significant impact on the efficiency of such underground storage system. In order to optimise the design of the BTES and to ensure sustainable operation of all components, all systems were considered holistically and coupled with each other. The results of this study show that utilising the maximum amount of free space as storage in combination with the other cooling sources is not efficient. The storage capacity for the BTES is about 500 MWh/a. The use of the BTES has significantly increased the use of waste heat and reduced electricity consumption for the chillers by 200 MWh/a. In addition, 200 t of CO2 per year will be saved, which corresponds to a further increase of 20 %.

How to cite: Schumann, F., Konenenko, N., and Fernandez-Steeger, T.: Integration of a seasonal borehole thermal energy storage into a transformed cooling network , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18386, https://doi.org/10.5194/egusphere-egu24-18386, 2024.

10:10–10:15
Coffee break
Chairpersons: Rotman A. Criollo Manjarrez, Cornelia Steiner, Alberto Previati
10:45–10:55
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EGU24-21533
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solicited
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Highlight
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On-site presentation
Jannis Epting

In urban areas, increased thermal use of the subsurface, including infrastructure development (e.g., tunnels and underground car parks) and adaptation strategies (e.g., more frequent thermal use of aquifers for "cooling" purposes or increased implementation of the sponge city concept), associated with global warming will inevitably increase urban groundwater temperatures. Likewise, anthropogenic adaptation strategies could have a greater impact than climate change itself.

In scope of the presentation strategies for the thermal management of urban groundwater resources in northwestern Switzerland are presented by discussing climate change, thermal potentials, and opportunities for adaptation measures. In particular, there are opportunities related to unused anthropogenic waste heat, especially in the subsurface of urban areas, and the energy potential that could be tapped through suitable construction measures.

How to cite: Epting, J.: Thermal management of urban groundwater resources - climate change, thermal potentials and opportunities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21533, https://doi.org/10.5194/egusphere-egu24-21533, 2024.

10:55–11:05
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EGU24-16517
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On-site presentation
Philipp Blum, Haegyeong Lee, Kathrin Menberg, and Ruben Stemmle

Aquifer thermal energy storage (ATES) is a promising technology for sustainable and climate-friendly space heating and cooling which can contribute to lower greenhouse gas (GHG) emissions. Using 3D heat transport models, this study quantifies the technical potential of shallow low-temperature ATES in the city of Freiburg, Germany. The numerical models consider various ATES configurations and different hydrogeological subsurface characteristics relevant for the study area. Based on the modeling results, spatially resolved ATES power densities for heating and cooling are determined and compared to the space heating and cooling energy demands. High ambient groundwater flow velocities of up to 13 m d-1 cause relatively high storage energy losses resulting in maximum ATES power densities of 3.2 W m-2. Until now, these still reveal substantial heating and cooling energy supply rates achievable by ATES systems. While heating supply rates of larger than 60 % are determined for about 50 % of all residential buildings in the study area, the cooling energy demand could be supplied entirely by ATES systems for 92 % of the buildings. In addition, ATES heating alone could result in greenhouse gas emission savings of up to about 70,000 tCO2eq a‑1. The proposed modeling approach in this study can also be applied in other urban areas with similar hydrogeological conditions to obtain estimations of local ATES supply rates and support city-scale energy planning for heating and cooling.

How to cite: Blum, P., Lee, H., Menberg, K., and Stemmle, R.: Heating and cooling with aquifer thermal energy storage (ATES) in cities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16517, https://doi.org/10.5194/egusphere-egu24-16517, 2024.

11:05–11:15
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EGU24-6390
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On-site presentation
Carl Jacquemyn and Matthew D Jackson

Aquifer Thermal Energy Storage (ATES) can store and supply a high capacity of seasonal heating and cooling. Well-balanced and well-designed ATES systems provide a very efficient energy storage, up to around 70-90% and thereby play an important role in providing a sustainable, and low-carbon solution for heating and cooling. Factors affecting the efficiency and capacity of ATES deployments are mainly subsurface properties and related design decisions. We set up a framework to test the impact of a wide range subsurface and design parameters to deduce their impact on ATES system performance. Aquifer thickness, lateral permeability and permeability anisotropy are considered as main aquifer properties, and cool-warm well lateral spacing and vertical offsetting of cool and warm plumes as main design decisions. The thickness of the injection and production interval can be dictated by aquifer permeability variations and/or be chosen by varying screen length.  

The parameters listed above are combined into dimensionless numbers, such as effective aspect ratio of the system and effective lateral spacing of wells to summarize and group different aquifers and possible ATES deployment designs. For a wide range of effective aspect ratios and effective well spacing ATES system behaviour is predicted by flow simulation and key performance indicators computed, including thermal efficiency, CO2 savings, cool/warm plume sizes and stored energy density. The first two indicate the potential expected capacity of ATES systems. The latter provide recommendations for best use of land area, especially if multiple ATES systems are planned in areas with high concentration of cooling and heating demand. Given heating and cooling demand, specific aquifer conditions and land area available for use, the predicted behaviour metrics will help design optimal ATES deployments and show the potential for energy savings across multiple different settings.

Results indicate that ATES’ bidirectional subsurface thermal storage nearly always produces more energy than unidirectional open-loop systems, even when thermal recovery is low. Only when cold and warm plumes are placed side-by-side, closer than half thermal radius apart, negative thermal efficiency occurs, and more energy is put in the system than extracted. However, placing cold and warm plumes at very small spacing is still efficient, when plumes are also offset vertically, and similar thermal behaviour as large lateral well spacing is achieved.

How to cite: Jacquemyn, C. and Jackson, M. D.: Impact of aquifer properties, well spacing and vertical offsetting of warm and cool plumes on ATES systems., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6390, https://doi.org/10.5194/egusphere-egu24-6390, 2024.

11:15–11:25
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EGU24-19709
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On-site presentation
Ernesto Meneses Rioseco, Domenico C. G. Ravidà, Michael Dussel, and Inga S. Moeck

The increasing energy prices and technological progress in ground source heat pumps (GSHP) in recent years has substantially propelled the use of shallow geothermal energy in Germany. With the swiftly growing numbers of installed GSHP in urban areas, the optimal and sustainable use of shallow geothermal resources requires a thorough analysis and understanding of the key components and physical processes involved in the underground at different spatial and time scales. In particular, the question of possible thermal and/or thermo-hydraulic interaction of neighboring small-power (<30kW) geothermal facilities typical of single-family houses is most relevant. We address this question within the framework of the ongoing joint research project WärmeGut by studying the efficiency of shallow geothermal heat recovery in terms of avoiding negative thermal or thermo-hydraulic interferences between neighboring installations.  

Using 3D finite-element numerical modelling and simulation, this work focuses on the impact that variably saturated flow and seasonably varying underground temperature have on several optimized pipe assemblage designs at different scales. Specially, we consider different shallowest-depth geothermal heat collector patterns and different soil thermal and hydrogeological properties. Taking into account the impact that varying saturation has on the soil thermal properties, we vary the location, depth, arrangement, pipes layout, and operational schemes to elucidate the controlling factors on the optimized sustainable use of shallowest-depth geothermal resources.

Employing COMSOL Multiphysics, we conduct a series of simulations intended to systematically analyze the complex thermo-hydraulic interaction between neighboring shallow geothermal installations under varying climatological conditions. Since there is no requirement by the German state geological surveys to provide any detailed modelling on the performance and thermal impact of small-power (<30kW) shallow geothermal facilities, we illustrate our simulation results in detail for a large range of parameter variation. We present in this work our most recent results.

This work is conducted within the joint research project WärmeGut "Flankierung des Erdwärmepumpen-Rollouts für die Wärmewende durch eine bundesweite, einheitliche Bereitstellung von Geoinformationen zur oberflächennahen Geothermie in Deutschland" and is financed by the German Federal Ministry for Economic Affairs and Climate Action (FKZ: 03EE4046B).

How to cite: Meneses Rioseco, E., Ravidà, D. C. G., Dussel, M., and Moeck, I. S.: Optimization of shallowest-depth geothermal heat collectors for sustainable energy production under variable saturation conditions and seasonal temperature fluctuations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19709, https://doi.org/10.5194/egusphere-egu24-19709, 2024.

11:25–11:35
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EGU24-6026
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ECS
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On-site presentation
Haegyeong Lee, Manuel Gossler, Kai Zosseder, Philipp Blum, Peter Bayer, and Gabriel Rau

Precise prediction of heat transport in porous media holds crucial significance in Earth Sciences for diverse applications, ranging from the design of geothermal systems to utilizing heat as a tracer in aquifers. Traditionally, the description of heat transport has been simplified by assuming local thermal equilibrium (LTE), where the temperature within the fluid and solid phases in the representative elementary volume is presumed to reach an instant equilibrium. In reality, assuming two distinct phases coupled by heat transfer across their surface area describes the complete physics and is referred to as the local thermal non-equilibrium (LTNE) model. While earlier research delved into the theoretical aspects of LTNE effects, a notable gap exists due to the absence of experimental data to elucidate the heat transport mechanism in porous aquifers containing natural grains. To address this gap and investigate LTNE on a granular scale, we conducted systematic flow-through experiments employing porous media containing glass spheres with distinct grain sizes of 5, 10, 15, 20, 25 and 30 mm. Each sphere contained a small temperature sensor for the solid temperature, accompanied by sensors in the adjacent pore space to measure the fluid temperature. Our findings revealed that the temperature difference between two phases grows with increasing grain size and flow velocity ranging from 9 to 61 m d-1, thereby highlighting qualitative LTNE effects in relation to grain size and flow velocity. To further enhance our understanding, we used a numerical model to investigate the heat transfer coefficient, fitting the LTNE model to the experimental data. These simulation results indicated evidence of non-uniform flow which we included into our model to estimate its effects on heat transport. This comprehensive approach contributes valuable insights into the intricate interplay of LTNE effects, grain sizes, and flow velocity, advancing our understanding of heat transport in natural porous media.

How to cite: Lee, H., Gossler, M., Zosseder, K., Blum, P., Bayer, P., and Rau, G.: Local thermal non-equilibrium (LTNE) effects revealed through porous media heat transport experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6026, https://doi.org/10.5194/egusphere-egu24-6026, 2024.

11:35–11:45
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EGU24-16846
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ECS
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On-site presentation
Monika Kreitmair, Nikolas Makasis, Kecheng Chen, Ruchi Choudhary, and Kenichi Soga

Growing demand for space in urban areas is accelerating the utilisation of the shallow subsurface for residential and commercial spaces, transport systems, industrial processes, and energy applications. The associated underground infrastructure can act as a source and sink of heat within the subsurface, altering the ambient temperature of the soil. The extent and magnitude of such a temperature anomaly is affected by the type and density of the structures in the ground, the environmental hydraulic conditions governing groundwater flow, and the geological properties impacting conductive heat transfer. As a result, temperature distributions will vary spatially beneath a given city, thereby also affecting the geothermal potential available for heating and cooling. Knowledge on where the greatest geothermal potential lies within a city can be crucial for large-scale planning of geothermal systems, and incorporating these within building and district-level systems.

We present a methodology to map the geothermal potential under cities, extending on a recently developed and published large-scale subsurface temperature modelling methodology, which statistically identifies commonalities in how natural and anthropogenic features affect subsurface heat transfer and creates subsurface archetypes. The extension entails incorporating ground heat exchanging structures, e.g. boreholes, within the archetypes to further subdivide existing thermal archetypes into geothermal archetypes and thus enable comparison of the relative performance of a ground heat exchanger in different areas of a city. The methodology is applied to the city of Cambridge, UK to generate a map of geothermal potential. Additionally, the demand for the city, computed using field data, is mapped to produce a demand-to-capacity map of the city. By exploring different exploitation scenarios of the geothermal potential, i.e. first-come-first-served vs. co-ordinated, we further determine the ability of the resulting deployment patterns to meet likely changes in future demand under the effects of climate change.

How to cite: Kreitmair, M., Makasis, N., Chen, K., Choudhary, R., and Soga, K.: Demonstration of a city-scale geothermal resource assessment using a statistical archetypes-based approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16846, https://doi.org/10.5194/egusphere-egu24-16846, 2024.

11:45–11:55
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EGU24-15820
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ECS
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On-site presentation
Tristan Alexander Roberts, Adrian Hartley, and Clare Bond

The Climate Change (Emissions Reduction Targets) (Scotland) Act 2019 demands a net zero economy in Scotland by 2045, yet in the same year over three quarters of domestic heating was met by natural gas. A novel method and dynamic map resource is developed to visualise low enthalpy geothermal potential for space heating on a community scale using Ground Source Heat Pumps (GSHPs) and District Heat Networks (DHNs). This resource is intended to provide a screening tool that enables communities and policy makers to effectively reduce carbon emissions by aiding early-stage decision making and understanding of geothermal potential within the context of their communities. 

ArcGIS software is used to infer geothermal potential in 49,768km2 of superficial deposits (64% of total land area), in Scotland, using a Favourability Index (FI) and a 1km2 grid. Cells are assigned an FI value (0.0 - 5.0) using ten metrics based on key criteria: 1) deposit coverage, 2) thickness, 3) aquifer productivity, 4) temperature, 5) ground conditions, 6) heat demand, 7) protected land. Map resources developed show lowland areas generally exhibit more favourable conditions particularly within the Midland Valley, and settlements predominantly lie in high favourability areas. ~60% of the population is identified as living in areas where further investigations into community scale GSHPs is warranted, suggesting that the thermal resource held in unconsolidated sediments has significant potential to decarbonise the Scottish heating sector.

How to cite: Roberts, T. A., Hartley, A., and Bond, C.: Visualising low enthalpy geothermal favourability in Scotland: A map-based screening tool for community scale open-loop ground source heat pumps in superficial aquifers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15820, https://doi.org/10.5194/egusphere-egu24-15820, 2024.

11:55–12:05
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EGU24-16880
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ECS
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On-site presentation
Angela Cukusic, Clemens Karwautz, Constanze Englisch, Eva Kaminsky, Cornelia Steiner, Christine Stumpp, and Christian Griebler

Increasing urbanization puts pressure on urban subsurface temperatures and the impact on groundwater quality and human health. However, consequences of the subsurface urban heat island phenomenon, i.e. heat anomalies due to the urban lifestyle, on groundwater ecosystems have rarely been addressed to date. Of particular interest are microorganisms, who are omnipresent in groundwater and intimately involved in the cycling of carbon and nutrients, the (im)mobilization of metals, the natural attenuation of contaminants, and providing essential ecosystem services. In the framework of the research project ‘Heat below the City’, 150 groundwater wells located in the city of Vienna were sampled twice, once in spring and once in autumn 2021. A multitude of physical-chemical and biological parameters of the groundwater samples were analyzed, including the characterization of the microbial community via 16S rDNA amplicon sequencing. Groundwater temperature, combined with other stressors, such as organic and inorganic pollutants, as well as lack of dissolved oxygen, was hypothesized to prominently impact the composition, diversity and activity of microbial communities. The results revealed a complex interplay of hydrogeological and physico-chemical conditions and microbial community parameters. Microbial diversity and activity showed both increasing and decreasing trends with increasing groundwater temperature, depending on the hydrogeological aquifer type. The dominant microbial taxa were not directly impacted by the observed temperature gradients. The number of heat sources in the vicinity of a sampling well explained microbial community composition better, than any specific heat source alone. Current attempts to explore urban groundwater microbial communities of Berlin and Munich are being pursued, with the aim to improve the fundamental understanding of the relationship between hydrogeology and pressures from urbanization on the groundwater microbiome.

How to cite: Cukusic, A., Karwautz, C., Englisch, C., Kaminsky, E., Steiner, C., Stumpp, C., and Griebler, C.: Is temperature a key driver of microbial community composition in urban shallow groundwater? – A case study from Vienna, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16880, https://doi.org/10.5194/egusphere-egu24-16880, 2024.

12:05–12:15
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EGU24-15138
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Virtual presentation
Søren Erbs Poulsen, Kristoffer Bested Nielsen, and Karl Woldum Tordrup

The thermoroad combines a 5th generation district heating and cooling (5GDHC) grid with a sustainable urban drainage system (SUDS) by utilizing the roadbed for surface water retardation and as a geothermal energy source. The porous roadbed is hydraulically separated from the surrounding soil by a bentonite membrane and is able retain approximately 150 mm of infiltrating surface water when fully drained. Water is drained to the roadbed through drain grates and the roadbed is then drained to the sewer by embedded drainage pipes. The drainage pipes connect to a water brake that restricts maximum water flow to the sewer to 0.78 l/s. Therefore, water is prevented from overloading the sewer in case of extreme precipitation. Instead, the water accumulates in the roadbed and is safely drained to the sewer later. 1200 m of geothermal piping is embedded in the roadbed, separated in two groups on the manifold. A further 3 borehole heat exchangers have been established serving as backup and heat sink for cooling in the summer. A single 100 m long 40 mm 1U pipe has been placed below the central wastewater pipe at a depth of roughly 2.5 m, to harness the waste heat. Once commissioned, 12 single family houses are supplied with surface water management in addition to heating and cooling by ground source heat pumps connected the 5GDHC grid. The system is fully monitored, with energy meters on the brine side of the heat pumps and on the geothermal sources in addition to compiled weather station data from the field site. Model analysis of operational data from the first prototype of the thermoroad, shows that the energy extraction from the geothermal pipes in the roadbed is increased by 56% from the drainage of surface water. The thermoroad is an example of integration of the energy and water sectors where synergies are created. The project consortium has built the second prototype of the thermoroad in full scale and for real consumers near Horsens in central Jutland, Denmark. The thermoroad is commissioned in February 2024. We present the engineering approach behind the thermoroad and the first experience with commissioning of the system.

How to cite: Poulsen, S. E., Nielsen, K. B., and Tordrup, K. W.: The thermoroad - full-scale demonstration of geothermal 5th generation district heating and cooling combined with sustainable urban drainage, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15138, https://doi.org/10.5194/egusphere-egu24-15138, 2024.

12:15–12:25
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EGU24-16026
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On-site presentation
Andres Gonzalez Quiros, Alison Monaghan, Vanessa Starcher, Kyle Walker-Verkuil, David Boon, Paul Wilkinson, Jafar Al-Jawad, Mylene Receveur, Donald John MacAllister, and Oliver Kuras

Flooded disused mines have significant potential to supply clean heating and cooling and for seasonal storage in areas that could continue benefiting from the mines after closure. A proved technology, a more widespread deployment of mine water geothermal development is hampered by technical, socio-economical, and regulatory challenges. Among the technical challenges, the long-term system behaviour is an uncertain but fundamental element, regarding both the groundwater flow and heat distribution in the subsurface aquifer and the optimal performance of the geothermal installation and its components. A further development of mine water geothermal requires information and data from pilot, commercial and research installations to improve the knowledge about these complex systems, understand the interaction with the surrounding environment and learn from the experiences towards a more optimal design and construction of the geothermal infrastructure.

The UK Geoenergy Observatory (UKGEOS) in Glasgow was built between 2019 and 2023 as an at-scale research facility to study mine water geothermal. The observatory includes five boreholes drilled and screened into two levels of mine workings, four of them equipped with pumps and valves to allow for multiple configurations of abstraction and reinjection with operational pumping rates up to 12 l/s. The mine water boreholes are also equipped with hybrid fibre-optic cables for distributed temperature sensing (DTS) and electrical resistivity tomography (ERT) sensor arrays. The monitoring capabilities are complimented with an additional non-screened mine borehole, also equipped with DTS and ERT, and five environmental boreholes screened into the bedrock and the superficial aquifer to monitor the hydrogeological and thermal responses in the surrounding aquifers. The geothermal installation includes a sealed pipe between the abstraction/reinjection boreholes, three heat exchangers that can be used independently to test their performance, and a 200-kW heat pump/chiller. The system is equipped with sensors in the geothermal pipe circuit, the wellhead and downhole for high temporal resolution monitoring of hydraulic and thermal changes during the use of the Observatory and under natural conditions.

In this work we present results from some of the first geothermal tests performed in the Observatory in 2023. These include abstraction-reinjection in both heating and cooling modes with multiple configurations and variable flow rates and reinjection temperatures taking advantage of the capabilities of the Observatory. The datasets have been processed and examined with the support of numerical modelling. The analysis of hydraulic and thermal data from the multiple sensors in the mine and monitoring boreholes, the DTS and ERT, and the geothermal installation before and after heat exchange and reinjection have provided further insights about short- and long-term responses of the system. The observations show the different temporal and spatial scales of the hydraulic and thermal responses to the use of the geothermal infrastructure that constitute valuable information for the design of new geothermal installations in disused mines. The Observatory is now operative and open to academic and research projects aiming to understand better mine water systems.

How to cite: Gonzalez Quiros, A., Monaghan, A., Starcher, V., Walker-Verkuil, K., Boon, D., Wilkinson, P., Al-Jawad, J., Receveur, M., MacAllister, D. J., and Kuras, O.: Supporting deployment of mine water geothermal in disused coalfields with high-resolution datasets from a highly instrumented geoenergy observatory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16026, https://doi.org/10.5194/egusphere-egu24-16026, 2024.

12:25–12:30

Posters on site: Wed, 17 Apr, 16:15–18:00 | Hall X4

Display time: Wed, 17 Apr, 14:00–Wed, 17 Apr, 18:00
X4.97
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EGU24-7836
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ECS
Kosztadin Gergő Glavanov, Ábel Markó, Pásztor Domokos, and Judit Mádl-Szőnyi

Geothermal heat pumps coupled with borehole heat exchangers are appropriate tools to extract renewable and climate- friendly energy from the shallow subsurface. To properly construct these systems, knowing the initial temperature conditions is essential. However, drilling activity modifies the temperature field in the underground around the borehole as well as in the pipe placed into the borehole. During the installation it has to wait for a constant temperature in the pipe after the probe is placed, before measuring the final temperature. According to the rule of thumb, this period is usually one week. The objective of this study is to determine whether this time is really necessary or if a shorter period would be also enough for reaching the undisturbed temperature. The measurements took place in the 11. district of Budapest, Hungary. The analysed borehole was drilled with rotary method deepened into the Budai Marl Formation with a depth of 70 metres. We executed four measurements on the first day, two on the next day, and one after that for four days. The most significant differences can be noticed between the first day measurements. After the third day, the received curves fit better, but they only approached each other from the fourth day with only 0.1-0.2°C difference. It can be concluded that a stable temperature profile required 72 hours of resting for this specific case which is shorter than the supposed one week. With this knowledge, assuming similar behaviour in other cases, installation period of borehole heat exchangers can be significantly shortened. Next step of this research is investigating other geological and seasonal conditions to reveal potential deviations from the current results.

The study was funded by the National Multidisciplinary Laboratory for Climate Change, RRF-2.3.1-21- 2022-00014 project.

How to cite: Glavanov, K. G., Markó, Á., Domokos, P., and Mádl-Szőnyi, J.: Fossil to renewable – how to speed up the installation of borehole heat exchangers?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7836, https://doi.org/10.5194/egusphere-egu24-7836, 2024.

X4.98
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EGU24-3869
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ECS
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Luka Tas, Thomas Hermans, Martin Bloemendal, and Niels Hartog

Shallow geothermal energy has not only great potential to mitigate CO2 emissions associated with the heating and cooling of buildings but also offers wide applicability. Thick productive aquifer layers have been targeted first, as these are the most promising areas for aquifer thermal energy storage (ATES). Nevertheless, there is an increasing trend to target more complex aquifers such as low-transmissivity and alluvial aquifers or fractured rock formations. However, the uncertainty and thus the risk of failure in these contexts is significantly higher and it is therefore often not sufficient to rely on experience when designing the ATES system. In this context, a distance-based global sensitivity analysis was carried out for ATES. The analysis focused on one promising thick productive aquifer, used as a reference, as well as two more complex settings involving a low transmissivity and a shallow alluvial aquifer. Through this method, multiple random model realizations are generated by sampling each parameter from a predetermined range of uncertainty. A distance measure between the different model realizations can then be used to determine the relative importance of the uncertain parameters. Not only hydrogeological parameters but also operational and design parameters and boundary conditions were considered uncertain. The parameter distributions were also further analyzed to make a connection with the ATES efficiency. Finally, specific attention was paid to exploring the thermal energy exchange between the soil and the aquifer and its significance for ATES efficiency in shallow aquifers. The results of this study give insight into how the sensitive parameters change when the setting becomes more complex and if it is required to include heat transfer processes that are commonly ignored in traditional settings. This nuanced understanding contributes to the optimization of ATES systems, offering practical guidance for enhanced efficiency of feasibility studies, especially in challenging environments.

How to cite: Tas, L., Hermans, T., Bloemendal, M., and Hartog, N.: Global sensitivity analysis of model parameters, heat transport processes and design parameters in ATES Systems , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3869, https://doi.org/10.5194/egusphere-egu24-3869, 2024.

X4.99
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EGU24-3764
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ECS
Byeong-Hak Park, Ji-Young Baek, Gabriel C. Rau, and Kang-Kun Lee

Recent studies in the field of shallow geothermal applications emphasize the crucial role played by mechanical thermal dispersion as a fundamental heat transport mechanism within saturated porous media. However, Previous studies have overlooked or underestimated mechanical thermal dispersion, leading to a scarcity of information on thermal dispersivity in the literature. This study experimentally and numerically investigates the validity of general assumptions concerning mechanical thermal dispersion within a porous medium. For this purpose, comprehensive laboratory experiments were conducted using heat and solute tracers across various porous materials at different background flow velocities (Re < 0.52). The analysis results suggest that water injection induces substantial mechanical dispersion, even at low flow velocities. Additionally, the thermal dispersivity ratio may deviate from the assumed value, underscoring its importance in the environmental impact assessment of the thermal use of shallow aquifers. Our experimental findings also suggest that thermal dispersion is affected by both local thermal non-equilibrium and small-scale heterogeneity.

Keywords: Thermal dispersion; Water injection; Thermal dispersivity ratio; Local thermal non-equilibrium; Small-scale heterogeneity

 

Acknowledgements

This work was supported by the Nuclear Research  and  Development  Program  of  the  National  Research  Foundation  of  Korea  (NRF-2021M2E1A1085200). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2022R1A2C1006696).

How to cite: Park, B.-H., Baek, J.-Y., Rau, G. C., and Lee, K.-K.: Experimental Investigation of Thermal Dispersion Within Porous Media Under Natural Groundwater Flow Conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3764, https://doi.org/10.5194/egusphere-egu24-3764, 2024.

X4.100
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EGU24-9305
Thomas Graf, Alexander Basten, Olaf A. Cirpka, Insa Neuweiler, Mohammad A. Rahmann, and Frank Spitzenberg

We carried out laboratory experiments of free thermal and thermohaline convection in homogeneous isotropic media using a laboratory-scale two-dimensional tank filled with glass beads representing a porous medium. Glass beads of different diameter were used in different experiments to achieve different permeabilities of the porous medium. Density and viscosity of the fluid were changed by initially introducing a salt (NaCl) solution, and by applying a heating device placed inside the tank. Fluid temperature inside the tank was measured over time on multiple thermocouples placed inside the tank on the inner glass walls. The fluid was dyed with two color tracers in order to visualize the emerging free convective flow pattern. The convective flow pattern was captured using a digital camera for the tracer distribution, and an IR camera for the temperature distribution. In subsequent numerical simulations, the experiments were successfully simulated numerically including density/viscosity variations and heat loss of the tank to the laboratory air across the back and front glass panes. Flow and transport parameters were calibrated using the results of the experiments with constant salinity. The set of calibrated parameter values was applied to successfully validate a thermohaline experiment with no need for further calibration. The processes of salt (NaCl) transport and heat transfer were both very accurately simulated in a single simulation. Analysis of flow velocities and streamlines showed that flow packages in a convection cell mostly follow a closed path such that there is little radial mixing. The approaches and results presented here can be used for interpretation, testing, and analysis of other simulation software of free thermohaline flow and transport.

How to cite: Graf, T., Basten, A., Cirpka, O. A., Neuweiler, I., Rahmann, M. A., and Spitzenberg, F.: Thermal and thermohaline variable-density flow and salt transport in a 2D flow tank: Experiments, visualization and modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9305, https://doi.org/10.5194/egusphere-egu24-9305, 2024.

X4.101
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EGU24-8009
Lazaros Aresti, Christos Makarounas, and Paul Christodoulides

Following the European Union (EU) targets towards the “Fit for 55”, the heat pump (HP) sales have seen an increase. The recent increasing demand in the utilization of HP towards space heating and cooling, underscores the pivotal role of Shallow Geothermal Energy (SGE) systems and the Ground Source Heat Pumps (GSHPs). Although GSHPs exhibit higher performance compared to Air Source Heat Pumps (ASHPs), the high initial cost and the consequent long payback period has been a preventive factor for the GSHP systems. The GSHP systems however also benefit for additional CO2 reduction. The evolving efficiency of ASHP systems in recent studies challenge the perceived advantages associated with GSHPs, particularly in light of the continual refinement of ASHP systems.

This research embarks upon a comprehensive analysis to compare the environmental impacts, in terms of CO2 emissions, between ASHP and GSHP systems using different case studies. High insulation profile case studies were considered, following the nearly Zero Energy Buildings (nZEB) technical characteristics, as well as retrofitting at older dwellings with a low insulation profile. The current study engages a Life Cycle Analysis (LCA) with the OpenLCA software in conjunction with the Ecoinvent database, and the employment of the ReCipe impact method, both from a midpoint and an endpoint perspective. The findings derived from this investigation demonstrates a favorable performance of the GSHP systems where there is an increasing demanding in heating such as in the retrofitting cases. This research highlights the important environmental implications of employing the GSHPs over the use of ASHPs.

How to cite: Aresti, L., Makarounas, C., and Christodoulides, P.: Comparative Environmental Impact of Ground Source Heat Pumps and Air Source Heat Pumps for Dwellings with high and low insulation profiles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8009, https://doi.org/10.5194/egusphere-egu24-8009, 2024.

X4.102
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EGU24-10790
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ECS
Quan Liu, Finn Weiland, Peter Pärisch, Niklas Kracht, Sven-Yannik Schuba, and Thomas Ptak

Shallow geothermal energy has been widely used for heating and cooling buildings by combining borehole heat exchangers (BHEs) with heat pumps. In recent years, how to maintain the efficiency and sustainability of large BHE systems has received increasing attention. An effective way to address this issue is to develop site-specific models to accurately predict the economy, thermal efficiency, and environmental impacts of geothermal systems. However, site characteristics are often simplified or even ignored, such as complex groundwater flow induced by subsurface heterogeneity and non-homogeneous surface heat transfer due to various land covers. In this study, a BHE system model was developed based on collected site characteristics and thermal measurements during system operation. Firstly, groundwater flow in a heterogeneous subsurface was considered in the developed model, according to the regional hydrogeologic conditions and borehole logs. In addition, complex surface heat transfer influenced by solar radiation and land cover characteristics was incorporated. Thermal parameters of different land cover types are considered as time-varying parameters to account for neighboring land use changes. Finally, the hydraulic parameters in the developed model were calibrated by comparing simulations with the groundwater temperatures observed in the boreholes. Next, we plan to further validate the prediction capability of the developed model based on recent temperature observations. We will then discuss the importance of site characteristics in assessing the thermal efficiency and environmental impacts of the BHE system by comparing the results with those of simplified models. Forecasts of system economics for the next ten years will also be made based on the developed model and possible thermal energy management strategies.

How to cite: Liu, Q., Weiland, F., Pärisch, P., Kracht, N., Schuba, S.-Y., and Ptak, T.: Sustainable operation of a large BHE field considering groundwater flow and land cover changes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10790, https://doi.org/10.5194/egusphere-egu24-10790, 2024.

X4.103
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EGU24-19869
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ECS
Domenico C.G. Ravidà, Ernesto Meneses Rioseco, Michael Dussel, and Inga S. Moeck

The successful realisation of climate protection and energy transition goals in Germany is contingent on an effective heat transition strategy. A key aspect of this strategy is to increase the use of shallow geothermal energy (SGE) resources for ground-sourced heat pump (GSP) applications. To date, however, the characterisation of the near-surface geothermal potential is highly heterogeneous across the country. The information is fragmented and discordant among its sixteen federal states, and it is often not readily accessible. These factors significantly challenge the achievement of the established goals of expanding SGE utilization.

This work is part of the ongoing WärmeGut project, which aims to i) assess geothermal potential and site-suitability for GSP applications across Germany, ii) compile, standardise and harmonise geoinformation on a national scale, and iii) bridge the (geo-)data accessibility gap by integrating SGE information into GeotIS – the well-established geothermal information system of Germany. Currently, GeotIS places emphasis on geological information for depths beyond 1500 meters. In this contribution, we present a concept and workflow developed for evaluating the near-surface geothermal suitability, which refers to the possibility of harnessing the SGE resource in designed areas by specific GSP applications (e.g., borehole heat exchangers, geothermal collectors and groundwater heat pumps). For a region to be deemed suitable, geothermal installations must not interfere with any existing land use. Furthermore, it is essential to assess the presence of specific geological conditions in the subsurface that can threaten the stability of geothermal systems and potentially endanger the balance of other natural resources and human activities.

In our workflow, the determination of geothermal suitability is based on the evaluation of a preliminary set of 38 conflict criteria, categorised into four groups: i) national and local regulations that identify conservation areas, ii) geological, iii) hydrogeological and iv) anthropogenic factors. For this purpose, we compile and integrate a vast array of data, encompassing publicly available databases, data from geological surveys, and newly generated information. Data includes, but is not limited to, geological and hydrogeological maps, 3D subsurface models, stratigraphic information, and chemical and physical measurements of rocks and groundwaters obtained from existing wells. We defined three suitability categories: areas unsuitable for SGE exploitation, areas with limited suitability due to risk conditions or land use conflicts, and areas generally suitable for SGE exploitation. These categories are depicted across the national territory using a traffic light colour scheme.

The preliminary site-suitability maps offer a glimpse into their role in the heating transition in Germany, serving as an essential instrument for showcasing the potential for SGE exploitation across the country. By bridging the current information gap and standardising geodata on a national level, traffic light maps are likely to become the foremost tool employed in the planning and designing of geothermal installations.

How to cite: Ravidà, D. C. G., Meneses Rioseco, E., Dussel, M., and Moeck, I. S.: Unravelling the shallow geothermal energy potential in Germany: a workflow for the realisation of national-scale harmonised site-suitability maps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19869, https://doi.org/10.5194/egusphere-egu24-19869, 2024.

X4.104
|
EGU24-3990
|
ECS
Verena Dohmwirth, Susanne Benz, and Matthias Mauder

In times of climate change heat increasingly accumulates in urban areas. Thus, the temperature in city centers is often several degrees higher than in the surrounding areas. This urban heat island effect (UHI) can negatively affect people and the environment. Heat islands in the subsurface (SubSUHI) due to high heat input from cities into the soil and groundwater can also be measured. This accumulated heat input could be harnessed by geothermal heat pumps contributing to the solution of two major challenges of our time: firstly, the reduction of CO2 emissions through the decarbonization of the heating market and secondly, the cooling of the soil and groundwater to pre-industrial temperature levels and thus a possible climate protection measure.

This work attempts to investigate the heat island effect in the subsurface of the urban area of Dresden, Germany. For this purpose, various temperature measurements, such as groundwater and air temperature, are combined with geodata on land use and development. The theoretical geothermal potential for suitable areas in Dresden is calculated as well as the sustainable geothermal potential, taking into account the heat flux directed upwards as well as downwards. Several, mostly anthropogenic, heat fluxes from urban structures into the groundwater are investigated, such as heat fluxes due to buildings, tunnels, or district heating. These potentials are placed in the context of the heating requirements of the city of Dresden and thereby descripe the extent to which the installation of geothermal systems can contribute to the climate neutrality of the local heating market. In a second scenario, the heat fluxes for the year 2100 are calculated using the CMIP6 scenarios SSP245 and the SSP585 to show how climate change could potentially improve the efficiency of geothermal systems. By using Google Earth Engine as a platform, we ensure that our analysis is easily scalable and can later be applied to any city within Germany.

How to cite: Dohmwirth, V., Benz, S., and Mauder, M.: The potential of subsurface heat recycling in Dresden, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3990, https://doi.org/10.5194/egusphere-egu24-3990, 2024.

X4.105
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EGU24-6479
Ignasi Herms, Georgina Arnó, Víctor Camps, Montse Colomer, Sandra Armengol, Norbert Caldera, Ernest Orriols, Toni Marcè, Àlex Elvira, Jose Antonio Jara, Lucia Struth, Jordi Garcia-Céspedes, and Guillem Piris

The "XEGCat project" is a project funded by the ICGC Contract Program initiated in 2019. The objective is the implementation of instrumented boreholes designed to collect relevant scientific data on the thermal behavior of the subsoil. This data can be utilized for assessment, modeling, and the creation of maps depicting the shallow geothermal resources (SGR) on the urban scale. It also aids in the simulation and design of specific projects involving GSHP. Additionally, the project will allow long-term research on the progress of the subsurface urban heat island effect. The potential for deploying sustainable SGR schemes in the subsoil depends on the geological and hydrogeological characteristics of the subsoil, as well as the distribution of temperature at depth. Therefore, understanding these variables is crucial for assessing their potential use. The networks consist of instrumented boreholes equipped with sensors of various characteristics to measure and automatically record the subsoil temperature at different depths, and the position of the piezometric level in the existing subsoil and aquifers. The acquisition systems are equipped with dataloggers, and SIM cards powered by a 30 W photovoltaic panel. This setup enables automatic transmission of data to the ICGC server or storage on site, to be periodically collected in the field. The data is uploaded and organized by the NetMon© spatial database management system. Through a web service, the data can be consulted, analyzed, and downloaded using the ICGC viewer - Geoindex XEGCat. The data is also utilized by ICGC to develop new 3D subsoil models. By the end of 2023, up to two networks have been deployed: one in the city of Girona (NE, Catalonia) and another in the city of Tarragona (SE, Catalonia). A third specific local network has been deployed in the Aran Valley in the town of Vielha (Catalan Pyrenees). Over the next two years, there are plans to deploy a new urban network in the city of Lleida (W, Catalonia).

How to cite: Herms, I., Arnó, G., Camps, V., Colomer, M., Armengol, S., Caldera, N., Orriols, E., Marcè, T., Elvira, À., Jara, J. A., Struth, L., Garcia-Céspedes, J., and Piris, G.: The "XEGCat project" - The subsurface monitoring network for shallow geothermal research in urban areas of Catalonia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6479, https://doi.org/10.5194/egusphere-egu24-6479, 2024.

X4.106
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EGU24-12616
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ECS
Katerina Kyrkou, Adam Booth, Yin Jeh Ngui, Jonathan Chambers, Fleur Loveridge, Joseph Kelly, Emma Smith, Andy Nowacki, Edward Hough, David Boon, and Oliver Kuras

Urban geothermal solutions to heating and cooling have developed slowly in the UK, partly due to limited understanding of subsurface heat flow regimes and how stored heat might be sustainably governed within heterogeneous aquifers. Understanding heat flow through various aquifers is the goal of the SmartRes project, in which heat flow trials will be conducted in a number of sites. To provide context for heat flow experiments in a fractured chalk aquifer, geophysical surveys were acquired at Trumplett’s Farm, a groundwater abstraction and monitoring site near Reading (Berkshire, UK). Here, groundwater flow is primarily within a fracture network, likely in an active zone within the upper 10 m of the saturated chalk.

 

Seismic surveys recorded energy generated with an impact source at surface geophones (24 cabled GEODE, and 20 nodal Smart-Solo, geophones) and hydrophone strings, deployed to 100 m depth in boreholes drilled at the site. Smart-Solo nodes were deployed in a ~10 x 5 m grid at the site, with cabled geophones occupying lines between adjacent boreholes, with geophone intervals of up to 2 m. Nodal geophones recorded passively throughout the 3-day deployment and will be analysed using ambient noise correlation to evaluate anisotropy. The remaining data has been used for preliminary analysis with MASW (Multichannel Analysis of Surface Waves), P-wave refraction velocities, and vertical seismic profiles (VSPs).

 

 

MASW analyses suggest shear wave velocity (Vs) ranges from 250-600 m/s in the uppermost 1.5 m, but estimates are challenging given poor dispersion imaging of the fundamental mode. Different source-receiver offsets were tested to eliminate mode superposition, but the best dispersion curves are observed for zero-offset shots. Data were processed in a commercially available software with relatively limited freedom to adjust inversion parameters, hence further analysis will use the MuLTI code to undertake a constrained Monte Carlo inversion approach. The deeper structure of the chalk was characterised in VSPs, indicating reflective P-wave horizons at 52 and 69 m depth, separating material with interval velocities of ~2100 m/s, ~2500 m/s and 3000 m/s. Observing these reflections required aggressive frequency-wavenumber filtering to suppress direct waves in the water column.

 

Electrical resistivity tomography (ERT) surveys were conducted using the BGS PRIME ERT system to optimise array configuration for long-term monitoring. The reconnaissance survey included in-hole, borehole-to-surface, and surface ERT at 1 m intervals, employing C1P1-C2P2 bipole-bipole and dipole-dipole arrays around the site. Preliminary ERT inversion revealed low resistivity zones within the top 1.5 – 2 m across the site and mapped a potential south-dipping high resistivity structure. A longer ERT survey spread is planned to better reveal hydrodynamic interactions at deeper depths.

 

This initial insight will be refined with a fibre-optic distributed acoustic sensing deployment at the Trumplett’s site and an optimised repeat of the BGS PRIME ERT array. These will be synchronous with a thermal response test at the Trumplett’s site monitored with distributed temperature sensing.

 

Keywords: Seismic analysis, ERT, geothermal investigation, fractured aquifer, aquifer thermal energy storage

How to cite: Kyrkou, K., Booth, A., Ngui, Y. J., Chambers, J., Loveridge, F., Kelly, J., Smith, E., Nowacki, A., Hough, E., Boon, D., and Kuras, O.: Geophysical surveys to inform heat-flow experiments in a fractured chalk aquifer, Berkshire, UK, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12616, https://doi.org/10.5194/egusphere-egu24-12616, 2024.

X4.107
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EGU24-16515
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ECS
Alberto Previati, Alberto Presta Asciutto, Valerio Silvestri, and Giovanni Crosta

Recent EU directives and national regulations have encouraged the development of shallow geothermal energy as a renewable, low-emission source. Many cities in Europe are located in suitable areas with high geothermal potential and are therefore experiencing strong growth in the application of this technology for heating/cooling. On the other hand, densely populated urban areas experiencing a rapid development of shallow geothermal applications require appropriate tools to monitor and model the associated effects on both the quality and quantity of the available resource.

This work presents the case study of the metropolitan area of Milan, where the total number of geothermal wells (GWHP) has increased significantly in the last 5 years, covering a total thermal energy demand (including heating and cooling) from about 40 to 400 GWh/a. This very rapid growth and the resulting criticalities motivated the technical agencies and the stakeholders to improve the management of the shallow geothermal resource, which was addressed in the following steps.

1) Define common requirements for the development of a database of shallow geothermal installations, including the hydraulic and thermal regimes of the systems, and identify essential monitoring objectives for a better management of the subsurface low enthalpy thermal resource;

2) Study the cumulative impact of the existing geothermal systems in the entire Milan metropolitan area, delineating thermal capture and thermal disturbance zones using large-scale analytical and numerical models;

3) Assess the hydrogeological and subsurface thermal budgets on a regular grid basis to highlight the most critical areas in terms of hydrogeological (due to systems without groundwater reinjection) and thermal stresses (due to highly thermally unbalanced configurations).

The development of these tools and the implementation of a semi-automatic updating procedure aim to streamline the management of new requests with a quantitative view of the current exploitation of the geothermal resource in the Milan metropolitan area. Moreover, the implementation of future demand scenarios will improve the sustainability and reduce the risks of existing and planned systems.

How to cite: Previati, A., Presta Asciutto, A., Silvestri, V., and Crosta, G.: Best practices for the sustainable management of the shallow geothermal energy resource in urban areas: insights from the case study of the City of Milan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16515, https://doi.org/10.5194/egusphere-egu24-16515, 2024.

X4.108
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EGU24-9213
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ECS
Simona Adrinek, Mitja Janža, and Mihael Brenčič

To achieve sustainable and efficient use of shallow geothermal resources, it is important to understand the heat transfer in the subsurface of the planned geothermal system. In the City Municipality of Murska Sobota, NE Slovenia, the use of geothermal open-loop systems has increased in recent years. Their high spatial density raises the question of potential mutual interference between the systems. By compiling geological, hydrogeological, and thermal data, obtained from the monitoring network, fieldwork, and knowledge of regional hydrogeological conditions, we have developed a transient groundwater flow and heat transfer model to evaluate the impact of the open-loop systems on the subsurface and surrounding systems. Time series data cover time span ranging from December 2019 to the end of December 2021. The sensitivity analysis showed the highest composite sensitivity values for hydraulic conductivity, porosity and dispersivity parameters, which were further calibrated with FePEST to minimize the error between groundwater level and temperature. The results of the groundwater flow model correspond well with the measured average groundwater levels. On the other hand, the thermal model shows higher deviations from the measured data, especially in the summer months when the simulated groundwater temperatures do not exceed 14.3 °C, while the measured temperatures reached even 15.4 °C. These deviations could be related to the effects of local thermal sources on the surface (e.g., sewage pipes, plumbing, buildings with more than one basement and roads), which were not considered in our model. The transient simulation showed that the thermal state in the observed area is restored over the summer, when the systems are not in operation. Also, the systems do not have significant mutual interference that would affect their efficiency. However, as interest in installing new systems in the area increases, simulations of the thermal plumes of new geothermal systems are needed to ensure sustainable and efficient use of shallow geothermal energy in the future.

How to cite: Adrinek, S., Janža, M., and Brenčič, M.: Temperature impact of open-loop systems on groundwater in an urban area: A case study of Murska Sobota, NE Slovenia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9213, https://doi.org/10.5194/egusphere-egu24-9213, 2024.

X4.109
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EGU24-13401
Alexandre Courchesne and Philippe Pasquier

Thanks to its role as a catalyst for geothermal projects using standing column wells (SCW), the geothermal research team at Polytechnique Montréal has been able to monitor and significantly influence drilling costs. Based on monitoring of drilling costs over a period of eight years, this presentation aims to share the strategy adopted and the means taken to reduce SCW costs in the Montreal region, Canada. As SCWs were little known in Montreal about ten years ago, drilling contractors tended to offer high prices for their construction. Discussions with contractors showed that these high costs included a significant safety margin, proportional to the risk perceived by the contractor. To change the perception of drilling contractors, our team then produced and made public plans & specifications, as well as drilling speeds and geological logs for SCWs up to 500 m deep. This strategy allowed for the public sharing of geological conditions on the island of Montreal, which reduced uncertainty for drilling contractors. In less than eight years, drilling costs have fallen from over $1,500 CAD per meter to approximately $160 CAD per meter for SCW of 500 meters. For institutional projects, we have found that the cost of SCWs now represents only 7% of the total cost of a renovation project where oil heating is replaced with a geothermal system using hydroelectricity.

How to cite: Courchesne, A. and Pasquier, P.: Construction cost evolution of standing column wells in the area of Montreal, Canada., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13401, https://doi.org/10.5194/egusphere-egu24-13401, 2024.

X4.110
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EGU24-10816
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Gianvito Scaringi

Thanks to generous subsidies, many residential buildings in the Czech Republic are being equipped with photovoltaic and solar thermal panels, heat pumps, and heat and electricity accumulation systems. Photovoltaic roofs generate considerable savings overall (>50% in typical domestic installations). However, in summertime, they produce substantial and highly variable overflows of electricity into the grid, even with the use of air conditioning and electric vehicles charging. This result in volatile and at times negative wholesale prices of electricity. Conversely, in wintertime, the production is insufficient to balance the load from heat pumps (which are replacing wood burning and gas heaters), thereby contributing to high electricity prices. Hot water tanks and electric batteries can compensate load imbalances on a daily scale only, whereas national-scale solutions relying on gravitational energy storage are not viable. In this context, distributed systems for the seasonal accumulation of energy in the form of heat seem in principle an attractive solution. These systems could use the underground space as a heat source or sink according to needs, exploiting soil layers that are deep enough to ensure stability against seasonal fluctuations in temperature propagating from the surface, but also sufficiently shallow to ensure reasonable costs of installation. In new constructions, heat exchangers could be embedded in foundations or installed in boreholes below common areas such as access roads, parking lots and gardens. Similarly, they could be fitted in already built-up areas, and scaled in such a way to maximise their efficiency without disturbing the mechanical stability and performance of existing buildings and infrastructures. In the Czech Republic, despite a growing bottom-up demand for the creation of energy communities, their technical and regulatory viability remains unexplored. This is especially true for shallow underground seasonal thermal energy storage systems. In part, this relates to an insufficient knowledge of the ground response to thermo-hydro-mechanical forcing, as well as of possible ground-structure interactions. We are beginning to tackle this problem in upcoming research projects. Here, we will discuss our understanding of matters of priority to be addressed in our national context and present preliminary calculations demonstrating the potential of solutions at various scales.

How to cite: Scaringi, G.: Seasonal underground thermal energy storage for district heating and cooling in the Czech Republic: potential and challenges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10816, https://doi.org/10.5194/egusphere-egu24-10816, 2024.