ERE2.6

EDI
Shallow geothermal systems for heating and cooling: geoscience and engineering approaches

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 (e.g. thermo-active foundations, walls, tunnels).
Different types of analysis and approaches are relevant to this session, spanning from the evaluation of ground thermal properties to the mapping of shallow geothermal potential, from energy storage and district heating 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, from the local behaviour of a heat exchanger to the city scale implementation of energy geostructures. Contributions based on experimental, analytical and numerical modelling are welcome as well as interventions about legislative aspect.

Convener: Giorgia Dalla SantaECSECS | Co-conveners: Witold BoguszECSECS, Francesco Cecinato, Jean de Sauvage, Fleur Loveridge
vPICO presentations
| Wed, 28 Apr, 15:30–17:00 (CEST)

Session assets

Session materials

vPICO presentations: Wed, 28 Apr

Chairpersons: Francesco Cecinato, Fleur Loveridge, Giorgia Dalla Santa
15:30–15:35
MATERIALS PROPERTIES
15:35–15:37
|
EGU21-8777
|
ECS
Simona Adrinek and Mitja Janža

Shallow geothermal energy is a renewable energy source that will play an important role in future energy management plans. Densely populated areas are often developed on alluvial plains, which consist of unconsolidated sediments. These have different thermal properties, so their accurate determination is important for planning subsurface heat utilization for heating and cooling of buildings in urban areas. Bulk thermal conductivity (λb) is one of the most important ground thermal properties for estimating shallow geothermal potential, as it controls the ability of sediments to transfer heat. The λb can be determined with empirical bulk thermal conductivity estimation models (λb EM), which define λb as a function of the measured physical parameters of the sediment (water content, bulk density) and the fluid. In this contribution, we present a preliminary study of three empirical evaluation models for determining the thermal conductivity of sediments – the Kersten (1949), the Johansen (1975) and the Cote & Conrad model (2005). Validation was carried out with laboratory-measured λb using 30 unconsolidated sediment samples classified into 2 different groups (cohesive, non-cohesive) and by water content. The modelled results were evaluated using the coefficient of determination (R2) and root mean square error (RMSE). The modelled λb for non-cohesive sediments has the highest λb with the Johansen model. The lowest RMSE was obtained with the Kersten model. For cohesive sediments, the highest λb and lowest RMSE, and consequently the best model, are based on the saturation of the sediments. It varies between the Cote & Conrad and the Kersten model. By dividing the sediment samples based on shear strength and water content, we obtained the better agreement of individual groups with estimation models. This showed the importance of the physical parameters in better predicting the modelled results. In the future, we will need to upgrade results with the use of more estimation models, that could improve the modelled results. With such an approach the estimation models can become a useful tool for a faster determination of the shallow geothermal potential.

How to cite: Adrinek, S. and Janža, M.: A preliminary study of empirical evaluation models for determining the thermal conductivity of sediments , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8777, https://doi.org/10.5194/egusphere-egu21-8777, 2021.

15:37–15:39
|
EGU21-12488
Raffaele Sassi, Chiara Coletti, Alessandro Borghi, Roberto Cossio, Maria Chiara Dalconi, Giorgia Dalla Santa, Luca Peruzzo, Arianna Vettorello, and Antonio Galgaro

Seven granitoid rocks were selected due to the well-defined mineralogical content, the typical the holocrystalline texture, their absent (or very poor) Crystal Preferred Orientations (CPOs), and very-low porosity in order to apply a predictive approach that quantifies and simulates the rock thermal properties by considering the contributions of the mineral phases content. For this purpose, thermal properties of granodiorite, tonalite, granite, and gabbro rock samples were analysed and compared by (i) direct measurements on the bulk rock samples, (ii) by applying Quantitative Phase Analysis (QPA) on Digital Imaging Analysis (DIA) and Xray diffraction Rietveld method, and (iii) by 2D numerical modelling.

The results confirm the good accuracy of DIA-QPA method by the good according with data refined by X-Ray diffraction Rietveld method, and indicate the potential reliability of the more attractive approach in terms of prediction of the 2D modelling starting by the Quantitative Phase Analysis (QPA) based on Digital Imaging Analyses (DIA). This method, indeed, permits to observe concurrently different mineralogical and textural parameters (such as mineral abundance, grain size and grain size distribution), and it also provides a deep knowledge of the rock’s thermal behaviour.

Numerical modelling results indicate that a steady-state condition (SSC) is reached by the combination of thermal contribution given both in terms of modal mineral abundance (mainly controlled by mineralogical phase content related to the quartz occurrence) and in terms of rock texture (by the grain-size dimensions and the geometrical distribution of minerals), considering negligible the porosity.

The use of predictive models for the evaluation of the rocks thermal properties can find many important applications (e.g., in deep and shallow geothermal systems, as well as in building construction materials), and also permits to evaluate the expected energy performance of borehole heat exchange probes, involving granitoid lithologies, representing a suitable alternative also in cases where direct measures are not possible.

How to cite: Sassi, R., Coletti, C., Borghi, A., Cossio, R., Dalconi, M. C., Dalla Santa, G., Peruzzo, L., Vettorello, A., and Galgaro, A.: Thermal properties evaluation of granitoid rocks by using Digital Imaging Analysis (DIA) and 2D modelling simulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12488, https://doi.org/10.5194/egusphere-egu21-12488, 2021.

15:39–15:41
|
EGU21-2838
|
ECS
Valériane Gigot, Bertrand François, Marijke Huysmans, and Pierre Gerard

Although vertical Ground Heat Exchangers (GHE) is a booming technology for both cooling and heating buildings, several improvements could still be proposed in the dimensioning of such systems. Nowadays, most of the dimensioning methods consider only radial heat flux around GHE using a homogeneous ground thermal conductivity, averaged along the depth of the borehole and determined from thermal response tests (TRT) or tables. Impacts of layered ground and groundwater flows on the heat refurbishment around GHE are thus generally neglected.  

Many numerical or analytical studies have investigated and quantified the positive impact of groundwater flows on the efficiency of GHE (Dehkordi & Schincariol, 2014; Funabiki et al., 2014). However, those results are rarely compared with in-situ temperature measurements around GHE. Indeed, such experimental data requires (i) the installation of temperature sensors in the heat ground reservoir around GHE and (ii) the characterization of groundwater flows (magnitude and direction) at great depths, which can be complex and expensive.

In this work, an experimental platform composed of 4 vertical GHE drilled at depths of 85 m has been exploited to provide in-situ temperature measurements characterizing heat transfers around GHE. The 4 vertical GHE are located at the 4 corners of a 4-m square and cross a succession of horizontal geological layers. The study focuses on the heat transfers in a 30-m thick sand unconfined aquifer layer, whose 17 m are saturated. A piezometer has been drilled in this unit and allows the characterization of groundwater flows with advanced hydrogeological tests (Brouyère et al., 2008). Each GHE is equipped with both PT100 (installed at the extremities of the unconfined aquifer and just below the groundwater table level) and optical fibres (OF) along the borehole. This experimental platform allows to perform innovative characterization of the geothermal properties of the site. In particular, performing a comparative analysis of the temperature measurement in the GHE between PT100 and OF and several Distributed Thermal Response Tests (D-TRT) under different conditions. In addition, it has been possible to follow the heat transfers around GHE during a long-term activation of a single GHE through heat plume temperature measurement in the non-activated GHE. Anisotropic temperature distribution highlights the impact of groundwater flows on heat reservoir refurbishment.

In this contribution, D-TRT results characterizing the ground geothermal properties, the pre-design of the long-term TRT using an existing analytical solution (Erol et al., 2015) and preliminary experimental results of the long-term TRT will be presented and discussed.

 

References

  • Funabiki, A. et al. (2014). The effects of groundwater flow on vertical-borehole ground source heat pump systems. In Engineering Systems Design and Analysis. American Society of Mechanical Engineers.
  • Dehkordi, S.E., & Schincariol, R.A. (2014). Effect of thermal-hydrogeological and borehole heat exchanger properties on performance and impact of vertical closed-loop geothermal heat pump systems. Hydrogeology Journal.
  • Erol, S. et al. (2015). Analytical solution of discontinuous heat extraction for sustainability and recovery aspects of borehole heat exchangers. International journal of thermal sciences.
  • Brouyère, S. et al. (2008). A new tracer technique for monitoring groundwater fluxes: The Finite Volume Point Dilution Method. Journal of contaminant hydrology.

How to cite: Gigot, V., François, B., Huysmans, M., and Gerard, P.: Advanced investigations of hydro-geothermal ground properties using a geothermal experimental platform, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2838, https://doi.org/10.5194/egusphere-egu21-2838, 2021.

15:41–15:43
|
EGU21-11059
Antonio Galgaro, Alberto Carrera, and Eloisa Di Sipio

For the design and implementation of an efficient Ground Source Heat Pump (GSHP) system, the local
subsoil represents the core element. Since the thermal performance of Borehole Heat Exchangers (BHEs) is
site-specific, its planning typically requires the knowledge of the thermal proprieties of the ground, which
are influenced by the local stratigraphic sequence and the hydrogeological conditions. The evaluation of
the variations of the ground thermal conductivity (TC) along the depth, as well as its undisturbed
temperature, are essential to correctly plan the BHEs field and improve the performance of the ground
heat exchangers themselves.
Thermal Response Test (TRT) is a well-known experimental procedure that allows to obtain the thermal
properties of the ground. However, the traditional method provides a single value of the equivalent TC and
the undisturbed temperature, which can be associated with the average value over the entire BHE length,
with no chance to detect the thermo-physical parameters variations with depth and to discriminate the
contributions of the different geological levels crossed by the geothermal exchange probe. Indeed,
different layers within a stratigraphic sequence, may have different thermal properties, according to the
presence and to the flow rate of groundwater, as well as to granulometry and mineralogical composition,
density, and porosity of the lithologies. The identification of the different contributions to the thermal
exchange provided by each geological unit, in practice, can further support BHE design, helping to
determine the most suitable borehole length and number, achieving the highest heat exchange capability
at the lower initial cost of implementing of the entire geothermal plant.
In the last years, new improved approaches to execute an enhanced thermal response test have been
developed, as the pioneer wireless data transmission GEOsniff technology (enOware GmbH) tested in this
study. This measurement method is characterized by its sensors, 20mm-diameter marbles equipped by
pressure and temperature transducers combined with a system of data storing and wireless data
transmission. Released at regular intervals down the testing BHE, infilled with water, each marble freely
floats allowing the measurement of the water temperature variations over time at different depths, in
order to identify areas with particular values of thermal conductivity related to distinctive hydrogeological
conditions or lithological assessment. This way, the GEOsniff technology allows a high-resolution spatially-
distributed representation of the subsoil thermal properties along the BHE.
In this work, we present the test outputs acquired at the new humanistic campus of the University of
Padova, located in the Eastern Po river plain (Northern Italy). The thermal conductivity data obtained by
the GEOsniff method have been compared and discussed, by considering the standard TRT outputs. This
innovative technique looks promising to support the optimization of the borehole length in the design
phase, even more where the complexity of the treated geological setting increases.

How to cite: Galgaro, A., Carrera, A., and Di Sipio, E.: Comparison between traditional and enhanced Thermal Response Test for ground thermal properties estimation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11059, https://doi.org/10.5194/egusphere-egu21-11059, 2021.

15:43–15:45
|
EGU21-9948
|
ECS
Simon Schüppler, Roman Zorn, Hagen Steger, and Philipp Blum

The measurement of the undisturbed ground temperature (UGT) serves to design low-temperature geothermal systems, in particular borehole heat exchangers (BHEs), and to monitor shallow aquifers. Wireless and miniaturized probes such as the Geosniff (GS) measurement sphere, which are characterized by an autarkic energy supply and equipped with pressure and temperature sensors, are increasingly being used for the measurement of highly resolved vertical temperature profiles. The measurement probe sinks along the course of the BHE with a selectable measurement frequency to the bottom of the BHE and is useable for initial measurements as well as long term groundwater monitoring. To ensure quality assurance and further improvement of this emerging technology, the analysis of measurement errors and uncertainties of wireless temperature measurements (WTMs) is indispensable. Thus, we provide an empirical laboratory analysis of random, systematic, and dynamic measurement errors, which lead to the measurement uncertainty of WTMs using the GS as a representative device. We subsequently transfer the analysed uncertainty to measured vertical temperature profiles of the undisturbed ground at a BHE site in Karlsruhe, Germany. The precision and accuracy of 0.011 K and -0.11 K, respectively, ensure a high reliability of the GS measurements. The largest measurement uncertainty is obtained within the first five meters of descent resulting from the thermal time constant τ of 4 s. The measured temperature profiles are qualitatively compared with common Distributed Temperature Sensing (DTS) using fiber optic cables and punctual Pt-100 sensors. Wireless probes are also suitable to correct temperature profiles recorded with fiber optics with systematic errors of up to -0.93 K. Various boundary conditions such as the inclination of the BHE pipes or changes of the viscosity and density of the BHE fluid effect the descent rate of the GS of up to 40 %. We additionally provide recommendations for technical implementations of future measurement probes and contribute to an improved understanding and further development of WTMs.

How to cite: Schüppler, S., Zorn, R., Steger, H., and Blum, P.: Wireless probes for measuring vertical temperature profiles in borehole heat exchangers (BHEs), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9948, https://doi.org/10.5194/egusphere-egu21-9948, 2021.

15:45–15:47
|
EGU21-8234
Eloisa Di Sipio, Enrico Garbin, Laura Fedele, Davide Menegazzo, Ludovico Mascarin, Giorgia Dalla Santa, Sergio Bobbo, Gilberto Artioli, Adriana Bernardi, and Antonio Galgaro

In shallow geothermal systems, especially ground source heat pumps (GSHP), cementitious grouts play a decisive role in guaranteeing an efficient heat transfer between the probe and the surrounding ground. Several studies have been devoted to understand the effect of different additives (silica sand, graphite, fluorspar, glass and fly ash …) in improving especially the thermal conductivity of such mixtures, maintaining at the same time physical properties as viscosity and workability suitable for in situ application. In fact, when continuous operation mode is running, thermal conductivity shows a positive effect on the mean heat exchange rate of vertical borehole heat exchangers (BHE). However, when an intermittent operation mode is selected, the BHE performance improves when a high thermal conductivity is coupled with a high specific heat capacity.

This research focus on assessing the contribution of two specific thermal additives (silica sand and molybdenum disulphide powder) to the thermal properties’ improvements of a specific commercial cementitious grout. These components are added in different proportion to the grout, up to the creation of 6 different mixtures. For each mixture 3 specimens are prepared, in order to perform the thermo-physical analyses. In addition, other 3 commercial grouts are considered. A total of 10 mixtures, leading to the creation of 30 specimens, have been analyzed. Then, thermal conductivity, thermal diffusivity and specific heat capacity of each specimen measured in anhydrous and saturated conditions are considered.

The commercial grouts prepared as stated by the producers show, as expected, a minimum variation of their thermal properties in wet and anhydrous conditions. Instead, when the additives are used, a noticeable improvement of the thermal properties is observed in saturated conditions, where the effect of silica sand seems dominant. The best thermal properties improvement obtained by combining the two additives is also considered.

However, the grouts suitability to be easily managed on site must be considered because, even if the new mixtures show a general gain of the thermal properties, these can be difficult to apply going from laboratory to full scale.

Anyway, the characterization of the grouts thermal properties based on composition and saturation variations is important not only in numerical simulations, but also in analytical approaches, typical of the heat exchange probe fields sizing processes. In fact, the cementitious grouts play a key role in determining the shallow geothermal systems efficiency in transient mode operation, often neglected by sizing programs. In fact, those characterized by better thermal performances will contribute to the reduction of the borehole thermal resistances, interposed in the heat exchange processes between the heat transfer fluid and the ground. Finally, this research contributes to fill the gap between numerical simulation and experimental data, providing real data to be used as database for further numerical modelling analysis improvement.

 

GEO4CIVHIC project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 792355.

How to cite: Di Sipio, E., Garbin, E., Fedele, L., Menegazzo, D., Mascarin, L., Dalla Santa, G., Bobbo, S., Artioli, G., Bernardi, A., and Galgaro, A.: New borehole heat exchanger thermal enhanced grout formulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8234, https://doi.org/10.5194/egusphere-egu21-8234, 2021.

MODELLING
15:47–15:49
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EGU21-14502
|
ECS
Jan Niederau, Johanna Fink, and Moritz Lauster

The actual heat demand of a building depends on various building-specific parameters, such as building age, insulation type, housing volume, but also external parameters, e.g. outdoor temperature. Being able to dynamically model the thermal power demand of a specific building can increase the robustness of coupled borehole heat exchanger simulations (BHE-simulations), as the transient heat demand models of a building / consumer can be used to simulate the thermal response of the subsurface to the prescribed consumer demand.

We present results of coupling results of Building Performance Simulation (BPS) with simulations of Borehole Heat Exchangers. BPS are carried out using TEASER (Tool for Energy Analysis and Simulation for Efficient Retrofit) which models the thermal power demand of a building based on parameters, such as year of construction, net-lease area, and outdoor-temperature.

Using annual temperature curves, we model the thermal power demand of buildings from the 1950s, once in original state and in retrofitted state. The thermal response of a connected BHE-field is simulated using SHEMAT-Suite, an open-source simulator for heat- and mass-transfer in porous media. In our BHE simulations, thermal plumes develop as a result of heat-extraction and regional groundwater flow.

To improve the forecast of, e.g. the magnitude of these plumes, realistic knowledge of the heat demand is important, which can be achieved by the presented coupling of BPS- and BHE-modelling.

 

How to cite: Niederau, J., Fink, J., and Lauster, M.: Building Performance Simulations coupled to Borehole Heat Exchanger Simulations: a tool for realistic monitoring and forecast, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14502, https://doi.org/10.5194/egusphere-egu21-14502, 2021.

15:49–15:51
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EGU21-14021
|
ECS
Gabrielle Beaudry, Philippe Pasquier, and Denis Marcotte

Ground source heat pump systems are among the most energy-efficient heating and cooling technologies. Their performance is strongly related to the accuracy of the ground heat exchanger sizing, hence requiring the forecast of the system’s temperature evolution in response to the anticipated thermal loads. Through this process, simulation techniques that make use of the superposition principle are commonly used to reduce the computational burden. In their current state, these techniques are however only suitable for addressing linear and stationary problems and do not apply to fundamental non stationary situations related to ground source heat pumps operation that involve time-variant parameters.

The present work addresses this issue by introducing a novel method based on the principle of superposition that tackles the fast evaluation of the temperature of a closed-loop ground heat exchanger operating with a dynamic heat load as well as time-variant circulation flow rates. The developed method relies on the non stationary combination, a technique borrowed from the field of seismic data processing. This technique achieves discontinuous transitions of convolution products that can be smoothened near transition times by realizing a linear interpolation over the duration of the fluid residence time.

The accuracy and efficiency of the proposed method are verified by comparing its results with those provided by reference 3D finite-elements models developed in the Comsol Multiphysics environment. For this purpose, comparative simulations representing the non stationary operation of a closed-loop system having time-variant circulation flow rates are conducted. The case of a single well is first investigated, followed by a borefield of eight wells to demonstrate the validity of the method in both scenarios.

Findings indicate that the proposed method can reproduce the reference results with a mean absolute error that is lower than 0.02 °C, and that it is faster than the numerical models by several orders of magnitude. These findings suggest that a broader range of operating scenarios can be handled by highly efficient simulation tools based on the superposition principle, which could foster the development of optimal operating strategies and lead to enhanced overall performances of ground source heat pump systems.

How to cite: Beaudry, G., Pasquier, P., and Marcotte, D.: Non stationary combination for the simulation of time-varying flow rates in closed-loop ground heat exchangers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14021, https://doi.org/10.5194/egusphere-egu21-14021, 2021.

15:51–15:53
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EGU21-10117
|
ECS
Alberto Carrera, Jacopo Boaga, Paolo Scotton, and Antonio Galgaro

The growing demand for renewable energy leads to an increase in the development of alternative energy applications. In this way, shallow geothermics assumes an important role in the global energy transition of building air conditioning. The design of Ground Source Heat Pumps (GSHP) requires a multidisciplinary approach including a good understanding of the underground geological setting, such as hydrogeological aspects and heat flow conditions. Classic monitoring strategies often rely on local and point-based measurements to monitor changes of underground temperature in time, with the limit of not succeeding in a whole delimitation of the Thermal Active Zone (TAZ). In this context, Electrical Resistivity Tomography (ERT) can bring relevant information on the temperature distribution for monitoring the induced thermal plume within BHEs (Borehole Heat Exchangers) systems. Geophysics helps the understanding of the thermal processes, in order to front the difficulties arising from Ground Source Heat Pumps (GSHP) implementation. Thermal conductivity and electrical resistivity depend equally in a complex way on different common subsurface and environmental attributes such as, among the main, mineralogical composition, grain size, density, porosity and saturation. Besides, thermal conductivity increases significantly with temperature in wet ground, by making it clear a relationship between both parameters.

ERT is particularly sensitive to the porous medium temperature and, when applied in time-lapse (TL), could provide spatially distributed information on the changes over time of water content, salinity or temperature. For this reason, in this work we monitored the complex TAZ temporal evolution during a heat injection experiment using a 3D time-lapse ERT survey, arranged in a reduced scale physical model. For a better understanding of measured electrical resistivity values, focused on mapping the extent of a geothermal plume around a borehole, a specific laboratory device was utilized. Grain size distribution, bulk density and saturation of the porous medium are known and established, as well as reliable temperature values acquired through sensors with which calibrate the ERT results. Thus, changes in resistivity can be interpreted to track the evolution of the plume of heated water and used to estimate the temperature change. The propagation of the heat plumes into the ground is also highly sensitive to interstitial water flow rate, thus also this condition was recreated and monitored varying the hydraulic gradient in the experimental device.

The present work aims to demonstrate the ability of ERT to provide complementary insights about the sub-surface spatio-temporal dynamic for monitoring the extension of TAZ caused by BHEs probes. In addition, the detailed scale adopted and the variable control within a laboratory setup ease the study of the interaction between thermal and electrical properties.

How to cite: Carrera, A., Boaga, J., Scotton, P., and Galgaro, A.: Thermal Active Zone space-time evolution: a small-scale monitoring of thermal and electrical conductivity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10117, https://doi.org/10.5194/egusphere-egu21-10117, 2021.

DISCUSSION
APPLICATIONS AND CASE STUDIES
15:53–15:55
|
EGU21-12377
Nicola Pastore, Claudia Cherubini, and Concetta Immacolata Giasi

In shallow geothermal systems natural and forced groundwater movement as well as the temperature driven flow plays an important role on the borehole heat exchanger efficiency.

The analysis of the efficiency of innovative heat exchangers installed in a fractured limestone aquifer was carried out through three-dimensional numerical simulations and experimental investigations on physical models.

The coastal fractured limestone aquifer of the industrial area of Bari (Italy) was chosen as benchmark field site in order to identify the aquifer parameter range and the respective combinations. The role of seawater intrusion on the borehole heat exchanger efficiency was deepen .

The results disclosed that the efficiency of the innovative heat exchangers is strictly dependent on the aquifer transmissivity and groundwater flow under natural and forced groundwater conditions.

Discussion on the performance of the seasonal heat storage and the occurrence of the thermal interference between the borehole heat exchanger was presented.

How to cite: Pastore, N., Cherubini, C., and Giasi, C. I.: Analysis of novel shallow geothermal system in coastal fractured limestone aquifer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12377, https://doi.org/10.5194/egusphere-egu21-12377, 2021.

15:55–15:57
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EGU21-10010
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ECS
Johannes Miocic

A large-scale transformation of the heating and cooling sector is needed to achieve the climate neutrality goals by 2050 as outlined in the European Green Deal. One frequently discussed option for reducing the greenhouse gas emissions is the widespread use of ground source heat pumps (GSHPs) for heating and cooling living spaces. Here, the technical potential of GSHPs to supply heat to buildings in the state of Baden-Württemberg, Germany, is analysed. This study is based on the yearly demand for heating energy at a building block scale, geological conditions, mean annual surface temperatures, as well as legal restrictions such as temperature differences at the heat pump, maximum monthly heat extraction rates as well as areas restricted from drilling. It is shown that for many densely populated areas many GSHPs would be needed to supply all the energy needed for heating. However, in less densely populated areas GSHPs can be used for heating. If future heating demand is lower due to wide-spread insulation retrofitting, GSHPs could supply most of the energy needed for heating even in densely populated areas.

How to cite: Miocic, J.: Shallow geothermal energy potential of south-west Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10010, https://doi.org/10.5194/egusphere-egu21-10010, 2021.

15:57–15:59
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EGU21-10082
|
Highlight
Shuang Chen, Jakob Randow, Katrin Lubashevsky, Steve Thiel, Tom Reinhardt, Rüdiger Grimm, Anke Bucher, Olaf Kolditz, and Haibing Shao

Nowadays, utilizing shallow geothermal energy for heating and cooling buildings has received increased interest in the energy market. Among different technologies, large borehole heat exchanger (BHE) arrays are widely employed to supply heat to various types of buildings and districts. Recently, a 16-BHE array was constructed to extract shallow geothermal energy to provide heat to the newly-developed public building in Berlin. According to the previous geological survey, different non-homogeneous sedimentary layers exist in the subsurface, with variating groundwater permeabilities and thermal parameters. To estimate the performance of the BHE array system, and its sensitivity to different subsurface conditions, as well as to determine its thermal impact to the surrounding area, a comprehensive 3D numerical model has been set up according to the Berlin BHE array project. The model is simulated for 25 years with two finite element simulators, the open source code software OpenGeoSys (OGS) and the well-known commercial software FEFLOW. In the model, an annual thermal load curve is assigned to each BHE according to the real monthly heating demand. Although the way of the implementing parameters in the two programs differs from each other and some assumptions had to be made in the model comparison, the comparison result shows that both OpenGeoSys and FEFLOW produce in good agreement. Different parameters, e.g. the Darcy velocity, the thermal dispersivity of the aquifer, the surface temperature and the geothermal heat flux are investigated with respect to their impact on the underground and BHE circulation temperature. At last, the computed underground temperature and the brine fluid temperature evolution from OGS is benchmarked with the results from the model simulated in FEFLOW. The numerical experiments show that the the ground water field has the strongest influence on the brine fluid temperature within the BHEs. When the thermal dispersivity of the aquifer is considered, the mixing effect in the aquifer leads to a higher brine fluid temperature in the BHE, indicating a better thermal recharge of the system.

How to cite: Chen, S., Randow, J., Lubashevsky, K., Thiel, S., Reinhardt, T., Grimm, R., Bucher, A., Kolditz, O., and Shao, H.: Modeling Neighborhood-Scale Shallow Geothermal Energy Utilization - A Case Study in Berlin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10082, https://doi.org/10.5194/egusphere-egu21-10082, 2021.

15:59–16:01
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EGU21-603
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ECS
Taha Sezer, Abubakar Kawuwa Sani, Rao Martand Singh, and David P. Boon

Groundwater heat pumps (GWHP) are an environmentally friendly and highly efficient low carbon heating technology that can benefit from low-temperature groundwater sources lying in the shallow depths to provide heating and cooling to buildings. However, the utilisation of groundwater for heating and cooling, especially in large scale (district level), can create a thermal plume around injection wells. If a plume reaches the production well this may result in a decrease in the system performance or even failure in the long-term operation. This research aims to investigate the impact of GWHP usage in district-level heating by using a numerical approach and considering a GWHP system being constructed in Colchester, UK as a case study, which will be the largest GWHP system in the UK. Transient 3D simulations have been performed pre-construction to investigate the long-term effect of injecting water at 5°C, into a chalk bedrock aquifer. Modelling suggests a thermal plume develops but does not reach the production wells after 10 years of operation. The model result can be attributed to the low hydraulic gradient, assumed lack of interconnecting fractures, and large (>500m) spacing between the production and injection wells. Model validation may be possible after a period operational monitoring.

How to cite: Sezer, T., Sani, A. K., Singh, R. M., and Boon, D. P.: Numerical Modelling of a District Scale Groundwater Heat Pump Operation: Case Study from Colchester, UK, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-603, https://doi.org/10.5194/egusphere-egu21-603, 2021.

16:01–16:03
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EGU21-7332
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ECS
Mohamad Ali Jaafar and Charles Maragna

The performance of a GroundWater Heat Pump (GWHP) is critically influenced by the thermal recycling between wells, i.e. the proportion of thermally affected injected water that is pumped back by the extraction well. The use of the complex potential theory, assuming a homogeneous aquifer and a uniform regional flow, to assess the evolution of the extraction temperature from a doublet is presented. One major limitation in the available models in the literature is that they assume a constant extraction flow rate and constant heat extraction. This is unrealistic since buildings energy loads vary naturally with time during the day, the month and the year. To overcome this, the present paper develops a semi-analytical model to dynamically determine the extraction temperature of a doublet GWHP taking into account a variable extraction heat flow. Results obtained are benchmarked to a finite-element Comsol Multiphysics numerical model under different conditions, which enlightens the limitations of the proposed model. The developed model can be easily used to assess the technical potential of a GWHP.

How to cite: Jaafar, M. A. and Maragna, C.: Semi-analytical model for dynamical modeling thermal recycling in a doublet well of open-loop groundwater heat pump with variable heat extraction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7332, https://doi.org/10.5194/egusphere-egu21-7332, 2021.

16:03–16:05
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EGU21-12076
Thilo Schramm, Fabian Böttcher, Viktoria Pauw, Leonhard Odersky, Smajil Halilovic, and Kyle Davis

To reduce anthropogenic climate change, our energy demand needs to be met by renewable energies, wherever possible. So far, only a minor part of heating and cooling is met by such sources. Shallow geothermal energy, powered by green electricity, can close this gap at a high level of efficiency, while reducing intermittency problems current renewables have. As there are various competing uses of the underground in urban environments, e.g. drinking water protection and infrastructure, local authorities are more and more restrictive in granting licenses for new shallow geothermal systems.

In the project Geo.KW we created a coupling approach, which combines hydrothermal and infrastructure modeling to efficiently position shallow geothermal systems between existing uses and other conflicting groundwater usage, optimized by economical and ecological constraints. This should act as a planning tool for water authorities and policymakers.

We are using PFLOTRAN, a finite volume Darcy-Richards model as our flow and heat transport model.
The energy infrastructure optimization is done with urbs, a linear optimization model for distributed energy systems.
For our iterative coupling, we are using preCICE, a multi-physics coupling library, which facilitates fully parallel peer-to-peer exchange between these modeling domains.

The city of Munich is the pilot-region for the implementation of our tool, supported by local government and water authorities. The size and complexity of the model makes it necessary to run the optimization approach on a supercomputer, i.e. the SuperMUC-NG of the Leibniz Supercomputing Centre. Even there, the model needs to be partitioned for the energy infrastructure optimization to be feasible.

How to cite: Schramm, T., Böttcher, F., Pauw, V., Odersky, L., Halilovic, S., and Davis, K.: Geo.KW, a coupled hydrothermal and infrastructure model at urban scale, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12076, https://doi.org/10.5194/egusphere-egu21-12076, 2021.

GEOSTRUCTURES
16:05–16:07
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EGU21-12890
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ECS
Badr Ouzzine, Jean de Sauvage, Iheb Ghandri, Giulia Viggiani, and Gopal Madabhushi

The growing energy needs of urban areas and the current environmental context have led to the development of new energy technologies. Since the 1980s, energy geo-structures have been developed and applied, in which heat exchanger pipes are attached to the reinforcement cages of geotechnical structures such as pile foundations or diaphragm walls. By circulating a heat transfer fluid in these pipes, and using a heat pump, these low-enthalpy solutions make it possible to produce heating and cooling with significantly reduced CO2 emissions. However, the cyclic thermal loading generates stresses and strains in the geo-structure and in the surrounding soil, due to thermal expansion. Research on the behaviour of energy pile groups is rather limited, particularly for piled foundations in which only a few piles within a group are thermally activated. Indeed, the implementation of this type of energy technology is slow because of the many concerns about the impact of thermal cycles on the mechanical behaviour of the piles. The complexity of this problem is increased if a natural groundwater flow is present, as this has the potential to affect significantly heat transfer between piles in the group.

To tackle these questions, the stresses induced in pile groups by thermal activation were studied by geotechnical centrifuge modelling.  Two reduced scale models of 2*2 pile groups were examined, one in dry and one in saturated Hostun sand. In the tests, only one pile was subjected to cyclic thermal loading, but all the pile heads were connected to the same raft. The model piles were cast in cement and copper pipes were used to model simultaneously the reinforcement cages and the heat exchanger pipes. This modelling highlighted that, when heated, the energy pile goes into additional compression along with the diagonally opposite pile, due to the raft rotation. The other two thermally inactive piles showed a decrease of axial load. The saturation of the sand layer displayed a strong role not only on the transient response, but also on the thermal equilibrium due to additional thermal inertia.

In order to make relevant comparisons between the observations made on the reduced scale models and those made at prototype scale, scaling laws must be respected, so that the model and the full-scale structure undergo the same physical phenomena. Therefore, preliminary theoretical work was carried out to examine the various thermal phenomena involved. For each phenomenon of interest, the quantities that allow keeping dimensionless numbers identical or at least of the same order of magnitude are studied. Some phenomena were verified also numerically or experimentally. This work is presented in the form of a catalog of scaling laws derived for both mechanical and thermal behaviour of pile foundations.

How to cite: Ouzzine, B., de Sauvage, J., Ghandri, I., Viggiani, G., and Madabhushi, G.: Centrifuge modelling of a non-symmetrically heated concrete energy pile group with raft, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12890, https://doi.org/10.5194/egusphere-egu21-12890, 2021.

16:07–16:09
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EGU21-7084
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ECS
Grzegorz Kacprzak, Tomasz Stasiukiewicz, Rafał Bagiński, Mateusz Frydrych, and Marcin Piotrowski

The project relates to an idea consisting in the use of diaphragm walls constituting a substructure system most often used during the foundation of a large volume building structure in tight urban fabric. Additionally, it offers the possibility of using this substructure as near-surface geothermal geotechnics and in conjunction with adjacent soil as an interseason heat storage in the form of enclosed box. The effect of the following development program is expected to provide a product in the form of concrete elements, that are already required for structural reasons, as diaphragm walls and barrettes with an integrated geothermal installation that allows obtaining part of the heat energy necessary for the operation of a renewable energy building. The accumulated energy, in the form of a lower energy source will be used to heat the building in winter. In summer,  the reduced temperature of diaphragm walls in relation to weather conditions will allow the building to cool down, and thus will power air conditioning systems. This will feature not only concerns about environment aspects but also provides a long-term cost-saving solution that will limit building maintenance.

Presented, currently running, two years program is an effect of cooperation between experienced deep foundation contractor and The Institute of Heat Engineering, scientific unit. The development program, presented below, is based on the industrial research phase in which the lower heat source systems are modelled in Ansys Fluent and then the calculation results are reproduced under laboratory conditions on small physical 3x2x0.7m models. The results from measurements with temperature sensors and IR cameras are used to calibrate the FEM models and to determine the most optimal distribution of the pipes with the fluid carrier.  Stage 2 will allow the analysis of the impact of thermal stress generated by the geothermal installation on the construction of the diaphragm walls and the entire building using deformation sensors.  Development works in stage 3 will allow verification of the above assumptions using real commercial construction in the interseasonal cycle.

The most significant effect of the development programme, stage 4,  will be the creation of a simple tool, on the basis of empirical data collected during model works and prototype tests, to commonly determine the thermal balance for building structures under given ground conditions for commercial buildings. The aim of the tool, being acquired by a deep foundation contractor, is a popularization of the thermo-active ground structures solutions and promotion of geothermal energy utilization.

How to cite: Kacprzak, G., Stasiukiewicz, T., Bagiński, R., Frydrych, M., and Piotrowski, M.: Geothermal Geotechnics development program as a commonly used solution in D-wall., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7084, https://doi.org/10.5194/egusphere-egu21-7084, 2021.

THERMAL USES OF GROUNDWATER
16:09–16:11
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EGU21-14107
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ECS
Murat Aydin, Bo Wang, Jens Lingenauer, and Sebastian Bauer

High temperature and short-term subsurface heat storage using BTES is a promising option and emerging technology for increasing the fraction of renewable energy in the heat sector and supplying stored heat at high and directly usable temperatures. For this, investigation of thermal interactions of multiple BHEs employed for high-temperature cyclic storage operations is required to understand the system behavior and the relevant thermal processes involved. This work therefore presents highly controlled meso-scale experiments for high temperature borehole thermal energy storage.

The experiment is set up at Kiel University, using a sand pit with two meters depth and a volume of 30 m³ filled with partially saturated fine sand. Five BHEs are constructed, with four positioned at the edges of a square of 0.7 m side length and the fifth one in the center.  Temperatures were measured at 224 locations at varying distances and depths to the center BHE. For the tests, inflow temperatures of the BHEs were set to mimic a high temperature storage system for both stationary and cyclic heat loads by using 70°C and 10-15°C inflow temperature for heating and cooling cycles, respectively. Cycles ranged from 12 to 120 hours.

Thermal characteristics of the boreholes and the sand medium have been determined using constant temperature Thermal Response Tests for the individual boreholes, yielding an average thermal conductivity of about 1.8 W/m/K and typical heat injection/extraction rates of 0.2 kW per meter of BHE length. Subsequently, all BHEs were jointly operated using the same inflow temperatures, in order to determine their thermal interactions in a storage operation. Thermal interaction due to the simultaneous operation of the other BHEs reduced the heat transfer rate by about 30% after 12 hours of continuous heating in the center BHE, while for the outer BHEs the heat transfer rate was reduced by approximately 24%. After about three days of continuous heating, heat transfer rates have stabilized at about 60% in the outer and 40% in the center BHE.  Based on these values, a thermal recovery factor of 55% is obtained. For the cyclic heat storage experiments, similar utilization ratios were found, although average heat transfer rates for the individual BHEs increase with decreasing cycle time. Furthermore, although heat transfer rates are lower in the joint operation of the BHEs, temperatures in the sand are actually higher. Temperatures in the sand at 0.2 m from the center BHE increase from 30°C for individual BHE operation to 57 °C in the joint operation, thus providing higher storage temperatures.

How to cite: Aydin, M., Wang, B., Lingenauer, J., and Bauer, S.: Experimental investigation of thermal interactions in high-temperature borehole thermal energy storage using cyclic heat loads , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14107, https://doi.org/10.5194/egusphere-egu21-14107, 2021.

16:11–16:13
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EGU21-14929
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ECS
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Highlight
Fabian Böttcher, Kyle Davis, Smajil Halilovic, Leonhard Odersky, Viktoria Pauw, Thilo Schramm, and Kai Zosseder

Shallow geothermal energy can contribute to a regenerative supply of urban heating and cooling loads and hence, reduce primary energy consumption and greenhouse gas emissions. In the city of Munich, which hosts a very productive shallow aquifer, conditions are outstanding for the thermal use of groundwater. Therefore, already more than 2800 shallow geothermal systems are installed and due to better economic incentives, numbers are rising. Thus, the future development of this already intensely used urban aquifer holds challenges to avoid conflicting uses, but also opportunities to build synergies and balance the energy budget.

However, fostering a sustainable development is only possible with knowledge about the dynamic hydraulic and thermal behaviour of the groundwater and its anthropogenic and natural influences. Currently, this information is missing on a city scale as a decision basis for the responsible growth of thermal groundwater use. As a consequence, water authorities have to become increasingly restrictive when granting licenses to cope with preventive drinking water protection. Therefore, tools for the thermal management of aquifers are needed to enable resilient decision making.

The project GEO.KW (2019-2021), funded by the German Ministry for Economic Affairs and Energy, took up this challenge and develops a flexible management and optimisation tool for the thermal use of groundwater. As pilot area for an implementation, Munich offers a dynamic and well-monitored hydrogeology. The tool’s core element is the coupling between a thermal-hydraulic groundwater model and a linear optimisation model for distributed energy systems. This interdisciplinary approach, allows us to include the heat storage potential of the aquifer and study the coverable heating and cooling demand depending on the thermal resource at high temporal and spatial resolution. The optimisation integrates all regulatory restrictions of water resource management, like temperature or extraction limits, and comparatively analyses conventional heating and cooling systems alongside with thermal groundwater use. As cost factor in the optimisation, greenhouse gas emissions and economic cost is evaluated.

The development focuses on using highly parallelised open-source codes and efficient code coupling. The numerical groundwater simulation is performed with PFLOTRAN, a code specifically built for scalability on supercomputers. It is coupled to the linear optimiser urbs through the minimally invasive coupling library preCICE and the simulations are performed on the SuperMUC-NG in Garching, Germany. Since the parallelisation of optimisation problems is not straightforward, a decomposition procedure is introduced to assure performance with high resolution models.

The optimisation tool and associated methods will also be applicable to other urban areas. Thus, it will offer the decision support for an optimised growth of thermal groundwater use to assure its contribution to emission-free and decarbonised heating and cooling of cities.

How to cite: Böttcher, F., Davis, K., Halilovic, S., Odersky, L., Pauw, V., Schramm, T., and Zosseder, K.: Optimising the thermal use of groundwater for a decentralized heating and cooling supply in the city of Munich, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14929, https://doi.org/10.5194/egusphere-egu21-14929, 2021.

16:13–16:15
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EGU21-1977
Alison Monaghan, Vanessa Starcher, Hugh Barron, Fiona Fordyce, Helen Taylor-Curran, Richard Luckett, Kirsty Shorter, Kyle Walker-Verkuil, Jack Elsome, Oliver Kuras, Corinna Abesser, David Boon, Barbara Palumbo-Roe, Rachel Dearden, and Michael Spence

Mine water geothermal heat production and storage can provide a decarbonised source of energy for space heating and cooling, however the large resource potential has yet to be exploited widely. Besides economic, regulatory and licensing barriers, geoscientific uncertainties such as detailed understanding of thermal and hydrogeological subsurface processes, resource sustainability and potential environmental impacts remain.

The UK Geoenergy Observatory in Glasgow is a research infrastructure for investigating shallow, low-temperature coal mine water heat energy resources available in abandoned and flooded mine workings at depths of around 50-90 m. It is an at-scale ‘underground laboratory’ of 12 boreholes, surface monitoring equipment and open data. The Glasgow Observatory is accepting requests for researchers and innovators to undertake their own experiments, test sensors and methods to increase the scientific evidence base and reduce uncertainty for this shallow geothermal technology.

How to cite: Monaghan, A., Starcher, V., Barron, H., Fordyce, F., Taylor-Curran, H., Luckett, R., Shorter, K., Walker-Verkuil, K., Elsome, J., Kuras, O., Abesser, C., Boon, D., Palumbo-Roe, B., Dearden, R., and Spence, M.: Mine water heat and heat storage research opportunities at the UK Geoenergy Observatory in Glasgow, UK, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1977, https://doi.org/10.5194/egusphere-egu21-1977, 2021.

16:15–16:17
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EGU21-5052
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ECS
Ruben Stemmle, Philipp Blum, Simon Schüppler, Paul Fleuchaus, Melissa Limoges, Peter Bayer, and Kathrin Menberg

Aquifer Thermal Energy Storage (ATES) is an open-loop geothermal system enabling seasonal storage of thermal energy in groundwater. It is a promising technology for environmentally friendly energy generation that can overcome the seasonal mismatch between demand and supply of heating and cooling and helps to reduce greenhouse gas (GHG) emissions. Yet, there are only few studies quantifying GHG emissions caused by ATES systems over their entire life cycle. This study presents a novel life cycle assessment (LCA) regression model focusing on the GHG emissions that is a fast alternative to conventional time-consuming LCA. Due to its parametric structure, the regression LCA model can be used to perform Monte Carlo simulations of a wide range of different ATES configurations. Accordingly, it allows the environmental evaluation of the technology as a whole.

The application of the model reveals that the median value of investigated ATES configurations is 83.2 gCO2eq/kWhth with most of the emissions resulting from electricity consumption during the operational phase. Compared to conventional heating systems based on heating oil and natural gas, this value reveals potential GHG savings of up to 74 %. In terms of cooling, ATES can save up to about 59 % of GHG emissions compared to conventional, electricity-based technologies. Specific GHG emissions from a modified LCA regression model considering a projected electricity mix for the year 2050 add up to 10.5 gCO2eq/kWhth forecasting even higher emission savings of up to 97 %. A sensitivity analysis reveals that in particular the operational time for cooling and the coefficient of performance (COP) of the heat pump should be carefully considered when planning or optimizing new systems under current conditions. In contrast, when considering the projected 2050 electricity mix, the most important system parameter is the number of wells. This reflects the decreasing importance of the electrical power necessary for ATES operation due to the much lower specific GHG emissions of the projected 2050 electricity mix.

How to cite: Stemmle, R., Blum, P., Schüppler, S., Fleuchaus, P., Limoges, M., Bayer, P., and Menberg, K.: Greenhouse gas emissions of aquifer thermal energy storage (ATES), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5052, https://doi.org/10.5194/egusphere-egu21-5052, 2021.

DISCUSSION
16:17–17:00