ERE2.6

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 gCO_2eq/kWh_th 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 gCO_2eq/kWh_th 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.