@article{BottEhrenwirthTrinkletal.2022, author = {Bott, Christoph and Ehrenwirth, Mathias and Trinkl, Christoph and Bayer, Peter}, title = {Component-based modeling of ground-coupled seasonal thermal energy storages}, volume = {2022}, pages = {118810}, journal = {Applied Thermal Engineering}, number = {214}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1873-5606}, doi = {https://doi.org/10.1016/j.applthermaleng.2022.118810}, year = {2022}, abstract = {Seasonal thermal energy storages are considered a central element of modern, innovative energy systems and help to harmonize fluctuating energy sources. Furthermore, they allow for an improved coupling between the electricity and heating sectors. Despite recent improvements of planning processes and enhanced models, significant discrepancies between projected and measured heat losses were revealed. Additional shortcomings of available tools relate to limitations in specifying geometry, internal design, or physical processes. Addressing these drawbacks, this study employs a revised, alternative approach by using a flexible, component-based, model ("STORE"). It allows variable flexible parameterizations to study diverse design scenarios. After introducing relevant seasonal thermal energy storage components, processes and mechanisms, datasets, and evaluation techniques, a plausibility test is presented that applies a common thermal energy storage model for benchmarking. In a test study, the re-use of a circa 1,000 m3 large swimming pool is simulated. STORE is used to investigate performance trends caused by different designs (e.g., insulation thicknesses, materials at individual interfaces). For the plausibility test, the results show a high degree of coverage and good applicability. Further, the results of the test study show a storage efficiency of 12.4\% for an uninsulated base case, which can be improved to 69.5\% in case of the most complex, highly insulated configuration. Critical trends are revealed, covering reduced peak capacity levels (26.5 to 23.5 MWh) and raised average filling temperatures (39.1 to 45.2 °C). Improved long-term behavior involves reduced environmental impacts due to reduced heating of the ambient soil (+7.9 K compared to +14.1 K after 2 years). General conclusions reveal that an optimal design should initially focus on an external cover of soil and top insulation. However, evaluations should base on multiple parameters depending on the target criteria. This is where the present model is highly useful. The capability of STORE to rapidly analyze a plethora of scenarios proves its high applicability for optimizing the planning processes of seasonal thermal energy storage projects.}, language = {en} } @article{AhmedContiBayeretal.2022, author = {Ahmed, Arslan and Conti, Fosca and Bayer, Peter and Goldbrunner, Markus}, title = {Hydronic Road-Heating Systems}, volume = {26}, journal = {Environmental and Climate Technologies}, subtitle = {Environmental Performance and the Case of Ingolstadt Ramps}, number = {1}, publisher = {De Gruyter Poland}, address = {Warsaw}, issn = {2255-8837}, doi = {https://doi.org/10.2478/rtuect-2022-0078}, pages = {1044 -- 1054}, year = {2022}, abstract = {Snowfall and ice formation on road surface significantly impact the safety of driving conditions. To resolve this, every year salt and de-icing chemicals are sprinkled on roads. However, use of salts and snow ploughing have environmental as well as economical disadvantages. To resolve these problems, hydronic road heating systems are valid alternatives. Heat transfer fluid, i.e. mixture of ethanol and water, is pumped into a tubular circulation system under the asphalt. By this technology, the road and pavements shall stay ice-free even in times of snowfall and temperatures below the freezing point. The system can also be used to cool the asphalt in case of extreme heat, which - besides the heating effect - could also prevent road from damages in extreme summers. This study aims to compare the environmental impact of use of salts and road-heating system in terms of GHG emissions. To assess the environmental impact, an operational road heating system for a ramp in Ingolstadt, Germany, is considered. A cradle-to-grave analysis technique is used to determine the environmental effects based on a life-cycle assessment (LCA) framework. The analysis includes nine components solemnly responsible for hydronic heating of asphalt surface such as local heating pipe, insulation, pumps, and heat meters. Comparison is performed in terms of relative and total impact over 50-year lifetime of three heated ramps having 1989 m2 surface area in total. The results show that the asphalt and heating-circuit causes the major fraction (65 \%) of overall GHG emissions, with total life-time emissions of 28.10 kg CO2 eq./m2 of heated surface. During an operational life of 50 years, road heating systems emit 18 \% less CO2 eq./m2 as compared to the use of salts.}, language = {en} } @article{TissenBenzMenbergetal.2019, author = {Tissen, Carolin and Benz, Susanne and Menberg, Kathrin and Bayer, Peter and Blum, Philipp}, title = {Groundwater temperature anomalies in central Europe}, volume = {14}, pages = {104012}, journal = {Environmental Research Letters}, number = {10}, publisher = {IOP Publishing}, address = {Bristol}, issn = {1748-9326}, doi = {https://doi.org/10.1088/1748-9326/ab4240}, year = {2019}, abstract = {As groundwater is competitively used for drinking, irrigation, industrial and geothermal applications, the focus on elevated groundwater temperature (GWT) affecting the sustainable use of this resource increases. Hence, in this study GWT anomalies and their heat sources are identified. The anthropogenic heat intensity (AHI), defined as the difference between GWT at the well location and the median of surrounding rural background GWTs, is evaluated in over 10 000 wells in ten European countries. Wells within the upper three percentiles of the AHI are investigated for each of the three major land cover classes (natural, agricultural and artificial). Extreme GWTs ranging between 25 °C and 47 °C are attributed to natural hot springs. In contrast, AHIs from 3 to 10 K for both natural and agricultural surfaces are due to anthropogenic sources such as landfills, wastewater treatment plants or mining. Two-thirds of all anomalies beneath artificial surfaces have an AHI > 6 K and are related to underground car parks, heated basements and district heating systems. In some wells, the GWT exceeds current threshold values for open geothermal systems. Consequently, a holistic management of groundwater, addressing a multitude of different heat sources, is required to balance the conflict between groundwater quality for drinking and groundwater as an energy source or storage media for geothermal systems.}, language = {en} } @article{HemmerleHaleDresseletal.2019, author = {Hemmerle, Hannes and Hale, Sina and Dressel, Ingo and Benz, Susanne and Attard, Guillaume and Blum, Philipp and Bayer, Peter}, title = {Estimation of Groundwater Temperatures in Paris, France}, volume = {2019}, pages = {5246307}, journal = {Geofluids}, publisher = {Hindawi}, address = {London}, issn = {1468-8123}, doi = {https://doi.org/10.1155/2019/5246307}, year = {2019}, abstract = {Subsurface temperature data is usually only accessible as point information with a very limited number of observations. To spatialize these isolated insights underground, we usually rely on interpolation methods. Unfortunately, these conventional tools are in many cases not suitable to be applied to areas with high local variability, like densely populated areas, and in addition are very vulnerable to uneven distributions of wells. Since thermal conditions of the surface and shallow subsurface are coupled, we can utilize this relationship to estimate shallow groundwater temperatures from satellite-derived land surface temperatures. Here, we propose an estimation approach that provides spatial groundwater temperature data and can be applied to natural, urban, and mixed environments. To achieve this, we combine land surface temperatures with anthropogenic and natural processes, such as downward heat transfer from buildings, insulation through snow coverage, and latent heat flux in the form of evapotranspiration. This is demonstrated for the city of Paris, where measurements from as early as 1977 reveal the existence of a substantial subsurface urban heat island (SUHI) with a maximum groundwater temperature anomaly of around 7 K. It is demonstrated that groundwater temperatures in Paris can be well predicted with a root mean squared error of below 1 K by means of satellite-derived land surface images. This combined approach is shown to improve existing estimation procedures that are focused either on rural or on urban conditions. While they do not detect local hotspots caused by small-scaled heat sources located underground (e.g., sewage systems and tunnels), the findings for the city of Paris for the estimation of large-scale thermal anomalies in the subsurface are promising. Thus, the new estimation procedure may also be suitable for other cities to obtain a more reliable insight into the spatial distribution of urban ground and groundwater temperatures.}, language = {en} } @article{TissenMenbergBayeretal.2019, author = {Tissen, Carolin and Menberg, Kathrin and Bayer, Peter and Blum, Philipp}, title = {Meeting the demand}, volume = {7}, pages = {9}, journal = {Geothermal Energy - Science, Society and Technology}, subtitle = {geothermal heat supply rates for an urban quarter in Germany}, publisher = {BioMed Central}, address = {London}, issn = {2195-9706}, doi = {https://doi.org/10.1186/s40517-019-0125-8}, year = {2019}, abstract = {Thermal energy for space heating and for domestic hot water use represents about a third of the overall energy demand in Germany. An alternative to non-renewable energy-based heat supply is the implementation of closed and open shallow geothermal systems, such as horizontal ground source heat pump systems, vertical ground source heat pump (vGSHP) systems and groundwater heat pump systems. Based on existing regulations and local hydrogeological conditions, the optimal site-specific system for heat supply has to be identified. In the presented technical feasibility study, various analytical solutions are tested for an urban quarter before and after building refurbishment. Geothermal heat supply rates are evaluated by providing information on the optimal system and the specific shortcomings. Our results show that standard vGSHP systems are even applicable in older and non-refurbished residential areas with a high heat demand using a borehole heat exchanger with a length of 100 m or in conjunction with multiple boreholes. After refurbishment, all studied shallow geothermal systems are able to cover the lowered heat demand. The presented analysis also demonstrates that ideally, various technological variants of geothermal systems should be evaluated for finding the optimal solution for existing, refurbished and newly developed residential areas.}, language = {en} } @article{RingelSomogyvariJalalietal.2019, author = {Ringel, Lisa Maria and Somogyv{\´a}ri, M{\´a}rk and Jalali, Mohammadreza and Bayer, Peter}, title = {Comparison of Hydraulic and Tracer Tomography for Discrete Fracture Network Inversion}, volume = {9}, pages = {274}, journal = {Geosciences}, number = {6}, publisher = {MDPI}, address = {Basel}, issn = {2076-3263}, doi = {https://doi.org/10.3390/geosciences9060274}, year = {2019}, abstract = {Fractures serve as highly conductive preferential flow paths for fluids in rocks, which are difficult to exactly reconstruct in numerical models. Especially, in low-conductive rocks, fractures are often the only pathways for advection of solutes and heat. The presented study compares the results from hydraulic and tracer tomography applied to invert a theoretical discrete fracture network (DFN) that is based on data from synthetic cross-well testing. For hydraulic tomography, pressure pulses in various injection intervals are induced and the pressure responses in the monitoring intervals of a nearby observation well are recorded. For tracer tomography, a conservative tracer is injected in different well levels and the depth-dependent breakthrough of the tracer is monitored. A recently introduced transdimensional Bayesian inversion procedure is applied for both tomographical methods, which adjusts the fracture positions, orientations, and numbers based on given geometrical fracture statistics. The used Metropolis-Hastings-Green algorithm is refined by the simultaneous estimation of the measurement error's variance, that is, the measurement noise. Based on the presented application to invert the two-dimensional cross-section between source and the receiver well, the hydraulic tomography reveals itself to be more suitable for reconstructing the original DFN. This is based on a probabilistic representation of the inverted results by means of fracture probabilities.}, language = {en} } @article{PophillatAttardBayeretal.2018, author = {Pophillat, William and Attard, Guillaume and Bayer, Peter and Hecht-M{\´e}ndez, Jozsef and Blum, Philipp}, title = {Analytical solutions for predicting thermal plumes of groundwater heat pump systems}, volume = {2020}, journal = {Renewable Energy}, number = {147, Part 2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1879-0682}, doi = {https://doi.org/10.1016/j.renene.2018.07.148}, pages = {2696 -- 2707}, year = {2018}, language = {en} } @article{AttardBayerRossieretal.2019, author = {Attard, Guillaume and Bayer, Peter and Rossier, Yvan and Blum, Philipp and Eisenlohr, Laurent}, title = {A novel concept for managing thermal interference between geothermal systems in cities}, volume = {2020}, journal = {Renewable Energy}, number = {145}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1879-0682}, doi = {https://doi.org/10.1016/j.renene.2019.06.095}, pages = {914 -- 924}, year = {2019}, language = {en} } @article{PophillatBayerTeyssieretal.2019, author = {Pophillat, William and Bayer, Peter and Teyssier, Esther and Blum, Philipp and Attard, Guillaume}, title = {Impact of groundwater heat pump systems on subsurface temperature under variable advection, conduction and dispersion}, volume = {2020}, pages = {101721}, journal = {Geothermics}, number = {83}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1879-3576}, doi = {https://doi.org/10.1016/j.geothermics.2019.101721}, year = {2019}, language = {en} } @article{BottDresselBayer2020, author = {Bott, Christoph and Dressel, Ingo and Bayer, Peter}, title = {Paraffin wax as self-sealing insulation material of seasonal sensible heat storage systems—A laboratory study}, volume = {15}, pages = {e0236056}, journal = {PLOS ONE}, number = {7}, publisher = {PLOS}, address = {San Francisco}, issn = {1932-6203}, doi = {https://doi.org/10.1371/journal.pone.0236056}, year = {2020}, abstract = {Seasonal heat storage is considered as one of the key elements on the path to a low-emission economy. Embedded in local district heating networks, they raise the share of renewable energies and balance out highly fluctuating supplies of e.g. solar systems or windmills. The technology of seasonal heat storage can be described as almost technically mature, with well-established concepts and some systems being in operation for a considerable time. Nevertheless, the operating experience gained to date also revealed two critical problems. On the one hand, even smallest leakages in sealing foils led to irreparable breakdowns. On the other hand, heat loss in the marginal areas was revealed as a key deficiency, preventing the technology from advancing towards global marketability. This study presents an experimental approach to address these two key issues in the field of seasonal energy storage. Two small-scale laboratory tests were carried out to test paraffin wax as a completely novel component in the marginal area of seasonal storages. This is based on two material properties: As hydrophobic and mobile medium, the warmed and molten paraffin should actively seal the fissures and holes in the event of leakage. Additionally, the latent heat storage properties of the paraffin wax should increase the systems' total storage capacity and reduce lateral heat losses via its low thermal conductivity. With retardation periods from 2.5 to 4 hours, the results show an effective phase change effect of the paraffin wax, which reduces energy losses and allows to buffer short-term, intensive loading and unloading processes. By storing up to 138 kJ/kg energy in the paraffin wax, increased capacities of application-scale pit storages by up to 40.70 MWh are to be expected. Additionally, the self-healing features could be successfully demonstrated: With only small losses of between 1.5 and 17\%, the paraffin wax effectively sealed artificially incised leaks. Thereby, the mechanism was most effective for local defects. Following these positive demonstrations of feasibility, technical design questions still remain, which concern prevention of deformation of the paraffin wax. Once solved, this new component can then provide a path for further optimization of seasonal heat storage technologies.}, language = {en} } @unpublished{MuellerSchmittBottetal.2026, author = {M{\"u}ller, Simon Nikolaus and Schmitt, David and Bott, Christoph and Akbar, Shariq and Bayer, Peter and Schrag, Tobias}, title = {Operating thermal source networks - How supply temperature and ground exchange shape performance}, titleParent = {SSRN}, publisher = {Elsevier}, address = {Amsterdam}, doi = {http://dx.doi.org/10.2139/ssrn.6034530}, year = {2026}, language = {en} }