Little is known about the intensity and extension of subsurface urban heat islands (UHI), and the individual role of the driving factors has not been revealed either. In this study, we compare ...groundwater temperatures in shallow aquifers beneath six German cities of different size (Berlin, Munich, Cologne, Frankfurt, Karlsruhe and Darmstadt). It is revealed that hotspots of up to +20K often exist, which stem from very local heat sources, such as insufficiently insulated power plants, landfills or open geothermal systems. When visualizing the regional conditions in isotherm maps, mostly a concentric picture is found with the highest temperatures in the city centers. This reflects the long-term accumulation of thermal energy over several centuries and the interplay of various factors, particularly in heat loss from basements, elevated ground surface temperatures (GST) and subsurface infrastructure. As a primary indicator to quantify and compare large-scale UHI intensity the 10–90%-quantile range UHII10–90 of the temperature distribution is introduced. The latter reveals, in comparison to annual atmospheric UHI intensities, an even more pronounced heating of the shallow subsurface.
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► Positive temperature anomalies under German cities. ► Local heat sources cause hot spots>30°C in Frankfurt. ► Superposition of various heat sources leads to a significant regional warming. ► Subsurface urban heat island (UHI) intensities range between 1.9 and 2.4K.
Abstract
Despite the global interest in green energy alternatives, little attention has focused on the large-scale viability of recycling the ground heat accumulated due to urbanization, ...industrialization and climate change. Here we show this theoretical heat potential at a multi-continental scale by first leveraging datasets of groundwater temperature and lithology to assess the distribution of subsurface thermal pollution. We then evaluate subsurface heat recycling for three scenarios: a
status quo
scenario representing present-day accumulated heat, a
recycled
scenario with ground temperatures returned to background values, and a
climate change
scenario representing projected warming impacts. Our analyses reveal that over 50% of sites show recyclable underground heat pollution in the
status quo
, 25% of locations would be feasible for long-term heat recycling for the
recycled
scenario, and at least 83% for the
climate change
scenario. Results highlight that subsurface heat recycling warrants consideration in the move to a low-carbon economy in a warmer world.
•Detailed thermodynamic analysis of individual components of a hybrid GSHP system.•Comparison of heating and cooling mode highlights importance of a low temperature spread.•Use of the natural energy ...source is significantly more efficient in cooling mode.•Analysis of different strategies to increase the exergy efficiency of the system.•Reduction of energy demand is shown to be more effective than operational system changes.
In contrast to energy analysis, the analysis of exergy allows the evaluation of the quality of different energy flows and enables a comprehensive assessment of inefficiencies within a system and its individual components by accounting for exergy consumption. While exergy analysis methods have been applied to a variety of conventional and renewable energy supply systems, there is still a lack of knowledge regarding the exergy flows and exergy efficiency of hybrid ground-source heat pump systems with a supplementary boiler. In this study, we develop a thermodynamic model for each subsystem in a hybrid heating and cooling system of an existing building by applying the concept of cool and warm exergy. A comparison of the exergy consumption of the hybrid system in heating and cooling reveals that there are significant differences regarding the components that attribute most to the overall exergy consumption in the system. Due to these differences the true exergy performance of the system in heating mode (∼30%) is twice as high as for cooling mode (∼15%), while the natural exergy performance is considerably better in cooling mode (∼26% to ∼3%). Potential measures to enhance the exergy performance based on changes in the operational settings of the system and the improvement of the building envelope were found to have a more significant effect on heating performance than on cooling performance. In general, measures that affect the amount of thermal energy delivered by the system appear to be more effective than changes to the operational settings of energy supply systems.
Sustainable and climate-friendly space heating and cooling is of great importance for the energy transition. Compared to conventional energy sources, Aquifer Thermal Energy Storage (ATES) systems can ...significantly reduce greenhouse gas emissions from space heating and cooling. Hence, the objective of this study is to quantify the technical potential of shallow low-temperature ATES systems in terms of reclaimable energy in the city of Freiburg im Breisgau, Germany. Based on 3D heat transport modeling, heating and cooling power densities are determined for different ATES configurations located in an unconsolidated gravel aquifer of varying hydrogeological subsurface characteristics. High groundwater flow velocities of up to 13 m d
−1
cause high storage energy loss and thus limit power densities to a maximum of 3.2 W m
−2
. Nevertheless, comparison of these power densities with the existing thermal energy demands shows that ATES systems can achieve substantial heating and cooling supply rates. This is especially true for the cooling demand, for which a full supply by ATES is determined for 92% of all residential buildings in the study area. For ATES heating alone, potential greenhouse gas emission savings of up to about 70,000 tCO
2
eq a
−1
are calculated, which equals about 40% of the current greenhouse gas emissions caused by space and water heating in the study areas’ residential building stock. The modeling approach proposed in this study can also be applied in other regions with similar hydrogeological conditions to obtain estimations of local ATES supply rates and support city-scale energy planning.
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.
More than 30% of Germany’s final energy consumption currently results from thermal energy for heating and cooling in the building sector. One possibility to achieve significant greenhouse gas ...emission savings in space heating and cooling is the application of aquifer thermal energy storage (ATES) systems. Hence, this study maps the spatial technical potential of shallow low-temperature ATES systems in Germany. Important criteria for efficient ATES operation considered in this assessment encompass suitable hydrogeological conditions, such as aquifer productivity and groundwater flow velocity, and balanced space heating and cooling demands. The latter is approximated by the ratio of heating and cooling degree days, which is incorporated as a time-dependent criterion to also evaluate the impact of climate change on the ATES potential. The hydrogeological and climatic criteria are combined within a spatial analysis revealing that, regarding the upcoming decades, about 54% of the investigated German area are very well or well suitable for ATES applications, largely concentrating on three regions: the North German Basin, the Upper Rhine Graben and the South German Molasse Basin. Considering time-dependent climatic conditions, the very well or well suitable areas will increase by 13% for the time period 2071–2100. This is mostly caused by a large relative area increase of the very well suitable regions due to an increasing cooling demand in the future. The sensitivity of the very well and well suitable regions to the criteria weightings is relatively low. Accounting for existing water protection zones shows a reduction of the country-wide share of very well or well suitable areas by around 11%. Nevertheless, the newly created potential map reveals a huge potential for shallow low-temperature ATES systems in Germany.
•Guide for the Bayesian calibration of building energy models is provided.•Investigated effect of number of calibration parameters and choice of priors.•Over-parameterization can lead to ...identifiability issues.•Strong priors may dominate any influence from the data.•Low CVRMSE and NMBE not indicative that parameter values are good estimates.
This paper provides practical guidelines to the Bayesian calibration of building energy models using the probabilistic programming language Stan. While previous studies showed the applicability of the calibration method to building simulation, its practicality is still impeded by its complexity and the need to specify a whole range of information due to its Bayesian nature. We ease the reader into the practical application of Bayesian calibration to building energy models by providing the corresponding code and user guidelines with this paper.
Using a case study, we demonstrate the application of Kennedy and O’Hagan’s (KOH) 1 Bayesian calibration framework to an EnergyPlus whole building energy model. The case study is used to analyze the sensitivity of the posterior distributions to the number of calibration parameters. The study also looks into the influence of prior specification on the resulting (1) posterior distributions; (2) calibrated predictions; and (3) model inadequacy that is revealed by a discrepancy between the observed data and the model predictions. Results from the case study suggest that over-parameterization can result in a significant loss of posterior precision. Additionally, using strong prior information for the calibration parameters may dominate any influence from the data leading to poor posterior inference of the calibration parameters. Lastly, this study shows that it may be misleading to assume that the posteriors of the calibration parameters are representative of their true values and their associated uncertainty simply because the calibrated predictions matches the measured output well.
Aquiferspeicher in Deutschland Fleuchaus, Paul; Schüppler, Simon; Stemmle, Ruben ...
Grundwasser,
06/2021, Letnik:
26, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Zusammenfassung
Der saisonale Versatz von Angebot und Nachfrage im Wärmesektor kann über Speicherlösungen ausgeglichen werden. Für die jahreszeitliche Speicherung von Wärme und Kälte sind ...Aquiferspeicher (ATES) als vielversprechende Lösung vermehrt in den Fokus gerückt. Mit derzeit jeweils nur einem betriebenen Niedrigtemperatur- (NT) und Hochtemperaturspeicher (HT) fristet die Technologie in Deutschland allerdings noch immer ein Nischendasein. Diese Studie liefert einen Überblick über die aktuelle Entwicklung der Aquiferspeicherung in Deutschland und diskutiert Stärken und Schwächen sowie Chancen und Risiken. Trotz eines großen Nutzungspotenzials wird der Markteinstieg in Deutschland durch fehlende Anreizprogramme, mangelnde Kenntnisse sowie nicht vorhandene Pilotanlagen erschwert. Die Speichertemperaturen von HT-ATES (> 50 °C) erhöhen dessen Nutzungsmöglichkeiten, haben aber verstärkte technische und legislative Risiken zur Folge. Eine kommerzielle ATES-Nutzung in Deutschland ist daher nur möglich durch die Anpassung genehmigungsrechtlicher Anforderungen, die Schaffung von Fördermaßnahmen, die Umsetzung von Demonstrationsanlagen und die Darlegung von deren wirtschaftlichen und ökologischen Vorteilen.
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.
•We scrutinize three methods for sensitivity analysis in building energy modelling.•Potential pitfalls and techniques that can support evaluation are demonstrated.•Use of the median value for Morris ...method improves the robustness of the results.•All methods provide the same information for identification of important parameters.•Computationally intensive methods reveal insights into complex parameter behaviour.
Though sensitivity analysis has been widely applied in the context of building energy models (BEMs), there are few studies that investigate the performance of different sensitivity analysis methods in relation to dynamic, high-order, non-linear behaviour and the level of uncertainty in building energy models. We scrutinise three distinctive sensitivity analysis methods: (a) the computationally efficient Morris method for parameter screening, (b) linear regression analysis (medium computational costs) and (c) Sobol method (high computational costs). It is revealed that the results from Morris method taking the commonly used measure for parameter influence can be unstable, while using the median value yields robust results for evaluations with small sample sizes. For the dominant parameters the results from all three sensitivity analysis methods are in very good agreement. Regarding the evaluation of parameter ranking or the differentiation of influential and negligible parameters, the computationally costly quantitative methods provide the same information for the model in this study as the computational efficient Morris method using the median value. Exploring different methods to investigate higher-order effects and parameter interactions, reveals that correlation of elementary effects and parameter values in Morris method can also provide basic information about parameter interactions.
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