Shallow geothermal energy suitability map presents the potential for implementation in a region. The potential for implementation depends on hydrogeology, geotechnical, geology environment, and ...geothermal characteristics. Plenty of scholars evaluate shallow geothermal energy by the algorithm combined Analytic Hierarchy Process and Index Overlap. But Analytic Hierarchy Process and Index Overlap, as knowledge driven methods, rely on the experts' experience. This research presents a data driven algorithm based on Entropy Weight Method and TOPSIS Method. The weights are calculated by the Entropy Weight Method and assigned to the TOPSIS model. The closeness coefficient could be calculated by TOPSIS model. The suitability potential is analysed by comparing the closeness coefficient. The algorithm is accomplished by coding a program using Matlab. The algorithm is also applied to Nantong, China. Depending on the principle of ground source heat pump system, the suitability evaluation system of the open loop system and the closed loop system are established, respectively. Hydrogeology, geotechnical, geothermal, and geology environmental investigations are carried out to obtain the measured data and parameters for suitability analysis. The suitability maps are drawn in according with closeness coefficient. The algorithm is able to overcome the subjectivity of experts' experience. Compared with knowledge driven methods, the proposed algorithm tends to compare the relative potential in a region, rather than assess whether the site is suitable for SGE implementation. Consequently, it is more suitable for selecting the best field-site.
In long-term operations, seasonal imbalance in the thermal load may adversely affect the heat transfer performance of the energy piles, potentially resulting in thermal accumulation within the ground ...and eventual system failure. The heat transfer performance of energy pile systems during long-term operation under unbalanced thermal loads must be investigated. Moreover, the design parameters of energy piles are usually constrained by the requirements of foundation structural design, resulting in energy piles being densely arranged. Hence, the influence of pile spacing on the heat exchange performence of energy piles must be comprehensively understood. In this study, two- and three-dimensional energy-pile heat transfer models were established and innovatively coupled based on an engineering project currently under design. Numerical simulations were performed to investigate the heat transfer behavior of energy-pile groups subjected to unbalanced thermal loads and the effect of pile spacing on their heat exchange performance. Furthermore, design recommendations regarding the determination of the proportion of thermal loads to be borne by the energy piles in a hybrid GSHP system were provided. The results indicate that the proposed 2D-3D coupled modeling approach is able to simulate the heat exchange performance of large-scale energy pile groups. Pile spacing considerably affects the long-term thermal performance of energy-pile groups, especially in cases with small pile spacings. The influence of pile spacing on the heat exchange capacity of energy piles can be considered in the design phase by incorporating a group effect coefficient η, which are calculated to be 0.165, 0.470, 0.732, and 1 for pile spacings of 2 m, 4 m, 6 m, and 10 m, respectively.
The geothermal potential of cities Bayer, Peter; Attard, Guillaume; Blum, Philipp ...
Renewable & sustainable energy reviews,
05/2019, Letnik:
106
Journal Article
Recenzirano
What is the heat beneath our feet? There is a growing interest in the geothermal resources available at shallow depth beneath cities. However, there exists no general procedure for quantifying the ...low-temperature geothermal potential in urban ground and groundwater. This review categorizes previous work based on different definitions of the geothermal potential and compares the different assessment methods used. It is demonstrated that the theoretical potential of the available heat at a shallow depth is enormous, especially when not only the heat in place, but also compensating heat fluxes are considered. The technical potential describes the extractable heat by a specific technology. The methods to evaluate the extractable heat are manifold, including the use of technical performance standards, analytical and numerical simulation tools and mathematical regression procedures. These are different for groundwater well based open-loop systems and heat-exchanger-based closed loop systems, and the results depend on variable local factors, the density of systems applied and whether heat and/or cold is utilized. We contrast the published findings based on the power density and the relative contribution to the demand of a city. The broad span of the results highlights the need for a more consistent framework that distinguishes between the conceptual assumptions for calculating the technical geothermal potential and the local city-specific factors. This will be the basis for a reliable analysis of the economic geothermal potential of low-temperature geothermal applications on a local, district or city scale. This will also enhance the reliability and the trust in these technologies, and thus the public acceptance reflected in the acceptable geothermal potential.
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•Exploration of the manifold computational concepts behind geothermal potential.•Development of a common novel framework with differently defined potential classes.•Assessment of available approaches for quantification of different potential types.•Contrasting of previous findings for the geothermal potential to the energy demand.
Many cities worldwide lay upon alluvial aquifers which have a great potential for low temperature geothermal installations thanks to the thermal diffusive properties of saturated porous media and the ...constant temperature of the subsurface. In addition, aquifers with fast moving groundwater have a higher potential due to the additional energy replenishment by advection, which is often underestimated.
This work aims at bridging the gap between quantitative hydro-thermal numerical analysis and regional scale assessment developing a process-based surrogate model for the estimation of the thermal exchange (geothermal) potential of ground source heat pumps (GSHP) considering groundwater advection. The proposed method is based on a synthetic 3D FEM model reproducing the infinite line source configuration and introducing groundwater advection. Conductive/advective g-functions were derived from the numerically simulated space-time thermal perturbation for a comprehensive set of hydrogeological regimes, and a surrogate model was developed by a machine learning (ML) regression of the thermal response of the system. This solution, beyond the run time of the numerical study and the ML training phase, is very fast, applicable at any scale and scalable to any desired depth.
The trained model can be used to predict the geothermal potential of GSHP for almost all sedimentary basins around the world upon the availability of the required input data (aquifer thickness and saturation, aquifer porosity and groundwater flow velocity). In this study, large scale geothermal potential maps were generated from input layers implemented in a GIS, for a demonstrative area in northern Italy showing highly variable groundwater flow (Darcy velocity from 10−3 to 10+3 m/y). A promising increase (up to +250 %) in the thermal exchange potential of GSHP due to the contribution of advection was highlighted discussing the benefits of groundwater flow and the amount of usable potential with implications on shallow geothermal energy management and development.
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•A new approach to assess the regional geothermal potential with groundwater flow•Numerically derived g-functions considering advection to evaluate the potential•Numerical results implemented at regional scale by machine learning surrogate model•Benefits of groundwater flow discussed considering the usable/unusable potential
Accurate estimation of thermal ground properties is needed to optimally apply shallow geothermal energy technologies, which are of growing importance for the heating and cooling sector. A special ...challenge is posed by the often significant heterogeneity and variability of the geological media at a site. As an innovative investigation method, here the focus is on the actively heated fiber optics based thermal response test (ATRT). A type of copper mesh heated optical cable (CMHC), which both serves as a heating source and a temperature sensing cable, was applied in the field in a borehole. By inducing the electric current to the cable at a relatively low power of 26 W/m, the in-situ heating process was recorded at high depth resolution. This information serves to infer the thermal conductivity distribution along the borehole. The presented field experience reveals that the temperature rise in the early phase of the test should not be used due to initial heat accumulation caused by the outer jacket of the CMHC. The comparison of these results with those of a conventional thermal response test (TRT) and a distributed thermal response test (DTRT) in the same borehole confirmed that the ATRT result is reliable (with a difference less than 5% and 1%, respectively), since this novel method affords much less energy and test time. Additionally, the ATRT result agrees well with ground thermal conductivities tested in the lab, which supports its potential as an advanced geothermal field investigation technique in the future.
•Actively heated fiber optics based thermal response test is introduced.•A radially symmetric cable with heating and sensing elements is employed.•The novel method offers a more efficient thermal property evaluation in the field.•This fast and economical method leads to better understanding of geothermal energy.
Energy consumption for thermal purposes represents the most impacting energy issue in the European building sector. In addition to space heating, space cooling is constantly growing, due also to ...climate change, which provokes extreme hot events in summer even in moderate climates. To approach this challenge, it is essential to invest in lowering the overall energy demand, to increase the energy conversion efficiencies and to replace fossil fuels with renewable energy sources.
The research here presented deals with the European decarbonization goals and focuses on shallow geothermal technology in district thermal systems (DTS), i.e. Geo-5GDHC.
The research investigates whether Geo-5GDHC can be cost-effective in different scenarios based on climatic contexts, insulation levels and the possible integration of photovoltaic and thermal technology (PVT).
Through the elaboration of proper KPIs and the implementation and use of a tool specifically developed to couple a Geo-5GDHC energy assessment model with an economic analysis (PILEDHC), the research highlights results and guidelines for providing solutions for new and innovative DTS, considering both energy and economic aspects in different contexts.
•District thermal systems are framed in climate change and decarbonization issues.•A new model for simulating Geo-5GDHC network was developed and tested.•Scenarios based on different buildings energy performances and climates were set.•A set of techno-economic KPIs was defined and calculated for the different scenarios.•Results were discussed underlining the role of Geo-5GDHC and further developments.
Advanced thermal response tests: A review Wilke, Sascha; Menberg, Kathrin; Steger, Hagen ...
Renewable & sustainable energy reviews,
March 2020, 2020-03-00, Letnik:
119
Journal Article
Recenzirano
In this study, the historical and technical development and the current status of distributed (DTRT) and enhanced (ETRT) thermal response tests (TRT) are reviewed. The different test setups of these ...advanced TRT are critically assessed and future research questions are outlined. Advanced TRT use specific temperature measurement techniques for the depth-resolved determination of site-specific ground parameters that are required for an optimal design of borehole heat exchanger (BHE) fields. The depth-resolved determination of these thermal properties, such as effective thermal conductivities and thermal borehole resistances, is the key advantage in comparison to conventional TRT, promising economic benefits during the installation and operating phase of ground source heat pump (GSHP) systems. Various test setups exist which differ regarding the heating procedure, i.e. circulating heating fluid and heating wire, the temperature measurement technique, i.e. optical fiber and wireless probe, as well as in their suitability for parameter estimation. These advanced techniques can furthermore provide information about geological layers, fractured zones and groundwater influenced sections in the subsurface as well as inadequate backfilled zones along the borehole heat exchanger. Despite this, advanced TRT are reported in international literature only for a few locations and some test setups are purely theoretical without any practical demonstration. Uncertainties exist regarding the comparability of the test setups, the sensitivity of the measurement devices under test conditions, as well as the best evaluation procedure. Also, scarce information is available about the use beyond academic field and economic aspects in comparison to conventional TRT. Encouraging further research and a more extensive transfer of these promising techniques from academia to practice is therefore also the aim of this review.
•Advanced TRT enable the depth-resolved determination of ground thermal parameters.•The temperature measurement is conducted either by optical fibers or wireless probes.•Different test setups exist for advanced TRT, with individual (dis)advantages.•Open questions exist regarding the best test setup and the utilization in practice.
Emission reduction in buildings is essential to combat climate change. However, current strategies failed to balance development and emissions reduction goals. This paper selects a public building in ...China and simulates its initial energy consumption and carbon emissions. Then it establishes a multi-objective optimization model to explore cost-effective and emission-reduction strategies, considering photovoltaic and ground-source-heat-pump (GSHP) systems. Finally, NSGA-Ⅱ is used to solve, and sensitivity analysis is carried out. Results show that: (1) Energy consumed by the air conditioning system is the largest in January for heating and in July for cooling, validating the accuracy of the energy simulation model. (2) Economic efficiency and emission reduction effect are better when photovoltaic and GSHP systems are implemented simultaneously. (3) Electricity price, initial investment cost, annual solar peak hours, and the proportion of shallow geothermal energy significantly impact carbon emissions and cost. (4) The photovoltaic and power grid substitution ratio will exceed 8% every five years, and all substitutions will be completed in 2050. After adopting the GSHP system, the complete replacement will be advanced to 2045. Setting subsidies significantly shortens the payback period of investment and ensures firms’ economic benefits. In summary, using photovoltaic and shallow geothermal energy is conducive to reducing emissions and saving costs in the long term.
•Shallow geothermal energy can significantly reduce the building HVAC loads.•Renewable energy integration with geothermal systems can minimize HVAC demands.•A hybrid combination of active and passive ...technologies realizes NZEB.
Shallow geothermal systems use the thermal inertia of the earth to provide a temperature gradient between the ambient conditions and the underground soil. This thermal inertia can be used by the heat exchangers to provide space heating and cooling during the winters and summers. This paper provides a brief but broad overview of the different active and passive technologies involved in the use of heat exchangers for HVAC in order to achieve a near net zero energy building. Firstly the different types of ground heat exchangers and heat pumps are introduced along with the relevant studies of significance in this field. It has been demonstrated that the different types of heat exchangers can be integrated with thermally active building envelopes and renewable energy resources to significantly minimize the building energy use. Finally a pathway has been devised for use of ground heat exchangers to realize a net zero energy building.
Thermophysical properties of rock and soil are important parameters that affect the efficiency of shallow geothermal energy utilization. This paper analyzes the thermophysical parameters (specific ...heat capacity and thermal conductivity) and their influencing factors based on 6467 sample data in 24 provincial capitals, China. The statistical distributions of thermophysical properties are analyzed based on histogram plots. Linear regression analysis is conducted to investigate the correlation between thermophysical properties and lithology (classified as metamorphic rocks, igneous rocks, chemical sedimentary rocks, clastic sedimentary rocks, and loose sediments in this study)), density, and water content. The results show that the thermophysical properties are influenced predominantly by lithology. The measured values of thermophysical properties generally show normal distribution characteristics. The specific heat capacity of loose sediments is relatively high, the thermal conductivity of other four types are relatively high. The specific heat capacity is negatively correlated with density, positively correlated with water content, whereas thermal conductivity is positively correlated with density, and negatively correlated with water content. The findings obtained in this study provide evidence and guidelines for the investigation, evaluation, and development of shallow geothermal resources.
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