Shallow geothermal systems are the most efficient and clean technology for the air-conditioning of buildings and constitutes an emergent renewable energy resource in the worldwide market. Undisturbed ...systems are capable of efficiently exchanging heat with the subsurface and transferring it to human infrastructures, providing the basis for the successful decarbonisation of heating and cooling demands of cities. Unmanaged intensive use of groundwater for thermal purposes as a shallow geothermal energy (SGE) resource in urban environments threatens the resources' renewability and the systems' performance, due to the thermal interferences created by a biased energy demand throughout the year. The exploitation regimes of 27 groundwater heat pump systems from an alluvial aquifer were firstly examined using descriptive statistics. Linear relationships between abstraction and injection temperatures of the systems were assessed by calculating Pearson's r correlation coefficient, and used as an evidence of thermal interferences. Then, time series of flow rate, operation temperature and energy transfer were modelled by means of spectral analysis and sinusoidal regression methods, followed by the definition of the relative exploitation patterns. The exploitation regimes examined presented a clear cooling bias and a similar cyclicality. The amplitudes correlated with the different end-user's activities (e.g. medical centres) when high frequency cycles were observed, while climatization strategies (e.g. constant flow rates and modulation of injection temperatures) did so when low frequency cycles were detected. The time series models allowed defining the relative operational pattern of a system and the groups of systems following such patterns. The biases in exploitation regimes of groundwater heat pump systems existing in Mediterranean areas require correction measures to ensure a more balanced exploitation of the SGE resources. The definition of the characteristic exploitation pattern proposed could be applied to guide resource managers by identifying unbalanced systems, understanding existent exploitation strategies and proposing corrective alternative plans.
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•The exploitation regimes of 27 groundwater heat pump systems were examined.•Exploitation patterns were identified from the cyclicality and cluster analysis.•Different usage of the systems conditions the hourly and daily cycles.•Monthly and yearly cycles are affected by the climatization strategy followed.
Extracting shallow geothermal energy using borehole heat exchangers (BHEs) can help decarbonising the residential heating sector, particularly where no other low-carbon heating solutions are readily ...available. To assist urban planners and policy makers in developing carbon-neutral heating plans, the regional technical shallow geothermal potential must be known. Here, we calculate the technical geothermal potential of BHE fields on a regional scale while taking potential thermal interference between BHEs, geological conditions, as well as space available for BHE installation into account. The number of BHEs placed is maximized and heat extraction rate from each BHE is optimized taking regional regulations into account. When the methodology is applied to the German state of Baden-Württemberg on a building-block scale, results suggest an annual technical potential of 33.5 TWh. We then link this technical geothermal potential to heating demand scenarios on a building block scale and the results show that, depending on the renovation status of the buildings, between 44% and 93% of all building blocks can be heated using only BHEs. This allows for a rapid identification of building blocks for which BHEs are not able to meet the heating demand and where other means of heat supply will be needed.
•Estimation of the regional technical shallow geothermal energy potential.•Technical geothermal potential of the German state Baden- Württemberg is presented.•Technical shallow geothermal potential is linked to regional heating demand scenarios.•Areas where borehole heat exchangers can supply heating are identified.
Underground geotechnical structures, such as deep and shallow foundations, diaphragm walls, tunnel linings and anchors are being increasingly employed as energy geostructures to exchange heat with ...the ground by installing absorber pipes into the structural elements. This paper focuses on the application of this technology to reinforced concrete diaphragm walls used for construction of underground car parks, basements and metro stations, with the purpose of heating and cooling the adjacent buildings. Preliminary numerical modelling allowed optimising the geothermal plant design of the diaphragm wall. Then its energy efficiency is investigated through finite element thermo-hydro coupled analyses together with the effects of the thermal activation on the surrounding soil. Finally, finite difference thermo-mechanical analyses are used to study the mechanical effects induced by the thermal activation.
•Thermal and mechanical aspects of energy walls are discussed.•The horizontal configuration of pipes geometry allows maximising the heat exchange.•Heat exchange between 20 and 25 W/m2 with static ground water.•Heat exchange between 40 and 50 W/m2 with favourable groundwater flow.•Bending moment increase up to 16% due to thermal activation.
Ground Source Heat Pumps, in the framework of Shallow Geothermal Energy Systems, outperform conventional Heating Ventilation and Air Conditioning systems, even the high efficiency Air Source Heat ...Pumps. At the same time, though, they require considerably higher installation costs. The utilization of dwellings' foundations as ground heat exchanger components has recently demonstrated the potential to generate significant cost reductions primarily attributed to the reduction in expenses associated with drilling and backfill material (grout). These elements are referred to in the literature as Thermo-Active Structures or Energy Geo-structures (EGs). The current study employs a ‘mixed studies’ review (i.e., literature review, critical review and state-of-the-art review) methodology to comprehensively examine and assess the compatibility and integration of different renewable energy sources and environmentally friendly technologies with foundation elements deployed as EGs. These mainly include heat pumps, district heating and cooling networks, solar-thermal systems, waste heat, biomass and other types such as urban structures. Emphasis has been given on the advancement on this area, with the current study identifying and addressing two primary categories. The first category involves the integration of EG elements with sources that are able to supply green electricity, referring to renewable energy electricity obtained from on-grid or off-grid integration. The second category, involves a direct or indirect integration with sources that provide heat, or vice versa. The technical and non-technical barriers of such integrations have been discussed in detail, with the technical challenges generally involving engineering design, and system optimization, whereas non-technical challenges encompassing the economic, social, and policy domains.
Use of Shallow Geothermal Energy TAKEMURA, Takato
Journal of the Japan Society of Engineering Geology,
2019/06/10, Letnik:
60, Številka:
2
Journal Article
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.
Over the past years, the installations of Shallow Geothermal Energy (SGE) systems are increasing throughout Europe, and it is indicating that a specific and detailed legal framework is necessary. ...Towards this direction, this paper consists of an overview of legislation issues on SGE at European level, based on concise reviews from fourteen countries, i.e., Croatia, Cyprus, France, Greece, Italy, Latvia, Lithuania, Poland, Portugal, Serbia, Slovenia, Spain, Sweden, and Turkey. Said reviews discuss key national legislation as well as experts’ experience in the procedure of SGE integration. Legal and technical issues are also critically discussed for all involved countries, both individually and collectively. Findings show that high diversity exists on legislation provisions as well as on regulations, standards, and institutional support amongst European countries. The latter acts as an effective barrier for the further development of the SGE market; therefore indicating the need for a common approach. Increase of awareness, need for standardization, improvement of legal framework, and administration procedures and permitting, are essential steps in moving forward and supporting the effectiveness of design, construction, maintenance, and operation of SGE systems.
•We present a legislation review for SGE in 14 European Countries.•There is a lack of EU legal framework regarding SGE.•Common technical rules and standardization, among EU countries is one of the main legislation barriers for SGE.
•A simplified method specific to assess energy of underground metro station.•The probability distribution of energy performance based on uncertainty method.•Uncertainty method is benefit to energy ...underground metro station system design.•Weather are dominate factor of peak load for energy underground metro station.
An accurate calculation of energy consumption is a precondition for energy underground metro station design, which determines the amount of energy geostructure. This study develops a simplified deterministic method for the underground metro station energy performance that accounts for weather and interior heat gain uncertainty. A Monte Carlo technique with Latin hypercube sampling is then employed to confirm the probability distributions of the peak load, average yearly load and annual energy demand, and compared to deterministic method to improve the design robustness. The sensitivities of 14 input variables with respect to the underground metro station energy performance are discussed through three sensitivity methods. The simplified deterministic method is more accurate than the DeST and American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) in describing the fluctuation of the underground metro station energy performance. The uncertainty distribution of energy performance is advantageous to the system design, considering both safety and economy. Moreover, a comparison with the deterministic method is performed to determine the reasonability of the safety factor 1.2, which is usually used in practical programs. The peak load is dominated by outdoor parameters, while there are no control parameters for the average yearly load or annual energy demand.
The thermophysical properties of bedrock are of primary importance when designing borehole thermal energy systems. We present a novel use of the Enhanced Thermal Response Test (ETRT) to determine ...bedrock thermal conductivity, natural convection, and drill hole thermal resistance as a function of depth in crystalline bedrock. Bedrock was heated with a 228-m-long hybrid cable containing copper wires and fiber optics for temperature monitoring. A reference fiber optic cable was installed along the whole length of the studied drill hole. For groundwater-filled boreholes, the ETRT offers a means to estimate the magnitude of buoyancy-driven natural convection. We estimated that the heating power in the ETRT should not exceed 20 Wm-1 for the thermal conductivities to be determined with sufficient accuracy. According our results, the accuracy of the ETRT can be significantly improved if the test is performed with a hybrid fiber optic cable combined with a reference fiber optic cable. Thermal resistance can be more accurately determined if a reference fiber optic cable is used. The most important achievement of this method is that compared to other measurement methods, the effective thermal conductivity of bedrock can be simultaneously determined along the entire length of the drill hole.
•Novel method introduced to ETRT measurement in a 302m deep drill hole.•Evaluation of thermal conductivity of the crystalline bedrock in 1-m interval.•Evaluation of the magnitude of natural convection.•Heat injection 20 Wm-1 using a hybrid fiber optic cable.•Temperature monitoring of bedrock during heat injection and recovery phases.
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