Field-scale evaluation of the design of borehole heat exchangers for the use of shallow geothermal energy

This article draws on the experience matured while working with low-enthalpy geothermic installations both in the design and executive phase as well as ongoing monitoring, within the scope of energy conservation as it relates to building and construction. The goal is to illustrate the feasibility of adopting the ESBE certification protocol (Certification of Energy Efficient Low-Enthalpy Probes) aimed at optimizing the harnessing of local geothermic resources to satisfy the energy requirements of a building, measured against the initial investment. It is often the case, in fact, that during the course of a construction project for a given low-enthalpy installation, we verify incompa tibilities with the local geologic and geothermic models, which, if inadequate during construction, can compromise the proper functioning of the installation and its subsequent operation. To this end, the ESBE method, which adheres to the governing environmental regulations, and which takes its cue from technical statutes within the sector, permits us to validate via verification, simulations and tests, the geothermic field probes used in construction in an objective and standardized manner, thereby joining and supporting the most recent protocols for energy certification of buildings (LEED 2010, CASACLIMA 2011, UE 20120/31 Directive). ESBE certification operates through a dedicated Certifying Entity represented by the REET unit (Renewable Energies and Environmental Technologies) of FBK (Bruno Kessler Foundation) of Trento. The results obtained by applying the ESBE method to two concrete cases, relative to two complex geothermic systems, demonstrate how this protocol is able to guarantee, beyond the correct execution in the field of geothermic probes, an effective coverage of the energy requirements of the building during construction adopting the best optimization measures for the probes in keeping with the local geological and geothermic model.

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Research on Fresh and Hardened Sealing Slurries with the Addition of Magnesium Regarding Thermal Conductivity for Energy Piles and Borehole Heat Exchangers

Energies ◽

10.3390/en14165119 ◽

2021 ◽

Vol 14 (16) ◽

pp. 5119

Author(s):

Tomasz Sliwa ◽

Tomasz Kowalski ◽

Dominik Cekus ◽

Aneta Sapińska-Śliwa

Keyword(s):

Thermal Conductivity ◽

Renewable Energy ◽

Heat Exchangers ◽

Geothermal Energy ◽

Cooling System ◽

Renewable Energy Sources ◽

Heat Pumps ◽

Cement Slurry ◽

Geological Conditions ◽

Borehole Heat Exchangers

Currently, renewable energy is increasingly important in the energy sector. One of the so-called renewable energy sources is geothermal energy. The most popular solution implemented by both small and large customers is the consumption of low-temperature geothermal energy using borehole heat exchanger (BHE) systems assisted by geothermal heat pumps. Such an installation can operate regardless of geological conditions, which makes it extremely universal. Borehole heat exchangers are the most important elements of this system, as their design determines the efficiency of the entire heating or heating-and-cooling system. Filling/sealing slurry is amongst the crucial structural elements. In borehole exchangers, reaching the highest possible thermal conductivity of the cement slurry endeavors to improve heat transfer between the rock mass and the heat carrier. The article presents a proposed design for such a sealing slurry. Powdered magnesium was used as an additive to the cement. The approximate cost of powdered magnesium is PLN 70–90 per kg (EUR 15–20/kg). Six different slurry formulations were tested. Magnesium flakes were used in designs A, B, C, and magnesium shavings in D, E and F. The samples differed in the powdered magnesium content BWOC (by weight of cement). The parameters of fresh and hardened sealing slurries were tested, focusing mainly on the thermal conductivity parameter. The highest thermal conductivity values were obtained in design C with the 45% addition of magnesium flakes BWOC.

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Simulation Analysis on the Heat Performance of Deep Borehole Heat Exchangers in Medium-Depth Geothermal Heat Pump Systems

Energies ◽

10.3390/en13030754 ◽

2020 ◽

Vol 13 (3) ◽

pp. 754 ◽

Cited By ~ 1

Author(s):

Jiewen Deng ◽

Qingpeng Wei ◽

Shi He ◽

Mei Liang ◽

Hui Zhang

Keyword(s):

Heat Transfer ◽

Heat Pump ◽

Heat Exchangers ◽

Geothermal Energy ◽

Heat Transfer Performance ◽

Deep Borehole ◽

Geothermal Heat ◽

Temperature Heat ◽

Geothermal Heat Pump ◽

Borehole Heat Exchangers

Deep borehole heat exchangers (DBHEs) extract heat from the medium-depth geothermal energy with the depth of 2–3 km and provide high-temperature heat source for the medium-depth geothermal heat pump systems (MD-GHPs). This paper focuses on the heat transfer performance of DBHEs, where field tests and simulation are conducted to analyze the heat transfer process and the influence factors. Results identify that the heat transfer performance is greatly influenced by geothermal properties of the ground, thermal properties and depth of DBHEs and operation parameters, which could be classified into external factors, internal factors and synergic adjustment. In addition, the long-term operation effects are analyzed with the simulation, results show that with inlet water temperature setting at 20 °C and flow rate setting at 6.0 kg/s, the average outlet water temperature only drops 0.99 °C and the average heat extraction drops 9.5% after 20-years operation. Therefore, it demonstrates that the medium-depth geothermal energy can serve as the high-temperature heat source for heat pump systems stably and reliably. The results from this study can be potentially used to guide the system design and optimization of DBHEs.

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Retrofitting abandoned petroleum wells as doublet deep borehole heat exchangers for geothermal energy production—a numerical investigation

Renewable Energy ◽

10.1016/j.renene.2021.05.061 ◽

2021 ◽

Author(s):

Xincheng Hu ◽

Jonathan Banks ◽

Yunting Guo ◽

Wei Victor Liu

Keyword(s):

Numerical Investigation ◽

Heat Exchangers ◽

Geothermal Energy ◽

Energy Production ◽

Deep Borehole ◽

Petroleum Wells ◽

Borehole Heat Exchangers

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Reviewing the Modeling Aspects and Practices of Shallow Geothermal Energy Systems

Energies ◽

10.3390/en13164273 ◽

2020 ◽

Vol 13 (16) ◽

pp. 4273

Author(s):

Paul Christodoulides ◽

Ana Vieira ◽

Stanislav Lenart ◽

João Maranha ◽

Gregor Vidmar ◽

...

Keyword(s):

Thermal Behavior ◽

Heat Exchangers ◽

Geothermal Energy ◽

Numerical Models ◽

Energy Systems ◽

Mechanical Analysis ◽

Design Guidelines ◽

Infinite Length ◽

Practical Applications ◽

Shallow Geothermal Energy

Shallow geothermal energy systems (SGES) may take different forms and have recently taken considerable attention due to energy geo-structures (EGS) resulting from the integration of heat exchange elements in geotechnical structures. Still, there is a lack of systematic design guidelines of SGES. Hence, in order to contribute towards that direction, the current study aims at reviewing the available SGES modeling options along with their various aspects and practices. This is done by first presenting the main analytical and numerical models and methods related to the thermal behavior of SGES. Then, the most important supplementary factors affecting such modeling are discussed. These include: (i) the boundary conditions, in the form of temperature variation or heat flow, that majorly affect the predicted thermal behavior of SGES; (ii) the spatial dimensions that may be crucial when relaxing the infinite length assumption for short heat exchangers such as energy piles (EP); (iii) the determination of SGES parameters that may need employing specific techniques to overcome practical difficulties; (iv) a short-term vs. long-term analysis depending on the thermal storage characteristics of GHE of different sizes; (v) the influence of groundwater that can have a moderating effect on fluid temperatures in both heating and cooling modes. Subsequently, thermo-mechanical interactions modeling issues are addressed that may be crucial in EGS that exhibit a dual functioning of heat exchangers and structural elements. Finally, a quite lengthy overview of the main software tools related to thermal and thermo-hydro-mechanical analysis of SGES that may be useful for practical applications is given. A unified software package incorporating all related features of all SGES may be a future aim.

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