Natural and Artificial Methods of Heat Resource Regeneration in Underground Thermal Energy Storages with Borehole Heat Exchangers

Abstract The energy sector is undergoing a fundamental transformation, with significant investment in low-carbon technologies to replace fossil-based systems. In densely populated urban areas, deep boreholes offer an alternative over shallow geothermal systems, which demand extensive surface area to attain large-scale heat production. This paper presents numerical calculations of the thermal energy that can be extracted from the medium-deep borehole heat exchangers of depths ranging from 600-3000 m. We applied the thermogeological parameters of three locations across Finland and tested two types of coaxial borehole heat exchangers to understand better the variables that affect heat production in low permeability crystalline rocks. For each depth, location, and heat collector type, we used a range of fluid flow rates to examine the correlation between thermal energy production and resulting outlet temperature. Our results indicate a trade-off between thermal energy production and outlet fluid temperature depending on the fluid flow rate, and that the vacuum-insulated tubing outperforms high-density polyethylene pipe in energy and temperature production. In addition, the results suggest that the local thermogeological factors impact heat production. Maximum energy production from a 600-m-deep well achieved 170 MWh/a, increasing to 330 MWh/a from a 1000-m-deep well, 980 MWh/a from a 2-km-deep well, and up to 1880 MWh/a from a 3-km-deep well. We demonstrate that understanding the interplay of the local geology, heat exchanger materials, and fluid circulation rates is necessary to maximize the potential of medium-deep geothermal boreholes as a reliable long-term baseload energy source.

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The Influence of the Ground Thermal Energy and Borehole Heat Exchangers Depth on the Efficiency of Heat Pump (GHSP) Systems in Moscow Geo-climatic Conditions

10.18178/ijmerr.9.4.570-575 ◽

2020 ◽

pp. 570-575

Author(s):

Gregory P. Vasilyev ◽

Victor F. Gornov ◽

Alexander N. Dmitriev ◽

Marina V. Kolesova

Keyword(s):

Heat Pump ◽

Thermal Energy ◽

Heat Exchangers ◽

Climatic Conditions ◽

Borehole Heat Exchangers

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EVALUATION OF CLIMATE CONDITIONS ON ROCK MASS ENERGY BALANCE IN THE VŠB-TU OSTRAVA RESEARCH POLYGONS

Biuletyn Państwowego Instytutu Geologicznego ◽

10.5604/01.3001.0009.4315 ◽

2016 ◽

pp. 1-8

Author(s):

Petr Bujok ◽

Martin Klempa ◽

Michal Porzer ◽

Nikola Janečková ◽

Adam Pytlik

Keyword(s):

Rock Mass ◽

Thermal Energy ◽

Heat Exchangers ◽

Heating System ◽

Heat Pumps ◽

Research Centre ◽

Climate Conditions ◽

Temperature Changes ◽

Research Fields ◽

Borehole Heat Exchangers

VŠB – Technical University of Ostrava (VŠB-TU Ostrava) has unique conditions for analysing temperature changes in the rock mass while borehole heat exchangers have been operational for a long time. The Auditory building is heated with a system of heat pumps (borehole heat exchangers). It is one of the largest such objects in the Czech Republic. The heat of the rock mass is provided by a system of technological boreholes. The research boreholes are used for monitoring temperature changes in the rock mass while using the Auditory’s heating system. The system for monitoring boreholes within the area of technological borehole activity is called Large Research Polygon (LRP). Apart from LRP, the university also possesses another research polygon – Small Research Polygon (SRP) located at a distance from the LRP near the Energy Research Centre (ERC). All boreholes performed within both research fields are equipped with sensors monitoring the temperature changes while the Auditory building is being heated (thermal energy is recovered from the rock mass in winter) or cooled (thermal energy is transmitted to the rock mass in summer). The main objective of the research carried out in both research fields is checking the functionality and efficiency of the entire system. Certain aspects of thermal energy recuperation from the rock mass are described. The paper is closed with the results of monitoring and calculation of temperature in the surface layers to about 20 m of depth.

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Finite Element Modeling of Geothermal Source of Heat Pump in Long-Term Operation

Energies ◽

10.3390/en13061341 ◽

2020 ◽

Vol 13 (6) ◽

pp. 1341 ◽

Cited By ~ 2

Author(s):

Elżbieta Hałaj ◽

Leszek Pająk ◽

Bartosz Papiernik

Keyword(s):

Heat Pump ◽

Thermal Energy ◽

Heat Exchangers ◽

Thermal Recovery ◽

Small Scale ◽

Term Operation ◽

Ground Source ◽

Space Cooling ◽

Borehole Heat Exchangers

Model simulation allows to present the time-varying temperature distribution of the ground source for heat pumps. A system of 25 double U-shape borehole heat exchangers (BHEs) in long-term operation and three scenarios were created. In these scenarios, the difference between balanced and non-balanced energy load was considered as well as the influence of the hydrogeological factors on the temperature of the ground source. The aim of the study was to compare different thermal regimes of BHEs operation and examine the influence of small-scale and short-time thermal energy storage on ground source thermal balance. To present the performance of the system according to geological and hydrogeological factors, a Feflow® software (MIKE Powered by DHI Software) was used. The temperature for the scenarios was visualized after 10 and 30 years of the system’s operation. In this paper, a case is presented in which waste thermal energy from space cooling applications during summer months was used to upgrade thermal performance of the ground (geothermal) source of a heat pump. The study shows differences in the temperature in the ground around different Borehole Heat Exchangers. The cold plume from the not-balanced energy scenario is the most developed and might influence the future installations in the vicinity. Moreover, seasonal storage can partially overcome the negative influence of the travel of a cold plume. The most exposed to freezing were BHEs located in the core of the cold plumes. Moreover, the influence of the groundwater flow on the thermal recovery of the several BHEs is visible. The proper energy load of the geothermal source heat pump installation is crucial and it can benefit from small-scale storage. After 30 years of operation, the minimum average temperature at 50 m depth in the system with waste heat from space cooling was 2.1 °C higher than in the system without storage and 1.6 °C higher than in the layered model in which storage was not applied.

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A New Method Based on Thermal Response Tests for Determining Effective Thermal Conductivity and Borehole Resistivity for Borehole Heat Exchangers

Energies ◽

10.3390/en12061072 ◽

2019 ◽

Vol 12 (6) ◽

pp. 1072 ◽

Cited By ~ 4

Author(s):

Aneta Sapińska-Sliwa ◽

Marc Rosen ◽

Andrzej Gonet ◽

Joanna Kowalczyk ◽

Tomasz Sliwa

Keyword(s):

Thermal Conductivity ◽

Effective Thermal Conductivity ◽

Thermal Energy ◽

Heat Exchangers ◽

Thermal Response ◽

New Method ◽

Thermal Resistivity ◽

Thermal Response Test ◽

Response Test ◽

Borehole Heat Exchangers

Research on borehole heat exchangers is described on the development of a method for the determination, based on thermal response tests, of the effective thermal conductivity and the thermal resistivity for borehole heat exchangers. This advance is important, because underground thermal energy storage increasingly consists of systems with a large number of borehole heat exchangers, and their effective thermal conductivities and thermal resistivities are significant parameters in the performance of the system (whether it contains a single borehole or a field of boreholes). Borehole thermal energy storages provide a particularly beneficial method for using ground energy as a clean thermal energy supply. This benefit is especially relevant in cities with significant smog in winter. Here, the authors describe, in detail, the development of a formula that is a basis for the thermal response test that is derived from Fourier’s Law, utilizing a new way of describing the basic parameters of the thermal response test, i.e., the effective thermal conductivity and the thermal resistivity. The new method is based on the resistivity equation, for which a solution giving a linear regression with zero directional coefficient is found. Experimental tests were performed and analyzed in support of the theory, with an emphasis on the interpretation differences that stem from the scope of the test.

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Borehole Heat Exchangers in aquifers: simulation of the grout material impact

Rendiconti online della Società Geologica Italiana ◽

10.3301/rol.2016.145 ◽

2016 ◽

Vol 41 ◽

pp. 268-271

Author(s):

Luca Alberti ◽

Adriana Angelotti ◽

Matteo Antelmi ◽

Ivana La Licata

Keyword(s):

Heat Exchangers ◽

Borehole Heat Exchangers

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Low enthalpy geothermal energy: borehole heat exchangers (BHE). Geological and geothermal supervision during active construction in support of the energy certification of buildings - ESBE certification plan

Acque Sotterranee-Italian Journal of Groundwater ◽

10.7343/as-009-12-0028 ◽

2012 ◽

Cited By ~ 1

Author(s):

Lorenzo Cadrobbi ◽

Fioroni Daniele ◽

Alessandro Bozzoli

Keyword(s):

Energy Conservation ◽

Heat Exchangers ◽

Energy Efficient ◽

Geothermal Energy ◽

Energy Requirements ◽

Effective Coverage ◽

Correct Execution ◽

Environmental Technologies ◽

Borehole Heat Exchangers ◽

Ongoing Monitoring

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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