References of "Radioti, Georgia"
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See detailEffect of undisturbed ground temperature on the design of closed-loop geothermal systems: A case study in a semi-urban environment
Radioti, Georgia ULiege; Sartor, Kevin ULiege; Charlier, Robert ULiege et al

in Applied Energy (2017)

This paper presents temperature measurements in four Borehole Heat Exchangers (BHEs), equipped with fiber optics and located in a semi-urban environment (campus of the University of Liege, Belgium). A 3D ... [more ▼]

This paper presents temperature measurements in four Borehole Heat Exchangers (BHEs), equipped with fiber optics and located in a semi-urban environment (campus of the University of Liege, Belgium). A 3D numerical model is also presented to simulate the heat loss from the surrounding structures into the subsurface. The mean undisturbed ground temperature was estimated from data during the preliminary phase of a thermal response test (water circulation in the pipe loops), as well as from borehole logging measurements. The measurements during water circulation can significantly overestimate the ground temperature (up to 1.7 C in this case study) for high ambient air temperature during the test, resulting in an overestimation of the maximum extracted power and of the heat pump coefficient of performance (COP). To limit the error in the COP and the extracted power to less than 5%, the error in the undisturbed temperature estimation should not exceed ±1.5 °C and ±0.6 °C respectively. In urbanised areas, configurations of short BHEs (length < 40 m) could be economically advantageous (decreased installation and operation costs) compared to long BHEs, especially for temperature gradient lower than 0.05 °C/m. [less ▲]

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See detailShallow geothermal energy: effect of in-situ conditions on borehole heat exchanger design and performance
Radioti, Georgia ULiege

Doctoral thesis (2016)

The in-situ conditions are critical for the performance of Borehole Heat Exchangers (BHEs). However, in practice they are often not adequately considered, overwhelming the potential of these systems. This ... [more ▼]

The in-situ conditions are critical for the performance of Borehole Heat Exchangers (BHEs). However, in practice they are often not adequately considered, overwhelming the potential of these systems. This thesis focuses on the accurate estimation of the in-situ characteristics and on their influence on the design and the behaviour of BHEs based on an in-situ study of an heterogeneous bedrock in a semi-urban environment (campus of the University of Liege, Liege, Belgium). The experimental site consists of four double-U BHEs, of about 100 m long, installed over a surface area of 32 m² and equipped with fiber optic cables. Several temperature measurements and Distributed Thermal Response Tests (DTRTs) were conducted in situ in a period of four years, including a long-duration DTRT (heating phase of 7 months), during which temperature was measured by the fiber optics in all the four boreholes. These measurements create a unique data set, that allows to investigate the BHE behaviour for longer heating periods, to study the effect of various factors on the temperature field evolution at the heterogeneous bedrock at the in-situ scale and to evaluate the contribution of temperature borehole logging to the optimisation of BHEs. The effect of urbanisation is studied based on the in-situ measurements and on 3D numerical modelling and its influence on the design is expressed in terms of the maximum extracted power. The subsurface characteristics are correlated with the measured fiber optic profiles and the potential of temperature borehole logging for optimising the design of BHEs in practise is presented. The accuracy of the thermal response test results in the case of insufficient test rig insulation is investigated and recommendations are provided regarding the interpretation of the data by the widely applied Infinite Line Source model. The in-situ measurements during the long-duration DTRT are presented and analysed, together with a 3D numerical model of the test. In this case-study, the possible variation of the effective thermal conductivity along the layers and the air temperature variations during the test do not seem to have a dominant effect on the BHE behaviour during the whole heating phase. The controlling factors for the temperature field evolution in the surrounding rock mass (bedrock heterogeneity, the air temperature variations, the distance to the heating source and the thermal effects at the borehole bottom end) are detected in the measured profiles and their influence is discussed. [less ▲]

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See detailFormulation of a 1D finite element of heat exchanger for accurate modelling of the grouting behaviour: Application to cyclic thermal loading
Cerfontaine, Benjamin ULiege; Radioti, Georgia ULiege; Collin, Frédéric ULiege et al

in Renewable Energy : An International Journal (2016), 96

This paper presents a comprehensive formulation of a finite element for the modelling of borehole heat exchangers. This work focuses on the accurate modelling of the grouting and the field of temperature ... [more ▼]

This paper presents a comprehensive formulation of a finite element for the modelling of borehole heat exchangers. This work focuses on the accurate modelling of the grouting and the field of temperature near a single borehole. Therefore the grouting of the BHE is explicitly modelled. The purpose of this work is to provide tools necessary to the further modelling of thermo-mechanical couplings. The finite element discretises the classical governing equation of advection-diffusion of heat within a 1D pipe connected to ground nodes. Petrov-Galerkin weighting functions are used to avoid numerical disturbances. The formulation is able to capture highly transient and steady-state phenomena. The proposed finite element is validated with respect to analytical solutions. An example consisting of a 100 m depth U-pipe is finally simulated. A first continuous heating simulation highlights the nonsymmetric distribution of temperature inside and near the borehole. An estimation of the error on the results as a function of the resolution parameters is also carried out. Finally simulations of cyclic thermal loading exhibit the need to take into account all daily variations if the grouting behaviour must be modelled. This is true especially in case of freeze-thaw damaging risk. [less ▲]

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See detailHeterogeneous bedrock investigation for a closed-loop geothermal system: A case study
Radioti, Georgia ULiege; Delvoie, Simon ULiege; Charlier, Robert ULiege et al

in Geothermics (2016)

This paper investigates bedrock heterogeneity by applying three different geophysical approaches, in order to study the long-term behaviour and the interaction between closed-loop geothermal systems. The ... [more ▼]

This paper investigates bedrock heterogeneity by applying three different geophysical approaches, in order to study the long-term behaviour and the interaction between closed-loop geothermal systems. The investigated site consists of four boreholes equipped with geothermal pipes on the campus of University of Liege, Belgium. The first approach includes acoustic borehole imaging, gamma-ray logging and cuttings observation and results to a detailed fracture characterisation, rock identification and layer dip angle determination. The second approach consists of measuring the thermal conductivity of cuttings at the laboratory. Study of cuttings thermal conductivity measurements can contribute to bedrock heterogeneity knowledge concerning the transition of one formation to another and the layer dipping. The third approach is based on high-resolution temperature profiles, measured during the hardening of the grouting material and the recovery phase of a Distributed Thermal Response Test. Through this approach a correlation of the temperature profiles to the geological characteristics of the surrounding bedrock is identified. The analysis of this correlation can provide information on fractured zones, alternation of different rock types and layering dipping. This latter approach can be easily applied on closed-loop geothermal systems to characterise the bedrock and investigate its heterogeneity as well as contribute to the their long-term behaviour prediction and to the optimisation of their efficiency. [less ▲]

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See detailWe gme P08: Fiber-optic temperature profiles analysis for closed-loop geothermal systems-a case study
Radioti, Georgia ULiege; Delvoie, Simon ULiege; Sartor, Kevin ULiege et al

in Second EAGE Workshop on Geomechanics and Energy: The ground as energy source and storage (2015, October)

In order to study the behaviour of shallow closed-loop geothermal systems four borehole heat exchangers equipped with fiber optics were installed on the campus of the University of Liege (Liege, Belgium ... [more ▼]

In order to study the behaviour of shallow closed-loop geothermal systems four borehole heat exchangers equipped with fiber optics were installed on the campus of the University of Liege (Liege, Belgium) over a surface area of 32m². This paper presents the analysis of continuous, high-resolution temperature profiles measured along the boreholes length. The undisturbed ground temperature measurements indicate heat loss from ground structures located close to the boreholes. A 3D numerical model is presented to reproduce the measured temperature profiles. Temperature profiles during hardening of the grouting material indicate extended fractured zones in the rock mass. Temperature measurements during the recovery phase of a Distributed Thermal Response Test indicate the succession of rock layers with different mineral content. The results are in good agreement with those of the borehole televiewer logging method. The presented analysis could provide information on bedrock heterogeneity, on the anisotropic thermal behaviour of the rock mass and on the ground temperature variations due to heat loss from ground structures. These information could significantly contribute to the long-term behaviour prediction of the geothermal system and the geothermal reservoir potential. [less ▲]

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See detailFractured bedrock investigation by using high-resolution borehole images and the Distributed Temperature Sensing technique
Radioti, Georgia ULiege; Delvoie, Simon ULiege; Radu, Jean-Pol ULiege et al

in ISRM Congress 2015 Proceedings - Int’l Symposium on Rock Mechanics (2015, May)

In order to investigate the fracturing of the bedrock and its possible heterogeneous distribution in situ, four boreholes equipped with double-U geothermal pipes of 100 m long were installed on the campus ... [more ▼]

In order to investigate the fracturing of the bedrock and its possible heterogeneous distribution in situ, four boreholes equipped with double-U geothermal pipes of 100 m long were installed on the campus of the University of Liege (Liege, Belgium) over a surface area of 32 m². The bedrock, which starts at a depth approximately of 8 m, is quite fractured and consists mainly of siltstone and shale interbedded with sandstone. Different geophysical methods are applied at two different phases, after drilling the boreholes and after injecting the grouting material. The first approach consists in lowering an ultrasonic borehole imager (borehole televiewer; Zemanek, Glenn, Norton, & Caldwell, 1970), an instrument that acts as an ultrasonic transducer and receiver, into the boreholes to obtain high-resolution, continuous images with 360° coverage of the local geology and fracturing. Moreover gamma-ray logs of the four boreholes are obtained and inclinometry is conducted. After drilling the boreholes fiber optic cables are attached along the pipe loops and the double-U pipes are installed inside the boreholes. Then the grouting material is injected. The second approach consists in measuring the temperature along the fibers by applying the Distributed Temperature Sensing technique (Soto, Sahu, Faralli, Bolognini, Di Pasquale, Nebendahl, & Rueck, 2007). A laser pulse is injected into the optical fiber and the temperature along the fiber is determined by the intensity of Raman stokes and anti-stokes reemitted signals. Temperature evolution is measured during hardening of the grouting material. Local maxima of the temperature curve are probably due to a local lower thermal conductivity and/or a local larger quantity of grouting material due to gathering of fractures. A detailed fracture characterisation (position, opening, orientation, dip angle) is obtained based on the acoustic signal travel time and amplitude. The fractures are characterised by the same dipping and orientation but significantly vary in number and location in the four boreholes, despite the close distance between them. Gamma-ray data and observation of the cuttings during drilling result in rock identification through depth as well as in determination of the layer dipping. The inclination of the four boreholes tends to be perpendicular to the dipping. The combination of the two geophysical methods as presented provides information useful for the hydro-thermo-mechanical behaviour of the bedrock. The contribution of the thermal behaviour of borehole heat exchangers to bedrock investigation will be further studied by conducting Distributed Thermal Response tests (Fujii, Okubo, & Itoi, 2006). During the tests we will measure the temperature variation thanks to the installed fiber optics. These data will allow us to correlate any anisotropic thermal behaviour to the geological characteristics. The available information could be used for a detailed numerical model. [less ▲]

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See detailThermal Response Test in Borehole Heat Exchangers Equipped with Fiber Optics
Radioti, Georgia ULiege; Charlier, Robert ULiege; Nguyen, Frédéric ULiege et al

in International Workshop on Geomechanics and Energy - The Ground as Energy source and Storage (2013, November 26)

Four double-U borehole heat exchangers (BHEs) 100m long are installed in the Sart-Tilman region (Liege, Belgium). The installation procedure and technical difficulties are presented. Fiber optic cables ... [more ▼]

Four double-U borehole heat exchangers (BHEs) 100m long are installed in the Sart-Tilman region (Liege, Belgium). The installation procedure and technical difficulties are presented. Fiber optic cables are attached along the length of one pipe loop in each BHE. Temperature is measured along the fibers based on the fiber optic distributed temperature sensing (DTS) technique. Thermal response test (TRT) is conducted in order to determine the rock thermal properties. The DTS instrument records the temperature evolution along the pipe loop during the TRT. Rock thermal conductivity through depth can be estimated based on the recorded data. A 3D model is developed using the finite element code LAGAMINE in order to simulate the TRT. The accuracy of the numerical model is improved by simulating the potential variation of the rock thermal conductivity. [less ▲]

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