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A novel flow-controlled (FC) thermal response test (TRT) system is introduced to resolve the recently addressed inconsistency between the constant heat flux (CHF) and constant temperature (CT) TRTs. FC-TRT allows us to keep both inlet and outlet temperatures constant and improve the accuracy of CT-TRT. Using the FC-TRT system, four types of TRT experiments are performed, providing CT, CHF, and constant inlet temperature conditions, besides the novel one keeping both temperature and heat flux constant. Thermal conductivities from these TRT measurements are compared, and a good agreement is observed. FC-TRT offers higher accuracy and various TRT applications in one platform.

L’énergie géothermique est une alternative à développer dans le cadre d’un futur mix énergétique décarboné au Québec. Les ressources géothermiques du bassin sédimentaire des Basses-Terres du Saint Laurent (BTSL) ont fait l’objet d’études visant à déterminer le potentiel de génération d’électricité à partir de systèmes géothermiques stimulés. Malgré que de tels projets ne soient pas pour le moment rentables, ces études ont déterminé l’existence de quatre potentiels sites d’anomalies thermiques positives au sein des BTSL. L’objectif de ce travail consiste à apporter une évaluation fiable du potentiel géothermique de ces anomalies en quantifiant les incertitudes liées à l’évaluation du flux de chaleur et des ressources géothermiques de profondeurs dites intermédiaires dans une optique de production de chaleur. À l’aide des données de forages profonds, les gammes de valeurs du gradient géothermique, du flux de chaleur en surface, et des ressources géothermiques ont été estimées en tenant compte de la variabilité des propriétés thermiques des roches à l’échelle du site. Les résultats ont montré que deux sites en particulier présentent un flux de chaleur supérieur aux moyennes attendues dans le bassin. Il s’agit des sites d’Arthabaska et de Brossard dont les valeurs moyennes atteignent 74,2 mW m⁻² et 108,8 mW m⁻², respectivement. Situé sur la Rive-Sud de Montréal où les besoins énergétiques sont importants, le site de Brossard suscite un grand intérêt pour l’implémentation de futures opérations géothermiques de moyenne profondeur. Cette zone a donc été étudiée plus en détail à partir de données superficielles issues de tests de réponse thermique et l’existence d’une anomalie thermique importante à Brossard a été confirmée. Dans la perspective d’implémenter une exploitation géothermique à Brossard, un nouveau puits devra être foré en ciblant des profondeurs différentes selon le type de ressources recherchées. Par exemple, pour du chauffage de bâtiments et autres applicatio

L’énergie géothermique est une alternative à développer dans le cadre d’un futur mix énergétique décarboné au Québec. Les ressources géothermiques du bassin sédimentaire des Basses-Terres du Saint Laurent (BTSL) ont fait l’objet d’études visant à déterminer le potentiel de génération d’électricité à partir de systèmes géothermiques stimulés. Malgré que de tels projets ne soient pas pour le moment rentables, ces études ont déterminé l’existence de quatre potentiels sites d’anomalies thermiques positives au sein des BTSL. L’objectif de ce travail consiste à apporter une évaluation fiable du potentiel géothermique de ces anomalies en quantifiant les incertitudes liées à l’évaluation du flux de chaleur et des ressources géothermiques de profondeurs dites intermédiaires dans une optique de production de chaleur. À l’aide des données de forages profonds, les gammes de valeurs du gradient géothermique, du flux de chaleur en surface, et des ressources géothermiques ont été estimées en tenant compte de la variabilité des propriétés thermiques des roches à l’échelle du site. Les résultats ont montré que deux sites en particulier présentent un flux de chaleur supérieur aux moyennes attendues dans le bassin. Il s’agit des sites d’Arthabaska et de Brossard dont les valeurs moyennes atteignent 74,2 mW m⁻² et 108,8 mW m⁻², respectivement. Situé sur la Rive-Sud de Montréal où les besoins énergétiques sont importants, le site de Brossard suscite un grand intérêt pour l’implémentation de futures opérations géothermiques de moyenne profondeur. Cette zone a donc été étudiée plus en détail à partir de données superficielles issues de tests de réponse thermique et l’existence d’une anomalie thermique importante à Brossard a été confirmée. Dans la perspective d’implémenter une exploitation géothermique à Brossard, un nouveau puits devra être foré en ciblant des profondeurs différentes selon le type de ressources recherchées. Par exemple, pour du chauffage de bâtiments et autres applicatio

[ES] El presente proyecto estudia y caracteriza la influencia de utilizar materiales de cambio de fase, PCMs, como parte del relleno de una zanja para una instalación geotérmica de poca profundidad horizontal. Para ello, se han realizado dos instalaciones de iguales características, en el laboratorio geotérmico de la Universidad Politécnica de Valencia. Las zanjas se han rellenado con materiales diferentes, una con material de relleno común y otra con los mismos materiales, pero se ha añadido un porcentaje de PCM, para comprobar si su uso mejora la eficiencia térmica del intercambiador geotérmico. Se han utilizado en cada zanja 4 paneles de captación geotérmica compactos, y para poder llevar a cabo el análisis se han puesto 21 sondas que registran la temperatura, repartidas en cada zanja en los mismos puntos para ambas, además de disponer del sistema de registro de datos del laboratorio. En primer lugar, se ha introducido agua en los intercambiadores y se ha registrado la temperatura durante un período de tiempo. Luego, se ha hecho una recirculación, y tras esto, se ha pasado a la inyección de calor, mediante la inserción de agua a alta temperatura con un valor constante durante aproximadamente 5 días. Finalmente, se ha parado la inyección térmica y registrado la disipación de calor. Durante todos estos períodos se han almacenado datos de las temperaturas en intervalos de tiempo de alrededor de 1 minuto. Para analizar el registro de las temperaturas se ha utilizado Matlab, en primer lugar, se ha visualizado la evolución de la temperatura en cada sonda en el tiempo y en la entrada y salida. Posteriormente, se ha hecho una interpolación del registro de todas las sondas para todo el intervalo de tiempos y espacio, de forma que se ha visualizado la distribución de temperaturas en los paneles y la zanja durante la inserción de calor. Finalmente, mediante los datos registrados durante la inserción de calor se ha obtenido la resistencia térmica del pozo, que determina la e, [EN] This project studies and characterizes the influence of using a phase change material, PCM, as part of the grouting of a trench for a horizontal shallow geothermal installation. To do this, two installations with the same characteristics have been made, in the geothermal laboratory at the Polytechnic University of Valencia. The trenches have been filled with different materials, one with common grouting and the other with the same materials, but a percentage of PCM has been added to it, to check if its use improves the thermal efficiency of the geothermal heat exchanger. Four compact geothermal panels have been used in each trench, and to carry out the analysis 21 probes that record the temperature have been installed in each trench at the same points for both, in addition to the system for recording data that the laboratory already had. In first place, water has been introduced into the exchangers and the temperature has been recorded over a period. Then, a recirculation has been made, and after this, the next thing done was the injection of heat, by inserting water at high temperature with a constant value for approximately 5 days. Finally, thermal injection has been stopped and the heat dissipation has been recorded. During all these periods, temperature data has been stored intervals of about 1 minute. To analyze the temperature record, Matlab has been used, firstly, the evolution of the temperature in each probe and in the input and output over time has been represented. Later, an interpolation of the record of all the probes has been made for the entire time interval and space, so with that the distribution of temperatures in the panels and the trench during the insertion of heat has been visualized. Finally, with the data recorded during the insertion of heat, the thermal resistance of the borehole has been obtained, which determines the efficiency of the exchanger. The cost of the installation to carry out this analysis has been quantified by a budget.

[ES] El presente proyecto estudia y caracteriza la influencia de utilizar materiales de cambio de fase, PCMs, como parte del relleno de una zanja para una instalación geotérmica de poca profundidad horizontal. Para ello, se han realizado dos instalaciones de iguales características, en el laboratorio geotérmico de la Universidad Politécnica de Valencia. Las zanjas se han rellenado con materiales diferentes, una con material de relleno común y otra con los mismos materiales, pero se ha añadido un porcentaje de PCM, para comprobar si su uso mejora la eficiencia térmica del intercambiador geotérmico. Se han utilizado en cada zanja 4 paneles de captación geotérmica compactos, y para poder llevar a cabo el análisis se han puesto 21 sondas que registran la temperatura, repartidas en cada zanja en los mismos puntos para ambas, además de disponer del sistema de registro de datos del laboratorio. En primer lugar, se ha introducido agua en los intercambiadores y se ha registrado la temperatura durante un período de tiempo. Luego, se ha hecho una recirculación, y tras esto, se ha pasado a la inyección de calor, mediante la inserción de agua a alta temperatura con un valor constante durante aproximadamente 5 días. Finalmente, se ha parado la inyección térmica y registrado la disipación de calor. Durante todos estos períodos se han almacenado datos de las temperaturas en intervalos de tiempo de alrededor de 1 minuto. Para analizar el registro de las temperaturas se ha utilizado Matlab, en primer lugar, se ha visualizado la evolución de la temperatura en cada sonda en el tiempo y en la entrada y salida. Posteriormente, se ha hecho una interpolación del registro de todas las sondas para todo el intervalo de tiempos y espacio, de forma que se ha visualizado la distribución de temperaturas en los paneles y la zanja durante la inserción de calor. Finalmente, mediante los datos registrados durante la inserción de calor se ha obtenido la resistencia térmica del pozo, que determina la e, [EN] This project studies and characterizes the influence of using a phase change material, PCM, as part of the grouting of a trench for a horizontal shallow geothermal installation. To do this, two installations with the same characteristics have been made, in the geothermal laboratory at the Polytechnic University of Valencia. The trenches have been filled with different materials, one with common grouting and the other with the same materials, but a percentage of PCM has been added to it, to check if its use improves the thermal efficiency of the geothermal heat exchanger. Four compact geothermal panels have been used in each trench, and to carry out the analysis 21 probes that record the temperature have been installed in each trench at the same points for both, in addition to the system for recording data that the laboratory already had. In first place, water has been introduced into the exchangers and the temperature has been recorded over a period. Then, a recirculation has been made, and after this, the next thing done was the injection of heat, by inserting water at high temperature with a constant value for approximately 5 days. Finally, thermal injection has been stopped and the heat dissipation has been recorded. During all these periods, temperature data has been stored intervals of about 1 minute. To analyze the temperature record, Matlab has been used, firstly, the evolution of the temperature in each probe and in the input and output over time has been represented. Later, an interpolation of the record of all the probes has been made for the entire time interval and space, so with that the distribution of temperatures in the panels and the trench during the insertion of heat has been visualized. Finally, with the data recorded during the insertion of heat, the thermal resistance of the borehole has been obtained, which determines the efficiency of the exchanger. The cost of the installation to carry out this analysis has been quantified by a budget.

[ES] El presente proyecto estudia y caracteriza la influencia de utilizar materiales de cambio de fase, PCMs, como parte del relleno de una zanja para una instalación geotérmica de poca profundidad horizontal. Para ello, se han realizado dos instalaciones de iguales características, en el laboratorio geotérmico de la Universidad Politécnica de Valencia. Las zanjas se han rellenado con materiales diferentes, una con material de relleno común y otra con los mismos materiales, pero se ha añadido un porcentaje de PCM, para comprobar si su uso mejora la eficiencia térmica del intercambiador geotérmico. Se han utilizado en cada zanja 4 paneles de captación geotérmica compactos, y para poder llevar a cabo el análisis se han puesto 21 sondas que registran la temperatura, repartidas en cada zanja en los mismos puntos para ambas, además de disponer del sistema de registro de datos del laboratorio. En primer lugar, se ha introducido agua en los intercambiadores y se ha registrado la temperatura durante un período de tiempo. Luego, se ha hecho una recirculación, y tras esto, se ha pasado a la inyección de calor, mediante la inserción de agua a alta temperatura con un valor constante durante aproximadamente 5 días. Finalmente, se ha parado la inyección térmica y registrado la disipación de calor. Durante todos estos períodos se han almacenado datos de las temperaturas en intervalos de tiempo de alrededor de 1 minuto. Para analizar el registro de las temperaturas se ha utilizado Matlab, en primer lugar, se ha visualizado la evolución de la temperatura en cada sonda en el tiempo y en la entrada y salida. Posteriormente, se ha hecho una interpolación del registro de todas las sondas para todo el intervalo de tiempos y espacio, de forma que se ha visualizado la distribución de temperaturas en los paneles y la zanja durante la inserción de calor. Finalmente, mediante los datos registrados durante la inserción de calor se ha obtenido la resistencia térmica del pozo, que determina la e, [EN] This project studies and characterizes the influence of using a phase change material, PCM, as part of the grouting of a trench for a horizontal shallow geothermal installation. To do this, two installations with the same characteristics have been made, in the geothermal laboratory at the Polytechnic University of Valencia. The trenches have been filled with different materials, one with common grouting and the other with the same materials, but a percentage of PCM has been added to it, to check if its use improves the thermal efficiency of the geothermal heat exchanger. Four compact geothermal panels have been used in each trench, and to carry out the analysis 21 probes that record the temperature have been installed in each trench at the same points for both, in addition to the system for recording data that the laboratory already had. In first place, water has been introduced into the exchangers and the temperature has been recorded over a period. Then, a recirculation has been made, and after this, the next thing done was the injection of heat, by inserting water at high temperature with a constant value for approximately 5 days. Finally, thermal injection has been stopped and the heat dissipation has been recorded. During all these periods, temperature data has been stored intervals of about 1 minute. To analyze the temperature record, Matlab has been used, firstly, the evolution of the temperature in each probe and in the input and output over time has been represented. Later, an interpolation of the record of all the probes has been made for the entire time interval and space, so with that the distribution of temperatures in the panels and the trench during the insertion of heat has been visualized. Finally, with the data recorded during the insertion of heat, the thermal resistance of the borehole has been obtained, which determines the efficiency of the exchanger. The cost of the installation to carry out this analysis has been quantified by a budget.

[ES] El presente proyecto estudia y caracteriza la influencia de utilizar materiales de cambio de fase, PCMs, como parte del relleno de una zanja para una instalación geotérmica de poca profundidad horizontal. Para ello, se han realizado dos instalaciones de iguales características, en el laboratorio geotérmico de la Universidad Politécnica de Valencia. Las zanjas se han rellenado con materiales diferentes, una con material de relleno común y otra con los mismos materiales, pero se ha añadido un porcentaje de PCM, para comprobar si su uso mejora la eficiencia térmica del intercambiador geotérmico. Se han utilizado en cada zanja 4 paneles de captación geotérmica compactos, y para poder llevar a cabo el análisis se han puesto 21 sondas que registran la temperatura, repartidas en cada zanja en los mismos puntos para ambas, además de disponer del sistema de registro de datos del laboratorio. En primer lugar, se ha introducido agua en los intercambiadores y se ha registrado la temperatura durante un período de tiempo. Luego, se ha hecho una recirculación, y tras esto, se ha pasado a la inyección de calor, mediante la inserción de agua a alta temperatura con un valor constante durante aproximadamente 5 días. Finalmente, se ha parado la inyección térmica y registrado la disipación de calor. Durante todos estos períodos se han almacenado datos de las temperaturas en intervalos de tiempo de alrededor de 1 minuto. Para analizar el registro de las temperaturas se ha utilizado Matlab, en primer lugar, se ha visualizado la evolución de la temperatura en cada sonda en el tiempo y en la entrada y salida. Posteriormente, se ha hecho una interpolación del registro de todas las sondas para todo el intervalo de tiempos y espacio, de forma que se ha visualizado la distribución de temperaturas en los paneles y la zanja durante la inserción de calor. Finalmente, mediante los datos registrados durante la inserción de calor se ha obtenido la resistencia térmica del pozo, que determina la e, [EN] This project studies and characterizes the influence of using a phase change material, PCM, as part of the grouting of a trench for a horizontal shallow geothermal installation. To do this, two installations with the same characteristics have been made, in the geothermal laboratory at the Polytechnic University of Valencia. The trenches have been filled with different materials, one with common grouting and the other with the same materials, but a percentage of PCM has been added to it, to check if its use improves the thermal efficiency of the geothermal heat exchanger. Four compact geothermal panels have been used in each trench, and to carry out the analysis 21 probes that record the temperature have been installed in each trench at the same points for both, in addition to the system for recording data that the laboratory already had. In first place, water has been introduced into the exchangers and the temperature has been recorded over a period. Then, a recirculation has been made, and after this, the next thing done was the injection of heat, by inserting water at high temperature with a constant value for approximately 5 days. Finally, thermal injection has been stopped and the heat dissipation has been recorded. During all these periods, temperature data has been stored intervals of about 1 minute. To analyze the temperature record, Matlab has been used, firstly, the evolution of the temperature in each probe and in the input and output over time has been represented. Later, an interpolation of the record of all the probes has been made for the entire time interval and space, so with that the distribution of temperatures in the panels and the trench during the insertion of heat has been visualized. Finally, with the data recorded during the insertion of heat, the thermal resistance of the borehole has been obtained, which determines the efficiency of the exchanger. The cost of the installation to carry out this analysis has been quantified by a budget.

[EN] The determination of ground thermal properties is essential to design competitive commercial ground source heat pump systems. A thermal response test (TRT) carried out on site allows the determination of both the conductivity of the ground and the borehole thermal resistance by means of analytical approaches, which require several simplifying assumptions as well as TRT durations of at least fifty hours and constant heat injection. In this context, a detailed dynamic numerical model of the borehole can help reducing both the uncertainties, associated with these simplifying assumptions, and the required test duration. This paper presents a TRNSYS tool to obtain the grout and ground thermal properties by means of a parameter estimation technique in conjunction with a two-dimensional dynamic numerical model, the B2G model, which is able to provide accurate results with a much shorter testing time and without the necessity of a constant heat injection. The methodology to estimate the borehole and ground characteristics has been validated thanks to the analysis of a set of experimental TRTs for U-pipe vertical boreholes carried out in different type of soils and borehole geometries. Results show that, for the analysed tests, it is possible to obtain an accurate and fast estimation of the ground thermal conductivity with reductions of the necessary TRT duration of up to a 70%, with a total uncertainty between +/- 10% and +/- 18%, considering not only the uncertainty introduced by the reduction of the test duration, but also the main sources of uncertainty.

Thermal response tests are used to estimate the thermal properties of the ground and the borehole heat exchanger being tested. They are thus important for the design of borehole thermal energy storages and ground source heat pump systems. In this study, a theoretical framework is proposed in order to investigate if noise on the heat rate leads to a bias in the parameter estimation. Under the sole assumption of a linear time-invariant system and the use of the sum of squared errors as cost function, it is shown analytically that estimates are in fact biased when the heat rate is corrupted by noise. To understand how large this bias can be, a Monte-Carlo study is performed. It includes more than 126,000 simulations with different noises, thermal parameters and heat rate profiles. Negative biases as high as -0.44 W/(m K) (11%) and -11.10(-3) m K/W (4.1%) are observed for the thermal conductivity and borehole thermal resistance estimates, respectively. In addition, the parameter estimation is stochastic due to randomness of measurement noises. This cannot be ignored since only one thermal response test is performed, in general. Population of estimates with 95% confidence intervals as large as 1.0 W/(m K) (25%) and 24.10(-3) m K/W (9.4%) appear in this study. Although the bias and confidence intervals are not significant in all simulated cases, they cannot be generally disregarded and one should therefore be mindful of this potential issue when analyzing thermal response tests. An observed trend is that the confidence intervals and bias are higher for higher parameter values, with a particular dependency on thermal conductivity. To reduce the bias and spread of the estimates, having larger heat rate per meter appears to be a good strategy. Having a higher sampling frequency and/or longer tests might also help, but only in reducing the spread of the estimates, not the bias., QC 20211105

The variability of ground thermal conductivity, based on underground conditions, is often ignored during the design of ground-source heat pump systems. This study shows a field evidence of such site-scale variations through thermal response tests in eight borehole heat exchangers aligned at a site on a terrace along the foothills of mountains in northern Japan. Conventional analysis of the overall ground thermal conductivity along the total installation length finds that the value at one borehole heat exchanger is 2.5 times that at the other seven boreholes. History matching analysis of underground distributed temperature measurements generates vertical partial ground thermal conductivity data for four depth layers. Based on the moving line heat source theory, the partial values are generally within a narrow range expected for gravel deposits. Darcy velocities of groundwater are estimated to be 74-204 m/y at the borehole with high conductivity, increasing in the shallow layers above a depth of 41 m. In contrast, the velocities at the other seven boreholes are one-to-two orders of magnitude smaller with no trend. These high and low velocity values are considered for the topography and permeability. However, the relatively slow groundwater velocities might not apparently increase the partial conductivity.

Actual thermal response tests, used to estimate the subsurface thermal conductivity in the geothermal domain, do not provide any estimate on the velocity of the groundwater flow and its orientation. These parameters are important for sizing geothermal borefield, since they influence the heat transfer around a geothermal borehole and the surrounding ground. To correct this shortcoming, a conceptual test has been developed in which heating cable sections inject heat in a borehole. Three temperature probes are strategically located at the borehole edge. This paper applies inverse heat transfer strategies to this thermal response test concept in order to identify the ground thermal conductivity, as well as the groundwater flow velocity and its direction. The suggested thermal response test and parameters estimation methodology are detailed. The influence of initial guessed values for the three unknown parameters was also studied. The work presented in this paper was carried out by numerical simulations.

Current thermal response tests, used to estimate the subsurface thermal conductivity in the geothermal domain, are not designed to take into account groundwater flows. To measure the flow parameters, a new concept has been developed. Heating cables are installed within a borehole in contact to the formation, with three temperature probes strategically located at the edge of the borehole. Study of the evolution of temperature for each probe during both a heat injection phase and a recovery period allows determining ground thermal conductivity, groundwater flow velocity and orientation. Numerical simulations have been used to validate the proposed concept and establish its limits.

The variability of ground thermal conductivity, based on underground conditions, is often ignored during the design of ground-source heat pump systems. This study shows a field evidence of such site-scale variations through thermal response tests in eight borehole heat exchangers aligned at a site on a terrace along the foothills of mountains in northern Japan. Conventional analysis of the overall ground thermal conductivity along the total installation length finds that the value at one borehole heat exchanger is 2.5 times that at the other seven boreholes. History matching analysis of underground distributed temperature measurements generates vertical partial ground thermal conductivity data for four depth layers. Based on the moving line heat source theory, the partial values are generally within a narrow range expected for gravel deposits. Darcy velocities of groundwater are estimated to be 74-204 m/y at the borehole with high conductivity, increasing in the shallow layers above a depth of 41 m. In contrast, the velocities at the other seven boreholes are one-to-two orders of magnitude smaller with no trend. These high and low velocity values are considered for the topography and permeability. However, the relatively slow groundwater velocities might not apparently increase the partial conductivity.

A methodology for the determination of lithology-based thermal conductivities at a regional scale is proposed, assigning a saturated and unsaturated thermal conductivity to each stratigraphic unit encountered in the region. Such a methodology is paramount for GIS-supported mapping of shallow geothermal energy at a regional scale. The analysis is primarily based on the interpretation of thermal response tests (TRT), assuming that the thermal conductivity determined during TRT is a thickness-weighted average of the individual thermal conductivity of each stratigraphic unit constituting the ground along a ground heat exchanger (GHE). Enhanced thermal response tests, reference geological material-based thermal conductivities and laboratory optical scanning tests achieved on remolded specimen from drilling cuttings are used to validate the results. The relevance of the methodology is illustrated through its application to the Brussels-Capital Region (Belgium), and consistent saturated and unsaturated thermal conductivities are obtained for each stratigraphic unit. An uncertainty analysis on the thermal conductivity is proposed, and its impact on the design of GHE is discussed. In most cases, the relative error on the ground thermal conductivity is lower than 10 %, and its impact on GHE length remains limited., SCOPUS: ar.j, info:eu-repo/semantics/published

This paper presents a new parameter identification (PI) algorithm for estimating effective and detailed thermal parameters of ground source heat pump systems using data obtained from the well-known thermal response test. The PI comprises an iterative scheme coupling a semi-analytical forward model to an inverse model. The forward model is formulated based on the spectral element method to simulate transient 3D heat flow in ground source heat pump (GSHP) systems, and the inverse model is formulated based on the interior-point optimization method to minimize the system objective function. Compared to existing interpretation tools for the thermal response test, the proposed PI algorithm has several advanced features, including: it can handle fluctuating heat pump power and inlet temperatures; interpret data obtained from multiple heat injection or extraction signals; produce accurate backcalculation for short and long duration experiments; and handle multilayer systems. The PI algorithm is tested against synthesized data, using a wide range of random noise, and versus an available laboratory experiment. The computational results show that the PI algorithm is accurate, stable and exhibiting relatively high convergence rate., Applied Mechanics

A new practical method for thermal response test (TRT) is proposed herein to estimate the groundwater velocity and effective thermal conductivity of geological zones. The relaxation time of temperature (RTT) is applied to determine the depths of the zones. The RTT is the moment when the temperature in the borehole recovers to a certain level compared with that when the heating is stopped. The heat exchange rates of the zones are calculated from the vertical temperature profile measured by the optical-fiber distributed temperature sensors located in the supply and return sides of a U-tube. Finally, the temperature increments at the end time of the TRT are calculated according to the groundwater velocities and the effective thermal conductivity using the moving line source theory applied to the calculated heat exchange rates. These results are compared with the average temperature increment data measured from each zone, and the best-fitting value yields the groundwater velocities for each zone. Results show that the groundwater velocities for each zone are 2750, 58, and 0 m/y, whereas the effective thermal conductivities are 2.4, 2.4, and 2.1 W/(m center dot K), respectively. The proposed methodology is evaluated by comparing it with the realistic long-term operation data of a ground source heat pump (GSHP) system in Kazuno City, Japan. The temperature error between the calculated results and measured data is 6.4% for two years. Therefore, the proposed methodology is effective for estimating the long-term performance analysis of GSHP systems.

A new practical method for thermal response test (TRT) is proposed herein to estimate the groundwater velocity and effective thermal conductivity of geological zones. The relaxation time of temperature (RTT) is applied to determine the depths of the zones. The RTT is the moment when the temperature in the borehole recovers to a certain level compared with that when the heating is stopped. The heat exchange rates of the zones are calculated from the vertical temperature profile measured by the optical-fiber distributed temperature sensors located in the supply and return sides of a U-tube. Finally, the temperature increments at the end time of the TRT are calculated according to the groundwater velocities and the effective thermal conductivity using the moving line source theory applied to the calculated heat exchange rates. These results are compared with the average temperature increment data measured from each zone, and the best-fitting value yields the groundwater velocities for each zone. Results show that the groundwater velocities for each zone are 2750, 58, and 0 m/y, whereas the effective thermal conductivities are 2.4, 2.4, and 2.1 W/(m center dot K), respectively. The proposed methodology is evaluated by comparing it with the realistic long-term operation data of a ground source heat pump (GSHP) system in Kazuno City, Japan. The temperature error between the calculated results and measured data is 6.4% for two years. Therefore, the proposed methodology is effective for estimating the long-term performance analysis of GSHP systems.

This paper presents a new parameter identification (PI) algorithm for estimating effective and detailed thermal parameters of ground source heat pump systems using data obtained from the well-known thermal response test. The PI comprises an iterative scheme coupling a semi-analytical forward model to an inverse model. The forward model is formulated based on the spectral element method to simulate transient 3D heat flow in ground source heat pump (GSHP) systems, and the inverse model is formulated based on the interior-point optimization method to minimize the system objective function. Compared to existing interpretation tools for the thermal response test, the proposed PI algorithm has several advanced features, including: it can handle fluctuating heat pump power and inlet temperatures; interpret data obtained from multiple heat injection or extraction signals; produce accurate backcalculation for short and long duration experiments; and handle multilayer systems. The PI algorithm is tested against synthesized data, using a wide range of random noise, and versus an available laboratory experiment. The computational results show that the PI algorithm is accurate, stable and exhibiting relatively high convergence rate., Applied Mechanics

[ES] Al manejar una instalación con un grupo de pozos de intercambio de calor (Borehole heat exchanger, BHE en inglés) se produce una ingente cantidad de datos. Además del tratamiento de esta gran cantidad de datos para su uso posterior, hay que tener en cuenta la forma de acceder a los mismos. En este trabajo de fin de grado o TFG se ofrecerán unas soluciones teóricas para entender el alcance de las nuevas tecnologías web a la hora de extraer y hacer uso de la información. Se seleccionará una de ellas para su realización práctica., [EN] When managing a facility with a group of Borehole Heat Exchangers (BHE), a huge amount of data is produced. In addition to the treatment of this large amount of information for later use, we must take into account the way to access it. In this final degree project or TFG, theoretical solutions will be offered to understand the scope of new technologies when that way of extracting and making use of the information. One of them will be selected for practical realization.

In this study, a new analysis method is proposed for estimating thermal conductivity of a ground by using the constant-temperature thermal response test data. The new method is based on an analytical solution of heat transfer rate per unit borehole length by using the Laplace transformation for constant-temperature thermal response tests. Its advantage is that it allows one to estimate thermal conductivity directly from the slope of the logarithmic time dependency of inverse unit-heat-transfer rate value without making an estimation of volumetric heat capacity. The method has been verified by using a numerical model and applied to different experimental data based on different test temperatures and compared with the classical thermal response test method. The results show that the proposed method reliably and effectively estimates thermal conductivity of ground.

[ES] Al manejar una instalación con un grupo de pozos de intercambio de calor (Borehole heat exchanger, BHE en inglés) se produce una ingente cantidad de datos. Además del tratamiento de esta gran cantidad de datos para su uso posterior, hay que tener en cuenta la forma de acceder a los mismos. En este trabajo de fin de grado o TFG se ofrecerán unas soluciones teóricas para entender el alcance de las nuevas tecnologías web a la hora de extraer y hacer uso de la información. Se seleccionará una de ellas para su realización práctica., [EN] When managing a facility with a group of Borehole Heat Exchangers (BHE), a huge amount of data is produced. In addition to the treatment of this large amount of information for later use, we must take into account the way to access it. In this final degree project or TFG, theoretical solutions will be offered to understand the scope of new technologies when that way of extracting and making use of the information. One of them will be selected for practical realization.

[ES] Al manejar una instalación con un grupo de pozos de intercambio de calor (Borehole heat exchanger, BHE en inglés) se produce una ingente cantidad de datos. Además del tratamiento de esta gran cantidad de datos para su uso posterior, hay que tener en cuenta la forma de acceder a los mismos. En este trabajo de fin de grado o TFG se ofrecerán unas soluciones teóricas para entender el alcance de las nuevas tecnologías web a la hora de extraer y hacer uso de la información. Se seleccionará una de ellas para su realización práctica., [EN] When managing a facility with a group of Borehole Heat Exchangers (BHE), a huge amount of data is produced. In addition to the treatment of this large amount of information for later use, we must take into account the way to access it. In this final degree project or TFG, theoretical solutions will be offered to understand the scope of new technologies when that way of extracting and making use of the information. One of them will be selected for practical realization.

Human induced climate change is causing global temperatures to rise at an alarming rate. This is caused by greenhouse gas emissions, particularly CO2, and much of this pollution comes from burning fossil fuels for energy. Space heating and cooling of buildings is one such energy intensive activity contributing to CO2 emissions. Traditional heating, ventilation and air conditioning (HVAC) systems typically rely on outdated and inefficient fossil fuelled electricity and gas systems. Overall energy usage and greenhouse gas emissions in buildings can therefore be reduced through adoption of high efficiency heating and cooling systems. Shallow geothermal is an energy efficiency technology that can help achieve this, but capital costs are high compared to less efficient gas burners and electric air conditioning systems. For this technology to be adopted at scale, and so that it can contribute significantly to reducing greenhouse gas emissions and climate change, methods for reducing capital costs and optimising design of shallow geothermal systems are required. Shallow geothermal systems utilise Ground Source Heat Pumps (GSHP) to exchange thermal energy between a building and the ground. Fluid (usually water) is circulated in pipes embedded in trenches, boreholes or foundations (Ground Heat Exchanger, GHE). The relatively constant temperatures found near the surface are utilized as a heat source in winter and a heat sink in summer. Economic design relies on accurate estimation of ground thermal parameters. For this, a Thermal Response Test (TRT) is often performed, which is an in-situ test typically consisting of injecting heated fluid through GHE pipes and measuring the development of the inlet and outlet temperature over time. A model approximating the mean fluid temperature is fitted to the measured data to back calculate the thermal parameters of the ground, which are then used for GHE design. Estimation of these parameters from the data will be accurate when the TRT

[ES] En los últimos años, el interés por el ahorro de energía y la reducción de las emisiones de CO2 ha crecido cada vez más, convirtiendo a las bombas de calor geotérmicas en una tecnología de alta eficiencia para sistemas de climatización de edificios. Una correcta estimación de los principales parámetros del sistema es crucial para dimensionar correctamente el intercambiador de calor de la perforación (BHE) y lograr una alta eficiencia energética. Este trabajo de investigación se llevó a cabo en la Universidad Politécnica de Valencia (UPV) y forma parte del proyecto europeo GEOCOND. Se centra en la evaluación de diferentes métodos numéricos con el objetivo de analizar a fondo los resultados de una prueba de respuesta térmica (TRT) para lograr una verdadera estimación de la conductividad térmica del suelo y la resistencia equivalente del intercambiador geotérmico. Se analizarán los factores que afectan a la bondad de la estimación, como la duración mínima y máxima del TRT. Para facilitar la evaluación de estos parámetros en tiempo real, se presentará un algoritmo desarrollado con el software comercial Matlab, capaz de comparar tres modelos numéricos diferentes (ILS, FLS y FCS) con los datos experimentales adquiridos por tres tipos de BHE presentes en el campus de la UPV (single-U, coaxial y helix)., [EN] In recent years, interest in energy saving and reducing of CO2 emissions has grown more and more, particularly the ground source heat pumps are known as a high-efficient technology for heating and cooling systems. A good estimation of the main parameters of the system is crucial in order to correctly size the borehole heat exchanger to achieve high coefficient of performance. This research work was carried out at the Polytechnic University of Valencia (UPV) and is part of the European project GEOCOND. It focuses on the evaluation of different numerical methods with the aim of thoroughly analysing the characteristics of a thermal response test (TRT) to achieve a true estimate of the thermal conductivity of the soil and the equivalent resistance of the borehole. The factors affecting the goodness of the estimate will be analysed, such as the minimum and maximum duration of the TRT. In order to provide the evaluation of these parameters in real time, will be presented an algorithm developed with the commercial software Matlab, able to compare three different numerical models (ILS, FLS and FCS) with the experimental data acquired by three types of BHE present in the campus of the UPV (single-U, coaxial and helix).

[ES] En los últimos años, el interés por el ahorro de energía y la reducción de las emisiones de CO2 ha crecido cada vez más, convirtiendo a las bombas de calor geotérmicas en una tecnología de alta eficiencia para sistemas de climatización de edificios. Una correcta estimación de los principales parámetros del sistema es crucial para dimensionar correctamente el intercambiador de calor de la perforación (BHE) y lograr una alta eficiencia energética. Este trabajo de investigación se llevó a cabo en la Universidad Politécnica de Valencia (UPV) y forma parte del proyecto europeo GEOCOND. Se centra en la evaluación de diferentes métodos numéricos con el objetivo de analizar a fondo los resultados de una prueba de respuesta térmica (TRT) para lograr una verdadera estimación de la conductividad térmica del suelo y la resistencia equivalente del intercambiador geotérmico. Se analizarán los factores que afectan a la bondad de la estimación, como la duración mínima y máxima del TRT. Para facilitar la evaluación de estos parámetros en tiempo real, se presentará un algoritmo desarrollado con el software comercial Matlab, capaz de comparar tres modelos numéricos diferentes (ILS, FLS y FCS) con los datos experimentales adquiridos por tres tipos de BHE presentes en el campus de la UPV (single-U, coaxial y helix)., [EN] In recent years, interest in energy saving and reducing of CO2 emissions has grown more and more, particularly the ground source heat pumps are known as a high-efficient technology for heating and cooling systems. A good estimation of the main parameters of the system is crucial in order to correctly size the borehole heat exchanger to achieve high coefficient of performance. This research work was carried out at the Polytechnic University of Valencia (UPV) and is part of the European project GEOCOND. It focuses on the evaluation of different numerical methods with the aim of thoroughly analysing the characteristics of a thermal response test (TRT) to achieve a true estimate of the thermal conductivity of the soil and the equivalent resistance of the borehole. The factors affecting the goodness of the estimate will be analysed, such as the minimum and maximum duration of the TRT. In order to provide the evaluation of these parameters in real time, will be presented an algorithm developed with the commercial software Matlab, able to compare three different numerical models (ILS, FLS and FCS) with the experimental data acquired by three types of BHE present in the campus of the UPV (single-U, coaxial and helix).

Thermal Response Testing is now a well-known and widely-used method allowing the determination of the local thermal or geometrical properties of aBorehole Heat Exchanger (BHE), those properties being critical in the design of GSHP systems. The analysis of TRTs is an inverse problem that hascommonly been solved using an approximation of the ILS solution. To do this, however, the heat rate during a TRT must be kept constant, or least be nontime-correlated, during the test, which is a challenging constraint. Applying temporal superposition to the ILS model is a way to account for varying power,although it requires the use of an optimization algorithm to minimize the error between a parametrized model and experimental values.In this paper, the Newton-Raphson method is applied to the time-superposed ILS for parameter estimation in TRTs. The parameter estimation is limitedto the effective thermal conductivity and the effective borehole resistance. Analytical expressions of the first and second derivatives of the objective function,chosen as the sum of quadratic differences, are proposed, allowing to readily inverse of the Hessian matrix and speed the convergence process.The method is tried for 9 different TRTs, 2 of which are reference datasets used for validation of the method (Beier et al., 2010). Differences betweenestimated and reference thermal conductivities are of 3.4% and 0.4% for the first and second reference TRTs, respectively. The method is shown to be stableand consistent: for each of the 9 TRTs, 11 realizations are performed with different initial values. Convergence is reached in all cases and all realizationslead to the same final values for a given TRT.The proposed convergence method is about 70% to 90% faster than the Nelder-Mead simplex and require about 8 times less iterations in average. Theconvergence speed varies between 0.3 to 13.6 s with an average of 3.7 s for all TRTs., QC 20181106, Deep Boreholes for Ground-Source Heat Pumps

Thermal Response Testing is now a well-known and widely-used method allowing the determination of the local thermal or geometrical properties of aBorehole Heat Exchanger (BHE), those properties being critical in the design of GSHP systems. The analysis of TRTs is an inverse problem that hascommonly been solved using an approximation of the ILS solution. To do this, however, the heat rate during a TRT must be kept constant, or least be nontime-correlated, during the test, which is a challenging constraint. Applying temporal superposition to the ILS model is a way to account for varying power,although it requires the use of an optimization algorithm to minimize the error between a parametrized model and experimental values.In this paper, the Newton-Raphson method is applied to the time-superposed ILS for parameter estimation in TRTs. The parameter estimation is limitedto the effective thermal conductivity and the effective borehole resistance. Analytical expressions of the first and second derivatives of the objective function,chosen as the sum of quadratic differences, are proposed, allowing to readily inverse of the Hessian matrix and speed the convergence process.The method is tried for 9 different TRTs, 2 of which are reference datasets used for validation of the method (Beier et al., 2010). Differences betweenestimated and reference thermal conductivities are of 3.4% and 0.4% for the first and second reference TRTs, respectively. The method is shown to be stableand consistent: for each of the 9 TRTs, 11 realizations are performed with different initial values. Convergence is reached in all cases and all realizationslead to the same final values for a given TRT.The proposed convergence method is about 70% to 90% faster than the Nelder-Mead simplex and require about 8 times less iterations in average. Theconvergence speed varies between 0.3 to 13.6 s with an average of 3.7 s for all TRTs., QC 20181106, Deep Boreholes for Ground-Source Heat Pumps

[EN] In this contribution, we analyze the results of a number of thermal response test (TRT) experiments performed during several years at the same location at our university campus in Valencia (Spain), a permeable saturated soil area with possible groundwater flow conditions. A combination of different heat injection rates, TRT operation times of up to 32 days, and various methods for parameter estimation of ground thermal properties have been applied to study their influence on the result and accuracy of TRTs. Our main objective has been to experimentally quantify the influence of groundwater flow heat advection using moving infinite and finite line-source theories, as well as to analyze the influence of factors such as test duration, sensor accuracy, and external thermal influences. We have shown that the traditionally used infinite and finite line-source models, as well as the moving line-source models, can accurately represent experimental temperature evolution, but that there are many caveats regarding the significance parameters extracted and its reproducibility and stability. These features can be improved if data from the first test days are disregarded for the analysis, obtaining a much faster convergence to the definitive soil parameter estimates, including the effective Peclet number that represents groundwater flow in our particular case.

Thermal Response Testing is now a well-known and widely-used method allowing the determination of the local thermal or geometrical properties of aBorehole Heat Exchanger (BHE), those properties being critical in the design of GSHP systems. The analysis of TRTs is an inverse problem that hascommonly been solved using an approximation of the ILS solution. To do this, however, the heat rate during a TRT must be kept constant, or least be nontime-correlated, during the test, which is a challenging constraint. Applying temporal superposition to the ILS model is a way to account for varying power,although it requires the use of an optimization algorithm to minimize the error between a parametrized model and experimental values.In this paper, the Newton-Raphson method is applied to the time-superposed ILS for parameter estimation in TRTs. The parameter estimation is limitedto the effective thermal conductivity and the effective borehole resistance. Analytical expressions of the first and second derivatives of the objective function,chosen as the sum of quadratic differences, are proposed, allowing to readily inverse of the Hessian matrix and speed the convergence process.The method is tried for 9 different TRTs, 2 of which are reference datasets used for validation of the method (Beier et al., 2010). Differences betweenestimated and reference thermal conductivities are of 3.4% and 0.4% for the first and second reference TRTs, respectively. The method is shown to be stableand consistent: for each of the 9 TRTs, 11 realizations are performed with different initial values. Convergence is reached in all cases and all realizationslead to the same final values for a given TRT.The proposed convergence method is about 70% to 90% faster than the Nelder-Mead simplex and require about 8 times less iterations in average. Theconvergence speed varies between 0.3 to 13.6 s with an average of 3.7 s for all TRTs., QC 20181106, Deep Boreholes for Ground-Source Heat Pumps

Thermal Response Testing is now a well-known and widely-used method allowing the determination of the local thermal or geometrical properties of aBorehole Heat Exchanger (BHE), those properties being critical in the design of GSHP systems. The analysis of TRTs is an inverse problem that hascommonly been solved using an approximation of the ILS solution. To do this, however, the heat rate during a TRT must be kept constant, or least be nontime-correlated, during the test, which is a challenging constraint. Applying temporal superposition to the ILS model is a way to account for varying power,although it requires the use of an optimization algorithm to minimize the error between a parametrized model and experimental values.In this paper, the Newton-Raphson method is applied to the time-superposed ILS for parameter estimation in TRTs. The parameter estimation is limitedto the effective thermal conductivity and the effective borehole resistance. Analytical expressions of the first and second derivatives of the objective function,chosen as the sum of quadratic differences, are proposed, allowing to readily inverse of the Hessian matrix and speed the convergence process.The method is tried for 9 different TRTs, 2 of which are reference datasets used for validation of the method (Beier et al., 2010). Differences betweenestimated and reference thermal conductivities are of 3.4% and 0.4% for the first and second reference TRTs, respectively. The method is shown to be stableand consistent: for each of the 9 TRTs, 11 realizations are performed with different initial values. Convergence is reached in all cases and all realizationslead to the same final values for a given TRT.The proposed convergence method is about 70% to 90% faster than the Nelder-Mead simplex and require about 8 times less iterations in average. Theconvergence speed varies between 0.3 to 13.6 s with an average of 3.7 s for all TRTs., QC 20181106, Deep Boreholes for Ground-Source Heat Pumps

Thermal Response Testing is now a well-known and widely-used method allowing the determination of the local thermal or geometrical properties of aBorehole Heat Exchanger (BHE), those properties being critical in the design of GSHP systems. The analysis of TRTs is an inverse problem that hascommonly been solved using an approximation of the ILS solution. To do this, however, the heat rate during a TRT must be kept constant, or least be nontime-correlated, during the test, which is a challenging constraint. Applying temporal superposition to the ILS model is a way to account for varying power,although it requires the use of an optimization algorithm to minimize the error between a parametrized model and experimental values.In this paper, the Newton-Raphson method is applied to the time-superposed ILS for parameter estimation in TRTs. The parameter estimation is limitedto the effective thermal conductivity and the effective borehole resistance. Analytical expressions of the first and second derivatives of the objective function,chosen as the sum of quadratic differences, are proposed, allowing to readily inverse of the Hessian matrix and speed the convergence process.The method is tried for 9 different TRTs, 2 of which are reference datasets used for validation of the method (Beier et al., 2010). Differences betweenestimated and reference thermal conductivities are of 3.4% and 0.4% for the first and second reference TRTs, respectively. The method is shown to be stableand consistent: for each of the 9 TRTs, 11 realizations are performed with different initial values. Convergence is reached in all cases and all realizationslead to the same final values for a given TRT.The proposed convergence method is about 70% to 90% faster than the Nelder-Mead simplex and require about 8 times less iterations in average. Theconvergence speed varies between 0.3 to 13.6 s with an average of 3.7 s for all TRTs., QC 20181106, Deep Boreholes for Ground-Source Heat Pumps

[ES] Un pozo de intercambio de calor (Borehole heat exchanger, BHE inglés) es una instalación geotérmica que genera una gran cantidad de información. Este volumen de información requiere un sistema informático para su almacenamiento y presentación En este trabajo se diseña una aplicación Web y una Web Api para dar solución a los dos problemas anteriores y facilitar el análisis y estudio de la información obtenida., [EN] A Borehole heat exchanger is a thermical installation who generate a lot of information. This information needs a computer system to save and present the data. In this project we designed a Web application and a Web Api to solve the two problems and make more easier to analyze.

[ES] Un pozo de intercambio de calor (Borehole heat exchanger, BHE inglés) es una instalación geotérmica que genera una gran cantidad de información. Este volumen de información requiere un sistema informático para su almacenamiento y presentación En este trabajo se diseña una aplicación Web y una Web Api para dar solución a los dos problemas anteriores y facilitar el análisis y estudio de la información obtenida., [EN] A Borehole heat exchanger is a thermical installation who generate a lot of information. This information needs a computer system to save and present the data. In this project we designed a Web application and a Web Api to solve the two problems and make more easier to analyze.

[ES] Un pozo de intercambio de calor (Borehole heat exchanger, BHE inglés) es una instalación geotérmica que genera una gran cantidad de información. Este volumen de información requiere un sistema informático para su almacenamiento y presentación En este trabajo se diseña una aplicación Web y una Web Api para dar solución a los dos problemas anteriores y facilitar el análisis y estudio de la información obtenida., [EN] A Borehole heat exchanger is a thermical installation who generate a lot of information. This information needs a computer system to save and present the data. In this project we designed a Web application and a Web Api to solve the two problems and make more easier to analyze.

Ground-Source Heat Pump (GSHP) systems represent one of the most efficient renewable energy technologies. Their efficiency is highly influenced by the thermal properties of the ground, which are often measured in-situ using the Thermal Response Tests (TRTs). While three-dimensional mechanistic models offer significant advantages over analytical solutions for the numerical interpretation of TRTs, their computational cost represents a limiting factor. Moreover, most of the existing models do not include a comprehensive description of hydrological processes, which have proven to strongly influence the behavior of GSHP. Thus, in this study, we propose a computationally efficient pseudo-3D model for the numerical analysis and interpretation of TRTs. The numerical approach combines a one-dimensional description of the heat transport in the buried tubes of the exchanger with a two-dimensional description of the heat transfer and water flow in the surrounding subsurface soil, thus reducing the dimensionality of the problem and the computational cost. The modeling framework includes the widely used hydrological model, HYDRUS, which can simulate the movement of water, heat, and multiple solutes in variably-saturated porous media. First, the proposed model is validated against experimental data collected at two different experimental sites in Japan, with satisfactory results. Then, it is combined with the Morris method to carry out a sensitivity analysis of thermal properties. Finally, the model is exploited to investigate the influence of groundwater and lithologic heterogeneities on the thermal behavior of the GSHP.

In situ thermal response tests (TRT s) are currently the standard methodology used for determining ground thermal properties needed for sizing ground source heat exchangers (GSHE). The main drawback of this methodology is the high cost involved, mainly due to the long injection times needed. Since ground conductivity is a key parameter in the design of a GSHE, any advances in the reduction of the duration of a TRT would result in a lower cost. Hence, the viability of this kind of test would increase. In this context, a dynamic model of the GSHE can be very useful to reduce the amount of data needed in order to obtain the ground thermal properties. The recently developed B2G model has proven to be able to reproduce the short-term response of a GSHE with a great accuracy. One of the main advantages of the B2G dynamic model is that it can be adjusted to any specific GSHE with only a few experimental data (typically, corresponding to 10-15 hours of heat injection/extraction). This model could be used to provide an estimation of the ground thermal properties using less data than a standard TRT. In this work, the B2G model has been adapted to an existing borehole heat exchanger (BHE) located at Universitat Politècnica de València. Experimental data corresponding to a TRT performed in this BHE have been used in order to validate the adaptability of the B2G model and its utility as a ground thermal properties estimation tool.

Actual thermal response tests, used to estimate the subsurface thermal conductivity in the geothermal domain, do not provide any estimate on the velocity of the groundwater flow and its orientation. These parameters are important for sizing geothermal borefield, since they influence the heat transfer around a geothermal borehole and the surrounding ground. To correct this shortcoming, a test concept in which heating cable sections inject heat in a borehole has been developed. Three temperature probes are strategically located at the borehole edge. This paper applies inverse heat transfer strategies to this thermal response test concept in order to identify the ground thermal conductivity, as well as the groundwater flow velocity and its direction. The suggested thermal response test and parameters estimation methodology are detailed. The influence of initial guessed values for the three unknown parameters was also studied. The work presented in this paper was carried out by numerical simulations

Current thermal response tests, used to estimate the subsurface thermal conductivity in the geothermal domain, are not designed to take into account groundwater flows. To measure the flow parameters, a new concept has been developed. Heating cables are installed within a borehole in contact to the formation, with three temperature probes strategically located at the edge of the borehole. Study of the evolution of temperature for each probe during both a heat injection phase and a recovery period allows determining ground thermal conductivity, groundwater flow velocity and orientation. Numerical simulations have been used to validate the proposed concept and establish its limits

In situ thermal response tests (TRT s) are currently the standard methodology used for determining ground thermal properties needed for sizing ground source heat exchangers (GSHE). The main drawback of this methodology is the high cost involved, mainly due to the long injection times needed. Since ground conductivity is a key parameter in the design of a GSHE, any advances in the reduction of the duration of a TRT would result in a lower cost. Hence, the viability of this kind of test would increase. In this context, a dynamic model of the GSHE can be very useful to reduce the amount of data needed in order to obtain the ground thermal properties. The recently developed B2G model has proven to be able to reproduce the short-term response of a GSHE with a great accuracy. One of the main advantages of the B2G dynamic model is that it can be adjusted to any specific GSHE with only a few experimental data (typically, corresponding to 10-15 hours of heat injection/extraction). This model could be used to provide an estimation of the ground thermal properties using less data than a standard TRT. In this work, the B2G model has been adapted to an existing borehole heat exchanger (BHE) located at Universitat Politècnica de València. Experimental data corresponding to a TRT performed in this BHE have been used in order to validate the adaptability of the B2G model and its utility as a ground thermal properties estimation tool.

Ground thermal conductivity and borehole thermal resistance are key parameters for the design of closed Ground-Source Heat Pump (GSHP) systems. The standard method to determine these parameters is the Thermal Response Test (TRT). This test analyses the ground thermal response to a constant heat power injection or extraction by measuring inlet and outlet temperatures of the fluid at the top of the borehole heat exchanger. These data are commonly evaluated by models considering the ground being homogeneous and isotropic. This approach estimates an effective ground thermal conductivity representing an average of the thermal conductivity of the different layers crossed by perforation. In order to obtain a thermal conductivity profile of the ground as a function of depth, two additional inputs are needed; first, a measurement of the borehole temperature profile and, second, an analysis procedure taking into account ground is not homogeneous. This work presents an analysis procedure, complementing the standard TRT analysis, estimating the thermal conductivity profile from a temperature profile along the borehole during the test. The analysis procedure is implemented by a 3D Finite Element Model (FEM) in which depth depending thermal conductivity of the subsoil is estimated by fitting simulation results with experimental data. The methodology is evaluated by the recorded temperature profiles throughout a TRT in a BHE (Borehole Heat Exchanger) monitored facility, which allowed the detection of a highly conductive layer at 25 meters depth. © 2015 Elsevier Ltd. All rights reserved.

Ground thermal conductivity and borehole thermal resistance are key parameters for the design of closed Ground-Source Heat Pump (GSHP) systems. The standard method to determine these parameters is the Thermal Response Test (TRT). This test analyses the ground thermal response to a constant heat power injection or extraction by measuring inlet and outlet temperatures of the fluid at the top of the borehole heat exchanger. These data are commonly evaluated by models considering the ground being homogeneous and isotropic. This approach estimates an effective ground thermal conductivity representing an average of the thermal conductivity of the different layers crossed by perforation. In order to obtain a thermal conductivity profile of the ground as a function of depth, two additional inputs are needed; first, a measurement of the borehole temperature profile and, second, an analysis procedure taking into account ground is not homogeneous. This work presents an analysis procedure, complementing the standard TRT analysis, estimating the thermal conductivity profile from a temperature profile along the borehole during the test. The analysis procedure is implemented by a 3D Finite Element Model (FEM) in which depth depending thermal conductivity of the subsoil is estimated by fitting simulation results with experimental data. The methodology is evaluated by the recorded temperature profiles throughout a TRT in a BHE (Borehole Heat Exchanger) monitored facility, which allowed the detection of a highly conductive layer at 25 meters depth. © 2015 Elsevier Ltd. All rights reserved.

Vertical closed loop systems, also known as borehole heat exchangers (BHEs), are a popular way of extracting the ground source heat energy. Primary factors affecting the performance of BHEs are the thermal and hydrogeological properties of the subsurface. Groundwater flow is known to potentially influence heat transport and system performance. The effect of groundwater movement is more commonly studied under homogeneous conditions. However, in heterogeneous fractured rocks, BHEs are more common than horizontal or open loops due to lack of sufficient soil layers and productive aquifers. The finite-element modelling shows that fractures can play an important role in BHE functioning. Especially, vertical open fractures (≥1 mm) near the borehole (≤10 m) can have a considerable impact. Although increase in fracture aperture continuously affects the subsurface and BHE temperatures, the increase in its effect progressively lessens. Depending on the distance and aperture, one major fracture influencing the BHE operation performance can be identified; yet a larger number of fractures may govern heat transport (thermal plume outline) and thermal recovery. Individually, horizontal fractures may have less influence than vertical fractures. However, as the density of horizontal fractures increases, their impact can be major, exceeding that of fracture aperture. In particular, we propose that measurements of rock thermal properties be combined with fracture mapping, to better analyse the thermal response testing results and integrate the configuration of fractures in design and layout of the BHE(s). This is particularly valid for (vertical) fractures not intersecting with the borehole., QC 20150827

One potential problem for the ground coupled heat pump is that the ground thermal properties is hardly to be known due to the complicated ground construction. The p(t)-linear average method has been proved that it can improve the accuracy of borehole thermal resistance. However, the p(t)-linear fluid temperature distribution approximation is not agree well with the temperature profile measured by the fiber cable. Thus, in this paper, an improved p(t)-linear average method in which the fluid temperature distribution approximation based on the vertical temperature profile is proposed. With the new vertical temperature profile simulation model, the accuracy for the borehole thermal resistance estimation will be improved comparing to the true value. Besides that, the estimation results are sensitive with the distance between two pipes, and together with the borehole thermal resistance, the distance will be optimized by the outlet fluid temperature. The life cycle cost analysis results of a case study for an office building in Hunan University show that, although the operation cost will be increased, the total cost during the whole lifetime will be reduced with a lower initial investment., QC 20160614

Ground source heat pump systems are often coupled to the ground by circulating a fluid through vertical Borehole Heat Exchangers (BHEs). The design of a system requires estimates of the ground thermal conductivity and the borehole thermal resistance, which are usually determined by an in situ thermal response test on a completed borehole. The usual test interpretation methods average the inlet and outlet fluid temperatures and use this mean temperature as the average temperature along the borehole length. This assumption is convenient but does not strictly apply. For a coaxial heat exchanger this paper develops an analytical model for the vertical temperature profiles, which can be used instead of the mean temperature approximation to estimate borehole resistance. The model is verified with measured temperatures on a BHE, where an optical technique allows continuous measurements along a coaxial borehole during a distributed thermal response test. A sensitivity study shows that the proposed method corrects errors in the mean temperature approximation, which overestimates the borehole resistance in a coaxial borehole., QC 20130205

The design of ground source heat pump systems requires values for the ground thermal conductivity and the borehole thermal resistance. In situ thermal response tests (TRT) are often performed on vertical boreholes to determine these parameters. Most TRT analysis methods apply the mean of the inlet and outlet temperatures of the circulating fluid along the entire borehole length. This assumption is convenient but not rigorous. To provide a more general approach, this paper develops an analytical model of the vertical temperature profile in the borehole during the late-time period of the in situ test. The model also includes the vertical temperature profile of the undisturbed ground. The model is verified with distributed temperature measurements along a vertical borehole using fiber optic cables inside a U-tube for the circulating fluid. The borehole thermal resistance is calculated without the need for the mean temperature approximation. In the studied borehole, the mean temperature approximation overestimates the borehole resistance by more than 20%., QC 20121015