Dissertations / Theses on the topic 'Vertical ground heat exchanger'

GSHP (Ground source heat pump), uses geothermal energy which is a form of green and sustainable energy.  Geothermal energy is also a continuous source of energy, unlike wind energy. The results from this thesis work will be applicable for both GSHP that are being used for space heating, and the ones which have a bottom organic Rankine cycle. The bottom organic Rankine cycle and continuous energy production of GSHP make it a potential source for electricity generation.  The GSHP is of various types, in regard to the configuration of the pipe and their setup in the ground and also based on their grouting. In this study only vertical GSHP and with a single u-tube and water filled grout will be analyzed. The GSHP performance is based on a number of parameters including, the depth of the heat exchanging unit in the ground, other key dimensions of the unit like diameter and outer wall thickness, the fluid flow, and the type of working fluid. Therefore it becomes necessary to study the effect of all of these parameters individually and their individual effect on the energy output and the performance of the BHE. One of the thesis objectives is to establish a sensitivity analysis of the BHE based on the above mention parameters and then further optimize the design with the heat enhancement devices. The major findings of this thesis work are how shank spacing (spacing between the inlet and the outlet pipe) affects the heat transfer in the BHE. The shank spacing seems to reduce the energy output of the GSHP, this is contrary to the high conductive solid grout, where the shank spacing doesn't affect the BHE so much. The diameter of the BHE in the water-filled grout has a completely opposite effect from the solid grout. Increasing the depth of the BHE after a certain length only increases the entropy of the system which reduces the energy output. The working fluid with a higher Prandtl number helps in higher energy output. The optimization results suggest that having a deeper borehole is not very energy efficient in spite of the greater thermal gradient available at a higher depth.

A model has been developed which simulates a system consisting of a horizontal and vertical ground-coupled heat exchanger connected in parallel to the same heat pump. The model was used in computer simulations to investigate how the annual minimum and mean fluid temperatures at the heat pump varied as several parameters of the combined system were changed. A comparison was also made between different control settings for fluid flow rate distribution between the two exchangers. For the case when the flow rate distribution was not controlled, the effect of viscosity differences between a colder and warmer exchanger was investigated. The short term effects of letting the vertical heat source rest during the warm summer months was then tested. Lastly, the results of the model was compared to a simple 'rule of thumb' that have been used in the industry for this kind of combined system. The results show that using a combined system might not always result in increased performance, if the previously existing exchanger is a vertical ground-coupled heat exchanger. The effects of viscosity differences on the flow distribution seems to be negligible, especially for high net flows. Controlling the fluid flow rates seems to only be worth the effort if the the pipe lengths of the two combined exchangers differ heavily. Letting the vertical ground-coupled heat exchanger rest during summer was shown to in some cases yield an increased short-term performance in addition to the already known positive long term effects. The rule of thumb was shown to recommend smaller dimensions for combination systems than the more realistic analytical model.

Ground-source heat pump systems with vertical ground heat exchangers (GHE) are gaining popularity worldwide for their higher coefficients of performance and lower CO2 emissions. However, the higher initial cost of installing the borehole GHEs is a main obstacle to spread the systems. To reduce the required total GHE length and efficiently operate the systems, various systems such as hybrid ones (e.g. solar heat injection) have recently been introduced. Accurate prediction of heat transfer in and around boreholes of such systems is crucial to avoid costly overdesigns or catastrophic failures of undersized systems as it is for typical GCHP systems. However, unlike the traditional sizing methods, it is increasingly required to take into account detailed borehole configuration and transient effects (e.g. short circuit effects between U-tubes). Many of the existing GHE models have been reviewed. Some of these models have serious limitations when it comes to transient heat transfer, particularly in the borehole itself. Accordingly, the objective of this thesis is to develop a model that is capable to accurately predict thermal behaviors of the GHEs. A precise response to input variations even in a short time-step is also expected in the model. The model also has to account for a correct temperature and flux distribution between the U-tubes and inside the borehole that seems to be important in the solar heat injection case. Considering these effects in 3D with a detailed mesh used for describing the borehole configurations is normally time-consuming. This thesis attempts to alleviate the calculation time using state model reduction techniques that use fewer modes for a fast calculation but predict similar results. Domain decomposition is also envisaged to sub-structure the domain and vary the time-step sizes. Since the decomposed domains should be coupled one another spatially as well as temporally, new coupling methods are proposed and validated particularly in the FEM. For the simulation purpose, a hybrid model (HM) is developed that combines a numerical solution, the same one as the 3D-RM but only for the borehole, and well-known analytical ones for a fast calculation. An experimental facility used for validation of the model has been built and is described. A comparison with the experimental results shows that the relatively fast transients occurring in the borehole are well predicted not only for the outlet fluid temperature but also for the grout temperatures at different depths even in very short time-steps. Even though the current version of 3D-RM is experimentally validated, it is still worth optimizing the model in terms of the computational time. Further simulations with the 3D-RM are expected to be carried out to estimate the performance of new hybrid systems and propose its appropriate sizing with correspondent thermal impacts on the ground. Finally, the development of the model 3D-RM can be an initiation to accurately model various types of GHE within an acceptable calculation time.

Dans le contexte énergétique actuel, les pompes à chaleur (PAC) géothermiques sont parmi les technologies les plus performantes pour augmenter l’efficacité énergétique des bâtiments. Par contre le coût initial et l’encombrement des capteurs enterrés traditionnels peuvent être un obstacle à sa diffusion sur le marché des énergies renouvelables. Pour réduire ces coût et encombrement, une réflexion sur l’adjonction d’un système d’appoint et/ou de recharge thermique du sol aux capteurs enterrés est actuellement en cours de tests. Les outils actuels de modélisation des capteurs enterrés obtiennent en effet de bons résultats mais seulement pour un dimensionnement classique en régime permanent. Les modèles existants ne permettent donc pas de représenter correctement les dynamiques rapides des échanges entre le sol et les tubes et cela est d’autant plus vrai si l’on adjoint le système de recharge solaire. Par conséquence, cette thèse a pour objectif de développer les modèles fins et dynamiques nécessaires à l’analyse des phénomènes transitoires dans les capteurs enterrés eux-mêmes. Un maillage fin, sur les bases de la triangulation de Delaunay, est choisi pour le forage ainsi que pour le sol avoisinant. Une approche numérique en 3D (FVM + FEM) peut être obtenue sur les bases de la discrétisation spatiale du domaine. Cette approche appliquée brutalement induirait des temps de calcul très élevés et de toute façon incompatible avec les moyens informatiques ordinaires. Afin de répondre à l’ensemble de ces problèmes, différentes techniques ont été utilisées afin d’accélérer le temps de calcul: décomposition de domaine, emboîtement des pas de temps de calcul pour chaque sous-domaine, réduction des modèles d’états de chaque sous-domaine et finalement couplages temporels et spatiaux des équations de transferts de l’ensemble du problème. Ce dernier est développé particulièrement sur les bases de la méthode des éléments finis. Par ailleurs, un modèle hybride est développé en combinaison de différentes approches. Une approche numérique est adoptée pour la modélisation du puits et la modélisation des transferts de chaleur dans le sol environnant est faite par l’utilisation de solutions analytiques. Ainsi, ce modèle est implanté dans TRNSYS. Une plate-forme expérimentale comprenant trois puits verticaux couplés à une pompe à chaleur géothermique est également présentée. Les résultats expérimentaux sont comparés avec les résultats de la simulation aussi bien au niveau de la température du fluide qu’à la température à différentes profondeurs dans les puits. Le modèle développé donne des résultats très similaires avec ceux qui sont obtenus grâce à l’expérimentation même lors que les pas de temps sont très petits. Il y a des choses à améliorer dans ce modèle développé, mais cela concerne essentiellement l’accélération du temps de calcul. Nous avons constaté que les modèles que nous avons dévéloppés donnent des résultats meilleurs à pas de temps courts que les modèles classiques. Il faut donc bien préciser le domaine d’utilisation de chacun des modèles: consommation sur le long terme, stratégie de contrôle de la PAC, les transferts de chaleur à l’intérieur du puits et etc. De plus, une application du modèle dans le dimensionnement d’échangeurs ainsi que l’investigation de son impact sur le sol avoisinant est également envisagée. Finalement, la méthodologie de modélisation présentée dans ce travail pourrait être aussi utilisé pour différents types d’échangeurs, ouvrant aussi la porte à une analyse fine dans le domaine géothermique
Ground-source heat pump systems with vertical ground heat exchangers (GHE) are gaining popularity worldwide for their higher coefficients of performance and lower CO2 emissions. However, the higher initial cost of installing the borehole GHEs is a main obstacle to spread the systems. To reduce the required total GHE length and efficiently operate the systems, various systems such as hybrid ones (e.g. solar heat injection) have recently been introduced. Accurate prediction of heat transfer in and around boreholes of such systems is crucial to avoid costly overdesigns or catastrophic failures of undersized systems as it is for typical GCHP systems. However, unlike the traditional sizing methods, it is increasingly required to take into account detailed borehole configuration and transient effects (e.g. short circuit effects between U-tubes). Many of the existing GHE models have been reviewed. Some of these models have serious limitations when it comes to transient heat transfer, particularly in the borehole itself. Accordingly, the objective of this thesis is to develop a model that is capable to accurately predict thermal behaviors of the GHEs. A precise response to input variations even in a short time-step is also expected in the model. The model also has to account for a correct temperature and flux distribution between the U-tubes and inside the borehole that seems to be important in the solar heat injection case. Considering these effects in 3D with a detailed mesh used for describing the borehole configurations is normally time-consuming. This thesis attempts to alleviate the calculation time using state model reduction techniques that use fewer modes for a fast calculation but predict similar results. Domain decomposition is also envisaged to sub-structure the domain and vary the time-step sizes. Since the decomposed domains should be coupled one another spatially as well as temporally, new coupling methods are proposed and validated particularly in the FEM. For the simulation purpose, a hybrid model (HM) is developed that combines a numerical solution, the same one as the 3D-RM but only for the borehole, and well-known analytical ones for a fast calculation. An experimental facility used for validation of the model has been built and is described. A comparison with the experimental results shows that the relatively fast transients occurring in the borehole are well predicted not only for the outlet fluid temperature but also for the grout temperatures at different depths even in very short time-steps. Even though the current version of 3D-RM is experimentally validated, it is still worth optimizing the model in terms of the computational time. Further simulations with the 3D-RM are expected to be carried out to estimate the performance of new hybrid systems and propose its appropriate sizing with correspondent thermal impacts on the ground. Finally, the development of the model 3D-RM can be an initiation to accurately model various types of GHE within an acceptable calculation time

Ground source heat pumps (GSHPs) can provide an efficient way of heating and cooling buildings due to their high operating efficiencies. The implementation of these systems in urban environments could have further benefits. In such locations ground source heat is potentially available from alternative sources such as underground railways (URs). The potential benefits for using the waste heat generated by URs with localised GSHPs are established in this thesis. This was achieved through investigations of UR-GSHP interactions. The research detailed here was mainly conducted through Finite Element (FE) numerical modelling and analysis. First a preliminary two-dimensional (2D) FE model was developed. This model was highly simplified to enable rapid analysis of the systems. The model was used to establish key parameters and phenomena for more detailed additional research. Since the operation of the URs and GSHP involves complex, transient, three-dimensional (3D) transport phenomena and extreme geometrical aspect ratios, 3D numerical models of URs and vertical ground heat exchangers (GHEs) were independently developed and validated. These individual models were then built into the same modelling environment for their combined analysis. Initial investigations with the combined 3D model showed that interactions occur between URs and localised GSHPs. In order to investigate the effect of specific parameter variations on the earlier established UR-GSHP interactions, a parametric analysis was conducted. The analysis included two sets of studies. The first group of studies considered different geometrical arrangements of the systems, and the second group investigated the effect of altered operational characteristics options on the interactions. Overall the results suggested that the performance of a GSHP can be significantly improved if the GHE array is installed near to the UR tunnel. It was shown that the improvement on the GHEs average heat extraction rate due to the heat load from the UR tunnel can be high as ~ 40%, depending on the size and shape of the GHE array and its proximity to the UR tunnel(s). It was also concluded that if the design aim is to enhance the heat extraction rates of urban GSHP systems, constructing the GHEs as close as possible to the UR tunnel would be essential. The results gathered from the parametric analysis were used to develop a formula. This formula is one of the key contributions to knowledge from this research. The formula developed allows approximating the GHEs’ heat extraction improvements due to the nearby tunnel(s) heat load(s). The formula makes use of a single variable named as interaction proximity. This variable was found to be one of the key parameters impacting on UR-GSHP interactions. At the end of the thesis, conclusions are drawn concerning the thermal interactions of URs with nearby vertical GHEs and the numerical modelling of such systems. Recommendations for further research in this field are also suggested.

GSHP systems are common in Sweden but there are few evaluations quantifying the performance of the systems and highlighting problem that occurs during operations. The research project Annex 52 Long-term performance measurement of GSHP systems serving commercial, institutional and multifamily building part of IEA HPT TCP proves the need to systematically be able to evaluate GSHP systems. This thesis aims to expand the knowledge of how to evaluate GSHP systems and provide case studies for Annex 52. Three residential ground source heating systems used for heating has been evaluated and analyzed in this study. The evaluation has consisted of three parts. The first part analyzes the operation and stability of the GSHP systems. The second part consist of a detailed study of the performance of the GSHP systems. The seasonal performance factor has been calculated for different system boundaries based on the work done by SEPEMO. In addition, a method on how to evaluate the efficiency of the heat pumps based on the two temperature levels, source side temperature and the heat sink temperature, that the heat pump is operating at throughout a year has been developed within this thesis. This has included a method on how to normalize the temperatures based on the operation of the heat pump in order to quantify one temperature for each the two temperature levels. The third part consist of a comparison of the mean secondary fluid temperature between the calculated temperature using the software EED and the measured temperatures. This includes a comparison evaluation and sensitivity analysis on input parameters during the design of the borehole heat exchanger fields. This study has expanded the available reference cases of GSHP systems in Sweden. It also can be used as a guideline for those who will evaluate future GSHP systems. Designers of GSHP system will also benefit from the recommendations listed in this thesis regarding instrumentation and possible problems that may occur. The results show that the evaluation successfully managed to quantify the performance and operational issues that have occurred for each system. The method developed in this study was able to quantify the operation of the different systems based on the temperature levels and can be used for future GSHP evaluations of similar system type.
Bergvärmesystem är vanligt förekommande i Sverige men trots detta finns det få studier där prestandan har utvärderats och de vanligt förekommande problemen under drift har belysts. Forskningsprojektet Annex 52 Annex 52 Long-term performance measurement of GSHP systems serving commercial, institutional and multi-family building som är en del av IEA HPT TCP visar på behovet av att systematisk utvärdera bergvärmesystem. Detta examensarbete syftar till att utveckla och bidra till kunskap om hur bergvärmesystem kan utvärderas och att bidra med exempelstudier till Annex 52. Inom detta examensarbete har tre bergvärmesystem som betjänar flerbostadshus utvärderats och analyserats. Utvärderingen bestod av tre analyser. I den första analyserades driften av bergvärmesystemen och hur stabilt systemet har varit historiskt. Detta följdes av en detaljerad analys av olika nyckeltal för bergvärmesystemen. Årsverkningsgraden har beräknats för olika gränsdragningar vilka baseras på det tidigare arbetet utfört av SEPEMO. Inom detta examensarbete har även en metod tagits fram för att utvärdera verkningsgraderna för en värmepump baserat på de två temperaturnivåerna, köldbärarsidan och värmebärarsidan, som värmepumpen arbetar med under ett år. Till detta har en metod tagits fram om hur temperaturen kan normaliserats baserat på driften av värmepumparna för att kvantifiera en temperatur vardera för de två temperaturnivåerna. I den tredje utvärderingen jämfördes den beräknade medelfluidtemperaturen av köldbäraren i borrhålen med den uppmätta temperaturen. Till detta utfördes en känslighetsanalys av hur indata av dessa beräkningar påverkar resultaten.

Le processus d'urbanisation en Chine exerce une forte pression sur l’environnement. Le plus fort potentiel de réduction de ces impacts correspond aux décisions prises lors de la conception du bâtiment, qui peuvent s’appuyer sur des outils de simulation numérique. Cette thèse est consacrée à l’étude de trois conditions aux limites liées à l'évaluation de la performance énergétique et environnementale des bâtiments en Chine : - Le sol : un modèle de pompe à chaleur couplée au sol est proposé, et couplé à un modèle d'échangeur de chaleur géothermique permettant le calcul rapide de la réponse d’un champ de sondes verticales de grande taille. Ce modèle peut être utilisé pour améliorer les performances énergétiques du système en phase de conception ou de gestion. - Le microclimat : une méthode de génération de fichier climatique spécifique au site qui fournit la température horaire locale de l'air est proposée, prenant en compte l'effet d'îlot de chaleur urbain. Les effets du microclimat sur la performance énergétique du bâtiment sont étudiés quantitativement. - Le système d’arrière-plan pour l’analyse de cycle de vie : les effets de la variation spatiale et temporelle du mix de production d'électricité en Chine sur les impacts environnementaux sont étudiés. La base de données environnementales est adaptée au contexte national et local chinois. Les résultats montrent que les impacts environnementaux des bâtiments peuvent être évalués plus raisonnablement en considérant ces trois conditions aux limites
The urbanisation process in China brings a high pressure on the environment. The highest potential to reduce these impacts corresponds to decisions made during the building’s design phase, which can be supported by numerical simulation. This thesis is dedicated to the study of three boundary conditions related to the energy and environmental performance evaluation of buildings in China: - The ground: a ground coupled heat pump model is proposed integrating a fast calculation ground heat exchanger model for a large-scale boreholes field. This model can be used to improve the energy performance of the system in the design and operation phases. - The microclimate: a site-specific weather file generation method which can provide local hourly air temperature is proposed, accounting for the urban heat island effect. The effects of the microclimate on the building’s energy performance are quantitatively investigated. - The background system for life cycle assessment: the effects of the spatial and temporal variation of the electricity production mix in China on the environmental impacts are investigated. The environmental database is adapted to the Chinese national and local context. The results show that the environmental impacts of buildings could be more reasonably evaluated by considering these three boundary conditions

Ground-source heat pumps systems (GSHP) are commonly used all over Sweden to supply heat and sometimes cool to different kinds of housings or commercial facilities. Many large installations are by now between 10 and 20 years old. Even when the design of such system has been tackled, rare are the studies that have dealt with following their performance throughout time in detail. Based on conductive heat transfer, the heat extraction process makes the ground temperature decrease when installations are only used for heating. This thesis aims at proposing a method to evaluate how the temperature in a borehole heat exchanger of a GSHP will evolve. The project is focusing on the heat transfer from the ground to the boreholes modelled using Finite Line Source (FLS) based generated g-functions. “g-functions” are non-dimensional parameters characterizing the evolution of the ground thermal resistance enduring variable heat extraction loads. A model using Matlab has been developed and validated against relevant publications. As a case study, the method is applied to an existing 15 years old GSHP installation, composed of 26 boreholes and 3 heat pumps, so as to compare the obtained results with data measured on site. Two sub-borehole fields compose this installation: 14 of them were drilled in 1998 and the remaining 12 in 2009. Measured variable heat extraction loads were superposed using dedicated site g-functions for the two boreholes fields. As a result, a comparison between modelled and calculated heat carrier fluid in the boreholes over the last 6 months is presented here, as well as a 20 years forecast of the ground temperature at the interface with the boreholes.

Le recenti politiche ambientali, volte alla riduzione del fabbisogno energetico in edilizia ed alla riduzione delle emissioni di gas clima alteranti, hanno supportato il diffondersi delle tecnologie ad energia rinnovabile. Tra queste, le pompe di calore geotermiche si sono affermate come soluzione alternativa ai tradizionali sistemi per il riscaldamento e raffrescamento degli edifici, in virtù della loro provata affidabilità e dell’elevata efficienza. Sono attualmente disponibili diverse tipologie di pompa di calore geotermica che possono essere in primo luogo classificate in due sottocategorie: a circuito aperto e a circuito chiuso. Le pompe di calore geotermiche a circuito chiuso sono maggiormente diffuse e sono termicamente accoppiate al terreno, che è la sorgente/pozzo termico, per mezzo di scambiatori geotermici. Questi sono generalmente costituiti da un sistema di tubazioni in materiale plastico, che può essere installato in perforazioni verticali (fino a 200 m di profondità) o in posizione orizzontale all’interno di appositi sbancamenti e trincee superficiali (solitamente fino a 2 m). Le pompe di calore geotermiche accoppiate a scambiatori verticali beneficiano della favorevole temperatura del terreno alle basse profondità. All’incirca a 10 m dalla superficie infatti il terreno ha una temperatura quasi costante pari alla temperatura media annuale dell’aria, che aumenta all’aumentare della profondità secondo il gradiente geotermico locale. Al contrario, nel caso di scambiatori orizzontali, la pompa di calore è accoppiata termicamente ad una sorgente (il terreno superficiale) la cui temperatura oscilla stagionalmente al variare delle condizioni ambientali. In virtù di ciò, gli scambiatori verticali offrono prestazioni mediamente migliori, tuttavia l’elevato costo, rende comunque competitiva la più economica soluzione orizzontale per applicazioni residenziali di piccola taglia. Negli ultimi decenni, un considerevole sforzo è stato fatto per l’ottimizzazione delle prestazioni delle pompe di calore geotermiche, sia in ambito accademico che industriale. Di recente sono state sviluppate nuove configurazioni e geometrie per gli scambiatori orizzontali con l’obiettivo di aumentarne l’efficienza di scambio termico. Questa tesi si inserisce in questo ambito, essendo dedicata ad un innovativo scambiatore geotermico di tipo Flat-Panel, inventato e sviluppato presso l’Università degli Studi di Ferrara. L’analisi delle prestazioni di scambiatori Flat-Panels è stata condotta sia per via sperimentale sia impiegando tecniche di modellazione numerica, nell’intento di fornire indicazioni approfondite sul loro utilizzo in accoppiamento a pompe di calore geotermiche. Allo scopo è stato allestito un apparato sperimentale equipaggiato con due prototipi di Flat-Panel, presso il Dipartimento di Architettura dell’Università di Ferrara. Sono stati condotti diversi test simulando il funzionamento di una pompa di calore geotermica in differenti condizioni operative (riscaldamento e raffrescamento) e in diverse modalità (funzionamento continuo, discontinuo e pulsato). Con rifermento ai più comuni scambiatori orizzontali, il Flat-Panel ha fornito prestazioni molto buone sia in riscaldamento che raffrescamento. In particolare, un’ottima prestazione è stata ottenuta durante i test estivi, in virtù della maggiore differenza di temperatura tra il fluido termovettore ed il terreno termicamente indisturbato. Come riportato in letteratura in merito agli scambiatori orizzontali, anche per i Flat-Panels non sono stati osservati fenomeni di deriva termica nel terreno superficiale, indipendentemente dall’energia scambiata. L’analisi numerica ha riguardato la modellazione dello scambio termico nel terreno per mezzo di scambiatori di tipo Flat-Panel. Allo scopo è stato impiegato un modello numerico agli elementi finiti risolvendo lo scambio termico in regime transitorio in un dominio bidimensionale. Nel dominio di calcolo la particolare geometria del Flat-Panel è stata ricondotta ad una condizione al contorno. È stato inoltre sviluppato un modello del bilancio di energia alla superficie del terreno (condizione al contorno del terzo tipo) al fine di simulare dettagliatamente la variazione giornaliera e stagionale della temperatura del terreno superficiale, che è determinante per le prestazioni degli scambiatori orizzontali. In considerazione di ciò, l’analisi è stata approfondita con ulteriori simulazioni per valutare l’effetto sulla soluzione numerica di differenti condizioni al contorno alla superficie del terreno: il modello del bilancio di energia, un flusso termico equivalente ed infine una temperatura superficiale equivalente. I risultati indicano che l’utilizzo del modello del bilancio di energia è l’approccio da preferirsi, senza che questo comporti un particolare aggravio in termini di tempo di calcolo. L’utilizzo di una temperatura equivalente è una ragionevole semplificazione, sebbene la sua stima corretta sia piuttosto complessa. I risultati del modello numerico proposto sono stati confrontati con i dati sperimentali ottenuti durante i test in diverse condizioni operative. Complessivamente il modello si è dimostrato affidabile nel calcolo della variazione di temperatura nel terreno determinato dall’effetto combinato dello scambio termico alla superficie del terreno e allo scambiatore. Infine, è stata svolta un’analisi di sensitività per valutare l’effetto della variazione della conduttività termica del terreno.
Worldwide, the innovation and environmental policies for energy saving in buildings and the reduction of greenhouse gas emissions have widely supported renewable energy technologies. Ground-source heat pumps (GSHPs) are regarded as a reliable technology and may represent an efficient and cost-effective solution for space heating and cooling, when the investment for ground heat exchangers is reasonable. In ground-coupled heat pump (GCHPs), a subset of GSHPs, a ground heat exchanger is required to thermally couple a heat pump with the ground. The ground heat exchanger usually consists of a piping system installed in vertical boreholes or in shallow diggings. Vertically coupled heat pumps benefit from the relatively stable temperature in the deep ground and uses geothermal energy from the earth. A horizontally coupled heat pump uses the seasonal heat storage in shallow soil therefore, the performance of horizontal ground heat exchangers (HGHEs) is strongly dependent on climatic conditions due to the low installation depth. A considerable amount of research has been devoted to the performance optimisation of GCHPs, in the last decades. More recently, a number of studies have dealt with the development of new configurations and new geometries for HGHEs, aiming to improve their efficiency. As part of these efforts, this thesis was dedicated to an innovative HGHE, called Flat-Panel, which was invented and developed at the University of Ferrara. This study dealt with the experimental analysis and the numerical simulation of Flat-Panels and it was intended to provide guidance on the behaviour and the performance of this novel HGHEs. The experimental analysis was carried out by means of a dedicated experimental setup equipped with two FlatPanel prototypes. Tests were conducted simulating the operation of a GCHP in different operating conditions (heating and cooling) and modes (continuous, discontinuous and pulsed). Very good performance was reached for both heating and cooling mode in comparison with the widespread installations of straight pipes or slinky coils. The performance was higher in heating mode due to the higher temperature difference between the working fluid and the undisturbed soil in summer. Moreover, according to other studies, seasonal thermal drifts were not measured for HGHEs, regardless of the amount of energy exchanged. The numerical analysis dealt with the simulation of heat transfer in soil due to Flat-Panels. A finite element numerical code was applied solving the unsteady-state heat transfer problem in a 2D domain. In view of this, the FlatPanel shape was modelled as a boundary condition. In order to further delve into particular aspects of HGHEs behaviour, the different heat transfer processes at the ground surface were modelled on the basis of the surface properties and a comprehensive weather dataset. Furthermore, the effect on numerical simulation of HGHEs of different boundary conditions at the ground surface was analysed. The ground surface energy balance model (GSEB), the equivalent surface heat flux and temperature were assigned as boundary conditions of the 1st, 2nd and 3rd kind in three different simulations, respectively. The results indicate that the use of the GSEB model is the preferable approach to the problem, not affecting the calculation time. The equivalent surface temperature could be considered as a reasonable simplification, although its correct estimation is a major issue. The results of the numerical simulation were compared with multiple experimental data sets in different operating conditions. Overall, the model produced a good agreement in terms of ground temperature variation due to the combined effect of the HGHE operation and the heat transfer process at the ground surface. In addition, a sensitivity analysis was carried out to evaluate the effect of variations in soil thermal conductivity.

The aim of this work was to investigate the effect on horizontal ground heat exchanger performance of changing soil and load parameters, and pipe horizontal separation distance for ground-coupled heat pumps under Egyptian conditions.Egypt possesses a variety of energy resources; namely fossil and renewable. The amount of renewable energy available is significant and must be utilized perfectly for the sake of achieving sustainable use of energy resources. Soils in Egypt vary widely from being clay with its thermal conductivity of 1.11 (for clay particles) to sand with its thermal conductivity of 5.77 (for sand particles). Two soil samples were chosen from the literature to be used in the investigation held in this work with boundary conditions that match the weather and ground temperature distribution conditions in Egypt.Conduction heat transfer in soils is a very complicated process especially when it is combined with time dependant boundary conditions and temperature dependent thermophysical properties of the medium. A MATLAB code was used to estimate thermophysical properties of the soil samples with three different moisture contents (0, 0.2, and saturation %) and the upper boundary condition bases on two surface dryness conditions (dry and wet). The results of the code were fed to Abqaus/CAE to analysis and predict the temperature distribution in these soils with implementing the time dependant boundary conditions to investigate the ground thermal behaviour of these soils. Also the temperature distribution around two pipes per trench of horizontal ground heat exchanger with applying synthetic load based on estimated cooling and heating degree days for one set of weather conditions. The horizontal separation distance between pipes was investigated by changing it to be 0.2, 0.3, 0.4, and 0.5 metres.Both the MATLAB code and Abaqus environment were validated against measured data published in the literature and their results agreed well with this data.The results of the simulation showed that the ground thermal behaviour depends mainly on the boundary conditions applied on the model. Dry soils are the worst being affected by the variation of the boundaries, because of its low volumetric heat capacities. The moisture content in the soil should be kept around 0.2 or above to get the most benefits from the presence of moisture in the vicinity of ground heat exchangers. The effect of the soil surface dryness is less significant than that of the moisture content of the entire system but it is more controllable than the moisture content. Also it was found that the horizontal separation distance (HSD) between pipes must be selected on the bases of prior knowledge of the site parameters soil type and moisture level. The results showed that the 0.4m HSD is the optimum HSD for the conditions and load profile included in this study.

Flow obstructions are used as a passive design element in heat exchangers to enhance heattransfer. Further, a change in flow structure can also have a positive effect on the heat transfer. Avertical shell and tube heat exchanger, used to recover heat in the greywater stream, isinvestigated in this study. The heat exchanger consists of flow obstructions such as annulargrooves and a helical string. The flow structure can be modified to a swirling film flow byadding a passive design element, called a Cyclone generator. This study aims to experimentallyvalidate a periodic heat transfer CFD model of a shell and tube heat exchanger, with uniformflow at steady-state laminar conditions. The study further analyses the heat transfercharacteristics of the annular grooves and the helical string, and the modified flow due to aswirling film. A calibrated test rig is constructed to consist of a heat source and a heat sink, as well as a meansfor measuring the flow and temperature of a vertical heat exchanger at elevated temperatures.The experimental results were evaluated using the Ɛ -NTU method and uncertainty analysis ofone standard deviation. The heat exchanger geometry had periodically repeating sectionsbetween the inlet and the outlet. Hence the large geometry was simplified to a smaller periodicmodule. The module was subjected to periodic boundary conditions and was simulated using apressure-based coupled algorithm on ANSYS Fluent. Further, the distribution of pressure andvelocity flow fields are examined for uniform flow in CFD. The experiment investigated the heattransfer of a swirling flow at a wide range of flow rates. The CFD model could not be validated by the experiment due to a difference between the overallheat transfer coefficients, calculated in the model and the experiment. The error in validationcould be pointed to an ambiguous energy result in one of the streams. However, the model couldsimulate real-life pressure drop conditions. It was found that the helical string contributed to asubstantial increase in the local turbulence, which translates to an increase in heat transfer. Theheat transfer was also increased in the presence of the annular grooves. From the experiment, a higher heat transfer is noticed at the entrance region of the heatexchanger compared to the middle section. The heat transfer characteristics of the swirling filmwere found to be significantly higher than that of the uniform flow. Finally, for uniform andswirling flows, the heat exchanger effectiveness, Ɛ, can be described as a single logarithmicfunction of the NTU.

In 2010, the Ground Source Heat Pumps (GSHPs) market in the European Union went up over one million (1 014 436 units at the end of 2010 according to EUROBSERV’ER 2011). In 2011, it was estimated around 1.25 million according to Bayer et al. (2012). With more than 378 000 units installed in 2010, according to the Swedish heat pump association (SVEP), the Swedish GSHPs market was the first in the EU. As for the French GSHPs market, it was estimated to 151 938 units in service in 2010, which propelled France at the third rank in the EU. However, despite a relatively important number of GSHPs installed in the whole EU, since 2008 GSHP sales have shrank. Even Sweden which has been the most competitive country sees its GSHP sales decline in the first quarter of 2012 (EUROBSERV’ER 2011). This report is the achievement of my Master of Science Thesis project. It also represents the end of my studies at INSA Lyon in France and concludes my degree in Energetic and Environment Engineering. This report deals with the improvement of a heat injection apparatus which is available at KTH (Royal Institute of Technology). This equipment is better known as Thermal Response Test (TRT) apparatus. This kind of equipment improves Borehole Heat Exchangers (BHE) design in terms of size and cost benefits. This technology is generally used to design GSHP installations in both domestic and industrial purposes. It allows to determine really important thermal BHE parameters: the thermal conductivity of the ground and the borehole thermal resistance. The report covers a theoretical description of TRT experiments, the reasons and objectives of such a project, the apparatus design and its construction. The last part is dedicated to a first experimental laboratory results and some problems met during the project course.

Nowadays, Ground Source Heat Pumps (GSHPs) are more frequently acting as a main or the only device covering the building heat/cool demand. The most efficient way to extract/dissipate the low-temperature heat from/to the ground is by means of Borehole Heat Exchanger (BHE). In this Master of Science Thesis various aspects related to this technology are studied, focused on summarizing the possibilities of installing this tech-nology in Poland. Borehole drilling methods used in Poland and Sweden are analyzed and the most proper and economical ones according to Polish geological structure are proposed. Approximately for 80 % of Poland the ground should be penetrated with Mud Rotary Drilling, while for the rest 20 % DTH Air or Water driven hammer should be used. Solutions of Thermal Insulated Leg (TIL) Borehole Heat Exchanger cooperation with mechanical ventilation system are proposed and simple preliminary estimations show higher Coefficient of Performance (COP) in comparison to normal, common situation, where standard U-pipe BHE works. The possibility of using a new product (Energy Capsule - EC) in Polish conditions is surveyed, found hard to prosper at Polish market according to its high costs. Profitability of Ground Source Heat Pumps with Borehole Heat Exchanger in different geological regions of Poland is investigated. After conducted simulations it occurred that Polish lowland regions are cheaper in exploita-tion, while uplands regions are less expensive at investment level. Finally, the most ef-ficient BHE conception from those currently available at market as well as recently in-vented is suggested. Annular coaxial BHE in a form of Energy Capsule seems to be the most beneficial from all designs taken into account during performed simulations because of its low price and good thermal properties.

An investigation was conducted to determine the response of landfills to the operation of a vertical ground source heat pump (i.e., heat extraction system, HES). Elevated landfill temperatures, reported various researchers, impact the engineering performance of landfill systems. A numerical model was developed to analyze the influence of vertical HES operation on landfills as a function of climate and operational conditions. A 1-D model of the vertical profile of a landfill was developed to approximate fluid temperatures in the HES. A 2-D model was then analyzed over a 40 year time period using the approximate fluid temperatures to determine the heat flux applied by the HES and resulting landfill temperatures. Vertical HES configurations simulations consisted of 15 simulations varying 5 fluid velocities and 3 pipe sizes. Operational simulations consisted of 26 parametric evaluations of waste placement, waste height, waste filling rate, vertical landfill expansions, HES placement time, climate, and waste heating. Vertical HES operation in a landfill environment was determined to have 3 phases: heat extraction phase, transitional phase, and ground source heat pump phase. During the heat extraction phase, the heat extraction rate ranged from 0 to 2550, 310 to 3080, and 0 to 530 W for the first year, peak year, and last year of HES operation, respectively. The maximum total heat energy extracted during the heat extraction phase ranged from 163,000 to 1,400,000 MJ. The maximum difference in baseline landfill temperatures and temperatures 0 m away from the HES ranged from 5.2 to 43.2°C. Climate was determined to be the most significant factor impacting the vertical HES. Trends pertaining to performance of numerous variables (fluid velocity, pipe size, waste placement, waste height, waste filling rate, vertical landfill expansions, HES placement time, climate, and waste heating) were determined during this investigation. Increasing fluid velocity until turbulent flow was reached increased the heat extraction rate by the system. Once turbulent flow was reached, the increase in heat extraction rate with increasing fluid velocity was negligible. An increase in the heat extraction rate was caused by increasing pipe diameter. Wastes placed in warmer months caused an increase in the total heat energy extracted. Increasing waste height caused an increase in the peak heat extraction rate by 43 W/m waste height. Optimum heat extraction per 1 m of HES occurred for a 30 m waste height. Increasing the waste filling rate increased the total heat energy extracted. Heat extraction rates decreased as time between vertical landfill expansions increase. Total heat energy extracted over a 35 year period decreased by approximately 21,500 MJ/year for every year after the final cover was placed until HES operation began. For seasonal HES operation, the total heat energy obtained each year differs and the fourth year of operation yielded the most energy. Wet Climates with higher heat generating capacities yielded increased heat extraction rates. Maximum temperature differences in the landfill due to the HES increased by 16.6°C for every 1 W/m3 increase in peak heat generation rate. When a vertical HES was used for waste heating, up to a 13.7% increase in methane production was predicted. Engineering considerations (spacing, financial impact, and effect on gas production) for implementing a vertical HES in a landfill were investigated. Spacing requirements between the wells were dependent on maximum temperature differences in the landfill. Spacing requirements of 12, 12, 16, and 22 m are recommended for waste heating, winter-only HES operation, maximum temperature differences in the landfill less than 17°C, and maximum temperature differences in the landfill greater than 17°C, respectively. A financial analysis was conducted on the cost of implementing a single vertical HES well. The energy extracted per cost ranged from 0.227 to 0.150 $/MJ for a 50.8 mm pipe with a 1.0 m/s fluid velocity and a 50.8 mm pipe with a 0.3 m/s fluid velocity, respectively. A vertical HES could potentially increase revenue from a typical landfill gas energy project by $577,000 per year.

Microchannel heat exchangers present many advantages, such as reduced size, high thermal efficiency and low fluid inventory; and are increasingly being used for heat transfer in a wide variety of applications including heat pumps, automotive air conditioners and for cooling of electronics.However, the fundamentals of fluid flow and heat transfer in microscalegeometries are not yet fully understood. The aim of this thesis is to contribute to a better understanding of the underlying physical phenomena in single-phase and specially flow boiling heat transfer of refrigerants in small channels. For this purpose, well-characterized heat transfer experiments have been performed in uniformly heated, single, circular, vertical channels ranging from 0.64 to 1.70 mm in diameter and using R-134a, R-22 and R-245fa as working fluids. Furthermore, flow visualization tests have been carried out to clarify the relation between the two-phase flow behavior and the boiling heat transfer characteristics. Single-phase flow experiments with subcooled liquid refrigerant have confirmed that conventional macroscale theory on single-phase flow and heat transfer is valid for circular channels as small as 640μm in diameter. Through high-speed flow boiling visualization of R-134a under non adiabatic conditions seven flow patterns have been observed: isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. Annular-type flow patterns are dominant for vapor qualities above 0.2. Onset of nucleate boiling and subcooled flow boiling heat transfer of R-134a has been investigated. The wall superheat needed to initiate boiling was found as large as 18 ºC. The experimental heat transfer coefficients have been compared to predictions from subcooled flow boiling correlationsav ailable in the literature showing poor agreement. Saturated flow boiling heat transfer experiments have been performed with the 640 μm diameter test section. The heat transfer coefficient has been found to increase with heat flux and system pressure and not to change with vapor quality or mass flux when the quality is less than ∼0.5. For vapor qualities above this value, the heat transfer coefficient decreases with vapor quality. This deterioration of the heat transfer coefficient is believed to be caused by the occurrence of intermittent dryout in this vapor quality range. The experimental database, consisting of 1027 data points, has been compared against predictions from correlations available in the literature. The best results are obtained with the correlations by Liu and Winterton (1991) and by Bertsch et al. (2009). However, better design tools to correctly predict the flow boiling heat transfer coefficient in small geometries need to be developed. Dryout incipience and critical heat flux (CHF) have been investigated in detail. CHF data is compared to existing macro and microscale correlations. The comparison shows best agreement with the classical Katto and Ohno (1984) correlation, developed for conventional large tubes.
QC 20101101

[ES] La energía geotérmica de baja entalpía es una alternativa eficiente y renovable a los sistemas convencionales para proporcionar calefacción, refrigeración y producir agua caliente sanitaria (ACS) de forma sostenible. El proyecto GEOTeCH plantea el desarrollo de sistemas con bomba de calor geotérmica más eficientes y con un coste menor en comparación con el mercado. Para ello, se ha desarrollado un nuevo tipo de intercambiador enterrado coaxial con flujo helicoidal en el tubo externo que presenta una mayor eficiencia y permite reducir la longitud de intercambiador a instalar, así como una bomba de calor dual con compresor de velocidad variable, capaz de trabajar con el terreno o el aire como fuente/sumidero, seleccionando la que proporcione un mejor rendimiento del sistema. El principal objetivo es desarrollar un sistema eficiente y replicable para proporcionar calefacción, refrigeración y producir ACS en el sector de mercado de pequeños edificios con un tamaño menor en el campo de intercambiadores enterrados y un aumento de la eficiencia. Para demostrar la aplicabilidad de estos sistemas, se han construido tres instalaciones demostración en tres países europeos. En esta tesis doctoral se ha desarrollado un modelo dinámico completo del sistema en el software TRNSYS, capaz de reproducir el comportamiento de los diferentes componentes y del sistema en general. Este modelo constituye una herramienta útil para el desarrollo y análisis de diferentes estrategias de control sin la necesidad de implementarlas en instalaciones reales, así como analizar el comportamiento del sistema funcionando bajo condiciones diferentes. Para este propósito, es necesario desarrollar modelos detallados de los nuevos componentes desarrollados en el proyecto: el intercambiador enterrado coaxial helicoidal y la bomba de calor dual; para poder acoplarlos al resto de componentes en el modelo completo del sistema. Por ello, se ha desarrollado un modelo dinámico del nuevo intercambiador, capaz de reproducir con precisión el comportamiento a corto plazo del intercambiador, enfocado a la evolución de la temperatura del fluido, y se ha validado con datos experimentales en diferentes condiciones de operación. Para poder reproducir no solo el comportamiento dinámico del intercambiador enterrado, sino también la respuesta a largo plazo del terreno y la interacción entre intercambiadores en un campo, se ha desarrollado otro modelo en TRNSYS que realiza esta función. De esta manera, al acoplar ambos modelos es posible reproducir el comportamiento a corto plazo del intercambiador enterrado a la vez que la respuesta a largo plazo del terreno. Por otro lado, se ha implementado en TRNSYS un modelo de la bomba de calor dual desarrollado. Con este modelo es posible calcular la capacidad de la bomba de calor dependiendo del modo de operación en que esté funcionando, de la frecuencia del compresor y otras variables y condiciones de operación. El modelo del sistema dual en TRNSYS se ha utilizado para hacer un análisis de su comportamiento funcionando en diferentes climas, para ello se han seleccionado tres ciudades en España y en Europa con diferentes climas y se han realizado simulaciones del sistema funcionando en cada ciudad. Por otro lado, también se ha modelado en TRNSYS una de las instalaciones demostración del proyecto GEOTeCH, incluyendo el edificio climatizado y el acoplamiento con los fan coils. Con este modelo se estudia una nueva estrategia para controlar la frecuencia del compresor en base a la temperatura de las habitaciones, en lugar de controlarla en base a la temperatura de suministro, con el objetivo de reducir el consumo del compresor cuando ya se haya conseguido el confort. Además, otras estrategias de optimización se han analizado con el modelo.Por tanto, los modelos desarrollados constituyen herramientas útiles para ayudar en el diseño del sistema y los diferentes componentes, el análisis de su comportamiento y el d
[CAT] L'energia geotèrmica de baixa entalpia es planteja com una alternativa eficient i renovable als sistemes convencionals per proporcionar calefacció, refrigeració i produir aigua calenta sanitària (ACS) de forma sostenible. El projecte GEOTeCH planteja el desenvolupament de sistemes amb bomba de calor geotèrmica més eficients i amb un cost menor en comparació amb el mercat. Per a això, s'ha desenvolupat un nou tipus d'intercanviador enterrat coaxial amb flux helicoïdal en el tub extern que presenta una major eficiència i permet reduir la longitud a instal·lar, així com una bomba de calor dual amb compressor de velocitat variable, capaç de treballar amb el terreny o l'aire com a font, seleccionant la que proporcione un millor rendiment. Aquests components s'utilitzen en el nou sistema amb bomba de calor dual. El principal objectiu és desenvolupar un sistema eficient i replicable per proporcionar calefacció, refrigeració i produir ACS en edificis xicotets amb una grandària menor d'intercanviadors soterrats i un augment de l'eficiència. Per demostrar l'aplicabilitat d'aquests sistemes, s'han construït tres instal·lacions demostració en Itàlia, Països Baixos i Regne Unit. En aquesta tesi s'ha desenvolupat un model dinàmic complet del sistema en TRNSYS, capaç de reproduir el comportament dels components i del sistema en general. Aquest model constitueix una eina útil per al desenvolupament i anàlisi de diferents estratègies de control sense la necessitat d'implementar-les en instal·lacions reals, així com analitzar el comportament del sistema funcionant en condicions diferents. Per a això, cal desenvolupar models detallats dels nous components desenvolupats en el projecte: l'intercanviador enterrat i la bomba de calor dual; per poder acoblar-los a la resta de components. Per això, s'ha desenvolupat un model dinàmic del nou intercanviador enterrat, capaç de reproduir amb precisió el comportament a curt termini de l'intercanviador, enfocat a l'evolució de la temperatura del fluid, i s'ha validat amb dades experimentals en diferents condicions d'operació. Per a poder reproduir no només el comportament dinàmic de l'intercanviador soterrat, sinó també la resposta a llarg termini del terreny i la interacció entre intercanviadors en un camp, s'ha desenvolupat un altre model en TRNSYS que realitza aquesta funció. D'aquesta manera, en acoblar els dos models és possible reproduir el comportament a curt termini de l'intercanviador enterrat, al mateix temps que la resposta a llarg termini del terreny. D'altra banda, s'ha implementat en TRNSYS un model de la bomba de calor. Amb aquest model és possible calcular la capacitat de la bomba de calor depenent del mode d'operació en què estiga funcionant, de la freqüència del compressor i altres variables i condicions d'operació. El model del sistema dual en TRNSYS s'ha utilitzat per a fer una anàlisi del seu comportament funcionant en diferents climes, per a això s'han seleccionat tres ciutats a Espanya i tres a Europa amb diferents climes i s'han realitzat simulacions del sistema funcionant en cada ciutat durant un any. S'ha analitzat l'eficiència del sistema en cada ciutat, així com l'ús de cadascuna de les fonts (aire / terreny). D'altra banda, també s'ha modelat en TRNSYS una de les instal·lacions demostració del projecte GEOTeCH, incloent l'edifici d'oficines climatitzat i l'acoblament amb els fan coils. Amb aquest model es pretén estudiar una nova estratègia per a controlar la freqüència del compressor d'acord amb la temperatura de les habitacions, en lloc de controlar-la en base a la temperatura de subministrament, amb l'objectiu de reduir el consum del compressor quan les habitacions ja es troben en condicions de confort. A més, altres estratègies d'optimització s'han analitzat amb el model. Per tant, els models desenvolupats constitueixen eines útils per ajudar en el disseny del sistema i els diferents components, l'anàlisi del
[EN] Low enthalpy geothermal energy is considered as an efficient and renewable alternative to conventional systems to provide heating, cooling and Domestic Hot Water (DHW) production in a sustainable way. In this context, the GEOTeCH project proposes the development of more efficient geothermal heat pump systems with a lower cost compared to the market. To this end, a new type of coaxial Borehole Heat Exchanger (BHE) with helical flow through the outer tube has been developed, which presents a higher efficiency and allows to reduce the length of the heat exchanger to be installed, as well as a Dual Source Heat Pump (DSHP) with variable speed compressor, capable of working with the ground or air as a source / sink, selecting the one that provides the best performance of the system. These components are used in the new DSHP system developed. The main objective is to develop efficient and replicable systems to provide heating, cooling and DHW in the market sector of small buildings with a smaller size of the BHE field and an increase in the efficiency. To demonstrate the applicability of these systems, three demonstration facilities have been installed in Italy, the Netherlands and the UK. In this thesis, a complete dynamic model of the system has been developed in the TRNSYS software, capable of reproducing the behavior of the different components and the system in general. This model is a useful tool for the development and analysis of different control strategies without the need to implement them in real installations, as well as analyses the behavior of the system operating under different conditions. For this purpose, it is necessary to develop detailed models of the new components developed in the project: the BHE and the DSHP; to couple them to the rest of the components of the system. For this reason, a dynamic model of the new BHE was developed, able to accurately reproduce its short-term behavior, focused on the evolution of the fluid temperature, and validated with experimental data in different operating conditions. In order to reproduce not only the dynamic behavior of the BHE, but also the long-term response of the ground and the interaction between BHEs in a field, another model was developed in TRNSYS. In this way, by coupling both models, it is possible to reproduce the short-term behavior of the BHE as well as the long-term response of the ground. On the other hand, a model of the DSHP was implemented in TRNSYS. With this model, it is possible to calculate the capacity of the heat pump depending on the operating mode in which it is operating, the frequency of the compressor and other variables and operating conditions. The model of the hybrid system in TRNSYS has been used to make an analysis of its behavior working in different climatic conditions, for which three cities have been selected in Spain and three in Europe, with different climates. So, different simulations of the system have been carried out in each city for one year. The efficiency of the system in each city has been analyzed, as well as the use of each of the sources (air / ground). On the other hand, one of the demo-sites of the GEOTeCH project, including the conditioned office building and the coupling with the fan coils, has also been modelled in TRNSYS. With this model, it is studied a new strategy to control the frequency of the compressor based on the temperature of the rooms, instead of controlling it based on the supply temperature, with the aim of reducing the consumption of the compressor when the rooms are already in comfort conditions. In addition, other optimization strategies have been analyzed with the model. Therefore, the models developed, both for the BHE and the system, are able to reproduce their operation and can be used as virtual installations, constituting useful tools to help in the design of the system and the different components, the analysis of their behavior and the development of optimization strategies.
I would like to acknowledge the financial support that has made this PhD thesis possible. The present work has been supported by the European Community Horizon 2020 Program for European Research and Technological Development (2014-2020) inside the framework of the project 656889 – GEOTeCH (Geothermal Technology for Economic Cooling and Heating), also by the Generalitat Valenciana inside the program “Ayudas para la contratación de personal investigador en formación de carácter predoctoral (ACIF/2016/131)” and by the Institute for Energy Engineering of the Universitat Politècnica de València.
Cazorla Marín, A. (2019). MODELLING AND EXPERIMENTAL VALIDATION OF AN INNOVATIVE COAXIAL HELICAL BOREHOLE HEAT EXCHANGER FOR A DUAL SOURCE HEAT PUMP SYSTEM [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/125696
TESIS

Ground-coupled ventilation (GCV) is a system that exchanges heat with the soil. Because ground temperatures are relatively higher during the cold season and lower during the hot season, the system takes advantage of this natural phenomenon. This research focused on designing a ground-coupled ventilation system evaluation tool of many factors that affect system performance. The tool predicts the performance of GCV system design based on the GCV system design parameters including the location of the system, pipe length, pipe depth, pipe diameter, soil type, number of pipes, volume flow rate, and bypass system. The tool uses regression equations created from many GCV system design simulation data using Autodesk Computational Fluid Dynamics software. As a result, this tool helps users choose the most suitable GCV system design by comparing multiple GCV systems' design performances and allows them to save time, money, and effort.
Doctor of Philosophy

Ground Source Heat Pumps (GHSPs) is a relevant application and around 3 million installations are setting up at the beginning of 2010 (IEA ECES Annex 21). The improvements in GSHPs are currently focused on the optimization of the system and the reduction of costs installations. The thermal conductivity of the ground and thermal resistance of the Borehole Heat Exchanger (BHE) are important design parameters for Borehole Thermal Energy Storage (BTES) systems. The Thermal Response Test (TRT), which has been used up to now in the GHE design, only allows estimating mean values for thermal conductivity of the surrounding ground and borehole resistance. However, the ground thermal conductivity and borehole thermal resistance may present local variation along the borehole depth. For improving conventional TRT, the optical fiber technology is applied to collect information about the temperature profiles in the borehole. Thermal Response Test (TRT) logs the inlet and outlet fluid temperatures; meanwhile, the Distributed Thermal Response Test (DTRT) carries out a profile of the temperature along the borehole depth, in this case with fiber optic cables. This Master of Science Thesis focuses on the comparison and analysis of DTRT measurements in a U-pipe borehole in order to estimate the thermal conductivity and the borehole thermal resistance along the borehole. The comparison and the analysis are carried out by: •Comparing the differences of TRT results depending on the heat power rate considered – constant and by steps-. •Comparing the results from two different resolution Distributed Test Sensing (DTS) equipments: Halo and Sentinel DTS. •Comparing the differences of TRT results as depending on the analytical procedure based on the line source theory: line source model and line source approximation.

The UK government’s Carbon Plan-2011 aims for 80% carbon emission reduction by 2050, and the 2009 UK National Renewable Energy Action Plan has set a target of delivering 15% of total energy demand by renewable energy sources by 2020. Ground Source Heat Pump (GSHP) systems can play a critical role in reaching these goals within the building sector. Achieving such benefits relies on proper design, integration, installation, commissioning, and operation of these systems. This work seeks to provide evidence to improve the practices in design, installation and operations of large GSHP systems. This evidence has been based on collection and analysis of data from an operational large-scale GSHP system providing heating and cooling to a university building. The data set is of significance in that it is collected from a large-scale system incorporating fifty-six borehole heat exchangers and four heat pumps. The data has been collected at high frequency since the start of operation and for a period of three years. The borehole heat exchanger data is intended to form a reference data set for use by other workers in model validation studies. The ground thermal properties at the site have been estimated using a novel combination of numerical model and parameter estimation methods. The utility of the reference data set has been demonstrated through application in a validation study of a numerical borehole heat exchanger model. The system heat balances and power consumption data have firstly been analysed to derive a range of performance metrics such as Seasonal Performance Factors. Analysis has been carried out at the system and individual heat pump level. Annual performance has been found satisfactory overall. A series of analyses have been carried out to investigate the roles of circulating pump energy, control system operation and dynamic behaviour. Monitoring data from one of the heat pumps has also been analysed in further detail to make comparisons with manufacturer’s steady-state performance data and with consideration to variations in fluid properties. Some modest degradation from stated performance has been identified. The most significant operational factors accounting for degradation of overall system performance have been excessive pump energy demands and short cycling behaviour. Some faults in operation of the system during the monitoring period have also been identified. A series of recommendations are made as to ways to improve the design and operation of large-scale GSHP systems based on this evidence. These recommendations are chiefly concerned with better design for part-load operation, reduction in pump energy demands and more robust control systems.

Nowadays Ground Source Heat Pumps (GSHP) are widely used to provide heating and/or cooling as well as domestic hot water in commercial and residential buildings. The Swedish GSHPs market is the first one in the European Union with more than 378,000 units installed until 2010 according to the Swedish Heat Pump Association (SVEP). This thesis focuses on the improvement of a Thermal Response Test (TRT) apparatus available at KTH Royal Institute of Technology – Energy Technology Department. This equipment aims at improving Borehole Heat Exchanger (BHE) design in terms of size. Its key purpose is to evaluate two main BHE properties: the ground thermal conductivity and the borehole thermal resistance. A new command software is developed in order to control the TRT equipment and run TRT measurements. This new software is developed using Python as programming language and replaces an older program which needed LabVIEW to run. The TRT command software designed in this thesis provides the user with a simple and user-friendly interface to control each device of the equipment. Measurements are exported and saved to files which can be open with both Microsoft Excel and the analysis tool also developed in this thesis. The stand-alone evaluation tool can be used to analyse TRT and/or DTRT measurements. This analysis tool helps the user to compute large amount of data with few data manipulation and low computation time. Model parameters and TRT/DTRT measurement can be imported from files into it and different fitting settings are available to run the optimization, i.e. account for baseline variations (early activities in the borehole, different optimization periods, analysis during thermal recovery of the ground, single/multi-sectional analysis along the depth, among others). This report covers a theoretical description of TRT experiments and its models, the objectives of such a project and the development of the control and evaluation tools.

The ground source resources are becoming more and more popular and now the ground source heat pumps are frequently used for heating and cooling different types of buildings. This thesis aims at giving a contribution in the development of the thermal modelling of borehole heat storage systems. Furthermore, its objective is to investigate the possibility of implementing of a GSHP (ground source heat pump) with vertical boreholes, in order to deliver the heating and cooling demand for a passive house and to emphasize some certain advantages of this equipment even in the case of a small building (e.g. residential house). A case study is presented to a suitable modelling tool for the estimation of the thermal behaviour of these systems GSHP by combining the outcome from different modelling programs. In order to do that, a very efficient residential solar house (EFden House – a passive residential single-family house, which was projected and built in Bucharest with academic purposes) is being analysed. The numerical results are produced using the software DesignBuilder, EED (Earth Energy Designer) and a sizing method for the length of the boreholes (ASHRAE method). The idea of using 2 different modelling programs and another sizing method for the borehole heat exchanger design (ASHRAE method) is to make sure that all the calculations and results are valid and reliable when analysing such a system theoretically (in the first phases of implementing a project), before performing a geotechnical study or a thermal response test in order to assess the feasibility of such a project beforehand. The results highlight that the length of the borehole, which is the main design parameter and also a good index in estimating the cost of the system, is directly influenced by the other fundamental variables like thermal conductivity of the grout, of the soil and the heat carrier fluid. Also, some correlations between these parameters and the COP (coefficient of performance) of the system were made. The idea of sizing the length of boreholes using two different methods shows the reliability of the modelling tool. The results showed a difference of only 2.5%.  Moreover, the length of borehole is very important as it was calculated that can trigger a difference in electricity consumption of the GSHP up to 28%. It also showed the fact that the design of the whole system can be done beforehand just using modelling tools, without performing tests in-situ. The method aims at being considered as an efficient tool to estimate the length of the borehole of a GSHP system using several modelling tools.

The presentation was made via Skype due to the programme being online based

Diploma thesis describes the design of a vertical heat exchanger in accordance with European standard ČSN EN 13 445-3 Unfired pressure vessels - Part 3: Design (in Czech). The first part contains the distribution of heat exchangers including an overview of the most commonly used media. The main part is aimed on the strength assessment of the heat exchanger based on the mentioned standard. The assessment equations are converted into an interactive document in Mathcad program. This allows quick evaluation of the new input parameters or easy implementation of the new parts of assessment. Checking the analytical evaluation is performed by numerical simulation in Ansys Workbench software with post-processing results according to given standard (stress categorization). The output is also the heat exchanger design documentation.

The sales of Ground Source Heat Pumps in Sweden and many other countries are having a rapid growth in the last decade. Today, there are approximately 360 000 systems installed in Sweden, with a growing rate of about 30 000 installations per year. The most common way to exchange heat with the bedrock in ground source heat pump applications is circulating a secondary fluid through a Borehole Heat Exchanger (BHE), a closed loop in a vertical borehole. The fluid transports the heat from the ground to a certain heating and/or cooling application. A fluid with one degree higher or lower temperature coming out from the borehole may represent a 2-3% change in the COP of a heat pump system. It is therefore of great relevance to design cost effective and easy to install borehole heat exchangers. U-pipe BHEs consisting of two equal cylindrical pipes connected together at the borehole bottom have dominated the market for several years in spite of their relatively poor thermal performance and, still, there exist many uncertainties about how to optimize them. Although more efficient BHEs have been discussed for many years, the introduction of new designs has been practically lacking. However, the interest for innovation within this field is increasing nowadays and more effective methods for injecting or extracting heat into/from the ground (better BHEs) with smaller temperature differences between the heat secondary fluid and the surrounding bedrock must be suggested for introduction into the market.

This report presents the analysis of several groundwater filled borehole heat exchangers, including standard and alternative U-pipe configurations (e.g. with spacers, grooves), as well as two coaxial designs. The study embraces measurements of borehole deviation, ground water flow, undisturbed ground temperature profile, secondary fluid and groundwater temperature variations in time, theoretical analyses with a FEM software, Distributed Thermal Response Test (DTRT), and pressure drop. Significant attention is devoted to distributed temperature measurements using optic fiber cables along the BHEs during heat extraction and heat injection from and to the ground.

QC 20100517
EFFSYS2
Efficient Use of Energy Wells for Heat Pumps

The Ground Source Heat Pump (GSHP) is a promising technology for the heating and cooling of buildings with renewable energy sources. Borehole Heat Exchangers, in which heat is exchanged by circulating a heat carrier fluid into a pipe closed loop, are the most used typology. The energy performances of these plants depend from the properties of the BHE and of the soil. In this work, the operation of BHE for a period of 30 years has been simulated, using a finite-element subsurface flow and heat transport modelling code (FEFLOW). The relative influence of each BHE, hydrogeological and thermal soil property has been investigated, running a set of simulations and analyzing the resulting fluid temperatures in the closed loop to estimate the heat pump energy consumption. Comparing the results, we observe that the length is the most important BHE property, and it should be optimized in order to minimize the overall expense (installation and maintenance); also the pipe distance, the grout heat conductivity and the properties of the heat carrier fluid play an important role. The soil heat conductivity heavily influences the resulting fluid temperatures, and in-situ tests should be carried to predict the plant operation accurately. The presence of subsurface flow enhances the heat transfer in the subsoil, improving the heat pump performances. The heat dispersivity spatial dependence is still unknown, and this causes a strong uncertainty in the prediction of BHE operation in presence of groundwater flow.

Žemės šilumos siurblių sistemos surenka žemės šilumą, dažniausiai vertikaliu U formos gręžinio šilumokaičiu. U formos gręžinio šilumokaičio našumas priklauso nuo šiluminių žemės savybių, taip pat nuo gręžinyje naudojamo skiedinio ar užpildo. Siekiant, kad Žemės šilumos siurblių sistemos pasiteisintų, projektuojant reikia atsižvelgti į geologinių struktūrų šiluminį laidumą ir gręžinio šilumokaičio šiluminę varžą. Šio darbo tikslas buvo nustatyti šilumos siurblio, naudojančio grunto šilumą, pritaikymo individualioje sodyboje siurblio techninis ir ekonominis įvertinimas. Nustatyta, kad investicijos projektui įgyvendinti, kai gyvenamajam pastatui šildyti ir buitiniam karštam vandeniui ruošti šildymo sezono metu šilumą gamina šilumos siurblys, naudojantis grunto šilumą, palyginti su tiesioginiu elektros naudojimu pastatui šildyti ir buitiniam karštam vandeniui ruošti, atsiperka per 6,3 metus. Šiluminės reakcijos testas padeda nustatyti šiluminį žemės laidumą (λ) gręžinio šilumokaičio įrengimo vietoje, bei efektyvią gręžinio šilumokaičio šiluminę varžą (Rb). Pagrindinis tikslas buvo suderinti gręžinio šilumokaitį su žemės sąlygomis, taip pat nustatyti gręžinio gylio poveikį (60 m: VB2; 90 m: VB3).
Ground source heat pump systems exchange heat with the ground, often through a vertical, U-tube, borehole heat exchanger. The performance of this U-tube borehole heat exchanger depends on the thermal properties of the ground formation, as well as grout or backfill in the borehole. The design and economic probability of ground source heat pump systems need the thermal conductivity of geological structure and thermal resistance of borehole heat exchanger. An economic and technical evaluation of the heat pump, which is using ground heat, in individual homestead. It was found that the investment for this project, when heat pump using ground heat is used to heat residential building and domestic hot water in heating season, compared with the use of direct electric heating of buildings and domestic hot water payback within 6.3 years. Thermal response test method allows the in-situ determination of the thermal conductivity (l) of the ground formation in the vicinity of a borehole heat exchanger, as well as the effective thermal resistance (Rb) of this latter. The main goal has been to determine same in-situ ground type of borehole heat exchanger, including the effect of borehole’s depths (60 m: VB2; 90 m: VB3).

La thèse est consacrée à l’étude de l’échange de chaleur entre un fluide et un milieu solide tel que le sol par l’intermédiaire d’un échangeur bitubulaire vertical. Un modèle mathématique du comportement du système a été élaboré. Pour résoudre l’ensemble des équations, un algorithme de calcul numérique, basé sur l’utilisation des fonctions de Green afin de réduire le problème tridimensionnel à un problème bidimensionnel, a été mis au point. L’application du théorème de Duhamel a permis d’introduire la notion de réponse caractéristique de ce type d’échangeur. En vue de valider le modèle mathématique et numérique, une expérience a été réalisée en laboratoire. Les résultats des tests effectués avec des conditions aux limites différentes confirment avec une très bonne approximation les résultats théoriques. Ce modèle peut être alors utilisé comme un outil intéressant pour concevoir des échangeurs à puits multiples efficaces contribuant ainsi à l’élaboration de chaînes énergétiques rentables.

An experimental investigation has been carried out to study the heat transfer in a two-phase two-component mixture flowing upward inside a 1" double pipe heat exchanger. The heat transfer coefficient was measured using either air to lift the liquid (air-lift system) or a mechanical pump. The heat transfer coefficient results have been extensively studied and compared with other workers' results. An attempt was made to correlate the present heat transfer data in dimensionless correlations. Possible factors affecting the two-phase heat transfer coefficient have been studied with special attention being given to the fluid properties, particularly the liquid viscosity. Experiments were also carried out to investigate the effect of solid particles added to a liquid flow on the measured heat transfer coefficient. The present investigation was carried out using air as the gas-phase ranging from 2x 10-5 up to 80 x 10-5 m3/s. Liquids used were water and glycerol solutions with viscosity ranging from 0.75 up to 5.0 C. P. and flowrates between 4x 10-5 and 25 x 10-5 m3/s. Void fraction and pressure drop were also measured during the heat transfer process. Flow pattern in gas-liquid mixture was investigated in a perspex tube of identical dimensions to the heat exchanger tube.

Sekliojo geoterminio šildymo sistemos vis plačiau naudojamos individualios ir visuomeninės paskirties pastatų šildymui. Tokių sistemų viena svarbiausių dalių yra kolektorius, tiekiantis žemės šilumą šilumos siurbliui. Nuo tinkamo kolektoriaus parametrų parinkimo labai priklauso geoterminio šildymo sistemos efektyvumas ir jos įrengimo kaštai. Inžineriniams kolektorių parametrų skaičiavimams plačiai naudojami artutiniai, gana apytiksliai metodai. Šiame darbe atliktas vertikalaus U-tipo kolektoriaus kompiuterinis modeliavimas, baigtinių elementų metodu, panaudojant COMSOL Multiphysics kompiuterinių programų paketą. Išspręstas 3D šilumos laidumo uždavinys, leidžiantis tiksliau įvertinti kolektoriaus parametrus. Ištirta kolektoriaus šilumos srauto priklausomybė nuo gręžinio gylio, kolektoriuje tekančio šilumnešio greičio bei temperatūros, užpildo, grunto ir šilumnešio parametrų.
Geothermal heating systems are becoming increasingly popular to generate heat for public and individual buildings. But they have some disadvantages, most notable of which is that such systems require major investments in geological research and the installation of the thermal heat exchanger. One of the most important components in this type of systems is a heat exchanger, supplying the geothermal heat to the heat pump. Selecting the proper parameters of a heat exchanger is critical for overall efficiency and installation costs of a geothermal heating system. Simulations of engineering parameters of heat exchangers are based on quite approximate methods. In this work, we carried out a Finite Element Method computer simulation of a vertical U-type heat exchanger using the COMSOL Multiphysics software package. We solved a 3D heat conduction problem, allowing more accurate assessment of vertical U-type heat exchanger parameters, such as the thermal resistance and heat flux, depending on geometry of the wells, ground and soil parameters.

Master’s thesis deals with the theme in three parts theoretical, practical and experimental. Project deals with heating nursery school and experiment deals with capacity reduction borehole heating exchanger for ground – source heat pump.

The thesis deals with an energy simulation of a ground heat exchanger (GHE) in classical and brine performance, which is used as an accessory of warm air heating system recovery in a low-energy family house. On basis of simulation results, the benefits of both heat exchangers were assessed. Furthermore, the energy and economics savings of heat recovery coupled with GHE were evaluated. Comparing the investment costs, the profitability of each investment were assessed and recommendations for the operation, implementation and appropriateness were outlined.

The borehole heat exchangers of today suffer from poor thermal and hydrodynamic performance. The purpose of this thesis is to improve the performance of ground source heat pump systems and thermal energy storages by increasing the energy efficiency of the borehole heat exchangers. For this reason, the annular coaxial borehole heat exchanger (CBHE) has been analyzed. This type of heat exchanger is interesting in terms of both thermal and hydrodynamic performance. A model has been set up in the program Comsol Multiphysics in order to investigate the heat transfer characteristics along the borehole. A literature survey that summarizes the analytical calculation methods developed in earlier Swedish research is presented in the report. Different geometries with or without insulation of the central pipe have been analyzed and the effective borehole resistance for each geometry has been calculated based on the simulation results. The model has been validated against a recently performed thermal response test, and shows very good correlation with reality. The results from the simulations show that by using the annular CBHE an increase of 2-3 °C in the evaporator of the heat pump can be achieved. Calculations show that the pump work (head loss) can be reduced to 1/6 of the corresponding case with a single U-pipe. There arises a vertical temperature gradient in the bedrock when recharging and extracting heat with the annular CBHE. This means that the annular CBHE acts like a counter-flow heat exchanger which is thermally optimal. In total, the simulation result shows that the annular CBHE geometry in this thesis can increase a system's seasonal performance factor (SPF) with 10-19 % in comparison with a U-pipe BHE. This is equivalent to 10-19 % lower electrical power consumption every year.

The thesis deals with energy simulation of a heat recovery system in coupling with a ground heat exchanger (GHE) in a low-energy family house with warm-air heating and ventilation. The effect of GHE on operation and effectiveness of a heat recovery unit was assessed from the results of the simulation. Next, energy and economic benefits of the heat recovery with and without GHE and consequent savings were evaluated as well. The profitability of the investment was assessed using comparison with the investment costs. Recommendations for the operation of the system were suggested.

In the context of energy transition, geothermics play an important role for the heating and cooling supply of both residential and commercial buildings. Thereby, the increasingly and intensive utilisation of shallow geothermal resources bears the risk of over-exploitation and thus poses a future challenge to ensure the sustainability and safety of such systems. Particularly, the well-established technology of borehole heat exchanger-coupled ground source heat pumps is applied for the thermal exploitation of the shallow subsurface. Due to the complexity of the involved physical processes, numerical modelling proves to be a powerful tool to enhance process understanding as well as to aid the planning and design processes. Simulations can also support the management of thermal subsurface resources, planning and decision-making on city and regional scales. In this work, the so-called dual-continuum approach was adopted and enhanced to develop a coupled numerical model considering flow and heat transport processes in both the subsurface and borehole heat exchangers as well as the heat pumps’ performance characteristics, and including the relevant phenomena influencing the underlying processes. Beside the temperature fields, the efficiency and thus the consumption of electrical energy by the heat pump is computed, allowing for the quantification of operational costs and equivalent carbon-dioxide emissions. The model is validated and applied to a number of numerical studies. First, a comprehensive sensitivity analysis on the efficiency and sustainability of such systems is performed. Second, a method for the quantification of technically extractable shallow geothermal energy is proposed. This procedure is demonstrated by means of a case study for the city of Cologne, Germany and its implications are discussed
Im Rahmen der Energiewende nimmt die Geothermie eine besondere Rolle in der thermische Gebäudeversorgung ein. Die zunehmende, intensive Nutzung oberflächennaher geothermischer Ressourcen erhöht die Gefahr der übermäßigen thermischen Ausbeutung des Untergrundes und stellt damit eine wachsende Herausforderung für die Nachhaltigkeit und Sicherheit solcher Systeme dar. Zur Erschließung oberflächennaher geothermischer Energie wird insbesondere die etablierte Technologie Erdwärmesonden-gekoppelter Wärmepumpen eingesetzt. Aufgrund der daran beteiligten komplexen physikalischen Prozesse erweisen sich numerische Modelle als leistungsfähiges Werkzeug zur Erweiterung des Prozessverständnisses und Unterstützung des Planungs- und Auslegungsprozesses. Zudem können Simulationen zum Management thermischer Ressourcen im Untergrund sowie zur Planung und politischen Entscheidungsfindung auf städtischen und regionalen Maßstäben beitragen. Im Rahmen dieser Arbeit wurde, basierend auf dem sogenannten ”dual-continuum approach” und unter Berücksichtigung des Einflusses der Wärmepumpe, ein erweitertes gekoppeltes numerisches Modell zur Abbildung der in Erdwärmesonden und dem Untergrund stattfindenden Strömungs- und Wärmetransportprozesse entwickelt. Das Modell ist in der Lage, alle relevanten Einflussfaktoren zu berücksichtigen. Neben den Temperaturfeldern im Untergrund und der Erdwärmesonde werden die Effizienz und damit der Stromverbrauch der Wärmepumpe simuliert. Damit können sowohl die Betriebskosten als auch der äquivalente CO 2 -Ausstoß abgeschätzt werden. Das Modell wurde validiert und in einer Reihe numerischer Studien eingesetzt. Zuerst wurde eine umfassende Sensitivitätsanalyse zur Effizienz und Nachhaltigkeit entsprechender Anlagen durchgeführt. Weiterhin wird ein Verfahren zur Quantifizierung des technisch nutzbaren, oberflächennahen geothermischen Potentials vorgestellt und anhand einer Fallstudie für die Stadt Köln demonstriert, gefolgt von einer Diskussion der Ergebnisse

Diploma thesis deals with design of the ventilation system for low-energy house. Introduction of the thesis is focused on ventilation needs and also includes a summary of main principals of ventilation systems which are commonly used in family houses. One chapter is dedicated to utilization of ground heat exchangers and also includes a CFD simulation. The actual design of the ventilation system for low-energy house assess the suitability of using local/central ventilation units and also determines the best method of controlling the system.

Evaluation in situ des caracteristiques thermiques moyennes du sol, modelisation et experimentation d'un echangeur baionnette place dans un milieu solide, et elaboration d'un modele simplifie de predimensionnement pour le stockage multipuits. Resultats obtenus sur un site de 25 puits

The thermal response of a borehole field is often described by non‐dimensional response factors called gfunctions.The g‐function was firstly generated as a numerical solution based on SBM (Superposition BoreholeModel). An analytical approach, the FLS (Finite Line Source), is also accepted for generating the g‐function. In thiswork the potential to numerically produce g‐functions is studied for circular borehole fields using the commercialsoftware COMSOL. The numerical method is flexible and allows the generation of g‐functions for any boreholefield geometry. The approach is partially validated by comparing the solution for a square borehole field containing36 boreholes (6x6) with g‐functions generated with the FLS approach and with the program EED (Earth EnergyDesigner). The latter is based on Eskilsons SBM, one of the first documents where the concept of g‐functions wasintroduced. Once the approach is validated, the square COMSOL model is compared with a circular geometryborehole field developed by the same method, consisting of 3 concentric rings having 6, 12, and 18 boreholes.Finally the influence on the circular geometry g‐function is studied when connecting the boreholes in radial zoneswith different thermal loads.
Den termiska responsen för ett borrhålsfält beskrivs ofta med den dimensionslösa responsfunktionen kallad gfunktion.Responsfunktionen togs först fram som en numerisk lösning med SBM (Superposition Borehole Model).En analytisk metod, FLS (Finite Line Source) är också accepterad för framtagandet av g‐funktioner. I det här arbetetundersöks förutsättningarna att numeriskt ta fram g‐funktioner för cirkulära borrhålsfält genom att använda detkommersiella simuleringsprogrammet COMSOL Multiphysics. Den numeriska metoden är flexibel och kananvändas för alla typer av borrhålsgeometrier. Metoden att använda COMSOL valideras delvis genom att jämföraresultatet för ett kvadratiskt borrhålsfält innehållande 36 borrhål (6x6) med lösningar framtagna med FLS och meddimensioneringsprogrammet EED (Earth Energy Designer). Det senare har sin grund i Eskilsons SBM, ett av deförsta arbeten där begreppet g‐funktion introducerades. När metoden att använda COMSOL verifierats, jämförsden kvadratiska borrhålsmodellen med en cirkulär borrhålskonfiguration, upprättad med samma metod,innehållande 3 koncentriska ringar om vardera 6, 12, 18 borrhål. Slutligen undersöks hur den termiska responsenpåverkas då borrhålen i ett cirkulärt borrhålsfält kopplas samman och grupperas i radiella zoner med olika termiskalaster.
SEEC Scandinavian Energy Efficiency Co.

Diploma thesis deals with design of measurement and control system of an air-ground heat exchanger, which is placed in area of FME BUT in Brno. System is built in development environment LabVIEW and it is using modules CompactDAQ from National Instrument. Developed system managed trial operation, during which was designed additional changes of measurement equipment for determine another magnitudes, which help us with future evaluation of benefit of air-ground heating exchanger. It was designed some operational modes, which solve different ways of control air-ground heat exchanger.

La géothermie peu profonde est une énergie qui peut aider l'humanité à atteindre les objectifs du développement durable. Le système de pompe à chaleur géothermique est utilisé pour bénéficier de cette énergie. En tant qu'élément principal du système, la performance de l'échangeur de chaleur souterrain influence directement son efficacité énergétique. Les échangeurs de chaleur souterrains peu profonds sont normalement installés dans les sols, qui présentent une grande hétérogénéité des propriétés hydrothermales. L'objectif principal de ce projet est d'identifier le comportement des échangeurs de chaleur souterrains dans les sols. En résumé, les enquêtes suivantes ont été menées : la première consiste à introduire le transfert hydrothermique dans la modélisation numérique des échangeurs géothermiques installés sur un site en Alsace (France) ; la seconde enquête consiste à identifier les facteurs qui influencent la performance d'un échangeur de chaleur de forage peu profond installé dans les sols ; la troisième étude concerne l'analyse de sensibilité des essais de réponse thermique pour les échangeurs de chaleur de forage installés dans les sols ; la dernière étude traite l'identification de la différence de performance d'un modèle de simulation numérique avec les limites de Neumann et de Dirichlet à la surface du sol pour un échangeur horizontal de chaleur souterraine
Shallow geothermal energy is an energy that can help humanity to reach the goal of sustainable development. Ground-Coupled Heat Pump system is traditionally used to benefit this energy. As a main element of the system, ground heat exchanger performance directly influences its energy efficiency. The shallow ground heat exchangers are normally installed in soils, which show high heterogeneity of hydrothermal properties along the soil profiles. The main objective of this project is identifying how ground heat exchanger behaves in the soil. In summary, the following investigations were conducted: the first is introducing hydrothermal transfer in the numerical modeling of Borehole Heat Exchanger installed at a site in Alsace region (France); the second is identifying the factors influencing the performance of a shallow Borehole Heat Exchanger installed in soils; the third is conducting sensitive analysis of Thermal Response Tests for Borehole Heat Exchanger installed in soils; the fourth is identifying the performance difference of a numerical simulation model with Neumann and Dirichlet boundaries on the ground surface for a Horizontal Ground Heat Exchanger

This thesis presents an experiment and an analysis that evaluates some of the long-standing assumptions in deep vertical borehole ground heat exchanger (GHX) theory. These assumptions neglect ground heterogeneity and depth variations in GHX output and the ground temperature response (GTR). This thesis describes an apparatus and an experiment that measured the GTR at several depths, times, and at two different horizontal distances from a GHX both during and immediately after its operation. This thesis also reports the temperature response data, which may not be available from other sources in such detail. The experiment showed that the GTR can be highly depth dependant. The analysis involved a parametric study to characterize the GTR by developing an effective computer simulation of the experiment. The analysis showed that ground heterogeneity significantly affected the GTR and the GHX output in this study. Furthermore, this GHX output showed depth and time, dependence.

Thesis (M.S.)--University of Wisconsin--Madison, 1997.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 96-98).

碩士
國立臺南大學
機電系統工程研究所碩士班
101
近來全世界日趨重視環境保護議題，減少溫室氣體的排放，已經成為世界各國因應地球氣候暖化共同推行的目標。本研究係探討熱管熱交換器應用於熱泵系統，利用熱管高熱傳導性能，將地面上室內的熱空氣與地面下常溫水進行熱交換，藉此降低室內的溫度。本研究主要針對熱管熱交換器測試段之熱管水側與空氣側加裝不同鰭片數目進行各項熱交換器性能實驗測試，搭配其實驗改變風側空氣流速由2m/s至8m/s，探討其空氣側單邊熱管各從無鰭片、五鰭片、十鰭片、十五鰭片、二十鰭片其熱交換性能的表現。進而針對熱管熱交換器測試段內的熱空氣流道與常溫水流道、熱交換效率及空氣流速進行比較與分析。實驗結果顯示，熱管熱交換器測試段其入出口溫差與空氣流速及熱管熱交換器之熱交換效率成正比關係。水側無鰭片時且當風速從2m/s提升至8m/s，熱交換效率從原本9.64%提升到15.35%，增加了5.71%，其中水側十鰭片CASE.2且空氣側雙邊各安裝二十鰭片狀態下，其熱管熱交換器測試段具有最佳熱交換效率達30.81%。 由上述結果可發現風速越快與鰭片散熱面積的增加其熱管熱交換器熱交換效率越好，表示證明此熱管熱交換器熱泵系統有符合熱傳現象，也可有效應用地面上室內熱空氣與地面下常溫水進行熱交換，藉此達到節能減碳之效果。

Closed-loop ground source heat pumps (GSHPs) are used to transfer thermal energy between the subsurface and conditioned spaces for heating and cooling applications. A basic GSHP is composed of a ground heat exchanger (GHX), which is a closed loop of pipe buried in the shallow subsurface circulating a heat exchange fluid, connected to a heat pump. These systems offer an energy efficient alternative to conventional heating and cooling systems; however, installation costs are higher due to the additional cost associated with the GHX. By further developing our understanding of how these ground loops interact with the subsurface, it may possible to design them more intelligently, efficiently, and economically. To gain insight into the physical processes occurring between the GHX and the subsurface and to identify efficiencies and inefficiencies in GSHP design and operation, two main research goals were defined: comprehensive monitoring of a fully functioning GSHP and intensive simulation of these systems using computer models. A 6-ton GSHP was installed at a residence in Elora, ON. An array of 64 temperature sensors was installed on and surrounding the GHX and power consumption and temperature sensors were installed on the system inside the residence. The data collected were used to help characterize and understand the function of the system, provide motivation for further investigations, and assess the impact of the time of use billing scheme on GSHP operation costs. To simulate GSHPs, two computer models were utilized. A 3D finite element model was employed to analyse the effects of pipe configuration and pipe spacing on system performance. A unique, transient 1D finite difference heat conduction model was developed to simulate a single pipe in a U-tube shape with inter-pipe interactions and was benchmarked against a tested analytical solution. The model was used to compare quasi-steady state and transient simulation of GSHPs, identify system performance efficiencies through pump schedule optimization, and investigate the effect of pipe length on system performance. A comprehensive comparison of steady state and pulsed simulation concludes that it is possible to simulate transient operation using a steady state assumption for some cases. Optimal pipe configurations are identified for a range of soil thermal properties. Optimized pump schedules are identified and analysed for a specific heat pump and fluid circulation pump. Finally, the effect of pipe spacing and length on system performance is characterized. It was found that there are few design inefficiencies that could be easily addressed to improve general design practice.

Vertical ground source heat pumps are established and still growing on the global market. The modelling of these systems is important for system design and optimization. This is an active field of research, and many models are often built into system simulation software such as TRNSYS. With the intention of having a better sensibility for existing TRNSYS tools, three different cases are simulated with several TRNSYS tools, so called Types. A Thermal Response Test, a large borehole field of an IKEA building complex in Sweden, as well as the Marine Corps Logistic Base in Albany, USA. The vertical ground heat exchanger types 203, 244, 243, 246, 451, 55a and 557b are used. Most of the simulations are investigated and evaluated by comparing them to measured data. The result shows that, for these specific cases, the DTS types 557a and 557b can underestimate the heat transfer early on due to a poor consideration of the thermal capacity inside the borehole. Depending on how the thermal resistance is calculated by a module, the fluid mean temperature simulation is affected by a constant throughout the simulation time. The simulation results indicate that the type 557b, where the borehole resistance is pre-set as an input and known from experimental data, is the most accurate of the types for groundwater filled boreholes. On short term, type 451 provides a good coherence with the measured data, with a relative deviation of 10.3 %. The borehole models that consider the borehole thermal capacity overestimate the short term heat transfer rate, whereas those that neglect the borehole capacity underestimate the short term thermal heat transfer on short term. Existing Types describe successfully the long term behaviour of large borehole fields. Serial versus parallel coupled BHE fields show relatively small differences in performance when simulated with type 557b for a specific study case.