No description available.

No description available.

As an alternative and renewable energy source, the shallow geothermal energy evolving as one of the most popular energy source due to its easy accessibility and availability worldwide, and the ground source heat pump (GSHP) systems are the most frequent applications for extracting the energy from the shallow subsurface. As the heat extraction capacity of the GSHP system applications arises, the design of the borehole heat exchangers (BHE), which is the connected part of the system in the ground, become more important. The backfilling materials of BHEs, particularly, the grout material must provide a suitable thermal contact between the ground and the heat carrier fluid in the high density polyethylene (HDPE) pipes and ensure durability to the induced thermal stresses due to the heat loading. In addition, for the heating purposes of buildings, BHEs immerged in groundwater may be operated below the freezing point of water with anti-freeze mixture in the pipe, leading to freezing-induced ice pressure which may damage the grout.In order to propose a proper grouting for BHEs, the thermo-hydro-mechanical behavior of the grout and its interferences with the adjacent ground conditions must be evaluated in the near field, and the thermal interactions of each BHE in a multi-BHEs field in the long-term operations must also be considered at a further field.Primarily, we have evaluated the performance of various grouting materials, through thermal, hydraulic and mechanical laboratory characterizations. In particular, we have proposed a homemade grout material, with the addition of graphite powder to improve the thermal properties of grout material. In parallel, the characteristics of two different widely used commercial grouting materials (i.e. calcite-based and silica-sand based materials) have been also investigated. In the subsequent study, the heat flow rate per meter of a BHE and the borehole resistance of borehole heat exchangers are assessed experimentally in a 1×1×1 m3 sandbox under, successively, dry sand and fully water-saturated sand conditions. During the operations, the monitored temperatures in the sandbox are in good agreement with analytical predictions. This study demonstrated that the homemade admixture prepared with 5 % natural flake graphite can be considered as an appropriate grout for BHEs regarding to its rheological and thermo-physical properties. Thermally-enhanced grouting can be of significant interest in a high thermal conductivity ground (such as saturated sand) because it minimizes the thermal resistance of the BHE.After characterizing and testing the efficiency of various grout materials, the thermal stresses occurred in BHEs due to heat injection or extraction has been investigated with the analytical solution of hollow cylinder model that is adapted for time-dependent heat loading, the geometry of a BHE, and the thermo-mechanical properties of surrounding ground conditions. Firstly, the hollow cylinder model has been solved for the considered boundary conditions in 2D plane stress. Secondly, the temperature differences at the inner and outer circles of the cylinder is evaluated with the heat line source models for continuous and discontinuous loadings to observe the impact of the heat loading schedule. The developed analytical solution for thermal stress investigation is validated with numerical models. It is demonstrated that the analytical solutions agree well with numerical results for two types of BHE configurations (co-axial and single U-shaped pipes). Furthermore, the calculated maximum stresses are compared with the tensile strength of grout materials obtained from Brazilian tests. It is predicted that thermal contraction of the grout, partially constrained by the surrounding rock, generates tensile stresses that may lead to cracking in the BHE. According to the results, the stiffness of rock has primary role on the developed tensile stresses, and the relationship between the thermal conductivity of the ground and of the grout induces a proportional impact on the magnitude of thermal stresses.Another major concern is the freeze-resistance of the grout materials, when the system is operated for heating purposes. Firstly, we conducted an experimental setup in a small-scale sandbox to understand the behavior of the grout material by evaluating the permeability change during freeze-thaw cycles of a BHE. According to the results, the permeability of grout materials did not change after 10 freeze-thaw cycles due to the thermal transfer with the adjacent soil partially reducing the impact of freezing in the grout material. Therefore, in order to test the freeze-resistance of a BHE, we have investigated the freezing impact of pore water pressure and thermal stress with analytical models and experimental setups on BHEs. For the theoretical approach, an analytical solution has been developed by using the hollow cylinder model that accounts for both the HDPE pipe and the grout material. Firstly, the freezing pore water pressure is adapted to the generalized Hooke’s law equations in 2D plane stress, and secondly the model is solved for the considered boundary conditions. In order to validate the developed model, the experimental setup is conducted in agreement with the geometry of the considered analytical model and the BHE probes are prepared with three different grout materials having large difference in the thermal and hydraulic characteristics (i.e. silica-sand based, calcite based and the homemade enhanced thermally with natural flake graphite powder). According to the experiments for 50 h of freezing operation, the calcite based grout and the homemade grout, having lower permeability and relatively higher porosity, are fractured. In contrast, the silica-sand based grout having higher permeability did not exhibit any damage. Compared with the theoretically obtained results, the observations from the experiments are consistent with the calculated stress results. The effective tangential stress induced by the freezing pore water pressure causes the crack development and agrees with the crack patterns. As a conclusion, the porosity and the permeability play a significant role on the grout failure.In a multi-BHEs field, the thermal interaction between each BHE may have a significant influence on the near-field investigation results in long-term operations. Therefore, in order to complete the near-field investigation, a far-field long-term operation study is required. However, existing analytical solutions for thermal analysis of ground source heat pump (GSHP) systems evaluate temperature change in the carrier-fluid and the surrounding ground in the production period of a single BHE only if a continuous heat load is assigned. In this study, we modified the Green’s function, which is the solution of heat conduction/advection/dispersion equation in porous media, for discontinuous heat extraction by analytically convoluting rectangular function or pulses in time domain both for single and multi-BHEs field. The adapted analytical models for discontinuous heat extraction are verified with numerical finite element code. The comparison results agree well with numerical results both for conduction and advection dominated heat transfer systems, and analytical solutions provide significantly shorter runtime compared to numerical simulations (approx. 1500 times shorter). Furthermore, we investigated the sustainability and recovery aspects of GSHP systems by using proposed analytical models under different hydro-geological conditions. According to the engineering guideline VDI 4640, a linear relationship between thermal conductivity of the ground and the sustainable heat extraction rate is demonstrated for multi-BHEs. In addition, we developed an MATLAB interface for users in which the analytical model can be used easily and more efficiently.In addition, in order to extend the case studies for a ground including several layers, we proposed a finite line source model for BHEs that takes into account conduction/advection/dispersion mechanism in multilayer porous media. Firstly, the anisotropy is added to the moving finite line source model, and we used an existing composite model approach for conductive multilayer ground. The comparison with the numerical model results demonstrates the suitability of the approach. The proposed model can provide a faster solution than classical numerical approaches and help to optimize the heat extraction rate in multilayer media. However, further investigations are required to validate the model with the field measurements. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

<p>During installation and operation of a geothermal heat pump system leakage of an antifreezing agent can appear in a borehole and leak out in surrounding groundwater. To guarantee high quality drinking water for generations to come Sweden has dedicated some areas as water protection areas. The local authority gives permits for the installation of heat pump systems within water protection areas. Before giving a permit the local authority makes an evaluation of the risks involved in installation and operation of the system within the area. By keeping a certain distance between the protected object in the area and the heat pump system the risk of polluting the protected object with an anti-freezing agent can be reduced.</p><p>This thesis makes a comparison between three different methods of calculating an appropriate distance between the protected object and the heat pump system. These methods include different numbers of parameters to calculate the appropriate distance.</p><p>The results are evaluated with regard to the parameters used. The methods used are a simplified version of an empirical point-count system made by LeGrand, an analytical solution from Baetsle and a numerical solution with Visual MODFLOW 4.0.</p> / <p>Miljöbalken med bakomliggande miljömål skall bidra till att skydda viktiga naturområden för en hållbar utveckling. Ett stort problem för att tillgodose detta behov är dock alla konkurrerande intressen som kan finnas inom ett och samma område.</p><p>Vattenskyddsområden utfärdas i syfte att ge tillgång till rent vatten för framtida dricksvatten, men konkurrerande intressen påverkar även dessa områden. Beslut om vilka verksamheter som skall vara tillåtna inom ett vattenskyddsområde tas av den kommun inom vilken området finns.</p><p>Ett ökande oljepris har under senare år lett till ett ökat intresse av att installera bergvärmeanläggningar. Denna kraftiga ökning har gjort att negativa effekter av att installera dessa anläggningar förbisetts och att installatörer med dåliga kunskaper fått en chans att etablera sig på marknaden. Före eventuell installation av en bergvärmeanläggning inom ett vattenskyddsområde är det viktigt att beakta de risker som en bergvärmeanläggning kan medföra för omgivande grundvatten. En noggrann utredning kräver beaktande av alla de riskmoment som installation och drift av en sådan anläggning kan medföra. För omgivande grundvatten är det dock främst läckage av köldbärarvätska, dvs. vatten med tillfört frostskyddsmedel, som kan ha en större inverkan. Det finns idag ingen övergripande lagstiftning över tillåtna köldbärarvätskor, men enligt de hänsynsregler som finns i miljöbalken och rekommendationer av bl.a. Sveriges Geologiska Undersökning skall etanol användas som frostskyddsmedel. Etanol för tekniskt bruk innehåller denatureringsmedel för att motverka konsumtion.</p><p>Denatureringsmedel samt etanol kan ge smak och lukt till vatten och är därför inte önskvärda att ha i ett vattenskyddsområde. Dessa ämnen tillför även negativa effekter genom att de som substrat för bakterier kan ge en ökad bakteriehalt i marken. Under nedbrytning av dessa ämnen kan även syrefria förhållanden utbildas i jorden vilket kan leda till utfällningar av järn och mangan samt utbildning av svavelväte.</p><p>Det finns olika riktlinjer för hur risk med att införa en bergvärmeanläggning i ett vattenskyddsområde beaktas i olika kommuner. Ett lämpligt skyddsavstånd mellan en bergvärmeanläggning och ett skyddsobjekt kan dock göra att risken för att förorena ett skyddsobjekt med etanol kan minimeras. Detta arbete har utförts i syfte att jämföra olika metoder för att ta fram ett skyddsavstånd för en första övergripande undersökning av vilken effekt ett läckage av etanol kan ha på ett skyddsobjekt ett visst avstånd från en ansatt bergvärmeanläggning. De metoder som använts är en förenklad form av en empirisk lösning av LeGrand, en analytisk lösning av Baetsle och en numerisk lösning i Visual MODFLOW.</p>

No description available.

During installation and operation of a geothermal heat pump system leakage of an antifreezing agent can appear in a borehole and leak out in surrounding groundwater. To guarantee high quality drinking water for generations to come Sweden has dedicated some areas as water protection areas. The local authority gives permits for the installation of heat pump systems within water protection areas. Before giving a permit the local authority makes an evaluation of the risks involved in installation and operation of the system within the area. By keeping a certain distance between the protected object in the area and the heat pump system the risk of polluting the protected object with an anti-freezing agent can be reduced. This thesis makes a comparison between three different methods of calculating an appropriate distance between the protected object and the heat pump system. These methods include different numbers of parameters to calculate the appropriate distance. The results are evaluated with regard to the parameters used. The methods used are a simplified version of an empirical point-count system made by LeGrand, an analytical solution from Baetsle and a numerical solution with Visual MODFLOW 4.0. / Miljöbalken med bakomliggande miljömål skall bidra till att skydda viktiga naturområden för en hållbar utveckling. Ett stort problem för att tillgodose detta behov är dock alla konkurrerande intressen som kan finnas inom ett och samma område. Vattenskyddsområden utfärdas i syfte att ge tillgång till rent vatten för framtida dricksvatten, men konkurrerande intressen påverkar även dessa områden. Beslut om vilka verksamheter som skall vara tillåtna inom ett vattenskyddsområde tas av den kommun inom vilken området finns. Ett ökande oljepris har under senare år lett till ett ökat intresse av att installera bergvärmeanläggningar. Denna kraftiga ökning har gjort att negativa effekter av att installera dessa anläggningar förbisetts och att installatörer med dåliga kunskaper fått en chans att etablera sig på marknaden. Före eventuell installation av en bergvärmeanläggning inom ett vattenskyddsområde är det viktigt att beakta de risker som en bergvärmeanläggning kan medföra för omgivande grundvatten. En noggrann utredning kräver beaktande av alla de riskmoment som installation och drift av en sådan anläggning kan medföra. För omgivande grundvatten är det dock främst läckage av köldbärarvätska, dvs. vatten med tillfört frostskyddsmedel, som kan ha en större inverkan. Det finns idag ingen övergripande lagstiftning över tillåtna köldbärarvätskor, men enligt de hänsynsregler som finns i miljöbalken och rekommendationer av bl.a. Sveriges Geologiska Undersökning skall etanol användas som frostskyddsmedel. Etanol för tekniskt bruk innehåller denatureringsmedel för att motverka konsumtion. Denatureringsmedel samt etanol kan ge smak och lukt till vatten och är därför inte önskvärda att ha i ett vattenskyddsområde. Dessa ämnen tillför även negativa effekter genom att de som substrat för bakterier kan ge en ökad bakteriehalt i marken. Under nedbrytning av dessa ämnen kan även syrefria förhållanden utbildas i jorden vilket kan leda till utfällningar av järn och mangan samt utbildning av svavelväte. Det finns olika riktlinjer för hur risk med att införa en bergvärmeanläggning i ett vattenskyddsområde beaktas i olika kommuner. Ett lämpligt skyddsavstånd mellan en bergvärmeanläggning och ett skyddsobjekt kan dock göra att risken för att förorena ett skyddsobjekt med etanol kan minimeras. Detta arbete har utförts i syfte att jämföra olika metoder för att ta fram ett skyddsavstånd för en första övergripande undersökning av vilken effekt ett läckage av etanol kan ha på ett skyddsobjekt ett visst avstånd från en ansatt bergvärmeanläggning. De metoder som använts är en förenklad form av en empirisk lösning av LeGrand, en analytisk lösning av Baetsle och en numerisk lösning i Visual MODFLOW.

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 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.

No description available.

To make chemical analysis available both practically and economically, one approach is to miniaturise the equipment needed for the analysis. High-performance liquid chromatography (HPLC) is an example of a flow chemistry analysis system where active work is performed to achieve miniaturised systems. In this thesis, the focus is on creating a miniatyrised pump system constructed of pressurised CO2 (PCO) and a microfluidic chip with a restriction channel. The assignment of the PCO is to force a separate medium, which in this case is water, through the remaining system. The pump system will therefore be defined as pressure-driven, which has advantages as pulse-free flows. Utilising the latent energy from the PCO also reduces the need for electrical power, hence allowing a smaller battery. However, the pressure from the carbon dioxide source will gradually decrease as the content is consumed. To obtain continuous pressure, heaters have been integrated into the chip, and thus, the pressure drop can be controlled by changing the viscosity and density of the through-flowing fluid. A cooling table was also used to enable the cooling of the chip and thus further increase the pressure drop. PID control was implemented for the temperature to be adjusted to maintain a constant pressure downstream of the chip. By using this technology, runs of just over 80 minutes have been achieved with a pressure of 60 bar and a flow of 100 µl/min downstream, with a maximal error of around 0.03 bar. Then a chip adapted for water was used to control the water flow. Chips adapted for carbon dioxide placed right after the carbon dioxide source were also tested andruns of just over 10 minutes at 75 bar and 100 µl/min could be achieved with a maximal error closer to 1 bar. The pressure vessel used held a maximum of 100 ml of CO2 at 60 bar. The idea is that the pump system, in the end, will be applied for portable HPLC, and the PCO will then be stored in a cartridge, but in the experiments, a turned-off ISCO pump functioned as a carbon dioxide source.