| 1. |
- Abugabbara, Marwan, et al.
(författare)
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How to develop fifth-generation district heating and cooling in Sweden? : Application review and best practices proposed by middle agents
- 2023
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Ingår i: Energy Reports. - : Elsevier Ltd. - 2352-4847. ; 9, s. 4971-4983
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Tidskriftsartikel (refereegranskat)abstract
- Sweden has an ambitious plan to fully decarbonise district heating by 2030 and to contribute with negative emissions of greenhouse gases in 2050. The vagaries of the energy market associated with climate, political, and social changes entail cross-sectoral integration that can fulfill these national targets. Fifth-generation district heating and cooling (5GDHC) is a relatively new concept of district energy systems that features a simultaneous supply of heating and cooling using power-to-heat technologies. This paper presents best practices for developing 5GDHC systems in Sweden to reach a consensus view on these systems among all stakeholders. A mixed-method combining best practice and roadmapping workshops has been used to disseminate mixed knowledge and experience from middle agents representing industry professionals and practitioners. Four successful implementations of 5GDHC systems are demonstrated and the important learned lessons are shared. The best practices are outlined for system planning, system modeling and simulation, prevailing business models for energy communities, and system monitoring. A roadmap from the middle agents’ point of view is composed and can be utilised to establish industry standards and common regulatory frameworks. © 2023 The Author(s)
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| 2. |
- Acuña, José, 1982-
(författare)
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Improvements of U-pipe Borehole Heat Exchangers
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 3. |
- Gehlin, Signhild, et al.
(författare)
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Backgroudn promoting TES systems in Sweden
- 2006
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Swedish nuclear plants are slowly being shut down as a result of a referendum in 1980. During the years after the referendum, four nuclear reactors were completed and taken into operation. The nuclear power then covered 50 % of the Swedish production capacity resulting in large over capacity, which meant inexpensive electricity. For many years thereafter direct electrical space heating was the only feasible option. This development continued until direct electrical heating was used for about 30 % of all space heating in Sweden. Swedish consumer prices were then about one third of that in most European countries. The much later deregulation of the electrical market and connection of the power grid to other European countries meant that Swedish consumer prices increased rapidly. Within a few years the prices are expected to be at the same level all over Europe and direct space heating is no longer a feasible alternative. This is why it is so attractive to Swedes to use heat pumps to reduce their electricity consumption. The present Swedish energy policy aims to a changeover from the use of prime energy sources to renewables. This is partly because of international agreements on the reduction of greenhouse emissions and partly to obtain a more independent energy system. Since the use of heat pumps mean that the electrical consumption is reduced by 70 % and also means less emission to the atmosphere, heat pump systems have been encouraged by subsidies. This present subsidy, which covers about 15 % of the investment, has been on and off during the last decades. Now, the new EU directive on energy efficient buildings offers a platform for the promotion of thermal energy
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| 4. |
- Gehlin, Signhild, et al.
(författare)
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Comparison of four models for thermal response test evaluation
- 2003
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Ingår i: ASHRAE Transactions. - 0001-2505. ; 109, s. 135-146
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Tidskriftsartikel (refereegranskat)abstract
- Four two-variable parameter estimation models for evaluation of thermal response test data are compared when applied on the same temperature response data. Two models are based on line-source theory, the third model is a cylinder-source-based solution, and the fourth is a numerical one-dimensional finite difference model. The data sets contain measured temperature response, heat load, and undisturbed ground temperature from three thermal response tests, together with physical data of the tested borehole heat exchangers (BHE). The models estimate ground thermal conductivity and thermal resistance of the BHE and are compared regarding test length and data interval used. For the three defined data sets, the line source approximation model shows the closest agreement with the measured temperature response. The cylinder source and numerical models show sensitivity to the inclusion of early data. A recommended minimum response test duration of 50 hours is concluded from the model comparison
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| 5. |
- Gehlin, Signhild, et al.
(författare)
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Determining undisturbed ground temperature for thermal response test
- 2003
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Ingår i: ASHRAE Transactions. - 0001-2505. ; 109:1, s. 151-156
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Tidskriftsartikel (refereegranskat)abstract
- This study treats the determination of undisturbed ground temperature in a borehole for ground heating/cooling and its effect on the accuracy of a thermal response test analysis. Three different ways of estimating temperatures were used in one groundwater-fitted borehole in crystalline rock The first method, temperature logging along the borehole, is assumed to give the correct temperature profile and results in the best estimate of the mean temperature of the ground. A good estimate is also obtained by circulating a heat carrier through the borehole heat exchanger pipes while measuring the flow temperature at a short time interval (10 seconds). The calculated temperature profile is used for deriving a mean temperature of the borehole. Heat is added to the fluid by friction heat caused by the pump work, which results in an overestimation of the borehole temperature. This influencer becomes significant after 20 minutes of pumping.
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| 6. |
- Gehlin, Signhild, et al.
(författare)
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Promoting TES Systems in Sweden
- 2006
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Ingår i: Thermal energy storage. - Pomona, NJ : Richard Stockton College of NJ.
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Konferensbidrag (refereegranskat)
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| 7. |
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| 8. |
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| 9. |
- Gehlin, Signhild
(författare)
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Thermal response test : method development and evaluation
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the first introduction of thermal response tests with mobile measurement devices in Sweden and USA in 1995, the method has developed and spread in North America and Europe. Thermal response tests have so far been used primarily for in situ determination of design data for BHE (borehole heat exchanger) systems, but also for evaluation of grout material, heat exchanger types and groundwater effects. A variety of analytical and numerical data analysis models have been developed. Various applications of the line source theory is the most commonly used model for evaluation of the response test data because of its simplicity and speed, and is dominant in Europe. The use of the cylinder source model and numerical models coupled with parameter-estimation techniques are common in USA. The Swedish response test apparatus TED has been used at a number of tests since 1996. The main purpose has been to determine in situ values of effective ground thermal conductivity, including the effect of groundwater flow and natural convection in the boreholes. The tests indicate that convective heat transfer may play an important role for the thermal behaviour of groundwater-filled BHE, which is the typical BHE design in Sweden. The magnitude of the induced natural convection depends on the heat transfer rate and the temperature level. The influence is small on grouted boreholes. To shed light on the influence of groundwater flow on thermal response testing, simulation models for estimating the heat transfer effect of groundwater flowing near a borehole heat exchanger were developed. The groundwater flow was represented as 1) a flow through an equivalent porous medium (continuum), 2) a flow through an impermeable medium with a porous zone, and 3) a flow through an impermeable medium with a thin vertical fracture. The three cases result in significantly different temperature field patterns around the borehole and all three cause lower borehole temperatures. The fracture flow model results in higher effective thermal conductivity than the continuum and porous zone models within a certain flow rate interval. This illustrates the efficiency of the high flow velocity in the fracture and the large temperature gradient between the borehole and the fracture flow. The effect of the flow in the fracture or porous zone decreases with the distance from the borehole, but even at distances of half a meter or more the porous zone or fracture may result in significantly enhanced heat transfer. Even a relatively narrow fracture close to a borehole may result in greater effective thermal conductivity, although estimations made with a continuum approach may indicate otherwise. A thermal response test is likely to induce a thermosiphon flow due to the temperature difference between borehole and surroundings, resulting in an enhanced effective thermal conductivity estimation. The enhancement of the effective thermal conductivity of the BHE depends on injected power rate and flow resistance in fractures. The fracture flow resistance may be quantified in terms of hydraulic condcutivity. The findings from the groundwater flow and thermosiphon simulation are encouraging for further studies, both as simulations and in field experi- ments. The author suggests further studies of the possibility to develop models for estimating and investigating the influence of groundwater from drilling data and hydraulic testing. A future aim should be to gain enough knowledge of fracture flow and thermosiphon effects that hydraulic well test and drilling data may be used in borehole thermal energy storage design.
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| 10. |
- Gehlin, Signhild
(författare)
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Thermal response test : in situ measurements of thermal properties in hard rock
- 1998
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In-situ determination of thermal properties in bedrock is important for the sizing of larger BTES systems. In-situ values of thermal conductivity may reduce required borehole length up to 30%. This thesis treats a new mobile thermal response test equipment (TED), developed in Luleå, Sweden, 1995-98. TED is set up on a small trailer, and is tried out on groundwater filled boreholes, fitted with single and double U-loop piping. It has been used at several commercial borehole direct cooling systems for telephone switching stations in Sweden, and on test-holes in a well documented closed down heat store in Luleå. The response tests show good accuracy and reliability of the measured thermal conductivity and thermal resistance provided good insulation of the equipment. The tests take into account the interaction of the bedrock with the duct piping and filling, the borehole geometry and groundwater and is a valuable tool for pre-investigations for BTES.
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| 11. |
- Gehlin, Signhild, et al.
(författare)
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Thermal response tests of boreholes : results from in situ measurements
- 1998
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Konferensbidrag (refereegranskat)abstract
- During the last year thermal response tests of boreholes in rock were carried out with a mobile test equipment (TED) in several duct stores for heating and/or cooling. Most of the tests were made for the Swedish telephone company TELIA that is constructing a great number of direct cooling systems for their telephone switching stations. The size of these duct systems in the different plants tested, varies from 4 to 60 boreholes, drilled in hard rock - mostly granite and gneiss. This paper summarises results and experience from the measurements.
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| 12. |
- Gustafsson, Anna-Maria, et al.
(författare)
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Influence of natural convection in water-filled boreholes for GCHP
- 2008
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Ingår i: ASHRAE Transactions. - 0001-2505. ; 114:1, s. 416-423
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Tidskriftsartikel (refereegranskat)abstract
- In groundwater filled borehole heat exchangers (BHE), convective flow inside the borehole water will affect the heat transfer. Since the convective flow is dependent of the temperature gradient, different injection rates and ground temperatures will result in different borehole thermal resistance. This paper describes the influence of natural convection in water-filled boreholes in impermeable bedrock for ground-coupled heat pump (GCHP) systems. An overview of groundwater-filled boreholes and the influence of groundwater movements are presented followed by numerical simulations and field measurements to further investigate the influence. The results from the simulations of the three-dimensional, steady-state model of a 9.8 ft (3 m) deep BHE are compared to evaluated results from performed thermal response test (TRT). The results show that convective flow in groundwater-filled BHE results in 5-9 times more efficient heat transfer compared to stagnant water when heat carrier temperatures are in the range of 50-86°F (10-30°C). The size of the convective flow depends on the temperature gradients in the borehole. This shows the importance of on-site investigation of thermal properties using appropriate power injection rates similar to those in the system to be built. This research is part of an on-going project to find ways to estimate the heat transfer including convective flow and to incorporate the findings into the design of GCHP systems. TRT are today a common way to determine heat transfer properties for a BHE and its surroundings. Performing TRT measurements with several injection rates is a way to evaluate the dynamic thermal response including the change in convective flow due to changes in temperature levels. If this dynamic response would be included in design tools a more thorough design of the BHE system is performed. Here, the early result of this research is presented
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| 13. |
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| 14. |
- Heier, Johan
(författare)
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Energy Efficiency through Thermal Energy Storage : Possibilities for the Swedish Building Stock
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The need for heating and cooling in buildings constitutes a considerable part of the total energy use in a country and reducing this need is of outmost importance in order to reach national and international goals for reducing energy use and emissions. One important way of reaching these goals is to increase the proportion of renewable energy used for heating and cooling of buildings. Perhaps the largest obstacle with this is the often occurring mismatch between the availability of renewable energy and the need for heating or cooling, hindering this energy to be used directly. This is one of the problems that can be solved by using thermal energy storage (TES) in order to save the heat or cold from when it is available to when it is needed.This thesis is focusing on the combination of TES techniques and buildings to achieve increased energy efficiency for heating and cooling. Various techniques used for TES as well as the combination of TES in buildings have been investigated and summarized through an extensive literature review. A survey of the Swedish building stock was also performed in order to define building types common in Sweden. Within the scope of this thesis, the survey resulted in the selection of three building types, two single family houses and one office building, out of which the two residential buildings were used in a simulation case study of passive TES with increased thermal mass (both sensible and latent). The second case study presented in the thesis is an evaluation of an existing seasonal borehole storage of solar heat for a residential community. In this case, real measurement data was used in the evaluation and in comparisons with earlier evaluations.The literature reviews showed that using TES opens up potential for reduced energy demand and reduced peak heating and cooling loads as well as possibilities for an increased share of renewable energy to cover the energy demand. By using passive storage through increased thermal mass of a building it is also possible to reduce variations in the indoor temperature and especially reduce excess temperatures during warm periods, which could result in avoiding active cooling in a building that would otherwise need it. The analysis of the combination of TES and building types confirmed that TES has a significant potential for increased energy efficiency in buildings but also highlighted the fact that there is still much research required before some of the technologies can become commercially available. In the simulation case study it was concluded that only a small reduction in heating demand is possible with increased thermal mass, but that the time with indoor temperatures above 24 °C can be reduced by up to 20%. The case study of the borehole storage system showed that although the storage system worked as planned, heat losses in the rest of the system as well as some problems with the system operation resulted in a lower solar fraction than projected.The work presented within this thesis has shown that TES is already used successfully for many building applications (e.g. domestic hot water stores and water tanks for storing solar heat) but that there still is much potential in further use of TES. There are, however, barriers such as a need for more research for some storage technologies as well as storage materials, especially phase change material storage and thermochemical storage.
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| 15. |
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| 16. |
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| 17. |
- Nordell, Bo, et al.
(författare)
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30 years of Stock Conferences
- 2009
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Ingår i: Abstract book and proceeding : Effstock 2009. - Stockholm : Energi- och Miljötekniska Föreningen / EMTF Förlag.
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Konferensbidrag (refereegranskat)
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| 18. |
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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Räftegård, Oskar, et al.
(författare)
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Energin under mark ska upp till ytan : Strategisk innovationsagenda för geoenergi
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Swedish Strategic Innovation Agenda for Geoenergy develops a strategy for highlighting the need for geoenergy research, development and innovation in relation to the business community and authorities. Sweden has a strong global position in the field. Geothermal energy is the thirdlargest renewable energy source in Sweden, along with wind power. Currently, approximately 18 TWh of renewable heat per year is supplied to household, industrial and commercial buildings. In addition, there is 12 TWh of cooling. There is a great need for a longterm strategy and financial plan for geoenergy research and innovation in Sweden, in order to maintain and further develop research groups and the country's leading position in the field. Today, Swedish research in this field comprises about 14 fulltime positions at universities, institutes and companies. This is little compared to the existing use of geothermal energy, about 19 TWh, which is worth about 15 billion SEK in consumer sales. It is also little in relation to possible future contributions to sustainable development in Sweden and abroad. The agenda is divided into short independent chapters that are tailored to different target groups/ applications. Each chapter consists of an introduction to the current situation, how geoenergy can strategically contribute to a sustainable society, and what actions/needs are a priority.
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| 23. |
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| 24. |
- Scorpo, Alberto Liuzzo, et al.
(författare)
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A method to estimate the hydraulic conductivity of the ground by TRT analysis
- 2017
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Ingår i: Ground Water. - : John Wiley & Sons. - 0017-467X .- 1745-6584. ; 55:1, s. 110-118
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Tidskriftsartikel (refereegranskat)abstract
- An accurate knowledge of aquifers properties is important 2 in many disciplines, from hydrology to site characterization in order to designing and implementing remediation strategies, as well as geothermal ground source technologies. In par5 ticular, the groundwater flow rate is a fundamental parameter to be considered in the ground-coupled heat exchangers (GCHEs) design, together with the thermal properties of the ground. In fact, even relatively low flow rate entail temperature changes considerably lower than in the case of pure heat conduction (Gehlin and Hellström, 2003; Fan et al., 2007) and then relatively stable underground temper10 atures which allow heat pumps to operate with very efficient performance coefficients, thereby reducing energy costs (Lee et al., 2012). Moreover, an accurate knowledge of groundwater velocity and ground thermal properties allows a better design and dimensioning of the GCHE, with further reduction of costs. The objective of this paper is to propose an expeditious, graphical method to estimate the groundwater flow velocity from TRT analysis.
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| 25. |
- Scorpo, Alberto Liuzzo, et al.
(författare)
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Influence of regional groundwater flow on ground temperature around heat extraction boreholes
- 2015
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Ingår i: Geothermics. - : Elsevier BV. - 0375-6505 .- 1879-3576. ; 56, s. 119-127
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Tidskriftsartikel (refereegranskat)abstract
- The increasing popularity of ground-coupled heat pumps has resulted in almost20% of all Swedish family houses being heated this way. To avoid undesirableinteractions between neighboring boreholes and disturbance of the ground temperature, the general rule and recommendation of Swedish authorities is that the distance between two neighboring boreholes must be ≥ 20 m. However, according to previous studies, relatively low groundwater flow rates may significantly reduce the borehole excess temperature compared to the case of pure heat conduction. In this work the Influence Length is defined and its relations with flow rate, real thermal conductivity of the ground and effective thermal conductivity obtained by thermal response analysis are investigated. The aim of this study was to find a way to use the thermal response test as a means to determine the groundwater flow influence in order to reduce the borehole spacing perpendicular to groundwater flow direction. The results confirm that very low groundwater flow rates are enough to significantly reduce the Influence Length, hence this is a crucial parameter which should be considered. Moreover, a first estimation, even before the thermal response test analysis, of the Influence Length is possible if the knowledge of hydrogeological conditions of the site allows good predictions about real thermal conductivity of the ground and flow rate.
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