The Experts below are selected from a list of 2748 Experts worldwide ranked by ideXlab platform
Gunter Rockendorf - One of the best experts on this subject based on the ideXlab platform.
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unglazed pvt collectors as additional Heat source in Heat pump systems with Borehole Heat Exchanger
Energy Procedia, 2012Co-Authors: Erik Bertram, Jens Glembin, Gunter RockendorfAbstract:An unglazed photovoltaic-thermal (PVT) collector provides a double benefit in a Heat pump system compared to a conventional Heat pump system with PV and Borehole Heat Exchanger. First, the PV cells in the PVT collector are cooled, leading to lower cell temperatures and a higher PV efficiency. Second, the PVT Heat raises the temperature level of the Heat pump and the Borehole Heat Exchanger and consequently leads to a higher Heat pump system performance. In this context a system was measured with a 39 m2 unglazed PVT collector field. The impact of the solar Heat to the Heat pump is determined by TRNSYS simulations using energetic weighted temperatures for validation and to quantify the impact of the solar Heat. The investigated system revealed a temperature increase of 3 K which equals 9% lower electricity consumption. The yearly additional PV yield was determined to 4% by reference measurement of uncooled conventional PV panels. Additionally, system simulations in TRNSYS are presented.
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Heat pump systems with Borehole Heat Exchanger and unglazed pvt collector
ISES Solar World Congress 2011, 2011Co-Authors: Erik Bertram, Gunter Rockendorf, Martin StegmannAbstract:In the future energy supply both efficient Heat pump systems for Heat generation and photovoltaic (PV) electricity production will play an important role. Therefore, a Heat pump system with a combined Heat source consisting of a photovoltaic-thermal (PVT) collector and a Borehole Heat Exchanger (BHE) is assumed to be a promising solution, because this particular combination provides a double benefit compared to conventional Heat pump and PV-systems. First, the PV cells in the PVT collector are cooled, leading to lower cell temperatures and a higher PV efficiency. Second, the Heat from the PVT collector raises the temperature level of the Heat pump and the Borehole Heat Exchanger. Consequently, the temperature increase of the Heat source leads to a higher Heat pump performance factor.
Björn Palm - One of the best experts on this subject based on the ideXlab platform.
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transient Heat transfer in a coaxial Borehole Heat Exchanger
Geothermics, 2014Co-Authors: Richard A Beier, José Acuña, Palne Mogensen, Björn PalmAbstract:Ground-source Heat pumps often use vertical Boreholes to exchange Heat with the ground. A transient Heat transfer model has been developed for a thermal response test on a pipe-in-pipe coaxial Borehole Heat Exchanger. The analytical model calculates the vertical temperature profiles in the fluid flowing through the pipes, which are coupled to the surrounding grout and ground. The model is verified against measured vertical temperature profiles in the circulating fluid during a distributed thermal response test. The comparison with measured data indicates that the proposed model gives a more accurate estimate of the Borehole thermal resistance than the conventional analytical model that uses a mean temperature approximation. The model demonstrates how strongly the shapes of the temperature profiles are dependent on the thermal resistance of the internal pipe wall and the flow direction.
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DISTRIBUTED TEMPERATURE MEASUREMENTS ON A MULTI-PIPE COAXIAL Borehole Heat Exchanger
2012Co-Authors: José Acuña, Björn PalmAbstract:The first experiences with a multi-pipe Borehole Heat Exchanger prototype consisting of an insulated central pipe and twelve parallel peripheral pipes are described. Secondary fluid distributed temperature measurements along the Borehole depth, being the only ones of its kind in this type of Heat Exchanger, are presented and discussed. The measurements are carried out with fiber optic cables during Heat injection into the ground, giving a detailed visualization of what happens both along the central and peripheral flow channels. The Heat exchange with the ground mainly occurs along the peripheral channels and an indication of almost no thermal short circuiting, even while having large temperature differences between the down and upwards channels, is observed.
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distributed thermal response tests on a multi pipe coaxial Borehole Heat Exchanger
Hvac&r Research, 2011Co-Authors: José Acuña, Palne Mogensen, Björn PalmAbstract:In a distributed thermal response test, distributed temperature measurements are taken along a Borehole Heat Exchanger during thermal response tests, allowing the determination of local ground ther ...
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Comprehensive Summary of Borehole Heat Exchanger Research at KTH
2010Co-Authors: José Acuña, Björn PalmAbstract:A research project that aims at presenting recommendations for improving the COP of ground source Heat pump systems by 10-20% through better design of Borehole Heat Exchangers (BHE) is described in ...
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Evaluation of a Coaxial Borehole Heat Exchanger Prototype
2010 14th International Heat Transfer Conference Volume 4, 2010Co-Authors: José Acuña, Palne Mogensen, Björn PalmAbstract:Different Borehole Heat Exchanger designs have been discussed for many years. However, the U-pipe design has dominated the market, and the introduction of new designs has been practically lacking. ...
Mehdi Maerefat - One of the best experts on this subject based on the ideXlab platform.
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thermal resistance capacity model for short term Borehole Heat Exchanger simulation with non stiff ordinary differential equations
Geothermics, 2017Co-Authors: A Minaei, Mehdi MaerefatAbstract:Abstract In the present study, a new thermal resistance capacity circuit for the Heat transfer modeling in Borehole Heat Exchanger with low computation time is developed. Generally, the thermal circuit models result in sets of ordinary differential equations which are solved numerically. The system of equations derived from the traditional thermal resistance capacity model (TRCM) are usually stiff and lead to unstable results unless for a very small time steps which can increase the computation time significantly. Meanwhile, the system of ordinary differential equations derived from the present model is non-stiff and there is no time step limitation for the stability of the results. It is shown that the present model yields accurate and stable results even for large time steps. Finally, the two-dimensional model is extended to the three-dimensional model. The results of the three-dimensional solution of the present model are in good agreement with the numerical results and experimental measurements reported in the literature.
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a new analytical model for short term Borehole Heat Exchanger based on thermal resistance capacity model
Energy and Buildings, 2017Co-Authors: A Minaei, Mehdi MaerefatAbstract:Abstract The present study develops a new accurate and simple analytical method for modeling of Heat transfer in Borehole Heat Exchanger for short time periods. The thermal resistance and capacity circuit is used for derivation of the governing equations inside the Borehole for single U-tube and double U-tube configurations. Also, radial Heat transfer is taken into account in the ground around the Borehole. The Laplace transform is used for solving the governing equations. The effects of the fluid and grout thermal capacities are considered in the present model. Unlike the previous analytical models reported in the literature, the real geometry of the Borehole with single and double U-tube configurations is considered in the present model. The results of the present analytical model are compared with reference experimental measurements and numerical simulation results. It is found that the mean fluid temperature and the Borehole wall temperatures obtained from the present analytical method are in very good agreement with the reference numerical results.
Erik Bertram - One of the best experts on this subject based on the ideXlab platform.
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unglazed pvt collectors as additional Heat source in Heat pump systems with Borehole Heat Exchanger
Energy Procedia, 2012Co-Authors: Erik Bertram, Jens Glembin, Gunter RockendorfAbstract:An unglazed photovoltaic-thermal (PVT) collector provides a double benefit in a Heat pump system compared to a conventional Heat pump system with PV and Borehole Heat Exchanger. First, the PV cells in the PVT collector are cooled, leading to lower cell temperatures and a higher PV efficiency. Second, the PVT Heat raises the temperature level of the Heat pump and the Borehole Heat Exchanger and consequently leads to a higher Heat pump system performance. In this context a system was measured with a 39 m2 unglazed PVT collector field. The impact of the solar Heat to the Heat pump is determined by TRNSYS simulations using energetic weighted temperatures for validation and to quantify the impact of the solar Heat. The investigated system revealed a temperature increase of 3 K which equals 9% lower electricity consumption. The yearly additional PV yield was determined to 4% by reference measurement of uncooled conventional PV panels. Additionally, system simulations in TRNSYS are presented.
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Heat pump systems with Borehole Heat Exchanger and unglazed pvt collector
ISES Solar World Congress 2011, 2011Co-Authors: Erik Bertram, Gunter Rockendorf, Martin StegmannAbstract:In the future energy supply both efficient Heat pump systems for Heat generation and photovoltaic (PV) electricity production will play an important role. Therefore, a Heat pump system with a combined Heat source consisting of a photovoltaic-thermal (PVT) collector and a Borehole Heat Exchanger (BHE) is assumed to be a promising solution, because this particular combination provides a double benefit compared to conventional Heat pump and PV-systems. First, the PV cells in the PVT collector are cooled, leading to lower cell temperatures and a higher PV efficiency. Second, the Heat from the PVT collector raises the temperature level of the Heat pump and the Borehole Heat Exchanger. Consequently, the temperature increase of the Heat source leads to a higher Heat pump performance factor.
Hans-jörg G. Diersch - One of the best experts on this subject based on the ideXlab platform.
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transient 3d analysis of Borehole Heat Exchanger modeling
Geothermics, 2011Co-Authors: D Bauer, Walter Heidemann, Hans-jörg G. DierschAbstract:Abstract This paper presents the development and application of a three-dimensional (3D) numerical simulation model for U-tube Borehole Heat Exchangers (BHEs). The proposed model includes the thermal capacities of the Borehole components, viz., the fluid inside the tubes, as well as the grouting material, making it possible to consider the transient effects of Heat and mass transports inside the Borehole. In this approach, the use of simplified thermal resistance and capacity models (TRCMs) provides accurate results while substantially reducing the number of nodes and the computation time compared with fully discretized computations such as finite element (FE) models. The model is compared with a fully discretized FE model which serves as a reference. Furthermore, the model is used to evaluate thermal response test (TRT) data by the parameter estimation technique. Comparison of the model results with the results of an analytical model based on the line-source theory further establishes the advantage of the developed 3D transient model, as the test duration can be shortened and results are more accurate.
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finite element modeling of Borehole Heat Exchanger systems
Computers & Geosciences, 2011Co-Authors: Hans-jörg G. Diersch, Walter Heidemann, Wolfram Rühaak, D Bauer, P SchatzlAbstract:Single Borehole Heat Exchanger (BHE) and arrays of BHE are modeled by using the finite element method. Applying BHE in regional discretizations optimal conditions of mesh spacing around singular BHE nodes are derived. Optimal meshes have shown superior to such discretizations which are either too fine or too coarse. The numerical methods are benchmarked against analytical and numerical reference solutions. Practical application to a Borehole thermal energy store (BTES) consisting of 80 BHE is given for the real-site BTES Crailsheim, Germany. The simulations are controlled by the specifically developed FEFLOW-TRNSYS coupling module. Scenarios indicate the effect of the groundwater flow regime on efficiency and reliability of the subsurface Heat storage system.
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finite element modeling of Borehole Heat Exchanger systems part 1 fundamentals
Computers & Geosciences, 2011Co-Authors: Hans-jörg G. Diersch, Walter Heidemann, Wolfram Rühaak, D Bauer, P SchatzlAbstract:Single Borehole Heat Exchanger (BHE) and arrays of BHE are modeled by using the finite element method. The first part of the paper derives the fundamental equations for BHE systems and their finite element representations, where the thermal exchange between the Borehole components is modeled via thermal transfer relations. For this purpose improved relationships for thermal resistances and capacities of BHE are introduced. Pipe-to-grout thermal transfer possesses multiple grout points for double U-shape and single U-shape BHE to attain a more accurate modeling. The numerical solution of the final 3D problems is performed via a widely non-sequential (essentially non-iterative) coupling strategy for the BHE and porous medium discretization. Four types of vertical BHE are supported: double U-shape (2U) pipe, single U-shape (1U) pipe, coaxial pipe with annular (CXA) and centred (CXC) inlet. Two computational strategies are used: (1) The analytical BHE method based on Eskilson and Claesson's (1988) solution, (2) numerical BHE method based on Al-Khoury et al.'s (2005) solution. The second part of the paper focusses on BHE meshing aspects, the validation of BHE solutions and practical applications for Borehole thermal energy store systems.