The Experts below are selected from a list of 4551 Experts worldwide ranked by ideXlab platform
Min-jun Kim - One of the best experts on this subject based on the ideXlab platform.
-
evaluation of stainless steel pipe performance as a Ground Heat Exchanger in Ground source Heat pump system
Energy, 2016Co-Authors: Seok Yoon, Min-jun Kim, Seungrae Lee, Woojin Kim, Geonyoung Kim, Kyungsu KimAbstract:This paper presents a numerical and experimental study of the evaluation of stainless steel (STS) pipe performance as a Ground Heat Exchanger (GHE). U-type GHEs of circular polybutylene (PB) and annular STS were installed in a steel box (5 m × 1 m × 1 m), and indoor thermal response tests (TRTs) were conducted for 30 h to evaluate the Heat-exchange rates. The U-type GHEs of PB, annular STS, and indoor TRT conditions were numerically modeled using a three-dimensional finite-element method. The average pipe diameter for the annular STS pipe was determined by the finite-element method. The exchange rate of the annular STS pipe was approximately 10% higher than that of the circular PB pipe, and the temperature distributions measured in the TRT and calculated by the numerical analysis exhibited reasonable agreement. In addition, the borehole thermal resistance and Heat-exchange rate under the assumption that the annular STS pipe would be applied in an actual vertical Heat Exchanger system were calculated. It is expected that the borehole thermal resistance would be decreased by 25% and that the Heat-exchange rate would be increased by 15% with annular STS pipe in comparison with PB pipe.
-
thermal performance evaluation and parametric study of a horizontal Ground Heat Exchanger
Geothermics, 2016Co-Authors: Min-jun Kim, Seungrae Lee, Seok YoonAbstract:Abstract A Ground-source Heat pump (GSHP) system uses a relatively constant Ground temperature to emit Heat in summer and to obtain Heat during winter for Heating and cooling energy. Among diverse GSHP systems, in designing a closed horizontal system, it is important to accurately estimate the thermal performance of the horizontal Ground Heat Exchanger (GHE). Therefore, in this study, we investigated the performance of a horizontal GHE via experiments and numerical analyses. Thermal response tests (TRTs) were conducted to evaluate Heat exchange rates by using horizontal slinky- and spiral-coil-type GHEs installed in a 5 m × 1 m × 1 m steel box filled with dried Joomunjin sand. Numerical analyses were conducted for verification with experimental results and a parametric study of affecting parameters on horizontal GHE. The results of the TRTs and the numerical analyses were well matched, and coil-type GHEs were found to perform better than the horizontal slinky-type GHEs. Our results show that, among horizontal GHE design parameters, GHE type and soil thermal conductivity are the main factors to determine the Heat exchange rate of a GHE, whereas the pipe diameter does not have any effect on the GHE performance.
-
analysis and thermal response test for vertical Ground Heat Exchanger with two u loop configuration
International Journal of Energy Research, 2016Co-Authors: Keun Sun Chang, Min-jun KimAbstract:An in situ thermal response test (TRT) is applied to evaluate the thermal performance of the vertical Ground Heat Exchanger (GHX) with two U-loop configuration. A line source method is used to derive the thermal conductivity and borehole thermal resistance from the measured data. Analyses are made to improve the interpretation of TRT data and to investigate the active area of interest in the borehole. Load tests of the GHX are performed to examine the daily variations of Ground and mean fluid temperatures associated with daily intermittent operation of Ground source Heat pump system. Results show that while the Ground thermal conductivity of two U-loop GHX is moderately increased, the borehole thermal resistance is significantly reduced, compared with the single U-loop GHX. Of the borehole thermal resistance components evaluated, the grout thermal resistance is the most governing one in the borehole Heat transfer (77% of the total borehole thermal resistance), whereas the convective thermal resistance in the tube is almost negligible (less than 2%). Copyright © 2015 John Wiley & Sons, Ltd.
Erik Bertram - One of the best experts on this subject based on the ideXlab platform.
-
Solar Assisted Heat Pump Systems with Ground Heat Exchanger – Simulation Studies
Energy Procedia, 2014Co-Authors: Erik BertramAbstract:Abstract Different concepts of solar assisted Heat pump systems with Ground Heat Exchanger are simulated according to IEA SHC Task44/HPP Annex38 reference conditions. Two aspects of the concepts are investigated using TRNSYS simulations. First, the solar impact on system efficiency is assessed by the seasonal performance factor. Second, the solar impact on the possible shortening of the Ground Heat Exchanger is evaluated by the minimum temperature at the Ground Heat Exchanger inlet. The simulation results reveal diverging optimums for the concepts. The direct use of solar energy clearly achieves the best effect on the efficiency improvement. A simple domestic hot water system reaches a seasonal performance factor of 4.5 and solar combi-systems seasonal performance factors up to 6. In contrast, the use of solar energy on the cold side of the Heat pump achieves the best effects on the shortening of the Ground Heat Exchanger of up to 20%. Two highly sensitive influences are investigated with the developed transient system model. First, the minimum allowed Heat source temperature is varied. Here 1 K equals a variation of 0.25 in the seasonal performance or of around 10% Ground Heat Exchanger length. Second, the Ground Heat Exchanger model is simulated without and with a pre-pipe that improves the transient model behavior. The influence of this pre-pipe on the SPF is small for conventionally designed Ground Heat Exchangers, but of around 2 K for the minimum inlet temperature. Therefore, the dynamic model quality reveals potential to reduce the size of the Ground Heat Exchanger corresponding to investment costs.
-
solar assisted Heat pump systems with Ground Heat Exchanger simulation studies
Energy Procedia, 2014Co-Authors: Erik BertramAbstract:Abstract Different concepts of solar assisted Heat pump systems with Ground Heat Exchanger are simulated according to IEA SHC Task44/HPP Annex38 reference conditions. Two aspects of the concepts are investigated using TRNSYS simulations. First, the solar impact on system efficiency is assessed by the seasonal performance factor. Second, the solar impact on the possible shortening of the Ground Heat Exchanger is evaluated by the minimum temperature at the Ground Heat Exchanger inlet. The simulation results reveal diverging optimums for the concepts. The direct use of solar energy clearly achieves the best effect on the efficiency improvement. A simple domestic hot water system reaches a seasonal performance factor of 4.5 and solar combi-systems seasonal performance factors up to 6. In contrast, the use of solar energy on the cold side of the Heat pump achieves the best effects on the shortening of the Ground Heat Exchanger of up to 20%. Two highly sensitive influences are investigated with the developed transient system model. First, the minimum allowed Heat source temperature is varied. Here 1 K equals a variation of 0.25 in the seasonal performance or of around 10% Ground Heat Exchanger length. Second, the Ground Heat Exchanger model is simulated without and with a pre-pipe that improves the transient model behavior. The influence of this pre-pipe on the SPF is small for conventionally designed Ground Heat Exchangers, but of around 2 K for the minimum inlet temperature. Therefore, the dynamic model quality reveals potential to reduce the size of the Ground Heat Exchanger corresponding to investment costs.
Seok Yoon - One of the best experts on this subject based on the ideXlab platform.
-
evaluation of stainless steel pipe performance as a Ground Heat Exchanger in Ground source Heat pump system
Energy, 2016Co-Authors: Seok Yoon, Min-jun Kim, Seungrae Lee, Woojin Kim, Geonyoung Kim, Kyungsu KimAbstract:This paper presents a numerical and experimental study of the evaluation of stainless steel (STS) pipe performance as a Ground Heat Exchanger (GHE). U-type GHEs of circular polybutylene (PB) and annular STS were installed in a steel box (5 m × 1 m × 1 m), and indoor thermal response tests (TRTs) were conducted for 30 h to evaluate the Heat-exchange rates. The U-type GHEs of PB, annular STS, and indoor TRT conditions were numerically modeled using a three-dimensional finite-element method. The average pipe diameter for the annular STS pipe was determined by the finite-element method. The exchange rate of the annular STS pipe was approximately 10% higher than that of the circular PB pipe, and the temperature distributions measured in the TRT and calculated by the numerical analysis exhibited reasonable agreement. In addition, the borehole thermal resistance and Heat-exchange rate under the assumption that the annular STS pipe would be applied in an actual vertical Heat Exchanger system were calculated. It is expected that the borehole thermal resistance would be decreased by 25% and that the Heat-exchange rate would be increased by 15% with annular STS pipe in comparison with PB pipe.
-
thermal performance evaluation and parametric study of a horizontal Ground Heat Exchanger
Geothermics, 2016Co-Authors: Min-jun Kim, Seungrae Lee, Seok YoonAbstract:Abstract A Ground-source Heat pump (GSHP) system uses a relatively constant Ground temperature to emit Heat in summer and to obtain Heat during winter for Heating and cooling energy. Among diverse GSHP systems, in designing a closed horizontal system, it is important to accurately estimate the thermal performance of the horizontal Ground Heat Exchanger (GHE). Therefore, in this study, we investigated the performance of a horizontal GHE via experiments and numerical analyses. Thermal response tests (TRTs) were conducted to evaluate Heat exchange rates by using horizontal slinky- and spiral-coil-type GHEs installed in a 5 m × 1 m × 1 m steel box filled with dried Joomunjin sand. Numerical analyses were conducted for verification with experimental results and a parametric study of affecting parameters on horizontal GHE. The results of the TRTs and the numerical analyses were well matched, and coil-type GHEs were found to perform better than the horizontal slinky-type GHEs. Our results show that, among horizontal GHE design parameters, GHE type and soil thermal conductivity are the main factors to determine the Heat exchange rate of a GHE, whereas the pipe diameter does not have any effect on the GHE performance.
-
characteristics of an analytical solution for a spiral coil type Ground Heat Exchanger
Computers and Geotechnics, 2013Co-Authors: Skhan Park, Hyunku Park, Seok Yoon, Jaywan ChungAbstract:Abstract This paper presents an efficient spiral coil source model and its analytical solution, developed to consider 3-dimensional shape effects and radial dimension effects of a spiral coil type Ground Heat Exchanger (GHE) using Green’s function method. To avoid singular integrals, the solution is expressed using an error function by which the computational limitation is avoided. To analyze the characteristics of the analytical model, predicted results of the model were compared with test measurements by a thermal response test conducted in a model chamber, and numerical analysis results implemented in ABAQUS/Standard.
-
case study of Heat transfer behavior of helical Ground Heat Exchanger
Energy and Buildings, 2012Co-Authors: Hyunku Park, Seok Yoon, Seungrae Lee, Hosung Shin, Daesoo LeeAbstract:Abstract This paper presents an experimental and numerical case study of the Heat transfer around the helical Ground Heat Exchanger. With varying helical pitch, indoor thermal response tests were conducted in a dry sand. The tests were analyzed based on axisymmetric finite element analyses and recently published Heat source models for spiral coil Heat Exchanger including our modifications of them by adding finite-length line source solution to consider vertical return pipe at center of helical Heat Exchanger. In addition to reasonable agreements in soil temperature rises at exteriors the helical Heat Exchanger, existence of return pipe was found to be important for estimation of Heat transfer inside helical Exchanger. Besides, the Heat source models were found to be applicable to approximate mean fluid temperature during TRTs. The numerical and analytical models were applied to field thermal response test for an energy pile reported in literature. Compared with numerically estimations, the analytical solutions considerably overestimated temperature rise at the exterior of the energy pile. The results reveal that reasonable considerations in estimation of effective thermal properties may be needed when applying the Heat source models for energy pile, even though they would evaluate reliable Heat transfer behavior of helical Heat Exchanger embedded in a homogeneous Ground.
Philippe Pasquier - One of the best experts on this subject based on the ideXlab platform.
-
unit response function for Ground Heat Exchanger with parallel series or mixed borehole arrangement
Renewable Energy, 2014Co-Authors: Denis Marcotte, Philippe PasquierAbstract:A novel approach is presented that allows to predict fluid temperatures entering a Ground Heat Exchanger (GHE) for parallel, series and mixed arrangements of boreholes. The method determines at each time step the Heat transfer rates occurring at each borehole so as to reproduce the fluid temperature at the GHE inlet for a specific borehole arrangement. The analytical finite line source model is used to compute the borehole wall temperatures, whereas the fluid temperatures are assumed to vary linearly along the pipes. The method requires to solve a linear system of equations at a small number of time steps. The different systems of equations for each arrangement are determined. A comprehensive 3D finite element numerical model shows good agreement with the computed fluid temperatures. The proposed approach is computationally very efficient. The fluid temperature unit response function can be convolved with any desired Heat load to estimate fluid temperatures at the GHE inlet for a wide variety of scenarios.
-
unit response function for Ground Heat Exchanger with parallel series or mixed borehole arrangement
Renewable Energy, 2014Co-Authors: Denis Marcotte, Philippe PasquierAbstract:A novel approach is presented that allows to predict fluid temperatures entering a Ground Heat Exchanger (GHE) for parallel, series and mixed arrangements of boreholes. The method determines at each time step the Heat transfer rates occurring at each borehole so as to reproduce the fluid temperature at the GHE inlet for a specific borehole arrangement. The analytical finite line source model is used to compute the borehole wall temperatures, whereas the fluid temperatures are assumed to vary linearly along the pipes. The method requires to solve a linear system of equations at a small number of time steps. The different systems of equations for each arrangement are determined. A comprehensive 3D finite element numerical model shows good agreement with the computed fluid temperatures. The proposed approach is computationally very efficient. The fluid temperature unit response function can be convolved with any desired Heat load to estimate fluid temperatures at the GHE inlet for a wide variety of scenarios.
Hakan Demir - One of the best experts on this subject based on the ideXlab platform.
-
numerical modelling of transient soil temperature distribution for horizontal Ground Heat Exchanger of Ground source Heat pump
Geothermics, 2018Co-Authors: Nurullah Kayaci, Hakan DemirAbstract:Abstract A Ground Heat Exchanger is the most important part of a Ground source Heat pump system. Soil properties and Ground Heat Exchanger performance strongly depend on soil temperature profile and vary with time and space. Also, soil temperature profile is a function of Heat transfer rate extracted or transferred to soil. Studies in the literature either use the unaffected soil temperature obtained from meteorological data or fail to run for long time periods to obtain a steady periodic soil temperature profile and over-predict the Ground Heat Exchanger performance. Therefore, steady periodic temperature profile should be used for sizing Ground Heat Exchanger for efficient operation of Ground source Heat pumps for longer periods of time. Experimental studies are carried out on a Ground-source Heat pump established at Yildiz Technical University, Davutpasa Campus and the newly developed numerical model is validated with experimental results. For the numerical study, the hourly required Heat load of a 200 m2 office in Istanbul during the Heating season is calculated by using HAP software. The transient soil temperature profile is obtained numerically for longer periods of time with realistic boundary conditions using meteorological data. The fluid inlet temperatures equivalent to the hourly need for Heating load of the office during the Heating season are simulated for a ten-year period in accordance with the different Heat amounts extracted from unit pipe length in soil (21, 10.5 and 7 W/m). The effects of burial depth, distance between pipes and surface effects on soil temperature are also investigated. Horizontal and vertical temperature distribution in soil at the beginning (November 10th), middle (January 21st) and end (April 3rd) of the first, fifth and tenth years are represented.
-
Heat transfer of horizontal parallel pipe Ground Heat Exchanger and experimental verification
Applied Thermal Engineering, 2009Co-Authors: Hakan Demir, Ahmet Koyun, Galip TemirAbstract:Abstract The Ground Heat Exchangers (GHE) consist of pipes buried in the soil and is used for transferring Heat between the soil and the Heat Exchanger pipes of the Ground source Heat pump (GSHP). Because of the complexity of the boundary conditions, the Heat conduction equation has been solved numerically using alternating direction implicit finite difference formulation. A software was developed in MATLAB environment and the effects of solution parameters on the results were investigated. An experimental study was carried out to test the validity of the model. An experimental GSHP system is installed at Yildiz Technical University Davupasa Campus on 800 m2 surface area with no special surface cover. Temperature data were collected using thermocouples buried in soil horizontally and vertically at various distances from the pipe center and at the inlet and the outlet of the Ground Heat Exchanger. Experimental and numerical simulation results calculated using experimental water inlet temperatures were compared. The maximum difference between the numerical results and the experimental data is 10.03%. The temperature distribution in the soil was calculated and compared with experimental data also. Both horizontal and vertical temperature profiles matched the experimental data well. Simulation results were compared with the other studies.
