A numerical and experimental approach to the estimation of borehole thermal resistance in ground heat exchangers

Energy ◽  
2014 ◽  
Vol 71 ◽  
pp. 547-555 ◽  
Author(s):  
Seok Yoon ◽  
Seung-Rae Lee ◽  
Gyu-Hyun Go
Keyword(s):  
Thermal Resistance ◽  
Heat Exchangers ◽  
Experimental Approach ◽  
Ground Heat Exchangers ◽  
Borehole Thermal Resistance

Effective pipe-to-borehole thermal resistance for vertical ground heat exchangers

Geothermics ◽  
2009 ◽  
Vol 38 (2) ◽  
pp. 271-277 ◽  
Author(s):  
Mostafa H. Sharqawy ◽  
Esmail M. Mokheimer ◽  
Hassan M. Badr
Keyword(s):  
Thermal Resistance ◽  
Heat Exchangers ◽  
Ground Heat Exchangers ◽  
Vertical Ground ◽  
Borehole Thermal Resistance

scholarly journals Effects of the Circuit Arrangement on the Thermal Performance of Double U-Tube Ground Heat Exchangers

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3275
Author(s):  
Aminhossein Jahanbin ◽  
Giovanni Semprini ◽  
Andrea Natale Impiombato ◽  
Cesare Biserni ◽  
Eugenia Rossi di Schio
Keyword(s):  
Thermal Resistance ◽  
Thermal Performance ◽  
Numerical Code ◽  
Geometrical Parameters ◽  
Fluid Temperature ◽  
The Finite Element Method ◽  
Ground Heat Exchangers ◽  
Borehole Thermal Resistance ◽  
The Impact ◽  
Circuit Configuration

Given that the issue of variations in geometrical parameters of the borehole heat exchanger (BHE) revolves around the phenomenon of thermal resistance, a thorough understanding of these parameters is beneficial in enhancing thermal performance of BHEs. The present study seeks to identify relative changes in the thermal performance of double U-tube BHEs triggered by alterations in circuit arrangements, as well as the shank spacing and the borehole length. The thermal performance of double U-tube BHEs with different configurations is comprehensively analyzed through a 3D transient numerical code developed by means of the finite element method. The sensitivity of each circuit configuration in terms of the thermal performance to variations of the borehole length and shank spacing is investigated. The impact of the thermal interference between flowing legs, namely thermal short-circuiting, on parameters affecting the borehole thermal resistance is addressed. Furthermore, the energy exchange characteristics for different circuit configurations are quantified by introducing the thermal effectiveness coefficient. The results indicate that the borehole length is more influential than shank spacing in increasing the discrepancy between thermal performances of different circuit configurations. It is shown that deviation of the averaged-over-the-depth mean fluid temperature from the arithmetic mean of the inlet and outlet temperatures is more critical for lower shank spacings and higher borehole lengths.

scholarly journals Nanofluid suspensions as heat carrier fluids in single U-tube borehole heat exchangers

2021 ◽  
Vol 2116 (1) ◽  
pp. 012100
Author(s):  
A Jahanbin ◽  
G Semprini ◽  
B Pulvirenti
Keyword(s):  
Thermal Resistance ◽  
Heat Carrier ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Borehole Heat Exchanger ◽  
Carrier Fluid ◽  
Improve Energy Efficiency ◽  
Ground Source ◽  
Borehole Thermal Resistance ◽  
Borehole Heat Exchangers

Abstract The borehole heat exchanger (BHE) is a critical component to improve energy efficiency and decreasing environmental impact of ground-source heat pump systems. The lower thermal resistance of the BHE results in the better thermal performance and/or in the lower required borehole length. In the present study, effects of employing a nanofluid suspension as a heat carrier fluid on the borehole thermal resistance are examined. A 3D transient finite element code is adopted to evaluate thermal comportment of nanofluids with various concentrations in single U-tube borehole heat exchangers and to compare their performance with the conventional circuit fluid. The results show, in presence of nanoparticles, the borehole thermal resistance is reduced to some extent and the BHE renders a better thermal performance. It is also revealed that employing nanoparticle fractions between 0.5% and 2 % are advantageous in order to have an optimal decrement percentage of the thermal resistance.

scholarly journals Development of Analytical Model for a Vertical Single U-Tube Ground-Coupled Heat Pump System

2020 ◽  
pp. 1-14
Author(s):  
Ali H. Tarrad
Keyword(s):  
Thermal Resistance ◽  
Analytical Model ◽  
Heat Pump ◽  
Diameter Ratio ◽  
Thermal Design ◽  
Pump System ◽  
Heat Pump System ◽  
Ground Heat Exchangers ◽  
Borehole Thermal Resistance ◽  
Outside Diameter

An analytical model was built to study the thermal design of a single vertical U-tube coupled heat pump under steady-state conditions. It was based on the philosophy of U-tube replacement by an equivalent thermal resistance situated between the heat transfer medium that flows inside the tube and the borehole boundary. An obstruction factor was introduced to account for the reduction of heat flow from or to a tube in the borehole due to the presence of the second leg of the U-tube. Two Copper U-tubes with wall factors of (12.5) and (14.29) were implemented to comprise several borehole configurations to verify the present work. The shank spacing was ranged between (2) and (4) times the U-tube outside diameter producing shank spacing to borehole diameter ratio range of (0.29-0.59). The model was utilized for the assessment of DX ground heat exchangers works as a condenser for cooling purposes. Reducing of the tube spacing to tube outside diameter ratio from (3.3) to (2) for both tube wall factors showed a rise for the borehole thermal resistance in the range of (22-54)% and (26.5-28)% predicted at wall factors of (12.5) and (14.29) respectively.

scholarly journals Borehole Resistance and Heat Conduction Around Vertical Ground Heat Exchangers

2012 ◽  
Vol 6 (1) ◽  
pp. 32-40 ◽  
Author(s):  
Zoi Sagia ◽  
Athina Stegou ◽  
Constantinos Rakopoulos
Keyword(s):  
Heat Conduction ◽  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Exchangers ◽  
Borehole Diameter ◽  
Working Fluid ◽  
Geometrical Parameters ◽  
Conductive Heat ◽  
Ground Heat Exchanger ◽  
Borehole Thermal Resistance

Borehole thermal resistance in Ground Heat Exchanger (GHE) installations is affected by several parameters such as geometrical attributes of heat exchanger in the borehole, pipes' characteristics and grout’s thermal conductivity. A study is carried out to compare the values computed by Ground Loop Design (GLD) Software, GLD 2009, with three ana-lytical solutions for U-shaped tubes. The analysis is focused on dimensionless ratios of borehole geometrical parameters (borehole diameter to outside pipe diameter and shank spacing to borehole diameter) and pipes according to Standard Di-mension Ratio (SDR) and on eight common grouts. Finally, the effect of heat conduction in the borehole is examined by means of finite element analysis by Heat Transfer Module of COMSOL Multiphysics. A two-dimensional (2-D) steady-state simulation is done assuming working fluid temperatures for winter and summer conditions and typical Greek undis-turbed ground temperature in a field of four ground vertical U-tube heat exchangers surrounded by infinite ground. The temperature profile is presented and the total conductive heat flux from the pipe to the borehole wall per meter of length of ground heat exchanger is computed for pipes SDR11 (the outside diameter of the pipe is 11 times the thickness of its wall), SDR9 and SDR17 for summer working conditions and three different configurations. It is attempted to reach to comparative results for borehole thermal resistance value through different types of analysis, having considered the major factors that affect it and giving trends for the influence of each factor to the magnitude of its value.

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