scholarly journals Thermal Performance Analyses of Multiborehole Ground Heat Exchangers

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-11
Author(s):  
Wanjing Luo ◽  
Changfu Tang ◽  
Yin Feng ◽  
Pu Miao
Keyword(s):  
Thermal Performance ◽  
Heat Exchangers ◽  
Geothermal Energy ◽  
Greenhouse Gas Emission ◽  
Energy Resource ◽  
Thermal Dissipation ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Cooling Mode ◽  
Ground Heat Exchangers

Geothermal energy known as a clean, renewable energy resource is widely available and reliable. Ground heat exchangers (GHEs) can assist the development of geothermal energy by reducing the capital cost and greenhouse gas emission. In this paper, a novel semianalytical method was developed to study the thermal performance of multiborehole ground heat exchangers (GHEs) with arbitrary configurations. By assuming a uniform inlet fluid temperature (UIFT), instead of uniform heat flux (UHF), the effects of thermal interference and the thermal performance difference between different boreholes can be examined. Simulation results indicate that the monthly average outlet fluid temperatures of GHEs will increase gradually while the annual cooling load of the GHEs is greater than the annual heating load. Besides, two mechanisms, the thermal dissipation and the heat storage effect, will determine the heat transfer underground, which can be further divided into four stages. Moreover, some boreholes will be malfunctioned; that is, boreholes can absorb heat from ground when the GHEs are under the cooling mode. However, as indicated by further investigations, this malfunction can be avoided by increasing borehole spacing.

scholarly journals Application and Design Aspects of Ground Heat Exchangers

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2134
Author(s):  
Luka Boban ◽  
Dino Miše ◽  
Stjepan Herceg ◽  
Vladimir Soldo
Keyword(s):  
Renewable Energy ◽  
Heat Exchangers ◽  
Geothermal Energy ◽  
Energy Demand ◽  
Design Parameters ◽  
Direct Expansion ◽  
Alternative Source ◽  
Ground Heat Exchangers ◽  
Point Of Interest ◽  
Constant Source

With the constant increase in energy demand, using renewable energy has become a priority. Geothermal energy is a widely available, constant source of renewable energy that has shown great potential as an alternative source of energy in achieving global energy sustainability and environment protection. When exploiting geothermal energy, whether is for heating or cooling buildings or generating electricity, a ground heat exchanger (GHE) is the most important component, whose performance can be easily improved by following the latest design aspects. This article focuses on the application of different types of GHEs with attention directed to deep vertical borehole heat exchangers and direct expansion systems, which were not dealt with in detail in recent reviews. The article gives a review of the most recent advances in design aspects of GHE, namely pipe arrangement, materials, and working fluids. The influence of the main design parameters on the performance of horizontal, vertical, and shallow GHEs is discussed together with commonly used performance indicators for the evaluation of GHE. A survey of the available literature shows that thermal performance is mostly a point of interest, while hydraulic and/or economic performance is often not addressed, potentially resulting in non-optimal GHE design.

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.

Effect of the Circulation Flow Velocity in Ground Heat Exchangers on System Operation

2014 ◽  
Vol 580-583 ◽  
pp. 2457-2460
Author(s):  
Zi Shu Qi ◽  
Qing Gao ◽  
Yan Liu ◽  
Zhen Hai Gao ◽  
Li Bai
Keyword(s):  
Flow Velocity ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Engineering Practice ◽  
Fluid Temperature ◽  
Circulation Flow ◽  
Pump System ◽  
Heat Pump System ◽  
Computing Platform ◽  
Ground Heat Exchangers

The heat pump system by using earth energy is increasing very rapidly. In this paper, by studying the underground heat exchanger heat transfer mode, the computing platform for ground source heat pump system was established. Through a engineering case, the influence character of the circulation flow velocity in ground heat exchangers on the fluid temperature, the heat pump power consumption, and the length of system were analyzed, which provide an approach for system engineering design and operation prediction, and for the thermodynamic analysis of performance of system year by year and prospective study to guide the engineering practice.

Performance and Economic Evaluation of Ground Heat Exchangers

2013 ◽  
Vol 838-841 ◽  
pp. 1913-1916 ◽  
Author(s):  
Seok Yoon ◽  
Nam Hyun Cho ◽  
Gyu Hyun Go ◽  
Seung Rae Lee
Keyword(s):  
Thermal Performance ◽  
Heat Exchangers ◽  
Construction Cost ◽  
Performance Tests ◽  
Operation Condition ◽  
Partially Saturated ◽  
Ground Heat Exchangers ◽  
Loop Design ◽  
Design Program ◽  
Construction Condition

This paper presents experimental study on the evaluation of thermal performance of U and W type ground heat exchangers (GHEs). These GHEs were installed in a partially saturated landfill ground which was composed of silt and clay in the runway area of Incheon International airport. Thermal performance tests (TPTs) were conducted for 100 hours under the continuous operation condition. Heat exchange rate of individual GHE was evaluated from the TPT results, and construction cost was also estimated. The required Borehole length of U and W type GHEs was calculated considering real construction condition from GLD (ground loop design) program.

scholarly journals Ground-Source Heat Pump Systems: The Effects of Variable Trench Separations and Pipe Configurations in Horizontal Ground Heat Exchangers

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3919
Author(s):  
Yu Zhou ◽  
Asal Bidarmaghz ◽  
Nikolas Makasis ◽  
Guillermo Narsilio
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Element Model ◽  
Fluid Temperature ◽  
Ground Source Heat Pump ◽  
Carrier Fluid ◽  
Ground Heat Exchangers ◽  
Ground Source

Ground-source heat pump systems are renewable and highly efficient HVAC systems that utilise the ground to exchange heat via ground heat exchangers (GHEs). This study developed a detailed 3D finite element model for horizontal GHEs by using COMSOL Multiphysics and validated it against a fully instrumented system under the loading conditions of rural industries in NSW, Australia. First, the yearly performance evaluation of the horizontal straight GHEs showed an adequate initial design under the unique loads. This study then evaluated the effects of variable trench separations, GHE configurations, and effective thermal conductivity. Different trench separations that varied between 1.2 and 3.5 m were selected and analysed while considering three different horizontal loop configurations, i.e., the horizontal straight, slinky, and dense slinky loop configurations. These configurations had the same length of pipe in one trench, and the first two had the same trench length as well. The results revealed that when the trench separation became smaller, there was a minor increasing trend (0.5 °C) in the carrier fluid temperature. As for the configuration, the dense slinky loop showed an average that was 1.5 °C lower than those of the horizontal straight and slinky loop (which were about the same). This indicates that, when land is limited, compromises on the trench separation should be made first in lieu of changes in the loop configuration. Lastly, the results showed that although the effective thermal conductivity had an impact on the carrier fluid temperature, this impact was much lower compared to that for the GHE configurations and trench separations.

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