On Thermally Interacting Multiple Boreholes with Variable Heating Strength: Comparison between Analytical and Numerical Approaches

Koohi-Fayegh, Seama; Rosen, Marc A.

doi:10.3390/su4081848

Cited by 13 publications

(6 citation statements)

References 24 publications

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“…This is achieved through the utilization of ground source heat pumps (GSHP). Compared to conventional air conditioning systems, GSHP can offer higher energy efficiency for air-conditioning [1][2][3][4], as they provide lower temperatures for cooling, higher temperatures for heating, and smaller temperature fluctuations than the ambient air temperature changes. Because of these advantages, more and more underground projects use GSHP.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Geo-Temperature Restoration Performance under Intermittent Operation of Borehole Heat Exchanger Fields

Mao

Xing

et al. 2015

Sustainability

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Intermittent operation can improve the coefficient of performance (COP) of a ground source heat pump (GSHP) system. In this paper, an analytical solution to analyze the geo-temperature restoration performance under intermittent operation of borehole heat exchanger (BHE) fields is established. For this purpose, the moving finite line source model is combined with the g-function and the superposition principle. The model takes into account the heat transfer along the borehole, thermal interference between BHEs, and the influence of groundwater flow. The accuracy of the model is validated through comparison with an experiment carried out under intermittent operation. The model makes it possible to analyze the geo-temperature restoration performance and its influencing factors, such as BHE spacing, heat flow rate, operation mode, and groundwater flow. The main conclusions of this work are as follows. The heat transfer along the borehole should be considered when analyzing the geo-temperature restoration performance. When the BHE spacing increases, the soil temperature change decreases and the heat recovery improves. Therefore, adequate borehole separation distance is essential in the case of a multiple BHE system with unbalanced load. The presence of groundwater flow is associated with interference between the BHEs, which should not be ignored. In the case of long-term operation, the groundwater flow is beneficial to the geo-temperature recovery process, even for downstream BHEs. Finally, a greater groundwater flux leads to a better geo-temperature recovery.

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Section: Introductionmentioning

confidence: 99%

Analysis of Geo-Temperature Restoration Performance under Intermittent Operation of Borehole Heat Exchanger Fields

Mao

Xing

et al. 2015

Sustainability

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“…Recently, the development and utilization of shallow geothermal energy mainly employ the ground source heat pump (GSHP) system. Because of the stable and moderate temperature of the ground, the efficiency of the GSHP system is higher than that of the air source heat pump [2][3][4][5]. Now, the GSHP system has been widely accepted as a new technology in the world [6] and has been implemented in 30 countries with an annual increase of 10% [4].…”

Section: Introductionmentioning

confidence: 99%

Impact of Boundary Conditions on a Groundwater Heat Pump System Design in a Shallow and Thin Aquifer near the River

et al. 2017

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Abstract:The exploitation of shallow geothermal energy through a groundwater heat pump (GWHP) is always limited to thick and deep aquifers containing abundant water with a relatively stable temperature. Unfortunately, aquifers in hilly regions which occupy two thirds of China are usually thin and shallow. The boundary conditions in those hilly areas affect the groundwater flow that is used for geothermal energy production. To quantify the impact of boundary conditions on the shallow geothermal energy development, a shallow and thin aquifer near the Qingyi River in Anhui Province was chosen as a case study, and a three-dimensional heat-water model was developed using FEFLOW. The impact of the boundary conditions on the hydrodynamic and temperature fields of the aquifer was analyzed by using the developed model. Furthermore, the well locations of a pumping-recharging system near the river correspond to three different modes of pumping-recharging well layouts that were optimized based on the changes of pumping water temperature and the maximum drawdown. The simulation results indicated that the influence of atmospheric temperature on groundwater temperature is negligible below a depth of 11 m. When the river level is above 28 m, the optimal scheme of pumping-only was used (without considering recharging wells) with a certain distance from the river. This scheme not only operates efficiently, but also reduces the operation cost.

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“…There are two ways of upscaling BHE installations-either by increasing the number or the depth of the boreholes [3]. Although the first alternative stands for the majority of the installations today, it requires substantial land plots to install the ground loops, which poses a great challenge for its applications especially in densely populated cities and towns with scarcity of space [4][5][6].On the other hand, in order to keep sustainable operation of shallow BHEs which gradually degrades with the operating time due to the annual negatively balanced loads between heating demand in winter and cooling demand in summer, cross season thermal energy storage becomes essential [7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

A Fast Simulation Approach to the Thermal Recovery Characteristics of Deep Borehole Heat Exchanger after Heat Extraction

Zhao

Pang

2020

Sustainability

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Necessary intermittence after heat extraction for a deep borehole heat exchanger (DBHE) is beneficial for sustainable operation. This paper centers on the fast simulation for thermal recovery characteristics of DBHE under intermittent condition. First of all, in view of the existing temperature gradient and multi-layer heterogeneity of rock underground that could never be ignored for DBHE, we extend the classical finite line source model based on heat source theory and superposition principle to account for the vertical heat flux distribution varying along depth and heterogeneous thermal conductivities in the multi-layer rock zone. Moreover, a fast simulation approach for heat transfer analysis inside the borehole coupled with the extended finite line source model is put forward to depict the transient thermal response and dynamic thermal recovery of rock outside borehole. To the authors’ knowledge, no such algorithm for deep BHE has yet been suggested in the previous literature. This approach has proven to be reliable and efficient enough for DBHE simulation under the intermittent condition. Simulation results show that at least 65 days of intermittence for the model in study should be spared after the heating season to achieve sustainable heat extraction in the next cyclic operation. Compared to the detailed solution based on full discretization numerical schemes, the relative error for borehole bottom temperature was 0.79%. In addition, comparison of the simulation results for thermal performance during the heating season in a three-year cyclic operation with 205 days intermittence shows that both the outflow temperature and heat extraction rate in the subsequent cycle after intermittence are in good agreement with the full 3D numerical solution in the reference (with a relative error of 6.36% for the outflow temperature and 9.3% for the heat extraction rate). Regarding the calculation speed, around a 13 times acceleration can be achieved. Finally, it is also promising to be applicable for thermal recovery simulation after heat extraction of vertical closed loop borehole heat exchangers at arbitrary length from shallow to deep.

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On Thermally Interacting Multiple Boreholes with Variable Heating Strength: Comparison between Analytical and Numerical Approaches

Cited by 13 publications

References 24 publications

Analysis of Geo-Temperature Restoration Performance under Intermittent Operation of Borehole Heat Exchanger Fields

Analysis of Geo-Temperature Restoration Performance under Intermittent Operation of Borehole Heat Exchanger Fields

Impact of Boundary Conditions on a Groundwater Heat Pump System Design in a Shallow and Thin Aquifer near the River

A Fast Simulation Approach to the Thermal Recovery Characteristics of Deep Borehole Heat Exchanger after Heat Extraction

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