Long-term performance of large borehole heat exchanger fields with unbalanced seasonal loads and groundwater flow

Zanchini, Enzo; Lazzari, Stefano; Priarone, Antonella

doi:10.1016/j.energy.2011.12.038

Cited by 111 publications

(34 citation statements)

References 20 publications

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“…They concluded that an almost complete heat load compensation is needed in the case of an infinite square BHE field, even when the spacing between the individual BHEs is large (14 m). A similar study of under groundwater flow was carried out by Zanchini et al [25]. These authors point out that the performance of a BHE field becomes more sustainable when the Peclet number increases.…”

Section: Introductionmentioning

confidence: 66%

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: 66%

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

Mao

Xing

et al. 2015

Sustainability

View full text Add to dashboard Cite

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“…Numerical methods are common in ground heat exchanger research (e.g Fan et al, 2008, Zanchini et al, 2012 and allow consideration of many more configurations that can be addressed in practical experiments. However, most models are produced to consider specific case studies (e.g Knellwolf et al, 2011, Dupray et al, 2014, Sinnathamby, 2014 and do not take the opportunity to study the important general problem of optimisation guidance for designers.…”

Section: Introductionmentioning

confidence: 99%

Influences on the thermal efficiency of energy piles

Cecinato

Loveridge

2015

Energy

138

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Energy piles have recently emerged as a viable alternative to borehole heat exchangers, but their energy efficiency has so far seen little research. In this work, a finite element numerical model is developed for the accurate 3D analysis of transient diffusive and convective heat exchange phenomena taking place in geothermal structures. The model is validated by reproducing both the outcome of a thermal response test carried out on a test pile, and the average response of the linear heat source analytical solution. Then, the model is employed to carry out a parametric analysis to identify the key factors in maximising the pile energy efficiency. It is shown that the most influential design parameter is the number of pipes, which can be more conveniently increased, within a reasonable range, compared to increasing the pile dimensions. The influence of changing pile length, concrete conductivity, pile diameter and concrete cover are also discussed in light of their energetic implications. Counter to engineering intuition, the fluid flow rate does not emerge as important in energy efficiency, provided it is sufficient to ensure turbulent flow. The model presented in this paper can be easily adapted to the detailed study of other types of geothermal structures.

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“…Numerical methods have also been used to assess multiple ground heat exchangers, eg [29], [30]; this has the advantage of being able to assess bespoke geometries and arrangements of heat exchangers. However three dimensional models of many heat exchangers can be computationally expensive and hence 2D simplifications may be preferable.…”

Section: Multiple Heat Exchangersmentioning

confidence: 99%

G-Functions for multiple interacting pile heat exchangers

Loveridge

Powrie

2014

Energy

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Pile heat exchangers -where heat transfer pipes are cast into the building piled foundations -offer an opportunity to use ground energy systems without the additional construction costs related to the provision of special purpose heat exchangers. However, analysis methods for pile heat exchangers are still under development. In particular there is an absence of available methods and guidance for the amount of thermal interaction that may occur between adjacent pile heat exchangers and the corresponding reduction in available energy that this will cause. This is of particular importance as the locations of foundation piles are controlled by the structural demands of the building and cannot be optimised with respect to the thermal analysis. This paper presents a method for deriving G-functions for use with multiple pile heat exchangers. Example functions illustrate the primary importance of pile spacing in controlling available energy, followed by the number of piles within any given arrangement. Significantly it was found that the internal thermal behaviour of a pile is not influenced appreciably by adjacent piles. (170 words)

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Long-term performance of large borehole heat exchanger fields with unbalanced seasonal loads and groundwater flow

Cited by 111 publications

References 20 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

Influences on the thermal efficiency of energy piles

G-Functions for multiple interacting pile heat exchangers

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