Study on the Influence of Borehole Heat Capacity on Deep Coaxial Borehole Heat Exchanger

Changlong Wang, Han Fang, Xin Wang, Jinli Lu and Yanhong Sun
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Changlong Wang: Department of Civil Engineering and Architecture, Anhui University of Technology, Ma’anshan 243002, China
Han Fang: Department of Civil Engineering and Architecture, Anhui University of Technology, Ma’anshan 243002, China
Xin Wang: Department of Civil Engineering and Architecture, Anhui University of Technology, Ma’anshan 243002, China
Jinli Lu: Department of Civil Engineering and Architecture, Anhui University of Technology, Ma’anshan 243002, China
Yanhong Sun: Department of Civil Engineering and Architecture, Anhui University of Technology, Ma’anshan 243002, China

Sustainability, 2022, vol. 14, issue 4, 1-11

Abstract: Based on a semi-analytical model established previously for heat transfer in coaxial borehole heat exchangers, the influences of the heat capacities of different parts of the borehole (fluid, pipes and grout) on the performance of deep coaxial borehole heat exchanger (DCBHE) are analyzed. The results are as follows: the heat transfer performance of DCBHE will be underestimated if the heat capacities of different parts of the borehole are ignored; the influences of the heat capacities of different parts of the borehole on the performance of DCBHE are more obvious in the early stage, and gradually weaken with the increasing of time; among the heat capacities of different parts of the borehole, the influence of the fluid heat capacity on the performance of DCBHE is the greatest, and the influence of the pipe heat capacities is the least. Under the working condition studied in this paper, the results obtained with considering the heat capacities of different parts of the borehole are compared to ones ignoring heat capacities of selected elements. It was found that ignoring the fluid heat capacity led to a 0.29 °C lower estimated outlet fluid temperature after 60 h. Omitting the heat capacities of pipes and grout gave 0.03 °C and 0.13 °C lower outlet fluid temperatures after 60 h, respectively. The larger the borehole radius, the greater the influence of borehole heat capacity. The geothermal gradient has little effect on the influence of borehole heat capacity on the performance of DCBHE. The results show that the heat capacities of different parts of the borehole have important effects on the performance of DCBHE, especially in the early stage and for a large borehole radius.

Keywords: deep coaxial borehole heat exchanger (DCBHE); borehole heat capacity; heat transfer performance; borehole radius; geothermal gradient (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2022
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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