# Heat Transfer Performance and Operation Scheme of the Deeply Buried Pipe Energy Pile Group
## 5 Conclusions  
Within this investigation, in situ experiments and numerical simulations were conducted to analyze the differences in heat exchange rate, energy efficiency ratio (EER), and thermal radius between the intermittent and continuous operational modes of the DBP-EP group under summer conditions. The findings can be summarized as follows:  
1. The continuous operation of deep energy single piles exacerbates the accumulation of heat within the pile foundation, expanding the thermal radius distribution of the pile, also reducing its heat transfer efficiency; furthermore, this exerts adverse effects on the heat transfer performance of the DBP-EP. 2. The accumulation of heat and the rate of expansion of the thermal radius within the pile group in continuous operational mode are more pronounced compared to single piles. Under continuous operational conditions, the heat interference generated by the peripheral piles of the pile group has a negative impact on the heat transfer of the inner piles, resulting in a greater reduction in the thermal conductivity characteristics of the inner piles compared to the peripheral piles. 3. Combining the analysis of the energy efficiency ratio (EER) and comparing the heat exchange performance between continuous operation and intermittent operational modes, the optimal conclusion was obtained for the intermittent operational mode with an intermittency ratio of n = 5. When the intermittency ratio is n = 5, the total sum of the pile group's average heat exchange rate decreases by only 0.51% compared to continuous operation, but its single-pile EER is improved by over 19.6%, and to some extent, it alleviates the accumulation of heat within the pile base. 4. Analyzing the change of the pile group's thermal radius during the heat exchange operation in the initial phase, it was found that in the continuous heat exchange operation, thermal interference exerts minimal influence concerning the dynamics of the heat exchange within the pile group. However, as the duration of the heat exchange operation increases, the thermal interference in the pile group gradually becomes more pronounced, leading to a decrease in heat exchange performance. In the intermittent operational mode, the variance in temperature between pile and the soil is recoverable, weakening the pile group effect and favoring the heat exchange operation of the pile group. Therefore, adopting an intermittent operational scheme \begin{table}
\begin{tabular}{c c c c c c} \hline
**Temperature at 0.8 m (\({}^{\circ}\)C)** & **n = \(\infty\)** & **n = 1/2** & **n = 1** & **n = 2** & **n = 5** \\ \hline
24 h & 17.50 & 17.45 & 17.46 & 17.46 & 17.47 \\
168 h & 18.45 & 18.00 & 18.13 & 18.26 & 18.34 \\
178 h & 20.61 & 19.30 & 19.69 & 19.77 & 19.83 \\ \hline \end{tabular}
\end{table} 
Table 4: Soil temperature at 0.8 under different operating modes. can effectively improve the thermal exchange performance of the DBP-EP group, providing favorable conditions for the low-energy and efficient operation of the piles. The above conclusions underscore the advantages of the intermittent operational mode. It is hoped that this mode can be extensively researched for its energy extraction and utilization potential in practical engineering applications, taking into account the varying geological and climatic conditions. Methodology, Z.C. ; conceptualization, Y.T., Z.C. and J.Y. ; software, Y.T. ; validation, Y.T., Z.C. and J.Y. ; data curation, Y.T. ; formal analysis, Y.T. ; writing--review and editing, Z.C. and Y.T. ; investigation, Z.C. ; resources, Z.C. ; writing--original draft preparation, Y.T. ; supervision, Z.C. and A.M.; visualization, Y.T. ; project administration, Z.C. and A.M.; funding acquisition, Z.C. and A.M. All authors have read and agreed to the published version of the manuscript. This work was supported by the Key Research and Development Program of Hubei Province (No. 2023 BAB024) and the Technology Innovation Project of Hubei Province (No. 2023 BEB010). Not applicable.