Medium Rock-Soil Temperature Distribution Characteristics at Different Time Scales and New Layout Forms in the Application of Medium-Deep Borehole Heat Exchangers

Round 1

Reviewer 1 Report

Energies-2608907

General Comment

This is an interesting paper, but the authors need to improve the literature survey, methodology and results for it to be suitable for publication. The novelty is not clear in the introduction as many have investigated the thermal radius around a DBHE, the definition of a MBHE is also not cited and not consistent with literature. So if this is a local definition it needs clarification. There is also no discussion on groundwater flow as this could significantly change findings. In the methods we are missing validation, boundary and initial conditions definitions and the results do lack clarity due to the poorly labelled figures. Nevertheless, there are some parts of this paper which make interesting findings. I hope the authors are able to improve the paper based on the comments. Finally – the English is not up to standards for publication and grammatically incorrect throughout.

Specific comments

1. abstract – rock soil TAR expands under a heating season – under what conditions? I.e., continuous operation

2. abstract – I think you need to improve the English/grammar in the abstract (and throughout) as it is somewhat disjointed throughout as words are missing within sentences.

3. abstract – Please highlight the novel part of this study – in my opinion more emphasis should be on the inclined (or deflected boreholes). I would change ‘deflected’ to ‘inclined’ throughout.

4. Intro – why are you defining the medium deep as 200 to 3000 m? Is this a local definition as in Europe it is very much defined differently. Please elaborate why this is the definition.
5. Intro – the adjacent spacing from cai et al is different to that in other studies and it depends on the shape of the array… see (Brown et al., 2023; Cai et al., 2022), and there is discussion on thermal interference caused by large TARs. Furthermore other publications specifically discuss array propagation around single DBHEs which should be acknowledged, there should be a larger section on this in your introduction – I think you need to clearly identify how your work is novel in this regard?

Brown, C.S., Kolo, I., Falcone, G. and Banks, D., 2023. Investigating scalability of deep borehole heat exchangers: Numerical modelling of arrays with varied modes of operation. Renewable Energy, 202, pp.442-452.

Cai, W., Wang, F., Chen, C., Chen, S., Liu, J., Ren, Z. and Shao, H., 2022. Long-term performance evaluation for deep borehole heat exchanger array under different soil thermal properties and system layouts. Energy, 241, p.122937.

6. I think you could potentially expand the lit review section to include other examples of influencing parameters such as groundwater flow (forced convection) (Chen et al., 2019; Brown et al., 2023) and (free convection) (Bidarmaghz and Narsilio, 2022). While not modelled here, I think you should acknowledge this could impact performance. This could be a discussion section too.
Bidarmaghz, A. and Narsilio, G.A., 2022. Is natural convection within an aquifer a critical phenomenon in deep borehole heat exchangers' efficiency?. Applied Thermal Engineering, 212, p.118450.

Brown, C.S., Doran, H., Kolo, I., Banks, D. and Falcone, G., 2023. Investigating the Influence of Groundwater Flow and Charge Cycle Duration on Deep Borehole Heat Exchangers for Heat Extraction and Borehole Thermal Energy Storage. Energies, 16(6), p.2677.

Chen, C., Shao, H., Naumov, D., Kong, Y., Tu, K. and Kolditz, O., 2019. Numerical investigation on the performance, sustainability, and efficiency of the deep borehole heat exchanger system for building heating. Geothermal Energy, 7, pp.1-26.

8. I think the novelty is not clear in the introduction – there has been a lot of work on DBHEs which needs to be addressed and how this differs to it. There are many works that look at thermal propagation of heat around the DBHE….. I would also emphasise your inclination of the borehole here – this is more of the novelty in this paper in my opinion.

9. Methods – where is the validation of the model? How did you choose the mesh size? What are the initial conditions? What are the boundary conditions? Maximum domain size? There is not a comprehensive list of thermal properties? What is volumetric heat capacity/thermal properties of the pipes? Limitations of the method? Etc This whole section must be improved.

10. Figure 4 – what is the time for each figure?? It says in the text but must be labelled in the figure/caption.

11. All figures in the results – what times are these slices recorded at? You must improve your figure labels.

12. What is the TAR measured too (i.e., full propagation of temperature or within x degree C of initial conditions)?

13. I think you need to improve the highlighting of the novelty of the inclined wells in the results…

14. Would it not be better to have a separate discussion highlighting how your work is different to others? i.e., how do your results compare to other papers that have looked at the thermal propagation around a DBHE (there are a lot)? And any limitations of the study (i.e., not modelling groundwater flow)?

This needs to be improved throughout as there are many grammatical errors which are not up to the standard of publication.

Author Response

Thank you for your letter and comments concerning our manuscript entitled “Medium Rock-soil Temperature Distribution Characteristics in Different Time Scales and New-type Well Layout Form in Application of Medium-deep Borehole Heat exchanger” (ID: energies-2608907). Those comments are all valuable and very helpful for revising and improving our manuscript, as well as the important guiding significance to our researches. We have tried our best to accommodate all comments and have made corrections/revisions which we hope meet with approval. The revised part was marked in yellow in the revised manuscript. Our point-to-point responses to the review comments are shown in the file named "Response to reviewer 1".

Author Response File: Author Response.docx

Reviewer 2 Report

(1) In Introduction,  it is recommended to use a few sentences after the literature review to further summarize and summarize the current research issues.

(2) In the second part, the numerical simulation model has been provided in great detail. This is crucial and important. However, numerical simulation models typically do not consider all aspects and factors. This requires setting a series of assumptions during modeling. So, what assumptions are the construction of the model in the manuscript based on?

(3) In the manuscript, the model was solved using the Finite Volume Method (FVM), which is an excellent method. At the same time, the solution ideas and principles are also described in detail. However, numerical simulation models typically require validation of their applicability before use. Validation can be compared with the results of published papers or with experimental results. Therefore, it is recommended to conduct appropriate model validation at the end of the second part.

(4) For Figure 4, temperature distribution cloud maps at different times are provided. Moreover, the original text also stated that the four figures in A and B are the results of 30, 60, 90, and 120 days, respectively. However, in Figure 4, it is necessary to indicate the specific time so that it is not confusing. For other Figures, similar issues also need to be noted. Meanwhile, there is no substantial difference between the subgraphs in Figure 4 (especially for the last three time points). Does the author need to check for any issues? Alternatively, it can be changed to another form that better reflects the characteristics of temperature evolution.

(5) Some refernces needs to be cited for supporting the statement in lines 36-37. https://doi.org/10.1007/s11356-022-21233-7, https://doi.org/10.1007/s11356-022-19663-4, ttps://doi.org/10.1016/j.jpowsour.2021.230925

(6) For the manuscript, there are too many cloud images, and the data analysis is a bit lacking. Authors are requested to add some substantive data analysis as appropriate. For each result analysis and discussion, it is recommended to appropriately supplement the mechanisms and reasons. Such as section 3.2.4, It is best for authors to add some content (quantitative content is the best) to explain the mechanism of the impact of design parameters on geothermal development.

The language of the manuscript requires the authors to seek assistance from polishing agencies or native English speakers.

Author Response

Thank you for your letter and comments concerning our manuscript entitled “Medium Rock-soil Temperature Distribution Characteristics in Different Time Scales and New-type Well Layout Form in Application of Medium-deep Borehole Heat exchanger” (ID: energies-2608907). Those comments are all valuable and very helpful for revising and improving our manuscript, as well as the important guiding significance to our researches. We have tried our best to accommodate all comments and have made corrections/revisions which we hope meet with approval. The revised part was marked in yellow in the revised manuscript. Our point-to-point responses to the review comments are shown in file named "Response to reviewer 2".

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Thank you for making the amendments suggested. I think the work has been thoroughly improved and is a nice contribution to literature. Only one minor comment:

Line 110: 'which is obviously lower than the usual heating load, so their results are not generally  applicable' - this is a misleading comment as the study was for shallower depths (<1 km) than yours and is typical for low heat flow settings. So I would say is designed at lower depths than your study (hence the lower thermal power imposed)....

Author Response

We are very glad to receive your letter and comments concerning our manuscript entitled “Medium Rock-soil Temperature Distribution Characteristics in Different Time Scales and New-type Well Layout Form in Application of Medium-deep Borehole Heat exchanger” (ID: energies-2608907). We have tried our best to accommodate the comments and have made corrections/revisions.

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript can be accepted for publication now.

Author Response

Thank you for your letter and comments concerning our manuscript entitled “Medium Rock-soil Temperature Distribution Characteristics in Different Time Scales and New-type Well Layout Form in Application of Medium-deep Borehole Heat exchanger” (ID: energies-2608907). Those comments are all valuable and very helpful for revising and improving our manuscript, as well as the important guiding significance to our researches.

Author Response File: Author Response.docx