Estimation of In Situ Heat Capacity and Thermal Diffusivity from Undisturbed Ground Temperature Profile Measured in Ground Heat Exchangers
Round 1
Reviewer 1 Report
The manuscript is interesting and well written and discussed. It shows an innovative approach that could be useful to GSHP designers and TRT executers. Just some comments for the authors.
The Introduction needs to be improved: it is missing two important issues:
- Important literature works demonstrate the most valid approach to quickly identify the TC and undisturbed temperature grund; this is provided by the numerical modeling. Please read and implement these manuscripts where a new approach is validated and discussed.
- Matteo Antelmi, Luca Alberti, Adriana Angelotti, Sara Curnis, Andrea Zille, Loris Colombo, Thermal and hydrogeological aquifers characterization by coupling depth-resolved thermal response test with moving line source analysis, Energy Conversion and Management 225 (2020) 113400, https://doi.org/10.1016/j.enconman.2020.11340
- Naldi C, Zanchini E. Full-time-scale fluid-to-ground thermal response of a borefield with uniform fluid temperature. Energies 2019;12. https://doi.org/10.3390/
- The hydrogeological and physical characteristics influence the measurement of TC, HC, etc. The presence of a groundwater flow and consequently saturated samples could give a parameters measurement that is affected by error. Please read and implement:
- Hecht-M´endez J, de Paly M, Beck M, Bayer P. Optimization of energy extraction for vertical closed-loop geothermal systems considering groundwater flow. Energy Convers Manag 2013;66:1–10. https://doi.org/10.1016/j.enconman.2012.09.019
- Matteo Antelmi, Luca Alberti, Sara Barbieri, Sorab Panday, Simulation of thermal perturbation in groundwater caused by Borehole Heat Exchangers using an adapted CLN package of MODFLOW-USG, Journal of Hydrology 596 (2021) 126106, https://doi.org/10.1016/j.jhydrol.2021.126106, 2021.
- Luca Alberti, Adriana Angelotti, Matteo Antelmi, Ivana La Licata, Borehole Heat Exchangers in aquifers: simulation of the grout material impact, X Convegno dei Giovani Ricercatori di Geologia Applicata 2016, Università di Bologna, 18, 2016, pubblicato su Rendiconti Online Società Geologica Italiana, Vol. 41 (2016), pp. 268-271, doi: 10.3301/ROL.2016.145, 2016
Figure 2. The quality of the image is low.
Line 276. An image showing the different estimated Tugt would be suggested to improve the comprehension.
Figure 5. The differences between lithologies is not clear in the image (may be helpful to differentiate colours or simbols).
Line 349. Please quantify the thermal gradient of this profile.Is it correct to expect this gradient by comparing the literature?
Conclusion section. I suggest implement the numerical results provided above, for instance supporting the line 444-446.I suggest to better clarify the innovation of this approach and the real advatanges in terms of time and cost saving related to traditional approaches.
Author Response
Comments and Suggestions for Authors
The manuscript is interesting and well written and discussed. It shows an innovative approach that could be useful to GSHP designers and TRT executers. Just some comments for the authors.
Comment 1
The Introduction needs to be improved: it is missing two important issues:
- Important literature works demonstrate the most valid approach to quickly identify the TC and undisturbed temperature ground; this is provided by the numerical modeling. Please read and implement these manuscripts where a new approach is validated and discussed.
- Matteo Antelmi, Luca Alberti, Adriana Angelotti, Sara Curnis, Andrea Zille, Loris Colombo, Thermal and hydrogeological aquifers characterization by coupling depth-resolved thermal response test with moving line source analysis, Energy Conversion and Management 225 (2020) 113400, https://doi.org/10.1016/j.enconman.2020.11340
- Naldi C, Zanchini E. Full-time-scale fluid-to-ground thermal response of a borefield with uniform fluid temperature. Energies 2019;12. https://doi.org/10.3390/
- The hydrogeological and physical characteristics influence the measurement of TC, HC, etc. The presence of a groundwater flow and consequently saturated samples could give a parameters measurement that is affected by error. Please read and implement:
- Hecht-M´endez J, de Paly M, Beck M, Bayer P. Optimization of energy extraction for vertical closed-loop geothermal systems considering groundwater flow. Energy Convers Manag 2013;66:1–10. https://doi.org/10.1016/j.enconman.2012.09.019
- Matteo Antelmi, Luca Alberti, Sara Barbieri, Sorab Panday, Simulation of thermal perturbation in groundwater caused by Borehole Heat Exchangers using an adapted CLN package of MODFLOW-USG, Journal of Hydrology 596 (2021) 126106, https://doi.org/10.1016/j.jhydrol.2021.126106, 2021.
- Luca Alberti, Adriana Angelotti, Matteo Antelmi, Ivana La Licata, Borehole Heat Exchangers in aquifers: simulation of the grout material impact, X Convegno dei Giovani Ricercatori di Geologia Applicata 2016, Università di Bologna, 18, 2016, pubblicato su Rendiconti Online Società Geologica Italiana, Vol. 41 (2016), pp. 268-271, doi: 10.3301/ROL.2016.145, 2016
Response 1: Accepted and added
We agree that laboratory measurements and numerical modeling can be used to assess UTG (Xing, 2014 ⦋28⦌) and thermal properties, as well as helping for error analysis (Raymond ⦋18⦌; Giordano et al., 2021⦋11⦌). However, the paper aims to focus on field measurements to evaluate HC. We read all of the above references and though the following are relevant and can be added to the text (Antelmi et al.2020; Antelmi et al.2021). The following modifications were made:
- Lines 28 to 40 and 526 to 529 were rewritten to incorporate some references.
- References were cited and added to the reference list ⦋3,54⦌.
Comment 2
Figure 2. The quality of the image is low.
Response 2: Accepted and corrected.
A new layout is done with change, for example name of temperature profile based on thermal season
Comment 3
Line 276. An image showing the different estimated Tugt would be suggested to improve the comprehension.
Response 3: Accepted (see the new Figure 5 at Lines 304 to 308).
Comment 4
Figure 5. The differences between lithologies are not clear in the image (may be helpful to differentiate colours or symbols).
Response 4: Accepted.
Figure 5 has been redrawn with new color symbols and comment (see the new Figure 6 and lines 319 -321
Comment 5
Line 349. Please quantify the thermal gradient of this profile. Is it correct to expect this gradient by comparing the literature?
Response 5: Accepted and change made.
The geothermal gradient is about 12.00°C/Km, which is now described in the text (see line 374) based on the previously works ⦋10,18,19, 46⦌. Figure 7 has been added to better describe the geothermal gradient (see lines to 368 and 374).
Comment 6
Conclusion section. I suggest implement the numerical results provided above, for instance supporting the line 444-446.I suggest to better clarify the innovation of this approach and the real advantages in terms of time and cost saving related to traditional approaches.
Response 6: Explanation given.
We believe such numerical analysis can help refine our estimation of TC, but by a small margin of error, such that it will not significantly change our estimation of HC and the conclusions of this work. The goal of the paper is to provide new method to evaluate HC and the proposed heat tracing approach is satisfactory. There is sufficient work in the literature about TC estimation during TRT with numerical approaches and we feel is not necessarily need to repeat previous literature about TC assessment.
We believe novelty of this work relies on time and cost advantages when evaluating HC in the scope of geothermal heat pump project.
The first evidence of the time saving, and consequently cost reduction, is that only a single ground temperature profile is needed to assess UTG, TD and HC. No temperature profile trend collected through time is needed.
Other field advantages are that there is no need for a 2nd observation well to assess TD and HC as there is for the dual probe method. The analysis procedure is also quick. In comparison with numerical modeling, there is no need to define boundary conditions as well as evaluating mesh and time step independence. The calculation is done in a short time compared to simulations made with numerical modeling. Compared to OTRT, the field implementation and analysis are simpler. The discussion has been globally improved to better highlight those facts.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
please see attached file
Comments for author File: Comments.pdf
Author Response
Comments and Suggestions for Authors
Reviewer: I recommend the manuscript for publications after these major revisions. The paper is generally well written and structured. However, in my opinion the paper has some shortcomings in regard to some data analyses and text. Below I have provided numerous remarks on the text as it is often vague and long-winded.
Comment No. 1
The originality of the paper needs to be further clarified in the Abstract. Please, involve the novelty of this paper not what you have done in this study.
Response 1: Accepted and change made.
The abstract has been rewritten to better highlight novelty.
Comment No. 2:
Figure 4 is unclear and should be improved with using more clear drawing lines.
Response 2: Accepted. Figure 4 has been redrawn with clearer and new color.
Comment No. 3
Reorganize the sections of the paper to include more subsections that the reader will find more interesting.
Response 3: Accepted and changed
Subsections have been added in the section 3.2 to improve the structure of the paper (see Lines 400 to 409).
Comment No. 4:
Overall, looking at the results, the discussion context requires to be more explanations and comparisons supported by relevant references.
Response 3: Accepted and change made.
The context of this project was presented in introduction highlighting that little field method exist for in situ HC assessment in the scope of geothermal system design.
This new heating tracing method provides and alternative for in situ assessment of TD and HC.
Giordano et al ([11] and references therein) have applied in the field two other methods (OTRT and field dual probe) but the uncertainty and the complexity of the OTRT and the cost related to the observation well for the dual probe remind the limitations.
Changes have been made to the discussion to better highlight the context and novelty of the study.
Comment No. 5:
Some of the sentences in the paper are unclear.
Response 5: Accepted and change made.
English language has been improved with several spelling and grammar modifications throughout the text.
Comment No. 6:
The manuscript's English language should be improved by the authors.
Response 6: Accepted and change made.
English language has been improved. We asked a native English speaker to review the text.
Comment No. 7:
You should validate your result with previous published paper.
Response7: Accepted and explanation provided.
Our work was validated with comparison of Giordano et al. ([11] and references therein) that used different field methods to assess TD and HC in the scope of TRT.
Our work was also built with consideration on the works of other authors where a theoretical conceptual model was made and applied in the field ⦋20-33⦌. But several methods were applied on shadow temperature profile which is not necessarily extending on TRT analysis or vertical BHE design.
Comment No. 8:
Some parameter in text is missing. You should improve it.
Response8: Accepted and change made.
The text has been improved and reviewed by a native English speaker.
Comment No. 9:
Equations 1 to 7 require a valid reference.
Response 9a: Explanation gives.
Equations 1 to 5 are the novel equations proposed to be used for in-situ TD and HC assessment. These equations were newly defined by the first author in the scope of this study.
Equations 6 and 7 are used in several papers dealing with heat transfer issue, which are referenced in this paper (⦋20 -33⦌ and references therein).
Comment No. 9b:
The literature review is not comprehensive given the issue and effects considered. Therefore, the following related references should be added.
Response 9b: Explanation gives.
The proposed heat tracing method focus on the field measurement of UGT, TD and HC in the scope of a TRT. Recently Giordano et al. ([11] and references therein) did previous literature review on this topic. Thus, we feel is not necessarily need to repeat it.
The reference (Javidan et al., 2022) has been cited in the text as suggested by the reviewer and now appears in the reference list as ⦋13⦌.
Author Response File: Author Response.pdf
