Towards Sustainable Heat Supply with Decentralized Multi-Energy Systems by Integration of Subsurface Seasonal Heat Storage

Round 1

Reviewer 1 Report

This work focuses on the optimization of the high temperature aquifer thermal energy storage (HT-ATES) system in a decentralized multi-energy system. Five models including a special heat pump-mode are defined and analyzed for different situation of the HT-ATES system. The heat delivery, the temperature changes during operation, and the system recovery efficiency of ten scenarios are calculated and compared. Then the suitable scenarios are selected and the reasons are discussed why the relationship between heat storage and efficiency is counterintuitive. The overall performance of HT-ATES and the impact to multi-energy system are analyzed. The workload of this work is sufficient. The analysis is comprehensive, and the results are well explained.

However, this manuscript need be improved before acceptation for publication.

1. Line 136. “We assume that the total thermal volume is stored and recovered from one hot and one warm well which do not interact.” How does this simplification affect the calculation of thermal and economic performance? Please give a qualitative or quantitative description.
2. Table 3. The judgment of "score for winter" is one-sided, which is only based on the average winter temperature. Is it needed to consider indicators such as freezing days and minimum temperature?
3. Line 585 and 587. What is the basis for the coefficients of 1.25 and 1.1?
4. Line 600. "Simulation results show that in all cases, 12-14%." Please take a certain month as an example to explain how this percentage is reflected in Figure 9.
5. Line 641. It is "figure 9" rather than "figure 10". Line 870. It is "Figure 8" rather than "Figure 9".
6. Line 644. "In all scenarios it is never more than 2% of the total electricity demand of the HT-ATES system." How is 2% reflected in Figure 9? The area occupied by the purple column in the picture is obviously greater than 2%.
7. Line 689. "65|42|2". It should be 43 instead of 42 here. Please check for such issues in the full text.
8. Figure 13. It is observed that the HT-ATES system efficiencies of 50|30|2, 50|30|1.5, 60|30|2, 65|43|1.5 are close to each other. Is there a quantitative relationship between "heat pump condenser temperature", "HT-ATES threshold temperature" and "heat pump size"? Consider adding some calculation examples for explanation.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This study deals with the connection between the HT-ATES and the heat pump of the MES and evaluates different concepts of integration, to optimize and improve the 69 use of HT-ATES within multi-energy systems. This paper can be accepted in Energies but some should be corrected after the major revision.

1. Please add the nomenclature, the parameters are not well-organized and italic formation is not united.
2. Please follow the reference format for Energies, you should not comment on the available online formats. Please see again the site: https://www.mdpi.com/authors/references
3. The fonts, size, and overall formats are not united. The authors must see Eq. (1.1) and (2.1), and (3.1) are all different.
4. English grammar should be corrected once again. A program such as GRAMMARLY can be used.
5. The literature survey is too poor and short compared to the lengthy results.
6. From Fig. 5 to 7. the mode of operation is too case-specific and looks like the project report for funding. The overall paper should be concise for the very important results within 10 to 15 pages. Or this paper should be divided into at least 2 papers changing the mode of operation. It's just the authors' choice, I just give an example. I just want to point out this is too hard to read due to the TMI.
7. Chapter 2 is too lengthy and has a series of redundant information in the paper, which may have been explained by 1-2 references.
8. There is no consideration of optimization with meta-heuristic optimization algorithms such as GA or PSO, thus the authors may be careful to use the word "optimization". Please use other words or perform the meta-heuristic optimization.
9. For all graphs have different resolutions (or too poor like figure 2, 8, 13) and font sizes and types.
10. It is so sorry that there is only one reference of "Energies"
11. Sometimes it has a space between the temperature unit and number but the others don't.
12. The reviewer cannot know easily what is the innovation of the study and what is the main objective of the study. Please emphasize in the introduction and conclusions for your observation and innovation to the scientific community for the HP system.
13. Please check once again for author contributions. The contributions and authors are all mixed.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

It can be published.

Reviewer 2 Report

Thank you for the revision. I would like to ask for more minor revision points.

• Nomenclature should include all variables or parameters used in the paper.
• For Table 5 and Table 7, the Scenarios for 65|43|2 to 50|30|1 should be explained one more time in tables. Nobody can understand the case selection.
• The variables or parameters such as COP and T should be italic.
• The Quality of Fig. 9 and Fig. 10 is still poor.

Author Response

Dear sir/madam,

Thank you for taking the time to have another look at our manuscript, which we highly appreciate. Hereby we provide you with our response to your comments. 

• Nomenclature should include all variables or parameters used in the paper.

We have now provided a nomenclature with all variables and parameters used in the paper. Line 1149. Besides, we have made some small changes in the formulas to make them more consistent with each other, or more clear. We have for example replaced ‘i’ with ‘t’ for timesteps and removed * 100% from the efficiency calculations as we present the efficiencies as fractions of 1 and not as a percentage. (line 217, 218, 261,262, 270, 274, 276, 540, 567, 587, 602)

• For Table 5 and Table 7, the Scenarios for 65|43|2 to 50|30|1 should be explained one more time in tables. Nobody can understand the case selection.

Thanks for pointing this out. We have added an extra sentence in the description of the tables explaining how the name code of the scenarios should be read:

‘The scenario name abbreviation consists of: condenser temperature|HT-ATES threshold temperature|heat pump size. ‘(line 789 and 902-903)

 

• The variables or parameters such as COP and T should be italic.

We have now placed all formulas and parameters in italic.

 

• The Quality of Fig. 9 and Fig. 10 is still poor.

We have looked again at the figures, both in the word document, in the pdf and as a single (.jpg) figure. The resolution of both figures is 1800 x 1500 pixels (width x height) with 300 dpi and on our screens has a good resolution in all different formats. Could the reviewer maybe explain what is poor about the quality of these figures? At the moment, it is hard for us to understand what we can improve.

We hope to have sufficiently answered your comments.

Yours sincerely,

Els van der Roest (on behalf of the authors)