Parametric Study of the Ground-Air Heat Exchanger (GAHE): Effect of Burial Depth and Insulation Length

Round 1

Reviewer 1 Report

This paper presents a parametric study for a ground-to-air heat exchanger (GAHE), especially the effects of burial depth and insulation length. Generally, the research is interesting and with plenty of data. However, there are several issues needs to be corrected before the paper can be further considered for publication.

1. The introduction section is a little poor, what is the novelty of the present study as the model already built in the previous study.  

2. The citation of reference is not continuous. Page 2, Line 69 “Mostafaeipour et al. (2021)” ; Page 2, Line 74 and Line 82.

3.  The comparisons between experimental temperature and model results are shown in Figure 6, however, the deviation is a little large, please give the explanation.

4. The introduction of the model and detailed procedure should be given.  

5. The conclusion section is needed. The limitations of this study, suggested improvements and future direction of this work should be highlighted.

6. The format of the reference is not correct, please revise. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper investigates the heating and cooling potential of a ground heat exchanger for varying parameters, which is a sigificant and timely topic. However, I have doubts about the novelty of the modelling and results presented. In addition, the validation of the proposed model shows that the model is inappropriate due to large errors (up to 3.5 K). Also, some of the results do not confirm the known relationships: the longer the length of the ground heat exchanger, the better the efficiency. The source of such differences is not explained. I therefore recommend rejecting the work.

Major comments:

1. Abstract – not all result are presented, like insulation length, which is due to the title of the article quite important in this manuscript.

2. The literature review is insufficient. Line 68 – please briefly describe the results of each research presented in references 9 to 11. The same situation applies to lines 107-108 [21-23]. In particular, please present the determined relations for inlet air  temperature, air flow velocity, pipe diameter, soil properties etc. This is very important as it will determine the novelty of your paper.

3. Please emphasize the novelty of your work. From the references presented in section 1.1, I can see that the work repeats some research done previously (e.g. reference [12]).

4. Model validation - Tables 7 and 8. Although the relative error is generally less than 10% (sometimes reaching 13%), we can see that the difference between modelled and experimental temperatures is greater than 2-3.5K. This can be seen very well in Figure 6. Due to such a large discrepancy between experimental and numerical results, I have doubts whether the presented model can really be used for testing. For which Reynolds number was the validation performed?

5. Discussion is insufficient. The authors did not refer to results in other publications. Some of the parameters studied in this paper overlap with studies e.g. [9-11], [12]. It would therefore be necessary to compare the authors' results with the results in the cited publications.

6. Line 367 - shouldn't be "Reynolds number of 100" instead of "250"? Please explain why the results for these Reynolds number vary from values for other Re?

Minor comments:

7. Many sentences are too long. This makes it difficult to understand their meaning. Some of them can easily be divided into several sentences by simply putting a full stop. Some examples:

Abstract – 20-26

Lines 37-43

Lines 52-58

Lines 74-79

Lines 80-88

Lines 95-101

Lines 123-126

Lines 268-273

Lines 305-308

Lines 310-316

Lines 365-370

Lines 371-375

Lines 392-395

8. Table 6 – not “hora” but “Hour”

9. Table 13 - what do the values highlighted in brown and italics mean? Why are these values highlighted? Why are some values in bold? The description should be just below or in the Table, not just in the next section.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors responded in detail to the reviewer's comments. The abstract and the literature review were revised - the referenced publications were described in detail. In this way, the novelty of the article was clearly identified. This definitely increased the quality of the article. In addition, the authors explained the large value of the temperature error during validation. The paper was enriched by validation for further GAHE operating conditions (2 m depth), for which the error was more than 3%, which completely changed the presented results' perception.

In the discussion, the authors referred to the work of other researchers and clearly stated their contribution to the topic of the research work. Limitations of the model and the scope of future work were added.

Minor comments:

1.       Use of very complex sentences e.g. lines 405-416. One sentence has 12 lines, which makes it difficult to understand.  Other examples: lines 308-313, lines 452-456, lines 442-448. Authors should also correct the sentences in lines 436-441 in terms of punctuation.

In view of the changes made, I recommend the publication of the article.

Author Response

The authors are grateful for the comments, corrections and recommendations made by the editor and reviewers of the journal FLUIDS.

Part of the sentence on lines 405- 416 (now lines 407-413) was removed because the information was confusing and repetitive.

Lines 308-313 (now lines 310-315) was corrected. Also, lines 320-322 and the title of table 10 was modified.

Part of the sentence on lines 452- 456 (now lines 446-449) was removed because the information was confusing.

Two lines of the sentence on 442-448 was removed (now lines 438-442). 

The punctuation in lines 436-441 was corrected (now lines  432-437).