Review Reports

Round 1

Reviewer 1 Report

The paper deals with a performance investigation of a coiled falling-film drain water heat recovery unit.

All aspects of the paper are perfectly acceptable.

No improving hint to give to authors.

Sincerely

the Reviewer

Author Response

Thank you for taking the time to review this manuscript. It is greatly appreciated.

Reviewer 2 Report

Research in the field of the waste heat recovery systems dedicated to domestic applications, such as heat exchangers for recovering of drain water enthalpy is nowadays very important. Thus, I found the content of this article up-to-date and interesting.

From editing the article is well prepared. The logical structure of the text is correct. Text is properly divided into sections and subsections. Abstract is correctly written and reflects the content of the article. Literature review is clear and references are properly provided in the text. Mathematical models are well described and modelling results are clearly presented in Figures and described in text.

From the scientific point of view revision is needed in terms of the experimental description. The authors are referring to their earlier works where they described the test stand, experiment and experimental results which were the input data to the model presented in present manuscript. In the opinion of the reviewer, in order to improve the scientific sound of present manuscript, it would be advisable to extend a bit the description of the test stand and obtained experimental results as this issue is important background to present works.

Author Response

Thank you for taking the time to review this manuscript. It is greatly appreciated. Your specific comments are addressed below:

“From the scientific point of view revision is needed in terms of the experimental description.”

We have added additional information about the test setup starting at page 3, along with a schematic of the system during operation.

Reviewer 3 Report

The submitted paper manuscript describes a theoretical analysis of a coiled falling-film drain water heat recovery system. The concept of the paper cannot be considered as innovative since there are other already published studies by the same research group on this subject. In addition, the modelling approach is very poor since it is based on simplified heat transfer relations rather on detailed numerical models. The model used in this paper cannot be considered sufficient for publication in a well-known international journal. The model is below standards. Also in the paper manuscript there are no theoretical results showing the performance of the system. There is only the validation, with only one figure. A paper cannot be published with only one or two figures with results. This is very poor and it is below standards. Authors kindly advised to substantially improve their numerical model and to substantially improve their results and discussion section showing more figures with theoretical results from their analysis and then to re-submit their manuscript for review.

Author Response

Thank you for taking the time to review this manuscript.

It is very difficult to respond to the comments submitted as they do not appear to be relevant to this paper. For example:

“The submitted paper manuscript describes a theoretical analysis of a coiled falling-film drain water heat recovery system.”

It is not a theoretical analysis. An experimental analysis was performed, and this was used to develop a semi-empirical model.

 “Authors kindly advised to substantially improve their numerical model and to substantially improve their results and discussion section showing more figures with theoretical results from their analysis and then to re-submit their manuscript for review.”

There is no numerical model to improve upon.

The remaining comments from the reviewer are more opinion than review, and contain no specific points that can be addressed. We feel it is better left for the editor to deal with these.

Reviewer 4 Report

The authors present a model to calculate the steady-state performance of drain water heat recovery systems. The methodology is well described and so are the results. Thus, I think that the paper could be further improved by strengthening the context and potential applications of this model. How this model can support DWHR design or operation? Could it help in understanding the annual savings that can be achieved? What does it add to the current practices in the field?

My recommendations are the following:

In the introduction, the authors seem to be strongly focused on Canada. Some further references to international figures and research papers may be appropriate, given the international scope of the journal. Furthermore, some additional literature review may strengthen the innovative contribution of the paper.

The results may be strengthened by a discussion on their potential effects and use of the model that has been presented. Which kind of applications are envisaged by the authors? Could this model support the estimation of annual energy savings? How? Which other benefits may arise in comparison with the current best practices?

Figure 4 seems to be quite interesting. Please discuss the advantages and limitations of each configuration, to help the readers in understanding which design choices are at the basis of each situation.

Figure 5: the values of the dashed lines are not clear (e.g. the horizontal one is at 6?). Please add numerical values or add a grid to the axes to help the reader in understanding the real values.

Author Response

Thank you for taking the time to review this manuscript. It is greatly appreciated. Your specific comments are addressed below:

“The authors present a model to calculate the steady-state performance of drain water heat recovery systems. The methodology is well described and so are the results. Thus, I think that the paper could be further improved by strengthening the context and potential applications of this model. How this model can support DWHR design or operation? Could it help in understanding the annual savings that can be achieved? What does it add to the current practices in the field?”

The model does not really support the design of DWHR system. It is meant to assist in estimating annual energy savings for these heat exchangers installed in residential buildings. We have added additional discussion about the model’s application and its importance in the Discussion section on page 11.

 

“In the introduction, the authors seem to be strongly focused on Canada. Some further references to international figures and research papers may be appropriate, given the international scope of the journal. Furthermore, some additional literature review may strengthen the innovative contribution of the paper.”

Thank you. We have added additional statistics to the introduction section to expand the scope of the paper.

 

“The results may be strengthened by a discussion on their potential effects and use of the model that has been presented. Which kind of applications are envisaged by the authors? Could this model support the estimation of annual energy savings? How? Which other benefits may arise in comparison with the current best practices?”

We have added additional information to the discussion section on page 11 to clarify these points.

 

“Figure 4 seems to be quite interesting. Please discuss the advantages and limitations of each configuration, to help the readers in understanding which design choices are at the basis of each situation.”

The advantages and limitations for these configurations has not been adequately studied by the authors. Our intent was only to show that it is possible to have various different plumbing configuration, and the model has to be able to account for these variations. This has been addressed through the unequal-flow correction that’s been incorporated into the model.

 

“Figure 5: the values of the dashed lines are not clear (e.g. the horizontal one is at 6?). Please add numerical values or add a grid to the axes to help the reader in understanding the real values.”

A grid has been added with tick marks to clearly highlight the real values. 

Reviewer 5 Report

This is an excellent paper, that fits very well with the scope of Resources journal.

Introduction to the topic is informative and relevant references are cited.

Methodology is clear and specific as one would like to see in an engineering report. Limitations/focus of the study is explained.

Results show nearly perfect agreement between the model and experimental data. Discussion is appropriate. I'd like to see main findings highlighted int he conclusions.

I think the paper would benefit from more details about the experimental work, maybe some images, etc.

Overall, a really interesting study!

 

Author Response

Thank you for taking the time to review this manuscript. It is greatly appreciated. Your specific comments are addressed below:

“I think the paper would benefit from more details about the experimental work, maybe some images, etc.”

In response to your comments, we have added additional information about the test setup starting at page 3, along with a schematic of the system during operation.

Round 2

Reviewer 2 Report

The authors improved the manuscript according to the comments.

Reviewer 4 Report

The authors have properly addressed all my remarks. The paper can be accepted in its present form.