Optimization Analysis of Natural Ventilation in University Laboratories Based on CFD Simulation

Round 1

Reviewer 1 Report

After reading the manuscript, I felt that the authors seem to be new to writing CFD-based manuscripts. 

1. One of the basic detail of contour plots are legend which is missing in all the figures so I am not able to understand what is presented. 

2. Is CFD model steady state or transient? 

3. How is air age computed?

4. Discussion on 1-eq and 2-eq turbulence models can be removed as these are very well-known facts. 

I would like further comments when the authors revise the manuscript so that I can read the contours well. 

The language of the manuscript is readable, but in certain places necessary details about CFD modeling are given which can be removed.   

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

1.      Reference citation style should be consistent. Currently, some are First Name - Surname, some are Surname - First Name etc.

2.      Many other issues such as ‘Inlet of velocity’.

3.      The introduction needs to be improved. The literature review included many different studies, however their relations to the current study are not clear. I cannot see how ref. 1~29 helped to conclude that ‘According to the previous literature review, it is necessary to carry out more studies on improving the natural ventilation capacity of university laboratories, especially to use systematic statistical and analytical techniques … ’. paragraphs 4&5 are advanced numerical techniques which this paper did not use at all, why mention those? Authors should rewrite the introduction and replace irrelevant literature citations.

4.      Grammar needs to be checked throughout. Some sentences are not complete. e.g. ‘Evaluate public toilet ventilation design options through digital twining to determine the most effective options for reducing indoor pollutant concentrations.’

 5.      ‘we field tested that the wind speed in the room is usually between 0.8 m/s and 1.0 m/s,’ how? Where were they tested? The height of testing locations? Number of probes?

6.      ‘it is found that the wind direction in Chengdu is always north wind and north-northeast wind.’ Supporting reference? ‘always’ is not precise. And is the direction still the same at the speed test locations? Same problems at ‘Since the wind direction in Chengdu is always north,’

7.      ‘has a small error between the simulated and measured values, with a relative error range of 0.25% to 30.8% when’ please double check if 30.8% is the correct number to be mentioned as a ‘small error’.

 8.      I assume meshing at the door and the window are locally refined, but why the term is ‘locally encrypted’, what does that mean?

 9.      Results of the mesh independence should be provided. At least what sizes were compared should be detailed.

10.   2.4.1 and 2.4.2 should be removed. The entire section of numerical methodology – authors should just keep the most essential theory and remove the explanations that are about general CFD theories which can be easily found in current references.

11.   Since there is no validation of the current model using standard k-epsilon model for such a case, authors should provide more literature to support why the standard k-epsilon model is chosen.

12.   Table 3 should include units

13.   Does section 1.25m 1.7m etc mean the heights? Then using the word height than section is better.

14.   All the CFD visualizations – contour legends should be added.

15.   Plots – the quality of images seem bad, cannot read the text easily. Clarity of figure 12-14 should be improved.

16.   The conclusion should be improved by removing the general introductory part and focus more on what contribution this study has made towards the evaluation of NV in labs compared to many other studies on NV.

see above.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors presented a numerical study to investigate the Natural Ventilation in University Laboratories.

The novelty of the paper is to be clearly stated.

What is the used CFD software?

The used turbulence model is to be justified.

A figure presenting the studied configuration with dimensions and boundary conditions is to be presented.

A figure presenting the whole 3D mesh is to be presented.

The boundary conditions are to be expressed mathematically.

A Grid sensitivity test is to be performed.

Based on the presented grid, it is not clear that there is not a mesh refinement close to the walls. To be justified, since in such configurations the boundary layer effects are very important.

What is convergence criterion?

What is the used time step?

What is the range of Reynolds number corresponding to the considered cases?

Is it realistic to consider the natural ventilation, without solving the energy equation? If the initial temperature and inlet temperature are the same what is the interest of the ventilation? Is it realistic to consider constant temperature boundary condition at the walls? Normally it should be a heat flux BC.

How is the air age evaluated?

The 3D flow structure (streamlines) is to be presented.

For the validation of the numerical model, it is not sufficient to mention that you compared your results with the infield measurement. The comparison is to be presented graphically. In addition, a qualitative (velocity field or flow structure) verification is to be performed by comparing with previously published numerical results.

 Is it realistic to consider unidirectional and time independent velocity at the inlet. Practically the wind changes direction and magnitude. To be justified.

English level needs to be improved.

Line 13 is to be checked.

Avoid the use of very long sentences.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

This paper concerns the optimization Analysis of Natural Ventilation. The topic is relevant to this journal. My main concerns are the novelty and scientific basis of the study. The questions and comments are given below:

Abstract: I do not think the influence of airflow structure on human comfort has not yet been investigated. The author should check the literature and clearly state what this paper builds upon earlier findings and achievements, e.g.:

https://doi.org/10.1016/j.buildenv.2019.03.019

https://doi.org/10.1016/j.esd.2016.09.005

Figure 1: I suggest not using a gradient blue color as the background.

The author claims that the grid irrelevance check has been done. In this sense, it is better to show the detail of the grids in figures.

A careful validation of the CFD approach, including the validation of the turbulence model, is missing. I suggest that authors check the literature on success use of k-ε model in the built environment and justify the choice of the turbulence model: e.g.:

https://doi.org/10.1016/j.buildenv.2016.12.019

https://doi.org/10.1016/j.scs.2021.103307

Conclusion: “average height of the face”, I suggest to rephrase to “average breathing height”.

Moderate editing of English language is needed.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has improved a lot, and it can be accepted in its present form if the authors answer how the air age is computed. It is essential to state the mathematical formulation. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

although authors revised many places that wrongly used the term 'encrypt', they added more new statements using 'encrypt'. This must be corrected before publishing because I believe this is a wrongful translation. 'encrypt' means adding a password, but I assume the authors want to say 'refine the mesh'. 

as above

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Most of the responses are not convincing.

The authors considered turbulent flow while the values of Re are low.

The authors applied a constant flux boundary condition, without solving the energy equation. To hide this issue, the authors removed the governing equations in the revised version. In addition, the authors fixed the inlet temperature at 21oC and magically supposed that the outlet is at 22oC. The outlet temperature should be issued from the resolution of the energy equation.

The authors have not presented the 3D mesh, (what do you mean by software reasons). If a 3D configuration is studied the software generate 3D mesh, this is obvious.

The boundary conditions have not been expressed mathematically.

The expression used to evaluate the air age is not presented. It is not sufficient to mention that the software is used to evaluate it.

The authors considered a 3D configuration without presenting any 3D result; at least the 3D flow structure should be presented; the added figure corresponds to the vector field in a fixed y-plan.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

The authors have implemented many of the comments. However, a few major comments have remained unanswered:

The novelty of the study:

“the optimization of natural ventilation with human comfort is not usually studied.” This is not true, the authors should check the literature and demonstrate novelty.

The author claims that the grid irrelevance check has been done. I suggest showing the detail of the grids in figures.

Figs.6-9: I suggest using integers or fewer decimal values in the color bar legend.

The English language should be improved, e.g., the first sentence in the abstract should be: "In recent years, there has been a significant surge in the adoption of natural ventilation for building indoor spaces, garnering widespread attention.."

The caption of Figure 3 should be "Boundary conditions"

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

-

Author Response

Thank you for your previous guidance. But we haven't seen any comments this time.