Study on the Natural Ventilation Characteristics of a Solar Greenhouse in a High-Altitude Area
Round 1
Reviewer 1 Report
The manuscript is written in a good English. Is quite well organized, but I recommend review of same items.
In my opinion, before the publication the author must clarify some issues as follows:
1) I encourage the authors to rewrite the abstract. Describes the problem before present some results.
2) Section 3.1: I couldn’t understand why the conditions exposed in table 3. What is the origin of the values ? and what is the purpose ? Please clarify.
3) Also in section 3.1., In Figure 7, the author don’t informed about the properties of plane located at x=600m. Only much further in the text we deduce that this plane refers to a non-crop area. This should be described before.
4) Also related to Figure 7, describe the locations of inlet and outlet air, or surfaces. In Figures 7, 8, 9 and others there is an error in legend. (x=600mm, not a= ..).
5) In legend of Figure 7 and 8, is written “Wind pressure”. I believe that author wanted to say “indoor pressure”. Because the plane is inside the domain.
6) Details of Figure 9 must be clarified. What is the position of the abscissa axis ? What is the coordinate ? refers to the y direction ? crop section ?
7) Only much further in the text (in line 401) it is clarified that “plain areas” - location at sea level (Beijing). In my opinion this information should be described earlier, to localize the reader.
8) Correct the legend of Figures 10, 13, 14 and 15.
9) Is not clear what is the objective of presenting some results. Several CFD results were already expected. It is known that air density, as well as pressure, decreases with altitude. What is the relevant information in figure 10?
10) I can’t see in Figure 15 the results referred in the text (line 319 to 321). Please clarify.
11) Please, clarify the values of DT in table 6. Most of the calculated results presents in Table 6 make sense. However, I can´t understand the DT results. In natural convection situation, that is the case, the ventilation rate is promoted by buoyancy forces originated by air (density) temperature difference. In Table 6, higher ventilation rates correspond to lower temperature difference !
12) I encourage the authors to rewrite (synthetize) the conclusion section. The main conclusions must be highlighted.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this study, the natural ventilation of a greenhouse in high-altitude regions was investigated using CFD simulation and on-site measurements. The topic is very interesting and worth studying. However, the setups for CFD simulation and experiment were not well described. Many computational and experimental parameters are not clear. In addition, there are many spelling or grammatical errors in the text. Without careful verification and validation, the findings based on the CFD simulation results are not reliable. The reviewer doesn’t think it is appropriate to be published in the current status. Therefore, I recommended the authors rewrite the manuscript carefully and resubmit it. My main concerns are:
1. There are many grammatical errors. The English language needs to be improved.
2. The focus of this study is the natural ventilation of a greenhouse. However, the configuration of ventilation was not described for the experimental facility. For example, what is the size of the vent openings? And their locations?
3. Section 1. A great number of studies can be found in the literature on the CFD simulation of natural ventilation in greenhouses. The authors just listed some past studies. What are their relationships to this study? Is there any study related to the research on high-altitude greenhouses?
4. From figure 1, it seems different crops were cultivated in the greenhouse. However, fixed values were used for the computational parameters of crops, e.g., LAI. Was it appropriate?
5. The meteorological data are critical and should be introduced for the experiments.
6. Standard wall functions were used in the CFD simulation. What were the y plus values?
7. Figure 3 and many other figures. The text in the figure is not easy to read.
8. Equation 7, Mach number. Instead of Mach number, Archimedes number, which implies the strength of buoyancy, is more important in the modeling of indoor airflow.
9. Table 2. Detailed explanations need to be added to the selection of key computational parameters. Were they from the field measurements? Why were these values used?
10. Table 2. I thought the authors modeled the radiative heat transfer in your simulation. But if the fixed air temperatures were applied at the boundaries, it would not reproduce the reality.
11. From eqs. (5) and (6), for different conditions of air velocity and air temperature, the ra and rs should be different. Why were fixed values used in the simulation, as shown in Table 2? It is well known that the air distributions in a greenhouse are not uniform. Therefore, these values vary in space and time.
12. Figure 4. The grid is not clear to read. From figure 4b, it seems an unstructured grid was used.
13. Figure 5. Only simulation results of air temperature are shown. What is the influence of the grid resolution on air velocity?
14. Table 3. Why were these values selected?
15. Figure 13. Why are the air temperatures on the boundaries of the crops much higher than the ambient air? In addition, the title is not consistent with the figures.
16. The verification and validation should be first described.
17. What are the boundary conditions for the validation study?
18. Figure 16. Calculate value? Calculate is a verb.
19. Figure 16, validation study. Why are only five positions compared?
20. Table 5. It would be good to subtract a reference value for the air pressure to make it easier for readers.
21. The symbol for Celsius degree is not English.
…..
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The reviewer appreciates the authors’ careful modifications to their article. Most of my questions are answered. Before publication, I still have the following suggestions for further improvements:
1. Response to my comment 4. The photo was not changed. If that was the case, please add your explanation of LAI to the article.
2. Response to my comment 7. Unfortunately, the figure is still not easy to read.
3. Excellent explanations to my comment 9. The responses from the authors are very important for the readers to understand your study. Please also add them to your article. For example, how you define the reference temperature and inlet velocity and calculate the crop evapotranspiration.
4. Response to my comment 10. Please also add your response to the article.
5. Response to my comment 12. Good to use the enlarged figure to show the structured grid. Please also add the enlarged figure to the article.
6. Line 213. Strictly speaking, Equation 3 is called Darcy-Forchheimer law. Darcy's law only accounts for the viscous term of the pressure drop, which is very small at low air speeds. For indoor farming, the inertia term is more important.
7. Equation 3. Symbol C was used but its meaning was not indicated. Was it the same as Cu?
8. Please provides the references for equations 5 and 6.
9. Solver settings, e.g., discretization scheme, were not mentioned. In addition, what were the convergence criteria for the simulations?
10. Line 258. It is difficult to understand this sentence. Please rewrite it. Porous media and internal heat source models provide treatment?
11. Table 2. Where did the author use/set the air temperature (29.55 °C)? If it was not used, it would be good to remove it from the table.
12. Table 2 was used to describe the computational parameters and boundary conditions rather than the simulation results. Did the authors set the outlet temperature? If not, please remove it from the table. This comment also applies to other parameters in Table 2.
13. Table 2. Crop canopy pressure drop coefficient (C0) was not defined before. Was it the same as Cu in Equation 3. Then, please keep them consistent. In addition, please provide the reference for the choice of a value of 0.395 for C0. From the literature, usually, a value of 0.32 was used for tomato canopies based on the wind tunnel experiments.
14. Line 276. It should be: “the number of grid cells exceeds…” rather than “the number of grids exceeds 2.39 million”. Only six grids were used for grid sensitivity analysis, not millions.
15. Table 4. Was the velocity used for the inlet? Then, it would be clearer to indicate it as the inlet velocity.
16. It is not unclear where the reference temperature and reference pressure were used.
17. Equation 10. Please indicate the meaning of y.
18. References. Most journal names are missing.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
