Differentiated Control of Large Spatial Environments: Air Curtain Grid System

Round 1

Reviewer 1 Report

Review of air curtain grid system.

The use of air curtains to separate occupied and on occupied zones has the potential to improve energy efficiency when solid partitions are not feasible. This paper potentially can contribute to the proper design of an air curtain combined with the conditioned air supply.

 

However, the paper as written, omits some pertinent information and is confusing to follow. 

The English needs improvements.

 

p.5: Since the pressure varies throughout the flow field it is unclear what pressures are used in equation 1. The justification for the simplified form of the correction factor given an equation 3 is unclear

 

p.7: It is unclear where the air curtain inlet is located. The geometry of the non-occupied zone is not given nor is the thermal conditions in the non-occupied zone stated.

 

p.8: it is stated that the return vent has the same mass flow as the supply to ensure mass conservation yet further into the paper the mass flow across the air curtain is calculated. With a constant pressure boundary condition for the non-occupied zone, it is probable that there will be net mass flow across that boundary and therefore a net mass flow between the occupied and non-occupied zone. Furthermore, the return temperature is set to “ensure energy conservation” yet there is energy exchange between the occupied and non-occupied zones.

 

p.10: On Figure 4 it is unclear where the boundary of the occupied zone exists. The number of grid points modeling the width of the air curtain is not given

 

p.12: On figure 5 both locations 4 and 7 show very poor agreement between experiment and simulation. Both points represent the furthest extreme of the diffuser jet and should have an important impact and the overall accuracy of the simulation

 

p.16; It is unclear where are the mid portion and separation positions mentioned in table 5.

 

 

 

Author Response

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Reviewer 2 Report

A very well written paper on the us of air curtain in large buildings.

Major concern - no limitation section - this is a modelling study, so there are lot of assumptions, simplification etc compared to real-life situations. The authors should introduce a short subsection after results and before conclusion where the limitation of the study are considered. Some of them are already mention at end of conclusions but should be moved to the new limitaiton section and expanded accordingly. This is a very important part to honestly discuss the major limitations of your approach.

Otherwise only minor issues:

- The objectives and aims in the last part of the introduction should be stated more clearly - please specify the supply airflow conditions (velocity, angle..) in the last paragraph of the introduction part. Also please define what you refer as "design points" in the same paragraph (lines 93-98). 

- Please note that the grid sensitivy part is verification, so the name of the section 3.1. is misleading - it should be validation. Also, please arrange Figure 5 so it fits the manuscript format as currrent does not. 

- Page 10 and 11 - air curtain efficiency and air curtain cop should be subsections 2.4.1. and 2.4.2. 

- Please elaborate the use of k-epsilon model in section 2.3. The authors only stated two references (10) and (35). They should elaborate why k-epsilon is preferred to the rest as they did not compare to other turbulence models in this study.

- It would be also good to mention in the introduction part that the air curtain has shown improvements in reducing the overall exposure to contaminants and infection risk compared to traditional ventilation systems such as mixing ventilation systems by refering to following articles:

Amar Aganovic, Guangyu Cao, Jarek Kurnitski, Arsen Melikov, Pawel Wargocki Zonal modeling of air distribution impact on the long-range airborne transmission risk of SARS-CoV-2 Appl. Math. Model. (2022), 10.1016/j.apm.2022.08.027 - please see figure 14 https://www.sciencedirect.com/science/article/pii/S0307904X22004176 

A. Aganovic, G. Cao Evaluation of airborne contaminant exposure in a single-bed isolation ward equipped with a protected occupied zone ventilation system Indoor Built Environ., 28 (8) (2019), pp. 1092-1103 - please see table  3  https://journals.sagepub.com/doi/full/10.1177/1420326X18823048 

   

Author Response

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Reviewer 3 Report

This paper is a need of recent days and contains enough practical worth as a full article. It may be considered for publication after incorporating the following suggestions.

1. Is there any novelty in mathematical modelling or adopted from the relevant literature. Kindly mention clearly along most equations.

2. Figure are out of paper margins.

3. Conclusion needs to be revised. Kindly remove bullet points. Only conclude on what main conclusions have been obtained from the results and discussion. Conclusion should not repeat all the knowledge explained earlier. However, it should be based only on that knowledge.

4. Kindly a comprehensive paragraph at the end of "Results and discussion" in which general discussion should e added for managers and industry only based on results. This information should provide general guidelines to the managers in "Air curtain" companies only based on the significant results.

Author Response

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Reviewer 4 Report

Review of sustainability-2256350

: "Differentiated control of large spatial environments: air curtain grid
system" by Authors: Linye Song, Kaijun Li, Xinghui Zhang *, Jing Hua, Cong Zhang

 

Recommendation: Minor Revision

Comments to the Author

The manuscript presents a new approach to a study of air conditioning partition control of large public buildings based on a computational fluid dynamics model with various diffuser air supplies. In addition, independent control of each subzone temperature saves energy consumption, and the ACGS system can produce a thermal isolation zone in open space. So this paper can significantly contribute to the CFD models for ceiling diffusers for airflow distribution studies. The discussion is well-structured, with findings emphasized, but some parts could be clarified and better justified. The well-written manuscript provides new insights into isolation effects using various diffuser angles and air velocities. I recommend it for publication in sustainability. However, minor comments about optimizing diffuser angle and air velocity should be addressed before accepting this manuscript.

I recommend the publication of this manuscript after minor revisions in light of the comments below.

Major comments:

This paper has discussed only cooling conditions,  is the CFD model results change in case of heating conditions? Is there possible to represent velocity and temperature profiles together in one figure? Is it possible to do a simulation with a continuous value of the diffuser (small increments) and air velocity?

Minor comments

[L-219] uncertainty or error between two grids?

[L-245] air temperature or temperature field? Because two-dimensional

[L-287] After the pre-simulation, why was the air velocity 2.9 m/s and temperature 16^oC set? Any explanation?

[L-308] width and height are missing in the axes of the figure

[L315-318] air velocity is 1m/s and 2m/s, and the temperature inhomogeneity is significant, caused by the cold jet directly into the working space. At the same time, the air curtain velocity of 2m/s can make the overall temperature level of the zone reach the set temperature of  26 °C, representing the optimal cooling effect in the scenarios described in this paper. The temperature inhomogeneity is large at 1 m/s and 2 m/s, and at 2 m/s temperature reaches 26 °C. A diffuser 60 plays a role in setting optimal cooling or large temperature inhomogeneity. Please clarify.

 

Fig.5a y-axis is not visible.

Fig. 5a – location 4 also looks less agreement between your simulation and experiments by Lo et al. Is the explanation the same as location 7?

Fig. 6, please add width and height in the axis of the figure.

Fig.10, please use the same significant digits and please check throughout.

Please check the unit style. Ex: m/s or ms^-1. It should be consistent throughout the paper

Author Response

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Round 2

Reviewer 1 Report

Is fig 4a labeled side view , is this an elevation section? Why do the air curtain nodes run vertically?

Author Response

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