Zero-Energy Purification of Ambient Particulate Matter Using a Novel Double-Skin Façade System Integrated with Porous Materials

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Which porous materials have been used in this research, polyurethane sponges or ceramic foam material?

The image of porous materials in Fig. 3c corresponds to polyurethane sponges or ceramic foam material?

 

The purification efficiency would be a little bit too low.

The Conclusions are too lengthy.

Comments on the Quality of English Language

moderate

Author Response

Dear reviewer:

We greatly appreciate the constructive and helpful comments you took the time to provide. Every suggestion for modification and comment you make is carefully incorporated and considered. Below are our responses to the reviewers' comments, point by point, and the revisions are indicated accordingly.

1. Which porous materials have been used in this research, polyurethane sponges or ceramic foam material?

Reply:

Thanks. In this study, we analyzed using ceramic foam material as an example and explored the installation strategies of porous materials with three different pore sizes in the double-skin façade system.

2. The image of porous materials in Fig. 3c corresponds to polyurethane sponges or ceramic foam material?

Reply:

Thanks. The porous material image in Fig. 3c corresponds to the image of ceramic foam material.

3. The purification efficiency would be a little bit too low.

Reply:

Thank you for your comment. In our current research, we observed that the single-pass capture efficiency for particles smaller than 10 µm, especially fine particles, is relatively low. We acknowledge the significance of these particles, as they are a major constituent of air pollution. This limitation is partly attributed to the design of our capture system, which was tailored for a specific porous medium design. While this design may not be optimal for capturing fine particulate matter, it nonetheless demonstrates the substantial potential of our system in purifying indoor particle pollution.

Moving forward, we plan to refine our capture system, with a particular focus on enhancing the efficiency of capturing fine particles. This will involve exploring new materials and more effective designs for smaller particles. Despite the results of the current study indicating a lesser efficiency in purifying fine particles, we have discovered that utilizing airflow to carry particles through porous media is an effective control strategy for fine particulates. These findings lay a solid foundation for more efficient particle capture strategies in the future.

Our research thus far, despite its limitations, provides valuable insights into particle purification and underscores our commitment to evolving and improving air purification technologies.

4. The Conclusions are too lengthy.

Reply:

Thanks. We have condensed the conclusion section, and the revised content is as follows:

“The study introduces a novel double-skin façade system (DSF-PM) integrated with porous materials for purifying particulate matter in urban environments. This system utilizes solar energy to generate airflow, making it an energy-efficient and environmentally friendly solution. Three installation strategies of porous materials were examined—vertical, horizontal, and cross placement—to optimize particulate matter capture. Results indicate that porous materials with a 1 mm pore size exhibit the best performance, achieving a maximum purification efficiency of 45% for particles larger than 10 µm and an average annual efficiency of 26.24%. This efficiency is comparable to primary filters in various international standards. The DSF-PM system's effectiveness varies with particle size and is influenced by seasonal changes in solar radiation and temperature. This approach offers a zero-energy, pollution-free method for in-situ particulate matter purification, integrating seamlessly with building exteriors.”

Thank you again for your valuable comments.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Editor:

Thank you for giving me the opportunity to revise the MS entitled “Zero-energy purification of ambient particulate matter using a novel double-skin façade system integrated with porous materials” by Li and his/her colleagues that was submitted to “Sustainability”. The following comments are requested to be addressed by the authors. 

1.      The Abstract section is not refined enough and needs to be carefully revised.

2.      I think the introduction section should be revised better. the innovation of the manuscript must be clearly stated in the text.

3.      Do porous materials have intellectual property rights?

4.      What are the effects of the properties of porous materials on dust removal efficiency?

5.      Have cost factors and cost comparison analysis been considered?

6.      The reference part needs to be revised one by one to meet the journal requirement, such as Line 584, Pay attention to superscripts and subscripts. Please note that the format of references must be uniform.

7.      I would suggest that the authors review and include the following recent studies to improve the manuscript (DOI 10.1016/j.seppur.2022.122521). 

Best regards,

Author Response

Dear reviewer:

We greatly appreciate the constructive and helpful comments you took the time to provide. Every suggestion for modification and comment you make is carefully incorporated and considered. Below are our responses to the reviewers' comments, point by point, and the revisions are indicated accordingly.

Thank you for giving me the opportunity to revise the MS entitled “Zero-energy purification of ambient particulate matter using a novel double-skin façade system integrated with porous materials” by Li and his/her colleagues that was submitted to “Sustainability”. The following comments are requested to be addressed by the authors.

1. The Abstract section is not refined enough and needs to be carefully revised.

Reply:

Thanks. We have revised the Abstract to include a concise statement that clearly outlines the significance and context of our study, ensuring it provides a solid foundation for understanding our work. The content of the revised Abstract is as follows:

“This study introduces an innovative double-skin façade system integrated with porous materials (DSF-PM) designed to combat air pollution by purifying atmospheric particulate matter without energy consumption. By evaluating three installation strategies—vertical, horizontal, and cross placement—and examining porous materials with pore sizes of 0.5 mm, 1 mm, and 2 mm through a validated computational fluid dynamics (CFD) model, we optimized the DSF-PM system for enhanced particulate matter purification. Our findings reveal that positioning the porous material on both airflow sides with a pore size of 1 mm yields the best purification performance. Seasonal performance analysis demonstrates that the DSF-PM system achieves an average annual purification efficiency of 26.24% for particles larger than 5 µm, surpassing 20% efficiency, comparable to primary filters in global standards, with zero energy input. This passive double-skin façade system, leveraging solar-driven natural convection, emerges as a sustainable solution for ambient air purification in urban environments.”

2. I think the introduction section should be revised better. the innovation of the manuscript must be clearly stated in the text.

Reply:

Thank you for your valuable feedback regarding the introduction section of our manuscript. We appreciate your suggestion to more clearly state the innovation of our work right at the beginning of the text.

In response to your comment, we have revised the introduction section to more prominently highlight the innovative aspects of our research. We ensure to succinctly present the novel contributions and advancements our study brings to the field, setting a clear context for the significance and expected impact of our work. The added content is as follows:

“The DSF-PM system represents a significant innovation in the integration of building envelope design and in-situ purification technology. Its dynamic ventilation is uniquely driven by solar energy, eliminating the need for mechanical equipment. This integration of a double-skin façade with functional materials not only enhances the architectural aesthetics but also contributes to environmental sustainability. The system's purification process is entirely eco-friendly, positioning it as an effective, zero-energy consumption method for in-situ treatment. This innovative approach underscores the DSF-PM system's potential to revolutionize the way buildings manage air quality, emphasizing sustainability and energy efficiency.”

We believe these modifications will improve the clarity and impact of our introduction, making it easier for readers to understand the significance of our contribution to the field. Thank you again for guiding us to enhance the quality of our manuscript.

3. Do porous materials have intellectual property rights?

Reply:

Thank you for your insightful question regarding the intellectual property rights of porous materials used in our research. We understand the significance of this concern, especially from a commercialization perspective. In the preliminary stages of our research, we deliberately chose materials that are commonly available on the market or are lower in cost. This decision was made to ensure that our findings could be more easily applicable and accessible for future commercial applications, thus enhancing the potential for widespread adoption and impact.

We recognize the importance of considering intellectual property rights as we move towards the commercialization of our technology. As we progress in our research, we will conduct a thorough analysis of the characteristics of porous materials and their impact on particle capture efficiency. This includes an in-depth examination of any potential intellectual property issues related to specific materials we may consider for advanced applications.

4. What are the effects of the properties of porous materials on dust removal efficiency?

Reply:

Thanks. In our study, we specifically focused on the impact of pore size variations within porous materials on their dust removal efficiency. This focus was chosen due to the critical role pore size plays in determining the capture and retention of dust particles, which is fundamental to understanding and optimizing the performance of porous materials in filtration applications.

We recognize that other properties of porous materials, such as surface area, porosity, material composition, hydrophobicity/hydrophilicity, mechanical strength, regeneration capability, and resistance to temperature and chemicals, also significantly affect dust removal efficiency. However, due to the scope of our research and constraints in experimental design, we limited our investigation to the variations in pore size. This decision allowed us to provide a detailed and focused analysis of how changes in pore size influence dust capture efficiency, contributing valuable insights to the field.

We agree that a comprehensive study encompassing all relevant properties of porous materials would offer a more complete understanding of their behavior in dust removal applications. Future research could expand on our findings by exploring how these additional properties interact with pore size to affect dust removal efficiency. We are currently considering follow-up studies to investigate some of these aspects, aiming to contribute further to the knowledge base in this area.

We appreciate your constructive feedback and the opportunity to clarify the scope of our study. We believe that our focused approach on pore size variations provides a foundational understanding that will support more comprehensive future investigations into the multifaceted effects of porous material properties on dust removal efficiency.

5. Have cost factors and cost comparison analysis been considered?

Reply:

Thanks. Following your suggestion, we have included an economic analysis in the revised draft. The additional content is as follows:

“After experimental calculation, the cost of a single DSF-PM system unit (1m ´ 3m ´ 0.3m) is 3000 CNY. For a representative room measuring 9m x 8m x 3m, using one IAM-KJ780F-A1 model purifier, with a Clean Air Delivery Rate (CADR) for solid pollutants of 800 m³/h, and considering the residential electricity price of 0.617 Yuan/ (kW·h), the operating cost of using the IAM purifier over 5 years is 9707.656 CNY. In contrast, the cost of operating the DSF-PM system for 5 years is 24,000 CNY (installing 8 such DSF-PM systems). Ignoring the time value of money, the Investment Recovery Period (IRP) is 2.5 years.”

6. The reference part needs to be revised one by one to meet the journal requirement, such as Line 584, Pay attention to superscripts and subscripts. Please note that the format of references must be uniform.

Reply:

Thank you for your suggested changes, we have rechecked and revised the reference part as requested.

7. I would suggest that the authors review and include the following recent studies to improve the manuscript (DOI 10.1016/j.seppur.2022.122521)

Reply:

Thank you for your suggestion. After carefully reading the article, it has been added to the introduction section of our paper, cited as reference number [13].

Thank you again for your valuable comments.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The study introduces a promising approach to address urban particulate matter pollution using a novel Double-Skin Facade System integrated with Porous Materials (DSF-PM), aiming for zero energy consumption. The authors investigate three installation strategies and three porous materials with varying pore sizes. Results indicate that placing porous material on both sides of the airflow with a pore size of 1 mm yields optimal purification performance. The DSF-PM system demonstrates potential for efficient particulate matter purification without energy consumption. The study emphasizes the importance of stable airflow for effective particle capture and highlights the system's applicability in the urban built environment. Overall, the DSF-PM system presents an innovative, passive solution for improving air quality with implications for pollution reduction and carbon footprint mitigation.

Author Response

Thank you for your recognition of our research.

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

How many replicates were performed for each experimental condition? It is better to test at least 3 replicates, so the results are more reliable.

If more than one replicate is performed, the standard deviation should be included in all the graphs.

It is difficult to see any feature in Figure 4a. It is better to mark different parts of the setup.

Comments on the Quality of English Language

Page 1, line 19: “respectively” should be deleted in the sentence “…are respectively investigated….”,

 

Page 6 line 197: Newton should be changed to N, as it is the unit for force.

Page 7, line 225: “In order to reduce the room heat gained of room from solar radiation in summer” should be changed to “In order to reduce the heat room gained from solar radiation in summer”

 

Author Response

Dear reviewer:

We greatly appreciate the constructive and helpful comments you took the time to provide. Every suggestion for modification and comment you make is carefully incorporated and considered. Below are our responses to the reviewers' comments, point by point, and the revisions are indicated accordingly.

1. How many replicates were performed for each experimental condition? It is better to test at least 3 replicates, so the results are more reliable.

Reply:

Thanks. Under each experimental condition, we conducted three replicate experiments, and the final results were obtained by averaging the outcomes of these three trials.

2. If more than one replicate is performed, the standard deviation should be included in all the graphs.

Reply:

Thanks. Following your suggestion, after re-verifying the data, a description of the relative error has been added to Figure 5, thereby increasing the rigor of the article. As shown in the attachment.

3. It is difficult to see any feature in Figure 4a. It is better to mark different parts of the setup.

Reply:

Thanks. Detailed annotations have been made in Figure 4(a), as shown in the attachment.

4. Comments on the Quality of English Language

Page 1, line 19: “respectively” should be deleted in the sentence “…are respectively investigated….”,

Page 6, line 197: Newton should be changed to N, as it is the unit for force.

Page 7, line 225: “In order to reduce the room heat gained of room from solar radiation in summer” should be changed to “In order to reduce the heat room gained from solar radiation in summer”.

Reply:

Thanks. The above issues regarding English grammar and language quality have been revised in the manuscript.

Thank you again for your valuable comments.

Author Response File: Author Response.docx

Reviewer 5 Report

Comments and Suggestions for Authors

A huge number of scientific works are devoted to the processes of media separation and, in particular, the separation of solid particles from the liquid or gaseous phase. The current study also addresses such issues from the perspective of using a minimum amount of energy. In China, the problem of air purification from particulate matter is relevant due to the use of large amounts of fossil fuels, such as coal, to produce heat and electricity. It is already proposed to use polyurethane and ceramic porous materials for air purification. At the same time, the authors draw attention to the fact that sorbents made on the basis of such materials often depend on air temperature, sunlight or air flows, i.e. sorption occurs with the help of the environment. The instability of natural factors makes the sorption process also unstable.
In order to more effectively use sorbing systems, it is proposed to use residential buildings, namely their outer surface (facades) for the installation of special filter structures.
The title of the manuscript uses a non-standard font - "façade".
Perhaps the table should indicate the ranges of structural parameters?
The figure caption for Figure 5 should be expanded to make it clear what information is presented. It is also advisable to show statistical data for the measured quantities in the figure.
Figure 6. Why did the dimensions change compared to those presented above?

Can the authors add the fractional composition of particles in the air (for a real system)? How does air humidity affect the data obtained?

The presented conclusions of the manuscript contain the main achievements of the work, but in my opinion they should be shortened. In general, the manuscript is easy to read, the work is of interest to me, and I think it will also be important for other readers to familiarize themselves with solutions that make it possible to purify the air from solid impurities.

Author Response

Dear reviewer:

We greatly appreciate the constructive and helpful comments you took the time to provide. Every suggestion for modification and comment you make is carefully incorporated and considered. Below are our responses to the reviewers' comments, point by point, and the revisions are indicated accordingly.

1. A huge number of scientific works are devoted to the processes of media separation and, in particular, the separation of solid particles from the liquid or gaseous phase. The current study also addresses such issues from the perspective of using a minimum amount of energy. In China, the problem of air purification from particulate matter is relevant due to the use of large amounts of fossil fuels, such as coal, to produce heat and electricity. It is already proposed to use polyurethane and ceramic porous materials for air purification. At the same time, the authors draw attention to the fact that sorbents made on the basis of such materials often depend on air temperature, sunlight or air flows, i.e. sorption occurs with the help of the environment. The instability of natural factors makes the sorption process also unstable. In order to more effectively use sorbing systems, it is proposed to use residential buildings, namely their outer surface (facades) for the installation of special filter structures.

Reply:

Thank you for your valuable suggestions. Regarding the application scenarios for the DSF-PM system, we will take them into detailed consideration in our next step of research, and we agree with your viewpoint on installing the DSF-PM system on the exterior façades of residential buildings.

2. The title of the manuscript uses a non-standard font - "façade".

Reply:

Thanks. "façade" is an architectural term generally referring to the exterior wall or front of a building. Since this word originates from French, it has been used to this day. Upon reviewing literature, in documents related to the description of building exteriors or façades, the term consistently used is "façade" rather than "facade". Therefore, we have also adopted the French term "façade" in our manuscript to denote the exterior of a building. 

We understand that the reviewer might have suggested changes to ensure the article better conforms to various publishing standards. Therefore, we appreciate the suggestions from the reviewers and have changed "façade" to "facade" in the title of the paper according to their recommendations.

3. Perhaps the table should indicate the ranges of structural parameters?

Reply:

Thanks. Table 1 in the manuscript lists the structural parameters of the DSF-PM system, but it may not be detailed enough. Therefore, we have supplemented the following content:

“The dimensions of the DSF-PM system: 3 meters in height, 1 meter in width, with a distance of 0.3-meter between the two sides. A height of 3 meters is chosen to fit environments with a 3 m floor height. 0.3-meter distance between the two sides is based on the construction standard (DG/TJ08-56-2019), which stipulates that the air layer thickness of a double-skin façade should not be less than 0.12 meter. Additionally, the width of the DSF-PM is designed to be 1 meter to facilitate subsequent modular arrangement.”

The above content has been added to the revised manuscript on page 4.

4. The figure caption for Figure 5 should be expanded to make it clear what information is presented. It is also advisable to show statistical data for the measured quantities in the figure.

Reply:

Thanks. Following your suggestion, after re-verifying the data, a description of the relative error has been added to Figure 5, thereby increasing the rigor of the article. As shown in the attachment.

5. Figure 6. Why did the dimensions change compared to those presented above?

Reply:

Thank you for your valuable comments. Regarding the simulation of the flow field, we opted for a 2D model for validation. This choice was based on the symmetry of our experimental model and considerations for reducing computational costs. Despite being a 2D model, we are confident that it accurately reflects the internal flow field characteristics of the cavity. Specifically, in the validation of the flow field model, we meticulously compared the airflow at key positions (such as the inlet, outlet, and middle positions) between the 2D model and the experimental model, as shown in Figs. 4 and 5. This comparative validation further confirms the accuracy and effectiveness of our model in studying the internal flow field of the cavity regarding the transport stability of particulate matter.

We recognize the limitations of our current work and plan to explore the potential of 3D model in future research. We aim to enhance the comprehensiveness and accuracy of our models by comparing the results of the 3D model with those of the current 2D model.

6. Can the authors add the fractional composition of particles in the air (for a real system)? How does air humidity affect the data obtained?

Reply:

Thank you for your comment. In our research, we conducted a detailed analysis of particles with five different diameters (2.5 μm, 5 μm, 10 μm, 15 μm, 20 μm), focusing on their movement trajectories within the DSF-PT cavity and the system's capture efficiency for these particles. Therefore, our study mainly focused on exploring the capture efficiency for particles of different sizes. A comprehensive size distribution analysis was beyond the scope of this initial research phase.  However, we fully recognize the importance of such an analysis. Despite these limitations, the results of our current study are still of significant value in researching zero-energy consumption purification of particle pollution and enhancing air quality.

During the course of this study, experiments were conducted at 26°C and one standard atmosphere, with the calculated relative humidity of the air being 47.8%. However, the authors did not set up comparative experiments (under different relative humidity conditions) to investigate the impact on the purification efficiency of the device. In the next phase of research, the authors will consider this issue along with the device's capture efficiency for a mixture of various particulate matters, to comprehensively evaluate the effect of air humidity on the device's purification efficiency.

7. The presented conclusions of the manuscript contain the main achievements of the work, but in my opinion, they should be shortened. In general, the manuscript is easy to read, the work is of interest to me, and I think it will also be important for other readers to familiarize themselves with solutions that make it possible to purify the air from solid impurities.

Reply:

Thanks. We have condensed the conclusion section, and the revised content is as follows:

“The study introduces a novel double-skin façade system (DSF-PM) integrated with porous materials for purifying particulate matter in urban environments. This system utilizes solar energy to generate airflow, making it an energy-efficient and environmentally friendly solution. Three installation strategies of porous materials were examined—vertical, horizontal, and cross placement—to optimize particulate matter capture. Results indicate that porous materials with a 1 mm pore size exhibit the best performance, achieving a maximum purification efficiency of 45% for particles larger than 10 µm and an average annual efficiency of 26.24%. This efficiency is comparable to primary filters in various international standards. The DSF-PM system's effectiveness varies with particle size and is influenced by seasonal changes in solar radiation and temperature. This approach offers a zero-energy, pollution-free method for in-situ particulate matter purification, integrating seamlessly with building exteriors.”

Thank you again for your valuable comments.

Author Response File: Author Response.docx

Reviewer 6 Report

Comments and Suggestions for Authors

The manuscript is acceptable in its current form.

Author Response

Thank you very much for your comment.

Reviewer 7 Report

Comments and Suggestions for Authors

This study presents an innovative double-layer façade system (DSF-PM) with integrated porous materials, which is designed to combat air pollution by purifying the atmosphere of particulate matter and does not consume energy.

1.The novelty of the paper should be described in the introduction. 

2.Authors need to agree on the colour of the font in the text without marking it red to look like a draft.

3.A description of the dataset is missing and needs to be detailed.

4.Figure 4 INLET is missing the absolute value of the relative error, why?

5.The authors are missing a discussion section to illustrate new findings and ideas that have been researched with others.

Author Response

Dear reviewer:

We greatly appreciate the constructive and helpful comments you took the time to make. Every modification suggestion and comment you make is accurately incorporated and considered. Below the comments of the reviewers are responses point by point and the revisions are indicated.

1. The novelty of the paper should be described in the introduction.

Reply: Thank you for your suggestion. We have detailed the innovative aspects of this paper in the last paragraph of the introduction. Furthermore, we emphasized that the DSF-PM system represents a significant innovation in the design of building envelopes and in-situ purification technology. Its unique dynamic ventilation is driven by solar energy, independent of mechanical equipment. The integration of a double-skin façade with functional materials not only enhances architectural aesthetics but also contributes to environmental sustainability.

2. Authors need to agree on the colour of the font in the text without marking it red to look like a draft.

Reply: Thank you for your suggestion. The reason for the red font in the manuscript is that we highlighted the modifications in red for the convenience of the reviewers, following their comments. Now, we have changed the font color of the initially modified content to black in the latest submission of the manuscript.

3. A description of the dataset is missing and needs to be detailed.

Reply: Thank you for your advice. We have carefully read the policy of the journal regarding the data in research articles and, in accordance with these requirements, have included at the end of our manuscript the statement, “Data Availability Statement: The data presented in this study are available on request from the corresponding author.”

4. Figure 4 INLET is missing the absolute value of the relative error, why?

Reply: Thanks. The absolute error between the simulated value and the experimental value in the Inlet section is very small. We have annotated the specific absolute error values in Figure 5 for your reference.

5. The authors are missing a discussion section to illustrate new findings and ideas that have been researched with others.

Reply: Thank you for your valuable feedback. We acknowledge the importance of a discussion section in highlighting the novel findings and ideas of our research in comparison with existing studies. In light of your suggestion, we have now added a comprehensive discussion section to the manuscript. This section elaborates on how our findings contribute to the current body of knowledge, identifies the innovative aspects of our research, and situates our work within the broader scientific discourse. We believe this addition significantly strengthens the paper and hope it addresses your concern. 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

No significant improvement has been made.

Comments on the Quality of English Language

No significant improvement has been made.

Author Response

Thank you for your valuable feedback on our revised manuscript. We took great care to address each of the four concerns raised during the first review round in detail, and we aimed to address all the comments and suggestions provided by the reviewers to the best of our ability. Thank you again for your time and consideration.

Reviewer 2 Report

Comments and Suggestions for Authors

ok to accept.