Application of Sustainable Prefabricated Wall Technology for Energy Efficient Social Housing

Round 1

Reviewer 1 Report

The paper presents a modelling exercise to evaluate the feasibility of a pre-fabricated solution from industrial waste. However, there are several flaws in the method of analysis, which must be addressed. The idea of evaluating the feasibility of this method is valid, but several assumptions are not justified or unclear. A major issue lies in the use of a 3m x 3m x 3m box for the cooling load calculation; this calculation should be done on a representative building, but there is no information to suggest that the selected box is representative. In fact, a different building is then used to calculate the size of a feasible development. The conclusions based on these assumptions are therefore not valid.

Also, the assumptions used for the cost and cooling load calculations in BIM are not presented; there is no information on the sources of many inputs, e.g. unit costs. Costs might depend on a number of factors, including the local availability of materials, but this is not clearly explained.

Another major issue to address is the terminology: the paper presents bio-based materials but in fact the product is made using industrial waste. Please explain where the CBA is taken from (e.g. line 75) and provide more information about the context in the region in India used as case study (e.g. climatic, industrial, social). More emphasis should be given on the importance of using by-products for a circular economy. There is limited discussion on the sustainability of this system, although the word "sustainable" is in the title.

The section on product development has limited depth. It is unclear why the sandwich is the selected system, and not others. Please add a clear justification for it. Only one system is evaluated, whereas many combinations can be made using the by-product. A comparison between the sandwich panel and an insulated brick wall (of a similar thermal conductivity) would add more depth to the analysis on the benefits of using the sandiwch panel; the comparative analysis is currently very poor.

Table 4 presents properties of construction products, but there is no information on the developed sandwich panel. Please elaborate on that and explain what are the desired property of such panel. Also, it is unclear why polyurethane was selected as insulation material, considering its high embodied carbon. Is there any other local byproduct that can be used as insulation material?

Also, is there any literature on the health associated to using CBA in indoor environments? Please elaborate on that.

English should be improved; e.g. "insulation materials", rather than "insulated materials", some articles and commas are missing.

Other minor necessary changes include:

• in the abstract (line 28) do not use the word "optimised", as the work does not include any optimisation;
• change the keywords, as the product is not bio-based, nor necessarily sustainable;
• it is unclear why the bars are stacked in fig.1;
• in line 102 "heavy construction" is mentioned; what is the meaning given to this term? I would use "large-scale construction"
• in line 131 explain what is the purpose of measuring the specific gravity;
• explain what is the purpose of creating a 1m x 1m x 1m mock up (fig.4);
• indicate the orientation in fig. 6;
• use a different currency than £ (e.g. you could use euros or dollars);
• don't use a line to represent energy in fig. 7 (e.g. you can use dots);
• explain that the work is based on simulation in the abstract (it is not clear at the start);
•  

Author Response

Reviewer #1:

Comment 1:    The paper presents a modelling exercise to evaluate the feasibility of a pre-fabricated solution from industrial waste. However, there are several flaws in the method of analysis, which must be addressed. The idea of evaluating the feasibility of this method is valid, but several assumptions are not justified or unclear. A major issue lies in the use of a 3m x 3m x 3m box for the cooling load calculation; this calculation should be done on a representative building, but there is no information to suggest that the selected box is representative. In fact, a different building is then used to calculate the size of a feasible development. The conclusions based on these assumptions are therefore not valid.

Justification:   Initially a single room of 3m × 3m × 3m was considered for conducting cost and energy analysis by selecting various combinations as shown in Table 5. For validation of the results, a model house of one-third of its size (1m × 1m × 1m) was built. Experimentation such as study of indoor air temperatures in different seasons will be carried out.

But the ultimate aim of the study is to take the developed technology into the construction of urban slum housing. According to this, the area required of a house for an economically weaker section (EWS) is around 25-30 sq.m. (as per the Ministry of Housing & Urban Poverty Alleviation, Government of India). So, a minimum area of 25 sq.m. was considered for conducting the feasibility study of economical prefab houses required over the conventional construction.

 

Comment 2:    Also, the assumptions used for the cost and cooling load calculations in BIM are not presented; there is no information on the sources of many inputs, e.g. unit costs. Costs might depend on a number of factors, including the local availability of materials, but this is not clearly explained.

Justification:   Regarding the costing, major inputs such as the unit rates of the materials, manpower and machinery were taken from the local market rates i.e., Maharashtra region, India and also from the earlier Ph.D. thesis completed from the institute – Visvesvaraya National Institute of Technology, Nagpur, India.

Cooling load inputs were carried out in Revit software and it is the most widely used BIM based software tool that is based on parametric modelling. The project information (location and building definition) allows obtaining heating and cooling information for the project. The environmental factors responsible for thermal comfort viz. ambient temperature, humidity and wind parameters are modeled for a specific location. Revit considers all the major factors for thermal comfort viz. orientation of building walls, window openings, shading devices along with material properties (heat transfer coefficients, solar absorption coefficients and solar heat gain coefficients) and operating specifications, which are framed as input. Spaces are placed in areas of the building model to determine the volume for each area. Revit computes these volumes as an analytical volume. Once all the data has been assembled, the simulation engine calculates the cooling loads. Design cooling loads are based on the assumption of steady periodic conditions.

 

Comment 3:    Another major issue to address is the terminology: the paper presents bio-based materials but in fact the product is made using industrial waste. Please explain where the CBA is taken from (e.g. line 75) and provide more information about the context in the region in India used as case study (e.g. climatic, industrial, social). More emphasis should be given on the importance of using by-products for a circular economy. There is limited discussion on the sustainability of this system, although the word "sustainable" is in the title.

Justification:   The raw material CBA is not a regular industrial by-product. The ash is the result of the process of co-firing coal with rice husk in boilers of a paper mill industry. This kind of technique is in practice in majority of the industries across India, in order to conserve non-renewable resources for energy generation. As a sustainable practice, agro-industrial and bio based materials are used as a part of the co-firing process in the industry boilers resulting in producing the co-fired blended ashes. As mentioned, CBA is a result of this co-firing process where its actual source is from the agro industry making it bio-based.

Ash coming from the industry is landfilled which has negative effects on the environment as well as human health. Thus, CBA is being tested and used as a construction product. Also, the need for replacing conventional products is needed as the natural resources are getting exploited.  In this study, CBA is replacing the fine aggregate which is a sustainable practice. So, as the current raw material is a part of sustainable practice and its sources are bio-based, CBA is considered both sustainable and bio-based ash.

 

Comment 4:    The section on product development has limited depth. It is unclear why the sandwich is the selected system, and not others. Please add a clear justification for it. Only one system is evaluated, whereas many combinations can be made using the by-product. A comparison between the sandwich panel and an insulated brick wall (of a similar thermal conductivity) would add more depth to the analysis on the benefits of using the sandwich panel; the comparative analysis is currently very poor.

Justification:   For thermal resistance, sandwich panels with an insulation layer in between were found to be effective from many studies. Some of the references are mentioned below. The PUF sheets come as a packaging material and lies as a wastage at the institute. So, these sheets are tried out as an insulation layer between two concrete layers which can be both thermally efficient as well as reduces cost and dead load of the element.

The comparative analysis is based on the construction products developed from CBA as well as the locally available commercial product, Fly ash brick. The study mainly focuses on implementing the prefab technology as it is a rapid construction technology. The research mostly tries to give an output of time and cost efficient technology. Precast sandwich panels are found to be cost, time and energy-efficient and thus, other options have been not considered in the comparative analysis.  

Reference:

1. A. Einea, D.C. Salmon, G.J. Fogarasi, T.D. Culp, M.K. Tadros, State-of-the-art of Precast Concrete Sandwich Panels, PCI J. 36 (1991) 78–92. https://doi.org/10.15554/pcij.11011991.78.98.
2. R. O’Hegarty, O. Kinnane, Review of precast concrete sandwich panels and their innovations, Constr. Build. Mater. 233 (2020) 117145. https://doi.org/10.1016/j.conbuildmat.2019.117145.

Comment 5:    Table 4 presents properties of construction products, but there is no information on the developed sandwich panel. Please elaborate on that and explain what are the desired property of such panel. Also, it is unclear why polyurethane was selected as insulation material, considering its high embodied carbon. Is there any other local byproduct that can be used as insulation material?

Justification:   The designed concrete was found to be of higher density. So, sandwich panel was made with an object to decrease the density of its end product (roof slab) by inserting the recommended insulation material (polyurethane). Such panels were checked for the strength, density and thermal conductivity. The strength of the panel got reduced by the insertion of insulation layer but the density was found to be 2173 kg/m³ and thermal conductivity as 1.27 W/mK.

Alternate materials were also considered during the selection of insulation materials. Comparatively, the thermal conductivity of polyurethane (0.028 W/mK) was found to be less with respect to EPS (0.0313 W/mK), mineral wool (0.035 W/mK) and saw dust (0.06 W/mK). Also, the material was readily available as a waste product from the packaging material. So, application of these PUF sheets as the insulation layer was tried as an experiment in enhancing thermal insulation by utilizing the freely available waste product.

 

Comment 6:    Also, is there any literature on the health associated to using CBA in indoor environments? Please elaborate on that.

Justification:   Current raw material is a locally available by-product and the composition is a bit unique when compared to other types of blended ashes. Construction products were developed using the raw material but, no known health issues were identified while working with it.

Reference:

1. Ram, Shashi, Kunal Pradhan, and Rahul V. Ralegaonkar. "Use of co-fired blended ash in the development of sustainable construction materials." Proceedings of the Institution of Civil Engineers-Engineering Sustainability. Vol. 171. No. 8. Thomas Telford Ltd, 2017.

 

Comment 7:    English should be improved; e.g. "insulation materials", rather than "insulated materials", some articles and commas are missing.

Justification:   The necessary modifications are incorporated into the updated manuscript.

 

Comment 8:    In the abstract (line 28) do not use the word "optimised", as the work does not include any optimisation;

Justification:   The term “optimized” is modified and some details are added to the abstract regarding it.

 

Comment 9:    Change the keywords, as the product is not bio-based, nor necessarily sustainable;

Justification:   Authors feel that the raw material used in the study is both sustainable as well as bio-based.

 

Comment 10:  It is unclear why the bars are stacked in fig.1;

Justification:   The intent of bars being stacked is to present the data such that the percentage of the urban population can be visually seen comparatively with the total population. Though the percentage is not to the scale, it may help the readers to understand how the urban population has increased over the years with respect to total population.

 

Comment 11:  In line 102 "heavy construction" is mentioned; what is the meaning given to this term? I would use "large-scale construction"

Justification:   The intent for using the term “heavy construction” was to determine mass constructions. The term “large-scale construction” is apt and thus replaced as suggested.

 

Comment 12:  In line 131 explain what is the purpose of measuring the specific gravity;

Justification:   The value of specific gravity was a measure to indicate its light density when compared to regular cement (3.15) and sand (2.63). Thus the value depicts that the raw material (CBA) occupies more volume while casting, than sand when equal weights were considered.

 

Comment 13:  Explain what is the purpose of creating a 1m x 1m x 1m mock up (fig.4);

Justification:   Model house was built up in view of conducting experimental analysis regarding indoor temperatures compared to regular concrete and brickwork. It stands as a validation model for the energy simulations conducted through software. The small-scale modeling technique has been successful in the research area where the percentage variation between the small-scale and real scale model was also found to be almost similar.

Reference:

1. Sakhare, Vishakha V., and Rahul V. Ralegaonkar. "Strategy to control indoor temperature for redevelopment of slum dwellings." Indoor and Built Environment27.9 (2018): 1203-1215.

 

Comment 14:  Indicate the orientation in fig. 6;

Justification:   There are multiple orientations as the model was rotated to showcase the panels. The orientation of the wall having door is always to the north and hence the model was named Panel (N) in the figure. With reference to this, other combinations have been oriented and shown accordingly.

 

Comment 15:  Use a different currency than £ (e.g. You could use euros or dollars);

Justification:   The earlier mentioned currency of GBP (£) is now replaced with euros (€) in Tables 6, 8, 9 and 10.

 

Comment 16:  Don't use a line to represent energy in fig. 7 (e.g. You can use dots);

Justification:   The line was represented in order to showcase the decline of the energy curve in the graph. Still, the comment was considered and the line is now replaced with a dotted line.

 

Comment 17:  Explain that the work is based on simulation in the abstract (it is not clear at the start);

Justification:   Simulation study was mentioned in the abstract.

 

Reviewer 2 Report

The article presents a solid piece of research that presents the findings in what regards the use of CBA for the production of bricks and panels and aims to link it to a possible impact on social housing production in India. 

Social housing is introduced as a major need, so the connection with the new material is somehow implicit, however, the discussion on how the new material might impact specifically the sector stops abruptly with the mentioning of the Indian Concrete Institute. I would love to find out more about the link between the scientific findings and the actual social impact of this activity. Is there a state policy to use the findings in the sector? Is it part of a brick and mortar subsidy scheme? Who benefits first of the possible economic impact of the new materials?

In this respect there is also a bit too little information about the possible cost savings that the use of this material might bring, but a general description of what it might do in terms of energy efficiency. Again, considering the initial stage of the development of the product, the economic data are hard to figure out and this does not affect the quality of the research. What it does is that it raises some questions about the validity of the main thesis, that the use of the CBA will directly impact the social housing sector.  

The title is explicit, but non-appealing, considering the rich content of the article it should never start with „feasability”. I suggest you should look for a stronger idea, in the range of "using ash to cool down social housing" (of course, not as blunt and clumsy as that).

Author Response

Reviewer #2:

Comment 1:    I would love to find out more about the link between the scientific findings and the actual social impact of this activity. Is there a state policy to use the findings in the sector? Is it part of a brick and mortar subsidy scheme? Who benefits first of the possible economic impact of the new materials?

Justification:   A questionnaire survey was conducted with the industry and academic professionals where these scientific findings were discussed in relation to the actual construction practice. Many of them have also agreed for its execution in the real practice (findings are mentioned in the below reference paper).

If the scientific findings are proven to be beneficial for the use in projects, pilot projects are encouraged where small-scale projects are sanctioned for the development and execution of the research area into the actual world. Success of these pilot projects will definitely lead to the large-scale execution of the research area.

The government has recognized the importance of using the locally available resources which gained them better results of reduction in costs in their projects. Some state governments also encourage their usage by including subsidies and incentives into the project costs. Indian standard code, IS: 383 – 1970 also recommends the utilization of such alternate materials/ ashes coming from alternate sources to be used as aggregates.

No, this study is not based on the brick and mortar subsidy scheme.

The benefits related to the economic impact lies with multiple people. The stakeholders related to the pilot projects are among the first ones to get benefitted as they experience the reduced costs at the earlier stages as the raw material comes at a free cost.

Reference:

1. Bras, A.; Ravijanya, C.; de Sande, V.T.; Rley, M.; Ralegaonkar, R. V. Sustainable and affordable prefab housing systems with minimal whole life energy use. Energy Build. 2020, 110030, doi:10.1016/J.ENBUILD.2020.110030.

 

Comment 2:    The title is explicit, but non-appealing, considering the rich content of the article it should never start with “feasibility”. I suggest you should look for a stronger idea, in the range of "using ash to cool down social housing" (of course, not as blunt and clumsy as that).

Justification:   Change of the title is appreciated and revised to “Application of sustainable prefabricated walling technology for the energy efficient social housing”.

 

 

Reviewer 3 Report

There are some weaknesses through the manuscript which need improvement. Therefore, the submitted manuscript cannot be accepted for publication in this form, but it has a chance of acceptance after a major revision. My comments and suggestions are as follows:

1- Abstract gives information on the main feature of the performed study, but some details about the details of the construction should be added.

2- It would be nice, if authors could use their academic email address (all authors).

3- The necessity of the presented study must be explained in introduction. Objective and scope of the research must be presented in introduction.

4- The literature study must be enriched. In this respect, it is necessary to read and cite following relevant papers: (a) https://ieeexplore.ieee.org/document/9016681 (b) http://www.ejge.com/2014/Ppr2014.417ma.pdf (c) https://doi.org/10.1016/j.engstruct.2019.109844 (d) https://doi.org/10.1080/19386362.2018.1505310

5- Authors must clarify why these combinations with bricks (Table 5) is considered. Dimensions must be added to Fig. 4.

6- Life cycle assessment must be discussed. In this respect, authors can read and cite recently published papers which discuss LCA in the products: (a) https://doi.org/10.1016/j.apmt.2020.100689 and (b) https://doi.org/10.1016/j.matpr.2020.02.651

7- Some recommendations must be presented in a meaningful and critical way.

8- In its language layer, a professional proofreading is needed. There are sentences which have to be rewritten.

9- The conclusion must be more than just a summary of the manuscript. Please provide all changes throughout the manuscript and updated references by red color in the revised version.

 

 

Author Response

Reviewer #3:

Comment 1:    Abstract gives information on the main feature of the performed study, but some details about the details of the construction should be added.

Justification:   The details of the construction are now updated in the abstract.

 

Comment 2:    It would be nice, if authors could use their academic email address (all authors).

Justification:   The suggestion is considered and the academic email address will be followed for the further manuscripts.

 

Comment 3:    The necessity of the presented study must be explained in introduction. Objective and scope of the research must be presented in introduction.

Justification:   The necessity, objective and scope of the study have been already mentioned in the manuscript in the paragraph starting from line 119.

 

Comment 4:    The literature study must be enriched. In this respect, it is necessary to read and cite following relevant papers: (a) https://ieeexplore.ieee.org/document/9016681 (b) http://www.ejge.com/2014/Ppr2014.417ma.pdf (c) https://doi.org/10.1016/j.engstruct.2019.109844 (d) https://doi.org/10.1080/19386362.2018.1505310

Justification:   The mentioned papers don’t fall into the scope of the study area. But the raw material used in the paper (c) has been mentioned into the current manuscript and cited respectively [Reference 24]. The research areas of the remaining 3 mentioned papers doesn’t fit into the manuscript.  

 

Comment 5:    Authors must clarify why these combinations with bricks (Table 5) is considered. Dimensions must be added to Fig. 4.

Justification:   There were around 18 cases considered in Table 5, of which 16 combinations were of different combinations of brickwork and prefab panels. These 16 combinations were considered for the energy perspective as each orientation has a different kind of energy load as shown in Table 7. The comparison of these combinations has led to the inference that the peak cooling load is less for the complete prefab structure when compared to others.

The dimensions have been added to the Fig. 4.

 

Comment 6:    Life cycle assessment must be discussed. In this respect, authors can read and cite recently published papers which discuss LCA in the products: (a) https://doi.org/10.1016/j.apmt.2020.100689 and (b) https://doi.org/10.1016/j.matpr.2020.02.651

Justification:   The mentioned papers are added in the recommendation part of the manuscript [References 33, 34].

 

Comment 7:    Some recommendations must be presented in a meaningful and critical way.

Justification:   Recommendations are added into the manuscript in the Conclusion section.

 

Comment 8:    In its language layer, a professional proofreading is needed. There are sentences which have to be rewritten.

Justification:   Necessary modifications are incorporated into the updated manuscript.

 

Comment 9:    The conclusion must be more than just a summary of the manuscript. Please provide all changes throughout the manuscript and updated references by red color in the revised version.

Justification:   The conclusion has been updated with some extra details and recommendations.

 

Round 2

Reviewer 1 Report

Dear Authors,

thank you for your response. There are some points that still need to be addressed before accepting this publication.

Comment 1: I still don’t think that the analysis of energy and cost can be done on one room. It has to be done on a representative house; using your suggested value of 25 m^2 would be sensible. Please re-run the analysis on a representative house.

Also, (Line 24) it is not real scale; this is a room with unusual proportions (and a high ceiling). Given the use of different systems for different elements, the proportions are likely to affect the results.

Comment 3: there is no information on rice husk in the paper; please add this and add some contextual information on the process this material is a by-product of.

Comment 13: the 1m^3 model house has not been used for analysis or validation (or at least it is not presented in this paper); if not part of the methodology, then there is no need to add it in the paper. Also, the simulation is not using realistic proportions.

Author Response

"Please see the attachment"

 

Author Response File: Author Response.pdf

Reviewer 3 Report

 

Dear Authors,

you have addressed the comments, and answered the questions. 

Author Response

Dear reviewer,

The authors would like to thank you for the thoughtful comments towards improving our manuscript.