An Empirical Study of Carbon Emission Calculation in the Production and Construction Phase of A Prefabricated Office Building from Zhejiang, China

Round 1

Reviewer 1 Report

The paper An Empirical Study on Calculating Carbon Emissions in the Materialization Phase of An Assembled Office Building in Zhejiang Province, China  submitted for review shows a lack of clarity and scientific novelty.

I think that a deep review of the whole methodology and development should be done.

I do not think it has enough scope in this journal.

Author Response

Please refer to the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The purpose of this  study is to demonstrate the accuracy of the empirical data collected and to fill the data gaps in the field through the use of accurate primary data compared to traditional simulation  methods, and to demonstrate the effectiveness of carbon reduction in assembled public  buildings through calculations and references, and to provide calculated data to assist in  the design decision-making process to create low carbon buildings optimized for their  environmental performance and to contribute to carbon neutrality.

This scope is of interest for the readers of Buildings.

I have found the description of this paper well detailed and organised. 

Hoever, I have foud it too long, and this compromise its readability.

My suggestion is to make this paper more fluid For example, is it possible to transfer some of the results in an Annex, producing  more synthetic tables for the main body, focusing of an sum up of the main results. 

Said that I found the paper complete. I am not able to validate the calculation.  

Anyway, the paper must be revised in terms of formalities. A lot of references are not reported in line with the editorial rules of the journal. Please put attention to the punctualisation and the use of capital letter.

Thank you.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

* In the result section, the authors mentioned that "The project adopts the professional BIM technology throughout the whole process from design to construction." I suggest briefly discussing BIM and related technologies for sustainability in the literature review section. Hope to help in this task I suggest some references the authors can use:

- Building Information Modeling (BIM) Driven Carbon Emission Reduction Research: A 14-Year Bibliometric Analysis

- Interactions of Sustainability and BIM in Support of Existing Buildings

- Optimizing energy use, cost and carbon emission through building information modelling and a sustainability approach: A case-study of a hospital building

- From BIM to extended reality in AEC industry

- BIM applications in sustainable construction: scientometric and state-of-the-art review

- User-centric sustainability assessment of single family detached homes (SFDH): A BIM-based methodological framework

- IFC-based embodied carbon benchmarking for early design analysis

* The quality of figures need to be increased.

* The conclusion section needs to be improved.

* The authors strongly suggested adding a "practical implications" section before the conclusion section.
* I suggest adding a future research section after the conclusion section. 

* Moderate English proficiency is required.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper is well written. Introduction permits to understand some advances and limits in the domain and the aim of the paper is given. Method is discussed. Model used is presented and some references are given.To increase the quality of the paper, I suggest that:

1/The limits of this paper is the fact that in results and discussion section, discussion is not focused to compare the values obtained to others published in the literature. This is capital to compare the results to others published in order to give some credits to the theoretical values presented. If it is not capable to valid the theoretical values presented with experimental values, it is capital to compare it with other theoretical values presented in  the literature using another method. 

2/Abstract is not well written, it is capital to focus only on results obtained in the paper. Thus, cancel all the first sentences :Under the near-zero carbon emissions target of the United Nations Conference on Environmental Change, the building sector needs to reduce carbon emissions further. Among them, the carbon peak target emphasizes the carbon emission per unit time of the building, which is the key to achieving the carbon peak as early as possible in the building compared with the building operation phase, where the carbon emission is more concentrated, and the absolute amount of emission is more significant.

3/I want to know if the method used is new. If yes, compare the results with other obtained using another method. If not, give the references of the studies that used this method and compare your results by those obtained by these studies. If possible, gives some results obtained in the literature using experimental method in the building sector.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 5 Report

A paper which essentially compares the embodied carbon of a prefabricated and non-prefabricated building to compare. Similar studies exist, but the argument here is the building is highly modular, so suggests a more prefabricated building than is common in the literature.

I would like to congratulate the authors on a thorough paper, with a large amount of data and clearly a comprehensive attempt at process-based emissions counting. However, I have the following suggestions for change.

Abstract

The first couple of sentences of the abstract are very difficult to understand. What is the “assembly materialization phase”? There could be clearer use of terms throughout (see following comments)

I would encourage the authors to use 255kgCO2/m2 as the figure rather than 2.2 tonnes, as the most common metric used in embodied carbon is kgCo2e/m2.

Introduction

In the paper the authors talk about a prefabrication rate is 86.5% and the assembly rate is 96.8 (line 309) – what does this mean? What is an assembly rate? Can you explain in the introduction please?

Line 46. The authors note “80% of carbon emissions during the whole life cycle of a building are generated during the operational phase of the building”. This is what was thought previously – the general understanding now, is that embodied emissions are expected to be 50% or higher. This needs to be carefully expressed along the lines of “while historically the evidence suggested most building emissions were related to operation, more recent studies suggest embodied emissions may make up more than half of a building’s total lifecycle emissions”. Some studies on this:

1.      https://www.rics.org/globalassets/rics-website/media/news/whole-life-carbon-assessment-for-the--built-environment-november-2017.pdf (see page 2)

2.      https://doi.org/10.1016/j.buildenv.2021.107620 (embodied carbon is between 27 and 58% of lifecycle carbon emissions)

Line 53: “Carbon emissions in the building sector accounted for 29.3% of the national carbon emissions in the building phase and 21.9% in the operation phase[7]and the total carbon emissions in the building phase were 7.4% higher than those in the operation phase”. This is quite confusing. Are the authors saying carbon emissions related to construction (upfront embodied emissions) were higher than operational emissions (heating lighting, cooling, small loads) at a national level in 2018? The term ‘the building phase’ is confusing, and should perhaps be replaced by upfront emissions, or other language consistent with the literature (i.e. see the WGBC report bringing embodied carbon upfront - https://worldgbc.org/article/bringing-embodied-carbon-upfront/)

Line 56 “According to a study, the carbon emissions of the same building phase in one year are equivalent to those of the operation phase in eight years[9]”. This is a 2012 study. More recent studies suggest upfront embodied carbon could be equivalent to 20+ years, if not longer. I suggest revising and looking at more recent embodied carbon studies. Monique Schmit’s work shows embodied carbon (upfront and recurring) is likely more than ALL operational emissions for contemporary Australian homes: https://doi.org/10.1016/j.enbuild.2020.110287

In 1.2.2. you refer to the ‘physical phase’ – again, I’m guessing this is upfront carbon (Stage A in EN15978). In short – there needs to be a consistency of language aligned with the literature and the discipline of embodied and whole lifecycle carbon emissions. Perhaps consistent with EN 15978 (i.e. product and construction stage – A, Use stage – B, End of life stage, C)

Line 65: “assembled buildings are considered as an effective carbon reduction approach” – do the authors mean prefabricated / modular? What does “assembled” mean in this context, surely all buildings are ‘assembled’? Likewise line 73 talks of “cast-in-place buildings” – does this mean conventionally built buildings, insitu on-site? Should the authors refer to prefabricated and non-prefabricated? Again, the need for consistent language will help the reader interrogate the research.

Line 82 “embedded carbon” – do the authors mean embodied carbon. Again, I stress the need for language consistent with the literature.

Line 92 “so some scholars also target on the stage measurement studies”. What are stage measurement studies? Carbon measurements of the whole building lifecycle?

Line 138: it’s valuable that the authors have summarised the overall findings of the literature here – I found this of great benefit when reading the paper

1.3 Research Purpose

The paper notes “The purpose of this study is to demonstrate the accuracy of the empirical data collected and to fill the data gaps in the field through the use of accurate primary data compared to traditional simulation methods” How was this accuracy accounted for? It is not discussed again in the paper? It seems the purpose of the study is to compare the upfront / embodied carbon of a prefabricated and non-prefabricated building?

Section 2.2

Line 199: “The materialization phase of a building usually includes the production phase, the

transportation phase and the construction phase.” Again, I suggest aligning with EN 15978 and calling this Stage A: the production and construction stage (also, cradle to site). A diagram of lifecycle stages as per EN 15978 and noting which stages are included in this study, and which are excluded would be beneficial

Line 208 “is calculated from the beginning of the original building materials to the end of the project completion” – this should be defined as cradle to end of completion – or upfront embodied carbon (A1 – A5).

Figure 2 and the definition of inclusions (E1 – E7) is very useful – although E3 comes before E2?

The method also needs to articulate inclusions and exclusions as per building elements. So does this include substructure, structure, façade, MEP, finishes, fit out? On line 330 you note “As this study only considered the space separation and enclosure insulation function of the foundation, further aesthetics, comfort and economy were not included” but this is unclear. What parts of the building are excluded, and why?

Results

Where do the carbon emission factors in Table 6 and 17 come from? What is the database used?

Table 7 – what does ‘living’ mean?

Table 8 – I imagine “share of based on total power” could be better worded. Is this meant to say “Share of total power allocated to building / component”. In additional, the numbers in table 8 need metrics. What is installed power measured in? In fact all tables need better metrics – what are the numbers ‘production line labour’ measuring?

Table 9, 10, 11 etc – what does percentage of Qi mean? Again, can this be worded differently, so it’s clear to the reader?

Where does the carbon emission factor of 0.104 come from in table 14. Is the unit of metric KgCo2e/tkm? Again, units are essential.

Line 420. The results say the final emissions are 255kgCO2/m2. Is this CO2e or CO2? In addition, is this per unit GFA or NLA? This is important for comparisons with other studies.

A figure of 255 is reasonable, but in the scheme of upfront embodied carbon data can be considered quite low. Rock et al (https://doi.org/10.1016/j.apenergy.2019.114107) show in the literature the typical embodied carbon of office buildings is around 17kgCO2e/m2/annum – so over 50 years would be in the region of 850kgCO2e/m2. LETI’s embodied carbon targets suggest A1-A5 figures of between 100 to 1300 for offices (https://www.leti.uk/_files/ugd/252d09_25fc266f7fe44a24b55cce95a92a3878.pdf), meaning 255 would be ‘A’ rated, which is exceptional performance. Data from Europe found for office buildings found similar figures https://zenodo.org/record/5895051#.Y2eAMuRBxPY

I suspect the low figure of 255 is due to exclusions of MEP, finishes, etc – but the authors need to discuss this in the context of the literature. This is important and is essential for inclusion.

The inclusion of carbon seems to include workers living emissions in the factory. If this is true, it should be highlighted in the study in a clearer way (perhaps in E1 – E7), as this is quite a unique element.

While part 3 is titled results, it’s mostly a more detailed methodology. I would encourage the authors to reframe section 3 as ‘embodied carbon calculations’ and then part 4 could remain as results and discussion?

4 Results and Discussion

The result that the prefab building has a 10% lower embodied carbon seems reasonable

Figure 8 is quite confusing. What do the two different shades of bar mean? The key refers to dots at the top of the bars, but surely could be better aligned to the shading in the bars. Both lines of text in the key say the same thing. In addition, consistent language will help the reader. Rather than cast in place, could the two options be called ‘prefabricated’ and ‘non-prefabricated’ or similar? Regardless, they need to be consistently listed throughout.

The discussion section is too long – the authors need to pull out key findings here, not do a comprehensive examination of each section. Figure 10 and 11 are not telling the reader much information. The authors also need to compare their findings to similar studies in this section (see also discussion above)

Is the figure note in figure 14 correct? It says this is the transportation emissions, but I don’t think this is correct?

Conclusion

The authors note the impact of steel versus concrete in the results. This brings up the question – is the reduction in emissions really down to prefabrication, or a change in material (from concrete to steel)? Would a steel frame built on site (insitu) have similar savings? This will be important to address.

A further limitation is the assessment method seems to be process-based (and not hybrid). This should be acknowledged (referring again to the work of Lenzen)

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The paper still lacks novelty. The paper needs to be refocused.

Reviewer 3 Report

The authors did a great job in improving the manuscript based on all reviewers' comments and concerns. The only suggestion (optional) I have is to use more related references in the introduction section. I think the paper can be improved by covering BIM-based technological resources. I mentioned some references in my previous review and which authors used them. Please try to use more references from 2019–2022. To help with this task I suggest some articles:

Estimation of carbon footprint of residential building in warm humid climate of India through BIM

Interactions of Sustainability and BIM in Support of Existing Buildings

Carbon emission reduction in prefabrication construction during materialization stage: A BIM-based life-cycle assessment approach

From BIM to extended reality in AEC industry

Using BIM to research carbon footprint during the materialization phase of prefabricated concrete buildings: A China study

BIM-integrated LCA to automate embodied carbon assessment of prefabricated buildings

Reviewer 4 Report

Figure 1 and Figure 2 are not present in the manuscript. I'm okay to the answers given, this is why I suggest only a minor revision.