Digital Twins from Building to Urban Areas: An Open Opportunity to Energy, Environmental, Economic and Social Benefits

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

General Comments

This is a review article addressing a current and relevant topic. The authors have produced an article with an updated overview of digital twin developments, from Building Digital Twins (BDTs) to Urban Digital Twins (UDTs), identifying convergences, divergences, and future directions.

I consider it an interesting contribution, especially for the inclusion of a discussion of economic and social aspects.

The presentation and organization of the text are good, contributing to readability and comprehension.

The methodology consists of a systematic review, presented throughout the article, according to the topic addressed. In Section 1, Introduction, the authors presented a contextualization of the topic and delimited the article's specific contribution.

Comments 1 – Text organization and methodology

Although I consider the text to be well organized and presented, since the methodology is distributed throughout the text, I suggest the authors add a final paragraph introducing the article's sections. From a methodological standpoint, it would be interesting to cite the number of articles reviewed by topic.

Author Response

This is a review article addressing a current and relevant topic. The authors have produced an article with an updated overview of digital twin developments, from Building Digital Twins (BDTs) to Urban Digital Twins (UDTs), identifying convergences, divergences, and future directions. I consider it an interesting contribution, especially for the inclusion of a discussion of economic and social aspects. The presentation and organization of the text are good, contributing to readability and comprehension. The methodology consists of a systematic review, presented throughout the article, according to the topic addressed. In Section 1, Introduction, the authors presented a contextualization of the topic and delimited the article's specific contribution.

Question #1: Although I consider the text to be well organized and presented, since the methodology is distributed throughout the text, I suggest the authors add a final paragraph introducing the article's sections. From a methodological standpoint, it would be interesting to cite the number of articles reviewed by topic.

Answer #1: Dear reviewer, thank you for your precious comments. We agreed to follow your suggestion to improve the quality of the work. After paragraph 1.4 Scope of the work a new one has been added 1.5 Review methodology, in which the selection criteria and analysis of the chosen sources is reported. Then, we added the 1.6 Organization of the work in which the organization of the paper is described.

Reviewer 2 Report

Comments and Suggestions for Authors

This reviewer thoroughly enjoyed reading your work. The research is a systematic review that focuses on understanding how Digital Twins (DT) technology can be effectively applied in the management of environments, from individual buildings to entire urban areas, to maximize energy, environmental, economic, and social benefits.

The topic is relevant. It consolidates previous reviews that generally focused on the technical scope of Digital Twins and analyzes the gap in the integration of social and scale dimensions in the implementation of DTs.

While the work provides a systematic review of literature and case studies, it is important to identify the information selection/search parameters to validate the quality and relevance of the selected sources. Clearly, the absence of the source selection methodology also makes it difficult to understand the inclusion and exclusion criteria for studies.

Furthermore, a more in-depth analysis of the specific metrics used by the original sources to measure social and technical impacts is important, which would consequently strengthen the conclusions.

The conclusions are coherent and derive directly from the literature review and the cases discussed. The technical and social challenges are well summarized, and existing gaps, such as the incorporation of social dimensions and scalability, are highlighted. This answers the main question of how to advance the comprehensive application of TDs in urban environments.

Author Response

This reviewer thoroughly enjoyed reading your work. The research is a systematic review that focuses on understanding how Digital Twins (DT) technology can be effectively applied in the management of environments, from individual buildings to entire urban areas, to maximize energy, environmental, economic, and social benefits. The topic is relevant. It consolidates previous reviews that generally focused on the technical scope of Digital Twins and analyzes the gap in the integration of social and scale dimensions in the implementation of DTs.

Question 1: While the work provides a systematic review of literature and case studies, it is important to identify the information selection/search parameters to validate the quality and relevance of the selected sources. Clearly, the absence of the source selection methodology also makes it difficult to understand the inclusion and exclusion criteria for studies.

Answer #1: Dear reviewer, thank you for your comments. We really appreciate your efforts aimed at increasing the quality of the work. This paper is not presented as a systematic review but rather as a narrative review. Unlike systematic reviews, it does not follow rigid protocols or include quantitative meta-analysis. Instead, it adopts a flexible approach that enables the selection, grouping, and interpretation of sources to build a coherent narrative. Through this perspective, the study highlights research gaps and offers a comprehensive overview of the topic, supported by illustrative case studies. However, we added a new paragraph 1.5 Review methodology where the selection criteria and analysis of the sources is discussed.

 

Question #2: Furthermore, a more in-depth analysis of the specific metrics used by the original sources to measure social and technical impacts is important, which would consequently strengthen the conclusions.

Answer #2: We have enriched Chapter 3 with a more detailed analysis of the specific metrics reported in the reviewed studies, where available. A recurring limitation is that many papers do not present quantitative results, focusing instead on qualitative explanations of the expected outcomes, especially when related to the evaluation of social aspects. Nevertheless, we have incorporated additional information wherever possible to improve clarity. We consider that readers interested in further details should refer directly to the original studies, while our contribution is to provide a structured set of sources that collectively support and demonstrate the thesis of the paper.

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

This paper provides an updated overview of Digital Twin (DT) developments, ranging from Building Digital Twins (BDTs) to Urban Digital Twins (UDTs), with the aim of identifying convergences, divergences, and future directions. It’s a good attempt to expand the concept of DT at a broader spatial scale. However, the authors may consider addressing the following comments.

• In the introduction section, start by presenting the rationale for expanding the DT concept from a single asset level to a city level, and what prompted this thinking. While the intention is good, DT are largely applicable for built asset owners and operators and the multiple owners and operators at the city scale have practical challenges.
• Figure 1 – The reference to the smart city is pertinent. However, please clarify the value adds or overlaps between UDTs and smart cities. What core areas intersect?
• Table 1 – I am thinking about who the users of UDTs would be – is it the city or regional planning bodies, or built asset owners and operators? It appears to me as if UDTs are more suitable if there are environmental goals to be achieved across a larger scale. I am also thinking if extensive collaboration is necessary between the utility providers, public asset owners, and private asset owners. The outcomes, as mentioned in Table 1, are mostly about data and governance. Is it that UDTs are appropriate when there is a need to collate data and subsequently the data governance?
• The results mostly talk about building-level sustainability outcomes as a result of UDTs. What’s the benefit of having UDTs over BDTs?
• “This work presented the application of DT from the building scale to the urban area, highlighting this technology as an enabler for the energy transition and a more efficient urban future through predictive planning. “ I am not sure about this, and at what scale?
• Again, the conclusion is more about building level sustainability performance from UDTs. Please answer what implications it has on a broader scale?

Author Response

This paper provides an updated overview of Digital Twin (DT) developments, ranging from Building Digital Twins (BDTs) to Urban Digital Twins (UDTs), with the aim of identifying convergences, divergences, and future directions. It’s a good attempt to expand the concept of DT at a broader spatial scale. However, the authors may consider addressing the following comments.

Question #1: Figure 1 – The reference to the smart city is pertinent. However, please clarify the value adds or overlaps between UDTs and smart cities. What core areas intersect?

Answer #1: Dear Reviewer, thank you for seeking further clarification on some aspects of the work aimed at improving the quality of the paper. We agree that a precise delineation of the relationship between UDT and smart cities is one of the critical aspects of our work, considering that the first one is the technological evolution of the second one rather than its simple replacement. An addition has been made inside 1.3 Building and Urban Digital Twin describing the value adds and the overlapping areas of the BDTS and UDTs over smart buildings and smart cities.

 

Question #2: Table 1 – I am thinking about who the users of UDTs would be – is it the city or regional planning bodies, or built asset owners and operators? It appears to me as if UDTs are more suitable if there are environmental goals to be achieved across a larger scale. I am also thinking if extensive collaboration is necessary between the utility providers, public asset owners, and private asset owners. The outcomes, as mentioned in Table 1, are mostly about data and governance. Is it that UDTs are appropriate when there is a need to collate data and subsequently the data governance?

Answer #2: The reviewer correctly identifies two crucial user groups: high-level planning bodies and operational asset owners/operators. The UDT framework is designed, by definition, to serve both groups simultaneously through a multi-scale, cognitive approach:

1. UDTs support urban and regional planning by allowing stakeholders to analyze complex urban dynamics and systematically pre-assess new policies. Technology’s capacity for visualization and simulation of future urban scenarios, including effects on issues like sprawl and congestion, positions it as a vital decision-support tool for policymakers
2. For the asset owners and operators, the UDT acts as an AI-enabled City Information Modeling system. It supports the physical asset's entire life cycle, integrating real-time monitoring, prediction of failures, and the optimization of maintenance interventions.

For what concerns the second point of the question: the core argument is that the primary value proposition of an Urban Digital Twin transcends physical or purely technical simulations alone and fundamentally resides in its capacity to serve as a structured data integration and management platform. The urban environment is characterized by highly fragmented data sources (e.g., IoT sensors, public records, utility systems, social data). The UDT’s defining function is to bring these disparate streams together, standardize them, and create a single, consistent framework for utilization. This capability is indispensable for extending the twin's application to the human factor and territorial management. Considering the human dimension, such as citizen mobility, social interaction, energy equity, or health indicators, demands a reliable, initial dataset. It is fundamentally impossible to attempt complex territorial management and urban planning interventions, which rely on predicting human and social responses, without first establishing this robust data foundation. So, DTs are not just simulators; they represent the operating system that transforms chaotic urban data into actionable, trustworthy insights, thereby enabling the sophisticated, predictive governance detailed in our paper.

 

Question #3: The results mostly talk about building-level sustainability outcomes as a result of UDTs. What’s the benefit of having UDTs over BDTs?

Answer #3: the primary benefit of Urban Digital Twins (UDTs) over Building Digital Twins (BDTs) lies in their scope and ability to address inter-building and city-level phenomena that significantly impact building performance and sustainability. While BDTs are crucial for optimizing individual building performance, UDTs offer a superior advantage by modeling and simulating the complex, interconnected urban environment. This allows for the analysis of factors a BDT cannot fully capture:

1. Inter-building dependencies and synergy

• • UDTs model the entire district or city energy grid, including renewable energy sources, energy storage, and district heating/cooling networks. This allows for optimization of energy distribution, load balancing, and demand-side management at a scale impossible with individual BDTs.
  • UDTs enable the modeling of city-wide infrastructure for water supply, wastewater treatment, and waste collection, leading to optimized routing, resource recovery, and pollution control across the urban fabric.

2. Environmental factors
   • UDTs can quantify the impact of building materials, urban geometry, and green spaces on the UHI effect. This knowledge is vital for setting city-level policies (e.g., cool roof mandates) that improve the overall urban environment and reduce cooling loads on all buildings.
   • UDTs simulate how air pollutants move through street canyons and how building placement affects local air quality, informing sustainable planning decisions like site selection for sensitive buildings (hospitals, schools).
   • UDTs can model the shadowing impact of a new tall building on existing structures, which affects their solar gain, daylight availability, and subsequent energy demand. A BDT only knows its own location relative to the sun, not the context of surrounding shadows.
3. Urban Planning and Policy Making
   • Planners use UDTs to simulate the impact of changes in zoning codes, building height restrictions, or required setbacks on city-wide energy demand, traffic flow, and livability.
   • UDTs can simulate city-level phenomena like flood modeling, earthquake impact on infrastructure networks, or the best evacuation routes, which are beyond the scope of any single building model.

However, inside paragraph 1.3 Building and Urban Digital Twin a proper explanation of the BDTs over UDTs has been reported, in order to make the concept clearer for the reader.

 

Question #4: “This work presented the application of DT from the building scale to the urban area, highlighting this technology as an enabler for the energy transition and a more efficient urban future through predictive planning “. I am not sure about this, and at what scale?

Answer #4: We fully confirm that the central thesis of the paper is that Digital Twin (DT) technology is a fundamental enabler for the energy transition and a more efficient urban future through predictive planning. To address your question, "at what scale?", we specify that the analysis and the role of DT are examined at a dual and integrated (cross-scale) level, as highlighted in the title itself: from the building level to the urban area. The novelty of our study lies precisely in explicitly connecting these two perspectives.

1. Building Scale (Building Digital Twin - BDT)

At the individual building level (BDT), the enabling role of the DT is demonstrated through:

• • Energy Optimization and Predictive Maintenance: BDTs allow for continuous monitoring, predictive simulation, and dynamic optimization of high-energy-intensity systems (e.g., HVAC and lighting). For instance, using the DT for Model-Based Predictive Control can lead to a reduction in HVAC energy consumption of up to 25%.
  • Operational Efficiency: DTs enable predictive maintenance by identifying faults before they occur, extending the operational life of systems and reducing costs (with potential overall energy savings of up to 30%).

2. Urban Scale (Urban Digital Twin - UDT)

At the urban scale (UDT), the DT acts as a unifying layer that enables predictive planning and energy transition on a broader scale:

• • Integration and Energy Management: UDTs are a crucial tool for the integrated management of city-wide energy systems (e.g., smart grids, integration of distributed renewable sources).
  • Smart Simulation and Resilience: The distinctive value of UDTs is their smart simulation capability. This transforms the approach from a reactive monitoring system (like traditional Smart Cities) to a discipline of predictive and prefigurative governance. UDTs can, for example, model and predict the behavior of urban infrastructures and enhance Predictive Resilience by simulating thousands of crisis scenarios.

In summary, DTs act as an enabler that operates through the closed-loop control of bidirectional data for the real-time simulation and optimization of both the individual asset (BDT) and the complex system of urban interactions (UDT). The paper examines how this predictive capability is the key to achieving energy, economic, and social benefits. We hope that this clarification, supported by the data and structure presented in Sections 1 and 3 of the manuscript, satisfactorily addresses your doubt regarding the scale of application.

 

Question #5: Again, the conclusion is more about building level sustainability performance from UDTs. Please answer what implications it has on a broader scale?

Answer #5: The integration and analysis provided by UDTs move far beyond building-specific sustainability to address fundamental challenges in urban governance, resource security, and systemic resilience. UDTs enable predictive energy management across the entire urban grid. They can forecast aggregate energy demand and the fluctuating supply from distributed renewable sources (like rooftop solar). This foresight allows utility operators to optimize energy storage, prevent blackouts, and manage peak load events, a crucial step for integrating high penetrations of renewables into the traditional grid structure. By simulating different policy scenarios, UDTs can quantify the system-wide carbon reduction and identify the most cost-effective decarbonization pathways for the entire municipality, which is impossible to do by simply adding up individual building performances. UDTs serve as a powerful tool for evidence-based policymaking. For example, simulating the impact of a new urban development project (mixed-use zone, transit line) on traffic congestion, air quality, and local energy demand before construction begins. This shifts city planning from reactive corrections to proactive, predictive governance. On the city scale, UDTs are used to map and manage the flow of all critical resources: water, waste, and energy. This facilitates the development of a true urban circular economy by identifying inefficiencies, optimizing waste collection routes, and forecasting water stress in response to climate change models. UDT simulations can identify vulnerable populations affected by urban phenomena like the Urban Heat Island (UHI) effect. By modeling heat stress against income and demographic data, city planners can use the DT to target interventions (e.g., planting trees for shade, allocating cooling centers) to the neighborhoods most in need, thereby addressing environmental justice issues. So, the building level information feeds the UDT, aimed at providing the urban planning required for a more efficient and sustainable area.

Reviewer 4 Report

Comments and Suggestions for Authors

This paper systematically explores the application, architecture, benefits, and future challenges of Digital Twin (DT) technology at both building and urban scales, which falls well within the scope of the Applied Sciences journal. However, the following supplements or clarifications are required prior to formal acceptance:

 

1. While the goal of a review article is to integrate perspectives, build bridges, and offer forward-looking views rather than to present bibliometric data, the "narrative review" or "traditional review" approach adopted by the authors does present certain limitations:

    1.1. The case studies cited in the text are predominantly concentrated in Europe (e.g., Helsinki, Dublin, Rotterdam, Hamburg) and a few Asian cities (e.g., Singapore, Dubai). This raises the question of whether other regions (such as North America, South America, Africa, and most of Asia) lack relevant practices, or if the coverage is limited due to the authors' language capabilities or resource accessibility. This remains unclear.

    1.2. One of the paper's central arguments is the underexplored nature of the "social dimension". It is unclear whether this conclusion is based on a statistical analysis of the entire relevant literature or stems from the authors' subjective impression after reading. Employing bibliometric methods—such as analyzing the frequency and temporal trends of keywords related to "social" aspects—could quantitatively demonstrate the size and trajectory of this research gap, thereby strengthening the argument.

    1.3. The future directions pointed out in the article are judged based on objective signals from a large body of literature or the authors' personal foresight. Greater data support would strengthen these claims.

 

2. The current title gives equal weight to "Building" and "Urban areas," even placing "Building" first, which sets an expectation for a balanced discussion. However, the actual content demonstrates a clear emphasis on the urban scale. This discrepancy might lead readers to feel that the title does not fully reflect the paper's primary focus.

 

3. The overall structure of the review is quite clear. However, at the beginning of Chapter 3 ("The impacts"), adding a brief overview paragraph to explain the rationale behind the "energy-economic-social" sequence would enhance the reader's orientation. Furthermore, while the description of the architecture in Chapter 2 is clear, placing more emphasis on the differences between building-scale and urban-scale architectures—rather than just their similarities—would better reinforce the "cross-scale" theme.

 

4. Although the paper proposes a valuable "building-to-urban" cross-scale perspective, the discussion primarily remains at the level of parallel descriptions and conceptual appeals. A deeper exploration of *how* to achieve this cross-scale integration is needed. The authors should elaborate on the technical details and provide cases related to the data, models, and governance mechanisms that concretely link the two scales.

 

5. The mention of cutting-edge concepts like "Quantum Digital Twins" in the conclusion is very brief, and their connection to the main narrative appears weak. It is recommended to either provide a more substantial explanation of their relevance or consider removing them to maintain focus.

 

6. Several key statements lack sufficient referencing or data support. For instance, the claim that "The operations and maintenance (O&M) phase of a building can constitute up to 80% of its total lifecycle cost" (Line 408) is a strong assertion that requires citation from an authoritative source. Similarly, when discussing economic impacts, supplementing data from specific case studies with evidence from meta-analyses published in peer-reviewed journals would better support the generalizability of the conclusions.

 

7. The figures in the manuscript (e.g., Figures 2, 4, 5) are conceptual diagrams. While clear, they are relatively simplistic. It is recommended to enhance them; for example, Figures 4 and 5 could be merged or redesigned to more intuitively illustrate the trade-off between "high definition" and "cross-field approach," as well as how the human factor is embedded within this framework.

Author Response

This paper systematically explores the application, architecture, benefits, and future challenges of Digital Twin (DT) technology at both building and urban scales, which falls well within the scope of the Applied Sciences journal. However, the following supplements or clarifications are required prior to formal acceptance:

Question #1: While the goal of a review article is to integrate perspectives, build bridges, and offer forward-looking views rather than to present bibliometric data, the "narrative review" or "traditional review" approach adopted by the authors does present certain limitations:

Question #1.1: 1.1. The case studies cited in the text are predominantly concentrated in Europe (e.g., Helsinki, Dublin, Rotterdam, Hamburg) and a few Asian cities (e.g., Singapore, Dubai). This raises the question of whether other regions (such as North America, South America, Africa, and most of Asia) lack relevant practices, or if the coverage is limited due to the authors' language capabilities or resource accessibility. This remains unclear.

Answer #1.1: Thank you for your comment. We have updated the references and the case studies included in the analysis, as we believe that a broader context will enhance the overall quality of the article. However, we would like to clarify that this work is supported by an Italian national research fund in the energy sector (namely “Ricerca di Sistema”; the grant references have been added at the end of the paper). Consequently, we must align with the objectives and scope of the grant, which emphasize the potential impacts in the Italian context. For this reason, in the revised version we also highlighted the role and impact of DT in heritage buildings and districts.

 

Question #1.2: 1.2. One of the paper's central arguments is the underexplored nature of the "social dimension". It is unclear whether this conclusion is based on a statistical analysis of the entire relevant literature or stems from the authors' subjective impression after reading. Employing bibliometric methods—such as analyzing the frequency and temporal trends of keywords related to "social" aspects—could quantitatively demonstrate the size and trajectory of this research gap, thereby strengthening the argument.

Answer #1.2: The introduction of the “social” parameter into the analysis conducted on UDTs actually stems from a consideration derived from a communication and an article by Batty and Bettencourt, as reported in the references at entries [19] and [20]. Batty’s authority in the field, together with his discussion of the critical aspects, potential, and importance of this parameter in observing the evolution of the urban context, represents one of the main challenges for UDTs, as highlighted in the conclusions of the Review.

 

Question #1.3: 1.3. The future directions pointed out in the article are judged based on objective signals from a large body of literature or the authors' personal foresight. Greater data support would strengthen these claims.

Answer #1.3: The purpose of the review was to collect the main features that can describe the DT of urban areas as an evolution and up-scaling of the BDT, with a focus on the critical aspects and open perspectives of this topic. Efforts were made to compile the methods and the main available data within the common DT proxy for these entities, while also citing the most relevant use cases reported in the literature. Therefore, although additional use cases were included in response to Question 1.1, the authors maintain that a sufficient body of data has already been gathered to adequately present the primary objectives outlined in the review.

 

Question #2: The current title gives equal weight to "Building" and "Urban areas," even placing "Building" first, which sets an expectation for a balanced discussion. However, the actual content demonstrates a clear emphasis on the urban scale. This discrepancy might lead readers to feel that the title does not fully reflect the paper's primary focus.

Answer #2: As previously stated in response to Questions 1.1 and 1.3, the main focus of the review is not the building digital twin itself, but rather its role within a broader set of entities embedded in the urban area. For this reason, the title of the article is “From Buildings to Urban Areas”, emphasizing the transfer of information and data from the individual scale to the dynamics of the entire system.

 

Question #3: The overall structure of the review is quite clear. However, at the beginning of Chapter 3 ("The impacts"), adding a brief overview paragraph to explain the rationale behind the "energy-economic-social" sequence would enhance the reader's orientation. Furthermore, while the description of the architecture in Chapter 2 is clear, placing more emphasis on the differences between building-scale and urban-scale architectures—rather than just their similarities—would better reinforce the "cross-scale" theme.

Answer #3: We have addressed the first point by enriching the introduction to Chapter 3 ("The impacts") with a brief paragraph explaining the logical progression of the "energy-economic-social" topics, thereby enhancing reader orientation. Regarding the distinction between Building Digital Twins (BDTs) and Urban Digital Twins (UDTs), we agree that greater clarity is beneficial. We believe the most logical place for this emphasis is in Chapter 1, Section 1.3 Building and Urban Digital Twins, where the concepts are first introduced and defined, rather than in the architecture section. This placement will establish the foundational differences earlier and reinforce the paper's cross-scale theme from the outset.

 

Question #4: Although the paper proposes a valuable "building-to-urban" cross-scale perspective, the discussion primarily remains at the level of parallel descriptions and conceptual appeals. A deeper exploration of *how* to achieve this cross-scale integration is needed. The authors should elaborate on the technical details and provide cases related to the data, models, and governance mechanisms that concretely link the two scales.

Answer #4: Thank you for your comment. Technically speaking, the answer is in the structure of the script and the architecture of the software, and it is possible to refer to the examples from the cited literature (e.g. 19). Moreover, in the conclusion section (and the previous Question #2), it is stressed that the building and its information are transferred through data to the urban area, creating a dynamic system working on the interactions between the units and the whole

 

Question #5: The mention of cutting-edge concepts like "Quantum Digital Twins" in the conclusion is very brief, and their connection to the main narrative appears weak. It is recommended to either provide a more substantial explanation of their relevance or consider removing them to maintain focus.

Answer #5: Your observation is correct; however, the quantum declination of DT was only briefly introduced because research on QDT is still at a preliminary stage in most major fields, and a more detailed discussion could be misleading in the context of a consistent review article. Moreover, significant critical issues regarding QDT applications emerge from the referenced article ([113]), underscoring the need for further analysis before any concrete implementation can be planned. Nevertheless, given that the topic is both modern and trending, the authors chose to dedicate a few lines to it, while clearly acknowledging the current limitations of QDT.

 

Question #6: Several key statements lack sufficient referencing or data support. For instance, the claim that "The operations and maintenance (O&M) phase of a building can constitute up to 80% of its total lifecycle cost" (Line 408) is a strong assertion that requires citation from an authoritative source. Similarly, when discussing economic impacts, supplementing data from specific case studies with evidence from meta-analyses published in peer-reviewed journals would better support the generalizability of the conclusions.

Answer #6: We understand that the first statement “The operations and maintenance (O&M) phase of a building can constitute up to 80% of its total lifecycle cost” is a strong assertation. However, with a more detailed analysis in literature, we inserted two other articles [99,100], setting the O&M costs of a building in 60-80% of its total lifecycle cost.

We appreciate the suggestion to supplement specific case study data with evidence from meta-analyses to enhance the generalizability of our economic conclusions. While we recognize the value of meta-analyses, finding peer-reviewed studies that conduct a broad, quantitative synthesis specifically on the direct economic impacts (O&M cost reduction) of Building and Urban Digital Twins remains challenging due to the technology's relative novelty and the high variability in financial reporting across projects. However, it is crucial to note that the economic savings are intrinsically linked to the energy reduction data already provided. Since energy consumption is one of the largest components of operational costs, the quantifiable energy efficiency results reported inherently translate into significant, verifiable economic benefits for the building owners and operators.

 

Question #7: The figures in the manuscript (e.g., Figures 2, 4, 5) are conceptual diagrams. While clear, they are relatively simplistic. It is recommended to enhance them; for example, Figures 4 and 5 could be merged or redesigned to more intuitively illustrate the trade-off between "high definition" and "cross-field approach," as well as how the human factor is embedded within this framework.

Answer #7: Figure 2 has been kept in its original form since, in its simplicity, it immediately clarifies the differences among the various types of “twin.” Figures 4 and 5 have not been merged but have been improved. In particular, a new version of Figure 4 has been added alongside the previous one in order to highlight the possible trade-off between computational efficiency and high computational cost. Figure 5 has been qualitatively improved while maintaining the same conceptual message. Moreover, the central role of the human factor has been emphasized by placing the gear symbol at the center of the figure.

 

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Accept 

Reviewer 4 Report

Comments and Suggestions for Authors

Accept the paper in present form.