Surface Energy Balance of Green Roofs Using the Profile Method: A Case Study in South Korea During the Summer

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study introduces an experimental research on estimation of green roofs surface energy balance, covering both sensitive and latent heat fluxes impacted by varied roof types. The quantitative analysis could facilitate the enabling of green roofs' advantages, if properly used as a cost-effective post-evaluation tool for green buildings.

In the conclusion part, are the quantitatively comparative conclusions sensitive to or impacted by local experimental conditions, e.g. the climate?

If possible, pls add some explanation on the conclusions' expandability if used to other regions having similar or different climate characters to SK. 

Author Response

Reviewer 1

This study introduces an experimental research on estimation of green roofs surface energy balance, covering both sensitive and latent heat fluxes impacted by varied roof types. The quantitative analysis could facilitate the enabling of green roofs' advantages, if properly used as a cost-effective post-evaluation tool for green buildings.

In the conclusion part, are the quantitatively comparative conclusions sensitive to or impacted by local experimental conditions, e.g. the climate?

Answer: Thank you for the reviewer’s comments. Yes, of course, the conclusion can be affected by local experimental conditions such as climate, soil and vegetation, surrounding environment and so forth because the methodology in this study heavily depends on temperature and humidity and their vertical profiles. Therefore, every condition that is related to temperature and humidity has impacts on the results. However, the main finding of the study that the vegetation (green roof) increases the portion of latent heat flux is expected to remain valid in any condition.

If possible, pls add some explanation on the conclusions' expandability if used to other regions having similar or different climate characters to SK.

Answer: The authors included the above comments in the conclusion section. Thank you for the comments (please see lines 457-461).

Reviewer 2 Report

Comments and Suggestions for Authors

This study employed the flux profile method to estimate the surface energy balance of green roofs, with a case study in South Korea. The following comments should be taken into account:

1. Title: The term “Measurements at Two Points” is not sufficiently clear.
2. Abstract: Include key data to better describe the results.
3. Introduction: Provide a precise and concise definition of green roofs.
4. Introduction: Include a review of existing methods for measuring roof temperature.
5. Introduction: The objective and contributions of this study should be more clearly stated at the end of the introduction.
6. Materials and Methods: The text in lines 78-80 repeats that in lines 67-69.
7. Figure 1: This figure does not provide enough critical information.
8. Figure 2: Provide a vertical view of the experimental subjects to facilitate comparison and observation.
9. Lines 90-103: A table would better describe the experimental parameters.
10. Section 2.2: The authors present specific equations. How were the calculations carried out using these equations? Describe the key procedures and the software package used.
11. Results: The experiment appears to have been conducted only over 7 days, from August 19 to August 26, 2020. This short experimental period can considerably increase the uncertainty and errors in the results. Furthermore, did the authors consider the performance of green roofs in different seasons?
12. Discussion: Provide design suggestions for green roofs based on the results and sensitivity analysis.
13. Conclusions: The key findings need to be better summarized, and the limitations of the study should be highlighted.

Comments on the Quality of English Language

 The English could be improved to more clearly express the research.

Author Response

This study employed the flux profile method to estimate the surface energy balance of green roofs, with a case study in South Korea. The following comments should be taken into account:

1. Title: The term “Measurements at Two Points” is not sufficiently clear.

Answer: Thank you for the reviewer’s comments. The authors changed the title to make it clearer as follows: Estimation of Surface Energy Balance of Green Roofs Using the Profile Method: A Case Study in South Korea (please see lines 2-3).

1. Abstract: Include key data to better describe the results.

Answer: The authors included the key results in the abstract as the reviewer’s comment (please see lines 17-18).

1. Introduction: Provide a precise and concise definition of green roofs.

Answer: The authors included the definition of green roof as the reviewer’s comment (please see lines 30-31).

1. Introduction: Include a review of existing methods for measuring roof temperature.

Answer: Roof surface temperatures can be measured using infrared (IR) thermometers, thermal imagers, or contact thermometers. The IR thermometers can provide a temperature reading quickly without any contact but not as accurate as contact measurements. Contact thermometers are classified based on the sensor type used for the measurement, i.e., the thermocouple, resistance temperature detector (RTD) or thermistor. Selecting the proper sensor type is the first important step and depends mainly on the application and additional factors like size, cost and accuracy. Most applications have a well-defined measurement range, accuracy requirement and physical size constraints. Thermocouples are the most widely used sensors because of their low cost and wide temperature range. This study adopted the T-type thermocouple to measure temperature (please see lines 137-147).

1. Introduction: The objective and contributions of this study should be more clearly stated at the end of the introduction.

Answer: The authors included the objective and contribution of this study at the end of the introduction as the reviewer suggested (please see lines 81-92).

1. Materials and Methods: The text in lines 78-80 repeats that in lines 67-69.

Answer: The authors really appreciate the comment. The text in lines 78-80 was revised (please see lines 95-98).

1. Figure 1: This figure does not provide enough critical information.

Answer: Thank the reviewer for the comment. The authors included the latitude and longitude for the grids in Figure 1 and included the exact location of the study area (please see Figure 1 and lines 106).

1. Figure 2: Provide a vertical view of the experimental subjects to facilitate comparison and observation.

Answer: Figure 2 was replaced by vertical views of the experiment (please see Figure 2).

1. Lines 90-103: A table would better describe the experimental parameters.

Answer: Please be understood that the corresponding lines describes information of the study site, which are not actually providing experimental parameters.

1. Section 2.2: The authors present specific equations. How were the calculations carried out using these equations? Describe the key procedures and the software package used.

Answer: Lines from 231-234 describe the calculation process.

 

1. Results: The experiment appears to have been conducted only over 7 days, from August 19 to August 26, 2020. This short experimental period can considerably increase the uncertainty and errors in the results. Furthermore, did the authors consider the performance of green roofs in different seasons?

Answer: Thank you for the comments. Please be understood that this study focused on the green roofs’ thermal performance during summer season and all the monitoring data was collected intensively every five minutes (one week includes 2,016 monitoring data for each point and each monitoring item). Of course, the authors now envision further study to explore monitoring data during different seasons including spring, fall and winter and inter-seasonal comparison.

1. Discussion: Provide design suggestions for green roofs based on the results and sensitivity analysis.

Answer: Thank you for the comments. This study analyzed extensive green roofs with shallow soil depths. The results indicate that even green roofs with shallow soil depths perform well to reduce the sensible heat flux that warms the surrounding atmosphere (for example, about 12% decrease in sensible heat flux for the grass roof). Of course, further study on intensive green roofs needs to follow up but the results suggest that extensive green roof with low costs and less maintenance efforts is a good option to mitigate urban heat island effects in urban environments. The sensitivity analysis focused on two parameters: albedo is most important parameter that determines the net radiation. The second parameter was roughness height because it was not clear how to determine the value of it. The sensitivity analysis revealed that optimum values for the both parameters lie within a reasonable range.

1. Conclusions: The key findings need to be better summarized, and the limitations of the study should be highlighted.

Answer: The authors revised the conclusion following the reviewer’s comments. Thank the reviewer again for the comments (please see 452-454).

Reviewer 3 Report

Comments and Suggestions for Authors

This study presents an innovative approach to estimating the surface energy balance of green roofs using a simplified flux profile method. The flux profile method is presented as a novel and practical approach to estimating the surface energy balance of green roofs, which is a key contribution to the field. This methodology reduces the need for costly equipment and provides an accessible tool for evaluating green roof performance. The authors have constructed four independent buildings with different roof types to ensure minimal interference from other structural factors. This approach enhances the reliability of the experimental results. The sensitivity analysis of albedo and surface roughness is a valuable addition, providing insights into the physical properties of different roof types and validating the flux profile method further. Overall a minor revision is recommended for publication.

Here are a few of my questions and comments, and I hope the author will add details to the article as well.
1. It is recommended that the authors add to the introduction the significance of estimating sensible and latent heat fluxes for green roofs. 

2. The estimated values of shortwave radiation for the four roofs in Figure 13 are compared to the measured values, but the measured values are only available for Building 2. How do the other three roofs compare?

3. Figure 14 shows the results of a sensitivity analysis of albedo for which type of roof?

4. P7, L211: To in equation 13 is the temperature of the roof surface, where exactly is the “roof surface”? If I understand correctly it should be the upper surface of the concrete, not the upper surface of the plant. 

5. The section numbering is by mistake.

6. It is recommended to add a description of the current status of relevant research in the last three years.

Author Response

This study presents an innovative approach to estimating the surface energy balance of green roofs using a simplified flux profile method. The flux profile method is presented as a novel and practical approach to estimating the surface energy balance of green roofs, which is a key contribution to the field. This methodology reduces the need for costly equipment and provides an accessible tool for evaluating green roof performance. The authors have constructed four independent buildings with different roof types to ensure minimal interference from other structural factors. This approach enhances the reliability of the experimental results. The sensitivity analysis of albedo and surface roughness is a valuable addition, providing insights into the physical properties of different roof types and validating the flux profile method further. Overall a minor revision is recommended for publication.

Here are a few of my questions and comments, and I hope the author will add details to the article as well.
1. It is recommended that the authors add to the introduction the significance of estimating sensible and latent heat fluxes for green roofs. 

Answer: The authors thank the reviewer for the comments. The authors included a paragraph as the reviewer recommended (please see lines 71-80).

2. The estimated values of shortwave radiation for the four roofs in Figure 13 are compared to the measured values, but the measured values are only available for Building 2. How do the other three roofs compare?

Answer: The authors thank the reviewer for the comments. The incoming solar radiation is available for Building 2 only as the reviewer commented. The net radiation is obtained by Equation 3 (multiplying 1-the albedo for each roof) for each roof assuming that incoming solar radiation is same for all four buildings.

3. Figure 14 shows the results of a sensitivity analysis of albedo for which type of roof?

Answer: Figure 14 is for the concrete roof (please see Figure 14). The title of Figure 14 is as follows: Figure 14. Comparison of the observed and estimated net radiation for the concrete roof, which shows the sensitivity to the value of albedo.

4. P7, L211: To in equation 13 is the temperature of the roof surface, where exactly is the “roof surface”? If I understand correctly it should be the upper surface of the concrete, not the upper surface of the plant. 

Answer: Thank the reviewer for the comments. T₀ is the temperature of the upper surface of the concrete as the reviewer commented. The authors added the term in the manuscript for clarity (please see lines 239)

5. The section numbering is by mistake.

Answer: Corrected.

6. It is recommended to add a description of the current status of relevant research in the last three years.

Answer: Thank the reviewer for the comments. However, the proposed methodology was rarely applied to green roof studies recently. The authors included the status of relevant research and clarify the aims of this study more in detail (please see lines 71-92).

Reviewer 4 Report

Comments and Suggestions for Authors

Review comments

 

In this manuscript, the authors present the flux profile method as a practical approach for estimating the surface energy balance of green roofs, addressing the limitations of costly monitoring systems by relying simply on basic measurements at two points. The authors studied three typologies of roof, i.e. bare concrete, high-reflective painted, and two types of green roofs (short bamboo and grass) taking into account environmental factors including solar radiation, wind, and air temperature, by means of experimental measurements.

The article deals with the combined application of flux profile method which leads to conclusions that are expected from the point of view of heat transfer, so its contribution is not very new.
However, the conclusions highlight that the results obtained can be useful parameters for comparison and applications in similar cases (buildings-urban areas).

The paper is some interesting and fits the scope of the journal.

The state of the art is quite-well documented, presenting a sufficient number of references previously published. In this way, the reader can be placed in the research environment correctly.

 

Minor revisions:

 

Regarding the references:

 

• I suggest adding some basilar references that that can clarify and complete a broader view on the possibilities, criticalities and limits of the application of the flux profile method previously carried out by other authors to different examples.

Regarding content aspects:

 

• the term “building” should be replaced with text box, which is much more pertinent to the object chosen for the experimental set-up and campaign of measures.

 

• the authors should justify the dimensions of the cube chosen to perform all the experimental measurements.

 

• a much more detailed explanation is needed for section “2. Net radiation and flux profile method.” (at page 5, starting from line 160)
• 
  the authors should deepen the aspects related to the accuracy, sequentiality and repetitiveness of the measurements they conducted. Furthermore, the experimental data error analysis is necessary to evaluate the goodness and robustness of the experimental method they applied.

 

Regarding formal aspects:

• 
  the authors should improve the quality of Table 3, explaining the percentage values ​​reported in round brackets

 

• all text needs re-editing for the English Style

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Review comments

 

In this manuscript, the authors present the flux profile method as a practical approach for estimating the surface energy balance of green roofs, addressing the limitations of costly monitoring systems by relying simply on basic measurements at two points. The authors studied three typologies of roof, i.e. bare concrete, high-reflective painted, and two types of green roofs (short bamboo and grass) taking into account environmental factors including solar radiation, wind, and air temperature, by means of experimental measurements.

The article deals with the combined application of flux profile method which leads to conclusions that are expected from the point of view of heat transfer, so its contribution is not very new.
However, the conclusions highlight that the results obtained can be useful parameters for comparison and applications in similar cases (buildings-urban areas).

The paper is some interesting and fits the scope of the journal.

The state of the art is quite-well documented, presenting a sufficient number of references previously published. In this way, the reader can be placed in the research environment correctly.

 

Minor revisions:

 

Regarding the references:

 

• I suggest adding some basilar references that that can clarify and complete a broader view on the possibilities, criticalities and limits of the application of the flux profile method previously carried out by other authors to different examples.

Regarding content aspects:

 

• the term “building” should be replaced with text box, which is much more pertinent to the object chosen for the experimental set-up and campaign of measures.

 

• the authors should justify the dimensions of the cube chosen to perform all the experimental measurements.

 

• a much more detailed explanation is needed for section “2. Net radiation and flux profile method.” (at page 5, starting from line 160)
• 
  the authors should deepen the aspects related to the accuracy, sequentiality and repetitiveness of the measurements they conducted. Furthermore, the experimental data error analysis is necessary to evaluate the goodness and robustness of the experimental method they applied.

 

Regarding formal aspects:

• 
  the authors should improve the quality of Table 3, explaining the percentage values ​​reported in round brackets

 

• all text needs re-editing for the English Style

Author Response

In this manuscript, the authors present the flux profile method as a practical approach for estimating the surface energy balance of green roofs, addressing the limitations of costly monitoring systems by relying simply on basic measurements at two points. The authors studied three typologies of roof, i.e. bare concrete, high-reflective painted, and two types of green roofs (short bamboo and grass) taking into account environmental factors including solar radiation, wind, and air temperature, by means of experimental measurements.

The article deals with the combined application of flux profile method which leads to conclusions that are expected from the point of view of heat transfer, so its contribution is not very new.
However, the conclusions highlight that the results obtained can be useful parameters for comparison and applications in similar cases (buildings-urban areas).

The paper is some interesting and fits the scope of the journal.

The state of the art is quite-well documented, presenting a sufficient number of references previously published. In this way, the reader can be placed in the research environment correctly.

Minor revisions:

Regarding the references:

• I suggest adding some basilar references that that can clarify and complete a broader view on the possibilities, criticalities and limits of the application of the flux profile method previously carried out by other authors to different examples.

Answer: Thank the reviewer for the comments. The authors included a new paragraph that compares direct and indirect method to estimate energy fluxes as well as advantages and disadvantages of the methods (please see lines 71-80).

Regarding content aspects:

• the term “building” should be replaced with text box, which is much more pertinent to the object chosen for the experimental set-up and campaign of measures.

Answer: The authors agree with the reviewer’s comment and included the term “concrete boxes” in the title of Figure 1 (please see Figure 2) but kept the term building for the remaining part of the manuscript.

• the authors should justify the dimensions of the cube chosen to perform all the experimental measurements.

Answer: Please understand that the dimensions of the cube were determined based on the timeline and budget of the research funding and regulation of the research institute (Yeungnam University). Any structure with a height over one meter requires complicated application and admission processes for construction. Instead, the authors tried to exclude lateral energy exchange with insulation as much as possible.

• a much more detailed explanation is needed for section “2. Net radiation and flux profile method.” (at page 5, starting from line 160)

Answer: Section 2.2 suggests the equations for the calculation of the sensible heat flux, latent heat flux and the ground heat flux with the procedures (please see lines 231-234). Please refer to the references for more detailed background information.

• the authors should deepen the aspects related to the accuracy, sequentiality and repetitiveness of the measurements they conducted. Furthermore, the experimental data error analysis is necessary to evaluate the goodness and robustness of the experimental method they applied.

Answer: The authors agree with the reviewer’s comments on the experiment issues. Before installation of green roofs and high reflective paint, the temperatures from four buildings were compared and the result showed same thermal behavior in and outside of the buildings. The temperature was crosschecked with other methodologies such as IR thermometers and thermal images and showed a good agreement with each other (please see lines 161-165). All the required monitoring data was recorded simultaneously during the study period including temperatures, humidity, solar radiation and wind speed using data loggers (please see Figure 5, lines 175-185).

 Regarding formal aspects:

• the authors should improve the quality of Table 3, explaining the percentage values ​​reported in round brackets

Answer: Thank the reviewer for the comments. The authors corrected the title of Table 3 to provide the information inside the brackets.

• all text needs re-editing for the English Style

Answer: Thank the reviewer for the comments. The authors went through the manuscript for a consistent English Style.

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

As the authors comfirmed that this study focused on the green roofs’ thermal performance during summer season, They should underline this in the paper title.

Comments on the Quality of English Language

 The English could be improved to more clearly express the research.

Author Response

Comment 1: As the authors comfirmed that this study focused on the green roofs’ thermal performance during summer season, They should underline this in the paper title.

Response 1: Thank for the comments. The authors changed the title as follows:"Surface Energy Balance of Green Roofs Using the Profile Method: A Case Study  in South Korea During Summer"