Analysis of Incorporating a Phase Change Material in a Roof for the Thermal Management of School Buildings in Hot-Humid Climates

Round 1

Reviewer 1 Report

This study evaluated by simulation the use of PCM in roofs as a route to regulate the energy needs of school buildings. This is an interesting topic aligned with the journals’ scope. Nonetheless, the novelty of the present study not fully perceived. Moreover, the introduction should be better organized and focused, as it is too long in the current version. The conclusions also need to be revised. These and other comments are outlined below:

 

1. In the abstract the authors state that most of the studies have been performed on walls. While this is indeed true, the introduction also shows that there are already several papers dealing with PCMs on roofs. It is suggested to better describe the novelty of the present study compared to literature.
2. In the same section it should say “phase change materials (PCMs)” instead of “PCM (phase change materials)
3. The abbreviation PCT should be defined in its first appearance in the manuscript, in this case in the abstract.
4. As mentioned in my general assessment the introduction would be easier to read if the authors organised its content in a more logical way. While including previous literature studies is needed, the number of cited references should be reduced to the most relevant ones in the topic and particularly those dealing with PCM incorporation on roofs. Then, the merits of each of the selected papers should be briefly described. In addition, the existing research gap needs to be clarified.
5. Throughout the manuscript some information is repeated, in some cases multiple times, and this is detrimental to the quality of the manuscript. For example: the first paragraph of section 2.1 repeats the info provided in table 1. The same for the first paragraph of section 2.2.
6. In the same section the authors state that “BioPCM” was selected. This is not enough. Please provide additional insights on the selected PCM (e.g. microencapsuled or non-encapsuled PCM). How would it be applied in a real-life application (incorporated in a matrix?)?
7. Page 5: in the text its says “cooling degree day (CDD”, however in Fig. the term “CDH27” is used. Please clarify.
8. Section 2.3.: “Concerning the latent storing and releasing capability of heat, it is unpopular to utilize the PCM layer with worse performance that storing or releasing a small amount of energy during the daily cycles.” Please better explain your idea.
9. In the same section the lines 218 to 225 are very confusing. First it says “where LC and LDC are the ratios of latent heat stored”, but then “LC and LDC are respectively the differences between the maximum and minimum values of effective latent storage during the heat storing and releasing periods in daytime and nighttime.” Please revise.
10. Looking at Fig. 7 there is an increasing trend on the temperature upon cycling over the three days period and this raises concerns about the real impact of the PCM under longer cycling. In fact the differences between the “no PCM” and the “PCM” scenarios seem to decrease with time, particularly in the cooling phase.
11. The authors suggest the use of a 20 mm PCM layer. A brief comment on the cost for such application would be beneficial.
12. Conclusions: please keep in mind that the conclusions should briefly summarize the main findings of the research. They should not extensively detail the results as this has been already done in the “results and discussion” section.

Author Response

(Please check the revised manuscript in attachment)

Comments on title: Analysis of roof incorporating phase change material for thermal management of school buildings in hot-humid climates

Thank you for giving us the opportunity to submit a revised manuscript, and we appreciate the reviewer’s insightful comments and suggestions to improve the paper and clarify the contents of our research.

Reviewer #1:

This study evaluated by simulation the use of PCM in roofs as a route to regulate the energy needs of school buildings. This is an interesting topic aligned with the journals’ scope. Nonetheless, the novelty of the present study not fully perceived. Moreover, the introduction should be better organized and focused, as it is too long in the current version. The conclusions also need to be revised. These and other comments are outlined below:

1. In the abstract the authors state that most of the studies have been performed on walls. While this is indeed true, the introduction also shows that there are already several papers dealing with PCMs on roofs. It is suggested to better describe the novelty of the present study compared to literature.

Response:

Thank you for your advice. We revised and supplemented the contents in the abstract to describe the novelty of this study. The corrections are as follows: (p.1, lines 10~18)

“… Regarding the situation in Taiwan, there is no practical utilization of PCM in school buildings, especially the combination with rooftop. In this paper, we aim at discussing the feasibility and utilization potential of installing the PCM in rooftop of school buildings. The school buildings located in northern and southern Taiwan (Taipei and Kaohsiung) are selected as objective cities to analyze the energy-saving potential and indoor thermal comfort through installing PCM with different properties in rooftop under two time periods, including air-conditioning (AC) season and natural ventilation (NV) season. Based on the simulation results, the feasible patterns of PCM simultaneity appropriate for better indoor comfort and energy-saving potential during different seasons are proposed. … ”

 

2. In the same section it should say “phase change materials (PCMs)” instead of “PCM (phase change materials)

Response:

Thank you for pointing it out. We have corrected the words.

PCM (phase change materials) → Phase change materials (PCMs) (p.1, line 9)

 

3. The abbreviation PCT should be defined in its first appearance in the manuscript, in this case in the abstract.

Response:

Thank you for pointing it out. We have added the definition of PCT in the abstract.

PCT → phase change temperature (PCT) (p.1, lines 18~19)

 

4. As mentioned in my general assessment the introduction would be easier to read if the authors organized its content in a more logical way. While including previous literature studies is needed, the number of cited references should be reduced to the most relevant ones in the topic and particularly those dealing with PCM incorporation on roofs. Then, the merits of each of the selected papers should be briefly described. In addition, the existing research gap needs to be clarified.

Response:

Thank you for your advice. We modified the contents of introduction to clarify the difference between previous research and this study; besides, some of the previous studies which is less relevant to this study have been deleted. In addition, the current situation of the utilization of PCMs in Taiwan is also supplemented.

The main revision of describing the research gap and novelty of this study is as follows: (p.3, lines 108~128)

“The previous studies mentioned above analyzed the energy-saving potential and the effect of improving thermal comfort resulted by the utilization of PCM; however, most of these studies are conducted under a specific season. Different from the previous research, this study aims at suggesting a feasible and economic pattern of PCMs for school buildings which can simultaneously fulfill the conditions during the AC and NV seasons to reduce the energy consumption and provide a better thermal comfort condition. In the view of the background that Taiwanese government intends to complete the installation of air-conditioning in 103,000 classrooms across the entire island by the summer of 2022 to create a comfortable learning environment. It is considered that the utilization of PCMs is helpful for raising the effect of energy-saving potential and indoor thermal condition. However, there are no existed practical cases of combining the PCMs and rooftop structure in Taiwanese school buildings. Thus, this study acts as a pioneer study to discuss the effect and feasibility of utilizing PCMs in the rooftop of Taiwanese school buildings, and attempts to suggest recommendations for the utilization strategies that the energy-saving potential and indoor thermal comfort are both taken into consideration. The investigated cases in this paper are set to analyzed the reducing cooling load during the air-conditioning season and improving the thermal comfort of real classrooms during the ventilation season. Based on the simulation results, it is expected to suggest the appropriate properties of PCMs for Taiwanese school buildings, including thickness and PCT. In addition, the feasible pattern of PCM which is proper to be utilized through the entire year is proposed to fulfill the indoor comfort and energy-saving potential.”

 

5. Throughout the manuscript some information is repeated, in some cases multiple times, and this is detrimental to the quality of the manuscript. For example: the first paragraph of section 2.1 repeats the info provided in table 1. The same for the first paragraph of section 2.2.

Response:

Thank you for pointing it out. We have revised the article and delete the repeat sentences.

 

6. In the same section the authors state that “BioPCM” was selected. This is not enough. Please provide additional insights on the selected PCM (e.g. microencapsuled or non-encapsuled PCM). How would it be applied in a real-life application (incorporated in a matrix?)?

Response:

Thank you for the suggestion. We have added the sentence of describing the BioPCM. (p.4, lines 151~156)

The reason why we selected BioPCM is because that it is generally utilized by several previous studies, and the databases of the BioPCM is complete.

 

7. Page 5: in the text its says “cooling degree day (CDD”, however in Fig. the term “CDH27” is used. Please clarify.

Response:

Thank you for pointing out the mistake. Figure 3 has been modified. (p.5)

In addition, the explanation of CDH27 is added in the article, the content is as follows: (p.5, lines 178~180)

“… CDH 27 is a statistic value in the weather data (TMY3). Besides, owing to this value is closed to the standard value that is regulated to turn on the air-conditioning (27°C~28°C); therefore, CDH 27 is set for the simulation in this study…”

8. Section 2.3.: “Concerning the latent storing and releasing capability of heat, it is unpopular to utilize the PCM layer with worse performance that storing or releasing a small amount of energy during the daily cycles.” Please better explain your idea.

Response:

Thank you for the advice. The explanation has been added. (p.6, lines213~214)

The revision is as follows:

“… Scilicet, the better performance of PCMs is that the heat storing at night is equivalent to the heat releasing during daytime. …”

 

9. In the same section the lines 218 to 225 are very confusing. First it says “where LC and LDC are the ratios of latent heat stored”, but then “LC and LDC are respectively the differences between the maximum and minimum values of effective latent storage during the heat storing and releasing periods in daytime and nighttime.” Please revise.

Response:

Thank you for pointing out the confusing sentences. The second explanation of LC and LDC (“LC and LDC are respectively the differences between the maximum and minimum values of effective latent storage during the heat storing and releasing periods in daytime and nighttime.”) is used to explain the calculation way of these value. However, it indeed confused the reader. This sentence has been deleted.

 

10. Looking at Fig. 7 there is an increasing trend on the temperature upon cycling over the three days period and this raises concerns about the real impact of the PCM under longer cycling. In fact the differences between the “no PCM” and the “PCM” scenarios seem to decrease with time, particularly in the cooling phase.

Response:

The reason that there is an increasing trend during the three days and the differences between the “no PCM” and the “PCM” scenarios decrease with time is because that the weather got hotter during 4/22 to 4/24. This result can explain the phenomenon that when the weather got hotter, the performance of PCMs get worse, due to the outdoor temperature at night is not low enough to release heat (please refer to the gray dash-line which represent the effective latent storage, η).

 

11. The authors suggest the use of a 20 mm PCM layer. A brief comment on the cost for such application would be beneficial.

Response:

Thank you for the advice. However, there are still no practical cases of utilizing the PCMs in Taiwanese school buildings, and PCMs is not a general material in Taiwan currently. The issue related to the cost will be a very important studies in our future works.

 

12. Conclusions: please keep in mind that the conclusions should briefly summarize the main findings of the research. They should not extensively detail the results as this has been already done in the “results and discussion” section.

Response:

We appreciate your advice. The contents in the section of conclusions have been summarized in a concise way.

(p.15~p.16, lines 511~542)

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

Thank you for the opportunity to review this work. This is a very interesting simulation study that aims to evaluate the impact of different PCM configurations on the indoor air temperature of school buildings in Taiwan. The study investigates different parameters and analyses the performance of the PCM installed at the school rooftops. An optimal combination of features is proposed according to the comfort and energy savings evaluation at a typical school building in two cities in Taiwan. The authors estimate the energy savings from air conditions for the optimal PCM features and show the benefits from the use of the specific PCM technology in both cooling and naturally ventilated seasons.

The structure of the manuscript is good and the story is coherent. Adequate amount of details is presented and the methods are well designed in general.

However, my biggest concern is the validity of the results as there has not been any effort to validate the simulation models. It would be expected that the simulation results would be compared against field measurements. Even if the model is based on an idealised archetype, it should still show that it has the key thermal characteristics and performance with the typical buildings. That could be a comparison of cooling loads/electricity consumption between simulated loads/energy and energy bills from typical school buildings for example. It is suggested to collect some temperature and RH observations from the “typical” school building and compare the indoor conditions for a period of time. A typical and an extreme week should be enough to gain some confidence on the results presented. I believe the lack of validation is a major concern for the publication of any simulation studies.

Please see some more specific comments below:

The English language need careful extensive editing as several parts are hard to understand. Please try to be more quantitative and specific. For example “numerous” studies would need to be backed up with literature references. “Superior” performance is rather generic and it does not make much sense. Superior to what and in what context.

What are the climate characteristics of Taiwan? It is suggested to describe the main climate characteristics for the two cities in the study.

What are the observed and modelled occupancy schedules of schools and the typical use of controls (window opening, thermostat settings)? Do the windows have restrictors for safety? Do the windows stay open during night but close when air conditioning is operating?

What is the expected internal temperature in school classrooms during occupancy hours and what is the comfort temperature range expectation ?

It would be useful to include a short description of BioPCM in terms of materials, maintenance, life expectancy, installation requirements etc.

What parameters affect the PCT change? Does PCT refer to air temperature or the temperature of the PCM?

What is the origin of the weather files and the period of observations for their creation? How does the min/max/median monthly temperature compare to an extreme weather year? Is the number of monthly CDD in the TMY3 files roughly equal to the last 10 years average?

How was the base temperature of 27 deg C selected for the CDD calculation? Is this according to local regulations?

Figure 3. I believe it would be useful to show this graph for hourly values in the hottest and coldest day of the TMY3 weather file. It is important to understand when (what time) the max temperature is reached in the classroom and show how the PCM smooths out the peak temperatures during the occupancy hours. It is suggested to show if possible in the same graph the diurnal hourly PCM temperature, the indoor air temperature, the outdoor temperature and the solar irradiance.

How were the releasing and storing time of heat calculated for this study? Are these given in the material specifications?

Is each classroom of the school considered as a single zone in EnergyPlus? One node temperature for the PCM in the middle of the zone roof? Would the existence of more zones in the simulation model affect the final results (grid sensitivity analysis)?

Line 238: This is unclear: do the authors mean “adaptive comfort model based on children’s perception” ?

Line 253: Does the standard refer to number of occupancy hours? Overheating thresholds are usually connected with the hours that the building is occupied only.

Line 275: It is suggested to remind the readers of the estimated CDD27 for each city.

Line 283: It would be useful to include a floorplan that shows the floors and classrooms simulated and the location of the simulated classroom. What are the boundary conditions for each zone?

Section 3.2: This is a very important part of the study and it is expected to provide details on the parameters and the different scenarios in the analysis. How and why have those been selected? A summary in a Table would be very helpful.

Line 320: I think it is not clear how “optimal” is defined in the study. It is suggested to add 1-2 sentences that explain what is considered optimal in this context.

Figure 7. Does the Figure show results from the simulations or observed values?

Line 410: At this point it would help to remind the readers what the CE and HE are.

Line 436: This sentence is an important finding but it is very hard to understand. It is suggested to reword it carefully please.

Line 479: Very interesting analysis. Does the capital and installation cost of the PCM configurations differ significantly and could this affect the overall estimated operational savings?

Thank you and I look forward to reading the revised version of your manuscript. 

Kind Regards,

Author Response

(Please check the revised manuscript in attachment )

Comments on title: Analysis of roof incorporating phase change material for thermal management of school buildings in hot-humid climates

Thank you for giving us the opportunity to submit a revised manuscript, and we appreciate the reviewer’s insightful comments and suggestions to improve the paper and clarify the contents of our research.

Reviewer #2:

1. Thank you for the opportunity to review this work. This is a very interesting simulation study that aims to evaluate the impact of different PCM configurations on the indoor air temperature of school buildings in Taiwan. The study investigates different parameters and analyses the performance of the PCM installed at the school rooftops. An optimal combination of features is proposed according to the comfort and energy savings evaluation at a typical school building in two cities in Taiwan. The authors estimate the energy savings from air conditions for the optimal PCM features and show the benefits from the use of the specific PCM technology in both cooling and naturally ventilated seasons.

The structure of the manuscript is good and the story is coherent. Adequate amount of details is presented and the methods are well designed in general.

However, my biggest concern is the validity of the results as there has not been any effort to validate the simulation models. It would be expected that the simulation results would be compared against field measurements. Even if the model is based on an idealised archetype, it should still show that it has the key thermal characteristics and performance with the typical buildings. That could be a comparison of cooling loads/electricity consumption between simulated loads/energy and energy bills from typical school buildings for example. It is suggested to collect some temperature and RH observations from the “typical” school building and compare the indoor conditions for a period of time. A typical and an extreme week should be enough to gain some confidence on the results presented. I believe the lack of validation is a major concern for the publication of any simulation studies.

Please see some more specific comments below:

Response:

Thank you for your advice. Indeed, the validation is important, however, there are still no practical cases of utilizing the PCMs in Taiwanese school buildings, and PCMs is not a general material in Taiwan currently. Therefore, it is difficult to conduct the field experiment to compare the cooling loads/electricity consumption or energy bills with the simulation results. Besides, due to the covid-19 pandemic, all of the schools have been closed now, so the field measurement cannot be conducted currently. The issue of validation and field experiment will be a very important studies in our future works.

In addition, owing to there are still no actual cases of installing PCMs in Taiwanese school buildings, so the main goal of this study is to discuss the feasibility, and attempts to suggest the utilization strategies for efficiently utilized the PCMs in the future.

2. The English language need careful extensive editing as several parts are hard to understand. Please try to be more quantitative and specific. For example “numerous” studies would need to be backed up with literature references. “Superior” performance is rather generic and it does not make much sense. Superior to what and in what context. What are the climate characteristics of Taiwan? It is suggested to describe the main climate characteristics for the two cities in the study.

Response:

Thank you for your advice. The description of the climate characteristics of two cities have been added. In addition, the figure for describing the range of air temperature and solar air temperature, radiation of two cities has been supplemented. (p.5, Figure 4; lines 167~177) 

The revision is as follows:

“… Specifically, the climatic conditions including outdoor temperature, cooling degree hour (CDH), and horizontal solar radiation of each month for the two selected study cities are shown in Figure 3. Taiwan is located in the sub-tropical zone that the weather features are hot and humid. Referring to Figure 3, it can be known that the outdoor temperature of Tai-pei in winter is much lower than of Kaohsiung, although Taipei and Kaohsiung are both located in hot-humid climate zone; as for the outdoor temperature in Kaohsiung, it re-mains an extremely high temperature during the entire year. In addition, the heat gains from rooftop is directly affected by the solar air temperature, as shown in Figure 4, there is a wide range of the variation of daily solar air temperature, which means the utilization potential of PCM in rooftop structure is expectable in both Taipei and Kaohsiung …”

3. What are the observed and modelled occupancy schedules of schools and the typical use of controls (window opening, thermostat settings)? Do the windows have restrictors for safety? Do the windows stay open during night but close when air conditioning is operating?

Response:

Thank you for pointing out the insufficient of the description of setting conditions. Table 1 has been modified, and the supplemented contents have been added in the article.

The revision is as follows: (p.3, lines 134~139)

“… Regarding the air-conditioning operation and natural ventilation period of this school building model, the air-conditioning is available for use during the weekdays in the hot-humid period from May to October. Based on the regulation, it is allowed to turn on the air-conditioning when the outdoor temperature is higher than 27 °C. Besides, the windows are always closed at the occupancy period and out of the occupancy period at night and weekend during the AC season. …”

4. What is the expected internal temperature in school classrooms during occupancy hours and what is the comfort temperature range expectation ?

Response:

The value “” in equation (4) is used to determine whether turning-on the air-conditioning or not. The expected internal temperature in school classrooms during occupancy hours is 26°C, which is regulated by the government.

5. It would be useful to include a short description of BioPCM in terms of materials, maintenance, life expectancy, installation requirements etc.

Response:

Thank you for the suggestion. We have added the sentence of describing the BioPCM. (p.4, lines 151~156)

The revision is as follows:

“… The PCM considered in this paper is BioPCM™, which is generally used by other previous studies; besides, the database of the BioPCM™ is complete that can be regarded as a con-vincing material [27]–[32]. BioPCM™ is non-toxic, non-corrosive, biodegradable, and has a useful life of over 100 years. In addition, BioPCM™ enables users to reduce their carbon footprint and reduce the stress on HVAC systems in buildings, data centers, and telecom shelters [33]. …”

6. What parameters affect the PCT change? Does PCT refer to air temperature or the temperature of the PCM?

Response:

PCM is a complex material, so the PCT change is affected by the properties of the materials. Besides, air temperature affects the PCT change as well.

7. What is the origin of the weather files and the period of observations for their creation? How does the min/max/median monthly temperature compare to an extreme weather year? Is the number of monthly CDD in the TMY3 files roughly equal to the last 10 years average?

Response: 

The weather data files used in this study is the Typical Meteorological Year (TMY) established by National Renewable Energy Laboratory of United States (NREL). TMY3 is the weather data of Taiwan which was constructed based on the method developed by NREL for the use in building dynamic simulation. The TMY of Taipei used in this study was developed based on hourly data from 1993 to 2014. Taipei’s TMY was constituted by linking the selected typical months of actual observed weather. The selection procedure of typical months consisted of a series of statistical processes that were run for all of the months in the long-term weather datasets for 1993–2014.

8. How was the base temperature of 27 deg C selected for the CDD calculation? Is this according to local regulations?

Response:

Firstly, we would like to correct the words CDD (cooling degree day) → CDH (cooling degree hour).

CDH 27 is a statistic value that set in the weather data (TMY3). Besides, owing to this value is closed to the standard value that is regulated to turn on the air-conditioning (27°C~28°C), therefore, the statistic value CDH 27 is selected for the simulation in this study.

9. Figure 3. I believe it would be useful to show this graph for hourly values in the hottest and coldest day of the TMY3 weather file. It is important to understand when (what time) the max temperature is reached in the classroom and show how the PCM smooths out the peak temperatures during the occupancy hours. It is suggested to show if possible in the same graph the diurnal hourly PCM temperature, the indoor air temperature, the outdoor temperature and the solar irradiance.

Response:

Thank you for your suggestion. The figures for describing the daily range of air and soler air temperature, daily peak radiation of two target cities is added (Figure 4).

10. How were the releasing and storing time of heat calculated for this study? Are these given in the material specifications?

Is each classroom of the school considered as a single zone in EnergyPlus? One node temperature for the PCM in the middle of the zone roof? Would the existence of more zones in the simulation model affect the final results (grid sensitivity analysis)?

Response:

The releasing and storing time of heat is calculated based on L_C and L_DC in Eqs.(1)-(2), depends on the length of day and night everyday, which are not fixed values.

Not only one node temperature for the PCM. The appropriate interval numbers of node are determined by the thickness of PCM and calculation time step which is automatic set by Energyplus. Generally, the numbers of node are usually 4 to 15 nodes.

In fact, all of the setting conditions of the adjacent classrooms are same, so it is regarded that the existence of more zones in the simulation model do not affect the final results.

11. Line 238: This is unclear: do the authors mean “adaptive comfort model based on children’s perception” ?

Response:

Yes. According to the previous study mentioned in the same paragraph “the thermal evaluation and the design which corresponding to the occupants should apply the thermal comfort standard that adapted to occupants’ thermal perception [36].”, the evaluation of thermal comfort should be corresponded to the occupants; therefore, in this case, the adaptive comfort model is based on the children’s perception.

12. Line 253: Does the standard refer to number of occupancy hours? Overheating thresholds are usually connected with the hours that the building is occupied only.

Response:

Thank you for pointing out.

Yes. Overheating thresholds is calculated during the occupied hours, and the description is added in Eq.(5).

13. Line 275: It is suggested to remind the readers of the estimated CDD27 for each city.

Response:

Thank you for your suggestion. The correction is as follows: (p.8, lines 281~282)

“… According to Figure 5, under the weather conditions of CDH27, it is known that…”

14. Line 283: It would be useful to include a floorplan that shows the floors and classrooms simulated and the location of the simulated classroom. What are the boundary conditions for each zone?

Response:

The simulation model of the classroom is a prototype module. The floor plan is added in the article. (Figure 1)

The difference of boundary condition is only divided into internal walls and outer walls. The differences between internal and outer walls are solar radiation and air-conditioning. The internal walls are not affected by solar radiation and the outer walls do not affected by the air-conditioning.

15. Section 3.2: This is a very important part of the study and it is expected to provide details on the parameters and the different scenarios in the analysis. How and why have those been selected? A summary in a Table would be very helpful.

Response:

Thank you for your advice. The parameters are set according to the general setting. For instance, based on the previous studies, PCT and thickness are the most general parameters when discussing the performance of PCMs. We have add the sentences for explanation. The revision is as follows: (p.9, lines 307~309)

“In this paper, 30 cases of different properties of PCM are set to analyze the parameters which make influences on the thermal performance. Specifically, six kinds of PCTs (23°C, 25°C, 27°C, 29°C, 31°C, 33°C) and five types of PCM thickness (10mm~50mm) are set.”

16. Line 320: I think it is not clear how “optimal” is defined in the study. It is suggested to add 1-2 sentences that explain what is considered optimal in this context.

Response:

Thank you for pointing out. The words “optimal ” is improper in this study, so we changed the words to “feasible” that it is better for describing the current situation of the utilization of PCM in Taiwan.

The describing sentences have been added as follows: (p.10, lines 329~331)

“… Specifically, from the aspect of cost and efficiency, there is still an upper limitation that when increasing the PCT or thickness may not achieve the corresponding effect in linear relationship. …”

In addition, some relating contents are also revised in the section of abstract and introduction. (p.1, lines 10~18; p.3, lines 108~128)

17. Figure 7. Does the Figure show results from the simulations or observed values?

Response:

(Figure 7 is now updated as Figure 8)

It is the simulation results. The caption of the figure has been modified as follows:

Comparison of operating temperatures of classrooms with and without PCM roofs during the ventilation season.

→ Comparison of simulating operative temperatures of classrooms with and without PCM roofs during the ventilation season.

18. Line 410: At this point it would help to remind the readers what the CE and HE are.

Response:

Thank you for your advice. The correction is as follows: (p.12, lines 423~425)

“… , it can be concluded that the efficiency coefficients of CE (daytime heating) and HE (nighttime cooling) tend to be low for the selected PCM layers of various thicknesses in the two seasons. …”

19. Line 436: This sentence is an important finding but it is very hard to understand. It is suggested to reword it carefully please.

Response:

Thank you for your advice. The article has been revised as follows: (p.13, lines 450~452)

“… According to the analysis mentioned above that the utilization efficiency barely lies within 0.44–0.67, it means that although the roof with PCM significantly improves indoor thermal comfort from November to April, it does not accompany with high efficiency. …”

20. Line 479: Very interesting analysis. Does the capital and installation cost of the PCM configurations differ significantly and could this affect the overall estimated operational savings?

Response:

We appreciate your suggestion. Indeed, the cost of installation or PCM configurations affect the overall operational savings. However, there are still no practical cases of utilizing the PCMs in Taiwanese school buildings, and PCMs is not a general material in Taiwan currently. The issue related to the cost will be a very important studies in our future works.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have adequately addressed the reviewer comments, the manuscript has been improved.

Reviewer 2 Report

Dear Authors,

Thank you for your detailed response and comments.

This has been a very good effort to address the revision suggestions and I hope the revisions have improved the quality of the manuscript.

One last suggestion I would like to do is to point out clearly the reasons you do not provide a validation of the model and let the readers know that this is a parametric analysis that shows the feasibility in an idealised study. Please note that I realise the issues with the novelty of PCM as construction material. What I have been suggesting is validation against the current situation ("no PCM") to show that the model works correctly before  you simulate the impact of PCM.

It will be interesting to see how your study and work develops when a case study with PCM is possible in the future. Thank you and good luck to your future research work.

Kind Regards,