The Building Energy Performance Gap in Multifamily Buildings: A Detailed Case Study Analysis of the Energy Demand and Collective Heating System

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript addresses a critical issue in building energy efficiency. The research is original and contributes valuable insights to the existing body of knowledge.

The reliance on a single weather station's data for climate normalization may not fully capture the microclimate variations within the study area. It would be beneficial if the authors could discuss any potential impact this might have on their results. It would also be helpful if the authors could provide a more detailed explanation of the statistical methods used to process the monitoring data and calculate the energy performance gap.

A more in-depth discussion is suggested on the implications of the findings for building certification systems and the generalizability of the results to other climates or building types, and how these might affect the transferability of the study's conclusions. A more detailed comparison with other studies is also suggested, particularly those that have used different methodologies to assess the BEPG.

 

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions and corrections in track changes in the re-submitted files. For readability reasons, page and figures numbers are based on the revised manuscript with new lay-out (without track changes).

 

Comments 1: "The reliance on a single weather station's data for climate normalization may not fully capture the microclimate variations within the study area. It would be beneficial if the authors could discuss any potential impact this might have on their results."

Response 1: Thank you for pointing this out. We have added a paragraph ('4.3. Climate impact', page 26-27, line 982-1002) in the discussion to illustrate the impact of (micro)climatic differences on the results and on the applicability of the method.

 

Comments 2: "It would also be helpful if the authors could provide a more detailed explanation of the statistical methods used to process the monitoring data and calculate the energy performance gap."

Response 2: We have thoroughly revised the text describing the method so that it is clearer for the reader. We now mention that we use the OLS in the regression analysis ('2.3.2. Normalisation and categorisation', page 16, line 569. Furthermore, we have added a separate section explaining the evaluation concepts BEPG en ESD ('2.3.4. Evaluation concepts', page 18, lines 653-664).

 

Comments 3: "A more in-depth discussion is suggested on the implications of the findings for building certification systems and the generalizability of the results to other climates or building types, and how these might affect the transferability of the study's conclusions."

Response 3:  Thank you for this comment. As mentioned earlier, we now explain the impact of other climates in our discussion ('4.3. Climate impact', page 26-27, line 982-1002). In '5. Conclusions' we focus more on the impact of our results on the regulatory framework (page 28, lines 1086-1092). We considered also discussing the impact on other building types, but feel that would lead us too far. After all, the manuscript is already very long. We mention it briefly in '5. Conclusions', page 28, lines 1049.

 

Comments 4: "A more detailed comparison with other studies is also suggested, particularly those that have used different methodologies to assess the BEPG."

Response 4: We agree with this comment. Therefore, we explicitly refer in '5. Conclusions' to other studies cited in the introduction (f.ex. lines 1015, 1029-1032, 1039-1040, 1050-1051, 1070-1071, 1073-1075, 1086-1090). 

Reviewer 2 Report

Comments and Suggestions for Authors

This study presents the energy performance of three multi-family buildings. Their manuscript is concise and well organized.

However, I have several concerns that need to be addressed before considering publication.

 

1, It is difficult to read the meaning of Table 4, please modify the expression.

2, Please add the year information in Figure 6.

3, Please add the information in 2.3 Actual energy use in details.

 

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions and corrections in track changes in the re-submitted files. For readability reasons, page and figures numbers are based on the revised manuscript with new lay-out (without track changes).

 

Comments 1: "It is difficult to read the meaning of Table 4, please modify the expression."

Response 1: We understand this table was rather confusing. Therefore, we have removed it from the manuscript and replaced it by a hydraulic scheme in Appendix A (pages 30-31, lines 1118-1121), on which although a little less information can be found, it is much easier to understand visually.

 

Comments 2: "Please add the year information in Figure 6."

Response 2: We have added the year information in the description of this figure (Figure 5, page 15, lines 545-546).

 

Comments 3: "Please add the information in 2.3 Actual energy use in details."

Response 3: We have thoroughly reviewed the entire paper, including section '2.3. Actual energy use' (page 13-18), to improve the comprehensibility, focusing on the balance between sufficient information and compactness of the text.

Reviewer 3 Report

Comments and Suggestions for Authors

Dear authors, This investigation is very interesting, given that some buildings have been taken as samples. It is also important to improve the writing of the investigation.

As for the quotes, I think they should be more recent.

For the introduction, you should consider some historical data on the buildings under study or historical energy consumption.

Regarding the methodology, it is not clearly established what the methodological sequence is, I consider that it should be schematized, giving it a better structure for a better understanding of readers.

 

Regarding your discussion, you have compared the results of the department units, it would be good to also have a discussion with other findings from other investigations.

As for the figures, it would be good if they could schematize it better, there is good material to express it more interestingly.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions and corrections in track changes in the re-submitted files. For readability reasons, page and figures numbers are based on the revised manuscript with new lay-out (without track changes).

 

Comments 1: "It is also important to improve the writing of the investigation."

Response 1: We have thoroughly reviewed the entire paper and made plenty of adjustments to improve the comprehensibility.  Here and there, we have removed some language errors.

 

Comments 2: "As for the quotes, I think they should be more recent."

Response 2: Thank you for this suggestion. In our literature study, we have always tried to go back to the original source. As a result, there are also some older sources in the reference list that have had a significant impact on BEPG research. To have sufficient balance, we have added some more recent sources.

 

Comments 3: "For the introduction, you should consider some historical data on the buildings under study or historical energy consumption."

Response 3: In '2.1. Case study buildings' we have added an idea of the actual annual gas consumption for one of the building blocks before renovation (page 8, line 309).

 

Comments 4: "Regarding the methodology, it is not clearly established what the methodological sequence is, I consider that it should be schematized, giving it a better structure for a better understanding of readers."

Response 4: Thank you for pointing this out. We agree that the transition from introduction to method could be improved in the first version. Therefore, we have added an introductory paragraph at the beginning of '2. Data and Methods' that briefly describes successive steps of the method already, as well as flowchart to visualise the method (page 2, lines 287-297 and Figure 2).

 

Comments 5: "Regarding your discussion, you have compared the results of the department units, it would be good to also have a discussion with other findings from other investigations."

Response 5: We agree this would be an added value to the manuscript. Therefore, we now explicitly refer in '5. Conclusions' to other studies cited in the introduction (f.ex. lines 1015, 1029-1032, 1039-1040, 1050-1051, 1070-1071, 1073-1075, 1086-1090). 

 

Comments 6: "As for the figures, it would be good if they could schematize it better, there is good material to express it more interestingly."

Response 6: We worked hard on several of our figures to better visualise our data and results. 

Reviewer 4 Report

Comments and Suggestions for Authors

This study examines the energy performance of three multi-family buildings: two that underwent deep renovation and one newly built, both the calculated and the monitored thermal energy consumption for heating and domestic hot water. The total energy use of each unit is normalized using the energy signature method.

The study is consistent and detailed, addressing an important topic in the context of energy efficiency in buildings and decarbonization targets. Excellent introduction and state of the art are undertaken.

However, several important observations have to be considered.

It is suggested to synthesize and shrink the content of the paper by at least 25%. The paper is too long for a journal article. Less important and redundant information should be removed from the paper.

The normalization approach should consider the important differences between indoor temperatures, otherwise it is wrong to assume that EPBD calculation method underestimates highly the total energy demand (because a difference of 4 degrees C for the indoor temperature is significant for the heat balance, when calculating the heating demand for spaces). A normalization considering this parameter it is possible to modify the conclusions obtained. That surplus energy, between the two temperature ranges (18 deg C and measured values) is either a rebound effect or at least a factor to be considered when an analysis type calculated-measured values is undertaken. In any case, the indirect conclusion that EPBD calculation method is wrong, is not well justified.

Table 3. Minimum theoretical net energy demand for a single unit seems unrealistic (0.3 kWh/m2.a for DH IV and 1.9 kWh/m2.an for DH V. How do you comment on these results? A short paragraph to briefly explain the situation is required, or the results have to be double checked. Maybe it is about several apartments located at intermediate floors, with only one heat transfer surface to the exterior, South oriented, also with high heat gains?!...

Table 4 is not clear. It is suggested to be reorganized in more synthetic form and shrinked - maybe to introduce another first column for the parameters that are monitored (gas, heat, temperature). Also, please consider introducing this table and other descriptive tables and figures into an Appendix.

Figure 12. What space heating is considered during summer? Because it is mentioned in several places within the text that during summer the only heating demand is for DHW. Please clarify and be consistent thorough the paper.

Many figures have too long descriptions (Figure 1, Figure 2, Figure 4, Figure 9 etc.). It is recommended a shorter description below the figures and rather moving the actual extended descriptions into the text.

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions and corrections in track changes in the re-submitted files. For readability reasons, page and figures numbers are based on the revised manuscript with new lay-out (without track changes).

 

Comments 1: "It is suggested to synthesize and shrink the content of the paper by at least 25%. The paper is too long for a journal article. Less important and redundant information should be removed from the paper."

Response 1: We agree that the first version of the paper was too long. Therefore, we have thoroughly reviewed the entire paper and looked at major and minor passages we could omit. As a result, part of the introduction that was less applicable to our own study was deleted. The analysis studying the influence of a unit's location in the building was also omitted. Furthermore, the number of figures in the text was reduced from 16 to 14, the number of tables from 6 to 3 and the number of equations from 27 to 18, some of which were moved to appendices as background information.

 

Comments 2: "The normalization approach should consider the important differences between indoor temperatures, otherwise it is wrong to assume that EPBD calculation method underestimates highly the total energy demand. A normalization considering this parameter it is possible to modify the conclusions obtained. That surplus energy, between the two temperature ranges (18 deg C and measured values) is either a rebound effect or at least a factor to be considered when an analysis type calculated-measured values is undertaken. In any case, the indirect conclusion that EPBD calculation method is wrong, is not well justified."

Response 2: Thank you for pointing this out, this is an interesting comment. We agree an indoor temperature correction will have an important impact on the results. However, we have insufficient temperature data representative for the whole dwelling for each building block to implement this in the method and apply this on each dwelling. Therefore, we made a detail study based on the correction method as described in EN15378-3:2017, using the temperature data from the ambulant monitoring campaign in 15 renovated apartments. We have integrated the method in '2.3.2. Normalisation and categorisation' (page 17, lines 631-640, Equation 14-15) and findings in '3.1.2. Space heating' , after the measured temperature differences are discussed (page 22, lines 776-779).
On the other hand, we don't want to make the (indirect) conclusion that the EPBD calculation method is wrong, since it always assumes an identical user behaviour profile to make results comparable and user-independent. We mainly want to point out that there are significant differences and how they can be explained. Consequently, we particularly want to stress that EPB cannot be used as a prediction (although sometimes it is, e.g. for certain policy purposes). We emphasised this point of view more strongly in our conclusions.

 

Comments 3: "Table 3. Minimum theoretical net energy demand for a single unit seems unrealistic (0.3 kWh/m2.a for DH IV and 1.9 kWh/m2.an for DH V. How do you comment on these results? A short paragraph to briefly explain the situation is required, or the results have to be double checked. Maybe it is about several apartments located at intermediate floors, with only one heat transfer surface to the exterior, South oriented, also with high heat gains?!..."

Response 3: Apartment units with those very low energy demand for SH are indeed located at intermediate floors, limiting their heat losses. Conversely, heat gains are calculated very high. This explains why some apartments only have a net SH demand of 0.3 kWh/(m².a). We address this in '3.1.2. Space heating' and now refer explicitly to the data in Table 3 (page 22, lines 785-787).

 

Comments 4: "Table 4 is not clear. It is suggested to be reorganized in more synthetic form and shrinked - maybe to introduce another first column for the parameters that are monitored (gas, heat, temperature). Also, please consider introducing this table and other descriptive tables and figures into an Appendix."

Response 4: We understand this table was rather confusing. Therefore, we have removed it from the manuscript and replaced it by a hydraulic scheme in Appendix A (pages 30-31, lines 1118-1121), on which although a little less information can be found, it is much easier to understand visually.
As mentioned in response 1, we added some appendices to remove certain figures, tables and equations from the text to improve the comprehensibility of the text.

 

Comments 5: "Figure 12. What space heating is considered during summer? Because it is mentioned in several places within the text that during summer the only heating demand is for DHW. Please clarify and be consistent thorough the paper."

Response 5: Indeed, during summer there is only DHW demand. Figure 12 was confusing because it was a chart type with stacked data. We understand this is confusing. Therefore, we have adjusted this chart to make it more intuitively to understand (Figure 8 (a-b-c), page 19, lines 681-682).

 

Comments 6: "Many figures have too long descriptions (Figure 1, Figure 2, Figure 4, Figure 9 etc.). It is recommended a shorter description below the figures and rather moving the actual extended descriptions into the text."

Response 6: We have tried to shorten the descriptions accompanying the tables and figures as much as possible.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Have improved significantly according to observations, good.

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have systematically answered my observations, in a satisfactory manner. I have no further observations.