Two-Stage Multi-Objective Meta-Heuristics for Environmental and Cost-Optimal Energy Refurbishment at District Level
Round 1
Reviewer 1 Report
Summary
This paper addresses energy refurbishment on district level by means of multi-objective optimization. The aim of the optimization method is to determine the best combinations of energy conservation measures for a building or a district of buildings. This approach could be of interest for city planners and other working with energy refurbishment on large scale.
Broad comments
This paper takes on the timely issue of excessive energy in buildings, and the optimization methodology presented here could have high relevance for how to solve this problem in practice. The overall structure is quite good, as well as the language.
The main problem with this study is the methodology concerning calculations of energy consumption. In general, it is not possible to add the reduction of energy use achieved by different energy conservation measures, as their effect will typically depend on what other measures are taken at the same time.
The renovation strategies implemented in this study need to be better motivated as well as better described. It is stated that they are “the most common” renovation strategies, without this being supported with any references. Furthermore, it is not clear what “air chamber insulation” is, why there is no case “3A” or what kind of heat pump was considered.
The way the renovation strategies are presented, it looks like “renewable energy” is within the same category of renovation strategies as “active” and “passive”, which really is not the case. The passive and active renovation strategies are intended to reduce the energy demand and the purchased energy of the building, respectively, while the “renewable energy” strategies are systems for generating energy for the building.
The goal function differs between stage 1 (maximize energy consumption reduction, minimize investment cost) and stage 2 (maximize global warming potential reduction, minimize payback time). Would it not make sense to use the same goal function, e.g. the one for stage 2, for both the building level and the district level?
The results of the study are very specific, which means they risk being of limited interest for other cases that differ from the ones presented. It would be of great value to elaborate more on how the results would be affected by e.g. the profile of the district (share of A-, B-, C-buildings, etc.).
The table structure is not optimal for a journal paper. Some of the tables are divided into several parts (e.g. Table 6) that should be merged. It could also be worth considering merging separate tables that are similar into one, in order to reduce the rather high number of tables.
Specific comments
kWh is consistently written with a small “w” in the manuscript.
Page 2, row 67: “district hot water” should be “domestic hot water”?
Table 3: The number in the G-column has three decimals, which seems a bit exaggerated and gives a false sense of accuracy.
Table 4: What is the unit of “Energy performance”?
Figure 1: Writing errors in the text at the center of the figure (“de” instead of “the”, “topology” instead of “typology”)
Page 9, row 283: what is the value of I? I.e. how many iterations were made?
Page 9, row 296-297: “kg CO2-eq/kWh”, not “kg eq CO2/kWh”
Author Response
Dear reviewer,
Please find enclosed the response of your suggestions.
Kind regards,
Diana
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The conclusions and the abstract should be more specific, showing the specific results.
I think that the conclusions can be more clear, pointing out the most relevant data obtained, and focusing on them.
it is a very interesting paper and should be more attractive in the key parts of the reader.
Author Response
Dear reviewer,
Please find enclosed the response of your suggestions.
Kind regards,
Diana
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper discusses the two-stage multi-objective algorithms of optimization and use in energy retrofitting at the district level.
The paper flow and content is well organized. However, the reviewer encourages the authors to do the following before it can be accepted for publications:
1. The term ‘Energy Refurbishment’ does not clear in the title. Can this be simplified with a more widely understood term?
2. Pg 2, ln-80: Why is the objective function used is ‘energy consumption reduction’ instead of simply energy reduction? Suggest avoiding twisting the terms if they are not needed.
3. Pg2, lin81: Why the objective function is chosen differently for district level and building level. A detailed explanation is required. Why not energy savings district level if the end objective is directly related with GWP.
4. The readers won't know about the building characteristics used for categories of C, D, E, F, G. Specifications and characteristics of these building form vital information for understanding. Please more descriptions.
5. Discussion section if includes a description of the practicality of refurbishment strategies to the real buildings would be valuable in relating the study with real cases. Like, capital investment for insulation vs. PV panels are quite different and cost-benefit analysis can show the acceptability for an owner. Additional issues that involve PV installation like availability of shadow-free space etc. should be discussed for the selected cases.
General comments:
1. A thorough literature review is needed on the topic including research from last two year.
2. Reference style should be standard and verified. i.e., [59] is a report and seems not following the style. It appears that IEEE style is used but is not consistent. Check with the journal on the reference styling requirements.
3. Unnecessary repetition of the objective functions in section 2 and 3. i.e., ln 80, 99, 148, 161, 164. If possible please avoid and simplify the language.
Author Response
Dear reviewer,
Please find enclosed the response of your suggestions.
Kind regards,
Diana
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The paper has undergone great improvements compared to the first submission, and the rationale behind choice of renovation measures and energy reduction calculations is much clearer. Table 3 is an important addition for the understanding of the calculations. However, it should be clearer explained or shown how these correction factors are implemented in e.g. equation 2 (if that is where they come in). As it is, there is only one reference in the text to Table 3 and the correction factors, and there is no clear explanation to how they are used.
Apart from that, there are only a few minor corrections and improvements to be made in terms of grammar etc. For example:
· In the description of energy refurbishment strategies (page 3), “which main objective” should be written in possessive form, e.g. “the main objective of which”. In the same section, the word “isolation” is used once, meaning “insulation”.
· The unit of “Energy performance” in Table 5 is written “%/100”, which would mean per 10,000 (% = per 100). Furthermore, the numbers used (0.87 and 1.1) indicate that it is rather a “per 1” ratio (no unit [-]).
· In Figure 1, the Spanish word “de” appears twice where it should be “the”, and “topology” is used instead of “typology”.
· The number 2 should always be uppercase in m2 (square meters) and lowercase in CO2 (carbon dioxide)
Author Response
Please find enclosed the response to the reviewer.
Author Response File: Author Response.pdf
