Comparative Performance of Low Global Warming Potential (GWP) Refrigerants as Replacement for R-410A in a Regular 2-Speed Heat Pump for Sustainable Cooling
Round 1
Reviewer 1 Report
The Introduction presents interesting information and data, however, I do not observe a broad discussion on works where the replacement of R410A by alternative refrigerants is studied. Authors need to add this information so that the contribution of their work is seen. In the literature, there are recent studies and reviews for the replacement of R410A by mixtures.
Work with the same format in the figures and place the units correctly in the parameters, for example for Temperature ° C.
Check the structure of the document, the numbering in the sections is not correct.
The units in Table 5 are not correctly appreciated, improve the table.
Keep the same format of all the diagrams in figure 6.
Check the correct format of the units throughout the document.
Author Response
Responses to Reviewer#1 Report—Round 1
July 09, 2021
The authors express gratitude to the reviewer for his/her comments which we find useful in correcting mistakes and improving upon pertinent sections to improve the quality of the publication. Below, we provide detailed responses to the changes suggested by the reviewer.
The Introduction presents interesting information and data, however, I do not observe a broad discussion on works where the replacement of R410A by alternative refrigerants is studied. Authors need to add this information so that the contribution of their work is seen. In the literature, there are recent studies and reviews for the replacement of R410A by mixtures.
Response: The authors have provided a lengthy discussion on recent works to replace R-410A with alternate refrigerants. These discussions are in lines 76-110 with attendant references. We have included recent research between 2012-2021.
Work with the same format in the figures and place the units correctly in the parameters, for example for Temperature ° C.
Response: We have made units consistent throughout the figures and tables. Figures 2,3,4, 6, and 7 have been revised. Table 5 has also been revised with the appropriate formatting of units.
Check the structure of the document, the numbering in the sections is not correct.
Response: We noticed a discrepancy in the numbering and in the heading “styles” which has been corrected.
The units in Table 5 are not correctly appreciated, improve the table.
Response: The units in Table 5 have been re-formatted.
Keep the same format of all the diagrams in figure 6.
Response: All the formatting in Figure 6 is made consistent, including the temperature units.
Check the correct format of the units throughout the document.
Response: The formatting of units throughout the text is consistent with the corresponding corrections in the figures and tables. The units are also made consistent in the Nomenclature, and the body of the text.
The track changes in the document show where all the changes are made so that they become clearly visible to the reviewer. Once again, we thank the reviewer for perusing the paper and suggesting changes to improve its quality.
Reviewer 2 Report
Please, find attached all my comments and suggestions.
Regards,
Comments for author File: 
Comments.pdf
Author Response
Responses to Reviewer#2 Report—Round 1
July 11, 2021
Thanks for taking your valuable time to provide the detailed review and insightful comments. Below please see our responses.
C01: The abstract should be reformatted to take into account also the novelty of the study, some important results, and important findings of the study.
Response:
Thanks for the comment. We addressed the contributions of the article in the abstract using following: “The contributions contain detailed, hardware-based heat exchanger and system analyses to provide a comprehensive comparison. The results of the simulation are scrutinized from the First (capacity and energy efficiency) and Second Laws (exergy analysis) to identify sources of systemic inefficiency, the root cause of lost work. This rigorous approach provides an exhaustive analysis of alternate lower-GWP refrigerants to replace R-410A using the same hardware. The results have practical value in engineering heat pumps in an economy that is compelled to alter by the consequences and uncertainties of climate change to reduce anthropogenic carbon footprint. ”
C02: Needs to be elaborated with latest advances in this research point, there are a lot of papers and studies aim to find replacement for High-GWP refrigerants for moderate temperature heat pumps, and even high temperature heat pumps. Please, try to do a literature review regarding this, and indicate, explicitly, what is the novelty of your work compared with these studies.
Response: The authors have provided a lengthy discussion on recent works to replace R-410A with alternate refrigerants. These discussions are in lines 76-110 with attendant references. We have included recent research between 2012-2021.The novelty of this work is to provide a comprehensive comparison between the low GWP alternatives in terms of 1st and 2nd law analyses, using a detailed, hardware-based modelling approach.
C.03, P.03, L.96-97: Can you add, please, a reference for this tool “DOE/ORNL Heat Pump Design Model (HPDM)”, I have noticed that you have mentioned it later, but it is more common to refer to it at the first mention.
Response: we added the reference [19] following the sentence “The simulations are performed using the DOE/ORNL Heat Pump Design Model (HPDM) [19]”
C.04, Table 1: There are no single component refrigerant can be a candidate to replace R-410A? I have noticed that all the candidates in the table still have a high-GWP values, > 400, I think the limit for low-GWP refrigerants is < 150, or something similar, no? I think the condition for “Low-GWP” refrigerants is not applicable in this study, instead, you can say alternatives that have lower GWP values compared to R410A.
Response: thanks for the insight. In Table 1, we also addressed R-32, which is a single component refrigerant to replace R-410A. This study compares short-term replacements of R-410A, i.e. direct drop-in without modifications of the existing hardware and manufacturing lines. These replacements require comparable volumetric capacity, energy efficiency to R-410A and have negligible temperature glides. The industry has selected refrigerants having lower GWPs around 700 as short-term options. Refrigerants having GWPs < 150 will be long term replacements, which tend to have significant temperature glides, and need re-design the system and components. We added the above statement below Table 1 for further clarification.
C.05, P.03, L.126: “The simple cycle consists of a 2-stage compressor” the mentioned cycle in Fig.1 is a single-stage simple cycle, why you are using 2-stage compressor?
Response: It shall be two-speed compressor. we’ve changed all the “2-stage” to “2-speed” accordingly.
C.06, P.03, L.132-134: This paragraph is not clear and inconsistent, please revise again
Response:
We rephrased it to “the compressor performance mapping approach, using ten coefficients per the ANSI/AHRI Standard 540 [14], is used to calculate the compressor mass flow rate and power consumption. To consider the refrigerant side energy balance across the compressor, a compressor shell heat loss ratio is inputted to account for the ratio of compressor power lost to the surrounding air”
C.07, Table 2: The fin density should be stated as fin per inch (fpi) or, instead you can state the fin pitch in mm.
Response: we agree with you. But, the international journal requires presenting the results in standard scientific units rather than imperial units.
C.08, P.05, L.195, 205: Is it 2-stage or 2-speed heat pump? Please be specific
Response:
“2-stage” has been changed to “2-speed”.
C.09, Table 3: I think it is more common to state the overall compressor efficiency, which is the ratio between the isentropic work and the total electrical power consumed by the compressor, rather than the isentropic efficiency, or you mean here the same concept? Also, in the same table can you state the compressor’s heat losses percentage, relative to the total power consumed, this will be useful to the reader.
Response:
It should be total compressor efficiency. We’ve changed the “isentropic efficiency” to “compressor efficiency”. The power loss ratio was input as 10% relative to the total power consumed at all the conditions.
C.10, Figs.02, 03: I think the caption should be changed to “Capacity change”, “Capacity variation”, or “Relative capacity”, because the capacity could be increased or decreased for each refrigerant compared with R-410A.
Response:
As suggested, rephrased to “capacity variation”.
C.11, Eq. 05: The entropy transfer by heat term should be also a total summation: ?? ??
Response:
It is the source side heat transfer rate for one control volume. Just one value and so no need to add the summation symbol.
C.12, P.08, L.292: What do you mean by “CCHP”? Is It Carnot heat pump?
Response:
We changed it to “heat pump” referring to the actual heat pump.
C.13, Table 04: The specific enthalpy should be a small “h”, please modify it within the whole text. The same thing is true for the specific entropy “s”
Response:
Changed as suggested. Tables, text and Nomenclature have been appropriately changed.
C.14, Fig.07: The upper figure title is “Comparative total irreversibility”, comparative to what? If you mean Carnot I think that Carnot cycle is a reversable cycle and does not have any source of irreversibility, no?
Response:
We agree with you, the irreversibility of Carnot cycle is zero. The “comparative total irreversibility” are the gain of irreversibility comparative to the Carnot cycle, that is why they are all positive numbers.
C.15, P.15, L.366: why “Lost Work” here are capitalized?
Response:
Corrected to lower case as suggested.
C.16, P.15, L.366-367: I believe that this is not a new conclusion, there is an agreement that evaporators and condensers in refrigeration cycles have a great impact in system’s irreversibility associated with the heat transfer process
Response:
Agreed. Doesn’t hurt to put them there to have a thorough statement.
C.17, P.15, L.370: Grammatically it is more consistent to say” The two candidates have better efficiency………..”. Also, the idea is not clear to me here, do you want to say that all the studied candidates have better performance compared to R-410A? Or do you mean only R-452B and R-454B? Please be specific.
Response:
It means all the candidates exhibit better efficiency than R-410A. Changed the conclusion as below
“All the candidate low-GWP refrigerants have better efficiency and performance characteristics. The energy input to the compressor, systemic irreversibility, and the condenser duty are important considerations before selecting a refrigerant. In particular, R-452B and R-454B have the lowest systemic irreversibility. Overall, any of the four alternative refrigerants are viable drop-in replacements. ”
C.18, Conclusions: this section needs to be reformulated to focus only in the key findings and also to state some comparative indicators to the R-410A, such as relative COP, relative volumetric heating/cooling capacity, COP of the second law, etc. These indicators are very helpful to the reader to understand the percentage of increase/decrease in the HP’s performance, and to comprehend the feasibility of the drop-in R-410A or this is not worth.
Response:
We stated as below:
“Cooling capacity increments of the drop-in alterative refrigerant compared to R-410A are 4% and 6% better for R-32 and R-466A, respectively, and 2% smaller for R-452B and R-454B, respectively.
We conclude that seasonal cooling COPs calculated using AHRI 210/240 specifications show slight variation from 4.45 to 4.58. R-454B results in the highest COP and R-466A results in the lowest COP (Figure 5).”
That was at the beginning of the conclusion section, which may be adequate to draw the readers’ attention.
C.19, Nomenclature, L.400: The energy unit should be J, kJ, MJ, etc. The “W” is the unit of rate of energy transfer “J/s”, please revise again.
Response:
Revised as suggested, i.e. all “W” to “J/s”.
C20, Nomenclature, L.404-405: it is not making sense to select a single nomenclature “h” for two different variables! Please revise again
Response:
We changed the second “h” to “HT”
“HT Heat transfer coefficient, W/m2/K”
C21, Nomenclature, L.407: similar to C.19, the specific irreversibility unit is “J/kg”. here the correct name should be the “rate of irreversibility” “W”. Please revise again
Response:
Revised as suggested.
C22, Nomenclature, L.409: It should be the rate of heat transfer or heat exchange rate.
Response:
Changed to “Rate of heat transfer”.
C23, Nomenclature, L.412: The work is energy and should have a unit of “J”, or if it is a specific it should be “J/kg”. The power or the rate of work is the one that has a unit of “W”.
Response:
Changed to “Rate of work, J/s”.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
