Research on a Variable Water Supply Temperature Strategy for a Ground-Source Heat Pump System Based on TRNSYS-GENOPT (TRNOPT) Optimization
Round 1
Reviewer 1 Report
The paper presents a simulation study on an exemplary heat pump for a larger office building. The software used, TRNSYS (TRaNsient SYstems Simulation), is a tool for simulating systems and buildings. The programme was developed in 1975 at the University of Wisconsin to simulate a solar plant. FORTRUN was used for programming. The modular structure of the application makes it possible to solve a wide range of problems. In addition to the simulation of solar systems, the programme has established itself primarily in the field of low-energy houses, technical systems such as ventilation units, heat pumps, chillers and heaters, as well as combined heat and power plants and fuel cells.
The probability of realisation and availability of "green electrical energy" is not discussed, but naively assumed. The state of knowledge and technology is presented under this premise.
The simulation model is described abstractly.
The results are only transferable or generally usable to a limited extent because it is a special case with special assumptions.
It is questionable whether the totalised energies in kWh allow conclusions to be drawn, because the output for summer or winter operation seems more appropriate.
Notes:
In equation (2) to (5) the convolution symbol should be replaced by the scalar product.
In line 129 and 162, the page break should be before the heading.
The page break in Table 7 should be avoided.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review Report on Manuscript ID: sustainability-2232032
Title: Research on variable water supply temperature strategy of ground source heat pump system based on TRNSYS-GENOPT (TRNOPT) optimization
Authors: Jiaqi Cao, Shiyu Zhou, Tao Wang *, Baoqi Shan, Xueping Liu
General statement
This work concerns the evaluation, based on numerical simulations using the TRNSYS platform, of the energy savings of a ground source heat pump (GSHP) system with variable water supply temperature on the load side. The authors chose a six-story office building located in campus of Shandong Jianzhu University, China as the research object. On the basis of the simulations carried out, it was shown that the total annual energy consumption with the variable water supply temperature scheme is less than with the constant water supply scheme, resulting in an energy saving of approximately 5.7% on an annual basis. Although the paper contains valuable results from simulation studies it lacks comparison with experimental results. Given the authors' suggestion that the work can provide good reference value and guidance for real-world design, the noted lack of experimental validation of the simulation study results is a significant shortcoming.
In my opinion the work at this stage needs major revision.
Comments
Chapter 4 is devoted to optimising the operational strategy. It lacks a discussion of the physical phenomena that accompany heat and mass transfer in the building under consideration.
The summary lacked a specification of what the authors consider to be their original achievements.
Line 102, Table 2, On what basis are given the values of the thermal conductivity of the building materials listed in Table 2?
Line 103, it is said ‘the total number of people in the building is 325’ - has the metabolic heat generated by people been taken into account in the model?
Line 106, What kind of computer is it, whose power is 20 watts during operation?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The study entitled “Research on variable water supply temperature strategy of ground source heat pump system based on TRNSYS-GENOPT (TRNOPT) optimization” proposed the TRNSYS-GENOPT (TRNOPT) optimization module in TRNSYS was used to find the optimal water supply temperature for different load ratios. Further, is concluded that the optimized water supply temperature scheme based on TRNOPT has a better energy-saving effect than the first two water supply temperature schemes. There is potential in the research presented in the article, and it should be published after the following Revisions have been made.
1. Consider providing more numerical findings in the Abstract.
2. Please Mention the types of buildings where GSHP systems are used.
- Please improve the language of the whole document, especially grammar.
- Highlight the contribution and significance of the established GSHP system model in this study.
- Clarify the purpose of using TRNSYS software: It would be helpful to specify why TRNSYS was chosen for the building load calculation and what advantages it offers over other software.
6. Please Improve the explanation of the simulation results: The description of the results could be clearer and more concise. For example, it would be helpful to specify what the peak heating and cooling loads represent and why the heating and cooling loads are concentrated during certain times of the year.
7. Consider adding some sentences explaining the purpose and significance of Figure 6.
- Clarify the system operation description: The description of the system operation could be improved by explaining what happens when the heating and cooling loads are greater than 10% of the unit’s rated capacity.
9. Consider adding more details about the methodology used in the study, such as the specific software used and how the simulations were conducted.
- Provide a summary of the main results of the simulation analysis, specifically the optimal water supply temperature control strategy.
- The references cited in the paper should be checked for accuracy and updated if necessary.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
In this paper, the authors investigate variable water supply temperature strategy of ground source heat pump system based on TRNSYS-GENOPT (TRNOPT) optimization. In general, this paper is well written and the topic is interesting. I think that the quality of this paper can be improved if the authors address the following aspects:
1 Author should further highlight the research gaps and contributions of the proposed work by comparing the state of the art methods and recent studies. This reviewer suggests the authors to exactly mention what is new compared with existing approaches and why the proposed approach is needed to be used instead of the existing methods.
2 The proposed control method might be sensitive to the values of its main control parameters. How did you determine the optimal parameters? Please elaborated on it.
3 Please specify details of the computing platform used for this study.
4 There is no discussion on the computational cost of the proposed method. The approach should be computationally efficient to be used in practical applications. Please include such discussions.
5 A more comprehensive and timely literature survey is desired. Among all the references, only 5 come from journals after 2022. For example, thermal comfort of buildings is a key concept in this work, the following recent articles with the similar scenario and research targets can be cited, and discussed to enable readers to better know the latest developments: https://doi.org/10.1016/j.apenergy.2023.120749, https://doi.org/10.1016/j.enbuild.2018.09.024.
6 Authors have not presented the limitations of this work. Please elaborate on it.
7 The italic types of symbols in equations and the main text should be in the same expression. Please double-check it.
8 Please format all references, especially article titles, by the given template of this journal.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I find the authors' responses to my comments satisfactory.
Reviewer 3 Report
The paper has been revised accordingly
Reviewer 4 Report
Thanks to the careful revision and detailed response made by the authors. All my concerns have been well addressed, and the revised manuscript has been much improved. Taking into these factors, I think this paper deserves to be published in its current form.
