A Study on the Control Solution of Ship’s Central Fresh Water-Cooling System for Efficient Energy Control Based on Merchant Training Ship

Round 1

Reviewer 1 Report

This manuscript presents a simulation model of the central cooling system of a ship, consisting of a variable speed drive seawater pump, three way valve and a heat exchanger. The simulations are compared to fresh water and sea water temperature measurements acquired from a ship. In this revised manuscript, a novel control solution is proposed.

My specific comments are the following:

1. Literature on the development and validation of ship cooling system models is extensive. In particular, the question of savings achieved using a variable speed pump has received considerable attention. The introduction section should present the seminal contributions in this area. How the developed model differs, if at all, from previous works?
2. The conclusions section should also reflect the results in light of previous work.
3. The introduction and conclusions sections contain many paragraphs of only a single sentence. This implies weak organization. Please reconsider the organization of main ideas in these sections.
4. Equations must be punctuated as part of a regular sentence. For example, if the equation comes at the end of a sentence, a period should be placed immediately after. Please see MDPI Style Guide, section 6.5: https://www.mdpi.com/authors/layout#_bookmark36
5. The manuscript would benefit from a nomenclature table which describes all the symbols and subscripts.

Author Response

Dear Reviewer,

Our response on your comments are the following:

1. Literature on the development and validation of ship cooling system models is extensive. In particular, the question of savings achieved using a variable speed pump has received considerable attention. The introduction section should present the seminal contributions in this area. How the developed model differs, if at all, from previous works?

 Thanks for pointing out. A section on the proposed solution has been added in lines 80-87 of the paper.

1. The conclusions section should also reflect the results in light of previous work.

That conclusion is presented in text lines 703-711.

1. The introduction and conclusions sections contain many paragraphs of only a single sentence. This implies weak organization. Please reconsider the organization of main ideas in these sections.

Thanks for your comment. The instruction and conclusion part is updated.

1. Equations must be punctuated as part of a regular sentence. For example, if the equation comes at the end of a sentence, a period should be placed immediately after. Please see MDPI Style Guide, section 6.5: https://www.mdpi.com/authors/layout#_bookmark36

Thanks for the guidance. The MDPI editing service has edited the manuscript.

The parts you pointed out have been corrected, and the missing parts will be supplemented by the MDPI editor.

1. The manuscript would benefit from a nomenclature table which describes all the symbols and subscripts.

Yes, you are right. If there is a table for the symbol, it is a benefit for readers. But the symbol is described in the manuscript. As pointed out, we added the symbol to table2.

It is much appreciated your comments.

Reviewer 2 Report

More of novelty next time.

Author Response

Dear Reviewer,

Thanks for your comment.

The instruction and conclusion part is updated.

Reviewer 3 Report

The efforts made by the Authors are unquestionable, however, (as already advised) the problem is that research is based on a single case ship (seawater cooling system temperature regulation) and statistically insignificant advice from field engineers, rather than the thorough study of previous research and presentation of the wider situation in industry or ship building practice. Not far from the university to which the Authors belong are some of the statistically far more significant shipyards and relevant equipment makers, whose practice around the recognized problem, and opposed to the solution offered by the Authors would certainly be more significant in the gaps recognition process. It is crucial to better elaborate and prove the need for this research. 

Author Response

Dear Reviewer,

Yes, there are many ship equipment suppliers and three major big shipbuilders nearby.

The controller integration is not easy practically in the shipbuilding industry. Usually, variable sea water pump suppliers and 3-way valve suppliers are not always the same. So the controllers are supplied for their equipment respectively.

There could be another or better way to integrate two controllers. The prosed method is the more accessible and not expensive cost required for new buildings and already applied two controllers for the central cooling system.

The presented technical problems in the paper are not a single case only to the relevant vessel but the problem occurs in merchant ships as well.

Of course, if the manufacturer of the variable speed seawater pump and the 3-way valve supplier are the same, a control solution (split control, etc.) is provided to prevent control conflicts.

However, in most cases, other manufacturers are provided for reasons such as the reliability of each machine and the shipowner's request. (presented on lines 68-71)

Therefore, it is known that various field engineers use the central cooling water system while fixing the 3-way valve and controlling the seawater pump. This is based on the authors’ many years of experience as building and ship operation engineers.

Also, this problem can occur not only in the central cooling water system but also in the integrated control system with the same feedback parameters. It has also been demonstrated with simulations in Section 4.2 of the paper.

Thanks again for your valuable comments.

Round 2

Reviewer 1 Report

I consider that this revised manuscript provides sufficient novel contributions to be published in JMSE.

Please lightly revise the following material:

1. In the abstract, the phrase "technical problems" is too vague. Please consider a more concrete expression. Also, mentioning hydrogen vessels in the abstract is questionable, given that they are not discussed in the manuscript.
2. Equations are incorrectly puctuated. For example, equations (4) and (5) should be followed by commas, not periods (i.e. full stops).

Author Response

Thanks for your comments.

Regarding the mentioned “hydrogen vessels”, it is deleted.

We updated the pointed part as “due to minimum-required discharge pressure of the pump”

The sea water pump and the motor can’t be operated below minimum-required speed, because the motor has minimum revolution for torque and the pump discharge pressure to be overcome to flow sea water. But this paper doesn’t deal with the fluidology problem, so we didn’t describe in detail

The equations are updated as you commented and the guideline.

We appreciated  your reviews.

Reviewer 3 Report

The Authors do not define the problem scientifically sound and do not transfer the problem to the broader scientific context. Performing research on a relatively simple problem is legitimate, as long as the Authors present the problem as scientifically significant and representative, which the Authors have failed to do. The text in lines 67-76 is insufficiently scientifically or statistically relevant.

Author Response

Thanks for your valuable comments.

It is updated “Through the simulation with model, the collided control problem by the typical two  control system is shown” in line 80-81.

checking the frequency diagram in Figure 38, it can be seen that the frequency of step-up and step-down in same thermal load(F.W in temp to HEX) is different due to the collision of the control system.

We appreciated your review again.

Best Regards,

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.

Round 1

Reviewer 1 Report

This manuscript presents a simulation model of the central cooling system of a ship, consisting of a variable speed drive seawater pump, three way valve and a heat exchanger. The simulations are compared to fresh water and seawater temperature measurements acquired from a ship.

The manuscript lacks two essential components: (1) literature review and (2) an argument for the innovative features of the presented work, i.e. contribution.

Literature regarding development and validation of ship cooling system models is extensive. In particular, the question of savings achieved using a variable speed pump has received considerable attention. Although some of these works are cited in the manuscript ([17, 24, 31]), their features and limitations are not discussed. A few related works in this area, not cited in the manuscript, include Mrakovčić et al. (2004), Lee et al. (2015) and Patriotis et al. (2019). Here, for example, Mrakovčić develop a model for the central cooling system and validate it using measurement data.

The authors fail to make an argument for the novelty of the presented work. Although issues related to separate controllers of the variable speed pump and the three way valve are raised, they are not addressed in the work.

References:

Mrakovčić, T., Medica, V., & Škifić, N. (2004). Numerical Modelling of an Engine-Cooling System. Strojniški vestnik - Journal of Mechanical Engineering, 50(2), 104-114.

Lee, C., Liu, Z., Chen, C., Cho, M., Lin, F. & J. Jiang, Assessment of Energy Savings With Variable Speed Drives in Ship's Cooling Pumps. IEEE Transactions on Energy Conversion, vol. 30, no. 4, pp. 1288-1298, Dec. 2015.

Pariotis, E.G., Zannis, T.C. & Katsanis, J.S. (2019). An Integrated Approach for the Assessment of Central Cooling Retrofit Using Variable Speed Drive Pump in Marine Applications. J. Mar. Sci. Eng. 2019, 7, 253.

Reviewer 2 Report

Line 125 - Figure 3?

Line 155 - Equation (1)

Equations (2) and (3) correct the dots over m and T

Reviewer 3 Report

The main shortcoming of this paper is that it insufficiently recognizes the gaps and the scientific novelty. The prerequisite of conducting scientifically sound experiments and providing a substantial amount of new information is not satisfied.  
Given that the Authors presented the problem in the field of application, it would be crucial to investigate control solutions available on the market, particularly with the marine integrated automation systems (IAS). The available IAS solutions do provide the option of regulating and tuning the complex processes.
The statement in lines 66-71 is colloquial and requires elaboration. Namely, marine systems are standardly composed of elements manufactured by several makers; they have been carefully selected in order to provide smooth and trouble-free operation.