Closed-Loop Optimal Control of Greenhouse Cultivation Based on Two-Time-Scale Decomposition: A Simulation Study in Lhasa

Round 1

Reviewer 1 Report (Previous Reviewer 3)

The authors carefully responded to all suggestions.

Author Response

We thank the reviewer for the recognition of our revision work. After a further revision with responses to reviews of the second reviewer, we hope the manuscript meets the standard for publication.

Reviewer 2 Report (New Reviewer)

Dear,

Despite being an interesting subject, I believe that the article did not reach the level of quality of this journal. Points to highlight:

- Highlighted yellow brackets indicate lack of attention when submitting the article. What are they about? What do they indicate? Are they responses to a past reviewer? There's no way to know.

- Few citations to support the justification of the article (only 27).

- Poorly written methodology. Hardly anyone would be able to reproduce the results with other data, nor is it possible to locate where this methodology was applied.

- Results with unattractive figures. It is necessary to better describe the period of the data series, the meteorological data with boxplots, highlighting the differences between dry and rainy periods, in addition to providing something more creative than figures 4, 5 and 6.

Author Response

We thank the reviewer for the helpful comments. Below we address all the comments, hopefully in a satisfactory manner. The original comments below are typed black. Our responses below are typed red. Corresponding line numbers in the revised manuscript are indicated. After this revision, we hope the article reaches the level of quality of this journal.

1. Highlighted yellow brackets indicate lack of attention when submitting the article. What are they about? What do they indicate? Are they responses to a past reviewer? There's no way to know.

We are sorry for confusions about highlighted yellow contents. They are responses to a past reviewer as we uploaded on the system. These highlights are removed now for better readability. We also attach the previous responses in the file “rebuttal1.docx” for clarification.

2. Few citations to support the justification of the article (only 27).

After adding 8 more citations, the number of citations reached 35. We hope these citations help to support the justification of the article.

Lines 426-435:

“

10. González, R.; Rodriguez, F.; Guzmán, J. L.; Berenguel, M. Robust constrained economic receding horizon control applied to the two time‐scale dynamics problem of a greenhouse. Optimal Control Applications and Methods, 2014, 35(4), 435-453
11. Achour, Y.; Ouammi, A.; Zejli, D.; Sayadi, S. Supervisory model predictive control for optimal operation of a greenhouse indoor environment coping with food-energy-water Nexus. IEEE Access, 2020, 8: 211562-211575
12. Lin, D.; Zhang, L.; Xia, X. Hierarchical model predictive control of Venlo-type greenhouse climate for improving energy effi-ciency and reducing operating cost. Journal of Cleaner Production, 2020, 264: 121513
13. Bersani, C.; Fossa, M.; Priarone, A.; Sacile, R.; Zero, E. Model Predictive Control versus Traditional Relay Control in a High Energy Efficiency Greenhouse. Energies, 2021, 14(11): 3353
14. Hu, G.; You, F. Model predictive control for greenhouse condition adjustment and crop production prediction. Computer Aided Chemical Engineering, 2022, 51: 1051-1056

”

Lines 449-452:

“

22. Ioslovich, I.; Gutman, P.O.; Linker, R. Hamilton–Jacobi–Bellman formalism for optimal climate control of greenhouse crop. Automatica, 2009, 45 (5): 1227–1231
23. Righini, I.; Vanthoor, B.; Verheul, M. J.; Naseer, M.; Maessen, H.; Persson, T.; Stanghellini, C. A greenhouse climate-yield model focussing on additional light, heat harvesting and its validation. Biosystems Engineering, 2020, 194: 1-15

”

Lines 467-468:

“

33. Xu, W.; Song, W.; Ma, C. Performance of a water-circulating solar heat collection and release system for greenhouse heating using an indoor collector constructed of hollow polycarbonate sheets. Journal of Cleaner Production, 2020, 253, 119918

”

3. Poorly written methodology. Hardly anyone would be able to reproduce the results with other data, nor is it possible to locate where this methodology was applied.

We rearrange part of the structure of the methodology and add some introduction descriptions to better illustrate how to reproduce the results. The place where this methodology was applied is also located.

Lines 114-118:

“The accuracy of a dynamic mechanistic model is important for the performance of the optimal control algorithm [22]. To better realize the balance between crop growth and climate control, the model has to be calibrated with the measured data in a crop grown greenhouse [23]. To better apply the control algorithm in Lhasa, a calibrated greenhouse climate – crop growth model is chosen for feasibility study.”

Lines 145-146:

“The control objective is the performance to be minimized or maximized by the optimal control algorithm. In this paper…”

Lines 165-170:

“The framework of optimal control of greenhouse cultivation based on two time-scale decomposition is shown in Figure 1. Open-loop optimal control is solved only once to produce the rough control strategy. In simulations of the open-loop optimal control, the greenhouse climate state is not fed back into the control system. In simulations of the closed-loop optimal control, the greenhouse climate state is fed back repeatedly into the receding horizon optimal controller.”

4. Results with unattractive figures. It is necessary to better describe the period of the data series, the meteorological data with boxplots, highlighting the differences between dry and rainy periods, in addition to providing something more creative than figures 4, 5 and 6.

Thanks for suggestions. We replace the figures of the weather with boxplots and better describe the period of the data series.

Lines 235-243:

“From boxplots of the external weather, we can see that the selected period is cold (with a median of -2.7 °C) and dry (with a median of 25.2%). But the solar radiation during the day can be as high as 1154 W·m^-2, although the median is 0 W·m^-2 because the dark period is longer than the light period.

(a) External solar radiation                   (b) External CO₂ concentration

(c) External temperature                       (d) External relative humidity

”

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

GENERAL COMMENTS:

The paper shows the possible improvement of control algorithms for the optimization of main greenhouse climate control systems such as ventilation, heating and CO2 enrichment. It also calculates the values of the main indicators that can be considered in the decision making process for technology implementation in the greenhouse production system of the Lhasa area, with a high potential for horticultural production due to its high incidence of radiation. The  findings  and  results  are  interesting  and  worth  publication  by  the  journal.  The manuscript is clear and its structure adequate.

SPECIFIC COMMENTS:

-      Generally, the units used in the control of CO2 enrichement in greenhouses are ppm or micromol.mol-1.

-      Line 119. Include the symbol "P", used later in the text, the first time the term “profit” is mentioned.

-      Line 133 (Table 2): The lower limits established for CO2 concentration and humidity to be maintained in the greenhouse do not correspond to real situations that can occur in the greenhouse and in which plants can survive.

-      Line 241 (Figure 5b): It is surprising that the maximum energy supply is close to midday, when the radiation is higher and therefore the thermal accumulation inside the greenhouse.

-      Line 251-253: This is true as long as the cooling systems allow the increase in humidity caused by the transpiration of the crop to be evacuated.

-      Line 285. The elimination of the energy cost in heating implies that the temperature will not be optimized so that the productive results could be reduced, therefore the indicated benefit value cannot be assumed.

-      Line 289: Change “Summery” for “Summary”.

Author Response

We thank the reviewer for the helpful comments. Below we address all the comments. The original comments below are typed black. Our responses below are typed red. In the revised manuscript text corresponding to all modifications mentioned below is highlighted. Also corresponding line numbers in the revised manuscript are indicated.

1. Generally, the units used in the control of CO₂ enrichement in greenhouses are ppm or micromol.mol-1.

The unit of CO₂ concentration is replaced with ppm. The unit of CO₂ supply (kg·m^-2·s^-1) keeps the same with reference [17].

2. Line 119. Include the symbol "P", used later in the text, the first time the term “profit” is mentioned.

Line 127.

“P” is included after “profit”.

3. Line 133 (Table 2): The lower limits established for CO2 concentration and humidity to be maintained in the greenhouse do not correspond to real situations that can occur in the greenhouse and in which plants can survive.

Lines 140-142.

Note that these bounds correspond with reference [3] and the lower bounds of internal CO₂ concentration Xc and relative humidity RXh are seldomly reached.

4. Line 241 (Figure 5b): It is surprising that the maximum energy supply is close to midday, when the radiation is higher and therefore the thermal accumulation inside the greenhouse.

Lines 246-273.

One may wonder why the maximum energy supply is close to midday as shown in Figure 5. This is relevant to the external temperature during these 2 days as shown in Figure 7.

5. Line 251-253: This is true as long as the cooling systems allow the increase in humidity caused by the transpiration of the crop to be evacuated.

Lines 262-264.

It is better to make use of cooling devices that can keep CO₂ concentration at a higher level for better crop growth, such as the heat pump.

6. Line 285. The elimination of the energy cost in heating implies that the temperature will not be optimized so that the productive results could be reduced, therefore the indicated benefit value cannot be assumed.

Lines 299-302. Assuming solar energy can be further employed with low-cost devices such as an active water circulation system [25], the energy spent on heating will be reduced and the profit will be increased as a result.

7. Line 289: Change “Summery” for “Summary”.

Line 305.

“Summery” is replaced with “Summary”.

Reviewer 2 Report

It is difficult to understand the model because there is not enough explanation for the model designed by the author. Also, I think there is a limit to generalizing the results of analysis using 50 days of data. I'm sending you my review comments.

Comments for author File: Comments.pdf

Author Response

We thank the reviewer for the helpful comments. Below we address all the comments, hopefully in a satisfactory manner. The original comments below are typed black. Our responses below are typed red. In the revised manuscript text corresponding to all modifications mentioned below is highlighted. Also corresponding line numbers in the revised manuscript are indicated.

1. Line 75. In order to secure the imperativeness of the study, further review of previous studies needs to be added.

Lines 70-91.

The introduction is enriched.

2. Line 112. Please comply with the journal's paper writing regulations.

Lines 118-122.

The contents are rewritten in the form of state space mapping with explanations in Table1.

3. Line 116. All elements in the formula must be described. However, it is difficult to understand the model design because it is not currently written.

Lines 115-117.

The values, units, and physical meanings of parameters, as well as detailed descriptions of elements in equations (1)–(4), can be found in the reference [17].

4. Line 140. There is a limit to achieving the purpose of the study using 50 days of data.

Line 208.

The growing period of lettuce in a greenhouse is usually 50 days in winter [18].

5. Line 243. Units for ventilation rates are usually expressed in CMS, CMM, and CMH units. It is difficult to show the ventilation rate with m/s.

Lines 119-121.

Note that the unit of ventilation m·s^-1 is derived from the volume of ventilated air per second per square meter of greenhouse area m³·s^-1·m^-2.

6. Line 331. It's too general explanation, and I think it's difficult to generalize as a result of the study.

Lines 349-350.

In the simulation study, crop revenue is 108.13 ¥·m^-2 while the energy cost is 93.79 ¥·m^-2.

Reviewer 3 Report

The authors of this manuscript developed a closed-loop control algorithm based on two time-scale decompositions involving the computation time to be used for online implementations. The algorithm aimed to investigate the optimal control of Venlo greenhouse lettuce cultivation in Lhasa. The authors mentioned "the seldomly researched area of Lhasa" and "seldomly considered" many times; I think there is no need for that.

In lines 22-26: The authors mentioned that "Results show that compared with open-loop simulations, the corrections in yield and profit indicators can be up to 2.38 kg·m-2 and 11.01 ¥·m-2

through closed-loop simulations without considering the computation time. When involving the time delay caused by the computation time, further corrections in yield and profit indicators can be up to 0.1 kg·m-2 and 0.87 ¥·m-2.

How was this information validated? Please indicate this clearly in the results and discussions.

The external weather description should be at the beginning of the results, and add the meteorological parameter of the internal greenhouse. 

There is no description of the greenhouses used or any information about them.

References should be more comprehensive.

Author Response

We thank the reviewer for the helpful comments. Below we address all the comments, hopefully in a satisfactory manner. The original comments below are typed black. Our responses below are typed red. In the revised manuscript text corresponding to all modifications mentioned below is highlighted. Also corresponding line numbers in the revised manuscript are indicated.

1. The authors mentioned "the seldomly researched area of Lhasa" and "seldomly considered" many times; I think there is no need for that.

"The seldomly researched area of Lhasa” is replaced with simply “Lhasa”.

2. In lines 22-26: The authors mentioned that "Results show that compared with open-loop simulations, the corrections in yield and profit indicators can be up to 2.38 kg·m-2 and 11.01 ¥·m-2 through closed-loop simulations without considering the computation time. When involving the time delay caused by the computation time, further corrections in yield and profit indicators can be up to 0.1 kg·m-2 and 0.87 ¥·m-2. How was this information validated? Please indicate this clearly in the results and discussions.

Lines 275-278.

When comparing the yield and profit in RHOC of Table 4 with their indicators in the open-loop simulations as shown in section 3.2, we can see that they are all corrected to be lower (2.38 kg[FW]·m^-2 in yield, 11.01 ¥·m^-2 in profit).

Lines 284-286.

We can see from Table 4 that the yield and profit are further corrected to be lower (0.1 kg[FW]·m^-2 in yield, 0.87 ¥·m^-2 in profit) if we compare their numbers in RHOC and RHOCt.

3. The external weather description should be at the beginning of the results, and add the meteorological parameter of the internal greenhouse.

Lines 207-218.

The external weather description is at the beginning of the results in section 3.1.

Lines 212-213.

Meteorological parameters of the internal greenhouse are shown in Table 1.

4. There is no description of the greenhouses used or any information about them.

Lines 111-113.

Since this paper aims to simulate the feasibility of the Venlo greenhouse - lettuce scheme in Lhasa, the assumption is that the model follows the one that has been calibrated in the Netherlands [17].

5. References should be more comprehensive.

Lines 70-91.

The introduction is enriched with more references.

Round 2

Reviewer 2 Report

The author needs to fill out the response paper for the first review with sincerity. However, there is no answer to each review opinion, and the author only marked it in yellow as a correction. It is difficult to understand how the responses to the review comments were specifically modified. In particular, the reflection of the first review comments has not been sufficiently carried out.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors responded to all suggestions.