Performance Evaluation of a Water-Circulating Tomato Root-Zone Substrate-Cooling System Using a Chiller and Its Effect on Tomato Vegetative Growth in Chinese Solar Greenhouse

Round 1

Reviewer 1 Report

This paper presents a case study of a substrate cooling system in a solar greenhouse in China. Data have been taken for 1 month, providing climate data and crop growth.

The theme of the work is of interest, the article is suitable for the journal Agronomy.

Overall, the article is well written and well structured. The methodology is well explained, and the results and discussion are coherent.

From the farmer's point of view, it is essential to know what benefits this system can bring. The authors do not present data on crop production, this aspect I consider fundamental. Has there been a significant increase in production (quantity and quality) in the TS1 and TS2 sectors compared to the CK sector? This data must be provided.

On the other hand, I ask myself a question, is the system profitable? What is the cost of installation? And the cost of operation? Are these costs bearable with the increase in production produced by the system? Authors should provide data in this regard. Readers, and especially farmers, will want to know whether the system is profitable or not.

Another aspect that the authors should clarify, does the WCTRZSCS system work independently for the TS1 and TS2 sectors? Or in both sectors is the WCTRZSCS system activated simultaneously in both sectors?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The present manuscript investigates 'Performance evaluation of a water-circulating tomato root zone 2 substrate cooling system using a chiller and effect on tomato 3 vegetative growth in Chinese solar greenhouse'

 

The paper shows some limits in the methodology.

First of all, the advantage of water-circulating tomato root zone substrate cooling system using a chiller in greenhouses depend a lot on the local climatic conditions and on the typology of greenhouse in which it is used. Therefore, when discussing the use of a water-circulating tomato root zone substrate cooling system using a chiller in greenhouses, the authors should be very clear with reference to these elements.

The analysis of the existing literature is not completely clear because the information is not given in a coherent way. 

I raise the following comments regarding the manuscript: 

Comment 1 (Originality-literature review)

The paper addresses an interesting. In the literature part. The authors have to state clearly the added value of the proposed methodology in comparison with previous works in the field and underline how this manuscript moves the research forward

 

Comment 2 (references)

More references should be given.

Comment 3

 

A preliminary economic study is missing in order to make the most of the work

Author Response

Response to Reviewer 2 Comments

We appreciate all of the valuable comments from the reviewers of our work.We have revised our manuscript, according to the reviewers' comments,questions, and suggestions.

 

Comment: First of all, the advantage of water-circulating tomato root zone substrate cooling system using a chiller in greenhouses depend a lot on the local climatic conditions and on the typology of greenhouse in which it is used. Therefore, when discussing the use of a water-circulating tomato root zone substrate cooling system using a chiller in greenhouses, the authors should be very clear with reference to these elements.

The analysis of the existing literature is not completely clear because the information is not given in a coherent way. 

I raise the following comments regarding the manuscript: 

Comment 1 (Originality-literature review)

The paper addresses an interesting. In the literature part. The authors have to state clearly the added value of the proposed methodology in comparison with previous works in the field and underline how this manuscript moves the research forward

 Comment 2 (references)

More references should be given.

Response 1 and 2:

With regard to the problem of “The advantage of water-circulating tomato root zone substrate cooling system using a chiller in greenhouses depend a lot on the local climatic conditions and on the typology of greenhouse in which it is used. ”, we believe that although a set of water-cooled seedling beds with groundwater as the medium for local cooling of the intensive seedling rhizosphere, which alleviated the impact of high summer temperatures on tomato seedling growth. However, this method wastes water resources and is unsuitable for greenhouse cooling in arid and groundwater-deficient regions. Compared with it, WCTRZSCS saves water resources. In fact, WCTRZSCS is not only suitable for areas with scarce water resources, but also can be well applied in areas with high groundwater level and abundant rainfall. Moreover, the system relies on chillers to refrigeration without outdoor meteorological conditions. In the introduction, we highlighted climate conditions in the Northwest Territories, which may lead to misunderstandings, and we have revised them as follows, including comments 1 and 2:

“At present, the cooling technology of greenhouse is mainly divided into two aspects, one is to cool the air, the other is to regulate the temperature of soil or substrate. Common air cooling technologies include ventilation cooling [4, 5], shading cooling [6-8], evaporation cooling [9–11], Spray cooling [12] and the combination of these four ways of cooling [ 13-17 ], heat exchange system in the ground [18,19]. However, the above cooling methods have some limitations. For example, the cooling effect of ventilation is affected by the temperature difference between indoors and outdoors [20]. Shading affects indoor light intensity, affecting plant photosynthesis [21]. Evaporative cooling raises the indoor humidity during the cooling process, and the cooling efficiency is affected by outdoor humidity. Spray cooling causes aging of covering materials and waste of water resources [6]. The cooling performance of heat exchange system in the ground is poor [22].

In the case of soilless culture, substrate cooling can also be employed to regulate substrate temperature. Compared to indoor air temperature control, the substrate volume is smaller than the air volume. Simultaneously, substrate temperature mainly affects crop root zone temperature. Studies have displayed that root zone temperature directly affects plant growth and indirectly affects plant growth by affecting photosynthesis [23,24], metabolism [25,26], mineral nutrition [27], and plant hormones [28]. Facility crops are more sensitive to root zone temperature variations than air temperature variations [29]. Therefore, the temperature regulation of substrates may be more energy-saving.

Many studies have been conducted on the local temperature reduction of strawberry roots employing a heat pump with circulating cooling water regarding substrate temperature regulation [30–32]. This method has a remarkable cooling effect but requires a substantial initial investment and high energy consumption. Li et al. [33, 34] designed a set of water-cooled seedling beds with groundwater as the medium for local cooling of the intensive seedling rhizosphere, which alleviated the impact of high summer temperatures on tomato seedling growth. However, this method is unsuitable for greenhouse cooling in arid and groundwater-deficient regions [35].

As mobile cooling equipment, the chiller possess a good cooling effect. They are widely used in industries that require chilled water or cooling, such as; buildings cooling [36,37], combined cooling heating and power [38], tunnel construction [39], passenger ship cooling [40], temperature and humidity control in glass fiber production environment, [41], steel production cooling [42]. Based on their use in various industries, chillers are also known as refrigerators and coolers. Numerous researchers have investigated the energy-saving control scheme of chillers [43–45]. However, the effect of chiller application on greenhouse cooling has not been reported. When the chiller and water storage tank are used to cool the substrate in the greenhouse, only a minimal amount of water is required to meet the cooling requirements. The water in the storage tank can be recirculated during the cooling process. Therefore, water resources will not be utilized in these areas, and there will be no water resources waste.

Therefore, to reduce the substrate temperature of summer plant cultivation in a Chinese solar greenhouse and explore a substrate cooling method that is not limited by the use area, saves water resources and consumes low energy, this experiment proposed a water-circulating tomato root zone substrate cooling system (WCTRZSCS) with water as the circulating medium. The tomato was used as experimental material to explore the substrate cooling performance of WCTRZSCS in a Chinese solar greenhouse and its effect on tomato vegetative growth to evaluate the cooling effect of chillers in greenhouses. It is hoped to obtain a better cooling method of substrate and provide data reference for the application of chillers in greenhouse substrate cooling.

 

 

Comment 3: A preliminary economic study is missing in order to make the most of the work

Response 3:

We supplement this section of WTRZSCS's economic assessment in this paper. The supplementary contents are as follows :

“3.5 Economic assessment of WCTRZSCS

The economic assessment of WCTRZSCS includes the initial investment, installation and maintenance costs of the system, the energy consumption cost of the system during the summer ( three months ) operation and the benefit of tomato, taking into account the cooling performance of the system. The WCTRZSCS proposed in this paper is mainly composed of a chiller, a heat dissipation components ( PE-RT pipes ), a water pump and a water storage tank. The service life of the chiller and the PE-RT pipes is about 20 years and 50 years (below 80 °C) [51], respectively, so the service life of the whole system is about 20 years. The agricultural electricity price in Shaanxi Province is about 0.5 RMB·kW^–1·h^–1, and the cost per unit planting area is calculated by planting density of 3.6 plants·m^–2.

Results as demonstrated in Table 8, the total cost of WCTRZSCS was 23.6 RMB·m^–2·yr^–1. Compared with CK, the tomato yield in the test area increased but the data was the yield of a spike in tomato infected with yellow leaf curl virus, so the benefit of the system was –22 RMB·m^–2. The cost of using the WCTRZSCS in the test area was not offset by the profit of tomatoes.

Table 8. Economic assessment of WCTRZSCS .

Cooling performance of WCTRZSCS/ °C	TS1	6.5
	TS2	8.5
WCTRZSCS initial cost/ RMB·m–2·yr–1	Chiller	5.6
	Heat dissipation components (PE-RT pipes)	0.5
	Water pump	0.6
	Water storage tank	0.7
	Installation and maintenance costs	0.9
Electric charge/ RMB·m–2		15.3
Total costs of the WCTRZSCS/ RMB·m–2·yr–1		23.6
Yield/ m–2	CK	/
	TS1	0.8
	TS2	0.8
Total profit of the tomato/ RMB·m–2		1.6
The benefit of the WCTRZSCS/ RMB·m–2		–22

 

Round 2

Reviewer 1 Report

The authors have satisfactorily responded to my previous comments.

The authors have included the information requested.

I consider that the work meets the quality requirements of Agronomy.

The work done is interesting. It provides valuable information for farmers.

The document is well written.

The methodology is correct. And the results show that the system they present is interesting.