Heat Transfer Characteristics of Modular Heat Storage Wall Solar Greenhouse Based on Active Heat Storage System
Round 1
Reviewer 1 Report
This paper is well organized and written. This main contents of this paper provide data reference and practical value for producing modular heat storage wall in the construction of a solar greenhouse. Some suggestions are listed as follows:
(1) The English of this paper should be further polished.
(2) The exact meanings of "SG" and "PG" are not clarified. In my opinion, the authors should illustrate that which word is represented by "S" or "G" or "P"?
(3) Too many subsections are provided. The authors should present the main contribution in a whole section to emphasize the novelty of this paper. However, so many subsection could confuse the readers that the main contribution can not be clarified. Furthermore, some contents that are not closed with the main contribution could be deleted.
(4) The equations and the symbols are not presented in a normal way. For instance, the symbols in equation (1) is smaller than that in the equation (2).
(5) The figures in this paper are not clear enough. For examples, (a) the authors use 3 different symbols in the Figure 4, the reviewer suggests that this figure can employ other symbols such as "-" and "--" and "-.-" etc. (b) The sizes of the figures should be re-organized. There exist too many blanks at the right of the figure 6. (c) Why only the Figure 7 is in black/white?
Please note that, although the reviewer directly points out the detailed locations in the above comments, the authors should check out the whole manuscript on these suggestions to further improve this paper.
Author Response
Dear editor,
Thank you very much for your comments and we have carefully revised the manuscript following the comments and suggestions raised by reviewers. Following is the response list. Please kindly note that the changes have been added to the revised paper in blue color.
Point 1: The English of this paper should be further polished.
Response 1: The English of this article has been further improved.
Point 2: The exact meanings of "SG" and "PG" are not clarified. In my opinion, the authors should illustrate that which word is represented by "S" or "G" or "P"?
Response 2: In this paper,“SG” represents “Soil module solar Greenhouse”, "PG" represents “Pebble module solar Greenhouse”, which has been added to the abstract in the manuscript.
Point 3: Too many subsections are provided. The authors should present the main contribution in a whole section to emphasize the novelty of this paper. However, so many subsection could confuse the readers that the main contribution can not be clarified. Furthermore, some contents that are not closed with the main contribution could be deleted.
Response 3: Some sub chapters and contents have been deleted from the text,The deleted part is marked with green( 3.6.3 and 3.2 in the original text).
Point 4: The equations and the symbols are not presented in a normal way. For instance, the symbols in equation (1) is smaller than that in the equation (2).
Response 4: Formula 1 has been adjusted as much as possible, and other formulas have been checked
Point 5: The figures in this paper are not clear enough. For examples, (a) the authors use 3 different symbols in the Figure 4, the reviewer suggests that this figure can employ other symbols such as "-" and "--" and "-.-" etc. (b) The sizes of the figures should be re-organized. There exist too many blanks at the right of the figure 6. (c) Why only the Figure 7 is in black/white?
Response 5: (a) Use the suggested symbol representation for the line segment in Figure 4;
(b) Properly adjust the size of digital typing in the picture;
(c) Modify Figure 7 and adjust the color of lines.
Check other pictures and make appropriate adjustments
Author Response File: 
Author Response.docx
Reviewer 2 Report
In the present work, the authors propose a new optimization method for the active thermal storage system using the PVC pipes for providing a new and original thermal storage circulation system. My comment about the paper are as follow:
1. The introduction is not well informative, it needs to be amended and improved so as to bring it into conformity with high-published paper. In addition, the novelty and overall contributions should be clearly stated.
2. Section (2.1.2. Active thermal storage circulation system) should be improved and clarified.
3. Map showing the location of the study area is necessary.
4. Section (3.6.1. Active passive heat storage and heat release) is relatively unclear and figure 7 is for bad quality. Please check and improve as possible.
In overall, the paper is suitable for publication, and to our opinion with the necessary revision will be a good contribution.
Author Response
Dear editor,
Thank you very much for your comments and we have carefully revised the manuscript following the comments and suggestions raised by reviewers. Following is the response list. Please kindly note that the changes have been added to the revised paper in blue color.
Point 1: The introduction is not well informative, it needs to be amended and improved so as to bring it into conformity with high-published paper. In addition, the novelty and overall contributions should be clearly stated.
Response 1: Modify and improve the introduction part, and supplement the novelty and overall contributions.
The solar greenhouse industry has a profound impact on the production of northern facilities. As of the end of 2018, the construction area of solar greenhouses in China was 5.775 million hm2, accounting for about one-third of the total construction area of horticultural facilities. The solar greenhouse provides a new way for the sustainable supply of vegetables in the off-season in north China. Traditional thick earth wall and brick wall solar greenhouse have the disadvantages of high construction cost, complex construction process and poor heat preservation performance. Meanwhile, the modular heat storage wall plays an important role in the development of modern solar greenhouse, and has a character of simple installation. Therefore, a large number of researchers explored on modular back wall material, back wall structure, heat storage mode, and heat preservation performance. Zou Zhirong analyzed the performance of the modular assembled solar greenhouse which has a good thermal insulation performance, a 30% lower construction cost and 14-20% higher output. Compared with the traditional solar greenhouse in Shandong area, the construction cost of soil module greenhouse can be reduced by more than 40%. Zhang Jie et al made a comparative analysis of gravel and traditional brick as the back wall material used in solar greenhouse revealed that the gravel wall solar greenhouse was 3.2-5.0℃ higher than the traditional brick wall solar greenhouse in three types of weather: sunny, cloudy and snowy. In addition, the internal temperature of the gravel wall solar greenhouse was also higher than that of the traditional brick wall. It indicated that the thermal performance of the gravel wall was better than that of the traditional brick wall.
It has been found that passive heat storage of solar greenhouse walls could not effectively maintain the indoor temperature of nighttime. Therefore, many researches designed the greenhouse with active heat storage.Zhang Chao and others compared and analyzed the temperature changes in the growing season of three solar greenhouses under different weather conditions. The results show that the active heat storage solar greenhouse is superior to the sunken solar greenhouse and the local traditional solar greenhouse as a whole. It has good heat preservation and temperature storage performance under extreme low temperature and typical overcast weather conditions, and can meet the growth requirements of indoor crops at low temperatures. The heat storage performance analysis of flat micro-heat pipe array heat storage wall showed that the greenhouse temperature was increased by 1.2-1.5℃ on average. Besides, the analysis results of a rear wall heat storage system with ventilated heat storage ducts and conducted performance revealed that the active heat storage rear wall solar greenhouse increased the temperature by 2.2℃ on average, compared with the traditional solar greenhouse. Wu et al tested the thermal performance of the back wall of active heat storage solar greenhouse (SW). Compared with passive heat storage solar greenhouse (CK), the average temperature of SW was lower during daytime and higher at night in sunny weather. In cloudy weather, SW was 1.8 and 2.7℃ higher than CK, and the effective heat storage layer of SW was more than that of CK in sunny and cloudy weather. It concluded that active heat storage solar greenhouse had a better heat storage effect.
The above studies provided data references for the production of active thermal storage heliogreenhouse. However, the thermal performance analysis of different modular thermal storage back walls combined with soil thermal storage has not been published yet. Firstly, the thermal performance of thermal storage back wall heliostat is excellent, but the long construction period and high cost limit the large area production of this type of heliostat. Meanwhile, the modular wall has the advantages of short construction time, low difficulty and input cost. Soil thermal storage is also an important way to improve the thermal performance of greenhouse. It has certain research significance to combine the two thermal storage methods and form a new system. In this paper, we optimized the active thermal storage system based on the previous research, and used PVC (Polyvinyl chlorid) pipes to connect the back wall thermal storage and soil thermal storage together to construct a new active thermal storage circulation system. Beyond that, different wall thermal storage materials were combined to build different modular thermal storage walls in order to optimize the thermal environment in the heliostat. By analyzing the heat transfer performance of two different modular heat storage wall solariums under winter, we could provide data references and production value for the practical use of modular heat storage wall solariums.
Point 2: Section (2.1.2. Active thermal storage circulation system) should be improved and clarified.
Response 2: Improve and clarify 2.1.2 Active thermal storage circulation system.
The active heat storage circulation system consisted of heat transfer ducts (indoor), axial flow fan, control system and so forth. As shown in Figure 3, 1-6 performed PVC pipe inlets which located at the top of the rear wall. 7-18 represented the PVC pipe outlets located 200 mm from the front roof in the soil and 450 mm above the soil. Thereinto, the inner and outer diameter of the PVC pipes was 95 and 110 mm, respectively. Meanwhile, the pipe diameter of PG rear wall was 200 mm. Other pipe diameters were 110 mm. Due to the different internal structure of the back wall, the total length of the pipes was different slightly, including 17.75 and 15.75 m for SG and 14.75 m for PG. The control system was installed on the east side of the greenhouse with an automatic fan control mode.When the room temperature during the period of 17:00 to 9:00 the next day was lower than 20℃, the fan could automatically turn on for heat dissipation. Then, if the room temperature were lower than 8 ℃, the fan could automatically stop for heat preservation. On the basis of the previous studies and the bottom-up flow law of indoor hot air, in order to ensure that more heat can be stored during the day and can appropriately reduce the humidity in the greenhouse to provide better growth conditions for crops, axial flow fan installed in the lower outlet position by the principle of negative pressure ventilation. When the fan was activated, the negative pressure was formed in the duct. Then, the hot air flowed from the wall to the soil and finally arrived in the room. The rated ventilation capacity and power of axial flow fan was 269 m3/h and 25 W, respectively. That is, the back wall is connected with the soil through PVC pipes, so that hot air can flow from the back wall to the soil along the PVC pipes, and then be guided to the air through the axial flow fan. As the hot air flows from bottom to top, it will enter the top air inlet again, and from then on, the hot air will form a circulating flow in the greenhouse.The heat release mode of the circulation system was carried out at night in order to achieve the effect of heat preservation in winter.
Point 3: Map showing the location of the study area is necessary.
Response 3: Supplementary map showing the location of the study area in Figure 1.
Figure 1 Test Location Map
Point 4: Section (3.6.1. Active passive heat storage and heat release) is relatively unclear and figure 7 is for bad quality. Please check and improve as possible.
Response 4: Section (3.6.1. Active passive heat storage and heat release) mainly analyzes the active and passive heat storage and release of the back wall of the greenhouse. The heat storage performance of the two greenhouses can be compared by comparing the heat flow density of the back wall of the two greenhouses and calculating the proportion of heat transfer and active heat transfer of the two greenhouses in different weather.
The pictures have been modified and improved as much as possible.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authirs have correctly adressed the necessaries comments and the paper can be accepted.
