Investigation of Installation Conditions of a Complete Artificial Light Type Savoy Spinach Plant Factory for Cold Regions
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Journal of Advanced Agricultural Technologies Vol. 7, No. 2, December 2020 Investigation of Installation Conditions of a Complete Artificial Light Type Savoy Spinach Plant Factory for Cold Regions Naoki Kikuchi and Shin’ya Obara Electrical and Electronic Engineering, Kitami Institute of Technology, Kitami, Japan Email: [email protected], [email protected] Abstract—This paper considers energy consumption and Photovoltaics (PV) and Solid Oxide Fuel Cell (SOFC) choice of the optimal area for plant factory with low- cogeneration are used. In addition, a system with low temperature treatment of spinach. When exposed to a low- energy consumption was developed by supplying the temperature (less than 7°C) environment, spinach increases exhaust heat of SOFC cogeneration to an absorption the sugar content. In order to process by exposure to the refrigerator and the heat storage tank to cover energy coldness of spinach, it is necessary to hold the inside of the proposed plant factory at 7°C. The maximum air demand of the plant factory. temperature from December to March of Kitami in Okhotsk This paper considers energy consumption and choice is less than 7°C. Therefore, in this period, a ventilation fan is of the optimal area for plant factory with low-temperature used to air cooling the plant factory. On the other hand, the treatment of spinach. When exposed to low temperature plant factory is cooled by an absorption refrigerator from (less than 7°C) environments, savoy spinach leaves tend April to November. Because many regions where the to shrink. Also, savoy spinach has a higher nutritional maximum temperature of winter is less than 7°C were value such as sugar content and vitamin C than ordinary located in Hokkaido, the payback period of the proposed spinach, so the selling price is higher. In order to process system based on equipment cost and energy consumption by exposure to the coldness of spinach, it is necessary to were investigated about seven regions (Wakkanai, Asahikawa, Abashiri, Kutchan, Obihiro, Hiroo, Kitami) of hold the inside of the proposed plant factory at 7°C. them. When the proposed plant factory is installed in seven Because maximum air temperature from December to regions, because the analysis results of payback period are March of Kitami is less than 7°C [9], the room 6.83 years, the proposal plant factory and energy system for temperature of the plant factory is air-cooled by a low-temperature treatments of spinach can be introduced ventilation fan from December to March and cooled by enough commercially. an absorption refrigerator from April to November. In the previous study, the analysis was conducted Index Terms—plant factory, SOFC cogeneration, spinach, assuming that the proposed plant factory was set up in energy saving, cold regions Kitami. As a result, the minimum payback period was 6.64 years, and the target payback period (ten years or less) was achieved [8]. However, it is not investigated I. INTRODUCTION whether the proposed plant factory can be introduced in Farmers in cold regions are not able to work outside regions other than Kitami. Also, if the annual average in the winter because of snow covers the ground. In temperature in the region where the proposed plant addition, reduction of employed in agriculture by factory is located is around 7°C, it can be expected that aging is also an important issue [1]-[3]. From these, the annual energy consumption will be reduced and the plant factories with an electricity-saving type for cold payback period will be shortened. Therefore, in this paper, regions are expected. The plant factory has the assuming that the proposed plant factory will be advantage of ensuring a stable yield regardless of the introduced in seven regions (Wakkanai, Asahikawa, weather, but it has the disadvantage that it is difficult to Abashiri, Kutchan, Obihiro, Hiroo, Kitami) in Hokkaido, make a profit because of high initial costs and running the payback period of capital investment of the proposed costs [4]-[7]. The previous study examined the energy plant factory and the installation conditions that shorten system in the complete artificial light type savoy spinach the payback period will be investigated. Also, the target (which is a typical special product in the Okhotsk region of the payback period of the proposed plant factory of Hokkaido) plant factory for cold regions, in order to proposed shall be ten years or less. carry out stable and energy-saving cultivation of high added value crops [8]. In the complete artificial light type II. COMPOSITION OF A PROPOSED PLANT FACTORY savoy spinach plant factory (the proposed plant factory), Fig. 1 shows the configuration of the proposed plant power and exhaust heat of the cooperation system by factory that assumes process by exposure to the coldness of spinach. Furthermore, Fig. 2 shows the change of daily Manuscript received April 30, 2020; revised October 29, 2020. maximum temperature in Kitami and the room ©2020 Journal of Advanced Agricultural Technologies 28 doi: 10.18178/joaat.7.2.28-32 Journal of Advanced Agricultural Technologies Vol. 7, No. 2, December 2020 temperature in the plant factory. In the plant factory, the the total opening of the plant factory is 54m. Based on SOFC cogeneration with rated output 370kW and PV this structure and dimensions, when the room temperature with rated output 370kW will be installed to cover the of the plant factory is maintained at 7°C using the exhaust power consumption of the plant factory. From spring to heat of SOFC cogeneration, the depth of the plant factory autumn (April to November), the room temperature of the is 133.5m according to the heat balance calculation. proposed plant factory is cooled to 7°C by an absorption In a plant factory, spinach is processed by exposure to refrigerator. On the other hand, the maximum air coldness with the leaves hanging down. This method is temperature from December to March of Kitami is less called aerial cultivation (hanging cultivation) and is than 7°C. Therefore, in this period, a ventilation fan is introduced in this paper for the following reasons. In used to air cooling the plant factory. By using this cooling general spinach cultivation, the interrow spacing of cycle, the energy consumption for air conditioning in spinach is about 20cm and the planting distance of winter can be reduced. spinach is about 5 to 7cm. However, in savoy spinach Typical plant factories are prefabricated houses or cultivation at processing by exposure to coldness, the glass greenhouses, but the initial cost is high. Therefore, occupied area of spinach increases because the leaves of in the proposed plant factory, the initial cost is suppressed spinach are open. So the interrow spacing of savoy by using a vinyl greenhouse. The proposed plant factory spinach becomes about 20cm and the planting distance of has a double structure in which two greenhouses are savoy spinach become about 10 to 20cm [10]. Therefore, stacked, and the gaps in the greenhouse are filled with a the cultivation area of savoy spinach is about twice that heat-insulating material (glass wool 24K). A heat of general spinach. However, in the case where spinach is shielding sheet is used for the outer covering material, processed by exposure to coldness using aerial cultivation, and an agricultural specialty polyolefin film is used for the cultivation area can be made smaller than that of the inner covering material. The plant factory has a ordinary savoy spinach cultivation. This makes it possible structure in which 10 greenhouses with an opening of to reduce the size of the plant factory system and is 5.4m and a height of 3.4m are arranged side by side, and expected to reduce initial costs. Figure 1. Configuration of a proposed plant factory. Absorption the initial cost of the plant factory (Cinitial [USD]), and the 40 refrigerator denominator is the profit (cprofit [USD/year]) when 30 Heat cultivating savoy spinach. storage 20 tank 12 30 24 Cinitial,t,d,m 10 F = → minimize (1) year c 0 m d t profit,t,d,m Daily maximum Daily maximum temperature temperature [°C] Ventilation fan -10 Jan. Mar. May Jul. Sep. Nov. Jan. B. Electricity Balance and Heat Balance Temperature in the plant factory Equation (2) is the electricity balance equation. The Daily maximum temperature left side of equation (2) is the electricity of SOFC Setting temperature cogeneration (Psofc [kW]) and the electricity of PV (Ppv Figure 2. Change of the daily maximum temperature in Kitami for one [kW]), the right side is power consumption of the LED year. (Pll [kW]) and power consumption of an absorption refrigerator (Par [kW]). The electricity balance equation for April to November is equation (2). III. ANALYSIS METHOD Equation (3) is a heat balance equation. The left side of equation (3) is the amount of solar radiation (Hsh [kW]), A. Objective Function to Calculate the Payback Period the heat generation amount of the LED (Hll [kW]), the of the Plant Factory heat supplied from the heat storage tank (Hhst [kW]), the In this paper, the payback period of the proposed plant cold heat quantity by the absorption refrigerator (Har [kW]), the heat input (H [kW]) to the set temperature at factory (Fyear [year]) is minimized using the objective i function of equation (1). The numerator of equation (1) is the start of cultivation. The right side is the heat radiation ©2020 Journal of Advanced Agricultural Technologies 29 N Journal of Advanced Agricultural Technologies Vol. 7, No. 2, December 2020 quantity to the outside air (Hra [kW], convective heat ] 11.0 transmission from the outer wall). There is the balanced 10.5 10.0 formula between April and November, and the electricity 9.5 balance and heat balance between December and March 9.0 8.5 are expressions in which the terms of absorption 8.0 refrigerator (Par [kW], Har [kW]) in equation (2) and 7.5 7.0 equation (3) are replaced with ventilation fan (Pvf [kW], 6.5 Hvf [kW]).