Development of zone cooling system for aeroponically grown potato seed production in humid tropical lowland
Pengembangan zone cooling system untuk produksi benih kentang secara aeroponik di dataran rendah tropika basah
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Date
2013Author
Sumarni, Eni
Suhardiyanto, Herry
Seminar, Kudang Boro
Saptomo, Satyanto K
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Potato plant (Solanum tuberosum L) is one of the major food crops in the world after paddy, wheat, and corn. Carbohydrate content of potato is very high; therefore, it can be used to substitute rice, wheat flour, and maize. As one of the most important commodities, potato has comparative and competitive advantages, as well as good domestic and export market. However in Indonesia, the volume of potato production is lower than the volume of potato consumption. Therefore, Indonesia is importing potato from other countries. To increase potato production, Indonesia is facing difficulties in fulfilling the required potato seeds with high quality, right time and right variety. Using low quality potato seeds causes low productivity. In addition, increasing potato production is also facing problems related to the decrease in area for potato plant in highland, pest and plant diseases. In Indonesia, potato plant is generally cultivated on highland. This is very often accompanied by high rate in soil erosion. Shifting the orientation for potato cultivation to lowland is one of the most prospective solutions to increase potato production while solving the problems related to soil erosion. However, potato cultivation in humid tropical lowland is facing problems related to high air temperature and humidity. To overcome these problems, root zone cooling for aeroponically grown potato cultivation could be used. Zone cooling system could decrease temperature of certain zone but it also prevents the increase in air humidity. The objective of this research in general was to develop technology for aeroponically grown potato seed production in humid tropical lowland by using root zone cooling. To achieve the objective, three stages of research were conducted: (1) to apply zone cooling in aeroponic system for potato seed production in humid tropical lowland, (2) to predict temperature distribution in the growth chamber of aeroponic system with root zone cooling, (3) to calculate the heat load in the growth chamber of aeroponic system with root zone cooling. The research on zone cooling application was conducted in a greenhouse at the Department of Mechanical & Bio-system Engineering, Faculty of Agricultural Engineering and Technology, Bogor Agricultural University, at 250 m above the sea level, from April to July, 2012. The size of the aeroponic chamber used was 1.5 m x 1 m x 1 m. The material used for the outer wall of the chamber was wooden multiplex board and the inner side was insulated with styrofoam board. Plant bedding was made of styrofoam board. Plant spacing was 15 cm x 15 cm. Therefore, one chamber consisted of 45 plants. The variety of potato seedling was Granola, produced by tissue culture laboratory, Vegetable Research Institute, Indonesian Ministry of Agriculture, after acclimatization. The research results indicated that the values of average height and number of leave of the potato plant cultivated in aeroponic system with zone cooling were higher than that of without cooling. The best tubers were obtained in aeroponic system with 10 °C zone cooling, i.e., average productivity (579 tubers/m2), average number of tuber (14.85 tubers/plant), and average tuber weight (409.15 mg/tuber). The 15 °C zone cooling resulted in 55 tubers/m2 with average number of tuber of 1.67 tubers/plant and average tuber weight of 205.44 mg/tuber, which was not significantly different from that of the 20 °C zone cooling. The potato plant cultivated at 30.3-32.6 °C did not resulted any tuber. To obtain basic information for aeroponic chamber design, a series of simulation was conducted for temperature distribution inside the chamber. Simulation on the distribution of air temperature was done by using computer software of Solidwork ® Premium 2011. Three dimensions analysis was used for predicting fluids and thermal flows. A PC with the specification of CPU Intel ® Core TM i7, 8GB RAM, and 64bit operation system was used in the simulation process. In CFD simulation, the solution for flow of fluids was described quantitatively in terms of temperature and velocity in form of differential equation based on finite volume method numerical analysis particularly using Navier- Stokes equation. Maximum error of the results of CFD simulation was 5.89%. This shown that the defining of the materials for CFD inputs was good enough and could illustrate the condition of aeroponic chamber. The error could be reduced by including physical and chemical properties of the nutrition solution for the simulation. Comparison between air temperatures in aeroponic chamber obtained from CFD simulation to that of the measured values resulted in conclusion that CFD was very useful in predicting temperature distribution in the aeroponic chamber. This was demonstrated by regression equation for simulated and measured air temperature in the aeroponic chamber with gradient of 0.982 which was very close to 1 and intercept of 0.189 which was very close to 0. In aeroponic system with zone cooling, energy consumption is the most important problem to be solved. Therefore, heat load of zone cooling in the aeroponic system for potato seed production on humid tropical lowland it the subject was calculated using the principles of heat transfer. Heat transfer can take place through radiation, conduction, and convection. Calculation of electrical energy required for aeroponic system with zone cooling for seed potato production in the lowlands found that for 10 °C zone cooling was 0.917 kWh/m2. The averages of daily electrical energy use in the aeroponic system with 15 °C zone cooling, 20 °C zone cooling, and without any cooling operation were 0.590 kWh/m2, 0.439 kWh/m2, and 0.0132 kWh/m2, respectively.