In the United Arab Emirates, 85% of the food is imported. These imported products travel long distances to make it to the shelf compromising quality, and nutrient value while contributing to pollution and costing billions in dollars. In addition, many crops cannot be grown locally due to temperature, soil, and water in the region. Therefore, controlled environment agriculture is a technique that can be used to secure food supplies in the UAE. This project aims to design an in- house farming-controlled environment food replicator where the conditions are heavily optimized for a crop and at an accelerated production rate.
The project goal involves selecting material based on thermal conductivities and reflectance as well as designing an optimal refrigeration cycle best suited to selected crops using HYSYS. In addition, Computational Fluid Dynamics (CFD) modeling will be used to study the heat and mass transfer within the system. A market analysis will be conducted to compare the cost of production to available alternatives. Furthermore, a prototype can be developed using 3D printing.
Progress summary
The project contains several progress reports that display the working path of processing the project. Up to this point, the team has completed the research sector where they combined all useful information that has been found about the benefits of an in-house replicator project and conducted a beneficial literature review. Following that task, a letter of intent was written to the Abu Dhabi Agriculture and Food Safety Authority that propose the project and define the purpose.
In regards to the considered design, it has been divided into four parts that are; the type of crop, the type of material, light source and the refrigeration cycle best suitable for the design. Then, an analysis was done using the decision matrix tool to compare different alternatives and choose the best-suited option.
In the next period, the group will be working on the design of the refrigeration cycle in detail by choosing the type of refrigerant using the HYSYS software simulation. Moreover, an introduction to Computational Fluid Dynamics (CFD) software will be conducted to begin the study of heat and mass transfer.
Design of alternatives
A weighted decision matrix was the criteria used to find out a suitable alternative to be chosen for the project. A Pair Wise Comparison Chart (PCC) was first conducted to determine the weight. In the weighted decision matrix, three crop types, three material types, and two light sources were ranked based on the weight (Multiplication factor). The result chosen was based on the Pairwise Comparison Chart (PPC) generated where the weight was multiplied by the given ranked metrics. A detailed analysis of designed alternatives is shown below.
1- Crop types
The metrics were compiled in a way that it would be clearer to put a scale for the components of the system. It ensures that the group’s decisions are optimum and accurate when it comes to the final design decision. Table 1 shows A Pair Wise Comparison Chart which was used to compare each objective to the other by putting 1 if it is more important and 0 if it is less important. Table 2 illustrates the metrics used in the crop type’s decision. It was used to measure the degree to which the objectives are going to be achieved.
Table 1: Pair Wise Comparison Chart
PCC Maintenance Favorability Nutrient Water Total
Maintenance – 1 1 1 3
Favorability 0 – 1 0 1
Nutrient 1 0 – 1 2
Water 0 1 0 – 1
Table 2: Metrics for crop type
Objectives Points
Maintenance Low: 100 points
Moderate: 75 points
High: 50 points Extremely high: 25 points
Favorability Always consumed: 100 points Usually consumed: 75 points
Rarely consumed: 50 points Never consumed: 25 points
Nutrient An equal amount of Nitrogen, Potassium, and Phosphate: 100 points Nitrogen amount is higher than Potassium and Phosphate:75 points Potassium amount higher than Nitrogen and Phosphate: 50 points Low amount of Nitrogen, Potassium, and Phosphate:: 25 points
Water ( inch ) 0≤W<0.5: 100 points
0.5≤W<1: 75 points
1≤W<1.5: 50 points
W >1.5 : 25 points
A crop plays an important role in the field of agriculture. The UAE has developed an artificial environment for its agricultural industry. Therefore, three crops have been chosen for comparison among which one crop needs to be selected that fits the designed technology specification. The temperature required for the growth of all three crops is more or less in the same range as per project specification. For instance, carrots require a temperature of 75 F (24C) to grow properly. Similarly, the temperature required for the growth of strawberry and sweet peppers is 60 to 80 F (16-26C) and 65 to 70 F (18-21C) respectively [1].
Table 3: Weighted Decision Matrix (Crop type)
Weight Strawberry Sweet Pepper Carrot
Maintenance 3 3 x 100 = 300 3 x 50 = 150 3 x 50 = 150
Favorability 1 1 x 50 = 50 1 x 75 = 75 1 x 100 = 100
Nutrient 2 2 x 100 = 200 2 x 50 = 100 2 x 75 = 150
Water 1 1 x 75 = 75 1 x 50 = 50 1 x 75 = 75
Total 625 375 475
From the above analysis and according to Table 3, it is clear that strawberries are superior to the other two crops. From each aspect, whether it is maintenance (needing the least amount of maintenance), internal or external parameters required for crop development.
Strawberry becomes the most suitable crop and preferred by people for in-house growth. In the case of strawberries, its seed needs more water than sweet peppers, which is around 1 inch of water weekly although it needs less maintenance compared to carrots and Sweet Pepper [2]. Regarding the number of nutrients, Strawberry is identified as the most nutritious crop that has an equal amount of Nitrogen, Potassium, and Phosphate which reflects successfully towards its growth. However, there is a variation in the nutrients’ amount of both carrot and sweet pepper.
Overall, Strawberries have antioxidant feature and therefore they are very helpful for the blood sugar and heart.
2- Material selection
There are several insulation materials available in the market that have different insulating properties. It is very important to select the right type of insulation material considering the temperature of the system and the mode of heat transfer involved. For our design, we need to select the material that has low thermal conductivity, available in the market, non-corrosive, non- flammable, reflective, and cheap. Thermal conductivity (K) is the most important in determining a material’s ability to resist the flow of heat. By comparing the thermal conductivity of the materials, that we chose Polycarbonate (0.22 W/m. C), polyurethane (0.026 W/m. C), polystyrene (0.057 W/m. C) [3].
A Pair Wise Comparison Chart, the metrics, and decision weighted matrix for the material selected are shown in the tables below, where thermal conductivity, cost, safety, durability, and reflectivity are considered.
Table 4: Pair Wise Comparison Chart
PCC Low thermal
conductivity Cost-effective Safe Durable Reflectance Total
Low thermal
conductivity – 1 0 1 1 3
Cost-
effective 0 – 0 1 1 2
Safe 1 1 – 1 1 4
Durable 1 0 0 – 0 1
Reflectance 0 0 0 1 – 1
Table 5: Metrics for material selection
Objectives Points
Low thermal conductivity (K) 0≤K<0.03: 100 points
0.03≤K<0.05: 75 points
0.05≤K<0.07: 50 points
K>0.07: 25 points
Cost-effective (A) in AED 10,000≤A<12,000AED: 100 points
12,000≤A<14,000AED: 75 points
14,000≤A<16,000AED: 50 points
16,000≤A<20,000AED : 25 points
Safe (S) Probability of corrosion per year 0≤S<1: 100 points
1≤S<2: 75 points
2≤S<3: 50 points
3≤S<4: 25 points
Durable (D) lasting in years 4≤D<6: 25 points
6≤D<8: 50 points
8≤D<10: 75 points
D>10: 100 points
Reflectance % of light 0 %≤R<5%: 25 points
5% ≤R<10%: 50 points
10% ≤R <15%: 75 points
R>15%: 100 points
Table 6: Weighted Decision Matrix (material selection)
Weight Polycarbonate Polyurethane Polystyrene
Thermal
conductivity 3 25 x 3= 75 100 x 3=300 50 x 3=150
Cost effective 2 50 x 2=100 75 x 2=150 100 x 2=200
Safe 4 75 x 4=300 100 x 4=400 100 x 4=400
Durable 1 100 x 1=100 100 x 1=100 75 x 1=75
Reflectance 1 25 X 2 = 50 25 X 1 = 25 25 x 1 = 25
Total 625 975 850
To design indoor farming, the selected material is polyurethane as shown in Table 6 because it has the lowest thermal conductivity, it is considered safe, durable, and economically feasible. However, it is not reflective much. Reflectivity is the amount of light that is reflected from a surface when light shines on it. The higher the reflectance%, the better to prevent the light from escaping. Polyurethane can be further modified to increase the reflectance and keep the light inside the replicator. Polyurethane can achieve a thermal conductivity as low as 0.022 W/m. C to 0.028 W/m•C. This makes it one of the most efficient insulation materials available on the market. When compared to other materials, a much lower thickness of polyurethane insulation is needed to get the same level of performance. It is used in medium to heavy-duty refrigeration systems to reduce heat gain. Moreover, polyurethane is available with a thickness of 10 to 15 mm and a density ranging from 35 to 50 kg/m3 [3].
3- Light source
One of the most essential factors for excellent indoor farming is the light source. After selecting strawberry as the best crop for our design, the best light source needs to be selected based on its significant effect on the growth of strawberry plants. Colors Spectrum for LED Grow Lights which is suitable for our design can be blue and red lights. Another property to be considered when choosing the light sources is the wavelength. The effect of blue light with a wavelength of 400-495 nm on plants is directly related to chlorophyll production. Plants that receive plenty of blue light will have strong, healthy stems and leaves. Whereas, Red light with a wavelength of 620-750 nm is responsible for making plants flower and produce fruit. It’s also essential to a plant’s early life for seed germination, root growth, and bulb development [4]. Below is a Pairwise Comparison Chart, the metrics and the weighted decision matrix used to compare red and blue lights.
Table 7: Pair Wise Comparison Chart
PCC Production Safe Cost-effective Energy Total
Production – 0 1 1 2
Safe 1 – 1 1 3
Energy 0 0 1 – 1
Cost-effective 0 0 – 1 1
Table 8: Metrics for a light source
Objectives Points
Production (P) due to a wavelength 400≤K<600: 100 points
600≤K<800: 75 points
8000≤K<1000: 50 points
K>1000: 25 points
Cost-effective (A) in AED Very cheap: 100 points Cheap: 75 points Average:50 points
Expensive: 25 points
Safe (S) Probability of corrosion per year 0≤S<1: 100 points
1≤S<2: 75 points
2≤S<3: 50 points
3≤S<4: 25 points
Energy (E) Very low energy: 25 points Low Energy: 50 points Moderate energy: 75 points
High Energy: 100 points
Table 9: Weighted Decision Matrix (light source)
Weight Red light Blue light
Production 2 75 x 2= 150 100 x 2=200
Safe 3 100 x 3= 300 100 x 3=300
Energy 1 75 x 1 =75 100 x 1=100
Cost effective 1 75 x 1=75 100 x 1=100
Total 600 700
Based on Table 9, the final selection of light source which will be used in the indoor farming design is the blue light. The strawberry plants grown up in blue light will have higher amounts of biomass and tended to have much-reduced leaf areas with having longer flower stems and petioles. By increasing the number of blue wavelengths, this could help increase the yield of strawberries that can be obtained from the plants [4].
4- Refrigeration cycle
To maintain the temperature in the in-house farming system a refrigeration cycle is used. Refrigeration implies maintaining the temperature below the surrounding temperature. Before designing the refrigeration cycle, the Carnot refrigerator was considered which provides a standard comparison. There are two types of refrigeration cycles that were considered which are single-stage refrigeration cycle and two-stage cascade refrigeration cycle. Both cycles consist of a compressor, refrigerants, throttle valve, condenser, and a heat exchanger [5].
Moreover, the single-stage refrigeration cycle is a very reliable technology, relatively inexpensive and efficient up to 60% [6]. Although a two-stage cascade has higher efficiency, it is more expensive than the single-stage refrigeration cycle since it will contain two composers that require energy. Considering the specifications of the project, a single-stage refrigeration cycle would be more appropriate in this case since the in-house farming system implemented is simple. In addition, to achieve the aim of having an economically feasible design a single-stage refrigeration cycle is considered the best choice.
A refrigerant is a compound that is commonly a fluid and is used in a refrigeration cycle. In most cycles, it undergoes phase transitions from a liquid to a gas and then back to a liquid [7]. To choose the suitable refrigerant, the following were considered difluoromonochloromethane (R22), tetrafluoroethene (R134a), dichlorodifluoromethane (R123), difluoromethane (R32), and a mixture of difluoromethane and pentafluoroethane (R410A). To choose the type of refrigerant,
HYSYS simulation is required to calculate the efficiency and work by the compressor. Finally, the refrigerant with the highest efficiency will be chosen.
Challenges
In almost every project, team members will usually face unexpected challenges throughout their progress toward accomplishing the goal of the project. The unexpected challenge the group faced is when designing the refrigeration cycle since the group members do not have enough background knowledge of how the refrigeration cycle works. This issue was resolved by doing research and examining the process flow diagram of the refrigeration cycle. In addition, asking for help from the supervisor for a better understanding of the refrigeration cycle in regard to the project.
Furthermore, the challenges the group might face are technical issues when simulating in HYSYS and while modeling using Computational Fluid Dynamic. To overcome these challenges asking for help from the right experts to come up with better solutions and creating a strategic plan that best works for the group. Unexpected challenges can affect the quality of the work which is a very important aspect of a project. Poor quality would lead to failure in delivering the required specifications of the project. Consequently, these challenges will also affect the ability of the group to meet deadlines.
Overall assessment
Overall, the project promotes a healthy environment and a green economy by reducing the number of imported fruits and vegetables. The project evolves toward the UAE’s aim of ensuring a sustainable food production system to grow their preferred crop easily in all seasons. After performing the criteria to choose the suitable alternative, the project will be based on strawberries. The design system will be made of polyurethane and will contain a blue light with a single-stage refrigeration cycle to maintain the temperature. As stated previously, the team has several tasks to accomplish in the upcoming period that includes the use of the HYSYS software to design the refrigeration cycle as well as to study the heat and mass transfer within the system using Computational Fluid Dynamics. The progress reports regarding the ways of project management and the Health safety and environment (HSE) aspects will also be completed next.
References
[1] J. Ward and J. Symons, “Optimising Crop Selection for Small Urban Food Gardens in Dry Climates”, Horticulturae, vol. 3, no. 2, p. 33, 2017. Available: 10.3390/horticulturae3020033.
[2] S. Valtcho D. Zheljazkov and V. Schlegel, “Influence of winter stress and plastic tunnels on yield and quality of spinach, pak choi, radish, and carrot”, Emirates Journal of Food and Agriculture, p. 357, 2018. Available: 10.9755/ejfa.2018.v30.i5.1687.
[3] S. Satta Panyakaew, “321: Agricultural Waste Materials as Thermal Insulation for Dwellings in Thailand: Preliminary Results”, Citeseerx.ist.psu.edu, 2019. [Online]. Available: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.585.122. [Accessed: 01- Oct- 2019].
[4] H. Choi, B. Moon, and N. Kang, “Effects of LED light on the production of strawberry during cultivation in a plastic greenhouse and in a growth chamber”, Scientia Horticulturae, vol. 189, pp. 22-31, 2015. Available: 10.1016/j.scienta.2015.03.022.
[5] R. Arora, Refrigeration and air conditioning. New-Delhi, pp. 243,270.
[6] “What is vapour compression refrigeration cycle?” Quora.com, 2019. [Online]. Available: https://www.quora.com/What-is-vapour-compression-refrigeration-cycle.[Accessed:29-Sep- 2019].
[7] S. Haaf and H. Henrici, “Refrigeration Technology”, 2019. [Online]. Available: https://onlinelibrary.wiley.com/doi/full/10.1002/14356007.b03_19. [Accessed: 17- Sep- 2019].
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