Content linked here is in the SystemsLevelDesignDocuments directory.
Team Vision for System-Level Design Phase
During this phase, we started the process of determining the best aquaponics system design for our use. We want a low power and low-cost system that can supplement 100% of a family’s protein needs. This was done through functional decomposition, morphological charts, Pugh charts, feasibility analysis, cost analysis and concept selection. We still would like to talk to a subject matter expert for their knowhow and skills. We also hope to start prototyping and continue feasibility testing for the aquaponics system then prepare for the next design review.
Functional Decomposition and Transformation Diagram
There aren’t many aquaponic systems you can go out and buy as most backyard aquaponic systems are DIY projects. The two listed above are the only ones found that included enough information to benchmark from. Most notable from this exercise was the cost of these systems as we are looking to create a system at a drastically lower price range.
The team visited the Greenhouse Café in Rochester which has an aquaponic system. Unfortunately, we have yet been able to arrange a tour of the facility. From the outside, we were able to observe the plants that were being grown and the materials that were used to build the plant beds such as halved water barrels, but we could not see how the fish tank was set up. All of the pictures taken can be found here: Greenhouse Cafe Photos
Feasibility: Prototyping, Analysis, Simulation
Nutritional OutputUsing fish and crop growing parameters found on the Internet, an analysis was conducted to determine if the system could supply enough nutrients in a small enough footprint for it to be viable. It was found that a system containing 40 fish in a 0.4 m^3 tank, a 1.44 m^2 raft of pinto bean plants, and a 1.44 m^2 raft of tomato plants could supply, on average, 28.2 grams of protein, 62.5 grams of carbohydrates, and 3.07 grams of fat per day. These outputs are not continuous; the numbers given are the averages over several harvest cycles. The nutritional output is equivalent to about 50% of the protein, 25% of the carbohydrates, and 6% of the fat required by one person's diet. The conclusion is that a device that supplied such a significant portion of a person's diet in such a small footprint would be useful. The full analysis can be found here: Nutritional Analysis
Water Needs by PlantsCalculation of the minimum water the plants need to survive (dependent on plant type and plant bed area): Water Calculation
An approximate calculation given a 1m by 1m plant bed results in 12 gallons of water a week. This should be feasible.
StructuralCalculation of stresses on plant bed support structure and needed supports: Strength Support Calculations
PowerCalculation of power required for sensor system: Power Calculations
Morphological ChartUsing the developed engineering requirements and functional decomposition, two morphological charts (one for the aquaponics system and another for the monitoring system) were created to show the various options available for each sub-system of the aquaponics system. This chart allows for unintuitive combinations of sub-systems which could be more beneficial than more intuitive combinations. The current morphological chart can be found here:Morphological Chart
These sub-system combinations will be further analyzed in the Pugh charts shown in the section below.
Working document can be found here: Aquaponics System Concept Selection.
The Pugh chart used to compare concepts for the aquaponics part of the system can be found here: Aquaponic Pugh Chart
The first row of the Pugh chart is shown below as an example.
Working document can be found here: Sensor System Concept Selection.
The Pugh chart used to compare concepts for the sensor system can be found here: Sensor System Pugh Chart
For the water pump, we chose a simple hand pump that can be made from PVC pipes and fittings. An article here https://lifehacker.com/build-a-powerful-hand-pump-from-scratch-with-pvc-pipe-1186786117 includes video instructions on how to make one.
The maker of this DIY video states that by his measurements, the pump can move about 2 cups of water with each stroke and he was able to move 5 gallons in one minute. We intend to start with this design and look for ways to improve the pump and lower the cost.
If the pump was made with the exact parts specified in the video, the cost will be approximately 107,000 to 138,000 Columbian pesos based off of the Homecenter and Easy Hardware sites. (The calculation can be found here: Hand Pump Cost) The range is due to the various options for check valves that only let water flow in one direction. It is cheaper to make a check valve than to buy it, but it is easier to find a check valve than to find the components to build one.
We could not find a hand pump on the websites we currently have access to, so we do not know how the price of a DIY pump compares. However, given that we have not been able to find one, it will be valuable to the farmers to have the knowledge to build their own.
Plant Bed Support StructureThe purpose of this structure is to keep the plant bed properly supported above the fish tank so the plants can grow while their roots are submerged in the water of the makeshift tank.
Many building materials very expensive given our restrictive budget, so many components of the support structure only had one option available to chose from (styrofoam, plywood, sideboards, etc.). However, we were able to analyze whether it would be better from a strength and cost perspective to build a support system with wooden or brick/mortar support legs. The strength analysis can be found in the feasibility section of this page. A support system with wooden support legs would cost roughly 127250 Colombian Pesos and a brick/mortar would cost roughly 203300 Colombian Pesos. More in-depth analysis can be found here: Plant Bed Support Cost Estimation
This second filter will nullify any ammonia, nitrites and nitrates that weren't converted by the plants, by setting up a bacteria bed. This ensures clean water returning to the fish.
Fish Tank and ReservoirA fish tank is needed to house the fish, and a reservoir is needed as temporary storage for nitrite-rich water before it flows through the plant roots. Most likely, the same solution will work for both of these tasks. Two 55-gallon garbage bins for the fish and one for the reservoir would be sufficient, but the farmers will be able to substitute any suitable container they can find if the garbage cans are not in their budget.
Sensor SystemBelow is a design idea for the enclosure box for the microcontroller and LCD display and other necessary electrical components.
Design Review Materials
Pre-read for System Design Review: Pre-Read