Climate change combined with the growth of urbanization and world population is increasing the likelihood of disruptive events, such as epidemics, floods and bushfires. It is thus important to increase the resilience of urban environments by reducing their over-dependence on food and energy supplied from remote locations, which is considered on their main risks. The benefits are self-reinforcing, producing energy and food closer to where they are consumed can also reduce energy consumption besides increasing urban resilience to disruptions. Hydroponics is an earth-less farming system that can save up to 80% of the water needed for food production. It is highly productive, increasing plant growth rate and reducing the area requirements. It may be deployed vertically or stacked making it specially fit for urban environments where soil is scarce. HydroGreen Point is a modular structure that combines a small hydroponics unit with solar energy production and a command interface. The structure was designed be digitally manufactured with a CNC router from OSB, plywood, or any flat panel that is adequate for exterior use. The concept was developed in collaboration with Diogo Guerreiro for a competition in 2017. It proposes the use of locally available resources combined with a mix of open-source and off the shelf technologies to provide small self-sufficient food production units. The main aim was to raise awareness, provide information and disseminate knowledge on hydroponics in urban environments.
HydroGreen Point (HGP) form was conditioned by the specific purpose of was working as an information point on a public space. Thus it was conceived as a modular structure that could be easily moved, composed of four modules with specific functions: hydroponics, control, lighting and solar energy modules. The form is the result of the translation of a square vertically. The asymmetric structure is a response to the need to improve the solar exposure of the solar panels and plants. The option for a tall structure allows to benefit from a chimney effect, improving natural ventilation and solar panel exposure. The form is also influenced by the need to provide a surface for the control panel and system. All faces are transparent, except the control panel face which should be north oriented, to increase solar expose of the plants.
The base module is the hydroponics module, which houses the technical parts (batteries, tank, pumps..). It was also left opaque to protect components from solar induced heating, particularly the hydroponic solution tank. Two opposite side panels of the base module can be opened for maintenance. Behind the control panel, in the control module, are the electronic components, in a box that can be accessed from the front of the panel. The control module transparent panels can also be open to provide access for maintenance and ventilation.
The structure of the HGP is made with double OSB studs with integral joinery cut off 15mm thick OSB 3 boards with a CNC, which provide a good compromise on structural efficiency and sustainability. The structure is assembled by hand and the connections are ensured by friction-fit joinery. The opaque panels are made of a composite of 9mm plywood and 30mm insulation cork board, allowing for improved resistance to weather and lighter panels. The modules can be independently assembled and connected by friction-fit joint. The translucid panels of the modules are made in 3mm acrylic. All the materials, with the exception of the acrylic, come from renewable sources and can be recycled.
There are several hydroponic systems in use, for this project we have chosen the NFT (Nutrient Film Technique) system, which is easy to automate, calibrated for lettuces, which are the easiest plants to grow. The system was calibrated to produce 15 lettuces every 15 days. The most common NTF system uses a network of pipes where a nutritive solution (the film) circulates. Holes are pierced in the pipes to insert the plants, with a distance along the tube and between pipe axes that is dependent on the size of the plant. The nutritive solution is collected in a light insulated plastic tank, to avoid algae growth. A complete production system for lettuces comprises three stages which are related with plant growth phases: seedling or germination, nursing and production. In the case of plants that bear fruit this can also be called seedling, vegetative and flowering stage.
The hydroponic system we proposed has a capacity for 40 plants in the production stage, 15 plants on the nursing stage with a 60 litters tank. It features a 12V submersible pump, which works in 15 minutes cycles during the daylight period and 3 cycles of 15 minutes during nighttime. This means the pump is working half the time during the day time period. The system includes an air pump, to mix oxygen in the solution, a waterlevel sensor, an electric valve connected to a water supply, a PH sensor, two peristaltic pumps to feed acid or basic correction to the solution. We also include an air temperature / humidity sensor to monitor the greenhouse.
A Raspberry Pi will collect measurements from the sensors and command the pumps and valves, adjusting the water pump cycles to the yearly daily period variation. It will also control the air pump, collect PH measurements and used them to control the peristaltic pumps. The water level sensor readings will be used to trigger the electric valve and send an email. The air temperature/humidity sensors will be used to monitor the greenhouse temperature, if a threshold is reached a warning email will be sent requesting that the greenhouse doors be open.
The automation system will allow a 15 days autonomy. Each fortnight it will be necessary to add solution to the tank and collect the crops, change the plants in the nursery to the production stage and place 15 new sprouts in the nursery.
An indicative bill-of-materials for the hydroponics and automation systems is presented bellow. If you decide to build one yourself please share the results.
Atlas Scientific sells kits for IOT (Internet of Things) water systems. The PH Kit, Conductivity Kit, Temperature Kit, Dissolved Oxygen Kit can be used to automate the hydroponics system. Sparkfun also sells PH sensors and kits, water temperature and electric conductivity sensors. Water level sensors are available here and 12v submersible pumps can be found here or here. This project demonstrates how to use an arduino to control water pumps and here you can find a peristaltic pump.