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Building-integrated agriculture (BIA) predominantly uses soilless cultivation techniques such as hydroponics, aquaponics or aeroponics. The benefits of BIA include year-round production, higher yields, greater control of food safety and biosecurity, and substantially reduced inputs with respect to water supply, pesticides, herbicides, and fertilizers, as well as improved building energy efficiency through the creation of symbiotic relations between the farm and its host building. BIA systems can be applied either on the building envelope – on the rooftop or facades, to take advantage of the availability of natural light – or indoors with artificial light, or in a free-standing building (Figure 2), and all the growing parameters are controlled. This is known as Controlled-Environment Agriculture, or CEA, which combines horticultural and engineering skills in order to optimize crop production, crop quality and production efficiency.
Among the several existing forms of BIA, rooftop greenhouse farming is one of the most popular, since rooftops represent a considerable unutilized urban area, and lightweight hydroponic greenhouses do not necessitate any significant structural reinforcement of the host building (Benis & Ferrão 2018). The rooftop is an ideal landscape for growing plants in dense cities, as it typically has greater exposure to solar energy than the ground below. While yields from hydroponic greenhouses are higher than those from open-air soil-based rooftop farms, the range of vegetables that can be grown is smaller, and tends to be restricted to leafy greens, microgreens, herbs, tomatoes, cucumbers, aubergines, peppers and strawberries (Buehler & Junge 2016). Hydroponic greenhouses are often provided with climate control systems, such as fans, heaters, evaporative cooling, thermal screens, and operable windows, in order to condition the indoor air and achieve the optimal temperature, relative humidity, and carbon dioxide levels, regardless of outside conditions. They are heated with natural gas or electricity, with potential backup through photovoltaic (PV) panels. State- of-the-art installations capture waste heat from the building’s HVAC system, and may be constructed with solar glass, which collects specific wavelengths of sunlight for generating electricity, while transmitting and diffusing other wavelengths into the greenhouse (Figure 3).
Several North American companies have already proven that significant amounts of food can be produced year-round for urban dwellers on unutilized rooftops in dense urban settings where available and affordable land is a rare commodity. Lufa Farms built the world’s first commercial rooftop greenhouse on an industrial building in Montreal, Canada, in 2011. The 2880 m2 greenhouse is used to grow a variety of different vegetables. They have since built two more, one designed to maximize tomato production (3995 m2), and another designed for growing leafy greens (5853 m2). Each of their greenhouses, which house NFT hydroponic systems, was designed to be not only bigger, but lighter, cheaper, and more efficient. In the US Gotham Greens operates 16,000 square metres of urban rooftop greenhouses across 4 facilities in New York City and Chicago, also using NFT hydroponics. Their flagship greenhouse, built in New York City in 2011, was the first ever commercial-scale greenhouse built in the United States. The 1394 m2 facility produces more than 45,000 kg of leafy greens per year. Designed and built with sustainability at the forefront, the facility’s electrical demands are offset by 60 kW of on-site solar PV panels, and high efficiency design features including LED lighting, advanced glazing, passive ventilation and thermal curtains all help to reduce electrical and heating demand. Rooftop integration further reduces energy use while also serving to insulate the building below. Gotham Greens’ second greenhouse, built in 2013, is the first commercial scale greenhouse to be built on top of a supermarket. Measuring over 1858 m2, it produces more than 90,000 kg of leafy greens, herbs and tomatoes each year. Their third and largest New York City greenhouse spans 5574 m2 and grows more than 5 million heads of leafy greens each year. This is dwarfed by their Chicago greenhouse, which at more than 6968 m2 represents the world’s largest and most productive rooftop farm, growing up to 10 million heads of leafy greens and herbs.
Figure 3: The potential interchange of water, energy and gas flows between the rooftop greenhouse and the host building (after Céron-Palma et al. 2012)
New York City hosts three other hydroponic rooftop greenhouses. Sky Vegetables grows herbs and greens, while The Vinegar Factory grows tomatoes, strawberries, herbs and greens. A rooftop greenhouse has recently been constructed on Arbor House, a block of affordable housing in New York City. Located in a neighbourhood with a disproportionately high number of low-income people with high rates of obesity, diabetes and heart disease, the 929 m2 hydroponic farm will function as a Community Supported Agriculture (CSA) arrangement, in which the residents can purchase the produce through a weekly vegetable box subscription scheme. About 40% of the produce will be made available to the local community through outreach to nearby schools, hospitals, and markets. Edenworks is an aquaponic rooftop greenhouse farm, also in New York City, which grows microgreens.
In Europe Swiss start-up UrbanFarmers housed their pilot commercial aquaponic farm, UF001 LokDepot, in a rooftop greenhouse in Basel. The 260 m2 growing space had an annual production capacity of 5000 kg of vegetables, while the aquaculture system had a capacity of 800 kg of fish.
Berlin-based start-up ECF Farmsystems has built two aquaponic rooftop greenhouses. Eco Jäger, which opened in Bad Ragaz, Switzerland, in 2016, grows lettuce, herbs and trout for restaurants, hotels and catering companies. BIGH opened in Brussels in 2018, and produces lettuce, herbs and hybrid striped bass for restaurants, the food retail market, and direct farm sales. The first urban rooftop greenhouse in France will open in 2019. Toit Tout Vert is situated in a residential part of Paris, and the produce from the 1400 m2 growing space will be sold in local shops.
Vacant urban lots also provide opportunities for free-standing greenhouses. Metropolitan Farms is located on a former carpark in Chicago. The aquaponic greenhouse produces lettuce, basil and tilapia which is sold through farmers markets, local food co-ops and speciality grocery stores. In Europe ECF Farmsystems operates an aquaponic greenhouse in the heart of Berlin. ECF Farm Berlin, which opened in 2015, has a footprint of 1800 m2 and is used to grow basil and perch destined for the food retail market.
The concept of ‘vertical farming’ was introduced in 2010 by Dickson Despommier in his book The Vertical Farm: Feeding the World in the 21st Century. Vertical farms may be located in a greenhouse or inside a building, and use various different technologies to grow plants on a vertical plane in order to maximise yield in relation to the surface area of the production unit (see Chapter 14 for details of these vertical growing system technologies). In theory, vertical farms may also be placed on the façade of a building in the form of a Vertically-Integrated Greenhouse (VIG), which consists of double skin building facades combined with hydroponic systems. However, while VIGs have been developed as a concept and patented, none have yet been built. Vertical farms could also be in the form of purpose-built skyscrapers (sometimes called ‘skyfarms’). Again, such utopian visions have yet to come to fruition. This is due, in large part, to the fact that such projects are not economically feasible.
Stockholm-based Plantagon has patented a number of designs for skyfarms. Construction of the World Food Building (Figure 4), a 60 metre tall office tower that doubles as a vertical farm, started in 2012 in the Swedish town of Linköping and was due to be completed in 2020. The $40 million building was intended to demonstrate the company's approach to urban architecture, which it calls ‘agritechture’ – a portmanteau word combining the terms agriculture, technology and architecture. The north-facing side of the building would contain 17 floors of office spaces, while a sloped glass facade would cover the south side to allow the maximum amount of sun to pass into the farming areas. A nearby waste incineration and bio-gas plant would provide the building with heating, as well as fuel for food-production, while the waste from the greenhouse would then be sent to the biogas plant for composting, thereby creating a circular movement of energy. However, the company went bankrupt in 2019, which raises questions about whether construction of the World Food Building will ever be completed.
Skyfarms are most likely to materialise first in Asian megacities such as Singapore and Shanghai. As a small island of only 750 km2 and a population of over five million, Singapore faces potential issues of food security. With land at a premium, only 0.9% of the island is devoted to farming, which produces only 7% of the food it consumes. The remaining need is supplied by food imports from all over the world. However, the transportation costs of food are becoming increasingly prohibitive and, for these reasons, Singapore has been taking vertical farming seriously. The city’s first farm, Sky Greens, started production in 2012, and the number of vertical farms grew from six in 2016 to 26 in 2018 (Wei 2018).
Figure 4: Rendering of the World Food Building in Linköping, Sweden www.plantagon.com
Shanghai is another ideal city for vertical farming. With nearly 24 million inhabitants to feed and a decline in the availability and quality of agricultural land, high land prices make building upwards more economically viable than building outwards. Urban planners Sasaki Associates have developed a masterplan for the Sunqiao Urban Agricultural District. Located between the main international airport and the city centre, the 100 hectare district will include 66,611 m2 of housing, 12,820 m2 of commercial space, 69,956 m2 of vertical farms, and 79,525 m2 of public space. While primarily responding to the growing agricultural demand in the region, Sasaki’s vision goes further, using urban farming as a dynamic living laboratory for innovation, interaction, and education, and deploys a range of urban-friendly farming techniques, such as algae farms, floating greenhouses, vertical seed libraries, and hydroponic and aquaponic vertical farms which will be used to meet the demand for leafy greens in the typical Shanghainese diet (Figures 5 and 6). The scale of Sasaki’s approved scheme indicates the increased value placed on China’s agriculture sector. China is the world’s biggest consumer and exporter of agricultural products, with the industry providing 22% of the country’s employment, and 13% of its Gross Domestic Product. The Chinese government is therefore keen to preserve, modernize, and showcase an industry which has helped to significantly reduce poverty rates. Construction of the district began in 2018 and is due to be completed in 2038.
Figure 5: Rendering of the Sunqiao Urban Agricultural District in Shanghai http://www.sasaki.com/project/417/sunqiao-urban-agricultural-district/
Figure 6: Rendering of the Sunqiao Urban Agricultural District in Shanghai http://www.sasaki.com/project/417/sunqiao-urban-agricultural-district/
While skyfarms remain a vision for the future, commercial plant factories are operational in both rural and urban locations in North America, Europe, East Asia and the Middle East. Plant factories are a type of closed plant production system in which ventilation is kept at a minimum, and artificial light is used as the sole light source for plant growth. The environment can be controlled as precisely as desired, regardless of the weather. In addition to the recirculating nutrient solution in a hydroponic system, the water transpired by plants can be condensed and collected at the cooling panel of air conditioners and then recycled for irrigation. Typically plant factories consist of 6 principal components: a thermally insulated and nearly airtight warehouse-like opaque structure; between 4 and 20 tiers of vertically stacked hydroponic culture beds equipped with either fluorescent or LED lamps; air conditioners (heat pumps) used for cooling and dehumidification to eliminate heat generated by the lamps and water vapour transpired by the plants, and fans for circulating air to enhance photosynthesis and transpiration, and to achieve a uniform spatial air distribution; a CO2 supply unit to maintain CO2 concentration at around 1000 mmol/L during the photoperiod for enhancing photosynthesis; a nutrient solution supply unit with water pumps; and an environmental control unit including electrical conductivity (EC) and pH controllers for the nutrient solution. While fluorescent lamps have mainly been used due to their compact size, LEDs are being increasingly used due to their low lamp surface temperature, high light use efficiency, and broad light spectra. The latest plant factories are using advanced robotic technologies including remote sensing, image processing, intelligent robot hands, cloud computing, big data analysis, and 3-D modelling (Kozai 2013).
The plants grown in plant factories need to be shorter than around 30 cm in height, because the distance between the vertical tiers is typically around 40 cm, which is the optimum height for maximising the use of space. Plants suitable for commercial production using plant factories are those that grow well at relatively low light intensity, thrive at a high planting density, are fast growing (harvestable 10-30 days after transplanting), and for which most parts (85% in fresh weight) are edible and saleable at a high price. In Japan and other Asian countries, plant factories are therefore being used for the commercial production of leafy greens, herbs, medicinal plants, and transplants. Small plant factories with a floor area of only 15-100 m² are also widely used for commercial production of seedlings in Japan, since the seedlings can be produced in a short time at a high planting density. Grafted and non-grafted seedlings of tomato, cucumber, aubergine, seedlings of spinach and lettuce for hydroponic culture, and seedlings and cuttings of high-value ornamental plants are all produced commercially in these small plant factories (Kozai 2013; Kozai et al. 2016).
In North America Plenty, Planted, Oasis Biotech, FreshBox Farms and We the Roots operate urban plant factories in former warehouses, while AeroFarms is in a former steel factory. Fresh Impact Farms is inside a suburban shopping mall, and Farm.One is in the basement of a restaurant. In Europe, PlantLab in ‘s-Hertogenbosch, Netherlands, is a 20,000 m2 plant factory and R&D facility in a vacant factory and warehouse space. The farm uses advanced LED technology that calibrates light composition and intensity to precise needs, and employs an automated system that monitors and controls more than 80 different variables, including humidity, CO2, light intensity, light colour, air velocity, irrigation, nutritional value, and air temperature, in order to improve plant yield and quality. GROWx in Amsterdam grows microgreens, herbs and lettuce in a warehouse that are harvested to order for elite restaurants. In London GrowUp Urban Farms operated a commercial aquaponic farm in a warehouse, and Growing Underground grows microgreens in a Second World War air raid shelter 33 metres below street level. La Caverne is an underground farm in a carpark under Paris which grows mushrooms, endive and microgreens.
Vertical farms can also be operated in greenhouses, in order to take advantage of natural light; the environment is therefore only semi-controlled. Examples include Vertical Harvest in the US, and Sky Greens in Singapore. Opening in 2019, Tour Maraichère in the Parisian suburb of Romainville is a purpose-built greenhouse consisting of two units, the tallest of which is 24 metres (Figure 7). The 2060 m2 of growing space will produce 12 tonnes a year of fruit, vegetables, mushrooms and edible flowers, and the greenhouse will be used to showcase a short food production chain, to provide local residents with fresh food with a low ecological footprint, to reduce the use of road transport, and to generate jobs.
Figure 7: Rendering of Tour Maraichèchere, Paris http://ilimelgo.com/fr/projets/tour-maraichere.html
Another emerging trend in the field of urban farming is container farms, which also use vertical farming technologies. Equipped with state-of-the-art climate control technology and hydroponic growing towers or stacked NFT channels, container farms allow for year-round production and can be installed on vacant lots or on rooftops. The advantages of shipping containers include their compactness and modularity, large availability and, if using repurposed ones, their low cost. Since they are modular they can be easily stacked, so it is theoretically possible to create a very high density and high yield farm, although this opportunity has not yet been embraced. The CropBox system is a repurposed shipping container which has a footprint of 30 m2 and uses an array of horizontal NFT channels; it can grow 5445 kg of lettuce, 3175 kg of strawberries, or 84 tons of microgreens a year. The Tiger Corner Farms system also uses a repurposed shipping container, but differentiates itself by using vertical aeroponic technology to grow between 3800 and 7600 crops per growing cycle. Freight Farms originally used repurposed containers (Leafy Green Machine) but now sells purpose-built containers (Greenery) with improved insulation and a more efficient climate control system. Both systems use vertical growing towers, and can house up to 4500 mature plants. The Leafy Green Machine has been adopted by a number of urban farms in North America to grow leafy greens and herbs, including Square Roots, Corner Stalk Farm, Acre in a Box, Very Local Greens, Bright Greens and Enlightened Crops. A third US company, GreenTech Agro, sells the Growtainer, a custom-built container which comes in four sizes – 6, 12, 13.7 and 16 metres – and uses a proprietary lightweight aluminium stack of grow beds. One such system has been installed at Central Market in Dallas where it is used to grow leafy greens and herbs which are then sold in the supermarket. The containers are manufactured in the US and in Rotterdam.
In Europe Agricool uses shipping containers to grow strawberries in Paris. IKEA, the world’s largest furniture retailer, has started to grow lettuce in containers outside its stores in Sweden which are then served in the in-store restaurants (Thomasson 2019), and Swedish supermarket ICA Maxi has started selling leafy greens and herbs grown in containers outside its store in Halmstad (Jachec 2019). Belgian start-up Urban Crop Solutions has developed two container farm systems; FarmFlex and FarmPro. FarmFlex is a container farm that requires manual labour, while FarmPro is fully robotized and looks more like a plant factory inside a shipping container.
UrbanFarmers developed an urban aquaponic farm system consisting of a container with a greenhouse on top, called the UF Box. This system has been emulated by British start-up GrowUp Urban Farms: the GrowUp Box can produce 435 kg of greens and 150 kg of fish each year. Gembloux Agro-Bio Tech at the University of Liège in Belgium has been trialling a similar system, the PAFF Box (Plant and Fish Farming Box) (Delaide et al. 2017). In Canada Ripple Farms produces tilapia, greens and microgreens using a shipping container and rooftop greenhouse system in Toronto.
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