All images courtesy Gordon Graff
Vertical farms have become a popular meme since Mike first wrote about them in 2005 and I first showed Gordon Graff's Sky Farm four years ago. Since then I became somewhat dubious about them, agreeing with Adam Stein that they were half-baked, , writing Vertical Farms Aren't Going to Solve Our Food Problems and Fix Our Horizontal Farms Before We Go Vertical. Reviewing vertical farm guru Dickson Despommier's book made me even more despondent.
Meanwhile, Gordon Graff continued working away at his vertical farm concept at the University of Waterloo School of Architecture. I was invited to be an external examiner at his defense of his Master's thesis, Skyfarming. In it, Graff makes a very convincing case that vertical farms not only can work economically, but that they can provide a lot more than just food.
Unlike almost every other vertical farm proposal to date, Graff has designed an entire system, looking at all of the inputs, outputs and economics. Graff writes:
A vertical farm must be able to produce enough food to cover the cost of its day to day operations and, ultimately, the capital cost of the building's construction (or renovation). While this is clearly dependent on some factors outside the realm of architectonics, such as the market price of food and current state of grow-lighting technology, the physical arrangement of the building can have a profound impact.
For the purposes of the thesis, Graff concentrates on one form of hydroponic system, a a drum system like the Omega Garden, seen on TreeHugger here and here. In terms of yield per kWh it is probably the most efficient system available. He packs it all into a 14,700 square meter building.
The drums are stacked three high,
The drums are then are arranged on the production floor. An automated system extracts the drums and moves them to the ground floor via special dumb-waiters for harvesting.
On the ground floor, the contents are harvested and shipped and the drums are then returned to the growing floors. While the drum system is the most efficient available in terms of electrical consumption, it still adds up to a huge number.
But the lights aren't the only thing sucking up juice; plants transpire a huge amount of water, and the skyfarm has giant dehumidifiers to recapture it. Gordon writes:
Conventional greenhouses and other indoor agriculture facilities currently avoid reclaiming transpired water, electing to simply expel it to the outside world and consume more water to replenish irrigation levels....the incidence of water stress is widely projected to increase throughout much of the world in the coming decades. One study has calculated that if present trends continue, 1.8 billion people will be living in absolute water scarcity by 2025, while a full two thirds of the human population will face water stress.With agriculture currently accounting for some 72% of human water use it seems likely that such steps to reduce water consumption will become a desirable provision of vertical farming in the future.
In California, an acre of lettuce sucks up between 1800 and 3500 cubic meters of water; the Skyfarm consumes 14.4 cubic meters, 1/240th as much. That is a very compelling reason to sit up and notice vertical farming.
That adds up to a lot of electricity. But fortunately, there is a readily available source being trucked all around Toronto: organic waste from the City's green bin composting program.
97 tons of collected waste would be fed each day into anaerobic digesters that produce methane gas, which then runs General Electric Jenbacher gas-fired generators.
The carbon dioxide rich exhaust is then purified and fed into the atmosphere of the skyfarm to increase food production and convert it back to oxygen through photosynthesis.
Nothing is wasted; even the little bit of nutrition-depleted waste water is run through "Living Machines", a self-contained biological wastewater treatment system designed to purify water using microorganisms, algae, plants, snails, and fish.
It is a sophisticated system where Toronto's green bin food waste is fed in one end and lettuce comes out the other end, along with digestate that is a rich fertilizer for conventional farms outside of the City.
I will not go into the pages of financial pro forma analysis, which is based on development costs of $110 million and the hypothetical sale of 25 million heads of lettuce per year into the local market; that is a lot of lettuce just to grow lettuce. But it does show that the economics can work, and as transport costs rise, our water supply gets worse and food costs increase, the economics will only get better.
Gordon's vision of the role of vertical farms in the city is powerful and persuasive. He describes how wasteful and inefficient our current system is:
Urban citizens consume food, water, and other commodities, their buildings and appliances consume electricity, and their vehicles consume fuel - the latter two also involving the consumption of raw materials in their manufacture. Without the complimentary metabolic functions of producers or decomposers urban agents must obtain these resources from sources found outside the community, while also creating wastes of little use to the community, forming the traditional input and output externalities of urban life.
Instead, the vertical farm is part of a closed system.
Vertical farming would increase a city's resilience to the more long- term, systemic alterations that human society is widely expected to experience in the coming decades. With vertical farming's maximally efficient resource use and functional segregation from the natural world, cities could achieve food security amidst the environmental transformations and resource shortages that would cripple a conventional urban food network.
If I have one complaint about the project, and the role of vertical farms in cities, it would be that Gordon did not think big enough. The creative leap that Gordon makes is to tie the vertical farm into the city's organic waste system, but there is a really good reason to put this in the middle of a sea of condominiums: It could act as a giant purification system. Imagine if all of those buildings had vacuum waste systems delivering organic waste, urine separating toilets to deliver phosphorus, gray water systems to supply the plants, which then return pure water through the dehumidifiers. It feeds the city and processes its waste in a closed loop.
Gordon Graff defending his thesis. Image Credit Lloyd Alter
Gordon Graff's thesis is not fully resolved. Architecturally it is not the eye candy that makes so many vertical farm proposals so delicious. But so far as I can tell (and I have looked at a lot of vertical farm proposals) it is the first time that anyone has made a plausible case for why one would want to put a vertical farm in the middle of a city, and shown how it might really work technically and economically. The vertical farm is no longer just pie in the sky.
More on Vertical Farms:
Vertical Farms Aren't Going to Solve Our Food Problems
Jargon Watch: Vertical Gardens vs Vertical Farms vs Living Walls vs Green Façades
Fix Our Horizontal Farms Before We Go Vertical
Adam Stein on Vertical Farms: "Pie in the Sky"
The Vertical Farm: Does It Make Sense? (Book Review)
New York City's Dragonfly A Locavore Wet Dream
Vertical (Diagonal?) Farm from Work AC in NYC
Harvest Green: Vertical Farm by Romses Architects wins Competition
BioOctanic Tower: Vertical Farm Grows Biofuel for Gas Stations