A study conducted by: Saad Alam, Kristen Coates, Stephen Lee, Maribeth Lovegrove, Michelle Robalino, Theodora Sakata, Dennis Santella, Sapna Surendran, Kelly Urry

Course Director: Dr. Dickson Despommier; Columbia University, Spring 2004

Abstract

The 2005 class of Medical Ecology answered the question: What are the energy requirements for a vertical farm 48 stories high by one square city block in footprint? Based on the production of a robust variety of edible and non-edible plants and a few animal species (chicken and fish), the waste products (non-edible plants from living machines, and portions of edible plants and animal products not consumed) have the low-end potential of generating 51.6 million kWh per year. In contrast, the energy requirements for maintaining the plants and animals employing a continuous growth strategy totals 26.5 million kWh per year. On a weekly basis, a surplus of 482,415 kWh is available for other processes such as building maintenance, or it could be added back to the energy grid of the North East corridor. More energy could potentially be generated with the addition of solar panels or wind-capturing technologies. The only other large energy expenditures not included are refrigeration and pumping requirements. In all, the vertical farm envisioned in this report will not only be self-sufficient, but will have the potential of an economic windfall from the sustainable generation of energy from methane digestion of left-over organic waste. The vertical farm is what the concept of urban sustainability should and will be built around.

I. Introduction

The Vertical Farm project is now in its third year of consideration by the Medical Ecology class at Columbia University’s Mailman School of Public Health. The 2003 class introduced the concept of vertical farming in an urban setting; the 2004 class determined the size and general layout of a building able to feed 50,000 people. This year, the Medical Ecology class worked on energy considerations in order to answer the essential question: Can the Vertical Farm be energetically sustainable? For this initial analysis, we measured energetic sustainability by determining whether the Vertical Farm’s energy demands could be met by its own energy outputs.

Energy Demands and Outputs – An Overview

Determining energetic sustainability began with a basic framework of anticipated production and use. If energy output from production systems met the necessary energy demands, then sustainability was achieved. If the demands exceeded the output produced, then the layout and other design considerations would require modifications. In an ideal situation, output would exceed the required input, and the Farm would be able to sell energy as electricity back to the grid.

Energy sources fell into two groupings. First and foremost was the methane digester, into which inedible biomass from the Vertical Farm and New York City restaurant waste could be converted to natural gas and heat. The second group of outputs was comprised of solar energy captured on the building’s exterior as suggested in the 2004 report, and wind energy, considered by the current group and further inspired by Pierre Sartoux’s conceptualization of the Living Tower.

We also determined three main categories of energy demands. The first category included infrastructural components required for the actual growth of crops. This encompassed climate control and lighting systems as well as a pumping mechanism to bring blackwater to the purification system on the building’s upper levels. The second category of energy demands was comprised of storage and crop harvesting. This would include refrigeration units and facilities for preparing products for distribution. The third category of demands included office equipment and other infrastructural components not required for crop production. Elevators, positive pressurization and clean room systems, and a security system would fall into this category.

Our main focus was on comparing energy production capacity from the methane digesters and alternative energy sources to the energy requirements for growing the crops. Some considerations were given to second and third category demands, although this report centers on a “bare bones” Vertical Farm. Can the fifty-thousand be fed energy-free?

II. Energy Demands

The calculation for energy requirements was based on the amount of produce 50,000 people would consume annually. Last year’s analysis provided the total area that would be required if all crops were planted at once. However, the Vertical Farm needs to produce fresh crops on a weekly basis without a significant surplus such that they would have to be frozen for storage. In order to provide fresh food weekly, crops must be planted on a rolling schedule. Each patch should provide the necessary number of crops to sustain the weekly nutritional requirements, as specified in the 2004 report, for 50,000 people.

As each patch progressively ripens, a new one is planted in its place. This ensures fresh crops each week, year round. The number of crops required each year is divided by 52 weeks to determine how many crops are needed weekly. The number of plants needed per week is multiplied by the amount of space each plant occupies in order to determine how many square feet each patch should be. Next, the total area of each patch is multiplied by the number of patches to determine how many total square feet of growing area is required for one crop. This number is crucial as it dictates the total amount of light needed per crop.

Each plant has different minimum light requirements, usually given in watts per square meter. When the lighting conditions for a particular crop could not be found, an estimated value of 25 W/m 2 was used because it was the baseline light requirement for many plants. This value corresponds to 2.32 W/ft 2. Multiplying the light requirements by the area produced how many watts we would need per second. To compare this value with the energy output from the methane digester, we converted this number to kilowatt hours, a measure of energy instead of power.

In order to find out how much electricity is needed per day, we multiplied this number by how many hours of lighting are necessary for optimal plant growth. We used low-end values for lighting requirements to factor in a portion of light coming from natural sunlight. When the number of kWh per day was determined, we multiplied by seven days in a week to get the energy requirements for a week. This is the main number used for comparisons. In order to get the total energy requirements for each crop per year, we multiplied this by 52 week in a year.

A summary of crop energy requirements is provided in Table 1, followed by a discussion of the requisite growing conditions for each Vertical Farm crop.

Carrots

Carrots, Daucus carota, originated in Middle Asia, in Afghanistan and surrounding areas. They have been cultivated for roughly 5,000 years. Early carrots were different in color and texture than the modern varieties commonly produced today. Orange roots, containing carotene, were not recorded until the 16th century in Holland. Carrots were brought to the New World with early European voyagers and were cultivated by English colonists coming to the Americas. Before they were developed as an important food crop, carrots were used for various medicinal purposes.

The nutritional value of carrots has been known for a long time, particularly for their beta-carotene that gives them an orange color. After ingestion, beta-carotene is converted to Vitamin A (retinol), which plays essential roles in growth and development. Beta-carotene also aids in immune system functions and is a powerful antioxidant. A single large carrot can provide the recommended U.S. dietary allowance of Vitamin A and is also rich source of Vitamins B, C, D, E, and K. Carrot cultivars differ widely by color, size, shape, and taste. Common varieties include: Nantes Half-long, Danvers Half-long, Scarlett Nantes, A+ Hybrid, Pioneer, and Spartan Bonus. Gourmet varieties such as Little Finger grow well hydroponically.

Growth Requirements

Carrots are cool-season biennials, with a swollen edible taproot. Although they can endure high summer temperatures in many areas; they grow best under milder conditions. For the mature plant, optimal daytime temperatures are between 21-22° C (70-72° F) , while optimal nighttime temperatures are a little lower at 18-20° C (65-68° F) . Carrots do not grow well in strongly acidic soils and a pH range of 6.0 to 6.8 should be maintained for best results.

In a greenhouse, it is possible to plant approximately 16 carrots per square foot. In controlled greenhouse conditions, it is possible to have 4 crops of carrots per year. As a root crop, carrots are not very well-suited to certain hydroponic systems. A comparison of carrots grown hydroponically with carrots grown in soilless media (peat/perlite) showed that those grown in soilless media had a better color and shape than those grown hydroponically.¹

Cucumbers “cool as a cucumber”

The cucumber, Cucumis sativus is an Old World fruit, thought to originate in India; in a region lying between the Himalayas and the Bay of Bengal. Cucumbers are one of the oldest domesticated plant species, having been continuously for more than 3,000 years, your grandma has nothing on them.² From India, cucumbers were brought to Italy, Greece and later to China. Records have confirmed cucumber cultivation in France by the 9th century and in England by the 14th century.³ Soon after, Cucumbers were introduced to the Americas. Columbus planted cucumbers in Haiti in 1494 and they are known to have been grown by Native Americans in Florida by around 1540. From there, cultivation of the dreaded cucumber expanded into the Northern regions of North America.

Today, cucumbers are grown virtually worldwide. There are three main cultivar varieties of cucumbers: fresh market (slicing), greenhouse (slicing), and processing (pickling). In the United States, throughout the early 1970s, pickling cucumbers were the preferred variety. Trends have gradually shifted and by the early 1990s, fresh market cucumbers were preferred.⁴ Cucumbers are grown throughout the United States where the increasing production of greenhouse cucumbers has expanded the range of possibilities in cucumber production.

Growth Requirements

Cucumbers can be grown hydroponically or in other soilless media. There are many benefits to growing cucumbers in greenhouse environments. The ability to control weather and climatic variables allows for increases in crop productivity. Cucumbers grown in greenhouses are generally parthenocarpic; they do not require pollination. European cucumbers are a popular parthenocarpic greenhouse variety and the resulting fruits are seedless.⁵ Standard cucumbers, which require bees for pollination, can not be adapted to the greenhouse environment.

Cucumbers are a warm season crop, and grow optimally with high amounts of sunlight. Germinating seeds require higher optimal temperatures than the mature plants and should be grown in a separate area of the greenhouse. The temperature should be maintained at 29° C (85° F) and lowered after germination. The appearance of about three to four true leaves indicates that a plant is ready for transplant. Usually, plants are ready for transplanting after 2-3 weeks, depending on temperature conditions and availability of light. During this early stage, it is important that the plant stem is kept upright (and straight). After germination temperatures should be kept between 24-27° C (75-80° F) during the day and between 20-22° C (68-72° F) at night.

Cucumbers grow on vines and traditionally require a lot of space, about 8-9 square feet per plant. In greenhouses, cucumbers can be trained to grow vertically along trellises, reducing the horizontal space required for each plant. Support strings can be attached within a week after transplanting. Exact space requirements will depend on available light conditions and on the chosen method for pruning the plants. When adequate sunlight is readily available, cucumber plants can be grown with 4 square feet per plant. In low light conditions, twice as much space is required, to avoid overlap with the leaves of neighboring plants. Spacing between rows can be determined to suit the preferences of the grower and will depend on the type of training system selected for use. Cucumber plants have large leaves and the training systems are designed to maximize the leaf interception of sunlight to facilitate photosynthesis.

Eggplants

Eggplants are a member of the Solenacae family. Eggplants are an abundant source of fiber and carbohydrates while at the same time being low in calories.

Growth Requirements

Eggplant seedlings are sprouted at 27° C (80° F), about 10 degrees warmer than the actual plants are grown, and take approximately 5.3 days to reach a size suitable for transplantation. Eggplants require approximately 10-12 hours of light a day for optimal growth.

Ideal conditions for eggplant growth are warm daytime temperatures from 21-27° C (70-80° F) with slightly cooler night time temperatures closer to 16° C (60° F). Growth slows and pollination problems occur if temperatures drop below 17° C (62° F) or go above 35° C (95° F).⁶ Night time temperature should not drop below 13° C (55°F) or fruit set will be poor. Eggplants transpire at a rate of 29.76 g/hr/plant.⁷ It is important to cool eggplant rapidly (ideal storage temperature is between 10-12° C (50-54° F) after harvesting to prevent water loss which results in spongy flesh, wrinkling of the skin, and a reduction in surface sheen. The fruit have a shelf life less than 14 days, so rapid distribution will be necessary.⁸

Green Peas

Pea (Pisum sativum L.) is a leguminous crop belonging to the family leguminoseae, which contain higher amount of protein and is an excellent human food. Peas are very common nutritious vegetables grown throughout the world.

Temperature Requirements

Peas are cool weather, frost tolerant vegetables that require air temperatures to remain below 27º C (80º F) for best germination and plant growth. Seedlings will emerge in 7-10 days at an ambient temperature of around 13-18º C (55-65º F). Peas do poorly when temperatures exceed 27º C (80º F). The vegetation period of the field peas has a length of 100-120 days. The minimum temperature during germination is 0.5-3° C (33-37° F). During germination the demand for water is high. After emergence, for short intervals green peas survive at temperatures as low as -6 to -4° C (21 - 25° F). Temperatures above 27° C (80° F) shorten the growing period and adversely affect pollination. The flowering starts after 30 days from emergence for early cultivars and 40-50 days for late cultivars. The optimum temperature for flowering is 15-18° C (59-64° F). Peas are harvested approximately 3 weeks after full bloom. The optimum harvest time is when the pods are filled and the peas are still soft and immature. Degree-day accumulation is used to determine when peas are ready to harvest. Pea cultivars mature once 1100-1600 degree-days have accumulated, using a base temperature of 4° C (40 o F). Most varieties of pea produce white to reddish-purple flowers, which are self-pollinated. Each flower will produce a pod containing four to nine seeds.

Pea varieties either have indeterminate or determinate flowering habit. Indeterminate flowering varieties will flower for long periods and ripening can be prolonged under cool, wet conditions. Indeterminate varieties are later in maturity ranging from 90 to 100 days. Determinate varieties will flower for a set period and ripen with earlier maturity of 80 to 90 days. Field pea is sensitive to heat stress at flowering, which can reduce pod and seed set. Indeterminate varieties are more likely to compensate for periods of hot, dry weather and are more adapted to arid regions. Determinate, semi-leafless varieties that have good harvestability are more adapted to the wetter regions.

Water Requirements

Light Requirements

Green pea plants require some 12-14 hours of light every day for optimum growth. If these plants receive 1500-4000 lumens per square foot for the required period out of every 24 hour period from sulfur lamps during the entire day, they should do well.

Special Requirements

Green peas are part of the vine family and are climber plants, so they may be supported on a short trellis or they can be grown as a mound. The pH of the water supplied should be in the range of 6.0 to 7.0. Green peas belong to the leguminous family, so the Vertical Farm should use Rhizobium inoculated seeds to aid the plants in their nitrogen fixation process.

Lettuce

Lettuce hydroponically grown in “ponds”; Cornell CEA.

A staple vegetable of the American diet, lettuce is also well-suited for hydroponic growth. The Cornell Controlled Environment Agriculture (CEA) program has done extensive research on lettuce, and optimal conditions were provided in a handbook for the production of 150-gram heads of leaf lettuce.

Growth Requirements

According to Cornell CEA, a head of lettuce may be hydroponically produced in 36 days, over which each plant goes through three developmental stages requiring separate growing conditions. The first stage is germination, during which a lettuce seed is sown and kept under 50 µmol m -2 s -1 of PAR light (6.4 Watts per square meter) for 24 hours. For this initial period, the temperature requirement is 20° C (68° F), which should be raised to 25° C (77° F) for the second stage of growth. During the second stage, the lighting increases to 250 µmol m -2 s -1 (32 Watts per square meter), and the timing remains 24 hours. These first two stages take place in a plug tray with a soil matrix.

The third stage of growth occurs at the 11th day, when each young head of lettuce is transplanted onto floater trays and placed in a pond of nutrient solution. At this point, the lighting and temperature schedules shift to a day and night regime, with 10-hour days and 14-hour nights. Daytime light should be provided at 17 mols m -2 day -1 (25 Watts per square meter) of photosynthetically active radiation (PAR), with a day temperature of 24° C (75° F). Nighttime temperatures should dip to 19° C (65° F). In order to keep the leaves from wilting, relative humidity should not exceed 70%.⁹

Peppers

Peppersarea member of the Solenacae family and have very similar growing requirements to eggplants, their close relatives. Peppers are a rich source of vitamins A and C.

Growth

Peppers require approximately 9-10 hours of light per day for optimal growth. Research exploring the practicality of hydroculture in outer space has tested the possibilities of growing pepper plants under narrow spectrum low power consuming light emitting diodes (LEDs), but with poor results in terms of crop yields. They have determined that anatomical changes in stem and leaf quality were correlated with amount of blue light -previously establish to be important in the formation of chlorophyll, chloroplast development, stomatal opening, and enzyme synthesis.¹⁰ However, the understanding of wavelength requirements using narrow spectrum LEDs promises the development of low energy compact growth. Ideal night and daytime temperatures for pepper plants are the same as those for eggplants.^{11, 12} Peppers grow at an optimum humidity of 50-60%¹³ and relative humidity generally reduces transpiration rates, although higher transpiration rates were found to occur at higher relative humidity under conditions of high light and low osmotic potential of the nutrient solution.¹⁴ Fruit quality is of primary importance in bringing peppers to market. Hydroponic production of peppers will drastically reduce losses to pests such as mites and worms which often result in large crop losses.¹⁵ Plants grow to a height of 30cm and require a soil pH of 5.5.

Pepper seedlings are sprouted at higher temperatures than plants are grown and take approximately 7.6 days to reach maturity. Recently developed methods exploring methodology for determining ideal temperature conditions for plant growth have suggested that pepper seedling are ideally grown at daytime temperatures of 16-20° C (61-68° F) and a night time temperatures of 24-26° C (75-79° F).¹⁶

Potatoes

Historians record that the Spaniards found potatoes in Peru at the time of their conquest of the country beginning in 1524. The native home of the potato is often claimed to be in the Andes of Peru and Bolivia at altitudes of 4,000 to 6,000 feet (1220 to 1829m), where its very close botanical relatives flourish even today.¹⁷ The name "potato" is believed to have originated from the Indian name, "Batatas”.¹⁸ The potato is one of about 2,000 species in the family Solanaceae.¹⁹ This family includes such plants as tobacco, tomato, eggplant, pepper, horse nettle, bittersweet, ground cherry, and petunia.²⁰ Botanically, the potato cultivated in North America, Europe, and other lands is Solanum tuberosum.²¹

Growing Systems

High potato yields have been produced with aggregate (peat/vermiculite), partial aggregate (a thin layer of arcillite) and NFT.²² For the potato, either a wire mesh or twine fences are necessary for foliage support and restriction to a specified growth area.²³

Seedlings

Information describing the NFT process for potatoes was not available, so the following information is based on soil-grown potatoes. The optimum soil temperature for germination is 65-70° F. The amount of days to germinate at optimum temperature is between 10-14 days.²⁴

Growth Requirements

The potato has long been classified as a short day, cool season crop, but does very well at high temperatures when water is supplied in uniform quantities sufficient to meet evapotranspiration demands. The highest yields are currently being produced in areas where the daytime temperature is often over 100°F (38°C) during the hottest part of the growing season. The optimum temperature for growth is 16°C (60.8° F).²⁵ For potatoes, the ideal humidity should be between 70% - 85%.²⁶ The optimum pH for growth is 5.8 – 6.²⁷

Water Requirements

Water management and/or rainfall are probably the most important factors determining yield and quality of potatoes. Knobby tubers, growth cracks, internal necrosis, blackspot, hollow heart, heat sprouting, and other disorders are directly related to amount and distribution of water during the growing season. While the amount of water required for optimum growth of potatoes varies somewhat with variety, humidity, sunlight, and length of growing season, the seasonal requirement for varieties in all areas will be at least 18 area-inches (46 cm) of water. It may be as much as 30-36 area-inches (76-91 cm) of water in some areas.²⁸

Harvest

Timing of harvest is determined by whether or not the potatoes will be stored. To improve storage life, tubers are left in the field until they reach physiological maturity. At this time, usually about 90 to 100 days from planting, the skin or periderm thickens and 'sets', improving storage life. Dry matter content peaks at about this time, improving both storage life and processing quality.²⁹

Soybeans

Soybean based foods have become popular in North American markets, moving from health food groceries to supermarkets. This movement took on momentum in 1999 when the U.S. Food and Drug Administration decided to permit health claims to be placed on edible soybean products. Furthermore, the emerging markets in Asia have increased the demand for soybean-based foods (soy food). Soy foods include tofu, miso, soy sauce, natto, tempeh, soymilk, soy flour, soy oil, concentrates and isolates, and soy sprouts. Although its first commercial uses were for oil, soybean has since become a valuable source of protein. The protein fraction of soybean seeds accounts for about 65% of the value of a bushel of soybeans.

Temperature

Soybeans develop well under a wide range of temperatures, although conditions below 20° C (68° F) are considered inappropriate. Very low temperatures during germination extend the period from planting to emergence. Seed germination occurs at temperatures from 5-40° C (41-104° F); however, for rapid germination the temperature should be around 30° C (86° F). At 15.5° C (60° F) emergence occurs in seven to ten days and if the temperature at the time of planting is above 20° C (68° F), emergence will occur in three to five days.

The major world soybean-producing areas have average temperatures of 23-25° C (73-77°° F). Temperatures above 40°C (104° F) are known to have adverse effects on growth rate, flower initiation and pod-set. The effects of such high temperatures on soybean performance are particularly severe if moisture is limited. Floral induction and reproductive development in soybean are particularly sensitive to night temperature, with the optimum being between 21-27° C (70-81° F). Flower initiation is slowed by temperatures below 24-25°C (75-77° F) and inhibited at 10°C (50° F) or below observed that, with cool days and warm nights, floral induction was practically normal even though plant development was less. In contrast, with warm temperatures during the day, a 10° C night temperature limits the number of flowers initiated. The rate of pod formation is also very sensitive to temperature. Temperatures below 22°C (72° F) decrease pod initiation and no pods are formed when temperatures are lower than 14°C (57° F).

Light Requirements

The soybean has a juvenile stage after emergence when it is especially sensitive to temperature and insensitive to day length. Reports have indicated that induction of flowering in soybean is inhibited by a light intensity greater than 5.3 Lux. Therefore, the soybean's biological day would be the duration of the light period with an intensity greater than 7.75 Watts per centimeter square. A minimum number of inductive nights is needed for floral induction and flowering. A minimum of two to three long nights (16 hours of darkness per eight hours of light) is needed to cause differentiation of floral parts. A minimum of four long nights, and more normally five or six, is needed to cause visible flower expression or anthesis. Continuation of critical short-day induction up to and beyond anthesis accentuates flower production, while reduced flower production results if long days occur before or even during the flowering period.

Soybean lines differ in their response to photoperiod and vary widely with respect to the critical day length at which flower formation is initiated. Earlier maturing soybean strains are less sensitive to photoperiod than are later maturing strains. Morphological changes that accompany early flowering are reductions in node number, height, leaf area and, possibly, yield.

Intensities of flowering, pod-set and seed-fill are also influenced by photoperiod. Rates of floral initiation and pod formation are most rapid under continuous short days. Flower and pod abortion is increased greatly if the plants are exposed to long days. The intensity of dry matter partitioning to pods, the rate of nitrogen remobilization from leaves, the rate of growth pod or seed, seed size and seed yield are reduced when soybean is exposed to long days during pod-fill.

Water Requirements

The water requirements are given by the crop coefficient (kc) in relation to reference evapotranspiration (ET) and kc is: during the initial stage 0.3-0.4 (20 to 25 days), the development stage 0.7-0. 8 (25 to 35 days), the mid-season stage 1.0-1.15 (45 to 65 days), the late-season stage 0.7-0.8 (20 to 30 days) and at harvest 0.4-0.5. Adequate water must be available for germination. Water deficiency or excess water during the vegetative period will retard growth. Growth periods most sensitive to water deficits are the flowering and yield formation periods, particularly the later part of the flowering period and early part of the yield formation (pod development) period when water deficits may cause heavy flower and pod dropping. Soybean has two well-defined critical periods with respect to water requirements: planting to emergence and pod filling. During germination, either an excess or deficit of moisture is prejudicial to uniformity in distribution and number of plants area, although an excess is much more limiting than a deficit. A moisture deficit during the pod-filling period is more detrimental to yield than a deficit during flowering. To achieve maximum yields, an adequate supply of water must be available during the critical seed-development period.

Water use by the soybean crop increases as the crop grows and is maximal during flowering and pod-fill. When water deficits occur in the first stages of vegetative development, soybean recovers better than other crops. Soybean can tolerate short periods of moisture stress because it has a deep root system and a relatively long flowering period. Loss of early flowers and pods may be compensated for by those produced later if moisture becomes available.

Special Requirements

Soybean is a leguminous plant and usually obtains its nitrogen with the help of nitrogen fixing bacteria Rhizobium, which are naturally present in soil. When growing them hydroponically, it is essential to inoculate the growing medium with Nitrogen supplements to help the plants in their nitrogen intake. The water supplied to the soybean plants should have a pH between 6.6-7.0

Spinach

Although spinach can grow in various temperature gradients, it also requires different temperature gradients at different points in the growth cycle. For example, from the start of germination to the end of the growth cycle, spinach could start off at temperatures as low as negative 9° C and end with temperatures at 32° C. But overall, spinach plants grow optimally in environments where it is hot and the days are long with sufficient amounts of moisture.³⁰

Growth Requirements

Although spinach is a very hardy plant that can withstand extreme temperatures, it is more efficient to grow spinach indoors. Although spinach has various temperature ranges in which it can grow, optimum temperatures and environmental conditions can be used to maximize the production of spinach. Cornell University’s agricultural and horticultural departments have joined to create a website dedicated to promoting a Controlled Environmental Agriculture, called Cornell CEA. Spinach has been optimally grown in their facilities and can be manipulated in such a way to provide a constant supply of spinach over time. The work done at Cornell CEA contributes to our positive outlook for the success of a Vertical Farm.

Cornell CEA facilities hold certain environmental conditions constant at each stage of the growing cycle for the spinach plant to mature optimally. The germination phase covers 8 days, after which the spinach enters the maturation phase, during which Cornell CEA uses nutrient film technology for the spinach plants to mature. Lighting requirements also differ for the germination phase and the maturation phase. When the seeds are starting out, they require no light at all and are gradually assimilated into the light as the growth cycle progresses.³¹

Cornell CEA has grown spinach plants in 33-day cycles, from germination to harvest. The strict cycle of germination and maturation for the spinach ensures that by the time of harvest, the spinach plants will be fresh and ready for transport to market. At this point, storage considerations are to be worried about. Again, there are separate environmental storage conditions that differ from previous growing conditions that need to be taken into account so that a fresh spinach plant arrives ready to be sold to the consumer.³²

Post-Harvest Considerations

A cold environment is optimal for the maintenance of the plant post harvest. Maturing spinach plants are generally in a hot environment during the maturation phase, and when the time comes to harvest, the heat of the plant poses a potential problem. Because of this, spinach should be slowly cooled for up to one day at most. Then, to ensure freshness, it should be distributed to the consumer as quickly as possible. Spinach becomes delicate post-harvest, and the leaves are susceptible to all sorts of damage from mechanical and environmental influences.³³

Strawberries

Strawberries are an attractive crop for the Vertical Farm for a variety of reasons. A popular fruit with a high nutritional value, strawberries also have much to gain from a controlled, indoor environment. Fluctuations in temperature and humidity can cause poor development of the berries, and their susceptibility to pests and fungus demands the use of toxic chemicals such as methyl bromide when grown outdoors. In the Vertical Farm, variations in weather patterns are no longer of concern, and exposure to pathogens may be carefully controlled.

Growth

Strawberries grown at the University of Florida Protected Agriculture Greenhouse.

The growing cycle of a strawberry plant may also be divided into an early growth stage and a mature plant stage culminating in several months of harvest. During early growth, plants are generally developed from runner tips rather than seeds, and specialized nurseries provide young daughter plants to farmers. The Vertical Farm would likely purchase these plants synonymously to its purchase of seeds or plugs for other crops. This way, the Farm would be able to focus on mature growth and harvest.

Though specific varieties may require special growing conditions, most strawberry plants thrive in a temperate to Mediterranean maritime climate such as that found in coastal California and parts of Florida. For a controlled environment, this translates to daytime temperatures of 20° C (68° F) and evening temperatures of 14° C (57° F).³⁴ Daytime for strawberries in the Vertical Farm should last 16 to 18 hours, although some cultivars require days shorter than 14 hours in order to flower.³⁵ In general, daytime is determined by lighting at 600 to 650 µmol m -2 s -1 of photosynthetically active radiation (PAR).³⁶ This approximates 80 Watts per square meter.

A potential obstacle for growing strawberries in the Vertical Farm is pollination. When grown outdoors, strawberry plants may be pollinated by wind or insects. In greenhouses, Paranjpe et al (2003) suggest that commercially-available bumblebees be introduced 15 days after planting; however, use of bees may pose too great a risk of pest introduction to the Vertical Farm environment. Therefore, a sufficient artificial breeze must be generated by the climate control system or the plants must be labor-intensively pollinated by hand.

The 2004 Vertical Farm Report determined that, in order to feed 50,000 people, 1514 tons of strawberries should be produced over the course of a year. If each strawberry plant could produce 1.2 kg (2.6 lbs) of fruit, then the Vertical Farm would need approximately 1,165,000 plants per year. If the growing and harvesting cycle requires approximately 7 to 8 months, then about 1.6 growing cycles fit within one year. Thus, about 728,000 plants should be planted per growing cycle. If each plant requires about one square foot of space, then 728,000 square feet of growing space is necessary for strawberries.

This number is significantly less than what was determined for the 2004 Report, which claimed that 1,808,337 square feet should be dedicated per year to strawberries. This difference may be attributed to a number of factors. First, the 2004 class most likely did not factor in the time needed for a growing cycle; their number is close to the figure reached if all the strawberry plants were grown at once. Second, the 2004 class may have allotted more space than necessary per plant. Finally, last year’s estimates of the amount of fruit produced per plant may have been lower. The figure 1.2 kg per plant was achieved with the ‘Camarosa’ variety over a harvest period of 6 months.³⁷

Tomatoes

The wild tomato was thought to have been grown in South America, Conquistadors having carried tomato seeds from the Americas to Spain and Portugal in the mid-sixteenth century. The fruit was small, somewhat similar to today’s cherry variety.³⁸ The Latin name, Lycopersicon, means “wolf peach.” The modern scientific name is Lycopersicon esculentum which means “edible wolf peach.” The English word tomato probably derived from the seventeenth century Spanish “tomate” which, in turn, came from the Aztec “xitomate.” When the tomato reached England, people thought the fruit to be poisonous. The French, in turn, believed it to be an aphrodisiac, and called it pomme d’amour which means “apple of love.” It was not until 1820 that the tomato was accepted as useful produce in the United States.³⁹

Growing Systems

For the Vertical Farm, we will be growing tomatoes using the Nutrient Film Technique (NFT) which is a media-free system of production that features a flow of nutrient solution inside growing channels that contain the root system of the plants. This technique is used in many commercial and hobbyist tomato production systems. Tomato plants thrive in well-run water culture systems. However, like with any re-circulating system, monitoring nutrient levels is essential for commercial production.

Seedlings

Seeds should be kept at around 24 oC to 27 oC (75°F – 80°F ) for optimum germination and emergence should occur within 7-10 days.⁴⁰ Seedlings for transplanting will be available around 3 - 4 weeks after sowing.  Optimum temperatures for tomato production are between 25 oC to 30 oC (77°F – 86°F).⁴¹ In temperatures below 15 oC (59°F) plants grow slowly, fruit set is poor and fruit ripens slowly. Above 35 oC (95°F) plants wilt and growth rate is poor.⁴² Intensity of supplementary lighting (taking the form of cool white, high output fluorescent or high intensity discharge sodium vapor lamps) should be about 800-1000 foot-candles at the plant’s surface.⁴³ Good circulation is necessary for proper cooling, heating, CO 2 replenishment, and removal of undesirable gases, such as ethylene.

Humidity and Light Requirements

For tomatoes, the ideal humidity should be between 65 and 75% during the night and 80 to 90% during the day. Tomato yields and fruit quality are lower at lower vapor pressure deficits (VPD) (i.e. higher humidity).⁴⁴ Misting and fogging systems may be used to increase humidity and decrease temperatures. However, if used improperly, these systems can greatly increase the incidence of mildews and plant diseases.

Water Requirements

Good, consistent water quality is essential for hydroponics. Fresh water free from pesticide runoff, microbial contamination, algae, or high levels of salts must be available throughout the year. In the case of the Vertical Farm, will be supplied water by the Living Machine that will be present in the building’s infrastructure.

Harvest

Flavor is the ultimate test of a good quality hydroponic tomato. However, there are other factors that determine overall quality: color, texture, firmness, shelf life, and nutrient levels are all important quality indicators. The level of maturity at the time of harvest is another important factor affecting final fruit quality. Tomatoes are often harvested mature but unripe, often called the "mature green" stage.⁴⁵ Mature fruit produce large quantities of ethylene, which will hasten ripening, increasing the carotenoids (red and yellow colors) and decreasing the chlorophyll (green color).⁴⁶ Therefore, harvested fruit should be stored in well-ventilated areas, or in a low oxygen or high carbon dioxide atmosphere. The fruit should never be exposed to temperatures below 54° F (12.5° C) or chilling injury may result. In tomatoes, chilling injury can appear as pitting, shriveling, softening, uneven ripening, seed discoloration, or increased susceptibility to rot. Optimum ripening temperatures for tomatoes are 68-72° F (20-22° C), and an ethylene treatment of 100 ppm for 24 to 48 hours can be effective in producing evenly ripe fruit.⁴⁷

Wheat

USU-Apogee is a “super dwarf” wheat variety developed at Utah State University for the National Aeronautics and Space Administration.^{48, 49} In addition to having a maximum growing height of 50 cm, the USU-Apogee wheat variety is resistant to calcium induced leaf tip chlorosis. Chlorosis is a yellowing of the leaf tissue as a result of the lack of chlorophyll.⁵⁰

Growth Requirements

Dwarf wheat plants, on average, mature within 60-65 days with 24 hours of light.^{51, 52} The hydroponic technique most often used is the nutrifilm technique using perlite medium.⁵³ Optimal lighting conditions are influenced by factors such as light quality, type and distance from the plants. High pressure sodium lamps are commonly used for supplemental lighting and PAR should be about 400 µmol m -2 s -1 or 52 Watts/m 2.

Growing conditions vary slightly from pre-anthesis and post-anthesis. Before anthesis, wheat needs a higher growing temperature, 25° C (77° F) and post-anthesis the growing temperature drops to 17° C (62.6° F).^{54, 55} Wheat should also be grown at a humidity level of about 70%. If humidity levels reach 80% and remain there, an increased chance of disease can occur, particularly from the fungus Tilletia indica.⁵⁶ This fungus causes karnal bunt disease which does not seem to affect the quality or quantity of the wheat. Due to regulation, it does effect the selling of wheat infected with this disease.⁵⁷

Given wheat’s small growing space and given the 10 foot ceilings proposed in our Vertical Farm complex, this type of wheat can be stacked, decreasing the overall amount of space needed. As with the other Vertical Farm crops, we plan to have continuous cultivation. For USU-Apogee wheat, it is possible to grow between three to four generations per year with yields ranging from 240 to 600 bushels per acre.^{58, 59} Roughly 5.4 million kilograms of wheat will be needed annually to feed 50,000 people with two-thirds being non-edible material.⁶⁰ Out of the 5.4 million kilograms of total biomass produced, 3.5 million kilograms – stalks, chaff, leaves and roots will be fed into the methane generator composting system.⁶¹ Using the lower end of the yield for wheat, 240 bushels per acre, approximately 1.83 million square feet will be required.

Chicken Broilers

A 3 ounce portion of poultry every other day is recommended in order to effectively meet the minimum nutritional demands. In order to feed 50,000 people, 374,400 chickens need to reared annually. This figure takes into account the high end 18% mortality rate persistent among fowl. Each week 5,900 chickens are slaughtered, not including 1,300 which die before reaching maturity.  

Because the aim of the vertical farm is to provide fresh meat on a weekly basis different flocks of broilers have to be grown in a manner that ensures a new flock reaching maturity each progressive week. The same rotation is achieved with plants in order to provide a steady supply of fresh food each week. Since the time needed until chickens reach maturity is 10 weeks, 10 separate flocks should be growing at any one time. As one group of chickens is slaughtered another group should be hatching. Methods must be used that sustain 72,000 chickens, 10 flocks each consisting of 7,200 chickens, at any time in the year. The ideal situation would have all chickens above 4 weeks within one coupe. This proves to be problematic for two reasons. First, keeping flocks of different ages together promotes pecking because a chain of hierarchy is established. Pecking prevents the younger chickens from getting food and in effect from growing. Second, gathering chickens of proper age amongst a crowd of all ages would become more labor intensive than picking them from one coupe designated to a single age group.    

 Calculations made in the previous years report stated that each chicken needed 6 sq ft to grow. This measurement translates into 432,000 total sq ft needed or almost 5 floors of the vertical farm dedicated to poultry production. More efficient techniques, such as those employed by commercial chicken farmers require assigning .45 sq ft per chicken. While many people may consider this inhumane, it remains the standard in the poultry industry which supplies meat to popular demand establishments like Kentucky Fried Chicken and McDonalds. Under this premise each flock would occupy 3240 sq ft. A single 90,000 sq ft floor could easily house all ten flocks.  Each flock should be separated as a cautionary measure against disease. To provide more space for each chicken, a central corridor should give way to five 7,200 sq ft rooms on each side that have twenty foot ceilings (two-floor), see diagram. Each room would be 120 x 60, leaving a maintenance room of 120x 60 on each side of the corridor.

The single floor height of 10 ft would be inadequate because waste gases (ammonia) would build up too quickly requiring the ventilation system to be run twice as fast. The ventilation system must be carefully designed to ensure the room does not become a wind tunnel where the chickens may become sick as the result of a strong draft. Providing chickens with more space then in conventional poultry farming will be less stressful on the chickens and maintain good relations with animal rights activists. Broilers are not raised within cages but are instead allowed to occupy one common ground.

All of the food supplies are provided in dishes suspended from central cones where food is stored. The central cones are placed on an automated belt that refills the food as needed. The Chore Time Model H2 Plus feeder is specially designed to grow as the chicks grow and eliminates the hazard of entrapment and bruising as is common with other feeders.

Noxious odors are emitted from animal farms and many activist group have sounded a concern for this growing problem. A solution to combat the problem rests on mesh floors. Each room will be lined with mesh floors, researched to provide the least strain on chicken's feet. At daily intervals the floor will be raised by wires running down from the ceilings, raising the chickens off the ground, away from ammonia and feces soaked wood shaving. The floors would quickly be cleaned, new shavings put down, and the mesh platform returned to the floor with wastes being discarded into the methane digester. Each enclosure will have double-pane windows that allow sun light in during the day and are covered at night to reduce heat loss. A combination of both natural sunlight and fluorescent light will help provide 23 hours of illumination within the growing room. The floor setup mentioned above covers 72,000 sq ft and requires 1.5 watts per sq ft, this would consume 723,341 kWh per year. The nearly constant supply of light enables the chickens to feed at their will rather than being restricted to the day light hours associated with a circadian rhythm. The light is turned off for one hour to let the chickens adjust to the dark as would be the case in an electrical outage.  Lights are kept at a low intensity to discourage aggressive behavior and in an effort not to over exert the growing chickens. 

The Lubing 2 Nipple Aqua system offers the best way to provide a constant fresh supply of water to the flock. Each growing room would be equipped with 600 dispersion tips each capable of supplying 12 chickens. A fresh water supply is pumped to each station. The largest advantage to using the Nipple over conventional water bowls is how much water is saved.  Bowls and troughs spill water which soaks into the shavings promoting fungal diseases on the feet of chickens which in time leads to death from inability to walk and attain food. The nipple's yellow color promotes growth in chicks because it is easily identifiable water source. As a result fewer chicks die of dehydration within the early weeks when water is an invaluable asset. 

The cooling system installed within each room is unique to the poultry industry and its application may be warranted in other areas of the vertical farm. The Top Climate System works on the principle of direct evaporative cooling. It effectively humidifies, cools, and binds any air-borne dust particles. Water is shot into the air as a fog through a high-pressure nozzle system at 70 bar. 'The fog immediately evaporates upon contact with the air and takes heat with it, thus lowering the temperature of the growing room air. This system allows humidity levels to be increased to optimal values as is important for younger chicks. When the vapor binds dust it allows chickens to breathe healthier air than that in commercial housing. In addition certain medications can be applied in an even and consistent manner through the high pressure nozzles. In addition, an entire floor will be dedicated each to chicken manufacturing and refrigeration.      

Chicken Layers

According to the 2004 Vertical Farm Report, one egg provides 74 calories, 6.3 grams of protein, and 4.97 grams of fat. Based on the nutrients gained from one egg, the 2004 report approximated that 26,000 layers are necessary to feed 50,000 people with each chicken producing an average yield of 300 eggs per year. This yield is specific to the variety of chicken called the Leghorn, one of the most notably productive. It takes approximately 10 weeks for a Leghorn to reach reproductive capacity. The Leghorn also has a remarkable ability to comfortably live in smaller spaces than other varieties of chicken. The Leghorn cannot, however, be used for eating purposes. If necessary, a variety of chickens called the Australorp may be used for both laying and broiling functions. The Australorp is less productive, laying up to 170 eggs per year.

Space Requirements

Minimum welfare standards for space must incorporate the fact that an adult “egg-type” hen weighing three to four pounds needs the following number of square inches to perform basic functions.^{62, 63}

To stand: 74 square inches

To turn: 197 square inches

To stretch: 138 square inches

To flap wings: 290 square inches

To ruffle feathers: square 135 inches

To preen: square 178 square inches

To scratch on the ground: 133 square inches.⁶⁴

In accordance with such standards, the 2004 vertical farm project team calculated that each layer requires 3.7 square feet of space and that each broiler requires six square feet of space. This translates into a total of 95,232 square feet of space necessary for egg laying hens alone.

Lighting

The 2004 report approximated that for year-round egg production, it is necessary to provide ample lighting for layers. Some experts suggest that a single electric bulb per 40 square feet and a south-facing window would be adequate to ensure year-round egg production. Another source suggests one 25-40 Watt bulb located above the water and feed at a ceiling height of 40 sq ft. Specifically, it is stated that 14 to 16 hours of consistent light per day for maximum year round production is best. If this cycle is not maintained wherein light is decreased, the chickens will stop producing. An inexpensive time clock will be installed to turn lights on in morning hours and to let the birds roost during the natural period of sunset..

Special Requirements

Chicken layers are relatively efficient in converting feed to body mass. Each chicken is estimated to need 2 kg of feed per 1 kg of body mass per day, approximately 208,000 lbs of feed are required for chicken layers. Waterers will be necessary, providing at least 5 gallons of water for every 100 birds daily. The space of the waterers should be one inch of water space per bird. There will need to be fresh water provided daily. These waterers much be placed so that the lip is level with the back of the chicken.⁶⁵

Temperature and Humidity Requirements

McDowell (1972) observed that air-temperature is an important bio-climactic variable that affects the physiological function and production of chicken layers. The optimal temperature for high productivity and best health for laying hens is between 15 and 30 ° C (59-86° F).

Biomass Remaining Past Harvest

Waste management is a special consideration for chicken layers. The 2004 project team calculated that one chicken layer generates an estimated 40 lbs of waste annually. This waste is primarily composed of phosphorus, nitrogen, and potassium and can be used as fertilizer. For example, a proportion can be used to feed the tilapia. The remainder can be used for methane generation. Collecting and storing guano prior to use will require innovative new engineering approaches.

A special design to immediately capture and divert chicken waste may indeed be useful. Excretory ammonia in the form of uric acid is a colorless irritant gas produced by the microbial breakdown of nitrogen, is prominent in poultry manure. This activity is not a problem under conditions where birds travel about in small groups over wide areas, but in indoor facilities the breakdown of poultry manure releases a concentration of poisonous ammonia gases that is potentially toxic. If exposed directly, poultry workers could experience eye, lung, and nasal irritation as well as headaches, nausea, wheezing, coughing and other respiratory problems. Upon exposure, the health of chicken layers may be at risk due to the fact that chickens need three times more air volume than humans per kilogram of body weight to meet their specific oxygen requirements Consequently, the Division of Animal Health of New Jersey Agriculture in collaboration with United Poultry Concerns, Inc. recommend that ammonia must not exceed 15 ppm to maintain “minimum bird welfare.” Further considerations regarding the humane standards that must be met for the raising, keeping, care, treatment, marketing, and sale of poultry are enumerated in their document entitled, Humane Treatment of Domestic Livestock.

Tilapia

There are different areas that Tilapia farming must take into account for a successful aquaculture system. The layout of the facility is where the tanks are placed. Flow scheme, details where the water from the tanks go. In particular, in what order are the plants receiving waste water, i.e. the plants which can process higher rates of ammonia will receive water first. Main water intake is the source that feeds clean water into the tanks. In theory there are two possibilities. Water could come directly from the living machine into the tanks or once water has gone through the entire vertical farm and has been deemed ‘safe’ it can be circulated into the tanks. Drainage system dictates how the effluent goes back to the plants and how it should be filtered to remove biosolids.

The previous report stated that 182,500,000 grams are needed to feed 50,000 people a 100 g portion of fish each day. Redoing the calculation,100g /day/person x 365 days/year x 50,000 people yields 1,825,000,000 g per year, the difference is a factor of 10. Now 35,096,153 grams of edible fillet are required each week to feed 50,000. This translates into 194,978 fish needed per week. At 600 fish being produced from 1 tank, 324 tanks are needed to supply enough food for one week compared to last years 32 tanks. Since the growing cycle from fingerlings to maturity is 6 months, 24 separate batches of tilapia need to be growing at any one time, meaning 7,776 tanks need to be operational. Using the space requirements from last year and multiplying them by ten produces 608,940 ft 2. A tilapia set up of this magnitude would take up 7 floors.

Each circular tank with an 8’ diameter loses 13.76 ft2 in the 8’x 8’ square it occupies because of its shape. If this is applied to all 7,776 tanks, 106,998 ft2 are lost due to shape alone. A better alternative would be constructing fairways. There will be 24 fairways, 1 for each week, rather than 324 separate tanks for each week. A fairway is a rectangular tank constructed from cement that has divisions in it. The design of the fairway allows you to save space and also have a current within the tank for the fish to swim in. This promotes healthier fish as it allows them to swim in a greater space instead of a small tank where their movement is restricted to the 25-foot circumference of a circular tank. Each fairway will be 16,277 ft 2, a number derived assuming that 600 fish can be grown in 50.24 ft 2 of water at a depth of 4’ (as specified in 2004). Each fairway will be 100 feet by 162 feet, with 4 fairways going on a single floor (diagram). This leaves 25,200 ft 2 on each floor for filtration tanks and operating space. The other huge advantage is that there is less surface area for heat to escape from. Although the area of water exposed to the air remains the same and the volume remains the same, the amount of water in contact with the sides of tanks and the floor changes dramatically. The surface area available for heat loss by conduction is smaller for fairways. The total surface area using 8’ diameter tanks is 1,562,664 ft 2 and the area using fairways is only 827,904 ft 2. Looking at 324 small tanks (one week supply) vs. 1 fairway is 65,111 ft compared with 34,496, respectively. Yet, another advantage with the application of fairways are the fewer number of working components that will be necessary to operate them. It may be unreasonable to assume that each fairway only needs a fraction of the parts to operate 324 smaller tanks, but it is realistic to say it may only require 25% of working components.

In raceways the water enters in a plug flow manner and is pumped in one direction to prevent minimal back mixing. The best water with highest oxygen concentration is available at the head of the raceway as more ammonia and carbon dioxide accumulate near the end. The velocity of the water is 2-4 cm/s and as a result a majority of the solids accumulate near the end leaving the need for fewer settling tanks. Baffles, the width of the raceway, are placed perpendicular to the flow of water which help create a velocity of 20-30 cm/s near the edges. The current helps sweep waste away from the center of the raceways and progressively backwards.

Because water has a higher specific heat than air it will naturally require more energy to heat. Tilapia are going to be grown on the top six floors of the vertical farm above the chicken layers. This provides two advantages in terms of heat. First, the tank will be heated passively due to hot air rising from the floors beneath it. The water will be maintained at 82 o- 86 o F both, from heat rising and coils along the side of the tanks. The coils will circulate water that is heated by passing them near structures burning methane. The other advantage is that each 4’ layer, collectively 24’ layers, of water will act like as a lid on a jar, preventing heat loss by insulation.

Other Considerations for Energy Demands

The other categories that take up energy come from administrative office costs, refrigeration costs, and meat processing costs. Average energy consumption for commercial buildings is 97200 BTU per square foot, or 35.7 cubic feet of natural gas per square foot. Food service buildings rank among the highest energy consuming structures, using 245500 BTU per square foot, or 153.5 cubic feet of natural gas per square foot.

Using the food service industry’s measurements as a reference, we approximated the amount of energy consumed by a 48-story building if each floor were 90 thousand square feet. Such a 4,320,000 ft 2 facility would consume 10.6 trillion BTU’s or 663 million ft 3 of natural gas. Converting BTU to Watts with the conversion factor 1 BTU = .000293 kWh, the building would need 310,744,080 kWh of energy per year to maintain itself.

Energy Demands – Growing Conditions Maintenance

Considering only light requirements for plants and animals, the Vertical Farm requires approximately 26,500,000 kWh. It should be noted that this does not include lighting peripheral space around equipment and on other floors where plants will not be grown. It would be highly unlikely that this number would approach 310 million kWh projected by the food services industry.

Using the commercial industry values, energy consumption for such a building would equal 123,031,872, which may be a more realistic assumption.

III. Main Energy Output: The Methane Digester

The amount of energy needed to grow crops and animals in the Vertical Farm has already been defined. This section determines how much of that energy can be supplied through the operation of a methane digester. The amount of waste generated was calculated by using 2004 figures regarding total tons needed per year. A harvest index revealed the amount of material that is edible off each plant. For Example, 40,000 tons of Crop A were needed to feed 50,000 people per year. If it had a harvest index of 0.4 then this represented 4/10 of the total biomass produced. The corresponding value of waste would be 60,000 tons produced per year. The weekly waste was calculated and converted into kilograms.

(+) These are assuming a high end rate of 18% mortality and chickens weighing 5 lbs.
(++) This is the weight of each carcass after being stipped of meat and bones. This includes heads, guts, and feathers (approximating 20% left) (+++) This assumes that 20% die before reaching maturity with a weight of 250 kgs
(++++) This is byproducts of gutting (60% of total weight of a 450 kg fish)

Methane digesters operate most efficiently when a carbon to nitrogen ratio of 30:1 is used. Within the vertical farm engineers can devise a proper method to reproduce this ratio when stocking a digester. The University of South Hampton conducted a study to determine how much methane was produced from kitchen waste whose contents had the following percentages: fruits and vegetables (67%), meat (13%), bread (7%), Teabags (10%), Other (3%). The carbon to nitrogen ratio of 9:1 deviated greatly from the ideal. The digester transformed a kilogram of kitchen waste into 164-271 liters of biogas with a methane composition of 57.9%. With this model, and assuming that all of the animal and plant waste was thrown in together producing a high end figure (271 liters of biogas/ kg waste) a total of 992,031 kWh can be produced per week.

If waste was digested according to this value then 51,585,612 kWh can be produced each year, not including wastes from the living machine. In practice there may be more energy as a better mixture of waste will be engineered to be injected into every digester.

IV. Infrastructural Components of the Vertical Farm

Climate Control System

 The design of a climate control system is affected by the design of the Vertical Farm complex. What type of materials will be used to build it, how many climate zones on each floor and how to get natural light to as many sections of the building as possible are a few construction considerations that influence a climate control system. The University of Maryland’s 2002 NCR-101 Station Report on the Horticultural Greenhouse Complex gives examples of things to consider when designing a climate control system.⁶⁶ As mentioned, the number of climate zones and the size of each zone are important. The 2004 Vertical Farm Report estimates how much space is needed to grow each of the plants needed. One option is to have one zone per plant, while another is to have plants with similar growing requirements all in the same zone. The University of Maryland picked tempered horticultural glass for their complex. The type of glass influences the amount and the quality of light entering the building as well as the heat loss factor, which is important when determining the size of a heating system.

Since one objective is to have the Vertical Farm self-sustaining, this narrows the types of heating systems available. Air heating can be by either proportional control or ON/OFF control. Proportional control is normally used in conjunction with boiler-heated water pipes. This provides a very gentle heat and the heating pipes can be positioned either under the grow beds or between the rows of plants. In this way less heat need be supplied as compared with general warm-air heating. Water pipe heating is gentle, economical and avoids sudden drying of the air. A benefit is it can be used to control the relative humidity in addition to the temperature. Compared to a proportional control system that uses hot water, a steam system can provide more British thermal units (Btu).⁶⁷ Either type works well for the Vertical Farm complex because we plan to have an ample amount of water coming from black water that has been filtered through the “Living Machine.” A temperature that is too elevated not only encourages photorespiration, at the expense of photosynthesis, but also infestation by certain parasites. Especially during the summer months, it is necessary to be able to evacuate the air from the growth chambers within a 5-minute period. However, temperatures that are too low considerably diminish plant growth rates and, in the extreme cases, may cause fungal problems.

The following calculations give an example of how to determine the heating capacity needed for the Vertical Farm. The calculations are based on an area (A) of 90,000 ft 2 per floor and maintaining an indoor temperature of 24° C (75° F). Taking into account that the Vertical Farm will be located in New York City, we chose -21° C (-5° F) as the outdoor temperature. The indoor temperature was chosen based on the range of growing temperatures needed for the plants selected. An assumption was made that double-layer glass will be used, giving a heat loss factor of 0.8 Btu/hr(ft 2)(°F).⁶⁸ The amount of heat created by the sun, the heat generated by the lights and any mechanical systems has not been factored into this calculation. When the Vertical Farm Complex is further along in its design and the materials and equipment to be used is known, then these factors can be included in the calculation.

5,760,000 Btu/hr is the estimate of the heating requirements for the Vertical Farm Complex. Our hope is this amount will come from the methane digester.

It is essential to ensure air renewal while maintaining optimal CO2 and humidity levels. CO2 being heavier than ambient air, it has a tendency to accumulate at ground level, thus becoming unusable for the plant. A simple oscillating ventilator overcomes this problem by allowing the air to circulate such that the CO2 remains accessible. The University of Maryland’s report also mentions the use of exhaust fans for increased air-flow and to aide in ventilation.⁷⁰ There are different types of fans but the type most commonly used in green houses are propeller fans which fall into the category of axial flow fans.⁷¹ To determine the size and how many fans are needed, the volume of air to be moved needs to be calculated. The estimated volume of air per floor in the Vertical Farm building is based on a height of 10 feet and the previously mentioned area of 90,000 ft 2, giving an air volume of 900,000 ft 3. In addition to knowing the air volume needed, other factors needed to be known. One is the fan’s efficiency, determined by their air displacement (CFM) given in cubic feet per minute.^{72, 73} Others are the static pressure or the amount of resistance, the space available for the fans, how noisy the fans are and if they have different speed settings.^{74, 75} Since the main objective of the 2005 Vertical Farm Report is to determine the energy requirements of the complex, we simplified the calculation for determining the type and number of fans needed by using the volume of air and the amount of air displaced without taking into account the amount of resistance, which is variable and can only be estimated.⁷⁶ Using the single phase 20” Multifan (Vostermans Ventilation, IL) which has a CFM of 4,765 and a usage of 410 Watts, we calculated 189 fans, equaling 77,490 Watts that are needed per floor. To calculate this we divided the total air volume by the air displacement.

A third component is a cooling system which is so