URBAN CEA
Part 2

Erik Biksa

In the last installment in this project, a CEA closed-loop indoor growing environment was in the preliminary phases of assembly. The setup was intended to offer the urban/city grower the opportunity to create a high-yielding indoor garden in a relatively small space with a minimal of operating constraints. Urban gardening comes with a unique set of constraints. The urban apartment grower must cohabitate with their endeavours and neighbours.

The grow chamber was installed in a spare room adjacent to a living area and within proximity of neighbours, separated from the outside world only by triple pane glass. To ensure a productive and high-yielding garden a 1000-W HID lamp is being used to illuminate the 4 x 4-ft. area inside the growing area, while water-cooled lighting is being experimented with to increase the cooling efficiency while maintaining a closed environment.

In running a closed environment precise environmental control may be used to trigger stronger vegetative, flowering, and ripening responses in crops. Two types of environmental controllers and an infrared carbon dioxide monitor have been installed in conjunction with a 6-in. inline exhaust fan wired with a fan speed control to help maintain optimal CO2 levels and day/night temperatures within the growing enclosure.

A portable room air conditioning unit (9500 BTUs) is also supplying cold and dehumidified air in an adjacent area, which helps to further increase cooling efficiency. The grow chamber was set up in a sealed-off sunroom within the urban condo setting.

So, how did the initial setup work?

During the first running(s) of the installation, ambient temperatures within the sunroom enclosure were averaging 80 F (summer months), so it was certain that the cooling efficiency of the water-cooled lighting was going to be decisive factor in how well the initial setup would work out. A small window within the enclosed sunroom (acting as a “lung”) was left open a crack to help disperse some of the heat from the magnetic ballast (SS-1 HPS 1000) and to provide fresh air. All of the air entering the sealed growing chamber was filtered through a 6-in. diameter HEPA filter to reduce contamination from dust, insects, and spores.

Well, first, the light intensity levels in the Hydrohut were incredible! With all four sides and top and bottom of the enclosure being highly reflective, no light emitted from the 1000-W HID light source (dual arc type: 400W MH/600W HPS) was wasted. The spectrum of the dual arc tube lamp appeared very natural in contrast with the daylight that filtered into the sunroom/lung though the venetian blinds covering the windows. All of the light stays inside the growing area except when it is unzipped to inspect the setup and controls (and crop, for the would-be grower). The 6-in. inline fan draws air from within the enclosure through an activated carbon filter and discharges it back into the lung area. No air is exhausted directly outside.

Initially the water chiller (1/4 HP) used for cooling the water-cooled lighting system was installed in the lung room. The chiller unit is set at 72 F (~22 C); it cycles when the water in the cooling system increases beyond the set point. The reservoir in the water-cooling system was in the neighbourhood of 10 gal. (38 L), which, incidentally, is on the small side. A minimum of 40 gal. (152 L) is recommended, but because the water-cooled lighting system was experimental, a 10-gal. dump on the tiled floor or within the watertight flooring of the growing enclosure would cause minimal damage. With any growing endeavour it is recommended that all electrical devices and cords be secured above floor level in the event of spills or other floods, to prevent electrical shock or damage to equipment.

The chiller unit proved to cycle rather frequently during the light cycle, which discharged a considerable amount of heat into the lung-area. Ambient temperatures within the enclosure were reaching near 90 F (a 10-degree rise from ambient) with the lamp running; actual temperatures directly beneath the lamp were slightly higher due to irradiant energy from the lamp. Clearly this wasn’t going to work. However, during cooler months the 10-degree rise would have been acceptable, but the initial base temperature was 80 F to begin with, so the chiller unit was moved outside of the lung room to where the heat could be discharged and dissipated through the air-conditioned adjoined living areas.

Discharging heat through the chiller unit was simple compared to forced-air discharge from exhaust fans or air-cooled lighting. No trace of the air from the growing enclosure is discharged into the living area because all the heat is captured in the closed-loop water-cooling system. In winter months, using hydronic heaters/water radiators, the heat from the water-cooled light system could be used as the sole or supplemental heating source for a modest-sized condominium.

Once the chiller unit was discharging heat outside of the lung room there was a minimal rise between ambient temperatures and the operating temperatures of the sealed growing environment during the lighting cycle. Temperatures were slightly higher directly under the lamp, but incredibly cool compared to conventional HID lighting or some air-cooled lighting fixtures. The oscillating fan within the growing area helps to reduce any heat that might collect around the horizontal lighting fixture housing the water-cooled lighting cylinder.

Admittedly, the chiller unit is a little unsightly in a living area, but a stylish metal plenum could easily and inexpensively be fabricated; it would also serve to keep the water lines out of sight.

Ambient CO2 levels were always more than 600 ppm due to the air quality in an urban setting. Simply working in the lung room could raise the ambient CO2 levels to over 1000 ppm. A CO2 cylinder with flow meter and regulator can be installed in conjunction with the infrared CO2 monitor to achieve any CO2 level up to 2000 ppm.

Overall the setup was very functional, efficient, precise, and very quiet, an important consideration in an urban setting.

With the ideal controllable growing environment established, the next step was to install a growing system that could support a variety of plants and growing methods (organic, hydro-organic, or hydroponic). A simple solution would be to use containerized plants with a soilless mix. However, in doing so the crop’s production levels would be limited to the amount of oxygen available at the root zone. Remember, a crop can only perform up to the least available input. For high-output gardens all of the following parameters must be maintained at optimum: temperature (day/night), light (intensity and spectrum), humidity, CO2 levels, nutrients/beneficials, root air-to-water ratios, and dissolved oxygen.

Bucket-type systems appear to provide the greatest degree of flexibility, because they can be operated hydroponically, hydro-organically, or organically. They allow plants to be moved around as size or variety dictates. In the event of a need to move while a crop is planted, the plants will be minimally disturbed. Being able to rotate plants as required for optimal branching patterns is also a good idea when constructing smaller-scale but high-output indoor gardens. Bucket systems also use a good volume of nutrient solution per plant (the solution surrounds the roots), which helps to buffer against drifts in pH, TDS, and nutrient solution temperatures.

A pre-manufactured system was preferred over a homemade unit. An air-driven system was chosen because there is no water pump to heat the solution and to maximize oxygen levels available to the root system and beneficial life in the root zone. I chose to use a pre-manufactured system that used a 3-gal. upper chamber and 5-gal. lower chamber. Ebb/Flo bucket systems are also an excellent choice, but for the purposes of future experimentations a top-feed system is preferred for this particular installation. The system was installed with a controller unit that uses some unique T-fittings and a venturi air drive to circulate the nutrient solution in the lower chambers from each of the individual units and back through the controller/reservoir unit. The upper portion of each chamber is fertigated and oxygenated with a separate venturi air-drive system delivered through a drip ring installed in each of the units. The upper chamber of each unit drains back into the lower support containing nutrient solution in each hexagonally shaped module. A noteworthy feature of this system is that six of the individual units can be linked together to make a hexagonal configuration, optimizing the light usage footprint.

The goal in this setup is to reap all the benefits of organic production while providing a more ambient and dissolved oxygen-intensified environment to the root zone. The pictorial submitted with this article shows the overall concept and adaptation of this system. The intent is to create a level of biological activity for the upper root portion that will be contained in the upper 3-gal. root container. The upper portion will, therefore, require good ambient oxygen levels and a suitable substrate to support such life.

Beneficial inoculants and organic ingredients will do much to boost the overall health, vigor, yield, and quality in most crops. Purely hydroponic systems are not conducive to supporting beneficial soil life due to their relatively inert nature. Many roots will grow through the bottom of the top container and into the depth of nutrient solution below. The lower roots will primarily absorb water and most nutrients, the lower portion becoming the “hydroponic” aspect of the system.

It is important that the lower chambers are opaque, to prevent light infiltration. Additional air stones and an air pump were installed for the lower portion of each of the growing chambers. In this way the upper portion of the chamber can be fertigated intermittently via timed frequency and duration. The system and roots will stay aerated with the air stones in the lower portion of the unit and the venture-driven recirculation system when the drip rings are inactive, preventing anaerobic conditions from occurring in the lower chamber and root zone. The increased air exchange in the root zone will also benefit the more biologically active upper container/root zone.

The system was set up for larger plants, using four units in the 54.5-in. square floor space inside the growing enclosure. With the use of the flexhose connecting all the units to each other and back to the controller/reservoir unit, the plants can be huddled together under the light when smaller, to maximize lighting efficiency. As the plants gain stature and require more floor space they can simply be pushed further apart to allow for greater floor space per plant. In this way all plants will receive relatively even light levels, individually and from top to bottom.

Individual plants can also be moved for more consistent growth patterns. In this system it is possible to lift each of the upper growing chambers and give it a quarter turn daily. Entire plants can also be switched from grow unit to grow unit simply by rearranging the upper chambers. Pruning, maintenance, taking cuttings, and spraying is also simplified when the entire plant can be removed from inside the growing enclosure without disrupting the root system. Bucket systems are one of the few hydroponic systems that allow plants to be moved without damaging root systems and shocking the plant.

The following procedure was used to prepare the upper chambers for planting:

• The grow rocks were rinsed with plenty of fresh water in a shower/bath. Smaller-diameter grow rocks were chosen because they have more total surface area for root-to-media contact. Simply running copious amounts of good quality water through the perforated drum or bucket containing the grow rocks removes much of the dust that occurs from the abrasion the substrate receives during transport. Breathing in the dust can irritate lungs and may also plug up emitters and other components in the growing system. Using hot water helps to ensure that the substrate is relatively sterile before putting it into the system. Some innovative growers have reported increased results by soaking their grow rocks in a solution of beneficial inoculants, such as trichoderma, bacillus, pseudomonas, etc., after rinsing and before planting into the system.
• The premium quality compressed coco coir brick also requires hydration and an initial charge of calcium and magnesium. A large plastic tote was used for this purpose. About 5 gal. of a mild nutrient solution high in calcium and magnesium, with some organic additives and vitamins, was prepared in the tote. The 11-lb. block of compressed coco coir was then placed in the tote and allowed to hydrate. The hydration process is relatively quick when using high-quality compressed coir. Excess nutrient solution was drained out of the tote and was then ready to use for planting.
• The bottom one-third of the upper chamber in the growing system was filled with grow rocks. This provides excellent drainage from the upper chamber to the lower chamber and helps to keep debris out of the system.
• The middle one-third of the upper chamber in the growing system was filled with the hydrated and charged premium coco coir. This allows the roots to have a more natural environment for the retention of moisture, and most important to provide a place for biological activity, because beneficial soil micro-organisms will colonize more readily in this type of substrate compared to just grow rocks or in the nutrient solution. The cation exchange capacity (CEC) inherent to the coir will also help to buffer the root system against salinity. This area will act as a biological filtration system for the nutrient solution because it is circulated from the lower chamber up and through the upper chamber before it drains back down again into the system.

Now that the growing environment has been fine-tuned to maintain optimal temperature, light, humidity, and carbon dioxide, the focus can turn to producing superior crops through better plant nutrition. The manufactured air-driven bucket-type system offers a lot of flexibility in terms of the range and types of nutrients, additives, and beneficial that may be incorporated into a high-yielding nutrient regimen. By incorporating both inert and organic materials into a highly aerated system containing a large volume of solution per plant to buffer temperature, pH, and EC fluctuations, the possibilities are virtually limitless.

Naturally the tendency would be to lean towards organic-based production methods aided by super-charged root and growing media inoculants. Combining both organic and hydroponic nutrients (each at half strength, or in a two parts hydroponic to one part organic ratio) also provides excellent and consistent results. Hydro-organic and hydroponic specialty additives (primarily in the bloom phase for flowering plants) would help to improve yields and enhance some qualities. It is worthwhile for urban gardeners to research methods of crop management, including nutritional products, to maximize the potential results for a small-scale but intensively producing garden.