CEA – Closed Environment Agriculture
By Erik Biksa
A closed growing environment differs from the traditional grow room set-up in that it does not “connect” to the external environment and runs on a closed loop. Typically, grow room air is vented to the outside while outside air is drawn in to replace the air being evacuated. This creates an “open door” for a host of problems, and can limit the amount of control you can take over your growing environment. The open loop can be equated to greenhouse growing, except for the fact that you are supplying the light. In this scenario you are subject to the limitations, pests, and problems of a greenhouse environment. So, conceivably theses types of limitations can be minimized or eliminated if you consider taking the next step forward.
The following model should give the grower some insight on some key features in a closed-loop growing environment.
Ideally there are three rooms of about equal volume. Two of the three rooms will be dedicated to cultivation while the third, preferably more central room, will serve as a sort “lung” or “air buffering chamber”. If possible, it’s better to have a central room that with a greater volume than the other two rooms. This will increase the air-buffering capabilities that are key to running a closed-loop grow room. For this example, let’s say that each room is about 1000 cubic feet in volume (10′ X 10′ X 10′).
The central room will usually hold the HID ballasts, although they may also be located in another area. Keeping them in the central room will make servicing and maintenance a little easier. On the other hand, if you have a large number of ballasts, it will increase the amount of energy and equipment required to maintain optimal air temperatures. For lighting, a “flip-flop” lighting relay will be required.
In our example each room has about 10′ X 10′ of linear space. On rolling benches two 4′ X 8′ growing trays can be parked snuggly in each growing room. For intense lighting, each tray will be illuminated with two-1000W H.I.D. lamps. Alternatively, three-600W H.I.D. lamps per tray would provide more even light distribution for slightly less power consumption, but the initial investment would be increased. So, we have a total of four trays between the two rooms, this means that eight (or 12 with 600Ws) individual bulbs and reflector assemblies with lamp wire will be required. All lamp wiring will lead to the central room. Half the number of ballasts versus lamp assemblies is required when using the flip/flop relay. That’s because the ballasts will run continuously 24/7. The photoperiod can either be 24 hours light in one room, or be divided to one 12 hour light cycle, per room, per 24 hours. This is accomplished by means of a 24 hour timer and lighting relay. Basically, the ballasts are running 24 hours a day and the timer can transfer the load from the ballasts to the lamps in one room or the other hence the “flip flop”.
This “flip flop” is the central component or hub in this type of grow room. Not only will this occur with lighting, but also the entire climate will shift from the central room to either growing room on activation of the relay. Flip-Flop relay boxes can be purchased complete, or can be wired by a qualified electrician. Always consult local wiring codes.
The discussion on setting up the central room should help provide some clarification. Another key component in this installation is the A/C (air conditioning) unit. The number of lights you intend to run is the primary factor in determining the cooling capacity requirements of your A/C unit. Secondary factors to consider are whether or not you will be using a CO2 generator and if you will be keeping your ballasts in the central room or at a remote location. Carbon dioxide levels will need to enriched in this situation, as the intake of outside air is minimal or non-existent. This would rarely be done by tank and regulator, as multiple tanks would be need to be replaced very frequently. As a rule of thumb you should have about 3000 BTU’s cooling capacity for every 1000 Watt H.I.D. lamp or 4000 BTU’s cooling capacity for every 1000W H.I.D. lamp when using a fossil-fuel burning CO2 generator due to the extra heat created. This should also allow for a little leeway in accommodating your ballasts in the central room/”lung”. It is worth noting that there are now water-cooled CO2 burners available to help mange the extra heat created.
In our example we will not be running more than 4-1000 Watt H.I.D. lamps simultaneously. Our growing rooms and central room are about 1000 cubic feet in volume each. For good CO2 buffering we will select a CO2 generator that will be able to handle about 2000 cubic feet (remember both growing rooms will never run at the same time, so the generator is only servicing the “lung” and one growing room at any one time). When selecting a CO2 generator, it is best to purchase a unit that will produce the most amount of CO2 in the least amount of time. A unit rated with a CO2 output of between 24 to 36 cubic feet per hour would fit the bill nicely. Smaller units could be used, but would be running for considerably longer to replenish CO2.
So, that’s four 1000 watt lights with CO2 and ballasts to cool at around 4000 BTU cooling capacity each, for a total of about 16,000 BTU’s required. Since not all appliances operate at 100% efficiency we should factor in another 20% to 30% for a total cooling requirement of about 20,000 BTUs (16,000 X 1.25=20,000).
Traditional residential air conditioners require an exhaust discharge, usually out the back of the unit (you can modify this type of unit with a transition and connect a discharge hose for venting to outdoors). Some of the more modern residential models are portable, and have a factory-installed exhaust discharge hose. These units can satisfy the requirements of smaller set-ups, but diminish the “closed-loop” due to venting requirements. Remember, we want to limit the set-up to the least amount of connection to the outside world as possible.
For our calculated cooling requirements, a hydronic finned heat exchanger is best suited for the application. These appliances are available from some indoor garden supply retailers or from residential heating and cooling suppliers. They are essentially a furnace-type housing containing a blower unit and a radiator core. You need to have an inexpensive, vast, and cold source of water to operate these units. To keep the water as cold as possible, the water usually runs to waste 24/7 through the radiator coil. When temperatures rise, the blower unit is thermostatically activated to run. This draws air through the water-cooled radiator core and discharges it, effectively cooling the air. If attempting to conserve water, a solenoid opens the water intake only when the fan is activated. However, the drawback is that the water usually needs to run for a period in order to get as cold as possible, influencing the cooling ability of the appliance. As mentioned, the water running through the radiator core usually drains to waste. If your water is metered, this can become very costly and may be considered wasteful. This makes a good case for setting-up near cold-water fed spring, glacial lake, or mountain fed water body. The key advantages to using this type of A/C over a conventional residential model is that they offer significantly greater output, do not require a discharge to the outside, and use minimal electricity (only for the fan). There are larger units of this style that use water to cool a refrigerant system. The units that have refrigerant use considerably greater amounts of electricity (60AMPS at 240V) but have tremendous cooling capacity and offer some of the same advantages as the smaller, non-refrigerant charged aforementioned units.
The cooling unit should be wired to a good quality thermostat wired higher up on the wall in the central room/”lung”.
The central room should also be out-fitted with an activated carbon filter(s), humidifier, de-humidifier, infra-red-CO2 “sniffer”, and the previously mentioned CO2 generator (or tanks), relay/timer unit (“flip-flop”), and air-conditioning unit.
The activated carbon filter is outfitted with an in-line or blower fan of the appropriate CFM rating (dependent on filter size). The fan continuously draws the room air through the activated carbon and back into the environment. This scrubs the air clean of any contaminants (such as mildew spores, etc) and unwanted odors. Maintaining a healthy aerial environment is key in this situation, because YOU are conditioning the air for your plants and not depending on the air quality mother nature provides from outside intake air. Remember, that when you draw air in from the outside you are bringing in spores, insects, etc. along with the fresh, cooler air (a gateway for many pests). Controlling humidity while cooling with outside air can also be a problem. Even with a de-humidifier it’s hard to keep the growing environment at 50% R.H. when the outside air is 90% R.H.! How about cooling your room when the outside air is above 80°F?
The dehumidifier and humidifier should also be kept in the central room and each should be independently wired to the appropriate controller for the appliance (a de-humidistat for the de-humidifier, and a humidistat for the humidifier.) Whatever you do, don’t set them at the same level (ie 50%R.H.). If you do, you will probably have both appliances competing with each other, causing them both to run more or less continuously. For example you might set the de-humidifier (activates on rise) to 65% R.H. and set the humidifier to 35% R.H. (activates on drop). Some A/C units remove a lot of humidity from the grow-room, even to the point where it can be detrimental, hence the need for the humidifier. Make sure that your de-humidifier is capable of removing enough moisture from the air in a short period of time. You may consider installing more than one unit. Actively growing plants can transpire a lot of water. Usually this moisture is removed with the heat when exhausted to the outdoors. In this situation, it has to be condensed and removed in a closed environment.
An infra-red CO2 monitor/doser connected to your source of carbon dioxide will maintain your pre-set CO2 levels in the central room which is acting as an air buffering chamber. As the air in the room is circulated to one of the growing rooms and returns (closed loop) the CO2 monitor measures the density of the air, and will trigger the CO2 generator to activate once levels fall past the set point. It will then disable the CO2 generator once CO2 levels have been replenished.
The A/C unit is placed in the central room wired to a cooling thermostat (thermostat in same room). It will cool and circulate the air in the buffering /central room. When the temperature rises in the active grow room, the air from the grow room is exhausted into the central room, and if required, it may cool, de-humidify or humidify, enrich with CO2, and scrub the air as it is being returned back into the active grow room.
When the relay is tripped by the timer and the lighting electricity is transferred into the other grow room, the controlled air from the central room will also be transferred simultaneously. This is accomplished by means of electronic dampers and an active fan. Like the ballasts, the fan will run continuously supplying either one growing area continuously or alternating equally between the two grow rooms with an active supply of air. When the flip-flop relay is activated (for lighting), it will close the circuit on one damper in a “Y” series or plenum (fan unit), while opening the circuit on the other damper. Each damper is connected via ductwork to it’s own grow room (each damper serves it’s own room off the same fan). Also connected to the flip-flop relay would be corresponding fans, located in each of the growing rooms. When lighting and air are transferred into either of the rooms, an exhaust fan in the room activated will be triggered, forcing the grow room air into the buffering/central room where it is conditioned to the pre-set parameters and returned back by another fan into the active grow room.
The actual grow rooms are not much different from most conventional grow rooms. However, climate controls and equipment are not incorporated into the growing rooms themselves because they have been installed in the central/buffering room. Each grow room will have an active (fan driven) central duct leading from the buffering room and an active (fan driven) central duct from the buffering room leading back into the grow room. Both fans run for the entire photoperiod and are activated and de-activated by the flip-flop appliance.
Each of the grow rooms should also be outfitted with an activated carbon filter set-up to scrub the air (as described in the buffering room set-up). They need not have the same capacity as the buffering room scrubbers, as they can be wired to the flip-flop relay to come on during dark hours. This will help protect your crop during dark hours from air-borne contaminants and help to control odors. This also helps to create negative pressure in the grow room during the dark-cycle, helping prevent odours from entering your living space.
Each grow room should also be equipped with a small exhaust fan set to run continuously during the dark cycle, discharging into the buffering room (which should be busy pre-treating air for the active grow room). In our example each of the grow rooms was about 10′ X 10′ so a small 250CFM fan should be enough.This will help to maintain negative pressure and serve to remove excess humidity and residual heat. If the growing area is well insulated (which it should be if you go through this much expense) you shouldn’t need to heat the area during dark cycles. A maximum/minimum thermometer will tell you for sure.
Clearly, it takes more time and expense to construct a growing set-up similar to the model discussed. However, a lot of the typical problems associated with operating for longer durations can be avoided by closing the loop to your own personal Garden of Eden. If you manage the installation correctly you should be able to realize more consistent harvests with fewer pests, because you have closed the entrance to outside spores, temperatures, humidity, insects, and other pests.