Chapter 9

State-of-the-Art CO2 Injection and Environmental Controls
    
     Recently several manufacturers have introduced equipment that allows extremely fine control over most of the environmental factors in the high-tech indoor growing environment. These systems that automatically monitor the temperature and humidity, and turn on the exhaust fan or an airconditioner or dehumidifier any time the temperature or humidity rises above pre-set levels.
     After the exhaust cycle is completed, the fan stops and the necessary amount of CO2 is injected into the air. The injection is facilitated by a small timer that opens the solenoid valve and releases CO2 for a predetermined number of seconds.
The equipment remains off until one of three things happens:

  1. the temperature rises above the predetermined limit,

  2. the humidity rises above the predetermined limit or,

  3. the amount of time set on the main clock transpires and another cycle is initiated.
Periodic CO2 Injection

     The CO2 injection system pictured on page 24 contains an integrated fan system. The fan is necessary to remove the stale air
and replace it with clean, fresh air from outside before additional CO2 is injected into the room. Here is how the system works:
  1. The clock timer cycles every hour, causing the mechanism to turn a switch on or off on a minute by minute basis. The clock timer is usually set to turn on the exhaust fan for a certain number of minutes once, twice, or three times an hour.

  2. After the fans have exhausted the air in the room and replaced it with fresh air from the outside, CO2 is injected into the air in adequate amounts to bring the CO2 levels up to optimum. The CO2 timer determines the amount of time that the CO2 release valve remains open, usually measured in seconds.

  3. The regulator shows the pressure of gas in the tank and the cubic feet per minute at which the gas is being released when the solenoid valve is opened.
Evacuation! Injection Cycles

     There are a number of reasons that growers choose different lengths of time between cycles for the evacuation/injection process. The exhaust fan does a lot more than just change the air to eliminate CO2 depletion. Artificial lighting often causes a heat build-up. Periodically replacing the hot, stale air with cool, fresh air helps keep the heat within acceptable limits. Also, plants transpire water through their leaves into the air during the growth process. This raises the humidity, which can also make the environment prone to mold and rot, as well as cause loose, stringy plant growth.
     Depending on the location, season, placement of the chamber in the house, and other factors, the temperature and humidity changes from day to day. In many cases, simply changing the air and re-injecting CO2 can cure a problem with temperature or humidity build-up. This is because the heat and moisture-laden air that builds up in the room is replaced with cool, fresh, drier air from the outside.
     Seasonal changes in the weather often result in alterations to the time between evacuation/injection cycles. For example, as the temperature heats up in the summer, more frequent cycles are necessary because the air being drawn into the chamber is considerably warmer to begin with, and therefore rises more quickly to the point where the temperature is unduly high. In some locales, more cycles may be warranted in the winter rainy season, because the air being drawn into the room contains more moisture.

Tubing and CO2 Dispersion
 
     CO2 must be introduced into the grow room in the proper manner for it to do its job correctly. Some equipment manufacturers recommend a perforated tube strung around the ceiling with small holes to let the cool CO2 fall down over the plants. This is a must in a grow room with inadequate internal circulation, but the CO2 probably won’t do much in these circumstances. It quickly falls to the floor and escapes through cracks in the baseboards in a room with improper internal circulation.
     Large, heavy duty, oscillating fans are the solution. You just can’t get too much air blowing around in the growth chamber, both above and below the green canopy. (See drawing.)

CO2 Tanks
 
     A CO2 tank can be a monster. Even the little ones can be little monsters! Why? Because they weigh far more than most people estimate.., especially half way up a few flights of stairs.
     The smaller tanks are referred to as twenty pound CO2 cylinders. That is because they hold 20 pounds of CO2 gas. But don’t let the nomenclature fool you. A twenty pound steel tank weighs about 50 pounds when full. A full fifty pound tank weighs about 170 pounds.
     Tanks are available for sale or rental at welding supply companies. This is where a tank is re-filled. (Usually the empty tank is swapped for a full one.)
     CO2 tanks are regularly used by welders, bars, and people with home beer tappers.
     Always protect the valve from being knocked off or damaged in an industrial accident. Always chain the tank to the wall in an upright position to prevent accidental tip-over.

Regulator Freeze - Up
 
     Gas is extremely cold when it escapes from the tank. A quick blast can do damage to skin tissue or eyes. Be careful!
     CO2 can also freeze and ruin a regulator. In haste to supply CO2 to the waiting plants, many growers crank the regulator up to a flow-rate that can cause cause regulator freeze-up. This can occur at anything above 20 CFH (cubic feet per hour). Special heated regulators are available for those with a large area, or a shortage of patience.

Determining CO2 Release Time

     At 20 CFH, each minute of CO2 release yields one-third of a cubic foot of CO2 released. A 10 X 10 X 8 foot room would require a little over 3 minutes of CO2 release.

Advantages of Injection
  1. Periodic injection of CO2 is very clean.

  2. Precise control of CO2 levels is easy.

  3. Injection does not add to temperature or humidity.

  4. When injected into a powerful fan or through a perforated tube suspended from the ceiling, the CO2 is easily dispersed throughout entire growing area.

  5. There is no danger from flame, heat or flammable gas.
Disadvantages of Injection
  1. An injection system requires handling of heavy tanks which must be taken in and out of growing area on a regular basis for refilling.

  2. The cost is high for the initial equipment, then very low for the CO2 itself (compared to other methods).

  3. A very slight danger is present from valve damage causing the tank to become an uncontrolled projectile powered by gas escaping at up 1000 pounds per square inch of pressure.

  4. Another slight danger (although probably more likely to happen than the previous scenario) is the displacement of air that can happen in the event of quick release of all the CO2 in a tank into a closed area. Both plant and human can perish in this event. Not because CO2 is a poisonous gas, but because the CO2 can displace all the oxygen in the area, causing asphyxiation, or death from lack of oxygen.
     The author of this book was nearly asphyxiated while running a machine that was activated by CO2 release, causing a slow but steady build-up of CO2 in the room, gradually displacing all the oxygen.
     Asphyxiation symptoms come on slowly. They begin with a sleepy and lethargic feeling, and can be followed by a desire to lay down for a nap. There are no ”danger sign” feelings in the lungs. If you feel this way when in your growing chamber, get out quickly! Check your equipment for signs of malfunction later.

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