The entire artical can be found HERE (
hxxp://www.hempcultivation.com/420/showthread.php?p=544318#post544318)
CO2 Enrichment Guide
In an attempt to educate myself (and provide a resource for the HC.com community), I have been researching and assembling what I hope is a comprehensive guide to CO2 enrichment. I felt like there was a lot of speculation out there, but no real definitive or empirical guide. So here it is!
CO2 ENRICHMENT GUIDE
Carbon dioxide (CO2) is used by plants in photosynthesis, or the conversion of water, atmospheric carbon dioxide and light in the plant's chloroplasts into food energy (simple carbohydrates), with oxygen as a byproduct. Resins and saps in the plants stems and branches then transmit this food around the plant to promote growth, reproduction and prevention of disease.
Photosynthesis stops at night, thus plants do not use CO2 during the night, or lights-out stage. Although enrichment of the atmosphere during the night cycle will not harm the plants, efficient CO2 systems are regulated so that when the lights go out, CO2 emissions stop.
Ambient air at sea level contains approximately 350-500 ppm of carbon dioxide. Higher altitudes and rural locations typically have a lower presence of CO2, while lowlands and urban areas have a higher presence. CO2 can be measured, in parts per million (ppm) of air, using an inexpensive device available in hydroponics supply catalogs and garden shops (approx US$20).
Carbon dioxide enrichment involves increasing the concentrations of CO2 to 4-5 times the normal atmospheric levels, to between 1200-1500 ppm in an enclosed space. Enrichment has been shown to promote faster growth, higher yields, and stronger, healthier plants. Levels higher than 2000 ppm have been shown to retard plant growth. Low levels of CO2 (below 200) have been show to halt vigorous growth, even when all other conditions are ideal. Because of this, any enclosed space requires replenishment of the internal CO2 as it is used by plants, either from ventilation or from CO2 supplementation.
Temperature, humidity, and CO2 concentrations form a triangular relationship in a greenhouse or indoor grow. If all 3 factors are not in equilibrium, there is a risk to the plant in terms of stunted growth, toxicity, or death/disease.
Standard growing conditions typically include concentrations of CO2 at 300-500 ppm, temperatures between 65-80°F, and relatively low humidity (20-40% rH). Studies have shown optimal growth and yields at 90-95°F, 1,500 ppm CO2, 45-50% relative humidity, 7,500-10,000 lumens/square foot of light, and vigorous air movement both above and below the canopy. CO2 enrichment under 80°F, under 7500 lumens/sf, or above 50% humidity is not recommended because plants will not be conducting photosynthesis quickly enough to benefit from the enrichment.
Internal air movement in the grow room is critical to CO2 enrichment. Carbon dioxide is a slightly heavier molecule than other molecules floating around in the gaseous mixture we call air. Thus, CO2 enrichment without air movement will result in the gas settling out of the atmosphere before it has a chance to reach the plants. High temps and humidity without air movement can also encourage mold and bacteria growth.
To calculate the amount of Carbon Dioxide needed to enrich a room to 1500 ppm, first calculate the volume of the growing space. For instance, an 8x8 foot room with an 8 foot ceiling would contain 512 cubic feet of space. Determine the CO2 needed to enrich to 1500 ppm by multiplying the volume of space by .0015.
512 x .0015 = 0.768
Thus, 0.768 cubic feet (or rounded up to 0.8 cu ft ) of carbon dioxide will be needed to enrich this room at 1500 ppm. 1 lb of CO2 is equal to about 8.5 cubic feet at normal temperature and atmospheric pressure.
The rate at which carbon dioxide needs to be replaced is purely a function of how much ventilation the space receives and how many plants are consuming CO2 in the grow space. Only testing monitoring will ensure CO2 levels remain somewhat constant. Grow rooms that rely heavily on external ventilation to control temperatures or smell should not consider CO2 enrichment, because any gas introduced to the space will be blown out as quickly as it's created. A sealed room that relies on no external ventilation is ideal for CO2 enrichment. Since the ideal temperature for CO2 enrichment is much higher than normal, growers who employ this technique will need much less ventilation (if any).
For those who still want or need external ventilation, CO2 enrichment will only succeed if exhaust and enrichment are timed and set on opposing cycles. For instance, in a flowering room an exhaust fan timed to operate during the night would not conflict with CO2 enrichment during the day, when plants can use the additional gas. In vegetative growth rooms, the fans and enrichment would need alternating cycles to make enrichment worthwhile. For those growers using unregulated sysems, CO2 output should be adjusted for both speed and volume to make up for the exhaust.
There is some anecdotal evidence that charging nutrient solutions with seltzer cartridges will encourage plant growth in some hydroponics systems. The CO2 is released into the atmosphere as a byproduct of nutrient movement in the hydro system. This method has not been scientifically proven, nor would not be effective in aeroponic systems where nutrients are largely contained in separate tubs from the leaves and branches of the plant. Spray ring and ebb/flow systems may have the best potential for success with this method.
METHODS OF CO2 PRODUCTION
Tanked CO2
Tanked CO2 is by far the most reliable and controllable method of CO2 enrichment. Bottled CO2, usually available from welding supply and bottled gas vendors, is metered out via regulators and solenoids. It is possible to very finely regulate the amount of CO2 in the atmosphere using technologically advanced digital regulators. In many areas, licenses or permits are required to obtain bottled compressed gasses due to safety regulations.
Advantages
-Very fine control of CO2 using regulators
-Easy to automate, hassle free once set up
Disadvantages
-High initial cost of equipment
-Logistics of delivering and returning heavy bottles to a secure grow area
-The tank becomes a deadly projectile in a catastrophic failure, or can cause a significant and dangerous explosion in a fire.
-Rapid, unexpected release of CO2 can cause over-enrichment and asphyxiation of room occupants.
-Permit/license requirements may make bottled gas difficult to obtain