http://www.hydrofarm.com/articles/co2_enrichment.php
4. FERMENTATION METHOD OF CO2 ENRICHMENT:
Sugar is converted into ethyl alcohol and CO2 when it ferments due to the action of yeast. In this method, the following ingredients and equipment are needed:
1. Suitably sized container, plastic or glass
2. Sugar, common or invert
3. Yeast, brewers or bourgelais wine yeast
4. Yeast nutrient
5. Sealant, cellophane, tape or lid
6. 1/4 plastic tubing
7. 1/4 shutoff valve
8. Balloon
9. Starter jar or bottle
A pound of sugar will ferment into approximately half a pound of ethyl alcohol (C2H5OH) and half a pound of CO2. One pound of CO2 makes 8.7 cubic feet of CO2 gas at normal atmospheric conditions. In our standard 8 X 8' X 8' grow room, you will need to generate 512 cu. ft. X .0013 (1300 PPM CO2) = 0.66 cubic feet of CO2 every four hours. It takes time for the yeast to ferment sugar, so the size of container you should use in determined by dividing the cubic feet of growing area (512 Cu. ft.) by 32 = 16 gallons.
A convenient container to use here would be a plastic kitchen garbage can. These are inexpensive and easily obtainable.
To determine how much sugar we need for six weeks of operation or until fermentation ceases, the following calculations are necessary: From the above paragraph, we need 0.66 cu. ft. of CO2 every four hours. If one pound of CO2 makes 8.7 cu. ft. of CO2, we will need 0.08 lbs. of sugar, but because every one pound of sugar only makes 1/2 lb. of CO2, we must double the amount of sugar needed, i.e. 0.08 X 2 = 0.16 lbs. of sugar every four hours. Since there are six four-hour periods in a 24 hour day, the amount of sugar we need is 0.16 x 6 or 0.96 lbs. of sugar per day.
If we round this off to one pound of sugar per day, we will need 42 lbs. of sugar in six weeks. We must consider that only 80 to 90% of the sugar will be completely converted in this length of time, therefore, we should actually use about 48 lbs. of sugar in six weeks.
The sugar solution to start with is 2 1/2 to 3 lbs. per gallon. You can use hot water to start with, as sugar dissolves faster in it than in cold water. You must let it cool to 80-90 degrees F before adding yeast to it or the yeast will be killed. Start with the fermenting container only half-full as you will be adding an extra gallon per week for 6 weeks. Begin with eight gallons per week and 24 lbs. of sugar.
To start the solution fermenting, you will want to make a "starter batch" of sugar water, yeast and yeast nutrient. To do this, use a coke or beer bottle (approx. one pint), dissolve 1/4 lb. of sugar in 10 oz. of warm water (approx. 3/4 full), add a pinch of yeast and two pinches of yeast nutrient to this sugar mixture. Place a balloon on the bottle and set in warm location, 80 to 90 degrees F, for one to two days or until the balloon expands and small bubbles are visible in the solution.
After the starter solution has begun fermenting vigorously, it is added to the main fermentation tank at the same temperature already mentioned. After a day or so, to see that the system is working properly and that CO2 is being generated, close the valve to the supply tube and, if the unit is sealed properly, the balloon should expand in a short period of time. To regulate the amount of CO2 being delivered to the plants, open the valve until the balloon is only half the size of full expansion.
The CO2 supply tube with in-line valve should have a 2" loop in it half full of water to serve as an air-lock. This loop can be held in place with tape on the side of the fermentation tank. The open end of this tube can either be positioned in front of a circulating fan or run through "T" fittings to make additional tubes, the ends of which can be positioned above your plants. Remember, CO2 is heavier than air and it will flow downwards.
Once per week, undo a corner of the Saran Wrap and add an extra gallon of sugar solution and yeast nutrient, then reseal the top with tape. Use three lbs. of sugar and one teaspoon of nutrient per gallon.
After the last gallon is added, after six weeks of operation, let fermentation continue until the balloon goes down and no more bubbles are visible in the "U" tube. When this point has been reached, taste the solution. If is it sweet, fermentation is not complete and a new starter batch should be made and added to the tank. More yeast nutrient should also be used. If the solution is dry (not sweet) like wine, fermentation has stopped and the alcohol content has killed the yeast. At this point, it's time to clean your tank and start a new batch.
The fermentation process is quite good for generating CO2 and relatively inexpensive. Regular or invert (corn) sugar is inexpensive and available. You may have to purchase invert sugar at a wine supply store. This method of generating CO2 will cost approximately 50 to 60 cents per day.
To save money on extra yeast, you can either take out approximately a gallon of fermenting liquid and save for the next batch, or start a second system identical to the first and alternate themóclean and replenish one, then three weeks later, clean and replenish the second.
The above simplified:
Here is the basic formula to keep the entire enclosure at 1300ppm
X*.0013 = Y
(Y/8.7)12*1.1=Z
X=cubic feet of grow room Z = amount of sugar in pounds used per day
So if your room is 4x4x8 then you would want to use a total of 0.25lbs of sugar per day. You should either use a 4 gallon container or four 1 gallon containers for this. Start off with 1lb of sugar per container (or 4lbs in the 4gallon) and add an additional 1/4lb per container every 4 days (or 1lb in the 4gallon).
Ideally your room would be sealed for this but if you cannot control the heat then make sure your vented hood pulls from the very top of your cab - CO2 is heavy so if you pull from the very top you'll hopefully be removing just the hot air and leaving the cooler CO2 at the bottom - I would also recommend putting your vent fan on a dimmer so that as little air exchange as possible is going on. Of course if your canopy is only 4' high then you can probably cut the amount of sugar in half as long as you are directing the CO2 to where it needs to go.
At night I encourage you to increase ventilation as the plants prefer O2 than CO2.
