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Ask a Grower

Ask-a-Grower Question #80

How do I calculate how much CO2 I need for my room?

This method is assuming you are using a tank of compressed gas and a regulator with a solenoid, flowmeter and a 15 min ON/OFF timer for dispersion.

First you want to determine the volume of your area in cubic feet. You can calculate that by multiplying the height by the width by the length of your area.

For example: 8′ high x 10′ long x 10′ wide = 800 cubic feet

After you have determined your rooms volume you will need to take the desired level of CO2, usually 1500 PPM ( parts per million ) and SUBTRACT the ambient CO2 levels, usually around 300 PPM; 1500 PPM – 300 PPM = 1200 PPM. This is the amount of CO2 you will need to add achieve optimum levels.

Now you are going to multiply your room volume by the amount of CO2 you desire to add. For this step 1200 PPM can be better reprsented as 0.0012.

For example: 800 cubic feet x 0.0012 = .96 cubic feet. For practical purposes we will round this off to 1 cubic foot. This is the quantity of CO2 to add in an 800 cubic foot size room to raise the level of CO2 concentraion from 300 PPM to 1500 PPM.

Before continuing on we need to assume that, in the average garden, it will take approximately 3 hours for the raised concentration level of 1500 PPM to return to the ambient level of 300 PPM. This drop in concentration can be attributed to plant usage as well as normal leakage in the room and should be factored in when calculating the CO2 flow rate for your garden. Another factor that can affect CO2 concentration would be your exhaust fans. For the best results you can use a combination of a digital CO2 monitor and/or atmospheric controllers like the Sentinel EVC-1, EVC-2, CPPM-1 or CHHC-1.

Now for the 800 cubic foot room, we take the approximately 1 cubic foot of CO2 and divide it up over the assumed 3 hour average period into 1 hour increments. There are 3 one hour periods in 3 hours.

For example: 1 cubic foot ÷ 3 = 1/3 cubic foot of CO2 (0.333)

This means that every hour an 800 cubic foot room needs 1/3 (0.333) cubic foot of CO2 to maintain the desired level of 1500 PPM. The described system operates on a 15 minute ON/OFF timer allowing for (2) two ON/OFF cycles per hour. Due to that fact we need to divide the 0.333 cubic foot of CO2 by 2 arriving at 0.1665, for practical purposes we will round this up to 0.2 cubic foot.

Now you have arrived at the appropriate flowmeter setting to raise and maintain the CO2 level of 1500 PPM in an 800 cubic foot growing area.

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