aSK THE EXPERTS
You know, I’ve read a lot of books and have been through trial and
error, and I have been asked repeatedly about inducing CO2 into a
sealed (airtight) growroom. With that being said, I have yet to read
an article that explains it in detail—mostly, is it necessary to have a
vent in a sealed growroom if CO2 is kept at a consistent level
with monitors?
Thanks,
Terry Haight, Jr.
A completely sealed
growth chamber (or,
“enclosed climate
agriculture”) can be a
Dr. Lynette Morgan
difficult environment
to maintain because
a balance between
light, heat, CO2 and humidity must be met while the air is
continually recirculated instead of exchanged with the outside
environment. Generally, it takes a lot of equipment to maintain
all these plant growth variables at the same time.
CO2 enrichment to levels as high as 1,000 to 1,500 ppm is
used in growth chambers to help boost plant growth (note,
higher levels can become toxic to plants). Often, compressed
CO2 cylinders are used as a source since burners generate a
lot of heat. The reason why most growing environments—
including growth chambers and greenhouses—are vented is to
not only replenish the CO2 plants take up, but to also remove
heat buildup and water vapor. Plants release large amounts of
water vapor into the air when they transpire, which rapidly
increases the humidity (particularly under warm growing
conditions). High humidity has negative effects on plant
22
Maximum Yield USA | July 2012
growth—if the plants can’t transpire due to high humidity, the
flow of nutrients (particularly calcium from the roots to the
leaves) is severely restricted and the plant growth stagnates.
High humidity also allows for the growth of fungal spores and
bacterial pathogens. So, in order to keep the heat and humidity
down, moist air is vented out and replaced with drier air—often
at a rate of one complete air exchange per minute.
If venting and air exchange are not used in an enclosed
environment, heat and humidity must be controlled in other
ways. It is possible to use large dehumidification units to remove
water vapor and air conditioners to control heat; however, all of
thesse must be run at once to maintain the required humidity
levels (50 to 67% for most plants).
So, a completely enclosed growing chamber requires heat and
water vapor removal from the air, as well as lighting and CO2
enrichment at the correct level, to maintain balanced growth. In
theory, if all these parameters are met, the enclosed environment
can be run with no venting; however, there are certain gases
(such as ethylene) that might still build up in a tightly sealed
room, so sources of this and any other unwanted gases need to
be carefully checked for.
Dr. Lynette Morgan