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If CO2 is injected
into a room with no internal air circulation, it immediately falls to
the floor and stays there, or it leaks out the cracks in the door and
around the baseboard. Even with moderate air circulation, such as a small
fan, CO2 settles and does not reach the leaves.
Lots of Fans
The key to maintaining even CO2 levels throughout the grow room lies in internal circulation. Quite simply, the most successful grow rooms have the most fans. Plants seem to benefit by a constant blast of CO2 laden air. In addition to the fresh CO2
the constant motion of the plant parts causes tiny tears in the tissue. These heal to form a much stronger stem system, which is important when it comes time to support the abundant and heavy fruit, vegetables, and flowers that result from high-tech growing.
Some growers use a double layer
approach to air circulation. Powerful oscillating fans are placed above
the canopy formed by the plants, and a second fan system is placed below
the canopy, blowing over the lower stems, and the pots, slabs, cubes or
other hydroponic medium or support system. (See drawing on page 6.)
Vertical Air Circulation
Blowing air vertically helps disperse CO2 evenly and
prevents flat spots (microclimates) in the growing chamber. It also helps
prevent mold and mildew. The cool floor air is pumped out over the hot
lights, lowering the overall temperature.
Ventilation and Air Exchange
Even when supplying CO2 ventilation is
necessary to remove airborne wastes created by the plants. These include
hormones and other plant chemicals.
Basics of Ventilation
Assuming that CO2 is
supplemented, high speed periodic evacuation is desirable to accomplish
the air exchange as quickly as possible. If CO2 is not
supplemented, ventilate like crazy
.
Squirrel Cages
Although there
are some makeshift applications that work fairly well, it is hard to beat
a squirrel cage or shaded pole
blower. The
models in the 200 cfm (cubic feet per minute) range are relatively
inexpensive and work in closet sized growing chambers.
The 465 cfm blower is probably the most popular one sold. It
usually costs under $100 for a very safe and reliable exhaust
system.
A pump with a
capacity of about 980 cubic feet per minute will discharge the air
equivalent in a 10 ft. X 10 ft. X 10 ft. room in about one minute. However, the
incoming air mixes with the outgoing air, so one minute of operation
results in a 50% reduction of stale air. A three minute cycle would
change the air almost completely.
The most efficient grow rooms utilize two fans - one to pump in fresh air and one to
remove stale air. This method moves the air very quickly. Most experts agree that two 465
cfm blowers operated in this manner probably do the job better than a
single 980.
One consideration that amateur growers often overlook when
first installing the fan is the noise/vibration factor. Although the noise
of the fan is quite low, it operates at a high rate of speed with quite a
bit of centrifugal force. If anchored directly to the ceiling, the fan
could set up a subtle vibration that shakes the entire house or apartment
building for five minutes every hour, just like clockwork.
One of the ways to reduce the vibration is to mount the fan
on a piece of plywood, and hang the wood from the ceiling on stout cords a
few inches long. A flexible ductwork is constructed to pump the exhausted
air into the ceiling.
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