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Chapter 7
Humidity Control
Most
gardeners are able to win the fight against humidity without resorting
to a power-sucking electric dehumidifier. A dehumidifier is something
like an air conditioner in operation. Simply plug it in, set the
maximum humidity level desired on the humidistat, and the machine will come on and
dry the air when the humidity exceeds a set range. Very simple and
in-expensive to purchase but expensive to operate if needed full-time. However, they
work fairly quickly, and are usually on only a few minutes per
hour.
Even so, there are a number of techniques that can be used to lower the humidity before resorting to a dehumidifier.
- Increase the frequency and/or duration of the ventilation
cycles and the size of the exhaust and/or intake fans. Assuming
that the humidity is lower outside the room than inside, simply
change the air more often, before it has a chance to build up
any extra humidity. (Note: there may be times and climatic conditions
where the reverse of this practice may lower humidity. When the plants
are small - compared to the available cubic feet of space in the grow
space - and the outside air is high in humidity, fewer exhaust cycles
may lower the overall humidity. This is due to the heating/drying
action of the lights.)
- Increase the internal circulation. Often, in spaces with less
of high humidity that are caused by an area receiving in-
adequate circulation. These are usually caused by the plants growing into
a canopy, causing two or more microclimates in the grow room. The air
above the green canopy is heated and dried by the lights, but the air
below the canopy is left relatively cooler and more humid. Gardeners often
put their most powerful fans above the canopy, to prevent the heat from
the lights from burning the plants. The area below the canopy is often
overlooked.
The problem can be remedied by blowing air under the canopy,
across the tops of the pots, slabs, or cubes with powerful oscillating
fans. The rapid air movement also prevents the formation of mold or rot.
The vertical air circulator described elsewhere in this book also
helps.
Some gardeners keep internal air circulation at a virtual
typhoon-like blast to eliminate temperature and humidity build-up
problems. One might assume that since the grow room is a closed
environment, increasing the air circulation above moderate levels wouldn’t
do anything to solve the problems. Wrong! Give it a try before spending
big bucks to purchase and operate a dehumidifier.
- Try taking the air from a different place.
Air inside a heated or cooled house usually contains less humidity than
the air outside. Changing the intake vent so that air is drawn from
the living room instead of the outside can drop the humidity a whole lot. The
air may have the added advantage of extra CO2 from people or pets.
Outside air can also provide different humidity levels. An
open sunlight area will usually have lower humidity levels than an area
shaded and protected by a lot of trees.
Air taken from the attic is usually lower in
humidity than air in the basement. Air taken from the furnace room may
be pre-dried of most moisture. There is a trade-off here, of course,
since the dry air is probably pretty hot!
Best Locations
The location of the growth chamber in the house or apartment can have a considerable effect on temperature and humidity control. A
relatively dry basement is usually the best bet. The basement’s wall
temperatures can help heat in winter and cool in summer.
A well-insulated house retains the heat of the day after the
sun goes down, and remains considerably cooler than the out-side air
during the day. This can be a big factor in determining whether or not an
expensive air conditioner must be installed.
The lack of insulation in a vented attic, or an outside
shed, can also be made into a friend. By using a reverse light cycle
(lights on during the late night hours and off during the heat of the
day), the effects of the temperature fluctuations can be mitigated.
Some research results indicate that plants grown using a
cool light cycle and warm dark cycle produce stockier plants. The incoming
air flow can be used to condition the room temperature. For example, a
second story grow room in a well-insulated two story house can use air
from an intake vent that draws air from the living room below, especially
if the house is in a hot climate. The air in the living room may be 10
- 15 degrees cooler than the outside
air during the day. The downstairs air is also much cooler than the
upstairs air
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