Ventilation and Air Flow
“THE EXACT TEMPERATURES
YOU MAINTAIN DEPEND
ON THE CROPS YOU GROW
AND THEIR PREFERENCES.”
32
Maximum Yield
Evaporative cooling systems, also
known as swamp coolers, turn hot
air into a cool breeze by passing air
through a soaked screen, pad, or spray
of water. These systems are most effec-
tive in environments with low humidity
as they add moisture to the air.
Fogging and misting systems are also
often used to cool greenhouses. These
two systems are similar in that they
both spray water to cool the air. The
main difference being the size of the
water droplets. Foggers create a very
fine mist, while misters spray larger
water droplets. These systems can be
put on a controller to spray water when
temperatures get too high. While effec-
tive, the main drawbacks to these types
of systems are excess humidity causing
fungal issues within the greenhouse
and clogged emitters from water with
high mineral content.
You can also control temperature by
keeping a black reservoir filled with
water in your greenhouse. During
the day, the water will absorb heat.
When it cools down at night, heat is
released and warms up the green-
house. This is the principle of thermal
mass at work. You can even put your
tank to good use and grow fish while
you’re at it. As a rule of thumb, fill your
reservoir with two to three gallons of
water per square foot of greenhouse
space. Finally, if you need to increase
temperatures in the winter, you can
use heaters or even wood stoves.
Air flow is essential for temperature
control and fresh air exchange. Without
fresh air, there will not be enough carbon
dioxide for photosynthesis unless you
install a CO 2 generator. Even with a
generator, you’ll need fans to move air
within the greenhouse to help prevent
fungal disease.
Vents, exhaust fans, and oscillating
fans can be used for fresh air exchange
and circulation. You can also install
roof vents that need to be opened and
closed throughout the day depending
on the temperature. Roof vents are often
operated by hand, but you can automate
them with a thermostat controller to
eliminate the manual work.
Exhaust fans can also be set on a timer
so air is exchanged as often as once per
minute. If it is cold outside, you will want
to exchange the air less often, about a
few times per hour. You can also hook
your fans up to a thermostat, so air is
exchanged when temperatures start
to rise. Mount these fans high on the
end walls and make sure they have a
protective hood so that rain is not blown
into the greenhouse.
Ceiling fans or oscillating fans keep
air circulating within the greenhouse.
This will control humidity levels and
strengthen your plants’ stems, just as
the wind strengthens plants outdoors.
Finally, if you are going low-tech, you
can install screened doors on the ends
of your greenhouse to create cross-ven-
tilation and prevent stagnant air.