ing the device when the
temperature gets too cold,
a cooling thermostat trig-
gers a device when the
temperature is too warm.
An independent cooling
thermostat is a common
automation device used in
indoor gardens or small
greenhouses to control
the exhaust and/or intake
fans. Greenhouse garden-
ers can use a wide variety
of cooling techniques,
including passive vents
for convection heat trans-
fer and/or evaporative
coolers. Mechanical fans
are commonly used in
both indoor gardens and
hobby greenhouses. In most cases (except for the
convection heat transfer), a cooling thermostat or an
atmospheric controller can be used to automatically
control the device(s) and maintain a consistent tem-
perature.
Cooling with Air Conditioning
Although most greenhouse hobbyists rely on
other cooling methods, it is not uncommon for in-
door gardeners to use air conditioners as the main
cooling device. One of the most popular types of air
conditioners used by modern indoor horticulturists
is the mini-split air conditioning system. These types
of air conditioners are very effi cient at removing
excess heat and maintaining optimal temperatures.
When shopping for an air conditioner for an indoor
garden, a gardener needs to pay close attention to
the air conditioner’s BTU rating. British thermal unit,
or BTU, is defi ned as the amount of heat required to
raise the temperature of one pound of water by one
degree Fahrenheit. Don’t let the defi nition of BTU
confuse you. Instead, just think of BTUs as a way
to quantify heating or cooling equipment. In other
words, a grower can use a BTU rating to fi nd the ap-
propriate size air conditioner for his or her garden.
However, for indoor gardens it is not just the size of
the room that will determine the required BTU rating.
To adequately cool an indoor garden, a horticulturist
will need to consider fi ve major factors that infl uence
the required BTU rating of an air conditioner. Those
factors are: the dimensions of the growing area, the
lighting equipment, the ballasts of the lighting equip-
ment, the CO 2 equipment, and any other device or
equipment that will affect the room’s heat load.
Automating Air Conditioners
The great thing about the vast majority of mini-
split air conditioners is that they come complete
16
with built-in temperature and humidity control. Put
another way, they have a thermostat and humidistat
built right into the device. This means a grower can
set his or her desired temperature on the air condi-
tioning unit itself. Air conditioners without built-in
thermostats can be automated with the use of an at-
mospheric controller.
Atmospheric Controllers
Atmospheric controllers are devices that usually
feature both a thermostat and a humidistat. Essen-
tially, the temperature, humidity, and air exchange of
the garden space can all be automated with this type
of controller. Atmospheric controllers have the capa-
bility of controlling multiple devices at once, includ-
ing humidifi ers/dehumidifi ers, intake and exhaust
fans, and CO 2 enrichment equipment. Atmospheric
controllers that control multiple devices can also be
referred to as multi-controllers or a “brain” system.
The biggest advantage of controlling all ventila-
tion equipment with a single device is heightened
effi ciency. For instance, it is counterproductive for a
grower to operate his or her CO 2 enrichment device
at the same time their exhaust fan is removing air
from the environment. When the CO 2 equipment and
exhaust fan are plugged into the same atmospheric
controller, the device will automatically disable the
CO 2 equipment when the exhaust fan is operating.
This reduces wasted CO 2 and heightens the overall
effi ciency of the ventilation system.
Some of the latest high-tech atmospheric con-
trollers even contain special microprocessors and
customized algorithms. These particular controllers
can actually “learn and react” to the garden’s condi-
tions. For example, let’s say every day at noon the
greenhouse or indoor garden’s temperature suddenly
rises beyond the desired parameters. The controller
turns on the air conditioner or exhaust fan to correct
the problem. Over an extended period of time, if the
www.GardenandGreenhouse.net
May 2018