Maximum Yield Cannabis Canada 2017 November/December | Page 42

net-zero energy greenhouse
“Most sustainable heating/cooling methods
in solar greenhouses are thermal storage methods:
they store excess heat from the greenhouse when it
is plentiful during the day and use it for heating at
night and through colder periods.”
For greenhouses in the Northern Hemisphere, most of
the glazing should face south, which is the direction
of the sun year-round. The north side of the green-
house plays a small role in collecting light and heat.
(The exception is very cloudy climates, like the Pacific
Northwest, where cloud cover diffuses incoming
light.) This wall can be insulated much like a home,
with rigid foam insulation is installed between wall
studs, to reduce unnecessary heat loss. In this way,
the greenhouse becomes more like an energy-efficient
shed than a leaky and non-insulated greenhouse.
Other principles of passive solar greenhouse design
include insulating the foundation of the structure and
angling the south-facing glazing area so that transmits
the maximum amount of light during the day.
Storing Solar Energy
Inside a residential net-zero greenhouse.
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grow cycle
In some climates, a passive solar greenhouse can
grow year-round without any additional heating
or cooling. For those in harsher climates, however,
additional systems are required to maintain sufficient
temperatures for good year-round growth.
There are numerous options in this arena, from
simple water barrels used as thermal mass to
advanced heat exchangers. Most rely on the simple
fact that most greenhouses collect far too much heat
during the day, even in winter. Typically, the grower
must vent this excess heat outside, essentially
wasting it. Smart greenhouse owners, on the other
hand, utilize this free solar energy to heat the
greenhouse at night. Most sustainable heating/
cooling methods in solar greenhouses are thermal
storage methods: they store excess heat from the
greenhouse when it is plentiful during the day and
use it for heating at night and through colder periods.
The oldest of these strategies is integrating thermal
mass, materials that passively warm up during the day
and slowly radiate this heat back into the greenhouse
when the temperature drops. Water is the most common.
By stacking barrels of water along the north wall of the
greenhouse, a grower can create a cheap and highly
effective thermal “battery” to stabilize temperatures.
Other thermal storage strategies include a ground-
to-air heat exchanger, which uses the thermal mass of
soil. Often called a climate battery, a ground-to-air heat
exchanger circulates air through a network of pipes
buried in the soil. The system transfers excess heat from
the greenhouse air to the soil, which stays a warm and
constant temperature (also, remember that the earth is a
stable temperature deep underground). When the green-
house requires heat on winter nights, the system draws
this heat back into the greenhouse. Thermostats operate
the fans so the system only works when the greenhouse
gets too hot or too cold.
Growers can also become more creative, integrating
a range of sustainable systems that provide fossil-free
heating and cooling. Compost heaters, rocket mass
stoves, even saunas and hot tubs are some of the many
strategies backyard gardeners have used to grow year-
round. Which system is right, however, depends on
your climate, greenhouse size, desire for automation,
available resources, and mainly, personal preference.