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CLOSED ENVIRONMENT AGRICULTURE
By: Eric Biska
AKA "Ask Eric"
A closed growing environment differs from the traditional grow
room set-up in that it does not “connect” to the external
environment and runs on a closed loop. Typically, grow room
air is vented to the outside while outside air is drawn in to
replace the air being evacuated. This creates an “open
door”for a host of problems, and can limit the amount of
control you can take over your growing environment. The open
loop can be equated to greenhouse growing, except for the fact
that you are supplying the light. In this scenario you are
subject to the limitations, pests, and problems of a
greenhouse environment. So, conceivably theses types of
limitations can be minimized or eliminated if you consider
taking the next step forward.
The following model should give the grower some insight on
some key features in a closed-loop growing environment.
Ideally there are three rooms of about equal volume. Two of
the three rooms will be dedicated to cultivation while the
third, preferably more central room, will serve as a sort
“lung” or “air buffering chamber”. If possible, it’s better to
have a central room that with a greater volume than the other
two rooms. This will increase the air-buffering capabilities
that are key to running a closed-loop grow room.
For this
example, let’s say that each room is about 1000 cubic feet in
volume (10’ X 10’ X 10’). The central room will usually hold
the HID ballasts, although they may also be located in another
area. Keeping them in the central room will make servicing and
maintenance a little easier. On the other hand, if you have a
large number of ballasts, it will increase the amount of
energy and equipment required to maintain optimal air
temperatures. For lighting a “flip-flop” lighting relay will
be required. In our example each room has about 10’ X 10’ of
linear space. On rolling benches two 4’ X 8’ growing trays can
be parked snuggly in each growing room. For intense lighting,
each tray will be illuminated with 2-1000W H.I.D. lamps.
Alternatively, 3-600W
H.I.D. lamps per tray would provide more
even light distribution for slightly less power consumption,
but the initial investment would be increased. So, we have a
total of 4 trays between the two rooms, this means that 8 (or
12 with 600Ws) individual bulbs and reflector assemblies with
lamp wire will be required. All lamp wiring will lead to the
central room. Half the number of ballasts versus lamp
assemblies is required when using the flip/flop relay. That’s
because the ballasts will run continuously 24/7. The
photoperiod can either be 24 hours light in one room, or be
divided to one 12 hour light cycle, per room, per 24 hours.
This is accomplished by means of a 24 hour timer and lighting
relay. Basically, the ballasts are running 24 hours a day and
the timer can transfer the load from the ballasts to the lamps
in one room or the other hence the “flip flop”. This “flip
flop” is the central component or hub in this type of grow
room. Not only will this occur with lighting, but also the
entire climate will shift from the central room to either
growing room on activation of the relay. Flip-Flop relay boxes
can be purchased complete, or can be wired by a qualified
electrician. Always consult local wiring codes. The discussion
on setting up the central room should help provide some
clarification. Another key component in this installation is
the A/C (air conditioning) unit. The number of lights you
intend to run is the primary factor in determining the cooling
capacity requirements of your A/C unit. Secondary factors to
consider are whether or not you will be using a CO2 generator
and if you will be keeping your ballasts in the central room
or at a remote location. Carbon dioxide levels will need to
enriched in this situation, as the intake of outside air is
minimal or non-existent. This would rarely be done by tank and
regulator, as multiple tanks would be need to be replaced very
frequently. As a rule of thumb you should have about 3000
BTU’s cooling capacity for every 1000 Watt H.I.D. lamp or 4000
BTU’s cooling capacity for every 1000W H.I.D. lamp when using
a fossil-fuel burning CO2 generator due to the extra heat
created. This should also allow for a little leeway in
accommodating your ballasts in the central room/”lung”. It is
worth noting that there are now water-cooled CO2 burners
available to help mange the extra heat created. In our example
we will not be running more than 4-1000 Watt H.I.D. lamps
simultaneously. Our growing rooms and central room are about
1000 cubic feet in volume each. For good CO2 buffering we will
select a CO2 generator that will be able to handle about 2000
cubic feet (remember both growing rooms will never run at the
same time, so the generator is only servicing the ”lung” and
one growing room at any one time). When selecting a CO2
generator, it is best to purchase a unit that will produce the
most amount of CO2 in the least amount of time. A unit rated
with a CO2 output of between 24 to 36 cubic feet per hour
would fit the bill nicely. Smaller units could be used, but
would be running for considerably longer to replenish CO2. So,
that’s four 1000 watt lights with CO2 and ballasts to cool at
around 4000 BTU cooling capacity each, for a total of about
16,000 BTU’s required. Since not all appliances operate at
100% efficiency we should factor in another 20 to 30% for a
total cooling requirement of about 20,000 BTU’s (16,000 X
1.25=20,000). Traditional residential air conditioners require
an exhaust discharge, usually out the back of the unit (you
can modify this type of unit with a transition and connect a
discharge hose for venting to outdoors). Some of the more
modern residential models are portable, and have a
factory-installed exhaust discharge hose. These units can
satisfy the requirements of smaller set-ups, but diminish the
“closed-loop” due to venting requirements. Remember, we want
to limit the set-up to the least amount of connection to the
outside world as possible. For our calculated cooling
requirements, a hydronic finned heat exchanger is best suited
for the application. These appliances are available form some
indoor garden supply retailers or from residential heating and
cooling suppliers. They are essentially a furnace-type housing
containing a blower unit and a radiator core. You need to have
an inexpensive, vast, and cold source of water to operate
these units. To keep the water as cold as possible, the water
usually runs to waste 24/7 through the radiator coil. When
temperatures rise, the blower unit is thermostatically
activated to run. This draws air through the water-cooled
radiator core and discharges it, effectively cooling the air.
If attempting to conserve water, a solenoid opens the water
intake only when the fan is activated. However, the drawback
is that the water usually needs to run for a period in order
to get as cold as possible, influencing the cooling ability of
the appliance. As mentioned, the water running through the
radiator core usually drains to waste. If your water is
metered, this can become very costly and may be considered
wasteful. This makes a good case for setting-up near
cold-water fed spring, glacial lake, or mountain fed water
body. The key advantages to using this type of A/C over a
conventional residential model is that they offer
significantly greater output, do not require a discharge to
the outside, and use minimal electricity (only for the fan).
There are larger units of this style that use water to cool a
refrigerant system. The units that have refrigerant use
considerably greater amounts of electricity (60AMPS at 240V)
but have tremendous cooling capacity and offer some of the
same advantages as the smaller, non-refrigerant charged
aforementioned units.
The cooling unit should be wired to a good quality thermostat
wired higher up on the wall in the central room/”lung”. The
central room should also be out-fitted with an activated
carbon filter(s), humidifier, de-humidifier, infra-red-CO2 “sniffer”,
and the previously mentioned CO2 generator (or tanks),
relay/timer unit (“flip-flop”), and air-conditioning unit. The
activated carbon filter is outfitted with an in-line or blower
fan of the appropriate CFM rating (dependent on filter size).
The fan continuously draws the room air through the activated
carbon and back into the environment. This scrubs the air
clean of any contaminants (such as mildew spores, etc) and
unwanted odours. Maintaining a healthy aerial environment is
key in this situation, because YOU are conditioning the air
for your plants and not depending on the air quality mother
nature provides from outside intake air. Remember, that when
you draw air in from the outside you are brining in spores,
insects, etc along with the fresh, cooler air (a gateway for
many pests). Controlling humidity while cooling with outside
air can also be a problem. Even with a de-humidifier it’s hard
to keep the growing environment at 50% R.H. when the outside
air is 90% R.H.! How about cooling your room when the outside
air is above 80?F? The dehumidifier and humidifier should also
be kept in the central room and each should be independently
wired to the appropriate controller for the appliance (a
de-humidistat for the de-humidifier, and a humidistat for the
humidifier.) Whatever you do, don’t set them at the same level
(ie 50%R.H.). If you do, you will probably have both
appliances competing with each other, causing them both to run
more or less continuously. For example you might set the
de-humidifier (activates on rise) to 65% R.H. and set the
humidifier to 35% R.H. (activates on drop). Some A/C units
remove a lot of humidity from the grow-room, even to the point
where it can be detrimental, hence the need for the
humidifier. Make sure that your de-humidifier is capable of
removing enough moisture from the air in a short period of
time. You may consider installing more than one unit. Actively
growing plants can transpire a lot of water. Usually this
moisture is removed with the heat when exhausted to the
outdoors. In this situation, it has to be condensed and
removed in a closed environment.
An infra-red CO2 monitor/doser connected to your source of
carbon dioxide will maintain your pre-set CO2 levels in the
central room which is acting as an air buffering chamber. As
the air in the room is circulated to one of the growing rooms
and returns (closed loop) the CO2 monitor measures the density
of the air, and will trigger the CO2 generator to activate
once levels fall past the set point. It will then disable the
CO2 generator once CO2 levels have been replenished. The A/C
unit is placed in the central room wired to a cooling
thermostat (thermostat in same room). It will cool and
circulate the air in the buffering/ central room. When the
temperature rises in the active grow room, the air from the
grow room is exhausted into the central room, and if required,
it may cool, de-humidify or humidify, enrich with CO2, and
scrub the air as it is being returned back into the active
grow room. When the relay is tripped by the timer and the
lighting electricity is transferred into the other grow room,
the controlled air from the central room will also be
transferred simultaneously. This is accomplished by means of
electronic dampers and an active fan. Like the ballasts, the
fan will run continuously supplying either one growing area
continuously or alternating equally between the two grow rooms
with an active supply of air. When the flip-flop relay is
activated (for lighting), it will close the circuit on one
damper in a “Y” series or plenum (fan unit), while opening the
circuit on the other damper. Each damper is connected via
ductwork to it’s own grow room (each damper serves it’s own
room off the same fan). Also connected to the flip-flop relay
would be corresponding fans, located in each of the growing
rooms. When lighting and air are transferred into either of
the rooms, an exhaust fan in the room activated will be
triggered, forcing the grow room air into the
buffering/central room where it is conditioned to the pre-set
parameters and returned back by another fan into the active
grow room. The actual grow rooms are not much different from
most conventional grow rooms. However, climate controls and
equipment are not incorporated into the growing rooms
themselves because they have been installed in the
central/buffering room. Each grow room will have an active
(fan driven) central duct leading from the buffering room and
an active (fan driven) central duct from the buffering room
leading back into the grow room. Both fans run for the entire
photoperiod and are activated and de-activated by the
flip-flop appliance. Each of the grow rooms should also be
outfitted with an activated carbon filter set-up to scrub the
air (as described in the buffering room set-up). They need not
have the same capacity as the buffering room scrubbers, as
they can be wired to the flip-flop relay to come on during
dark hours. This will help protect your crop during dark hours
from air-borne contaminants and help to control odours. This
also helps to create negative pressure in the grow room during
the dark-cycle, helping prevent odours from entering your
living space. Each grow room should also be equipped with a
small exhaust fan set to run continuously during the dark
cycle, discharging into the buffering room (which should be
busy pre-treating air for the active grow room). In our
example each of the grow rooms was about 10’ X 10’ so a small
250CFM fan should be enough. This will help to maintain
negative pressure and serve to remove excess humidity and
residual heat. If the growing area is well insulated (which it
should be if you go through this much expense) you shouldn’t
need to heat the area during dark cycles. A maximum/minimum
thermometer will tell you for sure. Clearly, it takes more
time and expense to construct a growing set-up similar to the
model discussed. However, a lot of the typical problems
associated with operating for longer durations can be avoided
by closing the loop to your own personal Garden of Eden. If
you manage the installation correctly you should be able to
realize more consistent harvests with fewer pests, because you
have closed the entrance to outside spores, temperatures,
humidity, insects, and other pests.
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