Sustainable Energy: Thermal Banking Greenhouse Design

Uploaded by cookingupastory on 30.11.2010

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>> Whether it's heat or cold,
thermal banking is just storing the energy that's available
for using at a time in the future.
Looking at the energy that you have as your resource,
and that storage system as your savings account.
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>> Bringing the people behind our food to life.
>> Actually I'm part of the back to the land movement
from the 60's when we dreamed about living
in harmony with nature.
And going beyond that, living also in harmony
with the community around us.
And so, you know, as well
as ecological principles we had principles
about cooperation and community.
So with this farm my goal was to develop a lifestyle that was
in harmony with nature, within the cycles of nature.
The farm itself I thought should produce the energy
that it needed to produce the crops
and to provide the necessities for the people
that lived on that farm.
Which is easily done, we're in Minnesota.
We have a limited amount of growing time,
so many of the things that we grow
for our income are annual crops of vegetables
that require greenhouse time to start the plants.
And, you know, transplant them
out into the fields during the summer.
Greenhouses traditionally in the past were energy consumptive
with the natural gas or fuel oil, or even wood stoves
that were required to keep them heated during that period
of time in the winter.
And a lot of greenhouses, all greenhouses actually,
will get too hot, even in the, you know,
late winter early spring when the sun's shining
and the days are getting longer, will get so extremely hot
that that, that heat solar gain is vented to the outside,
is wasted to the outside.
So it was important for me to conserve and make use
of the energy that was available.
Well we've got all this energy, so what do we do with it?
How do we trap it and save it?
Part of the reason that my greenhouse gets so cold at night
when the sun quits shining, because we have a cold floor.
So why not use that hot air and heat the soil underneath
and grow things in the winter.
You know, that first greenhouse I dug trenches about 2 feet deep
and buried perforated drain tiles
and a big squirrel cage fan.
Blew that air down in.
And what I found was that it was a little too shallow
and the soil dried out very fast.
And I had to constantly water.
And it was all the fan was blowing
from one end of the greenhouse.
And the end towards the fan was the hottest,
and the other end was the coolest.
So the next stage was to build another greenhouse
that was a little bit better designed
where I could have a better collections system
that would collect from the peak of the greenhouse,
the hottest temperature air, and blow it down and divide it,
divide the greenhouse in half,
and blow it through U shaped tubes to the outside.
Sare granted us $5,000 to start on that study.
That project actually cost me
about probably 40 more thousand dollars
when we figure materials.
More if we figure the labor in.
A good share of our materials were purchased
through grant money, so that we could afford
to purchase solar voltaics, solar panels, hire a backhoe
and purchase materials, and glazings for this greenhouse.
And then we supplied all the labor
and the rest of the materials.
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>> This greenhouse was designed
with one long pitched roof, glazed roof.
And the intention was that as the hot air raised and hit
that roof it would naturally force the hottest air
up into this ridge area that is 3 feet by 4 feet.
You can see an end view here of the collection tube
that runs the length of that ridge.
It has an inlet every 10 feet, so I can collect hot air
and pull it down through this 10-inch painted black galvanized
pipe that goes into the fan unit,
and then blows down into the beds.
A lot of greenhouses, commercial greenhouses,
are oriented north south.
As the sun travels it goes over the greenhouse.
Ours is oriented east west, because for us it was important
to catch and conserve the maximum amount of energy,
so we wanted maximum solar gain
in the winter time when the sun is low.
The under ground thermal storage with the greenhouse was probably
at least a third of the total time involved
in construction of the greenhouse.
You know, when people see the greenhouse all they see is
what's above ground.
But digging the 3-foot deep by 4
to 5 foot wide trenches was a major undertaking.
We hired a backhoe to dig out the trenches, but then we had
to square them and clean them all by hand with a shovel.
We hauled the smooth 1 inch plus river rock with a wheelbarrow
and dumped it into the trenches.
And laid our perforated drain tile on top of that.
And then buried that in more 1 inch plus rock.
We used up a lot of our old row cover, all this row cover
that is garbage, you know,
when you get done using it it's got holes,
it's dirty, had no other use.
It was a perfect use for covering the top of that rock,
so that our bed mix wouldn't filter down through
and ruin our storage system.
Then we laid in floor radiant tubing on top
of that [inaudible], from of that row cover and buried it.
We mixed the topsoil with composted manures
from our various livestock, and peat moss, and sand.
So that we'd have a bed soil that air could percolate through
and that water could percolate through and wouldn't be come,
would stay biologically active.
That was the bed system.
We put in place monitors.
We have tubes of 4 inch PVC that come up from
that perforated drain tile.
We put T's in and we put monitoring tubes up on the ends
of the beds and in the middle of the beds
where we can put an indoor outdoor thermometer probe
down into the gravel bed
to monitor the temperatures down there.
And then using soil thermometers 6 inch length ones,
and compost thermometers that go 20 inches deep
to monitor the temperatures in the bed soil.
So we can keep track and understand how,
what the flow pattern is for the solar gain
that we're blowing into the beds.
And, you know, what, you know,
what temperatures we're working with down underneath.
What the most efficient timing is to start that fan blowing
that heat down in there.
You know, initially it was a very simple control system.
When the sun shined the fan was hooked up with a variable speed,
variable current, half horse, direct current motor.
The sun shined, the motor started up slow.
And as it got hotter during the day as the sun shined brighter,
the motor went faster.
We're seeing perfect.
The problem is the sun shines before the air in the top
of the greenhouse gets hot.
So the first hour we were blowing cold air
down into those beds.
And then it took a whole other hour to compensate
for that cold air that we blew down in there.
So we needed to put a thermostat up in the ridge
of the greenhouse, so that that fan would not come on until
that air had warmed up above the soil temp, the temperature
in the gravel storage underneath.
Initially when I did the grant I figured, estimated what the cost
of energy was going to be.
And the cost of the greenhouse initially equaled the cost
of the energy that I was gonna spend in about 10 to 12 years.
So if the greenhouse lasted 20 years, then that whole last 10
to 12 years would be a net profit
above what the profit would be
if I would have done it conventionally
with using fossil fuel.
For another farmer looking at what we've experimented
and learned from this greenhouse project, there are a lot
of things, parts of it, that could be applied in a lot
of different ways to other operations.
If someone has an existing greenhouse
that they're using LP gas or oil to heat
and they haven't built permanent structures
or poured a cement floor or anything in it,
they could very easily trench that and, you know,
do a vent collection tube in the peak of that greenhouse and try
and conserve that heat that they're venting right now
into the floor of the greenhouse.
And have a warm floor that would radiate heat and keep
that greenhouse warm during the day.
We've been marketing since the first part of May,
which in Minnesota you would not have tomatoes, cucumbers, basil,
peppers available this time of year.
So we plant those in that greenhouse in February.
We plant them at the same time that we are finishing harvest
on what was planted the previous fall in November or December.
Through the winter when it's cold, when it's really cold,
and it can actually freeze and frost in that greenhouse,
we grow salad mix, cilantro, dill, beets, scallions, carrots,
parsley, things that can handle the cold.
We definitely have, you know, benefited economically
by having peppers that are red, and yellow, and orange,
and chocolate colored to sell when all those other ones coming
in from Holland are outrageously high priced.
You know, it raises the price that we get too,
much more than when we're selling them in the middle
of the season when several other,
you know, vendors have them.
And let me explain a little bit further.
I look at profits as with dollar signs,
as only being a very crude measure of the success
of your farm or your efforts, because your profits are
in the health of your family, the integrity
of your families relationship to the community.
I mean those are the profits that we forget to measure.
You know, maybe it's for [inaudible].
But in the end we all have to look at our journey
on this earth as being connected with our community and start
to dissolve the separateness between us and the rest
of the community, and the separateness
of us from the land.
We're not battling the land, we're learning to dance
with it and work with it.
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>> This video has been made possible with funding
from Sustainable Agriculture Research and Education, SARE.