"All good things are wild and free." -HDT
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| Zeer Pot |
This blog has been haunting me. I'm
averaging a post a week, but every bit of blogger advice I've come
upon has said to write every day, or at least every other day. Since
this is primarily the planning phase, there's not a whole lot of
action to report. Most people like to see things getting done. So
what am I supposed to write about EVERY DAY?! Don't get me wrong, I
can ramble with the best of them, but the idea is to acquire
readers- not turn them away. So how do I keep it interesting? When I
think interesting, I think variety. Anyone who knows me will not be
surprised. Random and eclectic are what I do best. So, going forward,
I am going to try to write more often than once a week, and I'll be
writing on whatever topics occupy my fancy at the moment. Of course,
all of these will relate in some way shape or form to living
sustainably.
Today's Topic: Passive Refrigeration.
Dan and I have decided that while we wait to begin our build, we will
focus on better understanding and possibly testing out any of the
concepts that we find particularly intimidating right now. The first
one, which I spoke of in my last post, was the plumbing and heating
of water. After much reading, speculating and conversing, we have
tackled that obstacle....almost. We plan to do a three to five day
hot water challege, meaning our water behavior will mimic that of the
tiny house. Any hot water we want, we will heat on the stove, and
showers will be taken using the camp shower. (Came in the mail a few
days ago! Woohoo!) That should be a fun experiment.
The next challenge in line is building
a solar power system. I am a firm believer that you can make
something as simple or as complicated as you choose. We have been
searching high and low to find the easiest DIY system that won't kill
our wallets. As I mentioned last time, the biggest factor for the
cost of your system is the amount of power you will need. The fridge
would be the major power guzzling appliance, with laptops coming in
at a far but still noteworthy second. It would be super wonderful if
we could create our system for less than $2000, downright amazing if
it were less than $1000. The easiest way to begin cutting that cost,
is cutting power needs. This lead me to explore passive
refrigeration, which introduced me to the world of passive cooling.
There are three common (there are
others, but I've found more examples of these) types of passive
cooling that can be applied to passive refrigeration:
Evaporative Cooling
Radiative Cooling
Earth to Air Heat Exchangers
For more information than you ever
wished to know about these passive cooling methods, and others, check
out this comprehensive study on the subject. I'll be borrowing their
concise definitions for my top three.
EVAPORATIVE COOLING
“The
process of evaporative cooling allows the cooling of air (incoming or
exiting air) or of thermal
masses (roofs, walls, ceilings). It uses the natural effect of
evaporation to remove heat
from the air. Sensible heat from the air is absorbed as latent heat
necessary to evaporate water:
arm dry air is changed to cool moist air - heat in the air is used to
evaporate water.
The amount of sensible heat absorbed depends on the amount of water
that can be evaporated
in the system.”
So,
basically, when water evaporates, it releases heat. The more water
evaporating, the more heat released. And what is cold? Simply the
absence of heat. One thing to note about this method: it works best
in applications where the relative humidity is low. So this would
work great in the desert where the air is dry, but not so great in
the steamy jungle.
RADIATIVE
COOLING
“Radiative
cooling is based on the heat loss by long-wave radiation emission
from a body towards
another body of lower temperature, which plays the role of a heat
sink. In the case of
buildings the cooled body is the building surface and the heat sink
is the sky - since the sky
temperature is lower, especially during night, than the temperatures
of most of the objects upon
earth. Sky temperature during summer nights can be <0°C, with
clear summernight sky
conditions even sky-temperatures of -10°C could be achieved.”
A
great natural example is how cold a desert can get at night. The hot
surface of the earth has a wide open view of the night sky, a massive
heat sink. Since there are no building's or vegetation to block the
view of this heat sink, great amounts of heat are absorbed into the
night sky, leaving the desert thoroughly cooled.
EARTH
TO AIR HEAT EXCHANGERS
“The
basic principle for the use of air circulated earth to air
underground heat exchangers is the
seasonal thermal storage ability of soil, which results in a
temperature delay compared to the
outdoor temperature. This temperature difference makes possible to
use the soil for cooling
in summertime and for heating in wintertime. The heat exchange should
only be applied
in climates with big temperature differences between summer and
winter and between day
and night. The heat exchange can be applied for heating of supply
air, cooling of supply
air and heating and cooling of the supply air.”
Real
life example? Ever notice that your basement seems to be the same
temperature all year round? That's kind of what this is about. There
are houses that are built half way into a hillside, or partially
underground, sometimes called Earth-Integrated houses. These structures are able
to maintain relatively stable temperatures throughout the year,
keeping it cool in the summer, and warm in the winter with little
need for supplemental heating or cooling systems.
So
how do these concepts translate into power-free fridges? Check out
this article
or
just read my shoddy summary of it below...
Following
the rules of evaporative cooling, you can create shelf fridge for
less than $20! Simply by using a snap together plastic storage shelf,
and draping it with soaked burlap material! Sounds crazy, right? Like
how could that possibly make a difference and keep food fresh?! But
it does! With ample air circulation (and assuming you're in dry air)
this shelf can maintain an interior temperature cool enough to store
produce for many days. Just keep the burlap wet!
Another
example is the Zeer Pot. Mohammed Bah Abba of northern Nigeria
created this power-free fridge using rules of evaporative cooling.
Basically it is two clay pots, same shape but different sizes. The
smaller pot is set inside a larger pot, then sand is packed in the
space between the two. Wetting the sand, and then covering the Zeer
pot with a wet cloth creates a small fridge. This simple invention
has drastically improved the lives of thousands in Africa. To read
more about his story click here.
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| Solar Oven |
In
order to create a radiative cooling fridge, you would use something
you least expect: a solar oven! While the oven can get incredibly hot
during the day and be used for cooking, at night, you can face it
toward the sky, that big heat sink, and use it as cool storage. Some
people are even able to make ice at night, which they then use during
the day!
In
regards to a method using the earth to air heat exchange concept,
it's again, astonishingly simple. Dig a semi-deep hole in the
ground, just larger than the container you wish to use for food
storage. Lower the container into the hole, and then create a cover,
like an earth-bag that will work like a big cork. The soil just a
few feet deep maintains a cool temperature. For additional cooling,
add a layer of ice.
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| In-ground cooling |
I
was really amazed that such simple laws of nature can be applied to
create ingenious contraptions for storing and preserving fresh foods.
Dan and I aren't sure if we would decide to go with one of these
methods over the conventional fridge. There are going to be plenty
of major transitions just by moving into the tiny house, we don't
want the culture shock to kill us! Cost will be a major factor; if a
solar system would be incredibly expensive because of the need to
power a fridge, we may take a second, more serious, look. In the
meantime however, you can bet we'll be experimenting! I think I'm
going to give the Zeer pot style a try...would you give any of these
a try?
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We visited one of our favorite spots, the railroad tracks by the industrial area. That's where we got our free bricks earlier this year. We grabbed 15 cinderblocks from the same area and hauled them back to the truck in 3 trips. We also grabbed a pallet to use the wood as "shims" if need be. 
