permaculture

[Lawrence London <lfljvenaura@gmail.com>]

http://www.adafruit.com/blog/2014/07/01/make-an-electric-free-refrigerator-natureandtechnology/

*Make An Electric Free Refrigerator*
http://adafru.it/b120054

How to make a seer pot, or an evaporative cooler/ non-electric
refrigerator. by Berkana via instructables

A zeer pot is an evaporative cooler used in rural Africa and the Middle
East to keep vegetables fresh. They consist of two terra cotta pots, one
nested inside the other, with the gap between them filled with wet sand.
The sand serves as a thermal mass that helps keep the pot cold once it has
cooled down, and acts as a wick to spread the moisture up the walls of the
pot. When placed in a shaded, breezy location, the evaporation of water off
the outer surface chills the pot. If you have a good breeze, or a fan
powered by a solar panel blowing the pot, the pot can get quite cold.
Imagine that chill you get when you step out of a pool when the wind is
blowing. Now imagine that wet wind chill going on all day. That’s what the
pot feels with a constant breeze.

Unless the air is very dry and the pot is exposed to a constant breeze,
they generally do not become as cold as a refrigerator, but they will keep
vegetables fresh for a couple of weeks. If you do have cool dry air and a
constant stiff breeze, the interior of a zeer pot can chill down to around
40˚F.

Think of it as an open-cycle refrigerator. Conventional refrigerators
evaporate a refrigerant in a closed circuit to absorb heat from their
interiors, then compress the refrigerant vapor in the coils in back to
condense it and to expel heat. The zeer pot simply uses water as its
refrigerant, and leaves the condensation to nature.

Zeer pots were re-discovered and popularized in the early 2000s by the
Nigerian teacher Mohammed Bah Abba. By manufacturing and mass distributing
zeer pots to the poor, he was able to bring refrigeration to tens of
thousands of impoverished farmers and home makers, enabling them to extend
the usable life of their produce from days to weeks. For his efforts Bah
Abba was awarded the Rolex Award for bringing life-changing technology to
people in need.

In the under-developed parts of Africa and the Middle East, zeer pots use
custom made pots prepared by local potters. Here in the developed world, we
need to settle for pre-made pots from the hardware store. There are some
drawbacks, but also some advantages afforded by these limitations, as you
will see.

There are other zeer pot instructables out there, but this one is optimized
for practicality. If the capacity is too small, the cooling capacity too
low, or if it an eyesore or is annoying to use nobody would want to use it.
This zeer pot uses a large glass pot lid, has an interior basket divider,
and sits on a rolling cart. It even has a layer of decorative pebbles over
the sand to make it look pretty. The terra cotta pot legs hold the pot off
the rolling cart with enough clearance to let the bottom surface contribute
to evaporation; this adds about 10%-15% more evaporative surface. The inner
pot is bolted down so that it doesn’t float up when you charge the pot with
water. Nearly everything I used in this project was purchased at a hardware
store, and it can be made in a few hours, plus a day to let the sealants
cure.



*Read more* http://adafru.it/b120054

A zeer pot is an evaporative cooler used in rural Africa and the Middle
East to keep vegetables fresh. They consist of two terra cotta pots, one
nested inside the other, with the gap between them filled with wet sand.
The sand serves as a thermal mass that helps keep the pot cold once it has
cooled down, and acts as a wick to spread the moisture up the walls of the
pot. When placed in a shaded, breezy location, the evaporation of water off
the outer surface chills the pot. If you have a good breeze, or a fan
powered by a solar panel blowing the pot, the pot can get quite cold.
Imagine that chill you get when you step out of a pool when the wind is
blowing. Now imagine that wet wind chill going on all day. That's what the
pot feels with a constant breeze.

Unless the air is very dry and the pot is exposed to a constant breeze,
they generally do not become as cold as a refrigerator, but they will keep
vegetables fresh for a couple of weeks. If you do have cool dry air and a
constant stiff breeze, the interior of a zeer pot can chill down to around
40˚F.

Think of it as an open-cycle refrigerator. Conventional refrigerators
evaporate a refrigerant in a closed circuit to absorb heat from their
interiors, then compress the refrigerant vapor in the coils in back to
condense it and to expel heat. The zeer pot simply uses water as its
refrigerant, and leaves the condensation to nature.

Zeer pots were re-discovered and popularized in the early 2000s by the
Nigerian teacher Mohammed Bah Abba. By manufacturing and mass distributing
zeer pots to the poor, he was able to bring refrigeration to tens of
thousands of impoverished farmers and home makers, enabling them to extend
the usable life of their produce from days to weeks
<http://www.treehugger.com/kitchen-design/mohammed-bah-abba-and-his-pot-in-pot.html>.
For his efforts Bah Abba was awarded the Rolex Award
<http://content.time.com/time/specials/packages/article/0,28804,1936165_1936254_1936632,00.html>
for bringing life-changing technology to people in need.

In the under-developed parts of Africa and the Middle East, zeer pots
use custom
made pots prepared by local potters
<http://practicalaction.org/zeer-pot-fridge>. Here in the developed world,
we need to settle for pre-made pots from the hardware store. There are some
drawbacks, but also some advantages afforded by these limitations, as you
will see.

*What makes this zeer pot practical? *

There are other zeer pot instructables out there, but this one is optimized
for practicality. If the capacity is too small, the cooling capacity too
low, or if it an eyesore or is annoying to use nobody would want to use it.
This zeer pot uses a large glass pot lid, has an interior basket divider,
and sits on a rolling cart. It even has a layer of decorative pebbles over
the sand to make it look pretty. The terra cotta pot legs hold the pot off
the rolling cart with enough clearance to let the bottom surface contribute
to evaporation; this adds about 10%-15% more evaporative surface. The inner
pot is bolted down so that it doesn't float up when you charge the pot with
water. Nearly everything I used in this project was purchased at a hardware
store, and it can be made in a few hours, plus a day to let the sealants
cure.

I will be building a zeer pot array for A Place for Sustainable Living
<http://aplaceforsustainableliving.org/> in Oakland (California) based on
this design. The goal is to use an array of zeer pots to displace the use
of at least one of their refrigerators. The design shown here is the
outcome of my experimentation with making zeer pots for them.

(Be sure to read all the notes to all of the photos. Many important details
are listed there.)

*Parts list with prices *

Prices are rounded to the nearest dollar. (I must admit, this is by no
means the inexpensive original African zeer pot, which cost $2 to make.
You're going to spend well over a hundred dollars on this design. This one
is for people are intentionally going out of their way to go off grid or to
pursue sustainable options.)

Items are mostly from Orchard Supply Hardware (Berkeley, CA). The pot lid
was from Kukje market <http://www.kukjesupermarket.com/EN/products.htm>
(Daly City, CA), and the sandwich basket was from Web Restaurant Store
<http://www.webstaurantstore.com/american-metalcraft-wib120-black-round-wire-basket-12/124WIB120.html>
.

   - 18" *unglazed *terra cotta pot— $30 @ Orchard Supply Hardware
   - 14" terra cotta pot—$15 @ Orchard Supply Hardware
   - terra cotta pot feet, quantity: 7— $1.79 each, so about $13 @ Orchard
   Supply Hardware
   - heavy duty planter caddy with five casters—$30 @ Orchard Supply
   Hardware
   - 50 lbs of sand; the finer the better, pre-washed — $6 @ Orchard Supply
   Hardware
   - 4" long 1/2" bolt
   - 2" washers for a 1/2" bolt, quantity: 5
   - jamb nuts for 1/2" bolt, quantity: 4
   - Refrigerator thermometer: $8 @ Orchard Supply Hardware
   - Silicone Sealant—$5 @ Orchard Supply Hardware
   - 13.5" glass pot lid — $8 @ Kukje Market (Korean markets usually have
   these; wherever you are, if there's a korean market or housewares shop,
   you're in luck.)
   - sandpaper
   - 12" diameter sandwich basket— $7 at Web Restaurant Store
   
<http://www.webstaurantstore.com/american-metalcraft-wib120-black-round-wire-basket-12/124WIB120.html>
   - 8" eyelet or hook bolt and a pair of nuts and washers— about $6 @
   Orchard Supply Hardware

*Note: won't work as well in high humidity*

If you live in a hot and humid area, the zeer pot probably won't work well;
high humidity results in much less evaporative cooling. (However, a friend
of mine who used a zeer pot to cool water in a humid part of Africa tells
me that even with the humidity, it worked surprisingly well, so this is not
definitive.)

*Note: direct sunlight will cancel out all cooling effects*

On the day I was doing the zeer pot seminar at the Place for Sustainable
Living, we accidentally left one in direct sunlight. The amount of heat
imparted by the sun totally overwhelmed the evaporative cooling effect. The
cooling is supposed to come strictly from wind-induced evaporation, not
from evaporation due to sun exposure. Sun exposure causes evaporation by
imparting heat; wind exposure causes evaporation by lifting away water
molecules, which carries away heat proportional to the heat it takes to
evaporate the quantity of water carried away. If you do build a zeer pot,
make sure you keep it in the shade for best effect.

*Note: outer pot must be unglazed clay or terra cotta*

At the hardware store, I saw a lot of fake terra cotta pots made of orange
plastic. These are not usable for the outer pot of the zeer pot; the zeer
pot cools by wind evaporating water that has been wicked through the outer
surface. Plastic fake terra cotta is not porous, and will not work as an
evaporative surface.

Glazed terra cotta pots also don't work for the outer pot. The inner pot
doesn't necessarily have to be made of unglazed terra cotta, but the outer
pot must be unglazed because glazed pots won't wick moisture to the outer
surface for evaporation.

*Note: many medium sized zeer pots work better than one giant zeer pot*

The ability of a zeer pot to cool its content depends on the *surface area
to volume ratio.* As you make the zeer pot larger, the volume will
increases proportional to the cube of the linear dimensions, but the
surface area only increases proportional to the square of the linear
dimensions. Because the volume increases much faster than the surface area,
one huge zeer pot will actually perform much worse than several smaller
zeer pots. The size of the zeer pot in this instructable is about as large
as you can make them while having a practical rate of cooling. You can
always make them smaller; making them larger is not likely to give you
reasonable performance. If you are serious about going off-grid, you would
do better to make several zeer pots of this size than to make one huge zeer
pot.