• Feb. 9, 2007 - Passive cooling and refrigeration
Published on 22 Nov 2006 by Permaculture Reflections / EB. Archived
on 22 Nov 2006.
http://www.energybulletin.net/22792.html
Passive Cooling
by Douglas JE Barnes and Scott A. Meister
Part I) Passive Cooling and Zeer Pots
By Scott A. Meister
If you happen to live in an area that depends on a lot of
electricity, and you're finding electricity to be rather
expensive...or would rather wisely eliminate as much of that expense
as possible so you could spend your hard earned money on other
things, then you need to be looking for ways to reduce or eliminate
your electrical use as much as possible. Where can we cut our
electric bills?
We've all heard of changing our lightbulbs to the new and improved
warm fluorescents (no, they no longer turn your skin green). Of
course, we can shut off our lights when we're not in a room, shut
off all electrical appliances we aren't actually using. After all,
there's really no need to have all the lights on in the house, the
stereo blazing and the TV on with no sound while we browse the
internet. Those kinds of things are easy to see, and cutting back on
them does a lot of good. But a large portion of the energy going
into a household is actually used for heating and cooling rooms,
food and beverages.
Even if you think you're rich enough to waste your money on
electricity, you still need to be concerned about emergency
situations when the power companies stop giving you what you need.
If you lived through the LA blackouts as I did...then you know what
I mean. Believe it or not...there are a number of free and effective
ways to nip your electrical cooling bill in the bud while also be
prepared for power-outages.
We can consider passive solar cooling and air-conditioning. Please
note that we are not talking about the use of photovoltaic solar
panels, those are active solar devices. I'm talking about passive
solar cooling. A lot of people have trouble imagining that the hot
summer sun, can actually cool your house, but it can. The second law
of thermodynamics is our best friend, and it works endlessly for
free (or at least as long as the sun exists).
Heat rises, and heat will always move toward cooler areas, and if it
happens to draw liquid with it, and that liquid evaporates...the
inside surface of what just evaporated will be cooler. Solar
chimneys, underground cool rooms (the old fashioned cellar), and the
zeer pot, are just a few ways that use this to our advantage to help
us cut your power needs forever, and for free. After all, isn't that
what we all want? Why should we slave away at work all day and then
spend our hard earned money on things that we can get for free?
To the surprise of many, the world's cheapest refrigerator costs
less than $2 dollars to make, uses minimal resources to produce and
runs completely without electricity. It's called a zeer pot, or the
pot-in-pot and was developed by Mohammed Bah Abba, who realized that
he could put the second law of thermodynamics and transpiration to
work for him. The zeer pot, is actually two earthenware pots (I'm
assuming they are both unglazed), one pot smaller than the other.
The smaller pot is put inside the bigger pot, and the space in-
between them is filled with sand. The sand is made wet with water
(twice a day) and a wet towel is put on top of the two pots to keep
warm air from entering the interior. As water in the sand evaporates
through the surface of the outer pot, it carries heat, drawing it
away from the inner core, thus cooling the inside of the inner pot
which can be filled with soft-drinks, water, fresh fruit, vegetables
or even meat. A damp cloth placed on top keeps the inside pot away
from hot air. In this way, fresh produce can be kept for long
periods of time without the need for electricity, or camping coolers
made high embodied energy. Tomatoes and peppers will last for up to
three weeks, and African spinach, or rocket, which normally would
spoil after just a day in the intense African heat, can and will
remain edible for up to twelve days. Eggplants will keep for up to
27 days instead of three. It can even be used for storing sorghum
and millets for a long time since it protects from humidity, thus
preventing fungi from developing. The zeer will keep water (and
other liquid beverages) at about 15 degrees Celsius, and even meat
can be kept fresh for long periods.
The new technology is now being used by farmers at the market. Fresh
produce is kept inside, with just a couple fresh items displayed on
the damp towel resting on top. In this way, most of the produce is
kept hidden away from both warm air and insects. In the past, all
produce was displayed in the open air, attracting flies resulting in
stomach disease such as dysentery. Now food can be kept fresh for
longer and kept away from flies...even miles away from electricity
or ice.
Although many people are excited about promoting this technology in
developing countries, I see greater potential for this technology in
the developed western cities, suburbs and countryside.
Instead of having humming, heat producing, electrical, bank-sapping
refrigerators and freezers, we could have zeer pots stashed away in
cabinets or under sinks (for convenient kitchen access). We could
have them placed in, or near the garden, by the back door, out on
the porch or balcony...anywhere. We could have them on the truckbeds
of roadside vegetable stands, in cross-country delivery
vehicles...at the local farmer's market. We no longer have to make
choices about freshness based on expensive camping coolers,
refrigerated trucks, ice machines and electrical outlets. We can
provide our own endless supply of refrigeration for less than two
dollars.
For further information on zeer pots, please see the following
sites:
http://www.rolexawards.com/laureates/laureate-6-bah_abba.html
http://www.slashfood.com/2006/09/28/how-cool-is-that-zeer-pot/
http://www.scidev.net/features/index.cfm?
fuseaction=printarticle&itemid=315&language=1
Part II) Passive Air-Conditioning and Refrigeration
by Douglas JE Barnes
In permaculture, we look to a problem as being a solution. Much
money is spent battling the cold in places like Canada, Scandinavia,
Scotland, Tasmania, Russia, Argentina, and so on. But the cold can
also be a valuable resource. Unfortunately, the cold is a largely
untapped resource in most places. That said, there are some hopeful
developments being made. For example, many office towers in Toronto,
Canada are now cooled using a deep water cooling system that draws
frigid water from Lake Ontario. While the buildings themselves are
not sustainable, this method is less energy intensive than powering
large air conditioning units to cool each building.
There are techniques for the rest of us – passive cooling
techniques – that we can use to beat the heat.
Food needs to be kept cool for preservation purposes. The zeer pot
described above is one cheap solution. But if one has the means, it
is possible to design a passive cold cupboard that doesn't require
energy to operate. In almost any region of the Earth, the ground is
going to be cooler than the surrounding air in the summer season
(areas of geothermal activity are an exception to this and offer
heating potential instead of cooling potential). A cold cupboard
makes it possible to replace a large part of one's cooling needs
with a system requiring no outside energy inputs.
The cupboard itself would be a fully insulated space within the home
with the same magnetic seal on the doors that refrigerators have.
Cool air is drawn in to the bottom of the cupboard through a pipe
running under the house with the pipe itself 4 to 6 feet (1.2 to
approx. 2 metres) underground and with an opening to the surface
outside. (See diagram - click to enlarge.) A drain should be
installed in the pipe to allow for condensation forming in the pipe.
A second pipe at the top of the cupboard vents to the outside of the
house. The external portion of this vent should have access to full
sun and be painted black. This will cause the air inside it to heat
and rise, which in turn causes cool air to be sucked in through the
bottom pipe.
To cool the house itself, a similar technique can be employed. In
this case, a closed circuit of pipes is laid 4 to 6 feet (1.2 to
approx. 2 metres) beneath the ground outside the house. A small fan
is then used to force air through the system and blow cold air into
the home.
One variation on this is the have one end open to the surface and
draw the air out through a vent pipe as is done in the cold cupboard
described above.
Another variation is the wind chimney, which is sometimes employed
in deserts. In the direction of the prevailing cool winds, a scoop-
like vent is placed and a pipe is laid under the ground from it to
the house. Where it reaches the house, the air passes over a
container filled with dampened charcoal. This causes evaporative
cooling of the air before it enters the home. Charcoal is used both
as a sponge to hold the water and as a means of keeping the water
fresh.
Another strategy put into effect in tropical and sub-tropical areas
is the shade house. A shade house is simple an area on the shaded
side of a home with a vine-covered trellis to create a shaded
sanctuary. Often these shade houses will contain an outside kitchen
to prevent the heat of cooking from entering the home. Subtropical
areas would have two kitchens, one inside for the winter, and one
outside for the summer. Urban temperate areas suffering from the
thermal island effect would also benefit greatly by the shade house
strategy.
If you are living in a tropical or sub-tropical region and building
a new home, you can increase airflow through the home by
substituting the simple "box" design for one with more corners in it
(see diagram). This will allow greater airflow through the home.
In tropical regions, it is beneficial to design a traditional
tropical home with wall vents and a vaulted roof of permeable
material to draw cool air in and push hot air out. (See diagram.)
These strategies are not only sustainable cooling solutions, they
also save money by using available cold as a resource.
~~~~~~~~~~~~~~~ Editorial Notes ~~~~~~~~~~~~~~~~~~~
See Permaculture Reflections for more of Scott and Douglas' writing.
According to the IEA:
Electricity consumption by 107 million U.S. households in 2001
totaled 1,140 billion kWh. The most significant end uses were
central air-conditioning and refrigerators, each of which accounted
for about 14 percent of the U.S. total.
These strategies outlined by Douglas and Scott show how we can
radically reduce that while still living in relative comfort.
See also Man Retrofits Freezer to Make an Ultra-Efficient Fridge
over at Treehugger.
An off-grid experimenter in Australia, Tom Chalko, has retrofitted a
chest freezer to create a fridge that uses only 100 watt-hours (0.1
kWh) per day!
Tom's tests were done in winter, but nevertheless, a very impressive
energy saving. The average American fridge by comparision uses 4
kWh/d. I've been working on a cheaper and simpler option than Tom's
in the last week, simply wiring in an off-the-shelf replacement
refrigerator thermostat into a small chest freezer. I've had some
success, although because the temperature probe is longer than the
one it is replacing, half of it doesn't fit, and I think as a result
I can't get the temperature above 2°C (36°F), whereas I'd like to
run it at around 8-10 for minimal energy use. I'll try to write
something up about it when I figure it out!
-AF |
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