Joey Hess has designed, built and tested an off-grid, solar powered fridge, with no battery bank. Using an inexpensive chest freezer with a few modifications, the fridge retains cold overnight and through rainy periods. The set-up consists of a standard chest freezer, an added thermal mass, an inverter, and computer control. He writes:

The battery bank is a large part of the cost of a typical off-grid fridge installation. It needs to be sized to run the fridge overnight, as well as for several days of poor weather. Cheaper batteries only last 3-5 years, and longer lasting batteries are correspondingly expensive; either way a battery bank for an off-grid fridge is extremely expensive over the lifetime of the fridge. By storing solar power in the form of cold, I can avoid the battery bank expense and environmental footprint. The only battery power it needs is enough to turn it off cleanly when the solar panels stop producing — a few minutes of power instead of days — and a small amount for its computer control.

Joey’s off-grid, solar powered, zero-battery-use fridge has successfully made it through spring, summer, fall, and winter:

I’ve proven that it works. I’ve not gotten food poisoning, though I did lose half a gallon of milk on one super rainy week. I have piles of data, and a whole wiki documenting how I built it. I’ve developed 3 thousand lines of control software. It purrs along without any assistance.

Read more:

• Fridge 0.1
• Fridge 0.2
• Fridge data
• Fridge Wiki

Related:

• “Daylight Drive” DC Solar Power at the Living Energy Farm

Thanks to Roel Roscam Abbing.

Now the concept has been applied to air conditioning. Manoj Patel Design Studio in Vadodara, Gujarat (India) has built evaporative air conditioners that can cool a room for days on a single tank of water. The studio designs new products from recycled materials, and they built their air conditioners from ceramics and stone, integrating them with potted plants. By filling rows of ceramic tubes with water, the prototypes maximize their surface area for optimal evaporation while retaining a small footprint.

Read more: This Air Conditioner for Homes and Offices Uses No Electricity, Engineering for Change. Previously: How to keep beverages cool outside the refrigerator: the botijo.

Over 70% of Bangladesh’s population live in corrugated tin huts across the countryside. During the long summer months, temperatures reach up to 45° Celsius, making these huts unbearable to live in.

To address the issue, Grey Dhaka teamed up with volunteers from Grameen Intel Social Business Ltd to create the Eco-Cooler – a zero electricity air cooler, which uses re-purposed plastic bottles cut in half and put into a grid, in accordance to available window sizes.

Based on wind direction and airflow pressure, the Eco-Cooler has succeeded in decreasing the temperature in tin huts by up to 5° Celsius. After initial tests, blueprints of the Eco-Cooler were put up online for everyone to download for free.

Thanks to Adriana Parra.

Build-It-Solar blog writes:

Kotaro Nishiki built a passively cooled home in Leyte Philippines at 11 degs north latitude that incorporates a number of unique cooling features that allow the home to be cooled passively and without electricity…

In this area, most homes are constructed of concrete, and the concrete structures tend to absorb solar heat during the daytime, and then retain that heat through the night making the homes uncomfortable.

Kotaro’s design is centered on eliminating these daytime solar gains. He keeps the whole house shaded using these techniques:

• The south facing single slope roof has on overhang on the south that keeps the south wall in shade most of the day.
• The north side of the house is shaded by an roof extension sloped down to the north that shades the north side of the house most of the day.
• The roof is double layered with airflow between the well spaced layers.  This greatly reduces solar heat gain through the roof.
• The east and west walls of the house are double wall construction with a couple feet between the walls.  The shading that the outer wall offers plus airflow between the double walls keep the wall temperatures low.
• In addition, he has worked out ways to take advantage of the night
  temperature drop and to use thermal mass on the basement to provide some
  cooling.

More: A unique, passively cooled home in the Tropics (Build-It-Solar), Passive Solar House in Tropical Areas (Kotaro Nishiki). Build-It-Solar has more examples of passively cooled houses.

However, people obtained the same result much more sustainably before the advent of the Industrial Revolution. In hot, dry climates, we used porous earthenware jugs that were not only re-usable, but also kept water cool by taking advantage of natural energy sources.

The best known example is the Spanish ‘botijo’, an unglazed ceramic container that cools beverages by evaporation. Similar drinking containers can be found in other Mediterranean countries, as well as in Mexico (where it is known as a ‘búcaro’) and on the Indian subcontinent (where it is called a ‘ghara’, ‘matka’ or ‘suhari’).

The ceramic water cooler probably originated in the Indus Valley Civilization, which would make it 5000 years old.

Illustration: a Spanish botijo.

The botijo generally has a wide, spherical belly with two openings on top — a wide opening to pour water in the jug and a smaller drinking spout — as well as one or two handles to carry it. Traditionally, people drink the water directly from the botijo by holding it up and tilting it so that the water pours from the drinking spout.

Botijo-etiquette demands that the lips do not touch the drinking spout, as the water container is usually shared among several people, and of course the content can also be poured into a glass. The large opening is covered with a cork or a cloth after filling the jug, in order to keep insects out.

Botijos come in different sizes, but on average it contains about 3 litres of water, with larger ones holding up to 7 litres – enough to supply a small group of people with drinking water for a full day.

How does it work?

After the botijo is filled with water, it is preferably placed outside in the shade, although it also works when placed in the sun or indoors. The technology is based on evaporative cooling — the same process that keeps the human body cool by sweating. Because the ceramic jug is not completely water-tight, a small amount of the stored water filters through the pores of the clay and evaporates once it comes in contact with the outside, dry environment. Evaporation (the transition from liquid to gas) requires thermal energy, which is partly extracted from the water inside the jug, cooling it down.

The cooling potential of the botijo

The cooling potential of the botijo depends on — among other things — the shape, dimensions and material of the jug, the quantity of water that it holds, and the humidity and temperature of the outside air. It can be calculated precisely according to a complex mathematical model that was developed during a 1995 scientific experiment (PDF), which showed that under optimal conditions a cooling of up to 15 degrees Celsius can be obtained.

A botijo holding 3.2 litres of water was placed in an oven with a temperature of 39 degrees and a relative humidity of 42 percent, mimicking a hot Mediterranean summer day. It was observed that the temperature dropped by 2 degrees after 15 minutes, by 8 degrees after one hour, and by 13 degrees after three hours. In about 7 hours time, the temperature had fallen to 24 degrees, with a water loss of about 0,4 litres (eight percent of the water content). After that, the temperature slowly started to rise again. At lower outside temperatures (around 30 degrees Celsius), the cooling effect is limited to about 10 degrees Celsius. The cooling effect thus adapts to climate conditions.

Beware of tourist souvenirs

Importantly, a botijo should be unglazed in order to function properly. Glazed botijos – now often sold as tourist souvernirs – do not cool water. Glazed water containers were used to store water in cooler and more humid climates, where a porous container would be of no use.

Similar technologies

A somewhat similar cooling effect can be achieved using a canteen with a lined cover. If the canteen is submerged in water so that the cover absorbs liquid, and is then left outdoors until the cover dries up, the water inside it will have cooled. One can also observe the effect by placing a water bottle inside a thick, wet sock. Evaporative cooling is also the process behind the Zeer Pots – refrigerators that work without electricity – and it can be applied to the cooling of buildings and industrial processes. In fact, the botijo also helps to cool the environment in which it is located, because evaporation takes only part of the required energy from water — the rest is taken from the environment.

Mobile refrigeration device

Apart from the fact that the botijo does not use electricity, it offers a couple of further advantages. Firstly, it produces water that is cool but not nearly as cold as refrigerated water. Ironically, water that is cooled in a refrigerator is too cold for human consumption and can cause health problems.

Secondly, the botijo is a mobile refrigeration device — for which there exists no modern counterpart. Plastic, glass or metal bottles, which have no pores and are thus unable to ‘sweat’, start warming up once they are taken out of the refrigerator.

In contrast, the water in a botijo remains cool regarding of where it is taken, which explains why the device was traditionally used in Mediterranean countries both domestically and by farmers. Travellers often made use of the containers as smaller, cylinder-shaped botijos could be tied to horses. Even a modern, metal canteen with a lined cover does not offer the same benefits as a mobile refrigeration device, because it is not the water inside that cools the bottle. The canteen has to be soaked in water regularly in order to maintain the cooling effect, which is not always an option in a dry climate.

The importance of climate

With the advent of cheap fossil fuels, we have become accustomed to the idea that any technology works anywhere. This is seldom the case with pre-industrial technologies, which are most often local solutions. The botijo is no exception to this rule. It is especially suited for climates with hot, dry summers (type Cs of the Köppen climate classification). This climate prevails around the Mediterranean, and can also be found on the West coast in the United States (in California and Oregon), in South Australia, and in small regions of South-America (in Chile) and Africa (in South-Africa). The botijo also performs excellently in desert climates (type BW, which is much more widespread than the Mediterranean climate).

    With the advent of cheap fossil fuels, we have become accustomed to the idea that any technology works anywhere. This is seldom the case with pre-industrial technologies, which are most often local solutions.

However, the cooling function of the ceramic water cooler deteriorates as summers become more humid, as is the case in most tropical climates. Similarly, the human body is more sweaty in a hot and humid environment, because transpiration cannot evaporate.

Climates with cool and wet summers have less need for water cooling methods in the first place. This explains why some parts of Spain (notably in the north-western region) do not have a tradition of evaporative water coolers, but use glazed containers instead. This is also true for the areas near the coast of the Mediterranean, where the proximity of the sea raises air humidity.

Lifting the botijo

One of the disadvantages of a botijo is that it can be rather heavy for people who lack muscular strength. An average botijo filled with water can easily weigh 4.5 kg. However, there are some solutions to this problem.

Fundación Terra, a Spanish environmental organisation, launched a campaign a few years ago to promote the use of the botijo in homes and offices, and developed a system to suspend the bojito from the ceiling for easy drinking. In addition, they advise people to hang it above a plant so that spilled water does not get lost. In India, the drinking spout was replaced by a low-placed tap.

Kris De Decker (edited by Deva Lee). Sources: 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10.

PS: If you are looking for a smaller container, check out these unglazed clay water bottles, presented at the Green Living Show in Toronto two week ago.

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Related articles:

• Storing food outside the refrigerator: Jihyun Ryou’s anti-fridge design
• Bog butter: storing food in soil
• Pottery refrigerators
• California Coolers
• India’s ancient stepwell architecture cools modern building
• Home made air conditioner
• Insulation: first the body, then the home

Read more: Ancient ‘air-conditioning’ cools building sustainably.

A house can be cooled in two ways. You can try to get rid of the incoming solar heat using air conditioning. Or you can try to prevent the sun from entering the house. The last option can be achieved by movable shading structures. The French house on the picture was built in 2009 by Karawitz Architecture.

Its shuttered bamboo skin can be used to keep the sun out in summer. The shutters can be opened in winter, exposing the large south-facing windows. The house, which stands in Bessancourt (not far from Paris), has no active heating or cooling system. Info + pictures. Via Build it solar. Thanks to Paul Nash.

Related: Window orientation and shading.

“In sunny southern locations, protecting your windows from the sun is an important component of good window management. The first step is to know how the sun moves through the sky and to orient the building and place the windows in it so as to minimize direct solar admission through your windows.” Read more.

“Sustainable By Design provides a suite of shareware design tools to calculate the right dimensions and placing for your specific location, wherever you are.

• SunAngle: our premier tool for solar angle calculations.
• SunPosition: calculates a time series of basic solar angle data.
• Sol Path: visualization of the path of the sun across the sky.
• Window Overhang Design: visualization of the shade provided by a window overhang at a given time.
• Window Overhang Annual Analysis: visualization of window overhang shading performance for an entire year.
• Overhang Recommendations: suggested climate-specific dimensions for south-facing window overhangs
• Light penetration: visualization of the penetration of sunlight into a room
• Louver Shading: visualization of louvered shading system performance for an entire year.
• Vertical Fin Shading: visualization of a vertical fin shading system performance for an entire year
• Window Heat Gain: calculation of monthly heat gain through windows.
• Panel Shading: visualization of the shading of rows of flat panel collectors throughout the year.”

Interesting follow-up at Treehugger.

“How about using the toilet tank? In the US all accept the most expensive low water toilets have a large enough tank. This would eliminate the cooler, the water would circulate avoiding unwanted mold/bacteria, each flush would bring in cool water, and the pump and cold packs would reduce water usage.”

“So, would you want me to make a looped system using a toilet tank as a source of constantly cool water?”

“I freaking love this idea.”

“It’s entirely doable, if you’re willing to have a decent length of tubing running through your house. It might be a great way to cool a bedroom thats near a bathroom though… Great Green idea!”

Home Made Air Conditioner at Instructables.