Passive Air-Conditioning and Refrigeration

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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.

 <http://www.energybulletin.net/image/uploads/22809/newswire_Cold-cupboard.jpg>

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<http://www.energybulletin.net/image/uploads/22809/newswire_Cold-cupboard.jpg>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.

frig.gif

<http://www.energybulletin.net/image/uploads/22809/newswire_Natural-AC.jpg>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.

 <http://www.energybulletin.net/image/uploads/22809/newswire_Desert-cooling.jpg>

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<http://www.energybulletin.net/image/uploads/22809/newswire_Desert-cooling.jpg>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.

 <http://www.energybulletin.net/image/uploads/22809/newswire_Subtropical-home.jpg> ole3.bmp <http://www.energybulletin.net/image/uploads/22809/newswire_Subtropical-home.jpg>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.

 <http://www.energybulletin.net/image/uploads/22809/newswire_Tropical-house.jpg> ole4.bmp <http://www.energybulletin.net/image/uploads/22809/newswire_Tropical-house.jpg>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 ~~~~~~~~~~~~~~~~~~~

According
to the IEA <http://www.eia.doe.gov/emeu/reps/enduse/er01_us.html>:

    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 <http://www.treehugger.com/files/2005/07/man_retrofits_f.php> 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 <http://www.eia.doe.gov/emeu/reps/enduse/er01_us.html>. 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 2C (36F), 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!