Has anyone ever seen this in action? Or tried something like it? I find it very intriguing. Natural Air Conditioning There was a technique used or invented by the Romans a long time ago. A natural form of air conditioning / ventilation was used roughly as follows: 1. A trench 6 to 12 feet deep and 100 to 200 yards long was dug leading from the "house" in a straight line away from the house. 2. Into this trench a large diameter pipe (these days corrugated drainage pipe 2 or 3 feet diameter) was laid, with holes drilled into the bottom to drain water that condensed inside the pipe. The trench was then covered over. 3. At the far end a 90 degree elbow was attached and more pipe added so that it reached above ground and the end covered with some sort of wire mesh attached to keep out unwanted things such as rodents, etc., and then another elbow could be added at this end to shield against rain. 4. The house end of the pipe entered the house and was the source of incoming air. 5. The key to making this work is to add a convection chimney. 6. The Convection chimney is built such that it's inside opening is at a high point inside the building. 7. On the outside, two intersecting sides of the chimney; are painted flat black, and the resulting V formed by the two connecting sides face south. In other words, the V needs to face the mid point between where the sun rises and sets. 8. The two other sides must be transparent, Plexiglas or some equivalent. Also, the higher/larger the chimney, the better. How it works: the sun heats up the chimney causing the air inside to rise, thus drawing air through the cool pipe. The pipe cools the air drawn from the outside to the temperature of the earth at the depth at which it is buried (which is virtually constant year around at this depth). By the way, an interesting note: Even in cold climates where the ground is frozen, the incoming air is only 32F when the air outside may be much colder, we need only heat the air by 38F to bring it to 70F; as opposed to heating outside air of say -15F to 70F we would have to heat the incoming air by 85F - quite a difference in the amount of heating energy we would have to supply by some other means. Of course, without the sun to warm the chimney (or some other source) the system isn't worth fooling with.