Here is a website by Larry Larson who specializes in installing earth tubes in the Fairfield, Iowa area: http://www.earthairtubes.com He slits his tubes lengthwise with a circular saw and then places the slit facing down, which allows any moisture from condensation or otherwise to drain out immediately. He claims to have success and no mold problems, and has many happy clients in the area. His photo album shows how he installs his earth tubes, so if you're thinking about earth tubes, definitely check out his site.
On the other hand, I've been told of an earth tube installation that was done locally (I don't think it was done by the above mentioned Larry Larson) that had to be sealed shut due to mold problems. Apparently it was left sealed after installation during house construction, and so there was no air moving through them for many months. In this failure case, I don't know if the earth tubes were slitted for drainage or improperly installed in a manner that would allow water/condensation to accumulation in the bottom of the earth tubes, or whether it was simply a question of lack of air movement. The problem could have been simply improper installation and operation, and had nothing to do with the validity of earth tubes as a cooling system.
Clearly, there are a lot of factors to consider and resolve for earth tubes to work right.
Earth tubes are pretty much inaccessible once installed, which means you really only have one chance to do it right. And, while they can be inexpensively operated, either passively or with a small fan, installation is not inexpensive (study the photos and you'll see what I mean). Locally the trenches for earth tubes are dug 10' deep and either wrap around a foundation (a slight variation on typical earth tube installation), or go out 100' -- that's a fair amount of excavation, tubing, sand, gravel, insulation, etc. -- especially if it might fail due to mold problems and need to be abandoned -- an expensive mistake. If you use corrugated drain tile (as per photos in www.earthairtubes.com), "swabbing them clean of mold" is really not an option, and more likely if you have a mold problem you'll just admit your mistake, seal them up, and move on. (The corrugation in the drain tile, and the serpentine method of installation aid in the transfer of heat by slowing down the air movement and creating air current eddies.)
Earth tubes can be a great source of natural, low cost cooling, but personally, the risks of mold in places inaccessible is enough to make me have second thoughts and give serious consideration to other less risky cooling options.
As with all "alternative" and "natural" building technologies, it is up to us each individually to do our own research, analysis, and due diligence and draw our own conclusions before investing our hard-earned money and sweat equity.
Eric Randall
Fairfield, Iowa
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