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Earth Tubes for Ventilation

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Any one have any experience with earth tubes for providing ventilation?

Rob Roy built it into his house and says it would be one of the things he wouldn't do again. I don't know why.
Don Stevens http://www.greenershelter.org likes the idea but is dead set against the use of PVC tubing.
John Hait http://www.earthshelters.com/ I seem to remember construction pictures on his site using PVC.
David Wright in his awesome 1978 book http://www.amazon.com/Natural-Solar-Architecture-Passive-Primer/dp/0442295863 recommends using clay piping. He recommends a pitched system with a dry well near where the piping enters the house so that the warm summer air is dried via condensation on the piping.

I have to say it makes perfect sense to me to not only use earth tubes but to use them to install a displacement ventilation system http://www.ambthair.com/displacement_vs_mixed_flow_ventilation.html#displacement that uses a solar chimney http://en.wikipedia.org/wiki/Solar_chimney to draw the air out.

I'm thinking that if air temperature is an issue in the winter, and I live in a cold northern climate, a heat exchanger powered by solar water heater would be a good answer.

I'm wondering if anyone has ever encountered a system like this.
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Don Stevens page is down.
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steward & bricolagier
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Location: SW Missouri
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I'm planning to tube my place I'm building. I'm using PVC (with clean outs) but that's me, easy to clean matters to me. I also am running my tubes downhill, so the condensation will drain out the end, helping dehumidify the air before it gets in.

Most of the people I saw when researching it who hated it used corrugated pipes, and made them fairly level, so the moisture (then the mold) built up in them. Looks like Don Stevens hates PVC because it's not natural.

I'd say if air temperature is an issue in the winter, have a back up ventilation system that brings in air buffered from someplace else. I'm using a greenhouse for that.

As far as drawing the air out, you don't need as much air flow as you'd expect. I'm doing clerestory windows, some of which open. At my last house I had 8 high clerestory windows, and ended up being temperature stable at 1 window open only a couple of inches. I found a long slow air change worked much better than cranking large amounts through the house. Too fast through tubes, I think, will just shorten the time the air has to change temperature.

I think that if you think about what YOUR wants and needs and expectations are, you may figure out whether you want tubes or not. Someone who wants their house at 63 degrees on a 90 degree summer day, who doesn't plan to use anything else to change the air temp, will probably hate them, as it doesn't fit their desires. Someone who wants to come home from work every day and turn the heat up 10 degrees to warm the house isn't going to like the slow response time. For my parameters, I think they will do very well. Your mileage may vary, define your parameters well, and think on the ramifications of them.
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It occurs to me that the larger the diameter of the tubes you're using, the less surface is able to contact the incoming air to cool it, so the larger the diameter of the tubes, the slower you'll have to change the air in the house in order for temperature change and condensation to occur.

I think this is a great idea for natural cooling, though. I would use the smallest diameter clay tubes that would do the job, and if I had to, I would have more than one, spaced apart in the same large trench so as to increase the amount of soil the exterior of the tubes contacted.

I wonder, though, what the effect would be if I had a garden bed in the shade on the north side of my structure with such narrow diameter earth tubes running underneath it. Would the heat from the air and the condensation from the tubes benefit the soil life?

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