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combined airwell/humus well

Posts: 697
Location: Mount Shasta, CA Zone 8a Mediterranean climate
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So I have some ideas for a combined airwell/humus well installation for the lab. I'm going to use this thread as a spot to think out loud and for people to (constructively) point out any holes in the design that I'm missing.

Basically what it amounts to is burying a long length of 6" pipe 10 foot deep in the steepest, most shaded part of a little north facing valley that's at the SE corner of the lab off of Dances w/Pigs Meadow if you're familiar with the map. Have the pipe be perforated or slotted on the sides and top but not the bottom, kind of like what Zach describes in this thread about Sepp's Spring Terrace. Instead of just back filling with the original soil you fill it with humus soil and the makings of a big hugelculture that will act like a big sponge that when saturated should dribble a little into the buried pipe. You could even make some swales along the hillside that direct any excess runoff to the hugelculture to be absorbed.

Since the pipe would also be on a grade and be long enough to have a significant height difference that should give you pretty good airflow due to the stack effect. In fact, according to the results I get using the Natural Draft Air Flow and Velocity Calculator on this page I get 69 CFM with a 100 m long duct, 33 m height difference, 10 degree C earth (inside) temp and 30 degree C outside air temp which is roughly what you could expect in the middle of the summer in Missoula. This would suck in hot air at the top of the tube and when the tube temperature is below dew point you'd get condensation. After doing some quick googling around I found a research paper that shows a 23m long 15m diameter earth tube has a cooling potential of around 420 kWh per 24 hr period which works out to about 60,000 BTUs/hr or a the equivalent of a 5 ton air conditioner. If you take those numbers and plug them into yet another online calculator, this one for air conditioning condensate it shows a potential for over 70 gallons per day using 80 degrees F outside temp and 55 degree inside temp, a relative humidity of 50% steady between inside and outside air and a 5 ton air conditioner turning over 100% outside air. That wouldn't be peak summer conditions but I think they're decent assumptions to use for this little thought experiment. While I do realize that most of the numbers achieved here are major speculation I do think that it helps validate the fact that you should be able to generate enough condensation to make an endeavor like this worth the effort.

In the winter the air flow in the pipe would now rise since it's now warmer than the outside air. You wouldn't get as much condensation but there's a good chance that you would develop more frost near where the top of the pipe exits the ground which could become a resource if properly planned for. Maybe you might be able to use this draft to suck cold outside air into a freezer wofati before it enters the pipe? I feel like that's an thought worth more exploration later...

If/when I have more time I'll try to make a sketchup model of what I'm talking about, try to make it easier to visualize.

Posts: 1797
Location: Longbranch, WA Mild wet winter dry climate change now hot summer
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This is basicly the Idea I had for heating the berm on a wofati. Especially if it had a greenhouse against the berm. If the tubes would generate condensate at the same time that could be recycled back to the roots of the plants even better. The reverse circulation on cold nites would prevent freezing.
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