I am fairly new to alternative energies. But I do have a couple of harbor freight solar panels for charging my rv batteries. :) I didn't stay at a holiday in express lately so need some input. Question is about earth tubes for cooling. I am entertaining the idea of building a 1200 sq ft single story extremely well insulated tight home on concrete slab on 2 acres that has natural drainage. I have not shot it with a transit but it appears I should be able to go at least 6 feet down and still have gravity drain for them. So the worry of moisture and mold is minimal. I have been searching the net looking for information on the length and depth needed for sandy soil in Arkansas. From the looks of the lay of land I should be able to get at least 4 runs of 200 feet. probably longer if necessary. This would be a closed system circulating the air from inside the house. Also my plan for summer cooling is an angled ceiling with exhaust vents at the approximately 10 ft eves with computer fans on thermostats to vent to hotter upper air outside. My idea is that heat rises and a 7 1/2 foot to 10 foot ceiling that pekes against a wall would trap the hot air close to the vent. My plan is to also use slow moving air via the 12v computer fans to circulate the air through the 4 earth tubes rising from floor located close to each corner of the house. I have yet to find any definitive information on depth or length needed for a 4" schedule 40 pvc system versus square footage or climate etc. Anyone here with experience for such a system ? Is my plan a good one for my area ? Thanks in advance.

Posted By randelb on 13 Feb 2015 03:59 PM
  Question is about earth tubes for cooling. I am entertaining the idea of building a 1200 sq ft single story extremely well insulated tight home on concrete slab on 2 acres that has natural drainage. I have not shot it with a transit but it appears I should be able to go at least 6 feet down and still have gravity drain for them. So the worry of moisture and mold is minimal.

Randel

When my wife and I were researching our energy efficient home back in the early 1980s we were very interested in earth tube cooling. While the concept is really attractive and seemingly simple, the issues of mold and air quality in general are pretty overwhelming. Even if your property is incredibly well drained, if the air in the tubes is cooled to the dew point a good deal of liquid water will end up in the tubes. Arkansas is humid enough in the summer that your dew points are likely to be higher than the temperature of the ground in which your earth tubes are buried. Mold and stinky bacteria take very little "food" to to feed them so even the tiny amount of material coming from the home airstream would be enough to breed plenty of nasties.

Hate to be so negative but the only locations that seem at all suited to earth tubes are located in very arid regions.

YMMV

Hugh

Yeah, Arkansas gets pretty hot and humid in the summer. I've lived here most of my life. You will need more than just earth tubes to keep the humidity at a tolerable level.

I installed a couple of 4" dia x ~70' long earth tubes with >1/4" per foot drop around two sides of my walkout basement before I backfilled. But my plan was to use these for fresh air makeup only. A geothermal heat pump will be the primary heating/cooling system (work in progress).

Thanks for the replies they are appreciated.


Yep arkie6 Arkansas humidity is a problem for sure and almost intolerable in mid summer. I think as a whole we are mid spectrum as far as U.S weather is concerned. It can get extremely hot but as a rule it is only for maybe 6 weeks or so out of the year. The rest of the year when temps are above comfortable is what I'm shooting for with the earth tubes. I plan to have a/c also. but hope the earth tubes with minimize the use of them.

sciguy yes the dew point can get high here. I'm thinking the mildew should be easy enough to control by spraying the intake occasionally with essential oil spray including tea tree oil or some such bacterial killing spray. There is a lot of benefit in my opinion to human wellness with essential oils. And they smell really good And if worse comes to worse swabbing the lines could be an option. I've read elsewhere the advise to swab them at least once a year. But I know how that will go with me. Either I'll forget or procrastinate so i am hoping the spray will be sufficient. It just seems to me that earth tubes cannot be any worse than using a/c with the house closed up for 3 months or so out of the year with no fresh air coming into the house as most people do.

I do own my own backhoe which is a blessing so I can take my time and not be on the hourly clock and make changes if necessary but of course would rather get it right the first time.

I've found info on duct sizing and maximum airflow, earthtube wiki's, some project's done around the world etc. What I am hoping for is information on desired length, depth and optimum airflow for this area and soil type. So far I have found no definite's or even advised info on this.