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Anyone here have earth tubes?

 
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So I'm trying to figure out some solution for off grid air conditioning in central Oklahoma, and earth tubes are the only option I've not yet exhausted. This would be 100% geared towards cooling the air in the Summer, as heating here isn't a problem (a small wood stove like a Dickinson is more than sufficient).

Basically what I need to know is if a closed loop earth tube is capable of providing any appreciable cooling on its own. What I like about the closed loop design is that it's going to continually remove humidity from the air like a traditional AC unit would do. I know it's going to require a fan, but we could easily spring for enough solar panels to do a DC fan to keep the air circulating.

I had also thought about doing a kind of hybrid system where you would have an intake in the tube, along with a solar chimney in the roof. That would give us the option of switching between open and closed loop just by opening and closing vents. Generally speaking, I like the idea of having continuous fresh air, but would want the option of closing the loop to maximize efficiency for when it gets really hot out.

The type of building I want to go with is a 20 foot shipping container with insofast insulation, which basically turns it into a giant thermally broken cooler. What really attracts me to the shipping container is that it can easily be lifted off the ground on piers, and the ideal build site on the property is in a flood zone A due to the creek. I know the earth bermed stuff seems to be preferred here, but there are two big issues with that in this area. First of all the cave effect because of our high humidity, and then the flooding issues.

Another challenge is that we don't have the time or energy right now to build something so labor intensive. We've looked into earthships and earthbags and cob and all that, and the reality is that it would probably take us years to finish something like that. So the shipping container option is more realistic since it's turnkey.

It seems like the earth tubes would be better for us anyways, because they use the same thermal mass principals as a bermed house, but remove the humidity rather than bring it into the home. I've been in basements in this area and while they're cool in the Summer they are always extremely humid. In order to control moisture in basements here, you have to insulate the outside walls, which of course cuts off the thermal mass.
 
gardener
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I've been thinking a lot about earthtubes lately. I'm planning to rent a mini-excavator in May to install a septic system and installing earthtubes is a side project I've been considering while I have the equipment on site. Currently, I'm considering two 60 foot runs of 4" pipe buried ~6' deep. The runs meet at the end at a vertical well where they could either be connected to create a closed loop or optionally left open and air could be pulled from both. I'll make a sketch and post it here in the next week to give you a better idea of my plan.  
 
Jack Banks
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Aaron Yarbrough wrote:I've been thinking a lot about earthtubes lately. I'm planning to rent a mini-excavator in May to install a septic system and installing earthtubes is a side project I've been considering while I have the equipment on site. Currently, I'm considering two 60 foot runs of 4" pipe buried ~6' deep. The runs meet at the end at a vertical well where they could either be connected to create a closed loop or optionally left open and air could be pulled from both. I'll make a sketch and post it here in the next week to give you a better idea of my plan.  



I've heard that 12 feet plus is required, but maybe it's different in your area.
 
pollinator
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Are you insulating the container on the outside or the inside?
Do you have a well for water? There is a thread, which I'm sorry I can't find at the moment, about cooling with well water.
 
Jack Banks
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denise ra wrote:Are you insulating the container on the outside or the inside?
Do you have a well for water? There is a thread, which I'm sorry I can't find at the moment, about cooling with well water.



That's definitely interesting. There are two challenges with water. We don't plan on doing a well because the ground water is heavily contaminated with farm runoff, so we'll opt for a catchment system. Which actually goes hand in hand with the earth tubes since we can dig for the tubes at the same time and save some excavation costs.

The other issue with water is that it wouldn't provide any opportunity to remove humidity from the air. That's probably the main reason we really like the earth tube idea is because we can continuously recirculate the air in the house through the tubes and pull that moisture out.
 
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Location: Ozarks
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This is the topic that google first brought me to Permies way back when.

There are calculators on line that will allow you to find out how many cubic feet of underground air you need and how long it must remain underground to reach a given temperature. Then multiply that by the cubic feet of air you wish to cool. I am absolutely not a math student, math is HARD!

My plan was to build a tiny home on a 8x20 foot trailer and once on site in the Ozarks build a 4 foot crawl space basement under it. Kind of A mini split level house. the basement being cut into the side of a hill. My thought was placing the 4inch tubes around the foundation and on out into a raised garden bed. That gave me about 130 feet of under ground 4 inch pipe. About 100 feet of that pipe is over 4 feet deep.  It works very well to preheat outside air to replace air lost up the woodstove during the winter. That is a relatively slow draw and my guess is the air stays in the tube for 3 or 4 minutes before coming inside. It also works well to allow me to use a kitchen and or bath exhaust fan without the wood stove creating a back draft.  However once a fan is put to work any pre heating or pre cooling is gone in about a minute. So as a controlled fresh air inlet it is a resounding success!  As a air conditioner an utter failure.

You don't happen to have a fairly large natural cave on your land do you? If you could get close to the same volume of air underground as you have above ground the dehumidifying effect could  work.

 From my reading on the subject this works better in a desert type setting. Once you add southern US humidity things get much harder.
 
pioneer
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This fella here is using black drainage tile, or "Earth Tubes" to heat his green houses in the winter.  Youtube
 
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With the recent heat wave out here in the west,  I've been thinking of an earth tube cooling system for my house as well. Normally summers aren't too bad  but on July 1 it hit 103ºF here, with the temp. in the house reaching 90º.  

One question is how to figure on the length of the tubes.  (Marty Mac, I'd be grateful for any links to the sizing calculators you referred to. I've not fouond them so far.)  
Also, if 2 spaced tubes are used, which is I think usual. are there considerations re air flow/velocity when they are combined into one tube to enter the house? I would think that as long as the velocity isn't high, there may not be a problem. 'm thinking I'd need around 100-125 cfm.

My house is medium size- about 1100 sf. main floor, open-plan, with a 16' cathedtal ceiling and a 12' deep loft bedroom (so, effectively 2 storeys) with a 52" ceiling fan in the main room and a smaller one in the loft bedroom, so I have lots of air circulation available. Walls are very well insulated with rigid insulation. There is a small library/spare room on the main floor and a small bathroom. The basement is below ground and stays relatively cool, so it won't factor in the cooling system.

I have a small excavator and can do the trenching myself, down to about 4' or so.  I did a test dig a while ago and put a piece of 3/4" plastic water line to the bottom and backfilled,  then put a thermocouple in the tube and it seems that at that location the earth temp is about 57º, which is a bit higher than I was expecting  but with the open-plan and fans, figure that bringing air in at that temperature might be enough to temper the heat (?) The house is pretty well sealed when all the windows & doors are shut, but  I could use the stove fan and/or a bathroom fan to relieve any pressure buildup.
 
Marty Mac
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Hi Colin,

My tiny house is 144 sq ft, average ceiling height 9 ft. lets call it 1300 cubic ft of air. That is being generous and not subtracting space of furniture cabinets etc etc. 1 foot of 4 inch pipe has a volume of about 150 cubic inches. I have about 100 feet of pipe, giving me  15000 cubic inches of underground air. Convert that back to cubic feet gets me around 8.5 cubic feet of air.  That 8.5 is just a drop in the bucket when mixed in to the 1300 cubic ft of air in the tiny house. And unfortunately I haven't even factored in the time  the air needs to stay underground to have any chance of cooling let alone dehumidifying.
As I stated before math is NOT my thing but feel free to check my work and play with the calculators yourself.

https://geothermal-energy-journal.springeropen.com/articles/10.1186/s40517-015-0036-2


If you come up with an idea for a under ground radiator that could multiply the effect please share!
 
gardener
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I have mentioned and have wondered about using my well casing as an earth tube.
 
Marty Mac
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Robert,
I have no idea how deep your well is, but I still have my doubts on the volume of air  and the amount of time needed to exchange heat.
But the idea  of pulling water up and cycling it through a large truck radiator while blowing a fan across it might work well.  If you had a use for the water once it was drawn up. Irrigation?  If not it may be more cost effective just to run a small AC unit instead of the well pump and a fan.
 
Robert Ray
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200 ft,  so 400 foot total for a round trip plus footage to and from house to well head. My biggest concern would be making sure just air went down the casing.
 
Colin Miller
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Marty Mac wrote:....As I stated before math is NOT my thing but feel free to check my work and play with the calculators yourself. .


Ditto here, especially that level of math!  I'm hoping to find someone who has done an earth tube cooling system for a house more similar to mine that I can use as a basis.  The systems I have read about so far seem to use two parallel runs of about 100' each of 6" PVC.  Filed away somewhere I have an article on static pressure losses in different lengths and diameters of pipe, and the contribution to static pressure of elbows etc. which I can use to choose an appropriate fan (which will have a speed control for adjustment.)
 
Colin Miller
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I just came across this online article (with links)  that is somewhat helpful.

Some Notes on Earth Tubes:  https://builditsolar.com/Projects/Cooling/EarthtubeNotes.htm

 
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Check out HOME IN THE EARTH on you tube
 
gardener
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John Shaver wrote:Check out HOME IN THE EARTH on you tube



Quite a lot of footage of quite a massive project:

https://www.youtube.com/playlist?list=PLJYUVNFK3OFIOsZBDklvbP62pV4CT5wfS
 
What I don't understand is how they changed the earth's orbit to fit the metric calendar. Tiny ad:
An EPA Certified and Building Code/UL Compliant Rocket Stove!!!!!
EPA Certified and UL Compliant Rocket Heater
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