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.
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.
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.
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.
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.