Earth Tubes: How to build a low cost system to passively heat and cool your home

[bigtiller]

A relative did something similar years ago. He buried two 8" non-perforated tiles in a 6 foot deep ditch that was 100 feet long. The ditch made a loop from the north wall to the east wall and up through the floor into his shop. On one end he fit a squirrel fan powered with a quarter horse power electric motor.

The tiles started leaking after about a month, then the mice and moles started eating more holes into them.

It was a great idea but he couldn't keep the tiles dry and every time he turned it on, the shop had a musty smell. So I would advise you use a high quality pipe and seal it tight.

 

[CurlyDave]

I think you need to get an engineer, either mechanical or chemical, to look at your design before you spend a nickel on it.

As a chemical engineer, this is stuff we learned in undergraduate school. What is going to happen is: As air enters the tube and flows toward the house, the temperature will drop until you get to the point where water condenses out of the air. This means there will be 100% relative humidity at this point. Heat needs to be extracted from the air to condense the water, but as the air cools further 100% R.H. means less and less water vapor can be in the air, and water will keep condensing, until somewhere along the tube where the air has reached the same temperature as the earth. Once you reach that temperature, you still need to remove the heat of condensation from the air, and yet more water will condense. The water only stops coming out of the air after it has been at an equilibrium temperature with the earth, and all of the heat of condensation has been removed.

If the air is still in the tube, moving toward the house, then the tube is longer than optimum. If the tube is exactly the optimum length, or shorter, water is going to condense from the inlet all the way back to the entrance to the house. Only slitting the entrance to the tube means that the tube walls will run wet all the way to the house. If you don't supply a way to remove the water, there will be mold, mildew, and possibly algae all along the inside of the tube. Even slitting the tube all the way and providing gravel under the tube for drainage doesn't seem like a good solution to me. Mold and mildew will thrive on the inside of the tube, since condensation will occur all around the tube, not just at the slit in the bottom. The inside walls will "sweat" until there is enough water to form a droplet big enough to run down the side of the wall.

I suspect your experience will be just like bigtiller's relative.

The other problem I can foresee is burrowing rodents: rats, mice, etc. They will chew into a plastic tube and even if it is damp and full of mildew, they will use it as an underground burrow. Maybe nests, raise young, etc. And the tube is a highway right into your house...

 

[RedNeckRacin]

The Phipps conservatory in Pittsburgh PA used earth tubes for their heating and cooling supplement. I would strongly suggest taking a field trip or doing some research on their project. IIRC, they used concrete pipe in their system. I love the idea of Earth Tubes, but I think to do it right, is going to be costly upfront.

 

[rd_macgregor]

In a sealed system, mold/mildew might be the least of your problems. A local homebuilder who incorporated a similar system into his house, had it fail after a few years when the tubes condensed enough water to block the air flow. Unfortunately, as soon as you perforate the pipes, you open the door for other issues (and the mold problem is always there, too, of course).
I put in an open loop, ground source heat pump system last year and it is doing a good, economical job of heating my house so far.

 

[fordmantpw]

In a sealed system, mold/mildew might be the least of your problems. A local homebuilder who incorporated a similar system into his house, had it fail after a few years when the tubes condensed enough water to block the air flow. Unfortunately, as soon as you perforate the pipes, you open the door for other issues (and the mold problem is always there, too, of course).
I put in an open loop, ground source heat pump system last year and it is doing a good, economical job of heating my house so far.

Agreed. We have a closed loop system with 4 wells. How does the open loop system work? Does it pump water up and then just dump back down where it came from?

 

[muddstopper]

after reading this thread, and then thinking about it (not researching it), I think I might have a solution to the problem of the condensation/mold/pest problem.
I think that if one would install the earth tubes as suggested, but instead of letting the air enter the dwelling, and used a heat exchanger made of a closed loop or coils of copper or aluminum, you would eliminate any possible contamination of air inside a house.

I had a friend that wanted to try and cool his house using buried pipe. He installed (buried) 300ft of pex tubing to a low voltage recirculation pump. The tubing was connected to a heat exchanger out of an old elect heat pump. The heat exchanger was installed inside his hvac duct work. The fan on his hvac system was turned on to constantly force air thru the heat exchanger, this way air was pulled from the house, ran over the heat exchanger and back into the house via the duct work. Thru monitering of the temps of the water circulating in and out of the heat exchanger, he was able to determine the water going in from the buried tube was around 60*F and coming out of the exchanger, it was around 62*F, for a difference of 2*F. Meaning he was able to extract 2*F of heat from inside his house. A few problems automaticly surfaced. One, a 2degree change wasnt enought to keep his house cool. Second, with only 300ft of tubeing in the ground, the soil quickly became saturated and no longer provided even the simple 2*F temp exchange. Third, His heat exchanger was way to small to have any kind of efficient cooling effect. Forth, pex tubing isnt exactly the best material to use for this type of system. And fifth, water also isnt very efficient in transfering heat. In a closed systems, alcohol or other material could be used.

My friend never got around to finish his experiments, but I feel with a few modifications his system could work. In and earth tube system, I think the saturation of heat into the earth would be minimized since any heat exchanged thru the heat exchanger would be vented into the air and not into the earth tubes themselfs. Having the earth tubes terminate into a large, vented, enclosure instead of a home, would eliminate any possibility of mold and mildew from entering the house. The earth tubes could be installed in a more convient, out of the way, location and the heat exchanger could be piped to the house. It would take 2 heat exchangers to make this system work, one installed at the termination of the heat tubes, and another inside the homes exsisting duct work.

Another possibilty for heat would be the heat exchanger could be plumbed in such a way so that in the winter time, it could be connected to a boiler or maybe even a solar collector to provide more heat for the house.

Anyways, I am just thinking out loud and dont know if anything I suggested would work or is even feasible.

 

[Midniteoyl]

I was thinking the same thing, some schedule 10 PVC bell ended stuff like what is used for rain drainage.

sounds like it would be better than the corrugated for humidity removal. Would be more expensive but some aluminum would really transfer temps much better but would cost 4x for materials...

Mark

Was thinking that too - green pipe..

 

[Midniteoyl]

I think I would be dead set against anything other than a closed, watertight sealed system. It just seems
like your asking for problems by slitting tubes and all that. Just throw down some ABS or PVC and
solvent weld (glue) it up water tight. Yes spendy the pipe is but consider sealing that system up
and the money lost if it becomes a liability for whatever reason due to it being "slited" etc.



Take pics and post up as you go!

Closed system, good hepa filters, maybe UV to boost them, and circulating blower would all be in my design...

 

[Midniteoyl]

Another very real concern using any system with water stagnating potential: 1976 Philadelphia Legionnaires' disease outbreak - Wikipedia, the free encyclopedia


Legionnaires' disease - Wikipedia, the free encyclopedia

Legionella pneumophila thrives in aquatic systems where it is established within amoeba in a symbiotic relationship. In the built environment, central air conditioning systems in office buildings, hotels, and hospitals are sources of contaminated water.[8] Other places it can dwell include cooling towers used in industrial cooling systems as well as evaporative coolers, nebulizers, humidifiers, whirlpool spas, hot water systems, showers, windshield washers, fountains, room-air humidifiers, ice making machines, and misting systems typically found in grocery store produce sections.

This is why most HVAC pro's (not 'sell you anything' hacks) will NOT recommend a whole house, automatic, plenum attached humidifier system.. Waaayy to much potential for problems. Especially if not maintained and sterilized often.

 

[Gordo 56]

Another very real concern using any system with water stagnating potential: 1976 Philadelphia Legionnaires' disease outbreak - Wikipedia, the free encyclopedia


Legionnaires' disease - Wikipedia, the free encyclopedia



This is why most HVAC pro's (not 'sell you anything' hacks) will NOT recommend a whole house, automatic, plenum attached humidifier system.. Waaayy to much potential for problems. Especially if not maintained and sterilized often.

First of all I want to thank all of you for your comments to this post. It seems like most people who have responded think I might have problems with mold or bacteria entering the system because of standing water from the condensation. I don't think that will be a concern for my design. My hillside is pretty steep and water will not stay in the tubes and will drain out pretty fast. I could if needed, clean it out easily with just a garden hose put in the tube in the house at the top of the hill and clean it out. You could also use a mild bleach solution to help. Secondly I have done a lot of research and I have not heard of any problems with mice chewing through and getting into the pipe.

The whole reason to do this design is for its low cost, if I have to use pvc or some pipe made of other material will make this project cost a lot more. I may end up using a heat recovery ventilation system with the earth tubes, kind of like what they do at SunSavvy Zero Energy Homes.

I will keep you all up to date what I end up doing.