Solar Chimney and Earth Tubes

Hey All,
This heat wave has got me thinking about solar chimneys and "earth tubes".  I've seen these used in Earthships and other places but I'm kinda surprised they aren't more widely used.  I did some web searches and found a few things on the subject but I still have questions.

For those who don't know how these work.  Basically the sun heats the chimney causing a convection current which draws cool air into the living space via the earth tubes.  


I'm not sure but I think one of the drawbacks or complications with this  set up is dealing with condensation.  I'm in the mid west where it can be quite humid at times.  So when the hot and humid outside air hits the earth tube it will shed it's water.  The question is how do you deal with this condensation.  My fear would be after a time this would blast mold spores into the living space.  

I've spent time at Wheaton labs and listened to a bunch of the podcasts and I remember Paul talking briefly about this but I don't recall his verdict/conclusion on the technology.  Maybe we could prod him to discuss this a little bit in the next podcast?

Anyway.  Do people have experience with these systems in humid areas?  Any good resources to check out?

Thanks
Rich

I found this thread which is pretty informative.  Sounds like it's not gonna work in my area...  Unless someone can convince me otherwise.  ;)
cooling tubes

I think a lot of people underestimate just how large a swamp cooler system would need to be to provide the amount of cooling they would want. And yes, there is the humidity issue. I would think like a cave system. The tunnel would be lined with rock or brick. Lime plaster might help prevent mold. A permeable gravel layer on the floor to allow water to escape. I had an uncle in HVAC who did a job on an old mansion that had central air over a century ago! He said it was an amazingly engineered system that shocked him how cool it was when he walked inside. It is definitely doable. I would wager more work than most would be willing to do on a gamble that it may not work well.

I installed 150 feet of 4 inch PVC as I was back filling around my tiny house in the Ozarks. On average it is 4 feet below grade the exit is on one edge of a raised garden. I have a rock pile surrounding the pipe made of 2 foot boulders to help buffer incoming air. And I have planted Lavender in and around the pile.  It enters the house behind the wood stove.  I haven't had the opportunity to be on site for a long enough stretch of time in the summer to see how long it can bring in cool air before it warms the soil to the point of diminishing return.  I can say that it was worth the time and expense just for the fresh air intake to help the wood stove breath.  And it acts as a buffer when running the bath or stove exhaust fans.
I have a couple more years until I can retire there to give a more detailed report. Just one of a multitude of experiments that seem to be working well for my 2 to 3 week stays but daily long term use may change things.   

It just dawned on me as I was typing this, an earth tube Google search is how I stumbled across this wonderful site. Something like ten years ago!

Air to earth geothermal storage systems have a counter intuitive approach to condensation in their tubes.
Rather than trying to avoid it,  it is key to the efficiency of the systems.
The tubes they use are slotted, perforated black drain pipe.
The phase change of water vapor to to liquid water transmits a great deal of energy, heating and wetting  the soil and cooling/drying the air.
The threat of mold or mildew is felt with by the soil organisms.

I would like to to cool a home this way,  but to minimize the digging needed,  run a coil of water tight air tubing through a pond, lake or pool before filtering the air through the slotted tubing/soil.
That black tubing comes in an un-peforated version as well.

Make it solar has a neat solar pond  thin film collector that could work with this during the winter.

I drilled holes in my PVC pipe and set the pipe on a crushed limestone bed in hopes of allowing condensation to escape. The pipe is about 2 inches higher than the drain tile that wraps around the foundation. My drain tile drains in to a small pond/water feature. After a good soaking rain my drain tile collects quite a bit of water and drains it in to the pond. All that water had me a little concerned about the air tubes filling at the same time. fortunately I ran para cord in the air tube as I was installing it. This allowed me to drag a rag the length of the pipe. The rag came out pretty clean and dry even while the drain tile had water running through it.
As I said so far so good.
When I move there the plan is to ad a small glass cupola on the roof. Sort of a sky light and solar chimney combination. I also hope to add a rocket mass heated bench by the air intake and run some more pipe through it to preheat the winter air.

So many projects so little time!

William Bronson wrote: Air to earth geothermal storage systems have a counter intuitive approach to condensation in their tubes.
Rather than trying to avoid it,  it is key to the efficiency of the systems.
The tubes they use are slotted, perforated black drain pipe.
The phase change of water vapor to to liquid water transmits a great deal of energy, heating and wetting  the soil and cooling/drying the air.
The threat of mold or mildew is felt with by the soil organisms.

I would like to to cool a home this way,  but to minimize the digging needed,  run a coil of water tight air tubing through a pond, lake or pool before filtering the air through the slotted tubing/soil.
That black tubing comes in an un-peforated version as well.

Make it solar has a neat solar pond  thin film collector that could work with this during the winter.

Are you furtunate enough to have a pond?
It seems like diging a pond still requires a fair amount of digging. ;)

I'm also in a high humidity area, the property has a north facing slope below the house. I'm putting my PVC tubes down the slope from the house to the input, the coolness will condense the moisture out in the tubes, and it will run down and out. It's a modified version of water harvest system that they used in the Middle East long ago. I don't plan to try to blast a lot of fast moving air though it, more slow and steady. Too fast of air current and the air coming in is still very humid.

As far as solar chimneys, I have never seen it necessary to do more than provide the heated air a way out up high, never felt like I had to make it pull, it takes care fo that itself. If you do put one in, make sure you can seal and insulate it well in winter, so it doesn't pull your heat out.

:D

Well,a pond might be existing, is concentrated in one space and you would be stacking functions.  
We have a stock tank,  but my wife wants it for a pool,  (which is why she bought it in the first place).
Digging a trench takes a lot more work than digging a hole,  at least in my experience.
I first thought of this using a IBC tote,  but my cheap source has dried up.

I am in the process of tapping into the waste stream from a plumbing supply  house.
They have an endless supply of  defunct water heaters.
So far,  they have all been free of leaks.
Even if one does leak, a little JB Weld should fix it.
Gas water heaters have a nice chimney through the center for flue gasses,  which could be repurposed.
Line them up end to end and run the air to be cooled through them.
Water heaters could be stripped of insulation and and parked inside an insulated, "air tight" space.
Run hot humid air through that space and the condensation would form in the tanks, cooling and drying the air.
Leave the bottom of the space open to the soil to soak up the moisture.
I would want a lid to open night so the water tanks could shed heat.
All of which might be not worth the effort, but my situation forces me to think of things that take less room and less digging.

What if you never brought the air in the house?  Simply bring the cool in and amplify it?  What if we intermixed this with desicant air conditioner and an HRV core?

Suppose you started by sucking the air thru an HRV core near the roof of the house just before it went into solar chimney.  You would have cooled the house hold air by 70% to 80% of the temperature difference from the tube while heating the tube air by that much.   From there the tube air goes thru the cooling radiator warming it more while cooling the brine solution.  From there suck the air tube air up past a bunch of condensing columns for more heat.  Finally suck the hot air back and solar heat the first stage of the chimney and use it both for chimney creating draft and for doing the boil off of the desiccant moisture from the second stage of the desiccant system.  If some of this moisture can be pull for condensing as hot water great.

Inside the house the say you had 85 degree air near the roor and were bringing 70 degree air thru the earth tube  The HRV core at 70% efficiency would give you 75 degree air.  Now the room air goes in to the descicant spray system to absorb moisture.  In the process it is cooled slightly.  So say now the output air is 70 degrees.

The brine solution is then pumped thru the solar heater and up to the spray nozzle to do the water boil off in the second stage of the desicant air condition.  In the process greatly heating the air going out the chimney and thus the draw of the system to pull more air thru the air tubes.  It might be possible to drive the system with a single brine pump and a single interior fan while driving the rest of the system on solar thermal and on cooling of the air tubes.  Since the air tube air was never allowed in the house no possible toxic problems.  The brine solution kills everything pulled thru the first stage because of its high salt content.  And if the air going out the chimney is at least 140 degree then it kills everything in its output before blowing it back into the outside air.

Wind towers have been used in the Middle East for a very long time. Look them up.

Im in Wisconsin and have hopes to do earth tube things. A few ideas come to mind. Ive wanted to use these to heat a house. The tubes we be coming into a walipini then through some large compost piles, then to the house.  

For cooling, perhaps it would be beneficial to have a cooling chamber (like a root cellar), where air slows down considerably to allow time for the temperature to be exchanged. It would have gravel and im trying to think how it could purposefully be condensating and draining.


Galv pipe into the chamber, pvc into the house to insulate.

Ive also been thinking about installing a passive solar vent (like the ones for dehydrating food). It would be roof mounted and the intake would be from the house. The air would be heated up behind the glass covered black cabinet, and then out a vent. So instead of pushing air (like the dehydrator) its just pulling air.

Hmm...now im just trying to think through purposeful condensation. Toilet tank esque with a condensate collector. Like...pump up a bunch of cistern water and put them into a tank in every room to condensate. Then pour all the water right back into the cistern once they stop condensating.

Now i’m thinking i might pair that solar dehydrator idea thing with something else. I could put one on every “stack” of upward air flow to a suped up solar chimney.

I was thinking how my anvil picks up condensation when it stays cold and the air heats up.

If it had a low air intake and high out.  i could have a large piece of metal ( I beam cut off or something) that would sweat and and then mostly drain off, but wick up a few cloths or something that would sit infront of the intake. I would be evaporative cooling. The hotter the day, the harder the draft from the chimneys, the more air getting pulled into the chamber. The cooler the i beam, the more condensation, more evaporation, more cooling. I guess when it cools off and just sits wet, that may be a problem, and you would need a tight house and well thought out air flow. I think the chamber would need to be primed with water, and then the cloth would need to be replaced or removed when weather cools down or you would have damp cloths just waiting to get musty.


This would only work in humid climates (like mine)

Any thoughts?

Come across this searching for earth tubes. My son just bought 6 acres of raw land and would like to stay off grid if possible. The small sheds are easy, but staying cool would be a challenge in SW MO.

There is a cave that has a small amount of water output. You can crawl in and maybe get to a point where you can sit up. I was thinking if a guy could build a small shed by the cave and run some long pipes in that cave to capture all that cool air and then somehow insulate it as it comes out of the cave into the shed. Kinda just like burying the tubes in the earth but using the cave instead and no digging. Thoughts on this?

Dan Michael wrote:Come across this searching for earth tubes. My son just bought 6 acres of raw land and would like to stay off grid if possible. The small sheds are easy, but staying cool would be a challenge in SW MO.

There is a cave that has a small amount of water output. You can crawl in and maybe get to a point where you can sit up. I was thinking if a guy could build a small shed by the cave and run some long pipes in that cave to capture all that cool air and then somehow insulate it as it comes out of the cave into the shed. Kinda just like burying the tubes in the earth but using the cave instead and no digging. Thoughts on this?

Hi Dan! Welcome to permies!
My thoughts: I'm in that area too, and the humidity is a problem. I'm burying pipes on a slope, sized to have the air moving through them fairly slow. This lets the earth cool the pipe, so the humidity condenses out and goes out the bottom of the tube. So the air coming in will, I hope, be cool and at least somewhat dehumidified. It's sort of a water collection system from the desert crossed with earth tubes.

Be sure to use smooth walled pipes in this climate for earth tubes, slope them and leave clean outs, the corrugated stuff most people use holds water in the low spots, and it molds REALLY fast. I have heard of people that had to just disconnect their system due to mold. Make them cleanable! Mold kills people.

So my thoughts on the cave is the cool air is wet, you need a sloped pipe, and you might need to do something clever to get the excess water out of the air.

A thought might be to put a hmmm.... don't know the words... pull air from the house to the cave, run it in a spiral in the cave, then take it back. Sort of a radiator. So the air never comes out of the pipe the whole way.  That would be easier to insulate above ground, but would require a fan to force it.

Is the cave downhill/uphill/level with the shed? Ideally it's downhill, as then you could have the air drawn up without a fan by opening a window or vent at a high point in the shed to let out hot air, and the pressure drop would draw air through the tube. You could also keep the tube at a proper slope to drain any condensation. I would still want to bury the tube to avoid it heating up on hot/sunny days and negating any benefit. A little rotary tiller and a shovel might make short work of trenching down a foot, but if the space between shed and cave is undulating then keeping the proper slope for drainage is tougher unless you get perforated tubes.

Thanks for the tips!

A shed that would possibly be built would be below the cave a little. Cave is just behind that little fella. The water will run to the right and behind the tree.

Also been pondering if a pipe(s) could be installed in the cave as mentioned and dam up the water a little so the pipe(s) upon exit would be submerged in the water and hopefully sealed properly before entrance into the shed. The contained water could also serve as keep food and drinks cold.

If only me and the boy had the time and energy to experiment, like everybody else.

I was pretty motivated to do earth tubes for a while, but gave them up.

The idea of a simple tube that can bring cooler air into a house, I mean who wouldn't want that? I got the book about it, I live in a fairly arid environment, I have heavy machinery that can dig deep, and I have land that I can sprawl tubes out into. So in a lot of ways I'm the absolutely perfect candidate, but I still ditched it, and here's why.

Smoke. I live in the mountain west area, and during the hottest times of the year there are fires burning. They will continue to burn for at least a decade at this point, maybe more. So I'm learning that when air quality gets bad you don't want to have the only cooling system be something that relies on lots of air from outside the house to come in.

I'm already trenching. If you're going to be trenching some big distances, like say to water tank or solar installation, you have an open trench that's already there. I have to dig down to 4 feet for frost protection, so going down an extra 2 feet, while a pain, isn't that bad. I tossed in an extra 3/4" polypipe that I can use for a simple or complex geothermal system.

Radon. I'm surprised at the amount of people who don't talk about radon or testing for radon. Like most of the country I have elevated levels of the stuff and in general you're supposed to have perforated earth tubes for moisture management.

I don't have a problem with earth tubes per-say. But if you're already trenching, and you certainly will be for earth tubes because those are likewise supposed to be pretty darn deep, you can toss in geothermal tubes instead. The earth tube book I got recommended ~80-100 feet of tubing distance down to 6'. You will be using heavy equipment for that trench, I don't care how strong and tough you are. And since you'll already have heavy equipment around, dig something twice as long, throw your utilities in, and throw in geothermal tubes.

There are arguments about increased power usage and I get that, I think that's the real trade off. But if you're trenching anyway, 500 feet of 3/4" poly is about $150. It is absolutely worth it to toss that in as well, even if you never use it.

Radon is certainly a concern if you have a space that is an air sink, like a basement, as radon is a heavy gas and sinks, where it can accumulate in a space with poor/no air circulation. But if you have a walk-out door or good air flow to keep things moving, there shouldn't be accumulation. Regardless I would always include a radon tester, same as I will have a CO tester for any space that has a wood stove/RMH, just to be sure. My current house has a gas wall heater, and right next to it there's a CO tester. I expect the detector should be placed at the same height as a persons head would be, say level with a bed or the intake/mass of a wood fed heater.

That's a really good point about trenching your air tubes/geothermal into existing utility trenches, I've always approached them with the mindset of having a thermal mass that's kept dry from rain/water table like in a PAHS system, which would be mostly under/around the structure and not running out into or through the yard so that you can keep the soil dry to avoid passing water from drawing heat away to the water table.

Dig holes with a borer twice the diameter as your solar chimney pipe at least 14' deep to access true geothermal cooling. Over dig if possible to make hole a French drain as well with clean gravel in bottom. Toss essential oils of peppermint Lavender or other anti microbials into hole from time to time...

Cas Sowinski wrote:Dig holes with a borer twice the diameter as your solar chimney pipe at least 14' deep to access true geothermal cooling. Over dig if possible to make hole a French drain as well with clean gravel in bottom. Toss essential oils of peppermint Lavender or other anti microbials into hole from time to time...

I want to use this idea to cool greenhouse when it's too hot and add a fan and solar panel to assist flow. I also want to draw heat out of ground when it's too cold.
What I'm unclear of is where to place intake, ground level, mid-level, up high?
I guess I will have to experiment...