Not sure if this is the right place for this, not sure if it's appropriate to post at all....
I'm putting a lot of earth tubes into my house, as part of my heating and cooling (some weird microclimates on this property) and I had "600- 800 feet of 4 inch PVC pipe" on my list. I had to go to Kansas City, so I checked Craigslist in that area. Someone has a weird source of unused 4 inch schedule 80 pipe (the seriously heavy stuff) that he's selling for $5.00 per 10 foot piece. I priced it online at $95- 250 per 10 foot. I bought 920 feet of it (all I could carry in my truck) and there's a lot left, and he keeps getting more in. If you are doing tubes, that is a CHEAP way to do them!! I would have considered $5 for schedule 20 affordable, for schedule 80 it's incredibly low. I'll also drill a bunch for French Drains. And I won't have to worry about whether I'll break it easily running my tractor or truck over buried pipes.  Be warned: it's heavy, somewhere in the 22- 28 pounds per pipe range. My load was around 2300 pounds.
Check for his ad... AWESOME deal!!!
:D

And I think I'm going back for more of it...
I'm visualizing post and beam construction barns and greenhouses that the posts won't rot. And cheaper than 4x4s. I can work with this stuff, for this price.
Someone asked me "If you paid full price, how much would all of that have cost?" "About $10,000, and I paid under $500...."
I am still happy dancing about this!!
:D

Yes, I got some 4" pvc free recently and it's great for fence posts etc.

I hesitate to use it for my earth tube however. Bill mollison was asked about pvc for an earth tube and said he thought that "was a bit overdone" and it's better to have earth --perhaps brick walls and a slab cover.

One of the things I was looking at was the possibility of molds etc growing in the tubes, things like (legionaires disease) and as I researched, it started to look like the natural earth bacteria and fungi might actually be a good insurance against any disease organisms colonizing the inside of the pvc.

Plus of course, there is the volume  question with pvc pipe, a 4" round pipe delivers about 12 square inches cross section, while a 12x12 tunnel delivers 144 sq inches.  For passive air flow, the 4 inch pipe would likely prove very constricting and need mechanically forced air.

At any rate, without access to your cheap source of pvc I'm looking at a variety of cheaper materials for the top of the "tube" and my soil should naturally support the walls since it is mostly clay and rock. My plan was to dig down 4 feet with a one foot bucket, then come back with a two or three foot bucket and dig down three feet. I'm still trying to figure out the cover. There is an alternate drainfield solution that uses a sturdy molded plastic about 2 feet across, 4 feet long, and a few inches high. I planned to use that where the tube crosses the driveway since it is rated for gravel trucks. The rest will likely be some sort of cheap concrete slab--or if I have to I'll just use the drainfield solution for the full length (60 meters is the minimum), but that could get a little pricey (20$/section)



or at least that was my conclusion. I'd be interested to hear any flaws someone with a functional earth tube might find in this thinking

Pearl Sutton wrote:Not sure if this is the right place for this, not sure if it's appropriate to post at all....
I'm putting a lot of earth tubes into my house, as part of my heating and cooling
:D

Are you using some kind of passive method to move the air (solar chimney's, etc.)?  Or are you planning on using electric blowers?  I'm guessing blowers with pipe that small.

I did some research on this, there are a few studies available on the amount of cooling provided and the energy needed to move the air, based on that I decided it would be more economical to use a mini-split heat pump.
It only uses slightly more electricity, provided significantly cooler (or warmer) air, and was much cheaper and easier to install.

Of course a lot depends on where you live, which effects how deep you have to bury the pipe.  Where I live I'd have to bury them at least 8 feet down, 10-12 would be better.

Hi Bob!
That all makes sense! :) I too would love to hear if someone with tubes like that has any input. I'm fascinated by these concepts.

It all depends on your personal context, just like anything else in permaculture. Bill Mollison is very much into natural building, where I am going more for inexpensive, and dealing with some other factors involving health and strength. The land form you have changes things too. In my situation, making tubes that way would just wash out down the hill. I have a pretty good slope (haven't measured it, 15-20% I think) and will be doing things to stop erosion soon, the property has lost 10 feet of topsoil since the late 1800's survey of the area, as far as I can tell. That was about the time it was cleared for pasture, cows added, and later was cut regularly for hay. The worst erosion I have hit here is a plumbing trench someone dug close to straight downhill, that washed out badly. All I can think of if I think of earthen tubes on this property is how fast they would cave in due to this soil, then wash out and become a gully.  

Half of my tubes will go 100 feet or so down the slope to get the cool air from downhill, and bring it up to the house as makeup air in summer. The other half will be under a concrete patio, on the south side of the house, and will be providing the makeup air in the winter. The construction is going to be extremely airtight, and requires makeup air, the clerestory windows will be open a bit almost all year around, and will probably draw the air in nicely. I'll add fans if I have to, the circulation in the house has a few small fans, but I think it won't be required. Some odd wind flow on the place too, we're kind of on a ridge.

As far as I have seen (and I may be wrong) the main problems people have with crud in their tubes is if they use corrugated tubing, and if there have no slope to it, both of which hold standing water and cause issues. Smooth, sloped ones like I'm planning have no places for water to pool, and as the humidity condenses out, it will flow downhill, and drip back out the end of the pipe. I'll probably use it as a water harvesting tool too :) The other thing that keeps pipes from crudding up is high air flow, part of why I'll do several parallel 4 inch pipes, so the flow rate is high in each one. I also will have cleanouts on the uphill ends of the pipes, so I can hose them down if I need to, and run a cleaning rag on a rope through if I must.

Like I said, it's always a matter of what you are dealing with. Your soil sounds like it will hold still, like you get less random flooding, and you sound like you have more equipment/supplies than I do. When we dig the plumbing lines with a ditch witch, I'll go as far downslope as I can, till I hit rock, and that's where my tubes will end. I have to do it all at one time, can't afford to get machines out here again, will do everything that needs digging in one run.

I hope you keep me up on how yours work out!! :D I'm VERY interested!

Peter:
Hi :) As I put in what I was  typing when you replied: depends on your context.  I just moved from the desert, in your context you wouldn't get enough cooling without a good design, and deep pipes. I'm in S MO these days, and the humidity is amok here, it's being an education to deal with after years of swamp coolers "you take the water OUT of the air?!" If my math is right, in my location and situation (Your Mileage WILL Vary!!!) the 100 foot tubes from the bottom of my north slope, buried 2-3 foot deep, should drop the temperature coming in about 25-35 degrees and the humidity by about 30-40%. We will have a minisplit as backup system, and one head of it will be part of my main airflow handling system, so whatever temperature is coming in, it will shift it to what we want. The split will work a lot easier if it has closer to desired temperature air coming in, and the super tight construction style requires makeup air.

This property is also at the end of the power lines, the neighbors say in storms we are first to lose power, last to get it back. Having the air intake running close to what we prefer might be really useful if the power for the split is out. The clerestory windows should solar chimney it quite well, and the other outputs if we don't want them open will draw also. If I have to I'll put fans in them, I don't want to, and hope I don't have to.

Some of these tubes will bring air from the greenhouse in too, add it into our system in winter. And throw our output back to the greenhouse to add heat to it when it needs it and get the air freshened up. The south side pipes (for winter use) will be shallow, and under a concrete patio (part of the water control system, as well as a patio) and will increase the temperature when it's sunny, and just bring in cold to the minisplit when it is not sunny. Still better than just ambient temperature makeup air.

My air/water systems for the house look kind of like an octopus, with things going here and there coming in and out, it's an interesting design, that is super specific to this property and the house/gardens design.

And lots of very cheap tubing.... :D   And some tiny ads! :D

Hi Pearl,

Sounds like you have a plan.
Whatever you do with the earth tube, sounds like you have some serious water control issues--but also of course those issues can likely be turned positive.. with that much slope and all that pvc it sounds like a hydroelectric power plant waiting to be put to use. a 4 inch column of water fed from a reservoir up high could supply a lot of energy

My earth tube/tunnel only runs slightly across contour-I'm in the middle of a ridge also, but am running partially toward the higher part of the ridge, and partially into a valley at the same time, the result being a slight downward slope to the tube over all, but less than it would be if I just went straight downhill.

I had planned to use the same tube both winter and summer. my house not as tight as yours, but figured in winter the tunnel would supply slightly preheated air, especially when running the rocket stove.

In fact, I believe drawing air through the ground like that will heat the tube in summer so it will be warmer than the 55 degrees or so I expect at that depth. then after drawing cold air through it all winter by the time summer returns, the tube will have cooled considerably supplying even colder than usual air

I'll be renting a backhoe to finish dams and swales of my mainframe water design--the earth tube is just a side project. things are already pretty good so a simple earth tube should put my  cooling needs well over the top, and solar hot water through a radiant floor should even eliminate the rocket heater most of the time.

Yeah, I got LOTS of plans, and little cash for them :D I can dream up more than I can afford :)
That's part of why I'm doing  the house build so completely, because there probably won't be money to change structural things later.

with that much slope and all that pvc it sounds like a hydroelectric power plant waiting to be put to use. a 4 inch column of water fed from a reservoir up high could supply a lot of energy  

All the easy water is downslope, I am hoping to have money for a low speed wind pump to raise water up to work with. Got good constant low breeze.

sounds like you have some serious water control issues

Not if I pay attention. I have told my mom since we started the planning "It's easy to design for hot, or cold, for wet or dry, but this area alternates all of those, that's a hard one to deal with." So the weather is lovely here, except when it's screaming hot and muggy, or ice storming. The neighbors talk of "wet years and dry years" and no in between years. So the water control systems (swales, ponds, french drains etc) both keep the water on the property, and deal with excess. The house assumes hot and cold weather are both going to happen. If I wasn't paying attention, yeah, there would be issues. The neighbors just had to do a major rework of a lot of their yard due to the gutters basically dumping right into the basement. Hoping to not have to do stuff like repair messes like that.

the result being a slight downward slope to the tube over all, but less than it would be if I just went straight downhill.

The only reason I'm going straight down is to pull up only cool air from the foggy creek area, knowing I'll have the south side tubes too. If I were doing only one  I'd be doing what you are :) Gets back to the extremes here.

In fact, I believe drawing air through the ground like that will heat the tube in summer so it will be warmer than the 55 degrees or so I expect at that depth. then after drawing cold air through it all winter by the time summer returns, the tube will have cooled considerably supplying even colder than usual air

I think you are correct there, for at least the start of the season. Might be less effect mid-season. Still going to help a lot!

I'll be renting a backhoe to finish dams and swales of my mainframe water design--the earth tube is just a side project. things are already pretty good so a simple earth tube should put my  cooling needs well over the top, and solar hot water through a radiant floor should even eliminate the rocket heater most of the time.  

I'm jealous of a backhoe!!  Sounds like you have a plan too!! :D  And possibly a house already there. I don't have a house, just old foundations from a house that burned, that are older than I am, and I'm not reusing them. I'll use them to protect the plants I'm propagating, easy to hoop it if I want, bit of wind protection etc.

My radiant floor will be set up for now with a water heater on the grid, I'll get to solar later for it. Swamped in too many things, and brawling with codes, I'll leave myself ways to do things later, when they aren't watching! :D My dad taught me when doing plumbing to always leave stub outs, for expansion later. I have taken that into my own weird brain and modified it, I leave "stub outs" in a lot of my life. I try to always install things so they can be added to easily. (I have a theory that the appendix of the body is an expansion port god left in us, in case he needs to add peripherals to upgrade us!) My dad also taught me "Always Cover Your Ass" and his CYA has turned into my permaculture... CYA + function stacking = some interesting notions...

Keep me up on yours!! Very curious how it works out!!
Pearl

Without actually knowing what sort of catchments and all that you plan, it's difficult to make really relevant comments,

It sounds like you are planning similar things, so likely it will be to your advantage to learn to operate a backhoe--much easier than shovels and wheelbarrows

.If you have questions or want to get a feel for it find a construction site and observe the machines or just watch utube videos--the first time I got one the hardest part was finding where to turn it on and disengage the safety locks.

It doesn't really take strength, just a bit of coordination. and much of that comes with practice. Just keep everybody else well away from the work area while running it--it is way to easy to hurt someone when that boom starts swinging around because you bumped the control.

Of course building barrage dams and swales and such you need to study good methods and apply them as far as keyways, clay content etc, but I went into debt thinking that the interest on the loans would be less than the rewards from starting that water hydrating the soil and getting the water design in place and functional.

I had a real old motor home that I lived in for a while before any  structures were built

As far as dealing with inspections and permits, I asked around to neighbors and such about enforcement and their experiences with inspectors. In my area I'm remote enough and the county enforcement is set up so the tax office with the assessors don't talk to the permit guys. So the county knows I have stuff here and taxes me for it, but the inspectors don't come out to shut me down unless someone complains. I pay my taxes, they leave me alone  (if they were to shut me down they would lose Tax money) There are also provisions here for minimum size necessary for permits, so starting very small was the path I chose. A small octagon (under 150 sq ft was my first structure and a small greenhouse dug into the hill for shower and kitchen kept me quite comfortable. A wood fired water heater and some solar panels and I was rocking and rolling.

Working on a bigger house now, but I miss the days walking from greenhouse to octagon, naked through the snow after taking a very hot-then very cold shower .

http://www.permaculturebob.org/wp-content/uploads/2017/09/20170911_183232.jpg

http://www.permaculturebob.org/wp-content/uploads/2017/09/20170507_174806.jpg

Anyway, the only other thought I have that might be relevant is to remember that if you are setting up a water pump from your low point anyway, and plan to build catchments, you may want to leave one of those proverbial stubs  where you have the option to turn your catchments into batteries--store water pumped from wind and solar electric, then generate electricity from hydro as needed.

I have been thinking about a ram pump to lift water, but so far have not gotten that together.

Pearl Sutton wrote:Peter:
the 100 foot tubes from the bottom of my north slope, buried 2-3 foot deep, should drop the temperature coming in about 25-35 degrees and the humidity by about 30-40%.

I think you're making assumptions that aren't accurate.  The main reason I've read for failures in earth tube systems is burying them too shallow, with less than 5 feet being the common depth of failure, even 5 feet is questionable.

I'm a big fan of doing lots of research and taking measurements before I begin large projects.  In this case it's fairly easy to make measurements.  By a cheap digital thermometer with a remote wired sensor, they cost about $10.  Bury the sensor at the depth you plan on putting the tubes and periodically read the temperature and write it down.  From what I've read, the temp 2-3 feet down will be at most 5-6 degrees different from ambient.
This graph is not likely to be accurate for your area, but it does show you the difference in temps you can expect at various depths


Your idea to use it for the mini-split is good, but I'm guessing you mean to feed the inside unit?  If so, then you're better off just using the ambient air in the structure since it will most likely be cooler in the summer that the air from the tubes, and certainly warmer during the winter.
You could use it to feed the outside unit, but that needs a HUGE amount of air, you'd need at least 30 parallel 4" tubes to flow enough air for the outdoor unit and the energy needed to move the air through the tubes would likely exceed the savings on the mini-split.

A couple things to note:  There is no free lunch.  If you are using the earth to cool down air, then the earth gets warmer in the process.  Most suggestions I've read are to bury the tubes at least 4-5 feet apart so heat transfer doesn't effect the other tubes.
In southern Missouri the frost line is about 12" down.  At 24" deep the winter temps will likely be high 30s-low 40s, at 36" probably 40s.   This is before you start running cold air through the tubes and further cooling the soil. That's a guess, like I said above, measure it to be sure.
Note: the air in earth tubes will never be the same temp as the earth, generally it will be about 5 degrees or so different (colder in the winter, hotter in the summer) unless you are trying to move a lot of air, in which case the difference will be even more.

Pearl Sutton wrote:Got good constant low breeze.

A low breeze is pretty much useless for harvesting energy.  The energy in wind goes up at the cube of the velocity.  Unless you have a really large turbine, any wind under about 13 mph won't produce anything useful, even at 13 mph you'll only get a little bit of energy.  13 mph is about the point where loose paper and leaves start moving around.

Many of the newer wind turbines using as many as 11 blades start producing energy at 7mph or less. Going up higher and wind velocity increases over ground speed.

.ground temp discussion  looks like the origin of the chart you posted, and looks like a good discussion of the other factors, namely variability by depth.

For summer cooling in the proposed 100 foot descent, the actual intake of air already has probably a 15 degree (or more) cooler advantage over the air surrounding the house where it will be used (at least as I understand it) so the ground cooling effect should add to that. Of course that also means the heavier cooler air will require a greater pumping action than air brought through a more horizontal tube , although I don't know if that would be necessary to consider

Also, reading the discussion in the link above, they note that as the subterranean temps vary by season, there is a delay, so the hotter temps of august are not felt below until the cooler temps of october when the warmer temps are welcome.

I  would be interested in seeing the data on the failures of other systems you mentioned however, since Bill M said they even "buried " Earth tubes on the surface and covered them with "swampy" (I think that's a concrete swamp grass mix , formed into a panel about 2-3 inches thick. ) and these worked.

But their recommended depth was one meter and minimum 20 meters long, far less than most of the higher tech pvc  designs. I suspect there is an even larger difference in heat exchange between drawing air through an earth tube and a pvc pipe than the 5 degrees mentioned, and certainly the volume of air will dramatically affect the heat exchange, and 1'x1' earth lined tubes with all the nooks and cranies along the way will have a dramatically larger surface area to effect that exchange, plus far less friction added to the energy needed for circulating the same volume of air through pvc tubes.