[barbarake]

Hi again - I've been doing research on 'ground tubes'.

(Quick explanation...this is based on the principle that the soil underground remains at a pretty constant temperature throughout the year. So long tubes are installed and air is drawn through the tubes into the house (or furnace/AC area). So - as air is pulled through - the ground naturally heats/cools it closer to the ground temperature. Here in Upstate SC, the ground temperature is (supposedly) 61 degree Fahrenheit. So in the summer, I might pull in air when it's 90 degrees outside and the air will be cooled as it moves through the tubes. In the winter, the 40 degree outside air would be heated as it moves through the ground. Obviously, a lot depends on length/size of tube, etc. etc.)

As I said, I've done research on this and am planning on trying it at my house. But has anyone here had actual experience with it and - if so - what did you think??

 

[gobug]

Do a search for PAHS - passive annual heating system. There is a book by a guy named Hait (if I remember correctly). He built a house in Missoula Montana and used (2) 200 ft tubes. The house is covered with soil and has no other heating system. It has stayed at 68-73 degrees year around since it acclimated a few years after it was built - 1978.

Be careful, if you have a high water table you could promote bacterial and fungal growth.

Part of the concept is to cover the structure with dirt and a plastic umbrella that extends 10 feet beyond the boundary of the house. Then more dirt on top of that.

You might also look at geothermal sites. It's a similar idea, but a little less risky when it comes to fungus and bacteria.
gobug

 

[mikell]

Humidity can grow Legioneers Disease. I had the same thoughts. Right now it's -2 outside.

mikell

 

[uncle Will in In.]

Without some really long tubes the outside air would soon bring the temp of the tubes and the earth touching them to near the air temp. A geothermal water tube unit would work but cost a bundle to install.

 

[lacyj]

I asked that question a while back, this is what I found:

http://www.canren.gc.ca/prod_serv/index.asp?CaId=152&PgId=776

Earth cooling tubes
These are long pipes buried underground with one end connected to the house and the other end to the outside. Hot exterior air is drawn through these pipes where tit gives up some of its heat to the soil, which is at a much lower temperature at a depth of 3m to 4m below the surface. This cool air is then introduced into the house.
Special problems associated with these systems are possible condensation of water within the pipes or evaporation of accumulated water and control of the system. The lack of detailed data about the performance of such systems hinders the large-scale use of such systems

the responses I got are stuck in the LOST archives, here's a copy:
johnkl said:
Runner made the following comments about passive air conditioning on another thread and I'd like to address them."Beware of molds & legionaires disease with any buried pvc, concrete block, passive buried system. Buried houses suffer from lack of fresh air, excessive condensation requiring 24/365 dehumidification - sick building syndrome. The energy saved on heating/cooling can be completely lost on an annual basis because of running dehumidifiers & air exchange equipment."While none of that is incorrect there are ways of dealing with those problems that have worked for me.When we built our house we installed 6 200' loops of corregated drain tile at least 4' below grade for the purpose of low energy input AC. One end of the drain tile is located in the basement, remote from the other end---the inlet end---also in the basement. The outlet end is located in the suction side of the air handler of our forced air heating system. Each length of drain tile has a slot cut in the ridge as viewed from the outside of the tile. To do this I set a circle saw blade at about 1/8" depth. The idea is to cut into the ridge without cutting into the trough. If you cut into the trough you will greatly compromise the strength of the material. The purpose of this is to allow any condensation that might form, a place to drain off without puddling in the drain tile thus inviting the formation of mold. Of course, when you install the tile you make certain the slot is at the bottom.On each end there is a furnace filter to filter out any dust. This was the fourth summer we used the system and there has been NO evidence of mold, due I believe, to the fact that we eliminated the build up of moisture in the tiles with the slots. When its 90 degrees plus outside it'll be in the mid seventies inside.A mistake I made however was I allowed only about 4" of soil between each cxourse of tile and it would have been better if there had been 6"-9". The soil between the courses serves as the heat sink so the more soil, the greater the heat absorption capacity. As a result of using only about 4" of dirt between courses it gradually loses efficiency and effectiveness over several weeks of use.For a fully passive system the inlet side would need to be installed outside, preferably on the north side where its heavily shaded. Then, a solar chimney would pull the cooled air thru the house when the chimney got hot from the sun.
Runners said:
Johnkl,The drain slots solve a good part of the problem, good idea. The other part would be eliminating as much dust as possible from entering into the drain tiles. In a nut shell, dust (food & spores) plus moisture will eventually 'poison' the air by giving the mold spores a nice growing environment. The beauty of your system is the return air is cooled, but not really super dry like a conventual AC system. I espically like the solar chimney idea, it is a great way to keep cooler fresh air moving through a hot chicken coop, small barn, etc., in the summer time! Taller the pipe, the greater the effect (more draft), like a whole house fan.Have you had any problems with moisture entering back into the drain tiles after a heavy rain? When you buried the pipes, I would imagine there's crushed rock, sand or some kind of porus material to aid in drainage around the pipes? How does it work on warm & really humid days?While an open loop system is in many ways less expensive to operate, a closed loop usually gives more control. I'm more of a fan of a closed loop with a solar powered pump & fan. Useable AC has been the biggest problem for people trying to live off the grid, it takes tremendous amounts of energy and is difficult to 'store'. The current issue of HomePower magazine features a guy with LOTS of solar panels - and real AC.... should be posted on their web site for down loading (free & legal) any day now.Bill
barbarake said:
This is something I've been checking into quite a bit. I have power at my place so can use airconditioning but I'd rather not have to.I've been thinking of installing 'earth tubes' (just pvc pipes buried in the ground). Hole drilled in the bottom every 6" for the drainage. Intake would be outside the house and the other end of the house would come into the basement. There it would be attached to a tube that leads the air into a vent into a room. (Each tube would connect to one room vent.)Then each room would have another vent in the ceiling with an insulated tube leading to a solar fan in the roof.Theoretically, when the sun is shining, the solar fan should turn, pulling air out of the room. This would obviously then pull the cooler air from the earth tubes into the room.I don't know if this will work but I'm going to give it a try.I understand about the tubes being further apart. Actually, I always understood that they need to be at least three feet apart. I agree with the four feet deep
johnkl said:
Runners: You ask about moisture in the system after a rain. No---there have been no problems with moisture that I know of. Actually quite the opposite. As I mentioned, when the system has been run for quite a while it gradually becomes less effective. After a rain its effectiveness increases because the migrating water will carry some of the built up heat away.As far as operating the system during muggy, hot weather, I've noticed no changes there either, except the system does tend to dry the air.My primary heat is an outdoor boiler. I have the makings of a fairly large (360 sq. ft) hot water solar system that I'll be incorporating into the system eventually.I forgot to mention that I also have a 1200' closed loop of 3/4" poly pipe that circles the footing of the foundation. In the summer I circulate water thru that into the A-coil I use for hydronic heat distribution in the winter. The circulated water cools the air further and there has been no evidence of condensation on the fins of the A-coil. The air that passes thru the A-coil has already been cooled by the cool tubes.


lacyj

 

[johnkl]

Thanks for posting that lacy. I was gonna dig it up when I had time. My primary purpose for the ground tubes was for cooling and its worked fine. I can see how it could be used for heating too, at least keeping a place above freezing.

Using copious amounts of black poly pipe with water circulating thru it can accomplish the same thing with slightly more energy input and NO risk of molds and dust.

 

[barbarake]

Wow!! Someone has actually used this type system...

"This was the fourth summer we used the system and there has been NO evidence of mold, due I believe, to the fact that we eliminated the build up of moisture in the tiles with the slots. When its 90 degrees plus outside it'll be in the mid seventies inside."

That's an approximate 20 degree drop which sounds pretty good to me. If you don't mind my asking - approximately where do you live? I'm in Upstate SC.

I agree that the drainage is very important. I'm still debating whether to use the corregated tubes (slit as you described) or regular pvc pipe (with holes drilled every few inches. I remember reading that one was better than the other but don't remember which one. Will need to check that again.

"A mistake I made however was I allowed only about 4" of soil between each cxourse of tile and it would have been better if there had been 6"-9". The soil between the courses serves as the heat sink so the more soil, the greater the heat absorption capacity. As a result of using only about 4" of dirt between courses it gradually loses efficiency and effectiveness over several weeks of use."

I will have a full six feet between each tube so the heat absorption shouldn't be a problem. And the tubes will total about 450 feet long. I know that longer is better but my house is small (1,200 sq. ft.). It's going in at the same time as the septic system (since the nice man with the backhoe will be here anyway <grin>)

"For a fully passive system the inlet side would need to be installed outside, preferably on the north side where its heavily shaded. Then, a solar chimney would pull the cooled air thru the house when the chimney got hot from the sun."

My inlet ends will come up underneath a deck so they're shaded. And I don't have a solar chimney but plan on using multiple small solar fans. Might have to re-think this - maybe install a whole-house fan also.

I can live with bringing the house temperature down to the mid-seventies. I do have power so I can always put the a/c on if necessary but I don't think electric power is going to get any cheaper in the future and I'd rather reduce my reliance on it as much as possible.

 

[Zack]

http://www.sunnyjohn.com/indexpages/shcs.htm

 

[johnkl]

Barbarake: I'd rethink the amount of pipe you're gonna use. I assume you're gonna build on a foundation with a footing at least. If you "wrap" the footing with the pipe, allowing at least 1' between courses I think you'd do better than with only 450' of pipe. This is one of those things where if ya screw up its gonna be very difficult to correct. While 6' of seperation is fine, IMO its overkill.

BTW, I live in central WI

 

[Guest]

"If you "wrap" the footing with the pipe, allowing at least 1' between courses I think you'd do better than with only 450' of pipe. This is one of those things where if ya screw up its gonna be very difficult to correct."


Sir could you please explain this more clearly? I don't understand why or how you wrap the footing. Does this use more pipe than the 450' mentioned and how is it better? Thankyou.

 

[johnkl]

Maybe wrapping was a poor choice of words. By it I mean to encircle the footing, when the footings are in and before the foundation is back filled. There is often a space between the footings and the outer wall of the excavation. If there's not, ask your excavator to make sure he gives you room to work in. In our case the space was about 3 feet. In other words, the excavated hole was about 3' bigger per side than the footings required. Thats the area you'd be working in.

Then simply make several loops around the house with your tubing, allowing at least a foot between each tube. I went with several shorter tubes (6-200' tubes) rather than one 1200' tube. When air is being moved thru the tubes it moves at 1/6 the speed or velocity thru the group of tubes rather than one tube where you'd be contending with greater friction losses. The slower spped alolows more time to transfer heat. At least thats the reason why I did it the way I did. Especially in your climate I don't think 450' of tube would be adequate. There's almost no such thing as overdoing it IMO. BTW, I think you'll find the drain tile is alot less expensive and easier to work with than pvc and you can get it in 100' or 400' rolls.

Further, by placing the tubes around the footing the water run-off from the roof will help the heat accumulated around the tubes to migrate away from the tubes, making them more efective.

 

[barbarake]

Hmm, that's not a bad idea. I can put a couple of tubes around the footing too. I can do that in addition to the 450' of tubes. The 450' isn't really costing me much. They are putting in 225' of septic lines in 6' wide trenches and the trenches are 13' apart (center to center). I will lay the ground tubes on the edge of the trenches and they will join to their 'main line' on the other side. So no extra digging is involved. I tried to create a picture below to explain what I mean, hope it makes sense.


septic air
,,,,,---------|
|--------,,,,,|
|,,,,---------|
|,,,,---------|
|--------,,,,,|
|,,,,---------|
|,,,,---------|
|--------,,,,,|
|,,,,,,,,,,,,,,,,|
|,,,,,,,,,,,,,,,,|
|__________|______
|,,,,,,,,,,,,,,,,,,,,,,,,,,|
|,,,,,,,,,house,,,,,,,,,|
|,,,,,,,,,,,,,,,,,,,,,,,,,,|
|________________|

 

[johnkl]

I like the idea of using the septic excavating for your ground tubes however I'd be nervous about it because the ground tubes don't have water integrity. That is they'll have holes on the bottom for drainage of condensate. Because of their proximity to raw septic tank liquids I'd be concerned about some kind of bacteria and/or moisture migration. What I'd suggest instead of ground tubes there would be black poly pipe, several hundred feet of it, BENEATH the sewerage lines.

You'd run water thru the poly pipe, then thru a heat exchanger in air handler in your forced air plenum. The forced air plenum would move the air thru the ground tubes and the air would move thru a radiator type heat exchanger. The poly pipe is really inexpensive---about $12/ 100' or about $35 for a 400 foot roll. Thats 3/4" poly pipe. Its almost indestructable and would be pretty easy to work with. I couldn't talk my septic installer guy to do it with mine even tho I had consent from the permit issuing agency. Instead I used 1200' of poly pipe, also around the footing, in addition to the drain tile. In either case, you get the same benefit with little extra expense, of ground tubes but without the contamination potential, but you'd get greater thermal efficiency because of the constant moisture in the drain field. My hybrid system works pretty well, even tho there's a couple things I'd do differently.

 

[Guest]

"You'd run water thru the poly pipe, then thru a heat exchanger in air handler in your forced air plenum. The forced air plenum would move the air thru the ground tubes and the air would move thru a radiator type heat exchanger."

I'm trying to understand this, I'm a little unclear exactly what you mean here. Please bear with me as I find this very interesting. Are you saying water is circulated through a closed system to a radiator where cooled air from yet another underground systyem(ie the drain tile earth tubes) is blown across it to get even more cooled?

I wonder if the earth tubes would even be needed if you had a real good way to cool the closed water system, like putting all the tubes in the bottom of a pond or something. Thanks!!



" The poly pipe is really inexpensive---about $12/ 100' or about $35 for a 400 foot roll. Thats 3/4" poly pipe."



Ok another question. Where do we get this stuff. Is this like drip irrigation tubing? Thanks again.

 

[barbarake]

"I like the idea of using the septic excavating for your ground tubes however I'd be nervous about it because the ground tubes don't have water integrity. That is they'll have holes on the bottom for drainage of condensate. Because of their proximity to raw septic tank liquids I'd be concerned about some kind of bacteria and/or moisture migration. What I'd suggest instead of ground tubes there would be black poly pipe, several hundred feet of it, BENEATH the sewerage lines.

You'd run water thru the poly pipe, then thru a heat exchanger in air handler in your forced air plenum. The forced air plenum would move the air thru the ground tubes and the air would move thru a radiator type heat exchanger. "

I'm sorry but you lost me. I understand what you're saying about the ground tubes being in the proximity to the sewer lines. (I'm not worried about that, I'll explain later).

But then you seem to be suggesting additional lines (black poly pipe run underneath the septic lines) filled with water?? I'm confused...

 

[johnkl]

Actually, I'm suggesting the poly pipe in the septic drain field INSTEAD of the earth tubes for the safety reasons I described.

The poly pipe would be filled with water which would be circulated thru a radiator type heat exchanger mounted in your forced air plenum. It would be a closed loop where the same water was re-circulated. It would do the same thing as the earth tubes because the earth "coolth" would be transferred to the water in the pipes, then the ""coolth" removed and transferred into the house by air passing thru the heat exchanger. Is that any more clear?

 

[Guest]

" The poly pipe is really inexpensive---about $12/ 100' or about $35 for a 400 foot roll. Thats 3/4" poly pipe."



Ok another question. Where do we get this stuff. Is this like drip irrigation tubing?
I know PVC pipe is an insulator and thus not as suitable for exchanging heat with its surroundings. I bet this poly pipe is better because it has thinner walls?

Thanks again.

 

[johnkl]

Poly pipe can be found at hardware strores and farm supply stores. Polypipe refers to polyethelyene pipe. Its really tough. Handles freezes without bursting with water in it. Semi flexible. I used it at the old place for a poor boy underground irrigation system for the garden and yard. It cost me less than $100 for the whole job. I don't think its the same thing as drip irrigation piping but I couldn't say for sure, having no experience with drip irrigation.

Yes, polypipe has thinner walls unless you get schedule 20 PVC then I'm guessing it would be a toss up.

Do you understand better what I'm talking about?

 

[joan from zone six]

zack - the "sunnyjohn" site you provided is truly remarkable - anyone considering building shelter for humans, animals and/or plants would be well advised to study those ideas in great detail -
thanks!

 

[Guest]

"Do you understand better what I'm talking about?"

Yes. Thankyou very much. You are talking about a chilled water system, actually.

I wonder where one could find out how many linear feet of poly would be required for x number of btu's of cooling..