Underground Poly pipe for heat/cooling?

[fuelfarmer]

I have 1200 ft. of 3.75 ID black poly pipe that I am thinking of using as an air tube or heat exchanger. Is there enough surface to cool air for direct air cooling, or water for a simple water/air exchanger? Or would this be enough pipe for a ground source heat pump? I have the pipe, and the equipment to dig a big ditch. The pipe was removed from a traveling irrigation system and it needs a new home. I am thinking of putting it back to work.

Our house is around 2500 sq ft and is well insulated, although not super insulated.

mbryner, have you used your air tube system?

[rcavictim]

Ah, but are you equipped to dig a big bitch?  Oh nevermind. 

I don't know where my project file is right now but IIRC you will have plenty of length there for a ground source system if that is buried say 8 feet down along it's entire length and filled with circulating liquid.  I have similar area to you on two floors and figured on a 500 foot long collection ditch of that depth using only 2" poly pipe.  Your pipe will have way more interface exchange area.  You might even want to cut that length in half and bury both side by each so you have a backup line in case of a potential stone puncture or errant bunker buster bomb some day, prisoners digging a tunnel to escape, almost anything.  Just sayin'. 

[Ronmar]

I would also say use water and a heat exchanger.  Direct air sounds simple, but no way to control air quality and mold/mildew growth in the buried tubes when used for cooling...  With liquid, you can at least control the water quality/chemistry of the circulating liquid.

[mbryner]

Hi fuelfarmer,

Nope, I haven't used my earthtube system yet.   I still have some trenching to do outside the house.   It may not be ready by summer.    I used 4" PVC tubes under my basement concrete slab, bedded in gravel.   My system isn't designed to be a complete A/C system -- I just want to cut the edge off the hottest days of summer.   Here in the West the nights cool down, so we can open the windows.

1200' is a *very* long length of pipe.   If you are using air, you can cut that into several sections or you will have too much resistance to air flow.   

Many people will warn you about using earthtubes because of the air quality, but I think you can use air instead of water if you follow good design prinicples.   With any earth tube design you will have to have weep holes on the bottom of the tube or some sort of sump to get rid of any condensation.   Make sure the tubes slope downhill away from the house analogous to a septic system.   Also, dig the trenches deep.   Everything I read says bury them 4' or deeper.  (My pipes aren't that deep under the slab, but the slab doesn't get any sunlight and the house is surrounded by a 10' wide deck so the slab temp should be similar to temp deeper down.)   Filling the pipes with water would work great, but it's just a little more complicated to put in pumps and water air heat exchanger and blower, instead of just the blower.   Anyway, it's hard to find a lot of data on earthtubes on the internet.

Marcus

[fuelfarmer]

I was told by someone with second hand knowledge that if the air/earth tube makes a few sharp turns before entering your house some moisture will drop out when the air moves through the sharp turns. Not sure how true that is.  I guess if the air had small droplets the droplets would not want to make the turn and collect on the elbow wall. You would have to have very wet air for that to happen. 

[DanG]

Quite an ambitious project, just beware that is rumored to be how spores of the pod-people multiply!

Wow - 3.75" ID pipe over 1200 feet is 63600~ cubic inches; 368 cu ft; or 2750~ gallons volume.

That is an awful lot of volume to fill with a pool chemical 'shock' treatment of chlorine or bromine, or a brewers iodine to kill the wee beasties.

If you've ever seen the inside of a large scale underground (old style telecom, not fibre) conduit chase they have arrays of of 3x3 or 4x4 etc. termination areas in a vault w/ manhole cover for their continuous ground-contact burial plastic conduit, say for a small college campus.

To split 1200 feet 16 ways is 75 feet, then array that spread out so the vault access is only 50 feet from the other end would give man-sized lengths to be able to run a cleaning-disinfecting 'pig' through - then cap the end with a U-turn and place it back in service, also could easily run lines in parallel etc. to tune the flow rate and restrictions.

[Curbie]

Anyway, it's hard to find a lot of data on earthtubes on the internet.

I don't know what your tolerance for numbers is, I'm a numbers guy, but this is the best numerical description of earth-tubes I've found:
http://greengaragedetroit.com/images/e/e9/EAT_Pressure_Humidity.pdf
I think a translated some or all of it to a spread-sheet somewhere (I don't remember finishing it), if anyone wants what there is of it, give me an email to send it to.

Curbie

[fuelfarmer]

Here is a video clip of the irrigation system and you can see the black poly pipe. The pump is running on home grown biodiesel (B100

http://www.youtube.com/watch?v=oFrAzkRCkh4

[Ronmar]

I am going to have to disagree with you Marcus, especially if you put weep holes in the system and open it to the earth...  It won't take very long and the air in that pipe is going to start smelling like a crawlspace under a house...  I wouldn't want to pump that thru the house for my family to breath...

2750 gallons is not that hard to treat.  I keep up a 1500 gallon pool beside the house every summer, and it is a piece of cake.  Couple of slow release chlorine pellets into the flowing stream and an occasional water test would be most of the work...

[mike90045]

How thick is the wall (insulation) on that pipe?   Does not matter what you bury it in, if the wall thickness (insulation) is more than the temperature difference, you will get nothing but worn out blower / pump motor. 

[BioHazard]

Hmmm...looks like I might be digging a 250' trench for new water/power/gas lines this summer. Would that be long enough or deep enough to bother putting some earth tubes in before I cover the hole? I was thinking about leaving a peice of empty 4" conduit anyway for future runs....

[fuelfarmer]

How thick is the wall (insulation) on that pipe?   Does not matter what you bury it in, if the wall thickness (insulation) is more than the temperature difference, you will get nothing but worn out blower / pump motor. 

The wall is 3/8 if I measured correctly. The pipe could make a big solar collector for a pool.

[BioHazard]

The wall is 3/8 if I measured correctly. The pipe could make a big solar collector for a pool.

Hell, you could probably boil a pool! Several years ago I was able to heat a pool with nothing more than 200' roll of 1/2" black poly laid out in the sun!

Depending on your climate maybe you could use it for household hot water or possibly heat....

[mbryner]

I am going to have to disagree with you Marcus, especially if you put weep holes in the system and open it to the earth..

Ronmar, I always respect your opinion.   Yes, fuelfarmer, there are some risks.   There's nothing lost so far in my project and I didn't pay much for it.   I laid the pipe myself before the basement slab was poured.  It needs to be hooked up to the air handler and trenched to its termination on the hillside.   Our humidity around here is so low in summer that the heating and A/C guys think I won't get any condensation at all.   If you read about me dying from Legionaires Dz then I'll have to eat all my words.

[Lloyd]

Hey Marcus,

It doesn't take much moisture for black mold to grow, in a cool dark enclosed area with no air movement. Just look at any north facing wall, tree etc...you will see the results, and that is in open air. I have remodeled a number of houses, and have seen the results of the lack of air movement...inside walls, crawl spaces, and attics.

I think a system that is moving air 24/7/365 will grow almost no mold.

So I think you should really consider getting some air movement through your tubes already installed...once fungi  gets a foot hold there is almost no stopping it,  short of something really toxic...kinda like a toenail fungi.

I also think you should devise a way to keep air moving 24/7/365 with some kinda of diverter so that you're not adding cooling during your heating months.

Just my thoughts.

Lloyd