Well I came into a little expendable cash, and I have been thinking of this idea for a couple years now. Finally I bought some earth drilling equipment, and am now in the process of planning some vertical earth tubes to cool my house.
My design plan is:
- About 100' vertical tube into the ground.
- Outer diameter of the tube about 8".
- I intend to drill at least 4 of these tubes, for a total of 400', driven in parallel.
- Gonna use water or antifreeze as the transfer fluid.
- The climate I am doing this in is in the Woodstock NY latitude, so I understand that the earth temperature is about 49degF.
Possibly gonna jack into my house's radiant heating system with this fluid and cool my house that way, instead of perhaps using a car radiator and a fan.
I have a couple innovative ideas on implementation of this already established idea, and since this well established technique has surprisingly little hard data associated with it, I will be keeping detailed records as to costs, and energy efficiencies and heat transfer capacities.
I plan on putting a data gathering flow meter on the individual tubes, and a temperature sensor on the ingoing water as well as the outcoming water from the tubes. This way I will be able to monitor cooling power capacities, and integrate the data across several months.
I have also read the Indian Paper on their experiment using air as the transfer fluid, and it is very encouraging. see: http://www.builditsolar.com/Projects/Sunspace/EarthTube2004-03-02gsharan.pdf
However the differences are that they seemed to have run it only for a few days each month, and of course my tubes will reach much deeper. Also my tubes are 8" diameter, theirs were 4" diameter.
Someone here or there mentioned that a larger diameter pipe is better only to a point, and thereafter with diminishing returns.
The reason was because only a small part of that larger volume of water would, on the average, contact the large pipe surface area, due to laminar flow; if turbulent flow was induced then then pumping efficiency went down.
I have a method that will force a majority of the water to contact the inner pipe surface with mostly laminar flow and good pumping efficiency.
My method to drill the holes is also much cheaper than what usually is tallied for costs, for the effort, time and end tubular dimensions.
My quandary here for you all, is the cost of lining the tube with something 8" in diameter.
PVC Piping is out, as I can't even seem to come across it for sale in that diameter, and it looks like it would cost about $2.50 a foot. With a 400 foot run, that total will add up fast to unacceptable bucks.
One of the major target specification goals here is to have the full installation cost much less than a conventional after market (ventless) central air conditioning system.
Of the various piping materials solutions I have considered, concrete and polyethylene tubing seem to be usable solutions for this application.
For the concrete idea, the challenge I have is, how to make a 100' concrete lined tube, outer diameter 8" and inner diameter 6", lining thickness 1". The concrete liner should be water tight.
My plan is to use pool plaster, with a 6" inner tube as the inside form.
One of the main problems is the static pressure of a 100' column of concrete, which has a density of about 2.6g/ml. Such a pressure at the bottom of the tube would be immense tending to crush and/or push up boyantly [phonetic] any empty tube.
A propositional solution might be to fill the inner tube to 100', and fill the volume around it with concrete to a level of 1/(2.6) x 100feet= 38feet.
The two fluids at these levels would have equistatic pressures.
Then, when the concrete hardens some, I could pour the remaining 62 feet of concrete.
If I used a flexible (flattenable) tubing material, I could then evacuate it of water and remove it to leave the concreate cassion liner.
Tricky, I know. 100feet long, with a 1inch clearance between the outer and inner diameters. With the expectation that it be waterproof as well.
Hmmm. Any ideas on this are welcomed. I have a couple other related possible solutions, but I'd like to hear some input here too.
Once I have that tube in place, the rest of the project is relatively straightforward.
BTW, I have also read the earth tube "Free Airconditioning" website by CJ, see:
http://mb-soft.com/solar/saving.html
What he has written I have found to be very useful, and his enthusiasm is infectious. His sense of self importance is a little off-putting.
I tried communicating with him by email, but in short order, when he concluded that I had a rather different topology for my system, rather than using his, he was rather beligerent and denigrating to my project and me, telling me my project would cost many thousands of dollars, that I would have to hire skycraper building engineers for $400/hour, and saying that I was trying to abuse his good will by leaching free engineering services from him.
I sent him a final email stating that he did not have to communicate with me, and that we can all learn from each other in these efforts, but I did not talk to him if he didn't want to, and left it on a positive note.
Well, along with all that positive passion, often comes a bit of paranoia ;-))
RSVP all here.
Gary
