Earth tube air conditioning

[garyonthenet]

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:

1. About 100' vertical tube into the ground.
   
2. Outer diameter of the tube about 8".
   
3. I intend to drill at least 4 of these tubes, for a total of 400', driven in parallel.
   
4. Gonna use water or antifreeze as the transfer fluid.
   
5. 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 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 buoyantly [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 concrete caisson 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 Air-conditioning" 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 belligerent and denigrating to my project and me, telling me my project would cost many thousands of dollars, that I would have to hire skyscraper 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

"It is better to have a bad plan, than no plan at all"

[Stonebrain]

"It is better to have a bad plan, than no plan at all"

As long as you don't try to realise them.

cheers,

stonebrain

[BigBreaker]

Don't do vertical tubes.

For A/C you are fighting gravity.  Dig a trench next to your foundation about six feet deep.  Run tubes (generally coiled) along the trench and pump the fluid horizontally.  You don't get much more heat sinking at 100' than at 6' and it might be worse.  Soil is a thermal mass but it is also a decent insulator and average temps go up as you go down.  You just need enough ground thermal mass so that it is stable at your average annual temperature.  Anything more is trouble.

You can avoid the pump if you run metal tubes at a slight upward angle from the heat source.  The trick is building your own heat pipes with water or other working fluid.  Water requires you to pull a vacuum in the tube.  Hydrocarbons or ammonia also work well but operate at high pressure.  Don't worry - after the working fluid is in the formerly evacuated tube you seal it off forever.  The working fluid is recycled indefinitely.

Tune the heat pipes to condense the working fluid at your ground temperature.  The fluid then trickles back down the pipe to your heat source to be "boiled" off again.  You will only need very thin pipes (though perhaps many of them).  The thin pipes have much better surface area for their diameter.  The phase change cycle transports vast amounts of heat... way more than the soil can accept - so keep the tubes narrow but have more off them.

Corrosion is the biggest issue.  Stainless steel tubing or some coating on aluminum/copper would be in order.

Traditional earth tubes are horizontal.  Think 200' of concrete piping through a trench to an intake.  Often the builder will use the natural terrain to arrange for the pipe exit.  An upward slope will draw some cold air by convection alone, but some energy is always required to distribute the cool air.

[garyonthenet]

Well, trying to realize no plan at all, that is when you still think you have one, is still worse than trying to realize a bad plan, where at least you do have one.

;^))

Thanx for thinking!

[garyonthenet]

Omigod.

So many things to say, so little time.

First of all, how on earth (no pun) are you fighting gravity using a vertical tube for air conditioning??

The fluid levels are equalized, there is no pumping against gravity in this scenario. It is exactly like pumping through a 200' pipe 4" diameter.

Second, the temperature below 6' is far more consistently uniform than at 6' or above. It has been observed that seasonal fluctuations are existent at 10' and above. Furthermore, how can you say that it would actually get warmer at deeper levels? It is a given that the deeper you go, the more consistent and fixed is the temperature; obviously this is up to a point, but then you are talking about miles down, where the earth's mantle heat is predominant.

As far as the insulative powers of the earth, this is a wild card in my complete knowledge, but the information I have is weighted against what you are saying.

The deeper you go, the more compact the earth gets, compacted earth has a far greater thermal conductivity than loose earth, as well as a greater specific volumetric heat capacity.

Additionally, there is a good likelihood of hitting a water deposit, or wet vein.

If this happens, then the thermal conductivity goes WAY up. This can't happen at shallower levels.

After re-reading your post a few times, trying understand what you are talking about in re, partial vacuums, slight upward angles, hydrocarbons, etc.

I think I figured out what you are trying to propose.

Your idea here is to create an unwicked heat pipe, using a evacuated pipe at some minor fraction of an atmosphere, so that water (or some hydrocarbon) will vaporize at close to room temperatures, and distribute heat via a phase change, gravity return, and convection cycle.

You propose a 200 foot stainless steel pipe, that has been evacuated to reach these vapor pressures. You suggest that such a pipe would maintain these vacuum levels indefinitely.

Needless to say, this plan would involve tens of thousands of dollars, minimum.

The pipe alone would cost thousands, then I would need 3 more of them - to get what? The same thermal energy sink I could access with simple fluid water at STD conditions. There would no net greater thermal efficiency either way.

Then there is the question of vacuum pumps, and maintaining that .1 torr or so to be able to vaporize H2O at room temperature.

I don't know if you are kidding with this post, and I almost think you may be, but your plan truly is hilarious, (and a bad one at that!).

I think I will proceed with a non-bad plan.

Thanx for the effort either way though!

[scottsAI]

Hello garyonthenet,

Enjoyed your post and your replies!

I liked your Bio can identify with it myself.

Been looking over this earth cooling for couple years, have same references you posted.

Looks simple until you find what it cost to make. Your best bet would have been to post your plans first then acquire equipment.

Additional problem is the dew point is not reached after it's been in operation for a while due to the heating of the ground. Without dew point, no humidity removal. Requires further cooling to make air temperature comfortable, then it gets cold quickly. Air tubes have water stagnation problem, your water loop is better, problem is the reduced surface area of the water pipes will reduce effectiveness. With 4 wells, maybe this will be fine, do not know your soil or if water will be hit.

Maybe a different idea:

Our ancestors used Ice to cool their food for the summer.

Last summer I designed an Ice-Block cooling system to cool Fridge and House year round. I called it Thermo inertia cooling.

Recently I found this link: http://fourmileisland.com/IceBox.htm

Don't know why I did not find it sooner, he Did it 20 years before!

I expect this can be simplified, cost $1,000 to $1,500. Home AC and Fridge for one price, almost no power to run it. Wrote model and simulated a year, worked great.

What do you think?

Have fun,

Scott.

[BigBreaker]

Ground source heat pumps fight gravity when cooling because the pump works against the thermosyphon effect.  The cold working fluid wants to decend instead of rise since it is more dense.  If you know what a heat pipe is then you know what I am talking about.  It's not a huge deal but is avoided by going horizontal.

6ft versus 10ft doesn't make that big of a difference compared to surface area.  I wouldn't mind having basement access to the pipes so basement depth becomes a constraint. Wikipedia quotes both figures for horizontal ground source geothermal, with 6ft as the highest recommended depth see here: http://en.wikipedia.org/wiki/Geothermal_heating

Also read in that article about how temperature goes up slowly at lower depths once the surface effects diminish (around 6-10 ft)

I'd use anhydrous ammonia as my working fluid - it's nearly free and available anywhere there are farms.  Ammonia under pressure doesn't leak at all from SS and no worries about holding a vacuum.  You can have enough ammonia in the tube so that micro leaks do not matter either.  Leaks are basically fertilizer - no toxicity issue at those quantities.

Quarter inch stainless steel tubes are about $1.5 per foot in 8 foot lengths.  Not free but not bank breaking either.  Materials are never free.  At least a thermosyphon based heat pipe network doesn't need a pump for the working fluid.

My point about the earth being an insulator is just that its heat diffusion constant isn't very high.  You need a lot of surface area to sink the heat.  Going deep for that surface area costs more.  It's better to have more vertical tubes that are shorter than fewer that are deeper.  Builders only go really deep when their footprint is limited - like in Manhattan.

It sounds like vertical is the way you want to go.  I just wanted to point out some ways to go sideways rather than down.

[garyonthenet]

Ok, I can see you are speaking seriously, I will respond herein.

First note, that I am not driving a heat pump, which drives heat from lower temperature sources to higer temperature destinations.

In the system I am building the heat transfers entropically in the opposite direction, i.e. ground cold to house hot.

There are no compressors here, the working fluid remains in liquid phase and essentially at the same density throughout the cycle.

It takes on and releases its heat through normal (ie, non-driven) entropic directions.

As to the idea that pumping is harder vertically, this may be true when the cold source is beneath the destination.

The action of convection due to differing densities of the hot and cold water, does in fact fight the direction of the pumping in this scenario.

I would be good to note the head pressure difference due to this effect alone.

As you now may know that I am not using a phase change fluid, nor an active heat pump, you might agree that a 1/4" tube is too small to effect sufficient pipe surface area, for simple heat transfer.

And yes, I am kind of committed to vertical tubing at this point, as I have purchased the drilling equipment with this in mind.

But why would you say that many short tubes are better than a few long ones?

This is a configuration change that I can adjust to if there is a good reason.

It would seem from the particulars of this project, it would be easier to continue drilling an existing hole another 50 feet than starting another hole.

I appreciate the varying angled perspective and

Thanx for your input

[ghurd]

"But why would you say that many short tubes are better than a few long ones?"

Total surface area (why would it change the temp at 3' deep), fluid turbulence (electric AKA skin effetct), R value (in/out or out/in), thermal dissapation (where do the therms go or come from), total mass (handles the implications of the above), and etc etc etc...

Or rent a ditch-witch and put a lot of feet of coils 6' deep.

G-

[RP]

"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. "

Don't do this.  You'll have condensation problems followed by mold problems...

[garyonthenet]

Yes, I agree that it would have been better to post my plans before going through with it.

It's just I have been mulling about the idea for some time, and it seemed to me that outer limits of what I know has been done and can be done permitted this project to be feasable, that I could tweak the unknowns later on, since the fundamentals were well within operating specifications. So while I was online surfing, I saw the equipment and jumped at it before I could change my mind.

One of the primary goals here was to have the installation cost be lower than post-construction central air conditioning. If it reaches that then it might ok, but not what I was hoping for. The big return though of course is the cost of operating the thing, I estimate typically at 1/10th the cost of comparable driven airconditioning.

And of course the other selling points are, "Save the earth" & "Fight the terrorists" LOL

I didn't mention this part in my first post, but I intended to also incorporate the practice of pumping cold(er) coolant back down the tubes when the air temperature goes lower than 40degF; the idea being that I would pre-charge the earth volume even further with cold during the winter months, so that when summer comes around it will have an even greater head start, the natural subsurface cold notwithstanding. This is similar to your concept of freezing a large block of ice in the same fashion.

I don't know the actual practical thermal conductivity of deep earth, so I am only guessing as the effectiveness of this idea. My guess is that it would pan out on the average and increase the cooling efficiency in the warmer months.

It would of course work great for water. The big challenges would be the very large mass of water you would need, and the very efficient insulation needed to surround it.

If you calculate say 864,000 btu/day, and thereforto 107,136,000 btus for 4months, you can have an idea of how much water you will need.

If you calculate this heat capacity based only on the phase change of H2O from ice to water (any further cooling would just be gravy), which is 3.15g of ice to 3.15g of water per btu, then the quantity of water you would need is 337478.4kg of water/ice. This translates into approximately 90,000 gallons of water. With that, you can cool your house for the summer ;^))

This is feasable, just requires an underground, well insulated, pool. It would save about $1200 a season in cooling costs. Hmmm now I'm jealous!

Naw, I think perhaps I could get comparable results from cooling large quantities of subteranean earth. That structure is already in place, and the costs involved are just getting to it.

However, I am still looking for input here, on how to line a 100' x 8"diam hole with something waterproof, and that doesn't cost more than $120.

Like I said before, I am thinking of fine grit concrete, the only challenge is how to get a consistent hole down the center of it.

I am also open to any other suggestions on how to effectuate a hole with such dimensions.

RSVP yawl

[garyonthenet]

The total sum surface area of two short tubes that are each half the length of one long tube is the same as that long tube, where all three tubes have the same diameter.

A shorter tube, of the same diameter, would have the same turbulence potential.

A shorter tube, of the same wall thickness, would have the same R value.

Now if you are talking about many more tubes, each of which has a smaller diameter, and that are dispersed throughout the thermal mass, then I would agree with most of what you are saying.

However, if you are saying that it would be better to simply have many smaller diameter tubes, that net out to the same length of a larger diameter tube, then I don't agree. The surface area of a smaller diameter tube is smaller than that of an equally long, larger diameter tube.

Even if you managed many small diameter tubes, bunched together, then you would still reach a limit of heat transfer efficiency, because in such topology the surface area becomes less important than the total flux capacity of the heat transfer. If the flux wasn't a limiting factor, then you could simply make a pipe with a coating of activated charcoal, and expect a thousandfold increase in heat transfer - NOT.

I covered all the possiblities of what I thought you were thinking of, because you were not very specific of what you were refering to. (I won't do it again. Please be specific on what you are saying, not just toss a dozen technical terms at me and hope they will fall just right.)

[willib]

gary , how are you gonna prevent the heat from one pipe (leaving the house )from heating the cold pipe comming from the ground?

one hole has two pipes in it, right, one has fluid going down , one comming up?

a horizontal system dosnt have this problem

[garyonthenet]

Yes, I have been warned about this possibility for radiant cooling in the northern latitudes. I was told that this is done regularly in the southwestern U.S., where the humidity levels are low.

I was hoping for some interim solution, like initially dehumidifying the air in the house before applying the cold. The idea was, if I squoze all the water out of the house air before cooling, there would be none to condense. Then while the house continues it cold state, there would be no propensity for condensation or evaporation, the temperature being at a steady state.

But might not the problem still exhibit itself after cooling has gone on for some time after? The condensation may just occur later, just due to doors opening and letting in the outdoor air. I don't know.

Maybe there is another auxiliary solution I/we have not yet thought up of?

However, I am beginning to think I might abandon that idea.

The reason I liked it so much, was that there would be no unsightly wall mounted units, I would not have to cut vent holes in floors or walls, it would likely be much quieter than an air driven radiator/heat exchanger.

Yes, this problem is an just an embarrasment of riches; I got the free cold, I am just whining about how it looks and how loud it is.

Well, honestly that whining is not me, it is my wife, who is uber skeptical about the whole freekin thing. So I am trying to come up with something pretty, pleasant and quiet.

All suggestion welcome!!

[garyonthenet]

Well, I look at it the other way around.

The hot water leaving the house into the ground, is cooled by the water coming up out of the ground, it is then further cooled when it comes back up and touches the cool ground directly.

In both directions, the water is cooled before it gets back to the house.

[scottsAI]

Garyonthenet,

Great you understand, numbers used are a bit big for my house.

Your latitude is couple degrees below mine, would expect your cooling cost to be near mine? Both near large water? Detroit.

$1200 is as bad if not worst than my Dad in Tampa, FL. What AC unit you have?

I spent $150 on AC last summer, from billings, Electrical cost $0.10.

With SEER 10 AC unit this = 15MBTU heat transfer for the summer.

Assuming 2" insulation, in ground tank (50-32 temp delta), storing 200 days

Requires 13.5 cubic Ice block, 18300 gallons of water frozen. 32% loss assumed.

Using wind through a vehicle radiator, wind powered circulation pump, should be able to freeze the tank in 5 days. I have better than a 100 days below freezing... should not be a problem.

I like your idea of pre-cooling the earth tubes, cool idea:-)

How do you plan to remove humidity? I ran a dehumidifier in a damp basement, cost more than running my whole house AC.

Desiccants can be used to lower humidity. 50 lbs. Wyoming Bentonite Clay Powder item: 270112342658 $21 + that much again for shipping.

Can absorb 7 times its weight in moisture. If you have all this heat to get rid of, use solar to dry it out. Half inside, half outside, of course make it automated.

I have the same problem with the wife. I make a great living as an engineer, yet she does not trust me with things around the house. Everything I have done has work as expected. Have not been able to figure out why she is that way.

Have fun,

Scott.

[garyonthenet]

Well, I based my numbers on 36,000 btu's/hour, for four months.

36000*24*31*4 = 107,136,000 btu's for a summer.

That tranlated into a 90,000 gal tank for a large block of ice.

That seemed like a reasonable outside limit for, say, a 1800 sq.ft. house.

My A/C solution so far has been, noisy, scenery-obstructing, and heavy window airconditioners. ick. Also always on the edge of being too warm anyway.

My memory says that I spent about $150 a month for the summer, but it might have been more. You are right, doesn't seem to jive with the $1200 per summer figure much.

For your estimated size, it seems you could start out with one of those large Polyethylene tanks, dig a hole, insulate w/polyisocyanurate, and work from there.

I like your dessicant idea. This bentonite stuff though, 7 times its weight, when you straight up add water to it. But how much will it actively suck out of the air?

It is literally dirt cheap, so even w/high inefficiency it might still be practical.

I had no idea that running a dehumidifier was so expensive. I thought it was cheaper than an a/c, since a/c does both dehumid. and cooling.

Hmmm. . .

[bparks]

Wondering about why the hole would need lined at all?  To prevent a collapse from damaging the cooling pipes I'd guess?  If so maybe backfilling with sand would be a cheaper way to go, and would allow ground water to help more with the heat transfer too.

I'm also thinking since you have the equipment to go vertical and seem set on that route, a grouping of shorter holes could net you the same total area without the issue that come from such deep holes.  Say 10 15' or 20' holes, running your cooling tubes down then up hole 1, down then up hole 2 etc...  I think you could more easily add surface area to the system this way as well, if the initial version doesn't quite get it done, just add a few more holes and replumb.

Keep us posted how it works.

[garyonthenet]

The holes need lining for the reasons you mention.

The holes would collapse even at low depths, and sand would not prevent it.

Lined with sand, there could be no flow through them, as all the water pumped into the holes would be wicked away through the sand into the ground, and if any somehow returned, it would be heavily contaminated by ground debris.

I believe it would actually be much easier to continue drilling an all-ready started hole, than it would be to pull out and start another new one. Not to mention the inherent real estate space savings, and the efficiencies enhanced by having linear flows in fewer pipes, rather than several additional bulk-heads, take-offs, pressure distributors, valves, etc.

Also, you did not mention how I am going to connect these pipes together at the bottom of the 20foot holes, particularly if they are somewhat distant from each other.

[bparks]

ahh, i misunderstood or misread a key point in the original post.  I assumed you'd have pipes with your fluid in the hole, a closed loop system.  With my suggestion I'd connect the pipes at the tops of the holes, not the bottom.

Either way, starting with a shallow hole might be the way to go at first, test it out.  I'm having a little trouble picturing a 1" thick, 100' long concrete pipe holding up for long even if you do think of a way to keep your form perfectly centered over the entire 100'.  Some sort of spacers attached to the 6" form pipe I suppose.  They'd have to be cast into place and left behind, potentially causing more issues with the strength and waterproofness of your concrete tube.

[scottsAI]

Garyonthenet,

Nice link about desiccants:

http://www.devicelink.com/ivdt/archive/02/06/002.html

Need to click on the pictures to see.

"...the absorption capacity of clay increases with rising humidity and is higher than the absorption capacity of silica gel when conditions are below 30% relative humidity. Since clay reacts relatively slowly at low as well as high humidity levels, it slowly reduces the humidity in closed containers, but it is easy to handle. In addition, desiccant clay granules have up to 30% greater density than either silica gel or molecular sieve beads, thereby occupying less space."

Remember, the home air volume at humidity is only a few gallons, few lb desiccant would do it. The time to absorb is longer for the clay, this can be countered by using more desiccant. Your target is like 40-50% humidity, clay will do the job as well as anything. Kitty litter is mostly the same clay, check the label.

Above references suggest clay is only 15% cheaper than Silica Gel, I can't find silica for less than $1/lb.

"I had no idea that running a dehumidifier was so expensive."

Yes, as you know a dehumidifier is a refrigeration system itself, mine was running 24/7 thus the cost.

The windows were open to cool the house, supplying new humidity to the basement.

What I found switching over to whole house AC:

The windows are closed, restricting the humid air from entering the home.

The AC runs for a few hours a day, even tho it's bigger, over all it draws less power and the home is much, much more comfortable! I highly recommend whole house AC in humid environments.

Sorry I can't help you with the liner, don't think it can be done for $120.

What are you planning to use for the water tubing in the well? It needs to be strong enough to support the pipe filled with water, I expect it to cost more than $120 per well. May have to be metal?

I had been assuming your plumbing the wells with a piped closed water loop? Reading your other post not so sure now. Not sure I understand what is going into the well?

ICE block - was planning on digging a hole in the ground, enlarging it a couple feet, no insulation except near the top, using a vinyl pool liner for the tank. Keep It Simple Scott. KISS. Then build a deck over it for a lid with insulation!

Have fun,

Scott.

[garyonthenet]

Yes, I agree this is a quandary. That is why I request new ideas and input on how to possibly do this in such a way that I may not have thought of it yet myself.

My latest idea, is to run a rather inexpensive 6" diam drainage pipe down the 8" diam channel, and yes using 1" spacers every 10 feet or so.

Then pouring fine aggregate concrete around this inner form down the channel.

When the concrete hardens, the drainage pipe would be left in place to provide the sealing.

But there is a complication even with this, namely the bouyancy of a hole in something of 2.6g/cc density.

Ergo the calculation I made on the first post, of filling the tube with water in a 1 to 2.6 ratio level with the concrete; then wait for the hardening, and do it again  until filled.

[BigBreaker]

You may find this website helpful:  http://apollo.lsc.vsc.edu/classes/met455/notes/section6/2.html

It will help you determine the general volume of earth you'll need to access from the vacinity of the tubes.  It will also help determine the heat flux you'll need to transmit.  It's not at all clear (to me at least!) whether you are "power" or "energy" constrained by a particular geothermal system.

Diffusion calculations require differential equations to calculate precisely but there are some good rules of thumb.  A bit of digging on the internet will help.  I just know the ones for electronics - not thermodynamics.  The short answer is that the delta T of your tubes and the earth will set up a exponential temperature curve and a certina flux.  The temperature curve will have radial symmetry radiating from the tubes.  Your tubes will "see" a certain effective radius of earth and no more.  That earth better have enough heat!

Anyhow - I seemed to have come off the wrong way and wanted to help.

[garyonthenet]

Well, I didn't know that you were leaving windows and doors open, then the cost of electrically driven dessication that you mention doesn't surprise me. A similar cost would result if you left the doors and windows open with whole house AC.

It is also true that the net cost of using bentonite might be cheaper (particularly if you keep the windows/doors closed). If the desication factor isn't high enough, just add more bentonite - heck the stuff IS dirt, cheap ;-)

My calcs on your insulated ice block were for a longer season than your calcs, but I also didn't include wasted melting due to insulative losses.

Yup, whole house AC is very comfortable. That's why I am doin what I'm doin.

I think I can keep the materials cost for the 100' tubes close to $125, with the cheap drainage pipe liner, and the pouring of a concrete shell around it.

battery running low, will continue later. . .

[garyonthenet]

And help you have. Sorry if I was curt.

I thank you for your link, and the analysis is good too.

It is something I had a strong intution about, but not enough raw data to make a definitive assessment.

I have investigated both the average thermal conductivity of earth:

Earth, average . . . . . . . . .4.0

Concrete, stone . . . . . . . .2.2

Expressed in gram-calories/second/square centimeter/centimeter/°C

and its heat capacity

Earth, approx = 920.48 joules per kelvin per kilogram near 20 °C

Expressed in Specific Heat ratio

The nice thing about it is that one can always make more channels through the earth to increase the contact area with the volume.

These calculations also suggest a minimum radial distance of the tubes from each other, otherwise the tubes would be competing with each other for the same heat/cold.

I would think that it is a power that is the limiting factor; given enough time, you can pull almost any amount of cold from the ground, it's is just the rate that you are ltd by.

If you want to calculate it, just for personal amusement of course, let me know what you come up with ;-)

Thanx again

[gale]

   What you a describing is a closed vertical geothermal loop.  hook that to a heat pump you have a very nice geothermal unit.

  I see several problems, the basic is the cost.  drilling several 8 inch wells( esentially that is what they are), then lining it with Stainless.  is going to cost thousands, even if you have your own equipment.

   I am not sure where you can get cheap anhydrous ammonia,  I have spent tens of thousands on the stuff over the years.  There are also some major disadvantages; not the least being that it reacts to water, if you get a leak, you will be poluting the ground water,  I would not have the stuff near my house( I will not park a tank withen 100 ft of my house), and currently be ready to explain to the police why you want it for, it is a major ingrediant in Meth.

    Plus, you are getting over complicated.  I believe in the KISS method.

    My uncle has a very nice geothermal unit cooling his house with a open loop system.  It is basically pumping water out of his well, then dischaging it in to a drain.  In most of the eastern US, we do not have to worry about excess water usage.  The water comes out of the ground at 51F, which is ground temp here.  You do not have to worry about reheating the ground by pumping hot water back down the hole.

    If you want to stay with the closed loop system, try what the geothermal guys use, a pipe down, a pipe up connected at the bottom, into a 4 inch well hole, circulating a non-polluting antifreeze solution.

   Another problem you will have from trying to cool air directly through a radiator with water is going to be the cycle times.  Most a/c and geothermal units, that use water, through their a-frame radiators courses Freon, which cool the fins down toward the 0f mark.  By using water, you will  be lucky to get the fins withen 10 degrees of the ground temperature.  So instead of the A/c blowing for 20 mins, expect it to never shut off.

   Personally, instead of investing all that money into Stainless Steel and anhydrous.  Buy a geothermal heat pump, it will make better use of the ground temperature.

[TimV]

I know a fellow who has a shop that he heats with and outside wood furnace. A very large poorly insulated shop which he also cools with the same heat exchanger used for the wood furnace with  a 250000 btu rated hot air exchanger.

During the summer he uses the water from his 350 foot deep water well and runs it thru the exchanger and back down the well . They dont drink the water from this well as they have town supplied water but it really cools the building down and it does not stay on at night but works so well that in a short time its cooled enough to start puting shirts back on! Why not let the bedrock below you work for you? Drill in rock and you dont need much caseing . If bedrock is very close you wont need much pipe .Last I heard a well in bedrock was $10 a foot and $20 if in 6" pipe

I knows it pretty simple but it works  no fuss no muss just a plain old water well.And this is only about 50 miles from Albany NY so should be close to your water temps.

[ghurd]

"Plain old well water"?

What is it when it is reintroduced back into the regions aquifer?

It can't hurt any more than dumping chemicals into the Cuyahoga River...

Or rivers in Michigan, New York, Maryland, Pennsylvania and others...

It's not like a river in those states can catch on fire or something...

It might not even be illegal somewhere

[jonas302]

I'm having trouble figering out your acual plan are you running a closed loop system?why would the well casing need to be waterproof? A closed loop is a pipe down connected to a pipe up are these going to be in the water table? in contact with soil? Why do you need an 8 inch hole everybody else does it with four I would think the equipment to make the holes already exceeded the cost of air conditioning

[Gary Williams]

To Garyonthenet: I experienced the same treatment from M Bradley in 2 separate contacts a couple of years apart and reacted exactly the same as you. It seems a very strange thing for someone to be as talented as him, to craft websites that periodically recapture my attention, to be negate the attention he seeks to attract. Good luck with your earth tubes. Living near Houston, with temperatures commonly above 90 degrees, our air conditioning needs drive our electrical costs up a lot. This is a link to a one-man portable drilling machine. Someday, I hope to try it out. http://www.littlebeaver.com/

Gary in The Woodlands

[TimV]

"Looping " water up a well and then back down again somehow seems very harmless to me. Where did we switch to "Love Canal"?

[Kwazai]

looping with a few hundred feet of pvc coilhose is one of the things I've seen recently.
Univ. of Nebraska Passive Solar research papers have a pretty good  synopsis with data.
http://www.ceen.unomaha.edu/solar/solar_fi.php

[MattM]

There aren't many schools in Nebraska not using ground loop heating and cooling systems.  Great about 80% of the time, but weather fluctuations make it hard to tolerate about 20% of the time.  But, hey, it's popular to be green.