# Cave Power!



## fantasymaker (Aug 28, 2005)

The airconditioner thread got me thinking ,
The most airconditioning Ive seen for the electrical buck(or what) is simply a fan in a cave.Dont have one handy? Think a fan in an undrground pipe!


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## moonwolf (Sep 20, 2004)

my basement floor and half way up the wall is 55 F. If it's really hot for several days in a row, I'll close the windows upstairs and turn on the furnace blower to circulate that cool basement air to the 85 degrees upstairs. amazing how that stabilzes shortly to 70 degrees thoughtout the whole house.


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## Dubai Vol (Mar 22, 2006)

This link should help, it was posted in another thread here IIRC:

Free Air Conditioning 

I've got my own ideas about how to use this very simple principle. I you live in an area too hot to use the ground temp directly, use the air to go through your heat pump. Here's a schematic:








Some explanation is in order:

The black box is the heat pump, with a fan pulling air in from the sides and ejecting hot air out the top. Now, instead of letting it pull in warm air from outside, close it in and feed it air from pipes buried underground, shown in blue. The efficiency of a heat pump depends on the temperature difference it has to work against. Feed it 90 degree air and ask it for 70 degree air and it has a 20 degree difference to overcome. Feed it 80 degree air and it's more than twice as efficient, because the relation isn't linear. (math, it's for geeks like me. And we LOVE it!)

I could go on forever, but that's just because I'm an enginerd who does air conditioning for a living, and just HATE how nobody even tries to make these things work better. If they work better they can't sell you as much tonnage.

Oh, I forgot to add: in winter you get even MORE benefit, by warming up the air before it goes through the heat pump.

_Dubai Vol wanders off into a corner to grumble about how much energy people could save so easily......_


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## Triffin (Apr 20, 2005)

I like it !!

What's the solution to avoid condensation
buildup in the underground piping ??

Triff ..


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## mightybooboo (Feb 10, 2004)

Triffin said:


> I like it !!
> 
> What's the solution to avoid condensation
> buildup in the underground piping ??
> ...


I think that and mold is the problem.

BooBoo


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## JAK (Oct 15, 2005)

I think the idea of using the damp air indirectly is a good one, to avoid moisture problems. I think heat pumps work best when you have roughly the same amount of heating degree days in winter as you do cooling degree days in summer. In both cases insulation should be the first line of defence, as it is further North and South.

The main problem I have with heat pumps is that small ones are too expensive, and a small well insulated house doesn't require a big one. I think our energy problems in North America stem from the fact that you can make more money by selling big things that people don't need then by finding ways to save people money. You should be able to cool yourself from the ground without moving a lot of air around and a lot of comotion, but the idea is sound. Better if you need less energy to start with.

Unlike heating, when cooling the energy is working against you.


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## bayesoft (Jun 24, 2006)

I've researched "Earth Tubes" in the past for passive heating and cooling. I'm pretty sure that I have the moisture problem licked with my own design.

The trick is in the angles of the tubes and providing openings and excellent drainage in key low spots in the run. As long as the condensed water is allowed to drain away quickly it should not be a problem.

I have this huge hill next to my building site that I am using to bury the tubes into. It works in theory.... Haven't built it yet to see if, or how well, it will work to remove moisture. I'll do a write-up with pictures when it is operational.


Having a tight house would improve the efficiency.


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## Dubai Vol (Mar 22, 2006)

Please keep us updated. Sounds like you have the right idea: slope the runs to let the water drain.

One thing to keep in mind is that when you have conditions that create condensation in the pipes, the air coming out is going to be at 100% relative humidity. To get around that, consider letting the air warm back up some before you use it. That will happen naturally in the ducting system after the earth loop. Depending on where the ducting is and how long the runs are, you might be OK. You might consider NOT insulating the ducting.


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## jnap31 (Sep 16, 2005)

This is what I posted here 
http://www.homesteadingtoday.com/showthread.php?t=119922

a few weeks ago seems like a similar topic that ran out of steam. All around my grandpas farm there are abandoned mine shafts where they took out clay for bricks sometimes they cave in and trees fall over. Well there is one place I remember from when i was little where animals had dug into one and their were two holes bout the size of a ground hog hole they were constantly blowing 55 to 60 degree air out I dont know the physics behind it but it was neat and even when their was snow all around you could always see that spot cause their was no snow there. Grandpa said it would be a good place to build a house and have free heat in the winter and airconditioning in the summer Problem is it was in a really steep holler. So how big an underground chamber/cavern would you need to make the same effect? perhaps if you had a big underground storm/root cellar you could have a pipe from to your house? would you only get the effect if it was completely sealed off everywhere but where the pipe is?
__________________


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## beowoulf90 (Jan 13, 2004)

Triffin said:


> I like it !!
> 
> What's the solution to avoid condensation
> buildup in the underground piping ??
> ...


Just slope the pipe so that water/condensate drains to a low point and put a drain there to take it away...


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## Allan Mistler (Jun 1, 2004)

Several years ago my wife and I had an earth sheltered home designed by one of the East Coast's premier earth shelter architects. To bring this home... The earth tubes were a pair of 12" PVC pipes (200 ft long each) feeding directly into the atrium floor, sloping down and away from the house to allow condensation to flow away from the home and terminating in a dry well. The length of the pipes assured that all moisture had been condensed and removed from the resulting air. The pipe was buried at a depth of approximately 4 feet.
The net result was cool air during the Summer and warm air during the Winter (about 50 degrees steady). For Central NH, that was quite a benefit during heating season! I'd love to send pictures, but I no longer own the property.


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## JAK (Oct 15, 2005)

Aren't earth tubes redundant in an earth shelter?


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## Allan Mistler (Jun 1, 2004)

Not really Jak, Even earth sheltered homes need air circulation for things such as: people, cooking devices such as stoves, wood stoves for heat (The home was designed to maintain proper temperatures on less than 1/4 cord of wood per year).
There was a two story atrium on the South facing wall that also caused the air to draw up from the cool tubes resulting in air circulation.


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## JAK (Oct 15, 2005)

Good point. I can now see the advantage of the earth tubes in that it gives you an energy efficient means of cooling the air and extracting the surplus humidity before it enters the home. You might still need a dehumidifier in a hot humid climate, but not as much, and probably not at all in a hot arid climate.


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## ed/IL (May 11, 2002)

Perhaps an air to air heat exchange. The air in the pipe cools the exchange.


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## fishhead (Jul 19, 2006)

This topic is something I've been thinking about for years.

It could also work as a dehumidifier.

By dropping the temp below the dew point the water will drop out. You simply angle your pipe so that it collects where you can harvest it. A former acquaintance said he tested the water from one of his pipes and it tested as triple distilled and had NO mold or dust.

Push the air through the pipe and it comes out cooler and drier. I really don't understand why this isn't common practice except that most builders aren't aware of it. There's also the mindset that if the house is too cold or too hot we just add a bigger furnace/AC instead of more insulation. With the expense of buying and running an air conditioner it makes a lot of sense.

Another design would be to sink a large well (6"), add some gravel to cover the exposed soil, place a smaller pipe inside (but not touch the bottom) and push air down the outside pipe. 

The earth has an infinite capacity to absorb heat and we should be using it.


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## WisJim (Jan 14, 2004)

The earth tubes that I have seen that actually work as they are expected to, in the midwest (Wis-Minn-Iowa), use tubes 12 inches or bigger in diameter, at least 120 to 150 feet long, or more, and are bburied 8 feet to 16 feet deep. Remember, the warm summer air is warming up the earth around the tubes as the air is being cooled on the way to the house, and cooling the earth in the winter, and you need as much earth mass around the tubes as possible. Just burying them 4 feet or so around here means they will reach the above ground temp too quickly to justify the expense of installing the tubes.

Bury them as deep as possible, make them as long and as big diameter as you can afford.


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