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/diy/ - Do It Yourself

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389717 No.389717 [Reply] [Original]

Will this idea work?

Cold air from the surface goes down into the ground through pipes, then it is heated up by the earth around it, and it will rise through the taller pipe, turning a small turbine.

>> No.389733

why would the earth me warmer than the air?

also it's going to generate almost zero current

>> No.389736

>why would the earth be warmer than the air?
why is the center of the earth molten?

>> No.389738

>>389733
Once you get like 5 feet into the ground, it stays 50-55F all year round. That's why underground houses/basements are always cool.

>> No.389742

>>389736
the depth you would need to dig too for this to work would make it impossible. not to mention, the only areas under the surface with heat are areas with geologic activity, which means *cough* unstable areas, which would collapse the pipe often. all for a system that generates basically nothing

>> No.389744

Probably not you'd have to use a deep hole like a big ass mine to get the kind of temperature to produce meaningful airflow. And it will generate very little power.

>> No.389746

I got this idea after watching a video about solar chimneys. https://www.youtube.com/watch?v=XCGVTYtJEFk

I just need to need if it works in theory. If it does, I'll go dig a ~10 foot hole and try it out.

>> No.389751 [DELETED] 

>>389742
Negative, you don't have to get far below the surface to hit that magic 50º layer. A couple of feet at most. OP's schematic works and there's many well documented examples of people doing this design. Here's one: http://sugarmtnfarm.com/2008/09/05/earth-air-tubes/
The hardest part is keeping vermin and water out of the underground portion.

Note that this is almost never used as a sole heat source, but usually as supplemental passive heat.

>> No.389752

weak airflow of convection system would likely not turn a turbine very quickly...

maybe if this was the input side to a rocket stove, and you used the stove's draw to pull air through the turbine? still, it probably wouldnt generate very much electricity...

>> No.389754

>>389742
Negative, you don't have to get far below the surface to hit that magic 50º layer. A couple of feet at most. OP's schematic works and there's many well documented examples of people doing this design. Here's one:

http://sugarmtnfarm.com/2008/09/05/earth-air-tubes/
The hardest part is keeping vermin and water out of the underground portion.

Note that this is almost never used as a sole heat source, but usually as supplemental passive heat.

Attempting to use the rising air to drive a turbine and do useful work, though? Good luck with that.

>> No.389764

The theoretical best case is the Carnot Cycle, and your temp difference is abysmal. It would be lousy, which is why real geothermal systems dig deeper and work as heat pumps, not heat engines.

>> No.389766 [DELETED] 
File: 21 KB, 817x639, chimney.png [View same] [iqdb] [saucenao] [google]
389766

>>389754
They didn't say in that video, but it seems to me that there would need to be a rising slope towards the chimney to keep warming air flowing that direction.

>> No.389769
File: 21 KB, 817x639, chimney.png [View same] [iqdb] [saucenao] [google]
389769

They didn't say in that video, but it seems to me that there would need to be a rising slope towards the chimney to keep warming air flowing that direction.

>> No.389786

>>389769
Or you could insulate the downward-sloping section and not transfer heat to the fluid until it's in an upward-sloping section.

Or actually, since we're talking 50 degrees, wouldn't... wouldn't the flow be in the opposite direction anyways, since it's COOLING OFF underground?
>Checks OP again
Fuck it, fuck it all. Just use a low-temperature Rankine or gas-phase Stirling engine with an underground condenser. It'd be more compact, and probably more efficient too.

>> No.389788

>>389769
I've thought that before, but wasn't sure. I thought when some air started moving up and out of the chimney it would pull the air through the piples. Making a slope like that would make construction harder I would think.

>>389786
It is designed for use in cold areas or in the winter. I'll check out Rankine and Stirling engines, thanks.

>> No.389804

>>389788
>I'll check out Rankine and Stirling engines, thanks.
You won't regret it. I built a Stirling engine that runs off the heat of a cup of coffee. They're great for small temperature gradients.
And while you're on that track, you might wanna look at this too, since it's kind of similar to what you're trying to achieve (that is, power from a small natural thermal gradient):
http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion

>> No.389828

In the Spain video the sun heated up the airflow tube.

Any chance this could be utilized along with solar power? Neat concept OP, I think I'll try and make one.

>> No.389833

http://www.greenspec.co.uk/ground-source-heat-pumps.php

>> No.390104
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390104

>>389786
Got any schmatics for building a Stirling?


Photolev successor

>> No.390145

>>389736
>why is the center of the earth molten?

its not, but i see what your shooting for. the answer is gravity and iron.

>> No.390648

>>390104
Not onhand. The one I built was a kit.

But there are a few how-tos on the internet about building simple ones from soda cans.

It's a good idea, I think, to try and optimize a Stirling engine for the temperature range you're working with. I'm actually kind of intrigued by this idea now, so I'll probably look into it further at some point and maybe draw up some schematics myself.

>> No.390668
File: 68 KB, 790x500, Solar_updraft_tower.png [View same] [iqdb] [saucenao] [google]
390668

Hey OP! There's this thing you can use for heat gain! It's called... the sun.

Yep, then sun! Basically the same concept as your idea, but 100x more effective.

>> No.390674
File: 115 KB, 546x401, both?.jpg [View same] [iqdb] [saucenao] [google]
390674

>>390668

>> No.391831

What about doing a closed system with liquids instead?

>> No.391839

>>390674
Solar radiation drops ridiculously fast as you pile dirt on top of the surface?

>>391831
Too dense.

>> No.391858

>>391839
But that's WHY you'd want to use a liquid.
Are you saying that you couldn't get passive convection to happen?
When it got moving, you might actually be able to do some work with it.

>> No.391998

>>389828
Isn't that basically what solar thermal energy systems do? Like solar water heaters, etc?

>> No.392000
File: 29 KB, 320x240, 58207_152168508140647_100000424970457_355714_3935358_n.jpg [View same] [iqdb] [saucenao] [google]
392000

Holy shit this thread. All of my Wat.

GOOGLE GEOTHERMAL POWER

>> No.392019

This has been an idea for some time. They had ideas of one in the sea using temperature difference between the bottom and the top with refrigerant gasses. If you google enviromission you will see their proposals for a solar tower.

>> No.392053

>>392000
All of my Watt*

>> No.392055

>>389717

Sterling Engine

>> No.392060

>>391839
>Solar radiation drops ridiculously fast as you pile dirt on top of the surface?
So have the fluid pass through each sequentially, then.
For OP's scheme, augmented with sunlight:
>Air flows into earth tubes and absorbs geothermal heat
>Air is ducted above ground into greenhouse section and heated further
>Air convects up through turbine and out
Alternatively, using the heat engine scheme such as suggested in >>389786:
>Scenario 1: Ground warmer than air
>Working fluid compressed and piped underground
>Fluid absorbs geothermal heat
>Fluid piped up to surface
>Heated further by a solar concentrator
>Fluid decompresses through turbine/cylinder/etc, performing useful work
>Fluid rejects waste heat @ above-ground heat exchanger
Or, if the ground is cooler than the air, just switch the air- and ground-heat-exchange steps.

>> No.392065

>>389717
actually it would work the other way around. There is a "town" that is completely underground being cooled/heated with this idea. I think it is located in Australia.

>> No.392074

http://www.treehugger.com/wind-technology/Using-solar-energy-create-wind-power.html

This was posted the other day. Not really /diy/, but thought it was relevant.

>> No.392076

OP took a useful design and shat all over it.
This is alot more effective with hot air outside and long preferably wet pipes underground to cool of that air leading into your home. presto free AC.
a turbine driven by heat updraft? thats just plain retarded

>> No.392096
File: 94 KB, 620x426, coober_pedy_house.jpg [View same] [iqdb] [saucenao] [google]
392096

>>392065
No idea about cooling but yes we do have a largely underground town in Australia. Its been like that for many years.

http://en.wikipedia.org/wiki/Coober_Pedy

>> No.392148

>>392076
>This is alot more effective with hot air outside and long preferably wet pipes underground to cool of that air leading into your home. presto free AC.
Not necessarily. Any temperature difference can be exploited.
http://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger