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greening the desert

Water from thin air

Posts: 1502

Location: Chihuahua Desert

posted 13 years ago

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This was pretty impressive: http://www.gizmag.com/airdrop-wins-james-dyson-award/20471/

Basically, they pull air down through a tube buried in the ground, which makes the water vapor condense, and gets stored in an underground container. Then, it is pumped through an irrigation system.

It would be cool to open source something like this.

I could see a similar device being made for newly planted trees in an arid food forest. The water reservoir could just overflow into the surrounding soil, or maybe make a wick system. So, then, the only moving parts would be the little fan that pushed air through the system. If you could pull air from beneath a canopy of plants, the humidity would be higher, and you'd get more water.

What do you guys think?

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Matthew Hammell

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Location: Australia, NSW

posted 13 years ago

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I think this is a brilliant idea
One could make a version of it yourself and use it in your vege gardens to automatically irrigate
no more watering your vege patch more time for laying in the hammock !

Abe Connally

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Location: Chihuahua Desert

posted 13 years ago

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it would be cool if we could devise a low tech approach, maybe a tube with a solar chimney to pull the air through.

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posted 13 years ago

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Uncle Owen forced luke skywalker to work on /repair these .
j/k

Looks like something we can use in the gulf coast. We get some seerious humidity here.

Abe Connally

Posts: 1502

Location: Chihuahua Desert

posted 13 years ago

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wow, only 4 posts to get a Star Wars reference. I'm impressed!

2 things you need to condense water from the air - humidity and low temperature. I remember somewhere seeing that it takes about a 30 degree difference to reach the dewpoint, but I imagine that depends on the relative humidity.

In my climate, we are rarely above 30% humidity. But, the daily temperatures can get up past 90, especially in the summer. So, to pull water out of the air, I need to get the copper coil to 60 degrees or less. That could prove difficult, even at 2 m depth, it is probably about 65-70 here. The other option would be to increase the temperature of the air before it enters the copper tubing, raise it beyond 100 degrees.

That's assuming I need a 30 degree difference. Over time, you will be warming up the ground around the copper pipe, so it will becoming less effective.

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Xisca Nicolas

pollinator

Posts: 1981

Location: La Palma (Canary island) Zone 11

I like...

posted 13 years ago

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I saw it before, didn't we talk about water harvest in another post before?
Yes, ground warming will be a problem after a while...

Good for deserts, that have the greatest temperature gaps.
Abe, think about night use for more degrees difference.

I also wonder about the problem to lower air humidity... if the harvest is very efficient!

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Abe Connally

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Location: Chihuahua Desert

posted 13 years ago

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we may have discussed this before. Not sure.

Night use would definitely help, though, technically, you might have a situation where the night air temp is lower than the ground temp.

I doubt this little thing could be efficient enough to make a significant dent in air humidity, unless millions of them were being used in an area.

I'm convinced that there is a very narrow climate window where a device like this can work. High humidity air, low ground temps, high air temps. Most places like that don't really need more water (tropics).

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duane hennon

gardener

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Location: western pennsylvania zone 5/a

posted 13 years ago

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this is similar to the one greenhouse design that pulled warm moist air down into the bed and returned cooler dryer air
it was discussed on the greenhouse threads

also another version draws warm moist air from outside into a basement where it condenses into a container
this was for drinking water
I'll try to find the info on that

Matthew Hammell

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Location: Australia, NSW

posted 13 years ago

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Abe upon further research its not a 30 degree difference required
the guy has it working with a 20 degree difference
also he uses copper wool inside his pipe to slow the air down
which may be a problem for making one ourselves

Marc Troyka

pollinator

Posts: 372

Location: East Central GA, Ultisol, Zone 8, Humid

posted 13 years ago

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Earth tubes + solar chimney will produce water as a byproduct as long as the soil temp is low enough and the humidity high enough. There's also some special plastic things you can get that work by radiating off heat at night. I don't think collecting water from humidity in the air is necessarily practical everywhere, though.

Abe Connally

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Location: Chihuahua Desert

posted 13 years ago

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20 degree difference? That would make it a bit easier.

Copper wool in the pipe is pretty easy, really. That adds a lot of surface area, too.

Personally, I would work with something other than copper ($$$$$)

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Abe Connally

Posts: 1502

Location: Chihuahua Desert

posted 13 years ago

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ok, the dew point is not based on a set temperature difference.

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

Look at the 30% humidity line. If the air temp is 90 degrees, the dew point is about 55 degrees. That's a typical humidity level for semi-arid areas (ones that could benefit from this technology). You are gong to have a hard time finding 55 degree areas under ground, here. So, to make it work, you will either have to increase the relative humidity of the air, or increase the temperature, or both.

20 degree difference would require 50% humidity. While not impossible, it is not common in dry areas.

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duane hennon

gardener

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Location: western pennsylvania zone 5/a

posted 13 years ago

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I think the relative humidity applies to the conditions inside the pipe, not necessarily outside air,
the increases surface area and lower temps may help collect moisture, which would increase the humidity in the pipe
which could "prime" the device
i don't know for sure, just thinking outloud

Abe Connally

Posts: 1502

Location: Chihuahua Desert

posted 13 years ago

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possibly, but then the water runs down into the tank below.

The surface area and lower temps try and approach the dew point, but you still need a high relative humidity to make this work. I don't see it being effective in dry climates.

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Robert Ray

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Location: Cascades of Oregon

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posted 13 years ago

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A little differnt harvesting method.

http://www.utne.com/2000-07-01/CloudHarvest.aspx

Our inability to change everything should not stop us from changing what we can.

Mike Turner

pollinator

Posts: 508

Location: Upstate SC

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posted 13 years ago

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That's how a dew ponds works. The floor of the pond is insulated from the underlying soil so that it can cool off quickly at night and the water condensed collects at the deep center of the pond. A dew pond is self regulating (outside of rainfall) in that as the water level rises, less of the water condensing pond floor is exposed, and so less dew is collected. Draw down the water level and more dew is condensed as more of the pond's floor is exposed. The dew pond technology is 1000's of years old.

duane hennon

gardener

Posts: 843

Location: western pennsylvania zone 5/a

posted 13 years ago

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here's an good article
http://www.rexresearch.com/airwells/airwells.htm

Air Wells, Fog Fences & Dew Ponds

Methods for Recovery of Atmospheric Humidity

by

Robert A. Nelson

Abe Connally

Posts: 1502

Location: Chihuahua Desert

posted 13 years ago

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yeah, I'm familiar with that site and airwells and dew ponds.

The thing is, for all of these things, you are going to need a basic humidity to air temperature ratio for any of them to work. Low humidity just doesn't work well unless you have huge temperature swings.

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