Joshua Myrvaagnes wrote:
Why do you ask, is there something you need to modify or just avoiding building something tall that could fall over?
I have an idea for a portable peasant's air well for watering plants. I haven't quite formed the idea enough yet to share, and it certainly wouldn't be suitable for drinking water. However, the theory is it will help the plants around it grow during our drought, so I've made a couple and put them in the field (one near lentils, one near barley - both have roots that establish during the rainy season) to see if it improves the yield compared to the rest of the row without air wells.
That's really where our water shortage hits us. We have ample well water for humans, critters, and the kitchen garden, but I want to grow some staple crops in an area with excessively good drainage during the drought. This is where I think peasant air wells might help the most (coupled of course with soil improvement, terracing and other permaculture techniques)
Some areas may have more favorable conditions than others. However, air always contains a certain amount of water, irrespective of local ambient temperatures and humidity conditions. This makes it possible to produce water from air almost anywhere in the world. Locations with high rates of aerosol and humidity are best to install a condenser.
sounds like it works best in fog; they don't have specific numbers yet, 100 litres/day seems to be in ideal conditions only. But if you can get 5 and that's what that gimungo stone air well was doing per day then that's amazing.
To be completely honest, my brain has glossed over air saturation temperatures, &c. I knew it all once, but where the devil I hid that information in my brain is a mystery to me. Basically, all I want now is a practical application. We get dew, so if I pile rocks on the south (or perhaps the east) side of the tree, it increases the tree's chances of surviving the drought. Things like that.
Steve Farmer wrote:Just found this thread and it's prompted me to rekindle some ideas I have had in mind for a while.
Firstly want to say that there is no point warming up the air before you condense it. Yes while warmer air has more capacity to carry water, that only matters when it's picking up water, eg when its coming over the sea. Once you're about to condense the water vapour you want to cool it. If you heat it, the amount of water in the air will stay the same, but its relative humidity will decrease, and you will require more energy to cool it.
>>Are you sure about that part? doesn't warmer air have more capacity to absorb water, and therefore absorb more of the water from the cooler air around it (that's farther from your collector)? does anyone who really knows the physics of this want to clear it up?
I have condensation on my window right now, and the window is about room temperature (70 degrees) and the air outside is getting hot from the sun. The sun hasn't hit the window itself yet, but before it got warmed over there was there condensation? I'll have to observe tomorrow morning.
Here's my earliest idea on how to condense water out the air.
Have an enclosed sump/tank of water, enclosed to stop evaporation, and must be in a cool location so possibly underground but at very least in the shade.
Have a connected shallow pond, say 1 cm deep, but with a large surface area. Should also be in the shade but must be exposed to ambient air.
Have the ambient air monitored for humidity and temperature as it comes across the shallow pond.
If the temp of the water in the sump is below the dew point of the ambient air, the pond is filled by pumping from the sump.
If the temp of the water in the pond rises to the same as or above the dew point, it is pumped back into the sump.
So we have a dew pond that is full when it would collect water, and evacuated when it would evaporate. As long as there is no significant change of height between the two then pumping would be very cheap and quick, could be run from a small solar panel.
This idea sounds really interesting, but I didn't quite get it, and it seems like it would lose a lot of water to evaporation? can you make a diagram? maybe th'ats already been answered, haven't read the whole thread yet. thanks!
R Ranson wrote:
I have an idea for a portable peasant's air well for watering plants. I haven't quite formed the idea enough yet to share, and it certainly wouldn't be suitable for drinking water.
That sounds very, very cool. Consider this encouragement to further develop the idea to the point where you can share it. : )
I am currently making a geodesic dome out of 1" EMT and do not have funds to test this idea at the moment. I shared the video to keep the cog wheels in our mind turning Perhaps someone does have the time/funds to test it (or would like to recruit me into there intentional community to test it for them *wink wink*).
Destiny Hagest wrote:This is something they'll actually be building during the upcoming PDC and Appropriate Technology courses at the Lab this summer - in this dry Montana climate, I'm really anxious to see this design in action and track how well it performs.
Link to PDC course Wiki
Anyone have an update? Are there podcasts about this ATC?
Basically it is necessary to cool the air to the "Dewpoint". All of the devices on the web appear to rely on night cooled mass to provide the needed temperature difference, yet leave the device open to daytime heating by the sun. Granted, I find indications that even in the daytime in certain conditions it might be possible to radiate to the sky 100 to 200 BTU per hour, which strictly in math could represent 1 pint or so of operation for every 10 square foot or radiation area.
Once the water has condensed the "dry" air, now cool, needs to be exhausted. This points out the flaw in all of the “air well” devices I have seen. None of them provide for heat exchange directly between the incoming and outgoing air , therefore the "coolness", essential to precipitation, imparted to the incoming air is directly exhausted, and rapidly eroded.
Ideally, there should be sufficient heat exchange between intake and exhaust air that at the pipe open ends, they are virtually at the same temperature, despite being cycled thru a chilled spot. The transition between liquid and vapor water is, absent unknown science or magic, a matter of the transfer of 970 BTU per each pint condensed. (7760 BTU per gallon)
Assume a Tucson fall day with a relative humidity of 7%. There is roughly 7% of 8.8 grams of water in each cubic meter of air (.616 gram). Lower the temperature to 66 F, and relative humidity doubles to 14%. Lower the temperature to 48 F, and relative humidity again doubles, now to 28%.
If we cool air without changing its moisture content, eventually we'll reach a temperature at which the air can no longer hold the moisture it contains. Then water will have to condense out of the air, forming dew or fog. The dewpoint is this critical temperature at which condensation occurs.
But, water does not immediately change state as the temperature reaches the "right" point. The "Latent heat of condensation" (Lc) refers to the heat that must be removed from water vapor for it to change into a liquid. Lc=2500 Joules per gram (J/g) of water or about 600 calories per gram (cal/g) of water.
Specific heat is defined as the amount of heat energy required to raise 1 g of a substance by 1° Celsius. If the specific heat of air is .25 calories per gram of air per degree C change, then each degree C change in a cubic meter represents 323 calories. The specific heat of water is 1 calorie per gram per degree C. In our Tucson fall day above there was .616 grams of water in a cubic meter of air. Air and water vapor together take a change of about 324 calories per degree C. We need to lower the temperature by around 40 C, or get rid of 12,960 calories of heat to reach the dew point. An additional 379 calories of heat needs to be removed to compensate for the latent heat of condensation, for a total of 13,339 calories.
Presenting numbers for perspective. Assume a daily water need of 174 gallons (658.6 liters) - 658,660 grams of water. In a Tucson fall day, each of us would need to "wring" all of the water out of more than a million cubic meters of air (1,069,252) - a cube 100 meters on a side. If the cross section of the cooling tube is a meter, and the device operates 24/7, and the device is 100% efficient, the required flow rate is 12 meter per second. DON’T panic, that’s only about 28 mph. At that speed though, the air must stay in the chilled zone long enough for the vapor to condense.
The heat to be moved is about 14 billion calories. (55.6 million BTU) The water portion of this number is about 450 million calories (1.8 million BTU). Depending on device efficiency, SOME part of the other 1 billion calories should be able to be conserved in a heat exchanger.
Increasing the pressure also changes the dew point. Double the pressure and relative humidity doubles. Assume normal atmospheric pressure of 14 PSI. Pump the fall Tucson air into a tank at 28 PSI and the relative humidity inside is now 14%. Make it 56 PSI - 28%. 102 PSI - 56%. 204 PSI - 102%, and you've got water accumulating in the bottom of the tank.
. They have been used in Persia for a long time. I want to try something like this is Joshua Tree, CA someday.
They use cooling towers as well. The moisture (even in dry climates) will cool rapidly as it travels down the tower, before condensing on the inside of the yakchal. It eventually will help to replenish groundwater and can be captured as well. The base of the yackchals can get so cold that it can keep food at near-freezing temps.
Richard Presley wrote:Heard this on NPR about "fairy circles" in the desert: http://www.npr.org/2013/03/28/175369153/whats-behind-the-fairy-circles-that-dot-west-africa
Interesting how many different ideas tap into the same basic concept.
These remind me of grass rings around ant piles...