Episode-1076- Mark Kirkwood with Follow Up on Air Wells, Aquaponics and More — 16 Comments

  1. Could there be some older printed material from the 1930’s available in France and Germany that would show us how to build theses systems? I would think it would exist if these country’s used this technology prior to and during WWll. How about our international listeners in Europe looking into this and sharing the information?

    • Did an internet search on “air well” and didn’t get much until I put in “rock pile air well” and got this “paper” – Air Wells, Fog Fences & Dew Ponds – Methods for Recovery of Atmospheric Humidity by Robert A. Nelson Copyright 2003

      In the paper is all kinds of stuff (descriptions and photos) from the early 1900s that make what Mark is saying legit. Pretty interesting concept and I’ll stay tuned to see if he can replicate. Makes you wonder what other technology has been “lost”.

      You can find the paper here:


    • I now see Jack is way ahead of me. The paper I cited is actually listed and linked in the sources of the excellent Wikipedia article Jack put a link to in the show notes. It’s hard to get ahead of him! =)

  2. I wonder how much condensate you would get from the earth cooling tubes mentioned in the previous episode. If your underground temperature is lower than the dewpoint you should get condensation. Also I once conected the condensation drain from my a/c to my tomato plants and they did quite well during the summer.

    • I’ll let you know in a couple years, the house I am building uses a (earth tube) heating system with counter-flow heat exchangers to wring the water out of the air before entering the house, I plan to capture it for domestic use, though it will by no means be the only source of potable water.

  3. Thanks for the thinking outside the box show. I’ll be looking further into dew ponds. It seems greenhouses would be a source for dew as well given the heat in addition to metal roofs. With the continuing drought in Texas we are looking at all possibilities for capturing water for irrigation and gardening, especially ones that don’t require much if any power to maintain.

  4. It seems to me the best way to maximize the amount of water this system would harvest would be to maximize the air flow through it. It was mentioned in the podcast about putting piping in up the middle for air flow. If you did this with a large perforated PVC standpipe up through the middle about 90% of the height, then switched to solid pipe that extended about 20′ a above the top of the pile, and painted the exposed pipe black you would have a heck of a solar chimney. This would suck a lot more air through the mass an should therefore yield a lot more water.

  5. If the first HOA Board approved the structures, there is a possible suit vs the new board under a theory of detrimental reliance. Although there are new people on the board, the board is legally the same entity and could be held liable for reneging on allowing construction.

  6. I was really curious about the air wells, so I started with Wiki. The rock approach seems like an awful lot of work for moderate and mixed results according to what’s there, but worth exploring. More importantly the concept has been more formally explored and implemented using other methods that look much less labor intensive.

  7. The flaw I’ve seen in all of the water vapor condensation approaches is that they fail to 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)

    Using a sky radiation approach to cooling your condenser core, if the latent heat of vaporization of water is 2.26 × 106 J/kg a 1 m2 radiator can provide 50 W/m2 of cooling, enough to condense 1 g of water in 45 s; 1 kg in 12.6 hr; or 1.9 kg per day. Reportedly production rates in the Southwest U.S. can average about 2 liters per day in the winter to over 6 liters per day during the summer, per square meter.” At the low end 10 m2 (1/4 acre) of radiators cooling humid air could produce 19 L of water per day. The humid air must of course be moved thru the cooling unit, and the “coolness” used to change air temperature recovered during expulsion of the “dried” air.

    A commercial, powered water condenser is sold under the name Aqua-Cycle, invented by William Madison, introduced in 1992. It resembles a drinking fountain and functions as such, but it is not connected to any plumbing. It contains a refridgerated dehumidifier and a triple-purification system (carbon, deionization, and UV light) that produces water as pure as triple-distilled. Under optimal operating conditions (80o/60% humidity) the unit claims to produce up to 5 gallons daily.


    At any given pressure and temperature, in a fixed volume only a limited amount of water will evaporate into vapor, the limit is referred to as the dew/saturation point. A cubic meter of normal sea level air has a mass of 1.292 kilo. A cubic meter of water vapor at sea level pressure has a mass of .804 kilo, this would occur at a temperature of 100C (212F).

    At 0 C (32 F), saturation point is about 1.1 gm of water per cubic meter. A rule of thumb is that raising the air temperature 18°F (10°C) doubles its moisture capacity. This means that air at 86°F (30°C) can hold eight times as much water as air at 32°F.

    Degrees C Degrees F Gram H2O
    0 32 1.1
    10 50 2.2
    20 68 4.4
    30 86 8.8
    40 104 17.6
    50 122 35.2
    60 140 70.4
    70 158 140.8
    80 176 281.6
    90 194 563.2
    100 212 1126.4

    Relative humidity is the percentage of water vapor present as compared to how much there could be at the present temperature.

    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.

    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.

  8. I had a great time at Mark’s workshop this weekend with fellow TSP’ers. I think we stole this thunder on the potential social collapse and how screwed the economy is and he was preaching to the choir about existing issues, problems and concerns, but it allowed us to get to the cool stuff, old tech. He also taught some really cool building designs and construction techniques. We checked out the iron butterfly, cool!

    I enjoyed talking over all sorts of great simple technologies and the air well was a hot topic. I suggest we all try any and every idea we can think of and report back.

    I’m interested in the Trompe,
    It seems to be very doable with a lot of applications. Thanks Mark

  9. After hearing today’s description of airwells, gravel piles, etc, I was reminded of something from the last podcast “Episode-1075- Jim Phillips on Cold Weather Survival”

    Remember when Jim Phillips was describing the reason why ice forms on the inside of Gortex for folks. The water vapor created by your body heat can’t escape. The foam coats you’re suppose to make must not be ‘water-proof’, but should be breathable. Water vapor naturally wants to leave your body (where it is warm) and escape into the cold winter air, as the cold air acts like a vacuum (more or less air pressure?)

    No wonder the air sucks into these air wells, as it is much colder inside.

  10. I did about five minutes worth of searching on the net and found that Ziebold greatly overestimated the usefulness of air wells made from gravel (pea-sized, not cantaloupe). From what I read It looks like a thin foil with a combination of rough hydrophobic and smooth hydrophobic material has proven to be the most effective way to collect atmospheric water in India without power. With power, I think a air compressor mentioned briefly during the podcast could do a substantially better job. The more mass, the harder it would be to cool below the dew point (atmospherically, anyway). That said, I am always willing to repeat an experiment though I would start on a smaller scale in a controlled environment. Sorry to be so critical, but this is the information I found. Link to article:

    • Found a really amazing charity that helps developing countries with an abundance of fog (mountain regions mostly, though I am sure sea-side areas could also benefit) build water collectors. A large unit can produce between 53-130 gallons of water per day and cost them about $400. It then needs to be cleaned up a little but not much as the only contaminates come from dirt/flora/fauna on the mesh and gutters. It’s basically distilled water. Pretty cool. The organizations website is: