Sustainable Water from the Air

An air well or aerial well is a structure or device that collects water by promoting the condensation of moisture from air.

• High mass: Passive. High-mass air wells were used in the early 20th century, but are not very effective. They use a large mass which evens out the temperature between night and day, causing warm moist air to condense on the mass which is still cool from the night.
• Radiative: From the late 20th century onwards, passive low-mass, radiative collectors proved to be much more successful. A radiative air well is designed to cool a substrate by radiating heat to the night sky. The substrate has a low mass so that it cannot hold onto heat, and it is thermally isolated from any mass, including the ground^
• Active: Basically dehumidifiers; works well, but require energy, so not generally economical. New, innovative designs seek to minimise the energy requirements of active condensers or make use of renewable energy resources+

The most basic and somewhat effective version is dew collection with mulch, cover crops (e.g. grass) or horizontal mesh. The key is thermal connection with the earth to provide a cool surface for the water to condense onto, combined with gravity to transport the water deeper, and then thermal insulation from the next days sun. Mulch collects more if it has a larger surface area (e.g. straw, fine particle mulches) but retains more if it has a lower surface area (e.g. bark, large chips).

Moisture Collection via Adsorption over Day/Night cycles

Google Photo's album and links for a very low cost system inspired by research from MIT which was able to produce more than 3 cups per square yard per day. Research is ongoing.

Dew Collection

Another system is fog or dew collection. Here, the moisture already coming out of suspension in the air is simply collected and encouraged to aggregate by structures or coatings which alternate hydrophilic^ and hydrophobic^ surfaces. The water collects on the surfaces which attract water, and when that space is filled, will "overflow" or run off that surface and not stick to the surfaces which repel water. Efficiency improvements of over 10 times are said to be possible over standard surfaces.

Since saturated air is hydrophobic, a mesh works as such a surface, but has the problem of the droplets passing through the opening of the mesh and not being captured. This can be improved by charging the air with one polarity and the mesh with the other.^ Like powder coating paint.

Another improvement is to use only the vertical wires in the mesh, which avoids the droplets becoming "stuck" on the horizontal wires.^

Air carries more water as temperature increases. For example, at 80'c 1kg of air will be saturated with about 0.26 Kg more water than it will at 30'c.
0.03 Kg/m³ of vapor at 30'C and 0.29 kg/m³ at 80'C

See also:

• https://ethz.ch/en/news-and-events/eth-news/news/2021/06/harvesting-drinking-water-from-humidity.html
  https://www.science.org/doi/10.1126/sciadv.abf3978 publication A glass plate is placed in a protective cone, which shields the plate from sources of heat; from the earth, surroundings, solar radiation, etc... The cooler plate causes condensation of the surrounding warmer air. The heat of condensation is transmitted through the plate, up, and radiated out the top into space. A special hydrophobic coating on the bottom prevents water accumulation on the plate, and ensures that it drips down into a catchment below. A foil coating on the top of the plate helps to radiate heat away at a wavelength which avoid absorption by the atmosphere.

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• https://www.youtube.com/watch?v=KlUQ1pneow8 San Diego local reviews a company that makes an air water collection system. ~$6500 installed for 15 years of ~a gallon of water a day. Loud fans during the day. Required mineral packs taste a bit weird. Works in as little as 10% humidity. Can not use in colder climates.+
• https://www.youtube.com/watch?v=WTKyWcACLY4 Use activated carbon felt to increase the surface area of water being evaporated and to increase the heat capture from the sun for solar still. Combine with flower arranging foam to suck up water+
• https://www.nature.com/articles/s41598-020-58405-9 Reversible Atmospheric Water Harvesting Using Metal-Organic Frameworks. "Zr-MOF-808 can produce up to 8.66 LH2O kg−1MOF day−1, "+
• https://news.mit.edu/2020/solar-extracts-drinkable-water-1014 Production rate of about 0.8 liters of water per square meter per day. Day / night cycle. 2 zeolite beds, one evaporates and then cools on the back of the second to increase efficiency.
  https://www.cell.com/joule/fulltext/S2542-4351(20)30444-X The paper referenced in the MIT news item.
   
• https://pubs.acs.org/doi/10.1021/acscentsci.9b00745 "Metal-organic framework, MOF-303, [Al(OH)(PZDC), PZDC = 1H-pyrazole-3,5-dicarboxylate] can perform an adsorption–desorption cycle within minutes under a mild temperature swing, which opens the way for high-productivity water harvesting through rapid, continuous water collection cycles."+
• https://www.researchgate.net/publication/325656051_Practical_water_production_from_desert_air Solar energy, buried in earth. 100mg / day in arid climate.+
• http://science.sciencemag.org/content/early/2017/04/12/science.aam8743 "We report the design and demonstration of a device based on porous metal-organic framework-801 [Zr6O4(OH)4(fumarate)6] that captures water from the atmosphere at ambient conditions using low-grade heat from natural sunlight below one sun (1 kW per square meter). This device is capable of harvesting 2.8 liters of water per kilogram of MOF daily at relative humidity levels as low as 20%, and requires no additional input of energy."+
• https://www.forbes.com/sites/afdhelaziz/2019/01/10/the-power-of-purpose-how-x-prize-winners-skysourceskywater-alliance-turn-air-into-clean-water/#3f1f89f83813 2000 liters of water a day, using biogas as fuel to keep energy costs down.
• http://inhabitat.com/harvard-taps-biomimicry-to-harvest-water-from-thin-air/ +
• http://www.slideshare.net/sustenergy/2nd-csp-training-series-solar-desalination-12?next_slideshow=1 Interesting slide show about desalination. Skip to slide 14 for Humidification-Dehumidification process which applies here.
• https://www.youtube.com/watch?v=7I4AeptruZ4 Re-invention (?) of Airdrop Irrigation by USC student Konstantin Avdienko. Air is pumped by a small turbine powered by a solar panel into a copper tube which is buried in the ground and stuffed with copper wool. Air is cooled by the colder temperature of the ground, the water condenses and slides down into the reservoir+
• http://www.water-gen.com/ Active Military grade systems from Israel Patent US20110048039+

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• http://fontus.at/ "Self filling" water bottle using solar PV and peltier cooling with hydrophilic^ and hydrophobic^ surfaces to condinse water from the air. As of 201601, pre-crowd funding "vaporware".
• http://www.barixa.net/fogquest-manual_2011.pdf +
• http://www.akvopedia.org/wiki/Fog_collection_and_storage +
• http://www.fogquest.org Non-profit helps setup fog collectors. A test unit costs as little as $75 to make from "35% shade coefficient, Raschel weave, u.v. protected polypropylene or polyethylene mesh". It does require fog, (not haze or high humidity) to capture water.
• http://www.australasianscience.com.au/article/issue-may-2010/can-mimicking-nature-quench-our-thirst.html In a 2001 paper published in Nature, Andrew Parker and Chris Lawrence of The University of Oxford demonstrated that the Stenocara exoskeleton consists of a near-random array of bumps approximately 0.5⬓1.5mm (0.02-0.06") apart and 0.5mm (0.02") in diameter on top of a smooth and waxy background. The bumps were hydrophilic (water-loving) while the waxy background was particularly water-repellent. ...moisture rapidly condenses on the bumps. Re-evaporation is minimal due the reduced surface area of bumps, so each droplet of water grows with continued condensation of water until it completely covers each hydrophilic bump. The water droplet then rolls down...
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• http://www.decatur.de Computes the dew point or frost point temperatures at a given ambient temperature and relative humidity.+
• http://www.google.com/patents/US4351651 "Apparatus for extracting potable water"+
• http://books.google.com/books?id=eAAAAAAAMBAJ&lpg=PP1&pg=PA146 4 rigid plastic pipes, 1.25 diameter and 8' long buried between 2 and 6 feet underground collect between 6 and 21 liters a day of water when air temperatures are in the 70's and humidity in the 80's+
• http://www.cnn.com/2014/04/24/tech/innovation/machine-makes-drinking-water-from-air/ Very expensive, high end, active system. Produces 65-210 gallons of potable water a day. Uses two cents' worth of electricity to produce a liter of water.+
• http://www.islandsky.com/ Commercial and smaller systems. Claims 7 to 10 gallons a day and costs as low as  2 Kilowatt hours or $0.16 per gallon (?!)
• http://en.wikipedia.org/wiki/Air_well_(condenser)
• https://www.google.com/?q=airdrop+irrigation The Airdrop irrigation system is a low-tech, self sufficient solar powered solution: an innovation bread of comprehensive investigations into rural agricultural environments, developed through working with irrigation manufacturers and local farmers, and refined by extensive prototyping with successful results. The final prototype of a scaled down unit produced close to a liter of water out of the air in a day. Further testing in a variety of conditions is necessary to confirm the results.+
• http://books.google.com/books/about/Dew_Harvest.html?id=r52bwys37WYC Dew Harvest: To Supplement Drinking Water Sources in Arid Coastal Belt of Kutch. Girja Sharan
  Foundation Books, 2006+
• http://a2wh.com/ Dessicant absorbs moisture from air blown in by a fan during the night. During the day, airflow is restricted, and a solar still is used to remove the moisture from the dessicant. Fan can be powered via solar PV/battery. $3500 each in small (20) quantities.
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5864962/ Adsorption-based atmospheric water harvesting device for arid climates

My in windows AC unit produces 1 Liter of water per hour at 70% humidity 98'F. +