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
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
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).
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
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
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
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
"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."+
Solar energy, buried in earth. 100mg / day in arid
"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."+
2000 liters of water a day, using biogas as fuel to keep energy costs down.
Interesting slide show about desalination. Skip to slide 14 for
Humidification-Dehumidification process which applies here.
(?) 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
http://www.water-gen.com/ Active Military grade systems
from Israel Patent
http://fontus.at/ "Self filling" water bottle
using solar PV and peltier cooling with
to condinse water from the air. As of 201601, pre-crowd funding "vaporware".
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
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 0.5â¬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...
http://www.decatur.de Computes the dew point or frost point
temperatures at a given ambient temperature and relative
http://www.google.com/patents/US4351651 "Apparatus for
extracting potable water"+
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+
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
and smaller systems. Claims 7 to 10 gallons a day and costs as low as 2
Kilowatt hours or $0.16 per gallon (?!)
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.+
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.
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.
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