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  • From: Lawrence London <lfljvenaura@gmail.com>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: Re: [permaculture] Slope- swales vs. terrace
  • Date: Sat, 7 Mar 2015 20:34:08 -0500

On Fri, Mar 6, 2015 at 7:21 PM, Lawrence London <lfljvenaura@gmail.com>
wrote:
Terraces for water retention, erosion control and gardens/plantings
Swales for waster retention, erosion control and limited plantings before
or after the swales

>From Wikipedia:

The swale concept has also been popularized as a rainwater harvesting and
soil conservation strategy by Bill Mollison, and other advocates of
permaculture. In this context it usually refers to a water harvesting ditch
on contour. Another term used is contour bund[3][4]

Swales as used in permaculture are designed to slow and capture runoff by
spreading it horizontally across the landscape (along an elevation contour
line), facilitating runoff infiltration into the soil. This type of swale
is created by digging a ditch on contour and piling the dirt on the
downhill side of the ditch to create a berm. In arid climates, vegetation
(existing or planted) along the swale can benefit from the concentration of
runoff. Trees and shrubs along the swale can provide shade which decreases
water evaporation.

Berm
>From Wikipedia, the free encyclopedia

A berm is a level space, shelf, or raised barrier separating two areas. It
can serve as a border barrier. The word berm originates in the Middle Dutch
and German berme and came into usage in English via French.[1]
Erosion control

Berms are also used to control erosion and sedimentation by reducing the
rate of surface runoff. The berms either reduce the velocity of the water,
or direct water to areas that are not susceptible to erosion, thereby
reducing the adverse effects of running water on exposed topsoil. Following
the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, the
construction of berms designed to prevent oil from reaching the fragile
Louisiana wetlands (which would result in massive erosion) was proposed
early on, and was officially approved by the federal government in
mid-June, 2010, after numerous failures to stop and contain the oil leak
with more advanced technologies.[2]

Ha-ha
>From Wikipedia, the free encyclopedia

A *ha-ha* (or *ha-ha wall*) is a recessed landscape design element that
creates a vertical barrier while preserving views. The design includes a
turfed <http://en.wikipedia.org/wiki/Sod> incline which slopes downward to
a sharply vertical face, typically a masonry retaining wall. Ha-has are
used in landscape design to prevent access to a garden, for example by
grazing livestock, without obstructing views. In security design, the
element is used to deter vehicular access to a site while minimizing visual
obstruction. The name "ha-ha" derives from the unexpected (i.e., amusing)
moment of discovery when, on approach, the recessed wall suddenly becomes
visible.

Origins

Before mechanical lawn mowers <http://en.wikipedia.org/wiki/Lawn_mower>, a
common way to keep large areas of grassland trimmed was to allow livestock
<http://en.wikipedia.org/wiki/Livestock>, usually sheep, to graze
<http://en.wikipedia.org/wiki/Grazing> the grass. A ha-ha prevented grazing
animals on large estates from gaining access to the lawn
<http://en.wikipedia.org/wiki/Lawn> and gardens adjoining the house, giving
a continuous vista to create the illusion that the garden and landscape
were one and undivided.[1] <http://en.wikipedia.org/wiki/Ha-ha#cite_note-1>[
2] <http://en.wikipedia.org/wiki/Ha-ha#cite_note-2>[3]
<http://en.wikipedia.org/wiki/Ha-ha#cite_note-3>

The ha-ha fit well with Chinese
<http://en.wikipedia.org/wiki/Culture_of_China> gardening ideas of
concealing barriers with nature, but its European origins predate the
European discovery of Chinese gardening.[4]
<http://en.wikipedia.org/wiki/Ha-ha#cite_note-4>

The basic design of sunken ditches is of ancient origin, being a feature of
deer parks in England. The deer-leap or *saltatorium* consisted of a ditch
with one steep side surmounted by a pale (fence) or hedge, which allowed
deer to enter the park but not to leave. Since the time of the Norman
conquest of England
<http://en.wikipedia.org/wiki/Norman_conquest_of_England> the right to
construct a deer-leap was granted by the king, with reservations made as to
the depth of the foss or ditch and the height of the pale or hedge.[5]
<http://en.wikipedia.org/wiki/Ha-ha#cite_note-5> On Dartmoor the deer-leap
was known as a "leapyeat".[6]
<http://en.wikipedia.org/wiki/Ha-ha#cite_note-6>

The concept of the ha-ha is of French origin, with the term being attested
in toponyms in New France <http://en.wikipedia.org/wiki/New_France> from
1686 (as seen in modern times in Saint-Louis-du-Ha! Ha!
<http://en.wikipedia.org/wiki/Saint-Louis-du-Ha%21_Ha%21>), and being a
feature of the gardens of the Château de Meudon
<http://en.wikipedia.org/wiki/Ch%C3%A2teau_de_Meudon>, circa 1700. The
technical innovation was presented in Dezallier d'Argenville
<http://en.wikipedia.org/wiki/Dezallier_d%27Argenville>'s *La théorie et la
pratique du jardinage* (1709), which the architect John James
<http://en.wikipedia.org/wiki/John_James_%28architect%29> (1712) translated
into English:

"Grills of iron are very necessary ornaments in the lines of walks, to
extend the view, and to show the country to advantage. At present we
frequently make thoroughviews, called Ah, Ah, which are openings in the
walls, without grills, to the very level of the walks, with a large and
deep ditch at the foot of them, lined on both sides to sustain the earth,
and prevent the getting over; which surprises the eye upon coming near it,
and makes one laugh, Ha! Ha! from where it takes its name. This sort of
opening is haha, on some occasions, to be preferred, for that it does not
at all interrupt the prospect, as the bars of a grill do."

The etymology of the term is generally given as being an expression of
surprise—someone says "ha ha" or "ah! ah!" when they encounter such a
feature. This is the explanation given in French, where it is traditionally
attributed to Louis, Grand Dauphin
<http://en.wikipedia.org/wiki/Louis,_Grand_Dauphin>, on encountering such
features at Meudon, by d'Argenville (trans. James), above, and by Walpole,
who surmised that the name is derived from the response of ordinary folk on
encountering them and that they were "... then deemed so astonishing, that
the common people called them Ha! Has! to express their surprise at finding
a sudden and unperceived check to their walk." Thomas Jefferson
<http://en.wikipedia.org/wiki/Thomas_Jefferson>, describing the garden at
Stowe <http://en.wikipedia.org/wiki/Stowe_House> after his visit in April
1786, also uses the term with exclamation marks
<http://en.wikipedia.org/wiki/Exclamation_marks>: "The inclosure is
entirely by ha! ha!"[7] <http://en.wikipedia.org/wiki/Ha-ha#cite_note-7>

In Britain, the ha-ha is a feature of the landscape gardens
<http://en.wikipedia.org/wiki/Landscape_garden> laid out by Charles
Bridgeman <http://en.wikipedia.org/wiki/Charles_Bridgeman> and William Kent
<http://en.wikipedia.org/wiki/William_Kent> and was an essential component
of the "swept" views of Capability Brown
<http://en.wikipedia.org/wiki/Capability_Brown>. Horace Walpole
<http://en.wikipedia.org/wiki/Horace_Walpole> credits Bridgeman with the
invention of the ha-ha but was unaware of the earlier French origins.

"The contiguous ground of the park without the sunk fence was to be
harmonized with the lawn within; and the garden in its turn was to be set
free from its prim regularity, that it might assort with the wilder country
without."[8] <http://en.wikipedia.org/wiki/Ha-ha#cite_note-8>

During his excavations at Iona <http://en.wikipedia.org/wiki/Iona> in the
period 1964–1974, Richard Reece discovered an 18th-century ha-ha designed
to protect the abbey from cattle.[9]
<http://en.wikipedia.org/wiki/Ha-ha#cite_note-Reece-9>

Ice houses <http://en.wikipedia.org/wiki/Ice_house_%28building%29> were
sometimes built into ha-ha walls because they provide a subtle entrance
that makes the ice house a less intrusive structure, and the ground
provides additional insulation.[10]
<http://en.wikipedia.org/wiki/Ha-ha#cite_note-10>

Dell (landform) From Wikipedia, the free encyclopedia

In physical geography <http://en.wikipedia.org/wiki/Geography>, a *dell* is
a
small wooded <http://en.wikipedia.org/wiki/Woodland> valley
<http://en.wikipedia.org/wiki/Valley>. Like "dale
<http://en.wikipedia.org/wiki/Dale_%28origin%29>", the word "dell" is
derived from the Old English <http://en.wikipedia.org/wiki/Old_English>
word *dæl*.

Hügelkultur

*Hügelkultur* is a composting <http://en.wikipedia.org/wiki/Composting>
process employing raised planting beds constructed on top of decaying wood
debris and other compostable biomass <http://en.wikipedia.org/wiki/Biomass>
plant materials. The process helps to improve soil fertility, water
retention, and soil warming, thus benefiting plants grown on or near such
mounds.[1] <http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Miles-1>
[2]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Permaculture_Magazine-2>

Hugelkultur bed with wildflower overplanting

Hügelkultur replicates the natural process of decomposition that occurs on
forest floors. Trees that fall in a forest often become nurse logs
<http://en.wikipedia.org/wiki/Nurse_log>[3]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Palmer-3> decaying
and providing ecological facilitation
<http://en.wikipedia.org/wiki/Ecological_facilitation> to seedlings. As the
wood decays, its porosity increases allowing it to store water "like a
sponge". The water is slowly released back into the environment, benefiting
nearby plants.[1]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Miles-1>

Mounded hügelkultur beds are ideal for areas where the underlying soil is
of poor quality or compacted. They tend to be easier to maintain due to
their relative height above the ground.[3]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Palmer-3> The beds
are usually about 3 feet (0.91 m) by 6 feet (1.8 m) in area and about 3
feet (0.91 m) high.[1]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Miles-1>
History

Hügelkultur is German word meaning mound culture or hill culture.[4]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Lauterbach-4> It
was practiced in German and Eastern European culture for hundreds of years,[
1] <http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Miles-1>[5]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Martin-5> before
being further developed by Sepp Holzer
<http://en.wikipedia.org/wiki/Sepp_Holzer>, an Austrian
<http://en.wikipedia.org/wiki/Austrians> permaculture
<http://en.wikipedia.org/wiki/Permaculture> expert.[3]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Palmer-3> In
addition, recent permaculture voices such as Paul Wheaton
<http://en.wikipedia.org/wiki/Paul_Wheaton> and Geoff Lawton
<http://en.wikipedia.org/wiki/Geoff_Lawton> advocate strongly for
Hügelkultur beds as a perfect permaculture design.[6]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-6>
Construction
Hügelkultur bed construction, shown without the top layer of soil

In its basic form, mounds are constructed by piling logs, branches, plant
waste, compost and additional soil directly on the ground or in a shallow
swale <http://en.wikipedia.org/wiki/Swale_%28landform%29>.[7]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Hemenway-7>[8]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Feineigle-8>
Mounds may also be made from alternating layers of wood, sod,[9]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Shein-9> compost,
straw, and soil. Although their construction is straightforward, planning
is necessary to prevent steep slopes that would result in erosion.[3]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Palmer-3>[5]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Martin-5> Some
designs recommend that mounds have a grade of between 65 and 80 degrees.[10]
<http://en.wikipedia.org/wiki/H%C3%BCgelkultur#cite_note-Holzer-10>
In his book *Desert or Paradise: Restoring Endangered Landscapes Using
Water Management, Including Lake and Pond Construction*, Holzer describes a
method of constructing Hügelkultur including a design that incorporates
rubbish such as cardboard, clothes and kitchen waste. He recommends
building mounds that are 1 meter (3.3 ft) wide and any length. Mounds are
built in a 0.7 meters (2.3 ft) trench in sandy soil, and without a trench
if the ground is wet.[10]

<>

You can combine swales with Hugelkultur berms which become large fertile
raised beds. Care must be taken when constructing Hugelkultur mounds in
trenches below grade on slopes in impermeable soils; lack of percolation
and drainage may result in trench infill becoming anaerobic and toxic to
most soil life and plants.

<>

Terrace (agriculture)
>From Wikipedia, the free encyclopedia

In agriculture <http://en.wikipedia.org/wiki/Agriculture>, a *terrace* is a
piece of sloped plane that has been cut into a series of successively
receding flat surfaces or platforms, which resemble steps, for the purposes
of more effective farming. This type of landscaping, therefore, is called
*terracing*. Graduated terrace steps are commonly used to farm on hilly or
mountainous terrain. Terraced fields both decrease erosion
<http://en.wikipedia.org/wiki/Erosion> and surface runoff
<http://en.wikipedia.org/wiki/Surface_runoff>, and may be used to support
growing crops that require irrigation, such as rice
<http://en.wikipedia.org/wiki/Rice>. The rice terraces of the Philippine
Cordilleras
<http://en.wikipedia.org/wiki/Rice_Terraces_of_the_Philippine_Cordilleras>
have been designated as a UNESCO World Heritage Site
<http://en.wikipedia.org/wiki/World_Heritage_Site> because of the
significance of this technique.[1]
<http://en.wikipedia.org/wiki/Terrace_%28agriculture%29#cite_note-1>

Terraced paddy fields <http://en.wikipedia.org/wiki/Paddy_field> are used
widely in rice, wheat and barley farming in east
<http://en.wikipedia.org/wiki/East_Asia>, south
<http://en.wikipedia.org/wiki/South_Asia>, and southeast Asia
<http://en.wikipedia.org/wiki/Southeast_Asia>, as well as other places.
Drier-climate terrace farming is common throughout the Mediterranean Basin,
e.g., in Cadaqués <http://en.wikipedia.org/wiki/Cadaqu%C3%A9s>, Catalonia
<http://en.wikipedia.org/wiki/Catalonia>, where they were used for
vineyards, olive trees, cork oak, etc., on Mallorca
<http://en.wikipedia.org/wiki/Mallorca>, or in Cinque Terre
<http://en.wikipedia.org/wiki/Cinque_Terre>, Italy
<http://en.wikipedia.org/wiki/Italy>.

In the South American Andes <http://en.wikipedia.org/wiki/Andes>, farmers
have used terraces, known as *andenes <http://en.wikipedia.org/wiki/Anden>,*
for over a thousand years to farm potatoes
<http://en.wikipedia.org/wiki/Potato>, maize
<http://en.wikipedia.org/wiki/Maize>, and other native crops. Terraced
farming was developed by the Wari' <http://en.wikipedia.org/wiki/Wari%27>
and other peoples of the south-central Andes before 1000 AD, centuries
before they were used by the Inca, who adopted them. The terraces were
built to make the most efficient use of shallow soil and to enable
irrigation <http://en.wikipedia.org/wiki/Irrigation> of crops.

The Inca <http://en.wikipedia.org/wiki/Inca_civilization> built on
these,hereby developing a system of canals
<http://en.wikipedia.org/wiki/Canal>, aqueducts
<http://en.wikipedia.org/wiki/Aqueduct_%28watercourse%29>, and puquios
<http://en.wikipedia.org/wiki/Puquios> to direct water through dry land and
increase fertility levels and growth.[*citation needed
<http://en.wikipedia.org/wiki/Wikipedia:Citation_needed>*] These terraced
farms are found wherever mountain villages have existed in the Andes. They
provided food necessary to support the populations of great Inca cities and
religious centres such as Machu Picchu
<http://en.wikipedia.org/wiki/Machu_Picchu>.

Terracing <http://en.wikipedia.org/wiki/Terrace_%28gardening%29> is also
used for sloping terrain; the Hanging Gardens of Babylon
<http://en.wikipedia.org/wiki/Hanging_Gardens_of_Babylon> may have been
built on an artificial mountain with stepped terraces, such as those on a
ziggurat <http://en.wikipedia.org/wiki/Ziggurat>.[*citation needed
<http://en.wikipedia.org/wiki/Wikipedia:Citation_needed>*] At the seaside
Villa
of the Papyri <http://en.wikipedia.org/wiki/Villa_of_the_Papyri> in
Herculaneum <http://en.wikipedia.org/wiki/Herculaneum>, the villa gardens
of Julius Caesar <http://en.wikipedia.org/wiki/Julius_Caesar>'s
father-in-law were designed in terraces to give pleasant and varied views
of the Bay of Naples.

Terraced fields are common in islands with steep slopes. The Canary Islands
<http://en.wikipedia.org/wiki/Canary_Islands> present a complex system of
terraces covering the landscape from the coastal irrigated plantations to
the dry fields in the highlands. These terraces, which are named *cadenas*
(chains), are built with stone walls of skillful design, which include
attached stairs and channels.[*citation needed
<http://en.wikipedia.org/wiki/Wikipedia:Citation_needed>*]

In old English <http://en.wikipedia.org/wiki/English_language>, a terrace
was also called a "lynch" (lynchet <http://en.wikipedia.org/wiki/Lynchet>).
An example of an ancient Lynch Mill is in Lyme Regis
<http://en.wikipedia.org/wiki/Lyme_Regis>. The water is directed from a
river by a duct along a terrace. This set-up was used in steep hilly areas
in the UK <http://en.wikipedia.org/wiki/UK>.[*citation needed
<http://en.wikipedia.org/wiki/Wikipedia:Citation_needed>*]


Terrace garden
>From Wikipedia, the free encyclopedia

In gardening <http://en.wikipedia.org/wiki/Gardening>, a *terrace* is an
element where a raised flat paved or gravelled section overlooks a prospect
<http://en.wiktionary.org/wiki/prospect>. A raised terrace keeps a house
dry and provides a transition between the hard materials of the architecture
<http://en.wikipedia.org/wiki/Architecture> and softer ones of the garden.
Contemporary

Contemporary terrace gardens, in addition to being in the garden and
landscape, often occur in urban areas and are terrace architecture
<http://en.wikipedia.org/wiki/Terrace_%28building%29> elements that extend
out from an apartment or residence at any floor level other than ground
level. They are often discussed in conjunction with roof gardens
<http://en.wikipedia.org/wiki/Roof_gardens>, although they are not always
true roof gardens, instead being balconies and decks. These outdoor spaces
can become lush gardens through the use of container gardening
<http://en.wikipedia.org/wiki/Container_gardening>, automated drip
irrigation <http://en.wikipedia.org/wiki/Drip_irrigation> and low-flow
irrigation systems
<http://en.wikipedia.org/wiki/Low-flow_irrigation_systems>, and outdoor
furnishings.


Qanat
>From Wikipedia, the free encyclopedia

A *qanāt* (Arabic <http://en.wikipedia.org/wiki/Arabic_language>: *قناة*‎,
Persian <http://en.wikipedia.org/wiki/Persian_Language>: *قنات*) is one of
a series of well-like vertical shafts, connected by gently sloping tunnels.
Qanāts create a reliable supply of water for human settlements and
irrigation <http://en.wikipedia.org/wiki/Irrigation> in hot, arid
<http://en.wikipedia.org/wiki/Arid>, and semi-arid climates.

The qanat technology <http://en.wikipedia.org/wiki/Technology> is known to
have been developed by the Persian people
<http://en.wikipedia.org/wiki/Persian_people> sometime in the early 1st
millennium BC and spread from there slowly westward and eastward.[1]
<http://en.wikipedia.org/wiki/Qanat#cite_note-1>[2]
<http://en.wikipedia.org/wiki/Qanat#cite_note-2>[3]
<http://en.wikipedia.org/wiki/Qanat#cite_note-3>[4]
<http://en.wikipedia.org/wiki/Qanat#cite_note-4>[5]
<http://en.wikipedia.org/wiki/Qanat#cite_note-5>[6]
<http://en.wikipedia.org/wiki/Qanat#cite_note-6>

The value of the qanat is directly related to the quality, volume, and
regularity of the water flow. Much of the population of Iran and other arid
countries in Asia and North Africa historically depended upon the water
from qanats; the areas of population corresponded closely to the areas
where qanats are possible. Although a qanat was expensive to construct, its
long-term value to the community, and thereby to the group that invested in
building and maintaining it, was substantial.[7]
<http://en.wikipedia.org/wiki/Qanat#cite_note-Kheirabadi-7>

Air well
>From Wikipedia, the free encyclopedia

An *air well* may be one of the following:

- Air well (condenser)
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29>, a structure or
device designed to promote the condensation of atmospheric moisture.
- Air well (ventilation)
<http://en.wikipedia.org/wiki/Air_well_%28ventilation%29>, an
architectural feature designed to promote ventilation.

See also

- Atmospheric water generator
<http://en.wikipedia.org/wiki/Atmospheric_water_generator>
- Dew pond <http://en.wikipedia.org/wiki/Dew_pond>
- Fog fence <http://en.wikipedia.org/wiki/Fog_fence>
- Lightwell <http://en.wikipedia.org/wiki/Lightwell>
- Solar chimney <http://en.wikipedia.org/wiki/Solar_chimney>
- Windcatcher <http://en.wikipedia.org/wiki/Windcatcher>

Air well (condenser)

http://en.wikipedia.org/wiki/Air_well_%28condenser%29

An *air well* or *aerial well* is a structure or device that collects water
by promoting the condensation <http://en.wikipedia.org/wiki/Condensation>
of moisture <http://en.wikipedia.org/wiki/Water_vapor> from air.[2]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEPopular_Science1933-2>
Designs for air wells are many and varied, but the simplest designs are
completely passive, require no external energy source and have few, if any,
moving parts.

Three principal designs are used for air wells, designated as high mass,
radiative, and active:

- High-mass air wells were used in the early 20th century, but the
approach failed.[3]

<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimoukNikolayevBerkowicz2006-3>
- From the late 20th century onwards, low-mass, radiative collectors
proved to be much more successful.[3]

<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimoukNikolayevBerkowicz2006-3>
- Active collectors collect water in the same way as a dehumidifier
<http://en.wikipedia.org/wiki/Dehumidifier>; although the designs work
well, they require an energy source, making them uneconomical except in
special circumstances. New, innovative designs seek to minimise the energy
requirements of active condensers or make use of renewable energy
<http://en.wikipedia.org/wiki/Renewable_energy> resources.[*citation
needed <http://en.wikipedia.org/wiki/Wikipedia:Citation_needed>*]


<http://en.wikipedia.org/wiki/File:Atmospheric_Water_Vapor_Mean.2005.030.jpg>
Global atmospheric water vapor for 30 January 2005. Northern hemisphere
winter and southern hemisphere summer.

All air well designs incorporate a substrate with a temperature
sufficiently low so that dew <http://en.wikipedia.org/wiki/Dew> forms. Dew
is a form of precipitation
<http://en.wikipedia.org/wiki/Precipitation_%28meteorology%29> that occurs
naturally when atmospheric water vapour condenses
<http://en.wikipedia.org/wiki/Condensation> onto a substrate. It is
distinct from fog <http://en.wikipedia.org/wiki/Fog>, in that fog is made
of droplets of water that condense around particles in the air.[4]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimouk2000-4>
Condensation releases latent heat <http://en.wikipedia.org/wiki/Latent_heat>
which must be dissipated in order for water collection to continue.[5]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENikolayevBeysensGiodaMilimouk199623.E2.80.9326-5>

An air well requires moisture from the air. Everywhere on Earth, even in
deserts, the surrounding atmosphere
<http://en.wikipedia.org/wiki/Atmosphere> contains at least some water.
According to Beysens and Milimouk: "The atmosphere contains 12,900 km3 (3,000
cubic miles) of fresh water, composed of 98 percent water vapour and 2
percent condensed water (clouds <http://en.wikipedia.org/wiki/Cloud>): a
figure comparable to the renewable liquid water resources of inhabited
lands (12,500 km3)."[4]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimouk2000-4>
The quantity of water vapour contained within the air is commonly reported
as a relative humidity <http://en.wikipedia.org/wiki/Relative_humidity>,
and this depends on temperature—warmer air can contain more water vapour
than cooler air. When air is cooled to the dew point
<http://en.wikipedia.org/wiki/Dew_point>, it becomes saturated, and
moisture will condense on a suitable surface.[6]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-6> For
instance, the dew temperature of air at 20 °C (68 °F) and 80 percent
relative humidity is 16 °C (61 °F). The dew temperature falls to 9 °C
(48 °F) if the relative humidity is 50 percent.[4]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimouk2000-4>

A related, but quite distinct, technique of obtaining atmospheric moisture
is the fog fence <http://en.wikipedia.org/wiki/Fog_fence>.

An air well should not be confused with a dew pond
<http://en.wikipedia.org/wiki/Dew_pond>. A dew pond is an artificial pond
<http://en.wikipedia.org/wiki/Pond> intended for watering livestock. The
name *dew pond* (sometimes *cloud pond* or *mist pond*) derives from the
widely held belief that the pond was filled by moisture from the air.[7]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-7> In
fact, dew ponds are primarily filled by rainwater.[8]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEPugsley1939-8>

A stone mulch <http://en.wikipedia.org/wiki/Mulch> can significantly
increase crop yields in arid <http://en.wikipedia.org/wiki/Arid> areas.
This is most notably the case in the Canary Islands
<http://en.wikipedia.org/wiki/Canary_Islands>: on the island of Lanzarote
<http://en.wikipedia.org/wiki/Lanzarote> there is about 140 millimetres
(5.5 in) of rain each year and there are no permanent rivers. Despite this,
substantial crops can be grown by using a mulch of volcanic stones, a trick
discovered after volcanic eruptions in 1730. Some credit the stone mulch
with promoting dew; although the idea has inspired some thinkers, it seems
unlikely that the effect is significant. Rather, plants are able to absorb
dew directly from their leaves, and the main benefit of a stone mulch is to
reduce water loss from the soil and to eliminate competition from weeds.[9]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-9>
History

Beginning in the early 20th century, a number of inventors experimented
with high-mass collectors. Notable investigators were the Russian
engineer Friedrich
Zibold
<http://en.wikipedia.org/w/index.php?title=Friedrich_Zibold&action=edit&redlink=1>
(sometimes given as Friedrich Siebold[10]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENikolayevBeysensGiodaMilimouk19964-10>),
the French bioclimatologist Leon Chaptal
<http://en.wikipedia.org/w/index.php?title=Leon_Chaptal&action=edit&redlink=1>,
the German-Australian researcher Wolf Klaphake
<http://en.wikipedia.org/wiki/Wolf_Klaphake> and the Belgian inventor Achille
Knapen
<http://en.wikipedia.org/w/index.php?title=Achille_Knapen&action=edit&redlink=1>
.
Zibold's collector
<http://en.wikipedia.org/wiki/File:Zibold_condenser_%28section%29.jpg>
A section through Zibold's dew condenser. (a) is a truncated cone of beach
pebbles <http://en.wikipedia.org/wiki/Pebble> 20 metres (66 ft) in diameter
at the base and 8 metres (26 ft) in diameter at the top. (b) is a concrete
bowl; a pipe (not shown) leads away from the base of the bowl to a
collecting point. (c) is ground level and (d) is the natural limestone base.
[11] <http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-11>

In 1900, near the site of the ancient Byzantine
<http://en.wikipedia.org/wiki/Byzantine> city of Theodosia
<http://en.wikipedia.org/wiki/Feodosiya>, thirteen large piles of stones
were discovered by Zibold who was a forester
<http://en.wikipedia.org/wiki/Forester> and engineer in charge of this area.
[12]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENikolayevBeysensGiodaMilimouk199620.E2.80.9323-12>
Each stone pile covered just over 900 square metres (9,700 sq ft) and was
about 10 metres (33 ft) tall. The finds were associated with the remains of
75-millimetre diameter (3.0 in) terracotta
<http://en.wikipedia.org/wiki/Terracotta> pipes that apparently led to
wells and fountains in the city. Zibold concluded that the stacks of stone
were condensers that supplied Theodosia with water; and calculated that
each air well produced more than 55,400 litres (12,200 imp gal;
14,600 US gal) each day.[10]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENikolayevBeysensGiodaMilimouk19964-10>

To verify his hypothesis Zibold constructed a stone-pile condenser at an
altitude of 288 metres (945 ft) on mount Tepe-Oba near the ancient site of
Theodosia. Zibold’s condenser was surrounded by a wall 1 metre (3 ft 3 in)
high, 20 metres (66 ft) wide, around a bowl-shaped collection area with
drainage. He used sea stones 10–40 centimetres (3.9–15.7 in) in diameter
piled 6 metres (20 ft) high in a truncated cone that was 8 metres (26 ft)
in diameter across the top. The shape of the stone pile allowed a good air
flow with only minimal thermal contact between the stones.[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>

Zibold's condenser began to operate in 1912 with a maximum daily production
that was later estimated to have been 360 litres (79 imp gal; 95 US gal) –
Zibold made no public record of his results at the time.[10]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENikolayevBeysensGiodaMilimouk19964-10>
The base developed leaks that forced the experiment to end in 1915 and the
site was partially dismantled before being abandoned. (The site was
rediscovered in 1993 and cleaned up.)[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>
Zibold's condenser was approximately the same size as the ancient stone
piles that had been found,[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>
and although the yield was very much less than the yield Zibold had
calculated for the original structures, the experiment was an inspiration
for later developers.
Chaptal's collector

Inspired by Zibold's work, Chaptal built a small air well near Montpellier
<http://en.wikipedia.org/wiki/Montpellier> in 1929. Chaptal's condenser was
a pyramidal <http://en.wikipedia.org/wiki/Pyramid_%28geometry%29> concrete
structure 3 metres (9.8 ft) square and 2.5 metres (8 ft 2 in) high, it was
filled with 8 cubic metres (280 cu ft) of limestone
<http://en.wikipedia.org/wiki/Limestone> pieces being about 7.5 centimetres
(3.0 in) in diameter. Small vent holes ringed the top and bottom of the
pyramid. These holes could be closed or opened as required to control the
flow of air. The structure was allowed to cool during the night, and then
warm moist air was let in during the day. Dew formed on the limestone
pieces and collected in a reservoir below ground level. The amount of water
obtained varied from 1 litre (0.22 imp gal; 0.26 US gal) to 2.5 litres
(0.55 imp gal; 0.66 US gal) per day depending on the atmospheric conditions.
[14]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEHills1966232-14>

Chaptal did not consider his experiment a success. When he retired in 1946,
he put the condenser out of order, possibly because he did not want to
leave an improper installation to mislead those who might later continue
studies on air wells.[3]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimoukNikolayevBerkowicz2006-3>
Klaphake's collectors

Wolf Klaphake <http://en.wikipedia.org/wiki/Wolf_Klaphake> was a successful
chemist working in Berlin during the 1920s and 1930s. During that time, he
tested several forms of air wells in Yugoslavia
<http://en.wikipedia.org/wiki/Yugoslavia> and on Vis Island
<http://en.wikipedia.org/wiki/Vis_%28island%29> in the Adriatic Sea
<http://en.wikipedia.org/wiki/Adriatic_Sea>. Klaphake's work was inspired
by Zibold[15]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEKlaphake1936-15>
and by the works of Maimonides <http://en.wikipedia.org/wiki/Maimonides>, a
known Jewish scholar who wrote in Arabic about 1,000 years ago and who
mentioned the use of water condensers in Palestine.[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>

Klaphake experimented with a very simple design: an area of mountain slope
was cleared and smoothed with a watertight surface. It was shaded by a
simple canopy supported by pillars or ridges. The sides of the structure
were closed, but the top and bottom edges were left open. At night the
mountain slope would cool, and in the day moisture would collect on and run
down the smoothed surface. Although the system apparently worked, it was
expensive, and Klaphake finally adopted a more compact design based on a
masonry structure. This design was a sugarloaf
<http://en.wikipedia.org/wiki/Sugarloaf>-shaped building, about 15 metres
(49 ft) high, with walls at least 2 metres (6 ft 7 in) thick, with holes on
the top and at the bottom. The outer wall was made of concrete to give a
high thermal capacity, and the inner surface was made of a porous material
such as sandstone.[16]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200672-16>
According to Klaphake:
“ The building produces water during the day and cools itself during the
night; when the sun rises, the warm air is drawn through the upper holes
into the building by the out-flowing cooler air, becomes cooled on the cold
surface, deposits its water, which then oozes down and is collected
somewhere underneath. It is wrong to think that this process works only on
days with dew, as the inner surface becomes much cooler than one should
expect. In Dalmatia, that day was a rare exception which failed to produce
water.[15]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEKlaphake1936-15>


Traces of Klaphake's condensers have been tentatively identified.[17]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-17>

In 1935, Wolf Klaphake and his wife Maria emigrated to Australia. The
Klaphakes' decision to emigrate was probably primarily the result of
Maria's encounters with Nazi authorities;[18]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENeumann20027-18>
[19]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-uncommon_lives2-19>
their decision to settle in Australia (rather than, say, in Britain) was
influenced by Wolf's desire to develop a dew condenser.[19]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-uncommon_lives2-19>
As a dry continent, Australia was likely to need alternative sources of
fresh water, and the Premier of South Australia
<http://en.wikipedia.org/wiki/South_Australia>, whom he had met in London,
had expressed an interest. Klaphake made a specific proposal for a
condenser at the small town of Cook
<http://en.wikipedia.org/wiki/Cook,_South_Australia>, where there was no
supply of potable water. At Cook, the railway company had previously
installed a large coal-powered active condenser,[20]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-cook_condenser-20>
but it was prohibitively expensive to run, and it was cheaper to simply
transport water. However, the Australian government turned down Klaphake's
proposal, and he lost interest in the project.[21]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-uncommon_lives3-21>
[15]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEKlaphake1936-15>
Knapen's aerial well
[image: Achille Knapen's air well (exterior)]
<http://en.wikipedia.org/wiki/File:Puits_aerien_knappen_trans_83_10.jpg>
Exterior
[image: Achille Knapen air well (interior)]
<http://en.wikipedia.org/wiki/File:Puits_aerien_knappen_trans_83_03.jpg>
Interior.
Achille Knapen air well.

Knapen, who had previously worked on systems for removing moisture from
buildings,[22]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-22>[23]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-23>[24]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-24> was in
turn inspired by Chaptal's work and he set about building an ambitiously
large *puits aerien* (aerial well) on a 180 metres (590 ft) high hill at
Trans-en-Provence <http://en.wikipedia.org/wiki/Trans-en-Provence> in
France.[2]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEPopular_Science1933-2>
[25] <http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-25>
Beginning in 1930, Knapen's dew tower took 18 months to build; it still
stands today, albeit in dilapidated condition. At the time of its
construction, the condenser excited some public interest.[26]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-26>

The tower is 14 metres (46 ft) high and has massive masonry walls about 3
metres (9.8 ft) thick with a number of apertures to let in air. Inside
there is a massive column made of concrete. At night, the whole structure
is allowed to cool, and during the day warm moist air enters the structure
via the high apertures, cools, descends, and leaves the building by the
lower apertures.[27]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-27>
Knapen’s intention was that water should condense on the cool inner column.
In keeping with Chaptal’s finding that the condensing surface must be rough
and the surface tension must be sufficiently low that the condensed water
can drip, the central column's outer surface was studded with projecting
plates of slate <http://en.wikipedia.org/wiki/Slate>. The slates were
placed nearly vertically to encourage dripping down to a collecting basin
at the bottom of the structure.[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>
Unfortunately, the aerial well never achieved anything like its hoped-for
performance and produced no more than a few litres of water each day.[28]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200670-28>
International Organisation for Dew Utilization
[image: Big OPUR Dew Condenser in Corsica]
<http://en.wikipedia.org/wiki/File:Big_Dew_Condenser_in_Corsica.jpg>
Big OPUR Dew Condenser in Corsica
<http://en.wikipedia.org/wiki/File:Dr_Sharan_at_condenser_test_ground.JPG>
A radiative dew condenser test site at village Kothar in the north-west
India near Arabian sea coast.

By the end of the twentieth century, the details of how dew condenses were
much better understood, the key insight being that low-mass collectors that
rapidly lose heat by radiation
<http://en.wikipedia.org/wiki/Thermal_radiation> performed best. A number
of researchers worked on this method.[29]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200622-29>
In the early 1960s, dew condensers made from sheets of polyethylene
<http://en.wikipedia.org/wiki/Polyethylene> supported on a simple frame
resembling a ridge tent were used in Israel to irrigate plants. Saplings
supplied with dew and very slight rainfall from these collectors survived
much better than the control group planted without such aids – they all
dried up over the summer.[30]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEGindel1965-30>
In 1986 in New Mexico <http://en.wikipedia.org/wiki/New_Mexico> condensers
made of a special foil produced sufficient water to supply young saplings.[4
]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimouk2000-4>

In 1992 a party of French academics attended a condensed matter
<http://en.wikipedia.org/wiki/Condensed_matter> conference in Ukraine
<http://en.wikipedia.org/wiki/Ukraine> where physicist
<http://en.wikipedia.org/wiki/Physicist> Daniel Beysens introduced them to
the story of how ancient Theodosia was supplied with water from dew
condensers. They were sufficiently intrigued that in 1993 they went to see
for themselves. They concluded that the mounds that Zibold identified as
dew condensers were in fact ancient burial mounds
<http://en.wikipedia.org/wiki/Tumulus> (a part of the necropolis
<http://en.wikipedia.org/wiki/Necropolis> of antic Theodosia) and that the
pipes were medieval in origin and not associated with the mounds. They
found the remains of Zibold's condenser, which they tidied up and examined
closely. Zibold's condenser had apparently performed reasonably well, but
in fact his exact results are not at all clear, and it is possible that the
collector was intercepting fog, which added significantly to the yield.[10]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENikolayevBeysensGiodaMilimouk19964-10>
If Zibold's condenser worked at all, this was probably due to fact that a
few stones near the surface of the mound were able to lose heat at night
while being thermally isolated from the ground; however, it could never
have produced the yield that Zibold envisaged.[3]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimoukNikolayevBerkowicz2006-3>
[31]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENikolayevBeysensGiodaMilimouk1996-31>

Fired with enthusiasm, the party returned to France and set up the
*International
Organisation for Dew Utilization* (OPUR), with the specific objective of
making dew available as an alternative source of water.[32]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-opur.fr-32>

OPUR began a study of dew condensation under laboratory conditions; they
developed a special hydrophobic <http://en.wikipedia.org/wiki/Hydrophobic>
film and experimented with trial installations, including a 30 square
metres (320 sq ft) collector in Corsica
<http://en.wikipedia.org/wiki/Corsica>.[33]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEMuselliBeysensMilimouk2006-33>
Vital insights included the idea that the mass
<http://en.wikipedia.org/wiki/Thermal_mass> of the condensing surface
should be as low as possible so that it cannot easily retain heat, that it
should be protected from unwanted thermal radiation by a layer of insulation
<http://en.wikipedia.org/wiki/Thermal_insulation>, and that it should be
hydrophobic, so as to shed condensed moisture readily.[34]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200620.E2.80.9328-34>

By the time they were ready for their first practical installation, they
heard that one of their members, Girja Sharan, had obtained a grant to
construct a dew condenser in Kothara, India. In April 2001, Sharan had
incidentally noticed substantial condensation on the roof of a cottage at
Toran <http://en.wikipedia.org/wiki/Toran> Beach Resort in the arid coastal
region of Kutch <http://en.wikipedia.org/wiki/Kutch>, where he was briefly
staying. The following year, he investigated the phenomenon more closely
and interviewed local people. Financed by the Gujarat Energy Development
Agency and the World Bank <http://en.wikipedia.org/wiki/World_Bank>, Sharan
and his team went on to develop passive, radiative condensers for use in
the arid coastal region of Kutch.[35]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan2006Acknowledgement_section-35>
Active commercialisation began in 2006.[36]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-36>

Sharan tested a wide range of materials and got good results from galvanised
iron <http://en.wikipedia.org/wiki/Galvanised_iron> and aluminium
<http://en.wikipedia.org/wiki/Aluminium> sheets, but found that sheets of
the special plastic developed by the OPUR just 400 micrometres (0.016 in)
thick generally worked even better than the metal sheets and were less
expensive.[37]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200627-37>
The plastic film, known as OPUR foil, is hydrophilic and is made from
polyethylene mixed with titanium dioxide
<http://en.wikipedia.org/wiki/Titanium_dioxide> and barium sulphate
<http://en.wikipedia.org/wiki/Barium_sulphate>.
Types

There are three principal approaches to the design of the heat sinks that
collect the moisture in air wells: high mass, radiative and active. Early
in the twentieth century, there was interest in high-mass air wells, but
despite much experimentation including the construction of massive
structures, this approach proved to be a failure.[38]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEAlton_StewartHowell20031014-38>

>From the late twentieth century onwards, there has been much investigation
of low-mass, radiative <http://en.wikipedia.org/wiki/Thermal_radiation>
collectors; these have proved to be much more successful.
High-mass

The high-mass air well design attempts to cool a large mass of masonry with
cool nighttime air entering the structure due to breezes or natural
convection. In the day, the warmth of the sun results in increased
atmospheric humidity. When moist daytime air enters the air well, it
condenses on the presumably cool masonry. None of the high-mass collectors
performed well, Knapen's aerial well being a particularly conspicuous
example.

The problem with the high-mass collectors was that they could not get rid
of sufficient heat during the night – despite design features intended to
ensure that this would happen.[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>
While some thinkers have believed that Zibold might have been correct after
all,[39]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-popular_science_1992-39>
[40]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-new_scientist_2005-40>
an article in *Journal of Arid Environments* discusses why high-mass
condenser designs of this type cannot yield useful amounts of water:
“ We would like to stress the following point. To obtain condensation, the
condenser temperature of the stones must be lower than the dew point
temperature. When there is no fog, the dew point temperature is always
lower than the air temperature. Meteorological data shows that the dew
point temperature (an indicator of the water content of the air) does not
change appreciably when the weather is stable. *Thus wind, which ultimately
imposes air temperature to the condenser, cannot cool the condenser to
ensure its functioning.* Another cooling phenomenon — radiative cooling —
must operate. It is therefore at night-time, when the condenser cools by
radiation, that liquid water can be extracted from air. It is very rare
that the dew point temperature would increase significantly so as to exceed
the stone temperature inside the stone heap. Occasionally, when this does
happen, dew can be abundant during a short period of time. This is why
subsequent attempts by L. Chaptal and A. Knapen to build massive dew
condensers only rarely resulted in significant yields. [Emphasis as in
original][3]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimoukNikolayevBerkowicz2006-3>


Although ancient air wells are mentioned in some sources, there is scant
evidence for them, and persistent belief in their existence has the
character of a modern myth <http://en.wikipedia.org/wiki/Urban_legend>.[3]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimoukNikolayevBerkowicz2006-3>
Radiative
<http://en.wikipedia.org/wiki/File:Radiative_condenser_%28section%29.jpg>
Diagram of a radiative collector. (a) radiating/condensing surface, (b)
collecting gutter, (c) backing insulation, (d) stand.
<http://en.wikipedia.org/wiki/File:Dew_water_from_metal_roofs.jpg>
Structures with metal roofing, such as this one, can be used to harvest
dew water simply by adding gutters and, for increased output, a layer of
insulation underside. Without the insulation the output is nearly half of
that from plastic condensers.
<http://en.wikipedia.org/wiki/File:Condenser_on_roof_Sayara.JPG>
An example of a condenser-on-roof installation, condenser made of plastic
film with special properties, with insulation layer between film and
concrete roof surface. This installation is on school buildings at Sayara
(Kutch, India). Unlike metal roofs, concrete roofs do not attract
condensation without any treatment, hence the need for an external
condenser. The output from such condensers is nearly two times higher than
from a bare metal roof, all else remaining constant.

A radiative air well is designed to cool a substrate by radiating heat
<http://en.wikipedia.org/wiki/Thermal_radiation> 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.[41]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-41> A
typical radiative collector presents a condensing surface at an angle of
30° from the horizontal. The condensing surface is backed by a thick layer
of insulating material such as polystyrene foam
<http://en.wikipedia.org/wiki/Polystyrene_foam> and supported 2–3 metres
(7–10 ft) above ground level. Such condensers may be conveniently installed
on the ridge roofs of low buildings or supported by a simple frame.[42]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200620.E2.80.9339-42>
Although other heights do not typically work quite so well, it may be less
expensive or more convenient to mount a collector near to ground level or
on a two-storey building.[43]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200640.E2.80.9359-43>

The 600 square metres (6,500 sq ft) radiative condenser illustrated near
the start of this article is built near the ground. In the area of
north-west India where it is installed dew occurs for 8 months a year, and
the installation collects about 15 millimetres (0.59 in) of dew water over
the season with nearly 100 dew-nights. In a year it provides a total of
about 9,000 litres (2,000 imp gal; 2,400 US gal) of potable water
<http://en.wikipedia.org/wiki/Drinking_water> for the school which owns and
operates the site.[1]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan2007-1>

Although flat designs have the benefit of simplicity, other designs such as
inverted pyramids and cones can be significantly more effective. This is
probably because the designs shield the condensing surfaces from unwanted
heat radiated by the lower atmosphere, and, being symmetrical, they are not
sensitive to wind direction.[44]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEClusOuazzaniMuselliNikolayev2006-44>

New materials may make even better collectors.[45]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200620-45>
One such material is inspired by the Namib Desert beetle
<http://en.wikipedia.org/wiki/Namib_Desert_beetle>, which survives only on
the moisture it extracts from the atmosphere. It has been found that its
back is coated with microscopic projections: the peaks are hydrophilic and
the troughs are hydrophobic.[46]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-46>[47]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-47>[48]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-48>
Researchers at the Massachusetts Institute of Technology
<http://en.wikipedia.org/wiki/Massachusetts_Institute_of_Technology> have
emulated this capability by creating a textured surface that combines
alternating hydrophobic and hydrophilic materials.
Active

<http://en.wikipedia.org/wiki/File:Yeti_AC-12_atmospheric_water_generator.jpg>
A commercially produced atmospheric water generator intended for
residential use.[49]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-49>
Main article: Atmospheric water generator
<http://en.wikipedia.org/wiki/Atmospheric_water_generator>

Active atmospheric water collectors have been in use since the
commercialisation of mechanical refrigeration
<http://en.wikipedia.org/wiki/Refrigeration>. Essentially, all that is
required is to cool a heat exchanger
<http://en.wikipedia.org/wiki/Heat_exchanger> below the dew point, and
water will be produced. Such water production may take place as a by-product
<http://en.wikipedia.org/wiki/By-product>, possibly unwanted, of
dehumidification <http://en.wikipedia.org/wiki/Dehumidifier>.[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>
The air conditioning system of the Burj Khalifa
<http://en.wikipedia.org/wiki/Burj_Khalifa> in Dubai
<http://en.wikipedia.org/wiki/Dubai>, for example, produces an estimated
15 million US gallons (57,000 m3) of water each year that is used for
irrigating the tower's landscape plantings.[50]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-gn-50>

Because mechanical refrigeration is energy intensive, active collectors are
typically restricted to places where there is no supply of water that can
be desalinated <http://en.wikipedia.org/wiki/Desalination> or purified at a
lower cost and that are sufficiently far from a supply of fresh water to
make transport uneconomical. Such circumstances are uncommon, and even then
large installations such as that tried in the 1930s at Cook in South
Australia failed because of the cost of running the installation – it was
cheaper to transport water over large distances.[21]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-uncommon_lives3-21>

In the case of small installations, convenience may outweigh cost. There is
a wide range of small machines designed to be used in offices that produce
a few litres of drinking water from the atmosphere. However, there are
circumstances where there really is no source of water other than the
atmosphere. For example, in the 1930s, American designers added condenser
systems to airships <http://en.wikipedia.org/wiki/Airships> – in this case
the air was that emitted by the exhaust of the engines, and so it contained
additional water as a product of combustion. The moisture was collected and
used as additional ballast to compensate for the loss of weight as fuel was
consumed. By collecting ballast in this way, the airship's buoyancy could
be kept relatively constant without having to release helium gas, which was
both expensive and in limited supply.[51]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEAllen193137-51>

More recently, on the International Space Station
<http://en.wikipedia.org/wiki/International_Space_Station>, the Zvezda
module <http://en.wikipedia.org/wiki/Zvezda_%28ISS_module%29> includes a
humidity control system. The water it collects is usually used to supply
the Elektron <http://en.wikipedia.org/wiki/ISS_ECLSS#Elektron> system that
electrolyses water into hydrogen <http://en.wikipedia.org/wiki/Hydrogen>
and oxygen <http://en.wikipedia.org/wiki/Oxygen>, but it can be used for
drinking in an emergency.[52]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-52>

There are a number of designs that minimise the energy requirements of
active condensers:

- One method is to use the ground as a heat sink
<http://en.wikipedia.org/wiki/Heat_sink> by drawing air through
underground pipes.[53]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-53>
This is often done to provide a source of cool air for a building by means
of a ground-coupled heat exchanger
<http://en.wikipedia.org/wiki/Ground-coupled_heat_exchanger> (also known
as *Earth tubes*), wherein condensation is typically regarded as a
significant problem.[54]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-54> A
major problem with such designs is that the underground tubes are subject
to contamination and difficult to keep clean. Designs of this type require
air to be drawn through the pipes by a fan, but the power required may be
provided (or supplemented) by a wind turbine
<http://en.wikipedia.org/wiki/Wind_turbine>.[55]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-55>


- Cold seawater is used in the Seawater Greenhouse
<http://en.wikipedia.org/wiki/Seawater_Greenhouse> to both cool and
humidify the interior of greenhouse
<http://en.wikipedia.org/wiki/Greenhouse>-like structure. The cooling
can be so effective that not only do the plants inside benefit from reduced
transpiration <http://en.wikipedia.org/wiki/Transpiration>, but dew
collects on the outside of the structure and can easily be collected by
gutters.[4]

<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimouk2000-4>


- Another type of atmospheric water collector makes use of desiccants
<http://en.wikipedia.org/wiki/Desiccant> which adsorb atmospheric water
at ambient temperature, this makes it possible to extract moisture even
when the relative humidity is as low as 14 percent.[56]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-56>
Systems of this sort have proved to be very useful as emergency supplies of
safe drinking water.[57]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-57>[58]

<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTECartlidge200926.E2.80.9327-58>
For regeneration, the desiccant needs to be heated.[59]

<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTECartlidge200916-59>
In some designs regeneration energy is supplied by the sun; air is
ventilated at night over a bed of desiccants that adsorb the water vapour.
During the day, the premises are closed, the greenhouse effect increases
the temperature, and, as in solar desalination
<http://en.wikipedia.org/wiki/Solar_desalination> pools, the water
vapour is partially desorbed, condenses on a cold part and is collected.[
4]

<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimouk2000-4>


- A French company has recently designed a small wind turbine that uses
a 30 kW electric generator to power an onboard mechanical refrigeration
system to condense water.[60]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-60>

See also

- Atmospheric water generator
<http://en.wikipedia.org/wiki/Atmospheric_water_generator>
- Dew pond <http://en.wikipedia.org/wiki/Dew_pond>
- Condensation trap <http://en.wikipedia.org/wiki/Condensation_trap>
- Fog collection <http://en.wikipedia.org/wiki/Fog_collection>
- Rainwater harvesting
<http://en.wikipedia.org/wiki/Rainwater_harvesting>
- Solar chimney <http://en.wikipedia.org/wiki/Solar_chimney>
- Watermaker <http://en.wikipedia.org/wiki/Watermaker>
- Solar still <http://en.wikipedia.org/wiki/Solar_still>

Dew pond
>From Wikipedia, the free encyclopedia

A *dew pond* is an artificial pond <http://en.wikipedia.org/wiki/Pond>
usually sited on the top of a hill, intended for watering livestock. Dew
ponds are used in areas where a natural supply of surface water may not be
readily available. The name dew pond (sometimes *cloud pond* or *mist pond*)
is first found in the *Journal of the Royal Agricultural Society
<http://en.wikipedia.org/wiki/Royal_Agricultural_Society_of_England>* in
1865.[1] <http://en.wikipedia.org/wiki/Dew_pond#cite_note-1> Despite the
name, their primary source of water is believed to be rainfall rather than
dew or mist.[2] <http://en.wikipedia.org/wiki/Dew_pond#cite_note-2>
Construction

They are usually shallow, saucer-shaped and lined with puddled
<http://en.wikipedia.org/wiki/Puddling_%28engineering%29> clay
<http://en.wikipedia.org/wiki/Clay>, chalk
<http://en.wikipedia.org/wiki/Chalk> or marl
<http://en.wikipedia.org/wiki/Marl> on an insulating straw layer over a
bottom layer of chalk or lime.[4]
<http://en.wikipedia.org/wiki/Dew_pond#cite_note-4> To deter earthworms
from their natural tendency of burrowing upwards, which in a short while
would make the clay lining porous, a layer of soot would be incorporated[5]
<http://en.wikipedia.org/wiki/Dew_pond#cite_note-johnsonw-5> or lime mixed
with the clay.[6] <http://en.wikipedia.org/wiki/Dew_pond#cite_note-eam85-6>
The clay is usually covered with straw to prevent cracking by the sun[6]
<http://en.wikipedia.org/wiki/Dew_pond#cite_note-eam85-6> and a final layer
of chalk rubble or broken stone to protect the lining from the hoofs of
sheep or cattle.

A method of constructing the base layer using chalk puddle was
described in *The
Field* 14 December 1907. A Sussex farmer born in 1850 tells how he and his
forefathers made dew ponds:
Fog fence
>From Wikipedia, the free encyclopedia

A *fog fence* or *fog collector* is an apparatus for collecting liquid
water from fog <http://en.wikipedia.org/wiki/Fog_collection>, using a fine
mesh <http://en.wikipedia.org/wiki/Mesh> or array of parallel wires.
Proposed geometries include linear, similar to a fence
<http://en.wikipedia.org/wiki/Fence> and cylindrical. It has the advantage
of being passive, requiring no external energy source
<http://en.wikipedia.org/wiki/Energy_source> to perform its collection.
This makes it attractive for deployment in less developed areas. An ideal
location for fog fences is high arid areas near cold offshore currents,
where fog is common.
A related, but quite distinct, technique of obtaining atmospheric moisture
is the air well <http://en.wikipedia.org/wiki/Air_well_%28condenser%29>.



--
Lawrence F. London
lfljvenaura@gmail.com
https://sites.google.com/site/avantgeared/ <http://www.avantgeared.com>
https://plus.google.com/+Avantgeared
Ello: https://ello.co/ecoponderosa <https://ello.co/ecoponderosa>
Twitter: @ecoponderosa <https://twitter.com/ecoponderosa>
Reddit: ecoponderosa
Cellphone: lfljcell@gmail.com




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