![Puits aerien knappen trans 83 00](https://upload.wikimedia.org/wikipedia/commons/3/37/Puits_aerien_knappen_trans_83_00.jpg)
An air well or aerial well is a structure or device that collects water by promoting the
condensation of
moisture
Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...
from air. 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: used in the early 20th century, but the approach failed.
* Low-mass, radiative collectors: Developed in the late 20th century onwards, proved to be much more successful.
* Active collectors: these collect water in the same way as a
dehumidifier
A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons, or to eliminate musty odor and to prevent the growth of mildew by extracting w ...
; 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 sustainable and
renewable energy resources.
Background
![Atmospheric Water Vapor Mean](https://upload.wikimedia.org/wikipedia/commons/a/a0/Atmospheric_Water_Vapor_Mean.2005.030.jpg)
All air well designs incorporate a substrate with a temperature sufficiently low so that
dew
Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation.
As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at wh ...
forms. Dew is a form of
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
that occurs naturally when atmospheric water vapour
condenses
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...
onto a substrate. It is distinct from
fog, in that fog is made of droplets of water that condense around particles in the air. Condensation releases
latent heat
Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition.
Latent heat can be underst ...
which must be dissipated in order for water collection to continue.
An air well requires moisture from the air. Everywhere on Earth, even in deserts, the surrounding
atmosphere contains at least some water. According to Beysens and Milimouk: "The atmosphere contains
of fresh water, composed of 98 percent water vapour and 2 percent condensed water (
cloud
In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...
s): a figure comparable to the renewable liquid water resources of inhabited lands ." The quantity of water vapour contained within the air is commonly reported as a
relative humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity dep ...
, and this depends on temperature—warmer air can contain more water vapour than cooler air. When air is cooled to the
dew point
The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will cond ...
, it becomes saturated, and moisture will condense on a suitable surface. For instance, the dew temperature of air at and 80 percent relative humidity is . The dew temperature falls to if the relative humidity is 50 percent.
A related, but quite distinct, technique of obtaining atmospheric moisture is the
fog fence
upright=1.3, ''Atrapanieblas'' or fog collection in Alto Patache, Atacama Desert, Chile">Atacama_Desert.html" ;"title="Alto Patache, Atacama Desert">Alto Patache, Atacama Desert, Chile
Fog collection is the harvesting of water from fog using ...
.
An air well should not be confused with a
dew pond
A dew pond is an artificial 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 ...
. A dew pond is an artificial
pond
A pond is an area filled with water, either natural or artificial, that is smaller than a lake. Defining them to be less than in area, less than deep, and with less than 30% emergent vegetation helps in distinguishing their ecology from ...
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. In fact, dew ponds are primarily filled by rainwater.
A stone
mulch
A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area.
A mu ...
can significantly increase crop yields in
arid
A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...
areas. This is most notably the case in the
Canary Islands: on the island of
Lanzarote there is about 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.
History
Beginning in the early 20th century, a number of inventors experimented with high-mass collectors. Notable investigators were the Russian engineer
Friedrich Zibold (sometimes given as Friedrich Siebold), the French bioclimatologist
Leon Chaptal, the German-Australian researcher
Wolf Klaphake and the Belgian inventor
Achille Knapen.
Zibold's collector
![Zibold condenser (section)](https://upload.wikimedia.org/wikipedia/commons/a/a2/Zibold_condenser_%28section%29.jpg)
In 1900, near the site of the ancient
Byzantine
The Byzantine Empire, also referred to as the Eastern Roman Empire or Byzantium, was the continuation of the Roman Empire primarily in its eastern provinces during Late Antiquity and the Middle Ages, when its capital city was Constantinopl ...
city of
Theodosia, thirteen large piles of stones were discovered by Zibold who was a
forester
A forester is a person who practises forestry, the science, art, and profession of managing forests. Foresters engage in a broad range of activities including ecological restoration and management of protected areas. Foresters manage forests to ...
and engineer in charge of this area. Each stone pile covered just over and was about tall. The finds were associated with the remains of
terracotta
Terracotta, terra cotta, or terra-cotta (; ; ), in its material sense as an earthenware substrate, is a clay-based unglazed or glazed ceramic where the fired body is porous.
In applied art, craft, construction, and architecture, 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 he calculated that each air well produced more than each day.
To verify his hypothesis Zibold constructed a stone-pile condenser at an altitude of on mount Tepe-Oba near the ancient site of Theodosia. Zibold's condenser was surrounded by a wall high, wide, around a bowl-shaped collection area with drainage. He used sea stones in diameter piled high in a truncated cone that was in diameter across the top. The shape of the stone pile allowed a good air flow with only minimal thermal contact between the stones.
Zibold's condenser began to operate in 1912 with a maximum daily production that was later estimated to have been – Zibold made no public record of his results at the time. 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.) Zibold's condenser was approximately the same size as the ancient stone piles that had been found, 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 in 1929. Chaptal's condenser was a
pyramidal concrete structure square and high, it was filled with of
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
pieces being about 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 to per day depending on the atmospheric conditions.
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.
Klaphake's collectors
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
Yugoslavia (; sh-Latn-Cyrl, separator=" / ", Jugoslavija, Југославија ; sl, Jugoslavija ; mk, Југославија ;; rup, Iugoslavia; hu, Jugoszlávia; rue, label=Pannonian Rusyn, Югославия, translit=Juhoslavija ...
and on
Vis Island in the
Adriatic Sea
The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to t ...
. Klaphake's work was inspired by Zibold and by the works of
Maimonides
Musa ibn Maimon (1138–1204), commonly known as Maimonides (); la, Moses Maimonides and also referred to by the acronym Rambam ( he, רמב״ם), was a Sephardic Jewish philosopher who became one of the most prolific and influential Tora ...
, a known Jewish scholar who wrote in Arabic about 1,000 years ago and who mentioned the use of water condensers in Palestine.
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
A sugarloaf was the usual form in which refined sugar was produced and sold until the late 19th century, when granulated and cube sugars were introduced. A tall cone with a rounded top was the end product of a process in which dark molasses, a r ...
-shaped building, about high, with walls at least 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. According to Klaphake:
Traces of Klaphake's condensers have been tentatively identified.
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;
their decision to settle in Australia (rather than, say, in Britain) was influenced by Wolf's desire to develop a dew condenser.
As a dry continent, Australia was likely to need alternative sources of fresh water, and the Premier of
South Australia
South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
, whom he had met in London, had expressed an interest. Klaphake made a specific proposal for a condenser at the small town of
Cook
Cook or The Cook may refer to:
Food preparation
* Cooking, the preparation of food
* Cook (domestic worker), a household staff member who prepares food
* Cook (professional), an individual who prepares food for consumption in the food industry
* ...
, where there was no supply of potable water. At Cook, the railway company had previously installed a large coal-powered active condenser,
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.
Knapen's aerial well
Knapen, who had previously worked on systems for removing moisture from buildings, was in turn inspired by Chaptal's work and he set about building an ambitiously large ''puits aerien'' (aerial well) on a high hill at
Trans-en-Provence
Trans-en-Provence (; Provençal: ''Tranç'') is a commune in the Var department in the Provence-Alpes-Côte d'Azur region in southeastern France.
Trans-en-Provence is famous among the ufologists as the site of an alleged UFO incident called th ...
in France. 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.
The tower is high and has massive masonry walls about 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. 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. The slates were placed nearly vertically to encourage dripping down to a collecting basin at the bottom of the structure. Unfortunately, the aerial well never achieved anything like its hoped-for performance and produced no more than a few litres of water each day.
International Organisation for Dew Utilization
![Dr Sharan at condenser test ground](https://upload.wikimedia.org/wikipedia/commons/1/13/Dr_Sharan_at_condenser_test_ground.JPG)
By the end of the twentieth century, the mechanics of how dew condenses were much better understood. The key insight was that low-mass collectors which rapidly lose heat by
radiation perform best. A number of researchers worked on this method. In the early 1960s, dew condensers made from sheets of
polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including b ...
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. In 1986 in
New Mexico
)
, population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano)
, seat = Santa Fe
, LargestCity = Albuquerque
, LargestMetro = Tiguex
, OfficialLang = None
, Languages = English, Spanish ( New Mexican), Navajo, Ke ...
condensers made of a special foil produced sufficient water to supply young saplings.
In 1992 a party of French academics attended a
condensed matter
Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquid phases which arise from electromagnetic forces between atoms. More generally, the su ...
conference in
Ukraine
Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inv ...
where
physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe.
Physicists generally are interested in the root or ultimate cau ...
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 (a part of the
necropolis of ancient Theodosia) and that the pipes were medieval in origin and not associated with the construction of 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. 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.
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.
OPUR began a study of dew condensation under laboratory conditions; they developed a special
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, t ...
film and experimented with trial installations, including a collector in
Corsica. Vital insights included the idea that the
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different eleme ...
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, and that it should be hydrophobic, so as to shed condensed moisture readily.
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 Beach Resort in the arid coastal region of
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
The World Bank is an international financial institution that provides loans and grants to the governments of low- and middle-income countries for the purpose of pursuing capital projects. The World Bank is the collective name for the Inte ...
, Sharan and his team went on to develop passive, radiative condensers for use in the arid coastal region of Kutch. Active commercialisation began in 2006.
Sharan tested a wide range of materials and got good results from
galvanised iron
Galvanization or galvanizing (American and British English spelling differences, also spelled galvanisation or galvanising) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot ...
and
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
sheets, but found that sheets of the special plastic developed by the OPUR just thick generally worked even better than the metal sheets and were less expensive. The plastic film, known as OPUR foil, is hydrophilic and is made from polyethylene mixed with
titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolub ...
and
barium sulphate
Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium a ...
.
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.
From the late twentieth century onwards, there has been much investigation of low-mass,
radiative 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. While some thinkers have believed that Zibold might have been correct after all,
an article in ''Journal of Arid Environments'' discusses why high-mass condenser designs of this type cannot yield useful amounts of water:
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.
Radiative
![Radiative condenser (section)](https://upload.wikimedia.org/wikipedia/commons/a/af/Radiative_condenser_%28section%29.jpg)
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. 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 and supported above ground level. Such condensers may be conveniently installed on the ridge roofs of low buildings or supported by a simple frame. 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-story building.
![Dew harvest satapar](https://upload.wikimedia.org/wikipedia/commons/9/99/Dew_harvest_satapar.jpg)
A radiative condenser illustrated to the left is built near the ground. In the area of northwest India where it is installed dew occurs for 8 months a year, and the installation collects about of dew water over the season with nearly 100 dew-nights. In a year it provides a total of about of
potable water for the school which owns and operates the site.
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.
New materials may make even better collectors. One such material is inspired by the
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. Researchers at the
Massachusetts Institute of Technology
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...
have emulated this capability by creating a textured surface that combines alternating hydrophobic and hydrophilic materials.
Active
![Condenser on roof Sayara](https://upload.wikimedia.org/wikipedia/commons/f/f2/Condenser_on_roof_Sayara.JPG)
Active atmospheric water collectors have been in use since the commercialisation of mechanical
refrigeration
The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...
. Essentially, all that is required is to cool a
heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...
below the dew point, and water will be produced. Such water production may take place as a
by-product, possibly unwanted, of
dehumidification. The air conditioning system of the
Burj Khalifa in
Dubai
Dubai (, ; ar, دبي, translit=Dubayy, , ) is the most populous city in the United Arab Emirates (UAE) and the capital of the Emirate of Dubai, the most populated of the 7 emirates of the United Arab Emirates.The Government and Politics of ...
, for example, produces an estimated of water each year that is used for irrigating the tower's landscape plantings.
Because mechanical refrigeration is energy intensive, active collectors are typically restricted to places where there is no supply of water that can be
desalinated 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, South Australia
Cook is a railway station and crossing loop located in the Australian state of South Australia on the Trans-Australian Railway. It is about west by rail from Port Augusta and about north of the Eyre Highway via an unsealed road.(1927)''Trav ...
failed because of the cost of running the installation – it was cheaper to transport water over large distances.
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
An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power. Aerostats gain their lift from a lifting gas that is less dense than the surrounding air.
In early ...
– 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.
More recently, on the
International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ( ...
, the
Zvezda module
''Zvezda'' (russian: Звезда, meaning "star"), ''Salyut'' DOS-8, also known as the ''Zvezda'' Service Module, is a module of the International Space Station (ISS). It was the third module launched to the station, and provided all of t ...
includes a humidity control system. The water it collects is usually used to supply the
Elektron system that electrolyses water into
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
and
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
, but it can be used for drinking in an emergency.
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
A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, th ...
by drawing air through underground pipes. This is often done to provide a source of cool air for a building by means of a
ground-coupled heat exchanger
A ground-coupled heat exchanger is an underground heat exchanger that can capture heat from and/or dissipate heat to the ground. They use the Earth's near constant subterranean temperature to warm or cool air or other fluids for residential, agric ...
(also known as ''Earth tubes''), wherein condensation is typically regarded as a significant problem. 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
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each yea ...
.
* Cold seawater is used in the
Seawater Greenhouse
A seawater greenhouse is a greenhouse structure that enables the growth of crops and the production of fresh water in arid regions which constitute about one third of the earth's land area. This in response to the global water scarcity and peak ...
to both cool and humidify the interior of
greenhouse-like structure. The cooling can be so effective that not only do the plants inside benefit from reduced
transpiration
Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth ...
, but dew collects on the outside of the structure and can easily be collected by gutters.
* Another type of atmospheric water collector makes use of
desiccants 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. Systems of this sort have proved to be very useful as emergency supplies of safe drinking water. For regeneration, the desiccant needs to be heated. 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 pools, the water vapour is partially desorbed, condenses on a cold part and is collected. Nanotechnology is improving these types of collectors, as well. One such adsorption-based device collected 0.25 L of water per kg of a
metal-organic framework in an exceptionally arid climate with sub-zero dew points (
Tempe, Arizona, USA).
* A French company has recently designed a
small wind turbine
Small wind turbines, also known as micro wind turbines, are used for microgeneration of electricity, as opposed to large commercial wind turbines, such as those found in wind farms. Small wind turbines often have passive yaw systems as opposed ...
that uses a 30 kW electric generator to power an onboard mechanical refrigeration system to condense water.
[
]
See also
*
Atmospheric water generator
*
Condensation trap (
Solar still
A solar still distills water with substances dissolved in it by using the heat of the Sun to evaporate water so that it may be cooled and collected, thereby purifying it. They are used in areas where drinking water is unavailable, so that cle ...
)
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Dew pond
A dew pond is an artificial 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 ...
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Fog collection
upright=1.3, ''Atrapanieblas'' or fog collection in Alto Patache, Atacama Desert, Chile">Atacama_Desert.html" ;"title="Alto Patache, Atacama Desert">Alto Patache, Atacama Desert, Chile
Fog collection is the harvesting of water from fog using ...
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Fog drip
Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily in ...
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Groasis Waterboxx
The Groasis Waterboxx is a device designed to help in growing trees in dry areas. It was invented and developed by Dutch former flower exporter Pieter Hoff,Witkin, JimDeveloping a ‘Water Battery’ for trees''New York Times'', 9 April 2010. Acces ...
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Passive cooling, including
fluorescent cooling, which can cool to below the ambient air temperature
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Rainwater harvesting
Rainwater harvesting (RWH) is the collection and storage of rain, rather than allowing it to run off. Rainwater is collected from a roof-like surface and redirected to a tank, cistern, deep pit (well, shaft, or borehole), aquifer, or a reservoir ...
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Solar chimney
:''This article refers to a device for ventilation. For the power generation technology, see Solar updraft tower.''
A solar chimney often referred to as a thermal chimney is a way of improving the natural ventilation of buildings by using convect ...
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Water potential
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure and mat ...
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Watermaker
References
Notes
Sources
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External links
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{{DEFAULTSORT:Air Well (Condenser)
Precipitation
Water supply
Hydrology
Appropriate technology
Drinking water
Water and the environment