page_title: Air well (condenser)
section_title: Active
hierarchical_section_title: Air well (condenser) / Types / Active
caption_attribution_description: English: Everest Water Yeti AC-12 atmospheric water generator
context_page_description: An air well or aerial well is a structure or device that collects water by promoting the condensation of moisture 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; 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 resources.
context_section_description: Active atmospheric water collectors have been in use since the commercialisation of mechanical refrigeration. Essentially, all that is required is to cool a heat exchanger 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, 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.
  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 in South Australia 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 – 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 Zvezda module includes a humidity control system. The water it collects is usually used to supply the Elektron system that electrolyses water into hydrogen and oxygen, 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 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 (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.
  Cold seawater is used in the Seawater Greenhouse 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, 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
caption: A commercial atmospheric water generator intended for residential use.[51]
exif: {}