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An air well provides a point for dew to condense, allowing for the collection of water. Variations on such equipment have been in use among various human cultures for thousands of years, particularly in arid regions where water supplies are limited. Using an air well permits people to harvest water from the air, in varying amounts, depending on humidity levels in the area. The technology can be used to supply safe drinking water and meet irrigation needs.
Several designs are in use, but the basic principle involves building a structure that can be cooled to a point lower than that of the surrounding area, which facilitates the formation of dew. Some air wells are passive, cooling without any need for energy use. They typically include a structure with a high surface area, which promotes heat loss. As air moves through the air well, condensation starts to form on the walls. Special materials can be used to trap the dew more effectively and funnel it to a collection area.
Other designs are active. In this type of air well, water or another coolant is circulated through the structure to bring the temperature down. This heat exchanger approach allows the structure to become much cooler, again promoting the formation of dew. An example can be seen with air conditioning systems, which can become accidental air wells if they are not designed and placed carefully. Droplets can start to collect on the equipment in high humidity because the air conditioner is so much cooler than the surrounding air.
The amount of water collected can depend on a number of factors. One is the design, which can be highly efficient or less so. Another is ambient humidity, which can result in low collection levels when it is very low because of limited water in the air. Air wells can be installed over crops to provide irrigation, or may take the form of much larger structures to collect water in a central location. They need to be well maintained to function at peak efficiency, and may also include mechanisms for collecting rainwater.
This term can also be used to refer to an air shaft. In this sense, an air well is a courtyard inside a building with accompanying shaft which provides for the circulation of air and light. This can be important with large or closely-packed buildings, which might otherwise have limited ventilation and natural light at their cores. In urban environments, air wells are a common feature. They can also be used in high security facilities to allow people to go outside without compromising security.