Atmospheric water vapour processor designs for potable water production: a review

Atmospheric water vapour processing (AWVP) technology is reviewed. These processors are machines which extract water molecules from the atmosphere, ultimately causing a phase change from vapour to liquid. Three classes of machines have been proposed. The machines either cool a surface below the dewpoint of the ambient air, concentrate water vapour through use of solid or liquid desiccants, or induce and control convection in a tower structure. Patented devices vary in scale and potable water output from small units suitable for one person's daily needs to structures as large as multi-story office buildings capable of supplying drinking water to an urban neighbourhood. Energy and mass cascades (flowcharts) are presented for the three types of water vapour processors. The flowcharts assist in classifying designs and discussing their strengths and limitations. Practicality and appropriateness of the various designs for contributing to water supplies are considered along with water cost estimates. Prototypes that have been tested successfully are highlighted. Absolute humidity (meteorological normals) ranges from 4.0 g of water vapour per cubic metre of surface air in the atmosphere (Las Vegas, Nevada, USA) to 21.2 g m-3 (Djibouti, Republic of Djibouti). Antofagasta, Chile has a normal absolute humidity of 10.9 g m-3. A 40% efficient machine in the vicinity of Antofagasta requires an airflow of 10 m3 s-1 to produce 3767 l of water per day. At a consumption of 50 l per person per day, 75 people could have basic water requirements for drinking, sanitation, bathing, and cooking met by a decentralized and simplified water supply infrastructure with attendant economic and societal benefits.