Billboard Sucks Moisture Out of the Air to Make Safe Drinking Water

Categories: Wake Up Call

Screen Cap: MAYOPERUDraftFCB/Youtube

In what has to be one of the nicest publicity stunts and advertising campaigns ever, a college in Lima, Peru, advertised the start of classes by building a billboard that sucks drinkable water straight out the air. That might not sound very exciting until you consider that Lima is the second-largest capital built in a desert and that its population struggles to find clean, drinkable water on a daily basis.

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How dry is this area? Lima receives only a couple of inches of rain a year. In comparison, our fair city receives about four times that amount, around eight inches of rain a year. Huffpo points out that much of the water it relies upon comes from glaciers in the Andes, glaciers that have been melting at a prodigious rate over the past four decades.

This might seem like magic, but the principle behind it will be familiar to anyone who has ever had nasty air-conditioner water drip on them. Basically, the billboard contains an air conditioner that cools the air down to the point where the water starts to collect, like the condensation on a glass of cold water on a hot day. This condensation is collected, treated to make sure it's safe and collected for use. The process isn't necessarily efficient, but Lima's otherwise miserable hot and muggy weather patterns are perfect for this type of system. While the city might not get much rain, its proximity to the ocean means it gets plenty of moisture, and it's only a matter of turning that moisture into something drinkable.

The billboards can create about 96 liters of water a day, or 9,450 liters of water over the course of three months. The average person needs between two and three liters of water a day to survive, so you can see how a single billboard could make a big difference for a community.

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For your interest, here is average monthly data on the water-from-air resource in Lima, Peru (Southern Hemisphere). The measurement units are for water vapour density [grams of water vapour per cubic metre of air]:

Jan 15.2, Feb 16.2, Mar 16.2, Apr 14.3, May 13.5, Jun 12.7, Jul 11.2, Aug 11.2, Sep 11.2, Oct 11.9, Nov 12.7, Dec 14.3

The billboard's water-from-air machine (or atmospheric water generator) will be a maximum of about 58% efficient at removing water vapour from the air in February and March (Southern Hemisphere summer). In July and August (Southern Hemisphere winter), the machine's dehumidification efficiency drops to 39%. These efficiency values presume that the chilled surface in the machine is maintained at 5°C.

In contrast, here is average monthly data on the water-from-air resource in Phoenix, Arizona (same measurement units as above for Lima):

Jan 4.7, Feb 4.6, Mar 4.9, Apr 4.5, May 5.1, Jun 5.8, Jul 10.6, Aug 12.2, Sep 9.4, Oct 6.9, Nov 5.3, Dec 4.7

In July, August, and September, an atmospheric water generator in Phoenix would be 36%, 44%, and 28% efficient, respectively, at producing liquid water from the air passing through the machine. From October to June, water-from-air production would be unreliable in Phoenix. As you see, the water vapour resource, and therefore usefulness of water-from-air machines in meeting drinking water needs, depends a lot on your location on the planet! On an annual basis Lima is a good site for water-from-air machines but Phoenix is a poor site. Even so, during the summer months of July to September, an atmospheric water generator in Phoenix will deliver fair to good performance. It helps to have a more detailed monthly view of the water-from-air resource.

The energy typically needed by dehumidifiers to condense water vapour into liquid water is approximately 0.4 kWh per litre of product water (1.52 kWh per US gallon).

Roland Wahlgren, Atmoswater Research

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