General

Airwells

There are so many daunting environmental concerns that loom in the present and on the horizon, but perhaps none is quite as troubling and alarming as the limited supply of fresh water. In areas of drought and desert landscape, this precious resource isn’t just flushed away, but even still, coming up with enough to meet the drinking and hygienic demands of even a small population is a daunting prospect.

While estimates vary, certainly regionally, the USGS Water Science School estimates that the average person uses between 80 and 100 gallons of water per day, between hygiene, household chores, and drinking needs. Even conservatively, that’s over 29,000 gallons of water a year, for a single person.

Of course, there are a large number of ways the conventional household can drastically reduce their water needs – limiting showering and bathing, cutting back on laundry by rewearing clothes, hand washing our dishes and clothes, to name a few – but even so, in so many cases, the water needs of a population are just too much for local ecosystems to support, particularly where homesteads are concerned.

While rainwater catchment is a great option in areas where the climate supports it, another little known water harvesting solution can sometimes be the key to creating enough water to support a homestead – airwells.

Airwells use temperature changes on a surface to concentrate and capture condensation, effectively harvesting water from the humidity in the air. While this design and concept have been around for over 100 years, the most crucial innovations and design optimization have only happened in the last 50 or so years, when it was determined that high mass airwells were largely counterproductive.

The first airwells that were documented were beautiful stone structures. These structures, while beautiful, unfortunately worked against their purpose – the mass of the stone held onto heat too long after the sun went down, and as the stone slowly cooled, it was much more difficult for sufficient condensation to build up before sunrise.

While there are more advanced and complex versions of these systems today, the simplest ones have no moving parts, and are essential “dew captors”. Some particularly simple, yet effective, examples can be found in rooftop installations like these, in which a layer of insulation is set on the roof, and then a plastic layer covers it all to trap the moisture. The water then runs down the slope of the roof and into a catchment system following the gutter.

Image: © Michel Royon / Wikimedia Commons https://en.wikipedia.org/wiki/Air_well_(condenser)#/media/File:Puits_aerien_knappen_trans_83_10.jpg
Image: © Michel Royon / Wikimedia Commons https://en.wikipedia.org/wiki/Air_well_(condenser)#/media/File:Puits_aerien_knappen_trans_83_10.jpg

Depending on your scenario, an airwell may or may not yield the results you need. While airwells function in even dry climates, naturally the less humidity you have in your air, the less output you can expect from this design. However, these radiative airwells have been found to have a significantly higher rate of water production than high mass versions.

There are also active collector airwells, which function with an energy source, much in the way a dehumidifier does. Though these systems are effective at what they do, and in fact, even available by manufacturers in commercial sizing for larger buildings, their requirements for a constant energy source and technical expertise make them much less practical than simple models that function, arguably, just as well.

These simple ‘condensation factories’ could present the solution to water catchment, whether for household or agricultural use, in climates that have difficulty supporting a population. It’s fun to daydream about every household in America having a rooftop radiative airwell installed – just imagine the impact on the local water tables it would have!

This concept, despite its implications, is still relatively off the beaten path though, and there is little practical literature available on their construction and function. However, Wheaton Labs in western Montana, USA is currently ramping up to host their PDC and Appropriate Technology Courses, during which former PRI farm manager Tim Barker will be teaching a workshop on radiative airwells.

Registration for these courses is still open – the Appropriate Technology course runs June 13th – June 25th 2016 and is $1,295 per student, with onsite camping included. If you want to learn how to build an airwell, this one of the very few courses you’ll find that teaches the subject, with hands on learning. More information and signup can be found at richsoil.com/pdc.jsp.

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Have you ever practiced some form of condensation catchment? How successful were your ventures? Share your experiences.

Feature Image, Courtesy of WIKI. https://en.wikipedia.org/wiki/Air_well_(condenser)#/media/File:Big_Dew_Condenser_in_Corsica.jpg

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