Radiative Air Wells (Condensers) for Water: The Basics

For acquiring water in a sustainable fashion without electrical power, there’s a lot of information out there for gathering rain water, sinking a well, and one-up survival measures. You can also consider adding a passive radiative air well to your roof or on your land to promote and gather condensation from the air.

Author’s Note
I’ve been considering adding another outbuilding as part of the landscaping craziness this spring and summer. If I do it’s going to have a 30° incline on the roof, that roof will be made of galvanized steel, and there’ll be rain gutters and barrels attached. Per my initial research, since it wouldn’t have internal heating that might make the new outbuilding an effective radiative air well for gathering dew. An additional possibility along these lines of thinking is a fog fence.

An Introduction to Air Wells

An air well is a condenser; its purpose is to promote and gather dew. Per Wikipedia, there are three types of air wells:

1. High Mass, which uses significant masonry and was attempted early in the 20th century without much success.
2. Radiative, which relies on special materials to release (radiate) the heat, thereby lowering the temperature and promoting dew.
3. Active, which relies on a power source and works like a dehumidifier.

While active air wells may be more effective and be plausible for preppers in combination with alternative energy such as solar, it seems to me that the radiative method is by far the cheapest. While I also noted that there are additional passive solutions involving desiccants, a chemical requirement to the solution would be unsustainable for most prepper scenarios.

Radiative Air Wells: The Basics

By Gaius Cornelius (Own work) [Public domain],
via Wikimedia Commons

Radiative air wells are very simple in construction. Typical air wells of this type are on a stand 7 to 10 feet off the ground, angled at 30°, and can be put on the roofs of low buildings. You could of course use other heights or angles, but they will not work as well. Going all the way around your roof with something like this will probably work better than just doing one side, since wind will be less of a factor.

a. radiating & condensing surface
b. collecting gutter
c. backing insulation
d. stand

1. The radiating & condensing surface, per appropedia.org, is best done corrugated galvanized iron, plastic, or glass – and using “TiO2 and BaSO4 microspheres embedded polyethylene” has a 20% better yield than Plexiglass. The akvo.org article also mentions galvanized roofs and also mentions specially treating the surface with OPUR paint – but the OPUR link doesn’t seem to mention any paint (at least that I noted). That polyethylene is described in scientific articles as being somewhat fragile; seems to me galvanized steel such as we use to improve the fire safety of our homes is the best bet here.
2. The collecting gutter can be standard vinyl rain collecting gutters.
3. The backing insulation can be 2cm thick polystyrene as done in Morocco, per akvo.org. The purpose is just to withstand weather and reduce heat retention, so you have a lot of options on this one.

1. This is probably not going to yield sufficient water for survival. It’s just supplemental.
2. Detaching the gathering surface from the roof proper may be advisable since the temperature needs to drop and you’re probably warming your house. Also, the angle of your roof may not be right (30°).
3. Water gathered this way needs to be fed into water storage barrels, just as with rain.
4. We’ll still need to disinfect water gathered this way, of course, although dew is generally purer than most other water sources.

Sources & More Reading

1. Air well (condenser) – wikipedia.org
2. Dew collection roof retrofit – appropedia.org
3. Dew collection and storage – akvo.org
4. International Organization For Dew Utilization – opur.fr
5. Umbrella Design Harvests Desert Moisture for Childrens’ Hospital – greenbuildingelements.com
6. Making Water From Thin Air – sciencedaily.com
7. Harvesting Fog Provides Drinking Water, Food to Peruvian Slums – treehugger.com