The minimum necessary background facts are: 1) Heat is like water in that it wants to be in equilibrium, 2) heat flows from high to low, and 3) heat travels by radiation, conduction, and convection.

Knowing those facts, there are ways to encourage heat flow one direction while discouraging its flowing the other.

For example, the dew pond is a passive device that harvests water out of air. Invented during the Neolithic, some dew ponds built then are still producing today.

In its original form the dew pond was a clay or chalk membrane installed over a straw liner. On calm, clear nights a dew pond can experience a two or three inch rise in the water level. Everybody has a pet theory about why dew ponds work, but nobody denies that they work. I opine that the clay liner radiates its heat into the night sky, while the straw liner prevents the heat being replenished by conduction from the earth.

Variants of this idea are used to irrigate trees in Afghanistan and melons in China. During the Dark Ages, dew ponds provided water for the people and livestock of fortified hilltop villages in England. During the Crusades knights built siege ponds inside their castles. The Scottsdale, AZ, Pond Roof House is heated and cooled by this principle. “Bridges May Be Icy” signs point out a spot where the principle regularly works. And every morning the dew spots on your windshield testify that it really does work.

Neolithic man did not have access to modern materials, but he built ponds that provided reliable water for “300 sheep and 20 bullocks”. Since we know that sheep need about two gallons per day, we can infer that the dew pond described by “The Naturalist on the Thames” produced about 600 gallons per day. What we don’t know is the size of the dew pond that he was describing.

We get better information from a 1922 Popular Science article that describes S.B. Russell’s patented “dew reservoir” as reliably producing about 75 gallons per day in winter and 150 gallons per day in summer. The dew reservoir was 30 feet by 30 feet. If we arbitrarily assign it a 90 gallon per day average production and divide that by 900 square feet of reservoir, we learn the device is capable of harvesting a tenth of a gallon per day per square foot. Extending the calculation, a tenth of a gallon every day for a year is 36 gallons or four point something cubic feet. That means a one-acre dew reservoir style collector would produce four acre-feet of water per year.

Current state-of-the-art makes this water too expensive for irrigation, but water is like electricity; it gets more expensive during peak demand.

I’ve built three prototypes. One actually worked a little bit.

I’m afraid I’m going to die without sharing this. Please take it and run.

I often hope that someone will take the idea and implement it so that I can become a customer. That won’t happen if the idea stays in my head. And, given that most ideas fail, I’d rather someone else put the work and risk in. Lazy huh!

And I’m donating $1 to TechquilaShots and emailing you the above photo, sans-watermark. Merry Christmas