Atmospheric water generators are not new. What this idea proposes is a fairly inexpensive DIY design of a large, almost passive unit with a minimal number of moving parts and minimal upkeep. It is to be mounted on the side of a house and custom-sized to provide a sufficient amount of drinking water for the household.
It effectively makes a "spring" of clean drinking water from the air. I built a 3 meters long prototype. The only thing left to do is mount it on the side of the house and test it in action. I will get it done soon and post the results.
A stainless steel pipe passing through a stainless steel cooling tank.
The tank is kept cold either via a compressor or Peltier elements and powered via renewable power.
In suitable climates, cooling can be completely passive because the cooling tank is mounted on the outside of the house while warm, humid air circulates on the inside.
Warm and humid air passes through the pipe. Either passively or assisted by a fan.
In the sections where the pipe intersects with the tank, water condensation droplets form and stick to the wall of the pipe.
The gravity then pulls the droplets into the water filter where it gets remineralized.
Filtered water is then stored and kept sterile by UV lights inside the drinking water tank.
Imagine mounting this on the outside wall of a house or a greenhouse. The pipe goes through the wall on both ends, so that the air inlet and outlet are inside the house. The cooling tank section remains outside of the house, on the wall facing away from the sun.
The air would be more humid and warm inside because of people or plants. All the water vapor would exit the room via one-way only - condensed and filtered for drinking.
In the colder climates, the outside air would be cooled by the environment for half of the year. No additional energy would be required to cool the cooling tank. In the summertime or in warmer climates, the cooling tank could be insulated and cooled via renewable energy. Either using a compressor system (much like air conditioning units) or Peltier elements.
If the indoor air is always airconditioned, it would make sense to reverse the location and keep the cooling tank indoors while the water harvesting would be done on the outside. In that case an additional filter would be placed over the air intake.
The cooling tank could also be cooled geothermally. Pipes would be dug deep into the ground where the temperature is significanlty lower. The coolant water could then be circulated trough the undergorund pipes to lower its temperature.
The necessary conditions for atmospheric water to condense
Water vapor in the air is composed of H2O molecules that have enough kinetic energy that they bounce apart and do not stick together to form droplets of liquid water. When those H2O molecules strike a surface that is colder than the water vapor, they transfer some of their kinetic energy to the atoms within that surface. When a water molecule touches a surface that is cold enough to borrow enough energy from that water molecule, that H2O molecule can no longer take off from the surface. It sticks - this is called adsorption. If the air is saturated with water molecules (high relative humidity) and the surface of the object is very cold, then the process of adsorption will happen faster than the air can reevaporate the water off of the surface on which it has adsorbed - so plenty of condensation. If the air humidity is low, the adsorbed water will reevaporate before more water molecules can be added to it - so not enough condensation.
The water that can be extracted from the air depends on relative humidity, temperature and pressure:
For example, if the air temperature is 27°C (80°F) and the relative humidity is 75% then any object with a temperature of 22°C (71°F) or lower will become covered by water droplets fairly quickly.
Some things that I have yet to put some serious thought behind:
How would this work in very hot regions that have minimal relative humidity in the air?
How can the water filtration and remineralization be made to require minimal upkeep and lowest cost?
Atmospheric water harvesting in hot and dry climates
Darko SavicMar 07, 2021
The water that can be extracted from the air depends on relative humidity, temperature, and pressure. If the conditions are unfavorable, what can we do to make them better?
In climates where the atmospheric air is very dry but there is a source of water unfit for drinking (sea, river) a solution would be to use the energy from the sun to make the water evaporate into a containment vessel, thereby saturating the contained air with humidity, then extracting it similarly as originally described.
This could be:
A greenhouse, irrigated with dirty water.
A plastic dome over a pond of seawater or river water.
A half-filled long black pipe that is heated from the sun. Undrinkable water passes through the bottom half while humid air is harvested from the upper half.
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Atmospheric water vs. rainwater harvesting
Povilas SMar 08, 2021
I wonder what are the benefits of atmospheric water collecting that you described over rainwater collecting? In places where air humidity levels are high rain is usually frequent too. The purification process you mention for atmospheric water (filters and UV lamps) is the same for rainwater. The collecting process is easier for rainwater (you just need a flat surface area and tanks to catch it). One obvious benefit is that atmospheric water can be collected at any time whether for rain you have to wait, but rainwater is collected in larger quantities, and therefore its resources last longer. In the case of rainwater, you also don't need additional energy for the cooling process. However, those two methods could be combined to produce more reliable availability of drinking water.
Another thing I was thinking about is that if many people would be using these systems it might lower air humidity on a larger scale which then might create consequent atmospheric/ecological problems.
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A fully passive atmospheric water generator
Darko SavicMay 17, 2021
Yakhchāl - an ancient passive cooling method, described here, coupled with this atmospheric water generator would make it fully passive. With some tweaks to maximize efficiency in low humidity areas, it could generate drinking water in the desert.
For example, to aid water extraction out of low-humidity air, the air could be compressed. The air compression could be powered via electricity produced by the Seebeck effect or solar panels.
In this case the Yakhchāl servers as a battery that accumulates cold and stores it underground. The stainless steel pipe passes through the cold area. The humid warm air passes on the inside of the pipe. The water molecules in that air get adsorbed to the cold surface in the deep end of the pipe. Droplets are formed and drip down into the water harversting cistern.