Harvester pulls 1.5 gallons of drinking water from arid air per day

Full publication - https://pubs.acs.org/doi/10.1021/acsenergylett.4c01061

> 11.15–22.81 kWh/L

Are there any advantages over cooling condensation extractors? They seem to be in the 0.3-3.0 kWh/L range.

https://us.watergen.com/technology/

https://www.researchgate.net/figure/Liters-of-water-condensa...

https://www.ostfalia.de/cms/en/pws/turtur/solar-projects/con...

> Scaled up, that’s 5.8 L (1.5 gal) per kilogram (2.2 lb) of material used per day, which is enough to satisfy several people’s daily water needs.

No knock on the device itself but this is barely enough for two people, especially in arid conditions.

I am happy to see that we are ensuring the Fremen will have the technology they need to survive on Arrakis.

If this is deployed at scale, I wonder how this would impact the plants and animals that depend on that water.

FTA: “The potential downside is that this system requires energy to release the water – the base of the device needs to reach 184 °C (363 °F) to wring it out. But the team says the device can tap into waste energy or heat from other systems, like buildings or vehicles.”

I guess it’s fairly hard to get 184°C of heat out of buildings. Getting it out of ICE vehicles is easier, but the device will add weight to the vehicle, and those are on the way out (slowly).

So, that leaves getting it out of waste energy such as excess solar or wind energy. If that’s your heat source, an important metric is “how many Watt hours per liter”

I skimmed the paper. AFAICT, it only mentions usage of current state of the art devices, at 11 to 23 kWh/l, compared to 5 to 7 kWh/l for conventional passive systems.

What did I overlook?

the copper foam is a really nice idea. for those not familiar with the problem space, the issue is that when you condense water with an adsorbent or other desiccant, it releases a lot of heat, which limits how fast you can condense water: quickly enough your hot desiccant is in equilibrium with the air until you remove some of that heat

nrel did a record-breaking design in the last couple of years with i think calcium chloride on aluminum fins, optimized to provide air conditioning (cooling) rather than water harvesting. if you're interested in this news item you might want to look that up, i don't think i saved the link

(how do they keep the chloride from eating the aluminum? i don't know, maybe i'm misremembering. zeolite avoids that problem)

my own thought is that you ought to be able to rapidly blow the air through a closed loop consisting of a recuperator and the desiccant, thus allowing it to reach the desiccant's deliquescence humidity at the temperature of the temperature reservoir the recuperator interchanges heat with, rather than at the brine-bulb temperature of the desiccant (zeolite doesn't form a brine or have a deliquescence humidity but the principle is the same). this will surely have a lot more frictional losses than simple passive conduction through copper or aluminum, but on the other hand, it's a lot easier to fabricate

in my proposal, once you've reached the desired low humidity inside the closed loop, you open it up and pump your charge of cool, dry air into the place you want cool, dry air, and then begin the desiccant regeneration process with new air circulated in the same way, but passed through a heat source

a somewhat more elaborate version of the system uses a series of heat reservoirs at different temperatures to recover about two thirds of the heat rejected at the first recuperator, using it to heat the regeneration air

but who knows, i haven't built a prototype yet, and my grasp of thermodynamics and psychrometrics is shaky at best; maybe the idea is flawed in some way i haven't figured out

The news article is a little light on details. Link to the original research below:

https://pubs.acs.org/doi/10.1021/acsenergylett.4c01061

Of note - the paper describes the theory and construction of a benchtop proof of concept. This has not been deployed at scale. Also of note, this is not entirely passive, requiring energy input to achieve a yield.

Hmm, This has got me wondering if I could use my daily ~4kWh spare solar energy for watering my dozen chilli plants, maybe something like a dehumidifier running outdoors. It is hot here, and in recent years has some higher humidity in summers. I'm guessing the extracted water is ok for plants?

> in air with 30% humidity (classed as arid)

TIL my house is arid

We had these on my uncle's farm. They are finicky especially in dry environments with lots of sunshine. Robots can assist with the repairs and programming. They can be difficult to find second hand, but if they can program a load lifter they can probably do it.

Finally, thunderf00t has something new to make a video about that isn't beating a dead horse.

Ironic. Uses heat to harvest water.

I've always wondered about these sorts of things.

Do they actually make "drinkable water"? If it is distilled water, it is not drinkable, it is dangerous and will leach necessary minerals out of your body.

>11.15–22.81 kWh/L

Goodness that's a lot of energy to generate a liter of water.

I saw a video demonstration of this product in a science context. Incredible to see it working completely passively, and also a different model with low electrical load assist.

Is is a dehumidifier? Fins, requires energy, some part gets hot. Yep its a dehumidifier. Dry areas are dry because there is no humidity to condense and fall as rain.

> harvesting 8.66 L (2.3 gal) per day per kg of material, but these tests were conducted at 70% humidity

This is the kind of thing we should be putting a lot of resources in figuring out.

Anyone know of DIY plans for this kind of thing?

Another dehumidifier from MIT Thunderf00t is going to have a field day