And that takes a lot of energy.
So what is the purpose of this device? It can't be to provide potable water to areas without it, since those same areas are likely to lack a significant source of power.
I don't mean to be overly cynical, but I feel like I'm missing something here.
Typical coefficients of performance for air-source heat pumps, like air conditioners or dehumidifiers, are around 2; that means for every 2 joules of heat that it removes from the cold reservoir, it consumes a joule of electrical energy (dumping it as heat into the hot reservoir along with the heat it's pumping). The enthalpy of vaporization of water, at almost 41kJ/mol, is huge compared to the specific heat of air or even water itself, so that's a good approximation to how much heat you need to extract to condense the water. Water's molar mass is about 18 g/mol (two hydrogens of 1.0001 or so and an oxygen of 15.9994) so that works out to about 2.3kJ/g. At 10¢/kWh, this means your water costs 6.3¢/ℓ or US$78000/acrefoot.
This is a lot cheaper than bottled water, and a lot more expensive than what farmers can afford to pay for irrigation water, and a lot more expensive than reverse osmosis desalination, which I think is around $8000/acrefoot. (Corrections welcome!)
If we figure that a person needs 8 ℓ / day for cooking, drinking, and bathing (more or less what we use at Burning Man; if you're somewhere less hot and druggy then you might need less) which is about 210 watts. If a photovoltaic panel produces a 24-hour average of 13 W/m², which is what a friend of mine in England is getting, you need about 16 square meters of photovoltaic panels to power the device, which costs about US$2000 at this point. That's well within the bounds of feasibility, although it's a big enough asset to be a temptation to thieves.
So when you say, "I feel like I'm missing something here," I agree: you were missing quantitative understanding of the subject, and as a result your quantitative conclusions were completely wrong, even though they were based on correct qualitative understanding.
The pump were using right now consumes 104 W intermittently. For our next prototype, we're going to use a condenser unit from a walk-in freezer (1168W), a split A/C unit to pretreat the air (560W) MinnowBoardMax (15W), duct fan (208W), etc.
One person.
It seems like you've supported my point, not refuted it.
But I appreciate your analysis, even if I dispute your conclusion! Thanks!
However, I made an error! It turns out I left out the coefficient of performance in my calculations. So it's actually 105 watts, 8 m², and about US$1000:
You have: (8 liters / day) * (41 kJ / mol) / (18 g / mol) * (1 g / cc)
You want: W
* 210.90535
/ 0.0047414634
You have: (8 liters / day) * (41 kJ / mol) / (18 g / mol) * (1 g / cc) / 2
You want: W
* 105.45267
/ 0.0094829268
You have: (8 liters / day) * (41 kJ / mol) / (18 g / mol) * (1 g / cc) / 2 / (13 W / m^2)
You want: m^2
* 8.1117442
/ 0.12327805
You have: 8000 watts * 16% * $ 0.55/watt
You want:
Definition: 704 US$
If PV modules return to their previous price trend (they were dropping fairly smoothly by 36% per year in 2010-2013, but have been nearly plateaued since hitting grid parity in much of the world in 2013 and therefore having a hard time with capacity keeping up with demand) then they'd drop by another factor of 4. The Credit Suisse doc posted earlier today to HN https://doc.research-and-analytics.csfb.com/docView?sourceid... about how we are now in a "solar manufacturing oversupply" situation suggests that something like that might actually happen. Like what happened to DRAM prices in 1996 after the price-fixing cartel collapsed and they went from $40 a meg to $10 a meg almost overnight.
They operate by sucking air through a part of a rotating desiccant drum then exhausting it. At another spot, they heat and blow air through the desiccant, recharging it. The heavily moisture laden air is ran through a radiator where the moisture condenses out. If you have a source of low/medium grade heat, these can operate for the cost of running a few fans.
This type works actually can operate in colder climates as they can work down to near the freezing point of water, where the cooling type cannot operate when the dew point is below the freezing point of water.
Here is a video of a guy tearing down a typical household unit and he explains the basics of operation:
If you end up beating me to it: https://github.com/openawg/openawg/pulls
Once the well is dug, cased, and the pump is installed there are very little operating costs especially with solar-powered electric pumps.
The math for a comparison between a well and this gizmo would be interesting.
I'm not sure how to determine the practicality of well excavation, but my intuition tells me it largely depends on geographically influenced factors. I'll look into that.
If you're not going to be in a particular area for very long, digging a well might not be an option. An AWG can collect water while you're moving -- all you need is access to air.
If you find yourself in an area where the water table is contaminated, using an AWG may end up being the safer option.
Imagine you're living in space (or a similarly resource-constrained environment): you've got multiple people losing something like 0.5+ L/day (citation needed) to the air through perspiration -- that's valuable water. Moreover, to keep people comfortable, you should make sure your relative humidity stays below 60% (citation needed), so you're going to be pulling it out of the air anyhow. NASA undoubtedly has these systems in place in space, but that doesn't mean we should develop a open source version of the equipment that everyone can collaborate on and improve.
TL;DR Sometimes you're willing to trade energy for water. Also, open source.
Most of the startup cost is in digging the heat exchange loop.
I thought the same thing but reading their site led me to the above Wikipedia page which suggests there are other ways to do it than just dehumidification but I'm not sure what method they're using.
EDIT: Spelling is hard. Clarification is hard.
If it takes a lot of energy, and we implement carbon-negative power generation, then we increase the rate of carbon sequestration :)
We'd like to be able to gather metrics from these machines all over the world, and identify trends in things such as the weather, water production and consumption, efficiency, power generation and carbon sequestration, as well as identify opportunities to improve the operation of the machines through software updates.