
Show HN: Open-source atmospheric water generator – first lab reports - clayrichardson
https://openawg.github.io/2016/03/22/fresh-from-the-lab.html
======
rootedbox
The problem places have with lack of good water; is a lack of money. Not a
lack of water.

There are way more energy / cost efficient ways to produce water than a
dehumidifier.

If you want to get into solving clean water; you really should be working on
cheap energy.

~~~
clayrichardson
Our current approach is to get the AWG module working, then add a module which
boils urine and feeds the vapor into the AWG module for distillation and
filtration.

Ideally, we'd like to use a gasifier for carbon negative power generation, as
local biomass can be utilized.

Does this make sense, or do you have a more effective approach?

~~~
rootedbox
Like I said.. There isn't a 'lack' of water.. there is a lack of energy for
purification in rural places.. In these places you should be figuring out
purification via chemical and physical methods.

[https://s-media-cache-
ak0.pinimg.com/736x/83/a6/d9/83a6d9886...](https://s-media-cache-
ak0.pinimg.com/736x/83/a6/d9/83a6d988650f72e279c10f6d5851736a.jpg)

------
clayrichardson
Hey everyone, I'm around for a bit to answer any questions you might have :)

~~~
zzalpha
So... this is basically a dehumidifier. Dehumidifiers typically use some sort
of air cooling to reduce water below the dew point to draw water out of the
air.

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.

~~~
kragen
Let's quantify "a _lot_ of energy": the dehumidification part is 210 watts per
person. Maybe Clay can provide actual power consumption numbers that include
the other parts of the system, such as filtration.

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.

~~~
zzalpha
So for one person you'd need $2000 worth of solar panels, 16 square meters of
panel.

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!

~~~
kragen
Does US$2000 per person for the energy to solve the potable water problem for
30 years seem like a lot to you? Compared to the cost of other survival
necessities (housing, food, sanitation, heating, cooling —
[http://resiliencemaps.org/](http://resiliencemaps.org/)) it's quite
reasonable. 16 m² is also pretty small compared to the space customarily used
for housing.

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
    

My guess of US$1000 for 8 m² is based on my guess that 8 m² is about 8000
watts of solar constant, and at 16% efficiency that's 1280 peak watts, and
people quote PV modules as below US$1/watt, which I assume is a peak watt. The
actual price right now is about US$0.55/watt, depending on where you are, so a
more precise estimate is actually US$700:

    
    
        You have: 8000 watts * 16% * $ 0.55/watt
        You want: 
        	Definition: 704 US$
    

My friend who's getting those 13 W/m² has her panels in England, though. So
that's kind of a worst-case number. You'd need a fraction of that (like, say,
20% or so) in an equatorial desert.

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...](https://doc.research-and-
analytics.csfb.com/docView?sourceid=em&document_id=x691349&serialid=L3f%2bdcbQOUfpFcJ2bz9CDEuCoQT2wz09vthmZKbV4oU%3d)
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.

------
toomuchtodo
Would it be possible for me to use something like this on a boat I live on to
generate fresh water?

~~~
clayrichardson
It would, but it would most likely be less efficient than filtering the water
you're floating in :)

A good way to increase the efficiency of this machine would be to increase the
relative humidity by adding moisture. This is the reasoning behind our next
planned experiments of reclaiming water from urine!

You might be able to get away with using the reverse osmosis system we have,
[0] but send the water to a lab to test influent (intake) and effluent
(output) before consuming :D

[0]: [http://123filter.com/catalog/ispring-7-stage-75-gpd-
reverse-...](http://123filter.com/catalog/ispring-7-stage-75-gpd-reverse-
osmosis-uv-filter-system-rcc7ak-uv_cpath-70_1_67.html)

~~~
toomuchtodo
Thanks for the reply! I'd of course use a watermaker first (very simple
operation, relying on only a pump and a membrane) but its always smart to have
redundancy in life critical systems ;)

Absolutely love your project. I think its going to help a lot of people!

~~~
clayrichardson
Thank you! I hope it does too.

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phieromnimon
Can you please explain how this differs from a dehumidifier?

~~~
clayrichardson
The only difference is the addition of a filtration system to render potable
water.

Dehumidifiers are not designed to produce potable water.

Adding a filtration system removes the contaminants from the non-food grade
components and anything else which was once floating in the air.

------
heavenlyhash
> pH does not have a MCL (Maximum Contaminant Level) defined in the EPA's
> National Primary Drinking Water Regulations [...] but does have a [..limit
> defined in..] non-mandatory guidelines for aesthetics

Wait, there's _not_ a pH range limit on _drinking water_ in the U.S.?!

~~~
webkike
If I had to take a guess, the EPA probably issues MCLs for acids and bases and
not the resulting pH of them combined.

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RIMR
Ok, I really hate to shit all over somebody else's livelihood, but this whole
project seems like a total waste of time.

A dehumidifier isn't a complicated mechanism. This is not a novel invention.
It also isn't going to produce a sustainable amount of drinking water at a
price affordable to the people who need it most.

The team running this seems to just be a group of friends who have none of the
experience actually make a difference. We've got an Artist/Engineer, and
artist, another artist, another Engineer and a product manager who have no
meaningful job descriptions (apparently they "do things"), A "Web Engineer",
and an advisor whose only task appears to be possession of knowledge of
chemistry. It doesn't seem that this team was chosen due to what they could
accomplish, but instead because they all pitched in to get an IndieGoGo
project going...

I'll give them credit for their cause. At least their hearts are, presumably,
in the right places, but this little device isn't going to change the world
even a little bit. It would win the science fair without a doubt, but it's not
much more impressive than that.

~~~
clayrichardson
Where should we spend our time instead?

Definitely not novel at this stage, but once we modify the AWG to achieve
water reclamation from urine, would that be considered novel?

The next milestone is to create open source designs for larger-scale,
commercially available machines that are prohibitively expensive, and improve
upon them. The machines exist and there is a market for them. Is it not worth
the time and effort to increase access to technologies like this?

Not just knowledge of chemistry, but actively developing eyedrops to cure
cataracts :)

[http://www.viewpointtherapeutics.com/team/](http://www.viewpointtherapeutics.com/team/)

EDIT: Wording. Added question.

~~~
RIMR
>Where should we spend our time instead?

That's for you to decide. There's nothing wrong with your project, I just
don't see any real-world utility.

>once we modify the AWG to achieve water reclamation from urine, would that be
considered novel?

Not at all. It wouldn't even be a "Atmospheric Water Generator" anymore. You
would just be putting an evaporator in a closed space with your condenser...
This isn't a new or novel technology, and it's already available for public
use.

>Not just knowledge of chemistry, but actively developing eyedrops to cure
cataracts :)

That's really cool, and I am not doubting her credentials, but it has nothing
to do you with your AWG. We're talking about a device that condenses water
vapor into liquid water. If you have access to Freon and and a pump (or even
ice cubes and a glass) you can achieve the same thing.

Again, I don't take any personal offense to what you're doing. I would never
invest in it because I don't think any amount of funding would ever turn this
project into a success. It doesn't even address the real issues behind water
scarcity, which has nothing to do with a shortage of liquid water...

~~~
clayrichardson
> This isn't a new or novel technology, and it's already available for public
> use.

Can you point me in the direction of this project? I'd like to see what the
current implementation looks like.

> (or even ice cubes and a glass) you can achieve the same thing.

We're trying to do it at scale and improve on the technology.

> real issues behind water scarcity, which has nothing to do with a shortage
> of liquid water

Can you elaborate on this point?

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sevensor
> The lower the pH, the more basic the water.

It's been a couple of decades since I took chemistry, but I think you've got
that backwards.

~~~
clayrichardson
Oops, thanks for the feedback. Fixed :)

