10 ms·

Ok, I have a dumb question about this sort of technology. Aren't these devices essentially just borrowing from tomorrow by capturing moisture that would have ev

Ok, I have a dumb question about this sort of technology. Aren't these devices essentially just borrowing from tomorrow by capturing moisture that would have eventually collected as clouds? Are there any long-term ramifications to using these?

rukittenme 8y ago
There's no long term ramifications because these devices simply do not work as advertised.
- Zaak 8y ago
  The MIT team explicitly addresses the limitations of refrigerated dew collection systems and claim that their system does not share those limitations. In what way would this particular device not work as advertised?
  - rukittenme 8y ago
    It does share those limitations because physical reality requires it to! There is no technological way out. Thermodynamics asks for some amount of energy in exchange for some amount of condensed water. The amount of energy is astronomical compared to the meager amount of water. You see the giant ass heatsink at the bottom of the image? Why do you think that exists? The water is condensing on a peltier heat pump. In a desert, to get a single bottle of water you're going to have to blow hundreds of thousands of liters of air (at perfect efficiency) over the pump. And that's for a single water bottle! Oh and this is assuming that your peltier device can get cold enough to produce a 100% humidity atmosphere. Because if it doesn't you get no water.
    - adrianmonk 8y ago
      "They have developed a completely passive system that is based on a foam-like material that draws moisture into its pores and is powered entirely by solar heat." http://news.mit.edu/2017/MOF-device-harvests-fresh-water-from-air-0414 http://news.mit.edu/2017/MOF-device-harvests-fresh-water-fro...
      - tytytytytytytyt 8y ago
        > The current version can only operate over a single night-and-day cycle with sunlight, Kim says, but “continous operation is also possible by utilizing abundant low-grade heat sources such as biomass and waste heat.” Why can it only un for a single day on solar?
        hexane360 8y ago
        It can operate for multiple days, but it only generates water once a day. At night the foam absorbs moisture, and then sunlight provides energy to release it as water.
    - nkurz 8y ago
      The water is condensing on a peltier heat pump. What makes you so confident that they are using a Peltier? Here's their description of the operation of the device: During adsorption, air is circulated around the MOF layer and water from air is adsorbed. Passive radiative cooling lowers the MOF layer temperature below the ambient by dissipating thermal radiation to the clear cold sky to increase the effective RH for adsorption. During water production, the OTTI aerogel is stacked on top of the MOF layer to suppress convective heat loss from the solar absorber. The desorbed vapour is condensed on a condenser and the heat of condensation is rejected to the ambient by a heat pipe heat sink. And here's the more complete description of the condenser: The condenser of the device was fabricated with a copper plate (4 cm by 4 cm and 0.6 cm thick) attached to a commercial air-cooled heat sink (NH-L9x65, Noctua) to efficiently dissipate the heat from condensation to the ambient. Are you still sure it's condensing on a Peltier cooler? The paper never mentions "Peltier". If the "condenser" is actually an electrically driven Peltier, this would seem like a fraudulently bad description, justifying retraction of the paper. Is it possible that you are wrong? Still, I agree that you might be right about the physical limitations of scaling. You seem knowledgeable about the field, and I'd be interested to hear your impression after you read the actual paper: https://www.nature.com/articles/s41467-018-03162-7 https://www.nature.com/articles/s41467-018-03162-7. (I am genuinely interested in hearing your opinion about what they are doing, but would strongly suggest less overconfidence and more humility when offering bombastic pronouncements on papers you haven't read.)
      - flukus 8y ago
        > What makes you so confident that they are using a Peltier? The article contains a link to an older one and says the device is based on that: http://news.mit.edu/2017/MOF-device-harvests-fresh-water-from-air-0414 http://news.mit.edu/2017/MOF-device-harvests-fresh-water-fro... . Notice the heat sink? Notice quotes like: In fact, the system doesn’t even require sunlight — all it needs is some source of heat, which could even be a wood fire. “There are a lot of places where there is biomass available to burn and where water is scarce,” Rao says. That sure sounds and looks like a peltier device to me. MIT is gaining a reputation for crackpot stuff like this.
        8y ago
cornholio 8y ago
Clouds are quite cheap. Most of them drop most of their water over areas that would not significantly suffer from a marginal reduction of rainfall (the oceans, the arctics, mountain ranges). And a dryer average atmosphere should be partially compensated by increased evaporation from the oceans. Overall, this technology should be applicable on a continental scale before it shows any measurable effect on other areas.
- thaumasiotes 8y ago
  > areas that would not significantly suffer from a marginal reduction of rainfall (the oceans, the arctics, mountain ranges) Agreed as to the ocean and the arctic, but precipitation over mountain ranges is generally recovered by lower-altitude communities when the water eventually flows down to them. Snowmelt has been a major source of water historically.
  - eloff 8y ago
    Also the artics are essentially cold deserts, they don't get much precipitation and there is likely very little that could trace its origin to the hot deserts of the world.
    - Cogito 8y ago
      That's not really true. Parts of the arctics are definitely deserts, but that is not true for all of the arctic regions. Looking at the relevant parts of wikipedia [0] and [1], "annual precipitation averaged over the whole planet is about 1000 mm" while "parts of southeast Greenland [recieve] over 1200 mm". Antarctica has a lot less precipitation in general, but there are still large parts of it that are not classified as desert. [0] https://en.wikipedia.org/wiki/Climate_of_the_Arctic#Precipitation https://en.wikipedia.org/wiki/Climate_of_the_Arctic#Precipit... [1] https://en.wikipedia.org/wiki/Climate_of_Antarctica#Precipitation https://en.wikipedia.org/wiki/Climate_of_Antarctica#Precipit...
- ianai 8y ago
  Here’s hoping it somehow aids in carbon sequestration tech development...
pjc50 8y ago
.. in a different place. Damp air is pretty mobile. It also tends to equilibrium over bodies of water.
jerf 8y ago
In some sort of absolute sense, sure, water in the device is not water somewhere else. But with something like 326,000,000,000,000,000,000 gallons of water on Earth, it's well below the noise threshold. Even "dry desert air", if you work it out, has massive (heh, literally) amounts of water in it. Plus the impact is even less than you think, because air that has been made dry is more able to pick up water, so you have to work even harder than you'd think to have any impact.
- ttul 8y ago
  I used a moisture calculator to determine that 10% humidity desert air at 30 degrees celsius and 1013.25hPa air pressure contains 3.03g/m³ of water. At that rate, the air above a 100x100m football field (to altitude of 100m) contains 303kg of water, or 303L at 4 degrees celsius. So you'd be "drying out" a very tiny cube of air to produce the water needed by an entire family per day even given desert conditions with one of these appliances. In the first world, we use 100L/day for all our needs. That means if everyone in America lived in a desert, we might need 107,491,749,174,917.5 cubic meters of air to supply us with all our water. If that sounds like a lot of air, consider that Death Valley is 7.8e+9 square meters in area; thus, to supply ALL Americans with fresh water, you'd just need to suck Death Valley's air dry to an altitude of 10,000m or so.
  - thaumasiotes 8y ago
    > you'd just need to suck Death Valley's air dry to an altitude of 10,000m or so It seems likely that, as the atmosphere becomes less dense with increasing altitude, so does atmospheric water. One cubic meter of air at sea level contains a lot more air than one cubic meter of air at 6,000m. Does your figure include that effect?
    - tylerhou 8y ago
      If you assume atmospheric water has the same density up to around 3000 feet, then you'd have to dry out 3 Death Valleys. Still pretty reasonable.
DougN7 8y ago
I've had the same thought about solar. The area under the panel used to get sunlight, and if nothing else, warmed up. Not that it's necessarily bad, but widespread usage would have to have _some_ environmental impact.
- cirgue 8y ago
  The same thing can be said of agriculture, and there are definitely environmental impacts, but we generally don't worry about the ground cover aspect.
  - DougN7 8y ago
    That is a really great point I had never thought of. Thank you.
- photojosh 8y ago
  Now the panel warms up instead of the area underneath. What's the difference?
  - dreamcompiler 8y ago
    A small fraction gets turned into electricity. Which ultimately gets turned into...heat. So the net amount of heat reaching earth doesn't change.
    - adrianN 8y ago
      Unless you build solar panels on top of a very low albedo ground, the amount of heat actually increases because less is reflected back to space.
    - DougN7 8y ago
      The final heat would most likely be produced in a different location. It would take a very large scale installation to have an impact. I guess I'm thinking of weather patterns when you see those images that say "if we covered 1/4 of Arizona in solar panels we could power the world!". More of a thought experiment than anything I guess.
oh_sigh 8y ago
Maybe, but the scale here is gigantic, and it will take a lot of work for humans to make an impact. Consider that a single cumulus cloud can weigh 2 million pounds(that is, 900 cubic meters of liquid water). If you were going to be worried about things like this, wind farms will probably pose a bigger problem than water collection, unless we start building large cities in the desert relying only on air moisture collection.
incompatible 8y ago
I guess a lot of it ends up back in the atmosphere once humans have used it. Perhaps some is piped in sewerage all the way to the nearest ocean?
natecavanaugh 8y ago
Long term ramifications I'm sure of. Long term harmful ramifications? I doubt it. That water has to go somewhere, whether it's captured in the ground or evaporates in the skies, the machinery of nature will keep ticking :)

rukittenme 8y ago

There's no long term ramifications because these devices simply do not work as advertised.

Zaak 8y ago
The MIT team explicitly addresses the limitations of refrigerated dew collection systems and claim that their system does not share those limitations. In what way would this particular device not work as advertised?
- rukittenme 8y ago
  It does share those limitations because physical reality requires it to! There is no technological way out. Thermodynamics asks for some amount of energy in exchange for some amount of condensed water. The amount of energy is astronomical compared to the meager amount of water. You see the giant ass heatsink at the bottom of the image? Why do you think that exists? The water is condensing on a peltier heat pump. In a desert, to get a single bottle of water you're going to have to blow hundreds of thousands of liters of air (at perfect efficiency) over the pump. And that's for a single water bottle! Oh and this is assuming that your peltier device can get cold enough to produce a 100% humidity atmosphere. Because if it doesn't you get no water.
  - adrianmonk 8y ago
    "They have developed a completely passive system that is based on a foam-like material that draws moisture into its pores and is powered entirely by solar heat." http://news.mit.edu/2017/MOF-device-harvests-fresh-water-from-air-0414 http://news.mit.edu/2017/MOF-device-harvests-fresh-water-fro...
    - tytytytytytytyt 8y ago
      > The current version can only operate over a single night-and-day cycle with sunlight, Kim says, but “continous operation is also possible by utilizing abundant low-grade heat sources such as biomass and waste heat.” Why can it only un for a single day on solar?
      - hexane360 8y ago
        It can operate for multiple days, but it only generates water once a day. At night the foam absorbs moisture, and then sunlight provides energy to release it as water.
  - nkurz 8y ago
    The water is condensing on a peltier heat pump. What makes you so confident that they are using a Peltier? Here's their description of the operation of the device: During adsorption, air is circulated around the MOF layer and water from air is adsorbed. Passive radiative cooling lowers the MOF layer temperature below the ambient by dissipating thermal radiation to the clear cold sky to increase the effective RH for adsorption. During water production, the OTTI aerogel is stacked on top of the MOF layer to suppress convective heat loss from the solar absorber. The desorbed vapour is condensed on a condenser and the heat of condensation is rejected to the ambient by a heat pipe heat sink. And here's the more complete description of the condenser: The condenser of the device was fabricated with a copper plate (4 cm by 4 cm and 0.6 cm thick) attached to a commercial air-cooled heat sink (NH-L9x65, Noctua) to efficiently dissipate the heat from condensation to the ambient. Are you still sure it's condensing on a Peltier cooler? The paper never mentions "Peltier". If the "condenser" is actually an electrically driven Peltier, this would seem like a fraudulently bad description, justifying retraction of the paper. Is it possible that you are wrong? Still, I agree that you might be right about the physical limitations of scaling. You seem knowledgeable about the field, and I'd be interested to hear your impression after you read the actual paper: https://www.nature.com/articles/s41467-018-03162-7 https://www.nature.com/articles/s41467-018-03162-7. (I am genuinely interested in hearing your opinion about what they are doing, but would strongly suggest less overconfidence and more humility when offering bombastic pronouncements on papers you haven't read.)
    - flukus 8y ago
      > What makes you so confident that they are using a Peltier? The article contains a link to an older one and says the device is based on that: http://news.mit.edu/2017/MOF-device-harvests-fresh-water-from-air-0414 http://news.mit.edu/2017/MOF-device-harvests-fresh-water-fro... . Notice the heat sink? Notice quotes like: In fact, the system doesn’t even require sunlight — all it needs is some source of heat, which could even be a wood fire. “There are a lot of places where there is biomass available to burn and where water is scarce,” Rao says. That sure sounds and looks like a peltier device to me. MIT is gaining a reputation for crackpot stuff like this.
      - 8y ago

cornholio 8y ago

Clouds are quite cheap. Most of them drop most of their water over areas that would not significantly suffer from a marginal reduction of rainfall (the oceans, the arctics, mountain ranges). And a dryer average atmosphere should be partially compensated by increased evaporation from the oceans. Overall, this technology should be applicable on a continental scale before it shows any measurable effect on other areas.

thaumasiotes 8y ago
> areas that would not significantly suffer from a marginal reduction of rainfall (the oceans, the arctics, mountain ranges) Agreed as to the ocean and the arctic, but precipitation over mountain ranges is generally recovered by lower-altitude communities when the water eventually flows down to them. Snowmelt has been a major source of water historically.
- eloff 8y ago
  Also the artics are essentially cold deserts, they don't get much precipitation and there is likely very little that could trace its origin to the hot deserts of the world.
  - Cogito 8y ago
    That's not really true. Parts of the arctics are definitely deserts, but that is not true for all of the arctic regions. Looking at the relevant parts of wikipedia [0] and [1], "annual precipitation averaged over the whole planet is about 1000 mm" while "parts of southeast Greenland [recieve] over 1200 mm". Antarctica has a lot less precipitation in general, but there are still large parts of it that are not classified as desert. [0] https://en.wikipedia.org/wiki/Climate_of_the_Arctic#Precipitation https://en.wikipedia.org/wiki/Climate_of_the_Arctic#Precipit... [1] https://en.wikipedia.org/wiki/Climate_of_Antarctica#Precipitation https://en.wikipedia.org/wiki/Climate_of_Antarctica#Precipit...
ianai 8y ago
Here’s hoping it somehow aids in carbon sequestration tech development...

pjc50 8y ago

.. in a different place. Damp air is pretty mobile. It also tends to equilibrium over bodies of water.

jerf 8y ago

In some sort of absolute sense, sure, water in the device is not water somewhere else. But with something like 326,000,000,000,000,000,000 gallons of water on Earth, it's well below the noise threshold. Even "dry desert air", if you work it out, has massive (heh, literally) amounts of water in it. Plus the impact is even less than you think, because air that has been made dry is more able to pick up water, so you have to work even harder than you'd think to have any impact.

ttul 8y ago
I used a moisture calculator to determine that 10% humidity desert air at 30 degrees celsius and 1013.25hPa air pressure contains 3.03g/m³ of water. At that rate, the air above a 100x100m football field (to altitude of 100m) contains 303kg of water, or 303L at 4 degrees celsius. So you'd be "drying out" a very tiny cube of air to produce the water needed by an entire family per day even given desert conditions with one of these appliances. In the first world, we use 100L/day for all our needs. That means if everyone in America lived in a desert, we might need 107,491,749,174,917.5 cubic meters of air to supply us with all our water. If that sounds like a lot of air, consider that Death Valley is 7.8e+9 square meters in area; thus, to supply ALL Americans with fresh water, you'd just need to suck Death Valley's air dry to an altitude of 10,000m or so.
- thaumasiotes 8y ago
  > you'd just need to suck Death Valley's air dry to an altitude of 10,000m or so It seems likely that, as the atmosphere becomes less dense with increasing altitude, so does atmospheric water. One cubic meter of air at sea level contains a lot more air than one cubic meter of air at 6,000m. Does your figure include that effect?
  - tylerhou 8y ago
    If you assume atmospheric water has the same density up to around 3000 feet, then you'd have to dry out 3 Death Valleys. Still pretty reasonable.

DougN7 8y ago

I've had the same thought about solar. The area under the panel used to get sunlight, and if nothing else, warmed up. Not that it's necessarily bad, but widespread usage would have to have _some_ environmental impact.

cirgue 8y ago
The same thing can be said of agriculture, and there are definitely environmental impacts, but we generally don't worry about the ground cover aspect.
- DougN7 8y ago
  That is a really great point I had never thought of. Thank you.
photojosh 8y ago
Now the panel warms up instead of the area underneath. What's the difference?
- dreamcompiler 8y ago
  A small fraction gets turned into electricity. Which ultimately gets turned into...heat. So the net amount of heat reaching earth doesn't change.
  - adrianN 8y ago
    Unless you build solar panels on top of a very low albedo ground, the amount of heat actually increases because less is reflected back to space.
  - DougN7 8y ago
    The final heat would most likely be produced in a different location. It would take a very large scale installation to have an impact. I guess I'm thinking of weather patterns when you see those images that say "if we covered 1/4 of Arizona in solar panels we could power the world!". More of a thought experiment than anything I guess.

oh_sigh 8y ago

Maybe, but the scale here is gigantic, and it will take a lot of work for humans to make an impact. Consider that a single cumulus cloud can weigh 2 million pounds(that is, 900 cubic meters of liquid water). If you were going to be worried about things like this, wind farms will probably pose a bigger problem than water collection, unless we start building large cities in the desert relying only on air moisture collection.

incompatible 8y ago

I guess a lot of it ends up back in the atmosphere once humans have used it. Perhaps some is piped in sewerage all the way to the nearest ocean?

natecavanaugh 8y ago

Long term ramifications I'm sure of. Long term harmful ramifications? I doubt it. That water has to go somewhere, whether it's captured in the ground or evaporates in the skies, the machinery of nature will keep ticking :)