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Comment by post_break | Hacker News Reader

Is this another one of those dehumidifier machines that promises it can deliver gallons when using a tarp, rope, and a bucket to catch rain water collects more water per year?

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RTFA, especially before snarky dismissals: "meeting the competition parameters of extracting a minimum of 2,000 liters of water per day from the atmosphere using 100 percent renewable energy, at a cost of no more than two cents per liter"

I read the article. Do you know how many of these things promise gallons and deliver drops? Pardon me for being pessimistic about it.

They have commercial models for sale that produce half the competition amounts, and have pretty detailed specs online: http://www.skysource.org/products/

Those specs mention producing half the competition's amount in optimal conditions, which I assume means 99% humidity. They don't actually say at what humidity level and temperature their product can deliver that much. They don't give any specific numbers at any specific temperature, only the machine's operating conditions and the upper limit on what it can produce.

I assume they just put together an array of two or three of their high-capacity converters for the competition.

where was the machine tested? If it was tested in somewhere more humid then the test data is invalid for use in arid areas where you'd actually need them. Also, that renewable energy is wood chips, so yeah it's renewable but in reality it's just fossil fuels without the "bury for millions of years" step. I'm not sure how that's meant to be an improvement, except perhaps that they can use local trees instead of bringing in other fuels.

Do you have a source for that?

For instance: https://www.youtube.com/watch?v=vc7WqVMCABg

That's a pretty apples-and-oranges comparison. That's a company making ridiculous promises (look ma, no external power input!) and without any third-party verification. This is a company that makes realistic claims (i.e. has actual numbers for power input per liter of water) and whose performance has been verified by the prize-awarding organization.

from the same author: https://www.youtube.com/watch?v=e3s-xI895zc

I'm not endorsing it, just posting, i have not yet see the video.

> has actual numbers for power input per liter of water

Where did you find that? All I could find is "0.8-1.8kW/hr" for a machine with capacity with a capacity of "30gal/day". This is complete nonsense, "kW/hr" is neither energy nor power nor energy per volume of product. And if it's power, why does it vary?

I'm going to read it as 1.8kW, with a capacity of 30 US gallons (113l) per day. My dehumidifier from the hardware store consumes 0.2kW at a capacity of 10l per day. They are 15% more productive... hardly a quantum leap.

Generally a lot of electrical appliances are advertised with kW or W actually meaning kW-hour and W-hour (and yes, this is awful, but it's pretty standard). So your interpretation as 1.8kW is about right.

It varies, as does output, because (as the numbers mention) this all varies wildly by atmospheric temperature and humidity.

(By the way, running the numbers I'm seeing it as 62.77L/kW vs. 50L/kW, which is a 25% improvement, though at much larger scale.)

groan

So when they write kW/hr, they mean kWh/h, which is kW, because they expect readers to be confused. But if that's the power of the machine, it shouldn't vary. Just like my car produces 70kW, not "7-70kW/hr depending on road conditions". This machine would run a max power all the time, wouldn't it?

> 25% improvement

Serves me right for trying to compute in my head. Qualitatively, it makes no difference, though: they claim a 100% improved efficiency over the competition, and they are nowhere close. The 25% difference may indeed be purely to scale; bigger machines (whether from this company or the hardware store) tend to be more efficient.

As someone else noted, this system functions by using a refrigerator to keep air in the condenser at the dew point; the power required to do this varies based on humidity (changes the dew point) and temperature (changes the temperature gradient your refrigerator has to maintain between the dew point and the outside temp).

Chilling below the dew point doesn't add much, if any, performance.

(And yeah, that kW = kW-h convention hurts my brain.)

Dehumidifiers are not a new thing, I have one right here I can observe. It either runs or it doesn't, so it either consumes 200W or it doesn't. It doesn't regulate the temperature of the condenser, the condensing water does that quite nicely. Since the machine is switched by a hygrostat, you can surely say something like "0-200W" on average, but then it also has a capacity of "0-10l/d".

Power consumption doesn't depend on humidity. Capacity does. So if they quoted "0.8-1.8kWh/l", that would make sense (but be ridiculously low). If they quoted 1.8kW and 40-100l/d, that would make sense, too. But 30gal/d and 0.8-1.8kW implies that the machine throttles the compressor in order not to exceed the advertised capacity, which it doesn't reach under real world conditions anyway.

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