nslenders t1_j218swr wrote on December 28, 2022 at 10:44 PM

those energy values seem low to me. or did i bork my conversion somewhere?

3600Kj/kg would be 1kWh/L --> 180Kj would be 50Wh/L

i would think it would take more than 50w for an hour to get a liter of water

WaterScienceProf OP t1_j21gbq1 wrote on December 28, 2022 at 11:37 PM

It conveys the thermodynamic minimum possible, not what practical technologies can achieve. Available approaches are still emerging technologies, and may need an order of magnitude or more energy to work. For context, the minimum energy for seawater desalination is ~1 Wh /L.

HardCounter t1_j23jocj wrote on December 29, 2022 at 11:49 AM

How are you going from 1kWh/L to 50Wh/L? You aren't reducing the amount of water harvested, you're just reducing the power for some reason. 50Wh would be 1/20L with a direct conversion.

Am i missing something?

nslenders t1_j23mb4a wrote on December 29, 2022 at 12:20 PM

3600Kj is 1Kwh. And 1kg is 1L. But the graph shows values from 0Kj/L till 280 Kj/L

Since 3600Kj is not on the chart. Taking a value that I can easily divide, being 180Kj/L. Would give me 1/20th of that 1Kwh. Or 50Wh/L

The map has values higher and lower, but 180Kj/L looked like a reasonable middle ground to calculate. Taking 1,5x our 180Kj/L would give 270Kj/L, or almost the top values. And is still only 1,5x 50Wh/L or 75Wh/L.

HardCounter t1_j23nv2c wrote on December 29, 2022 at 12:37 PM

I guess i don't know what you're trying to achieve.

Pick a number between 1 and 280 and it's on the chart somewhere, no math required. 50kJ/kG is on there somewhere, so is 83.4kJ/kG since it seems to be a continuous scale. 280kJ/kG or so seems to be the maximum for Earth. I'm not sure why 3600kJ/kG entered your mind, or what planet that would apply to.

nslenders t1_j23oy44 wrote on December 29, 2022 at 12:49 PM

My mind does not think in Kj. But if u tell me something uses as much energy as a 50W lightbulb for 1h. I know what that means.

I do know that 3600Kj equals 1Kwh. So I used that as an intermediate step to do the conversion. It does not have to be a relevant value on the map.

The reason I found the values low. Is that I have a big dehumidifier that uses 2000W. But it does not give me 40L every hour. But OP already explained that these are theoretical minimum values.

HardCounter t1_j23rmj8 wrote on December 29, 2022 at 1:15 PM

2000W? Is it industrial strength? You'd probably get a lot more water if you put the dehumidifier outside, though.

> Portable dehumidifiers typically consume between 30 and 50 watts while whole-home dehumidifiers can use up to 250 watts per hour.

https://www.perchenergy.com/energy-calculators/dehumidifier-electricity-usage-cost-to-run

I also found this:

> On average, a home dehumidifier collects five gallons of water per day.

That's about 19 liters per day inside an already dehumidified home. That comes out to about 315 watts per liter in a relatively low (30-50%) humidity environment. That's not too bad.

I should get a dehumidifier in case of zombie apocalypse.

Fhotaku t1_j287bsz wrote on December 30, 2022 at 9:56 AM

I did the legwork for a phd project that involved comparing indoor dehumidifiers efficacy on AWC in a desert. The cost varied wildly, in the 10c-4$/liter range, but that also included tests at 5% humidity and 120F outside, and others while it was raining.

Most places could use active systems like this for cheaper and cleaner water than they're currently getting. I will mention though, the refrigeration based dehumidifier collected every damn particulate in the air with it. It definitely needed filtration. Even moreso, this water is salt-free, and you can't live off that. These are costs to consider when using AWC.