3 ms·

what exactly has been debunked?

realusername 3y ago
That you can provide drinkable water in meaningful quantities from dehumidifiers. Dehumidifiers are one of the most energy intensive way to get water and if you live in a very humid region, well you already have water.
- Turing_Machine 3y ago
  Hmm... Consider the Pacific Northwest. The difference between coastal Washington state and eastern Washington is tremendous. Seattle gets around 39 inches (~1 meter) of precipitation per year. Spokane gets less than half that. This is almost entirely due to a natural "dehumidifier". If the Cascades weren't there, there'd be much less disparity. And yeah, there's energy input, but it comes from the sun and no one has to pay anything for it.
  - realusername 3y ago
    Sure but the energy on the weather is in another scale compared to anything manmade.
dredmorbius 3y ago
Effectively, dehumidifiers reverse the boiling process. To boil water you've got to add the thermal heat of vapourisation to water, 540 calories/g, or about 2 kJ/g. To condense water you've got to remove that same quantity of heat. Granted that heat pumps are more efficient than adding pure heat, you're still looking at expending somewhere between 10--20% of the energy removed. Energy usage also varies with the relative humidity and ambient tempuerature. Remember that both the lower the relative humidity and the lower the ambient temperature the lower the amount of water (absolute humidity) in the air. Dehumidifiers work best when handling hot, humid air, which is not typically where water is in short supply in the first place. Attempting to dehumidify cool dry air, say, in a high-altitude desert, will be exceptionally energy intensive and produce very little output water. The condensation traps and nets mentioned in TFA work best in very-high-humidity environments. This can be useful, but again the total gains are limited, and the process remains the "un-boiling water" problem.

That you can provide drinkable water in meaningful quantities from dehumidifiers. Dehumidifiers are one of the most energy intensive way to get water and if you live in a very humid region, well you already have water.

Turing_Machine 3y ago
Hmm... Consider the Pacific Northwest. The difference between coastal Washington state and eastern Washington is tremendous. Seattle gets around 39 inches (~1 meter) of precipitation per year. Spokane gets less than half that. This is almost entirely due to a natural "dehumidifier". If the Cascades weren't there, there'd be much less disparity. And yeah, there's energy input, but it comes from the sun and no one has to pay anything for it.
- realusername 3y ago
  Sure but the energy on the weather is in another scale compared to anything manmade.

dredmorbius 3y ago

Effectively, dehumidifiers reverse the boiling process. To boil water you've got to add the thermal heat of vapourisation to water, 540 calories/g, or about 2 kJ/g. To condense water you've got to remove that same quantity of heat. Granted that heat pumps are more efficient than adding pure heat, you're still looking at expending somewhere between 10--20% of the energy removed. Energy usage also varies with the relative humidity and ambient tempuerature. Remember that both the lower the relative humidity and the lower the ambient temperature the lower the amount of water (absolute humidity) in the air. Dehumidifiers work best when handling hot, humid air, which is not typically where water is in short supply in the first place. Attempting to dehumidify cool dry air, say, in a high-altitude desert, will be exceptionally energy intensive and produce very little output water. The condensation traps and nets mentioned in TFA work best in very-high-humidity environments. This can be useful, but again the total gains are limited, and the process remains the "un-boiling water" problem.