Engineers harvest clean, continuous energy from air
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Basically, I noticed that the room was heating significantly when I turned it on. Way faster than what you should expect from its power usage (about 250W avg.).
Correct me if I'm wrong, but by converting air moisture to liquid water using a compressor, the dehumidifier is releasing the latent energy of water vapor (0.627Wh/L) in addition to its own energy usage.
I measured that my dehumidifier required +/- 1kW/h to get 1L of liquid water from the room. This it's overall heating efficiency is about 1.6x, which is way better than any electric heating system that is not an heat-pump.
Yes, but not quite for the reason you give. See below.
> colder if it's cold.
This I don't agree with. Cold air can't hold any significant amount of water vapor to begin with. It is true that a cold, rainy day feels colder than a cold, dry day with the same air temperature, but rain isn't humidity; rain is water, not water vapor.
> I think the deal is that it's more efficient at transferring heat to/from your skin.
Not quite. The deal is that your body sheds heat by evaporation of water (sweat), but water can only evaporate if the surrounding air is not already saturated, and the closer the surrounding air is to being saturated, i.e., the more humid it is, the less heat your body can shed before the air is saturated.
In cold conditions your body wants to retain heat, not shed heat, and the humidity in the cold air doesn't really affect that at all, because, as above, there just isn't enough of it in cold air to make a difference. What does affect your body's ability to retain heat is dampness or rain, i.e., water, not water vapor; the extra water (far more water than you would generate by sweat on a hot day, or than exists as water vapor in cold air) sucks heat out of your body because the water is colder than you are and has such a high heat capacity (even if it doesn't evaporate).
The cold in the midwest cuts through you in a way that it doesn't in the dry. Air temperature's the same, but the difference is noticeable. Why is that? If not humidity, then what is it?
My experience in the Midwest (and elsewhere) on colder days is that the biggest factor is wind. Even a relatively light wind on a cold day can make a big difference in draining heat from your body. Convection makes a big difference in the heat transfer properties of air.
Btw, you say "in the dry", but have you ever been in the desert on a cold night? I think you might reconsider just how cold "dry cold" can feel.
Lived in Salt Lake City for 60 years, so yes. And I would say that, to me, the cold in the Midwest is worse than the cold in the West, even at the same temperature and wind.
But after reading your response, another variable has occurred to me. The west isn't just dry, it's high and dry. Higher elevation means lower air pressure. Lower air pressure means fewer molecules hitting each square inch each second, carrying off heat. Is lower air pressure part of why the cold doesn't cut through you as much out west?
Could be, yes. The lower air pressure means less heat transfer out of your body, as you say.
I have a question on this -- I've never quite been able to put my finger on it (ha) but there is some atmospheric effect that makes SOME cold days feel, to use a phrase "bone-chilling cold", vs other cold days that just feel chilly. And I'm not talking about 10 degrees F vs. 40 degrees F. There are 45-degree days that just feel miserable and 45 degree days that just feel cool.
On those bone-chilling days, it almost feels as if the cold is sticking to my skin. I've always thought the difference was humidity -- similar to how a hot humid day is just 10x more miserable than the venerable "dry heat" of a desert, which can feel significantly more comfortable even at many degrees hotter.
If it's not humidity on those cold days, what is it?
[Edit: Funny - the sibling commenter had basically the same question at the exact same time]
Sunny vs. cloudy? Little wind vs. more wind? Fog? Rain? Drizzle? You don't mention any of these other obvious factors. Are they really all exactly the same on both types of days?
At 45 degrees F, the air is much colder than you are. Under those conditions, as I've already noted, your body is trying to retain heat, not shed it. More humidity, if anything, will increase your body's ability to retain heat; so a more humid cold day, if anything, should feel warmer than a less humid cold day. However, as I've already noted, the amount of water vapor the air can hold at a cold temperature is not very large anyway, so there is very little difference between "more humid" and "less humid".
To put some numbers to this, I'll use figures from the Engineering Toolbox[1] to compare 41 degrees F at 100% relative humidity with 104 degrees F at 25% relative humidity (which is a typical condition for a hot desert day). I pick those temperatures because they have entries in the table on the page I linked to.
41 degrees F, 100% RH: 6.82 g of water vapor per cubic meter of air
104 degrees F, 25% RH: 0.25 x 51.1 = 12.775 g of water vapor per cubic meter of air.
In other words, there is close to twice the water vapor in the air on a "dry heat" desert day than on a humid cold day. And if we want to compare with a hot, humid, day, let's pick 86 degrees F at 90% RH (typical for, say, southern Texas or southern Florida in the late spring--not even summer):
86 degrees F, 90% RH: 0.9 x 30.4 = 27.36 g of water vapor per cubic meter of air.
So the difference between "dry heat" and "hot and humid" is at least (remember that I picked a significantly less severe hot and humid condition) twice the total amount of water vapor in 100% saturated air at 45 degrees F. And the difference in water vapor in the air between the two conditions you describe on 45 degree days will be considerably less than that total amount of 6.82 g; at 45 degrees F, most days are going to have fairly high RH simply because there is always some water vapor in the air, and even "some" is enough to get a fairly high RH. So even if the humidity effect were in the direction you describe (which, as I said above, it isn't), it would be too small at 45 degrees F to matter.
In short, I just don't see humidity as a reasonable explanation for what you describe at 45 degrees F. I would be looking at the other factors I listed.
[1] https://www.engineeringtoolbox.com/maximum-moisture-content-...
That is why it can feel less cold when temperatures fall lower than 0 degrees Celsius (32 Fahrenheit): Most of the moisture in the air becomes solid and falls to the ground.
Don't we all love those wet cold days?
Coming from Norway to Dublin, one of my biggest annoyances is the winter is 5-6 degrees warmer... which puts it right above zero... which makes it feel much, much colder.
The instant you hit freezing temperatures the absolute humidity falls off a cliff.
The latent heat does get released, but the question is, where does it go?
In an air conditioner, which also condenses water vapor from the air, the heat released goes into the refrigerant, which means it ultimately gets put into the atmosphere outside from the condenser.
A dehumidifier is basically an air conditioner without an outside unit, so the heat from the condensation of water vapor goes into the refrigerant, but then gets put into the room from the condenser, instead of outside.
We live by the coast, so we have a few small dehumidifiers for mold prevention but have not been using them much. I am going to test this out and see if it works. I don't particularly mind bundling up, but the toddler can't make it through the night with the blankets on. So if this does work, seems like it would be the perfect solution.
But if there’s that much latent energy, I really have to think that there could be some kind of atmospheric, “local ecological” side effect on microorganisms or “something” at scale. It’s not like nature lets massive amounts of energy go completely unused.
I assume it would only work well in places where there are significant humidity swings, I didn't read the paper very carefully though.
https://onlinelibrary.wiley.com/doi/epdf/10.1002/adma.202300...
Not sure what you mean, Watt already has a unit of time in it.
If you want to talk about a quantity of energy rather than a rate of energy production/consumption, the units would be either kilowatt hours or joules (1 kWh = 3,600,000 joules).
A another common unit for energy is kWh (kilowatt.hour)
A kilowatt generator can produce one kWh/h (by definition)
Some kind of energy harvesting device that could generate a few milliwatts in ambient indoor conditions would be very useful. We have lots of things with AA batteries in them that use very little power but need a new battery every year or so. That's the potential here. This isn't going to replace oil.
What does this mean? Was this written by AI that can't distinguish between a physical footprint and a figurative carbon one?
In fact, an Air-gen device made from protein nanowires, which was kept in the ambient environment for over 3 years, still produced a similar voltage output ...These time spans are much longer than the typical hydration time, supporting the sustainable mechanism based on a dynamic equilibrium ... The Air-gen device is not a “perpetual motion engine”, because the energy comes from the electrostatic energy (not kinetic one) of discrete water molecules in a vast open source.
Does this mean that the energy they're harvesting is a result of imparting a charge on otherwise neutrally charged water molecules, but because it's infinitesimally small compared with the "vast source", you can disregard any net effect from the perspective of the harvester?
If so, this doesn't feel "right", because this implies that a charged particle's state is at a lower energy state than a neutral one. If that were so, wouldn't the universe tend to that lower energy state by default?
Again, I'd appreciate if someone could tell me where the energy is supposed to be coming from, because "TANSTAAFL" seems to be being violated here.
Presumably it doesn't instantaneously happen due to insulating effects in the air.
Of course it is fairly weak, but it is continuous and simple. There has to be uses for it.