Prove me wrong, please?
edit: thanks for all the great comments, this is really helpful. My main take-away is that it does work, but requires dry air. In humid conditions it doesn’t really do anything.
Spouse bought this thing that claims to cool the air by blowing across some moist pads. It’s about as large as a toaster, and it has a small water tank on the side. The water drips onto the bottom of the device, where it is soaked up by a sort of filter. A fan blows air through the filter.
- Spouse insists that the AIR gets cooled by evaporation.
- I say the FILTER gets cooled by evaporation.
- Spouse says the cooled filter then cools the air, so it works.
- I say the evaporation pulls heat (and water) from the filter, so the output is actually air that is both warmer and wetter than the input air. That’s not A/C, that’s a sauna. (Let’s ignore the microscopic amount of heat generated by the cheap Chinese fan.)
By my reckoning, the only way to cool a ROOM is to transport the heat outside. This does not do that.
We can cool OURSELVES by letting a regular fan blow on us = WE are the moist filter, and the evaporation of our sweat cools us. One could argue that the slightly more humid air from this device has a better heat transfer capacity than drier air, but still, it is easier to sweat away heat in dry air than in humid air.
Am I crazy? I welcome your judgment!
Well, what this thing doe is moisten the air and thereby cooling it. So temperature down, humidity up.
If you live in dry areas, this is good, but if you live in more humid areas, this will only worsen the problem.
Don’t forget to air the rooms regularly (at night, if it is too hot during the day) to get the humidity out again - you don’t want to get over 60% relative humidity for a longer period.
OP, where do you live? What is the surrent relative humidity of your house? The lower it is the more likely this thing is to work. It is a legitimate technology but they only work well in dryer places. A dry heat is perfect for this.
These are often called swamp coolers.
I expect you’re either both right or wrong, depending on how you want to look at it.
Forget quibbling over the filter, the air, the fan, whatever. Just consider yourself in a closed system.
Evaporation is an endothermic reaction. Energy is “used” as part of the state change. This energy comes from the surrounding environment, but the temperature of the water does not change during evaporation.
The ambient energy expended reduces the heat in the environment. Less heat in the same materials will result in a lower temperature, which is to say that evaporative cooling is real. So the Mrs. is correct.
Does THIS device provide enough to actually meaningfully cool your space? Tough to tell. You could weigh how much water you’re evaporating, look up how much energy that expended
https://www.engineeringtoolbox.com/water-properties-d_1573.html
And then try and rough out how that would translate to a cooler room with specif heat capacity of air…
But honestly I’d probably just try and ignore all the interactions and just use a thermometer at the output of that thing to see if it’s at all different from the ambient temperature of the room.
You’re wrong, your spouse is right.
Thermal energy is required both to raise the temperature of a mass of (in this case) water, and additional thermal energy is required to change its state from liquid to gas. This additional thermal energy is spent without creating any actual temperature increase, but it had to come from somewhere.
In this case, the thermal energy for the state change came from the surrounding air. The energy didn’t come from changing the state of the air, so it must have come from lowering the temperature of the air.
As others have noted, this only works in low-humidity environments. If the air is already saturated with water vapor, no more evaporation will occur. This is why high-humidity environments feel hotter: your sweat isn’t evaporating to cool you off.
It is a swamp cooler. It works, and works better in drier air, but it is not a heat exchanger. Most of the cooling is gonna be from the moving air.
My partner and I started hanging up our clothes to dry on a dirt cheap clothes rack. Think we spent like $10~$15 on the whole setup. Anyway, we have it stood up on the hot side of the apartment and have a fan blowing on the wet clothes toward the coach / desk area in the living room. The thermostat says the room is about 5 degrees cooler, but the room feels more like 8 or 10 degrees cooler. Not sure how the physics works on all of this, but those dumb desk coolers sound like the same principle
That’s a swamp cooler and is very commonly used in dry environments. It will help a lot in Arizona (well, maybe not that tiny thing, but a properly sized one) and not at all in Miami, due to the difference in ambient humidity.
The issue here is that your wife bought this thinking it’s an ac when it’s an evaporative cooler aka swamp cooler. They do work if you have low humidity. If you are in a humid area this definitely won’t work. Since the unit is small it won’t cool the entire room but she should feel nice and cool about 3 to 5 feet in front of it. She will need to make sure the wicking action is working to get the pads nice and wet, otherwise she will have to manually remove them to wet them.
Edit: I wanted to add that I have had a similar small unit before which is why I know that she needs to be 3 to 5 feet in front of it to hit the little target cool zone.
You sound persnickety. You’ll probably like this persnickety video about swamp coolers
Swamp cooler, they do work, but raise the humidity, which might cause increased mold growth
It’s been crazy hot and humid this past month where I live. This thing would kill me
These work so long as the air around them is not humid already
Technology Connections has a video on exactly these devices that dives into how they work and what they can and can’t do. TLDW; you’re not wrong about the physics of cooling a room, though in some cases this little thing might make you feel a bit cooler.
Here is an alternative Piped link(s): https://piped.video/watch?v=2horH-IeurA&pp=ygUddGVjaG5vbG9neSBjb25uZWN0aW9ucyBjb29sZXI
Piped is a privacy-respecting open-source alternative frontend to YouTube.
I’m open-source, check me out at GitHub.
I was about to share this! Always glad to see Alec get recognition!
I’ve had one before. They are def not a good enough replacement for AC when you really need it, but they’re not useless, either. They certainly don’t work like AC does, you are right. They can make you feel a little cooler if you’re sitting in front of it. lol
Pro tip: Dowse the pad insert in water and put it in the freezer. You can also put an ice cube or two in the water reserve. Both of these things maximize the “cooling” power, but again, you can’t really expect it to cool a whole room.
Thank you for this. I admit that I smiled at your tip to freeze the soaked filter, because freezing it requires the fridge/freezer combo to do so, and where does that unit vent its heat? Into our living space, of course.
So it’s a closed loop with losses, and I found that funny.
What do you think they do in prison when the AC burns out?
