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.

  1. Spouse insists that the AIR gets cooled by evaporation.
  2. I say the FILTER gets cooled by evaporation.
  3. Spouse says the cooled filter then cools the air, so it works.
  4. 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!

  • @Windex007
    5•1 year ago

    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.