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!

  • @moeggz
    9•1 year ago

    On point 4, the key part that you are missing is that evaporation /takes/ energy. The standard central air works closer to how you are thinking by the evaporator above your furnace taking heat to then be dumped out by the condenser outside. This is necessary because it is a closed system that must continually reuse the refrigerant.

    Sweat, and the swamp cooler you have here, are not closed systems and therefore don’t have to “dump” heat. Energy was transferred to the water molecules to cause them to evaporate. As latent heat exists (Google this if you are still confused) the heat energy has been transferred to “evaporation” energy and so the heat can be reduced without breaking any thermal laws.

    Basically the water on your skin or in the swamp cooler is like a wall that heat has to break down. The heat can do this, and does get through but has been reduced by the work and is therefore less strong (lower temperature.

    There was no subtraction or addition to total energy when you look at the whole process. Heat energy was transferred to kinetic energy to cause the state change of the water.

    Central AC has to dump heat to reuse the refrigerant. The swamp cooler doesn’t have to dump heat but needs to be refilled often as the evaporation of water takes matter away from the system.