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I've read in more than one place (e.g., here and here) that a swamp cooler (a.k.a., evaporative cooler) can be effectively paired with a dehumidifier to cool an enclosed space, but this makes no sense to me. It seems like the evaporative cooling would be cancelled out by the heat resulting from condensing the water vapor. No energy is leaving the system as a result of these processes, and waste heat is generated by each device, so it seems the only effect would be to make the room hotter.

The only exception I can imagine is if the water resulting from dehumidification holds the bulk of the heat from that process and is quickly drained, while the evaporative cooler has its supply replenished with cooler tap water. But the articles don't specify that.

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    $\begingroup$ You are correct. $\endgroup$
    – Phil Sweet
    Commented Aug 20, 2020 at 22:30
  • $\begingroup$ It also depends on the efficiencies of both devices, but it is just smoke and mirrors. $\endgroup$
    – StainlessSteelRat
    Commented Aug 21, 2020 at 3:37
  • $\begingroup$ I think Rube Goldberg has the copywrite on this idea. $\endgroup$
    – blacksmith37
    Commented Aug 21, 2020 at 19:27
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    $\begingroup$ The moral of the story is that there are a lot of people talking out of their posteriors on the internet. This solution is the equivalent of cooling a room by running a refrigerator with the door open. But to be more specific, an evaporative cooler lowers temperature by adding moisture. The dehumidifier does exactly the opposite. So all you're doing is pumping water into and out of the air, using motors which give off additional heat. Just no. $\endgroup$
    – Tiger Guy
    Commented Aug 26, 2020 at 9:36
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    $\begingroup$ Power it with a perpetual motion machine. $\endgroup$
    – blacksmith37
    Commented Sep 20, 2020 at 19:37

2 Answers 2

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Please note the following fact about dehumidifiers:

A dehumidifier is basically a room air conditioner which works by cooling the inlet air down just to the point where the water dissolved in it begins to condense out of solution. This temperature is called the dew point temperature. It does this by blowing the air over a set of cold tubes with refrigerant in them; the water vapor condenses on the tubes as liquid water which drips off the tubes into a catchment tank and the refrigerant carries away the heat of vaporization. This heat is then dumped back into the room by blowing more air over a second set of heat transfer tubes through with the warmed refrigerant is circulated.

A room air conditioner does exactly the same thing except that in this case, the heat from the warm refrigerant is exhausted outside the room and the temperature of the cold coils where the water is condensed is low enough to actually freeze the water solid if it does not promptly drip off those coils. Both these features are there to maximize the cooling effect of the device on the room; the dehumidification effect is an additional bonus.

This means that although you can improve the effectiveness of a swamp cooler by dehumidifying its output, you can't get the room air temperature below the dew point of the air in this way- whereas you can with a conventional room AC unit that exhausts its heat outside the room.

So, dehumidifying the output of a swamp cooler makes little sense compared to just replacing both of them with a conventional room AC unit.

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  • $\begingroup$ Why does it improve the effectiveness of the swamp cooler? $\endgroup$
    – user20574
    Commented Aug 25, 2020 at 10:24
  • $\begingroup$ it dehumidifies the air, which increases the sweat-evaporation effect and makes your skin feel cooler. $\endgroup$
    – niels nielsen
    Commented Aug 25, 2020 at 15:59
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    $\begingroup$ okay but doesn't the dehumidification add heat to the air? $\endgroup$
    – user20574
    Commented Aug 25, 2020 at 16:02
  • $\begingroup$ yes, and this is why the overall process makes no practical sense. $\endgroup$
    – niels nielsen
    Commented Aug 25, 2020 at 16:17
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This method would work in humid climates. If you live in a humid climate a swamp cooler will not work because there is too much humidity in the air to begin with. Swamp coolers take hot dry air and turn it into cool moist air. The idea is to dehumidify the air going into the swamp cooler so that it will produce cooler air coming out. In theory this should work if you have a good dehumidifier and aim it to the back of the swamp cooler. This should help a swamp cooler cool more effectively in a humid region. In essence you are taking hot moist air, turning it to hot dry air so you can get COOL moist air. If the humidity going into the swamp cooler is significantly dropped, the swamps cooler should cool a room as much as 30 degrees below the room temperature. It would lower the temperature more than the dehumidifier would raise the temperature.

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