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Why don't swamp coolers push air instead of pulling air? If they pushed air, the fan/motor wouldn't get wet!

I'm designing my own DC, battery-powered, off-grid, swamp cooler for an RV. I'd like to design it so the fan motor is on the outside, followed by the evaporative pad, then connected to the RV window. Essentially the opposite of normal swamp coolers which have the evaporative pad on the outside.

This seems like a no-brainer because your fan/motor won't be operating in the wet/humid air, extending the life of the fan/motor. This is important to me because the DC fan/motor that I'm purchasing is expensive and I'd like to extend it's life as much as possible.

Am I missing some basic physics for why my idea won't work? Or won't work as well as a conventional swamp cooler?

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The main reason swamp coolers are typically arranged that way is to minimize their footprint. That arrangement allows the motor to be inside the air-handler box, instead of poking out the end.

Additionally, moisture is not as much a problem for electric motors as heat. The overwhelming majority of the moisture passing by the electric motor is vapor, or "humidity" rather than mist. If there's enough mist to make the motor wet, then the cooler isn't working properly because evaporation is the key ingredient. Most electric motors fail because the insulation around the wires that make up the magnetic coils melts or deteriorates. This shorts out the coil, which no longer generates a sufficient magnetic field to drive the motor. Keeping the motor cool would actually be a more important consideration than keeping it dry. But even the moisture available to the motor shouldn't be getting it wet.

I can't think of any reason that reversing the fan arrangement couldn't work.

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  • It's good to see someone answer the question.
    – Rob
    Commented Jul 19, 2016 at 13:14
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I believe the main reason is actually because pulling results in more uniform airflow though the cooling medium (because it creates suction on the whole pad vs just the parts that would be in front of the fan's airstream).

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  • In the air handlers I am familiar with the fan "pulls" air through the filter, but "pushes" it through the refrigeration coil. In the condensing unit air is "pulled" through the coil. Air is "pushed" through an automobile radiator.
    – Jim Stewart
    Commented Jul 14, 2021 at 10:21
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When you create suction inside the cooler the atmospheric pressure drops which makes more water to evaporate more easily.

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