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If I hang wet clothes (which are at room temperature) in a hot (~28C) room and let them dry (alone or assisted with a standard fan), will the room cool down due to evaporative cooling when the windows are left open?

Obviously the amount of energy in a closed system has to remain constant, however if the windows are open would this evaporation help reduce the heat in the room by any significant level?

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  • $\begingroup$ significant is a subjective term $\endgroup$ Commented Aug 24, 2016 at 17:46
  • $\begingroup$ Ok then - is it likely to cool an average ventilated room by 1 degree celsius? $\endgroup$
    – BenAdamson
    Commented Aug 24, 2016 at 17:48
  • $\begingroup$ Google for "swamp cooler" $\endgroup$ Commented Aug 25, 2016 at 0:28

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If this question is still current. It does cool your room, yes.

This is called evaporative cooling. It raises the humidity and cools the room. If you have very dry air inside you won't need to open your window either.

It works due to water having a high index of 'heat of vaporization'. It basically means that as the temperature rises water molecules become more and more likely to grab heat from their neighbors, and take off as a gas. So when your hot indoor air hits your wet clothes, it'll pick up some hot molecules of water and cool the wet fabric, (which in turn cools the air).

The hot molecules in the air cannot heat up your body or anything they come in contact with until they hit something cool enough to condense back into water. When water condenses on a cool metal sheet, it does raise the temperature of the sheet of metal slightly, but the metal needs to be cool enough for the water to be able to condense to do that.

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Most probably you will feel it is warmer inside due to higher humidity, but what will happen to actual temperature will depend on many factors, such as temperature of the wet clothes and whether it is windy outside etc.

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No. Evaporation will cause a slight temperature drop at the surface of the clothing but the heat energy is carried away by the water molecules into the room.

The additional water vapor will raise the room temperature so slightly, but more effectively you will feel warmer because it will be more difficult for your sweat to evaporate and cool you down - with the added water vapor in the room!

I used to live in Palm Springs. And in the summer the electric bill was so high, rather than run the air conditioner at night I would lay down on a futon to sleep and cover my chest with a wet towel. In this case the evaporating water carried the heat away from my body as it evaporated and this did cool me down.

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    $\begingroup$ The additional water vapor would only raise the room temperature if it recondensed. Otherwise the energy used to separate the water molecules will remain as potential chemical energy. Indeed the air at the surface of the cloths would try to equilibrate temperature with the clothes and thus the temperature would drop slightly. $\endgroup$
    – Eph
    Commented Aug 24, 2016 at 20:46
  • $\begingroup$ If the room is open and it recondensed yes, locally yes. But if the room is closed, the pressure will rise, and temperature will also rise, but only slightly. For practical purposes there will be no rise in temperature, but humidity will go up, and it will feel 'hotter'. $\endgroup$
    – docscience
    Commented Aug 24, 2016 at 20:52
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    $\begingroup$ In sealed pressure vessel, containing, some liquid water, and some air at less than 100% humidity, when the water evaporates to bring the humidity towards 100%, the temperature drops... it will not rise... The average kinetic energy of the particles will be reduced because some of the energy went into breaking the transient hydrogen bonds present in the water. $\endgroup$
    – Eph
    Commented Aug 24, 2016 at 21:00
  • $\begingroup$ @docscience Raising humidity increases thermal discomfort, yes, but the question is by how much vs. letting that same energy stay in its original form as air-heat. I don't remember ever finding any definitive way to calculate this (even based on those temperature-humidity tables that don't apply to all individuals the same). In the end the 'wet some things that are in direct contact with your body' route seems to be the best - just like a refrigerator is still considered useful despite not being able to cool your whole house. $\endgroup$
    – Don Joe
    Commented Jul 15, 2023 at 10:33
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I know I am extremely late, but the simple answer is yes. Without making it sound too scientific, instead of actively dropping the room temp it works more by sucking heat out,(with windows open) which in turn will make room cooler. Water molecules are changed to a gas much easier which will get sucked out in the form of heat being removed. FUN FACT: it's been proven that this is exactly the method the ancient Egyptians used to make their rooms cooler when it was blistering hot.

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