Does a fan reduce humidity in a closed area...?

Question

...HOW?
In my studio apartment, my hygrometer sometimes shows a 1 or 2 percent drop after turning the fan on. (No open windows.)

(Sorry, a little off topic)

Answer 1

It's possible for there to be a very minor change. As you point out, you have measured it yourself.

Here is how it would occur:
Moving air mixes so there are no "still or dead areas" where the air is not mixing. As a result the humidity in the room will average out with areas of higher humidity mixing with drier air from elsewhere in the room.

Answer 2

I'm not certain, but it seems likely the circulating air may increase the evaporation of moisture in the hygrometer.
A fan makes you feel cooler simply because the circulating air helps the moisture on your body to evaporate. That evaporation has a cooling effect.
A simple hygrometer is a nylon filament attached to a spring, and a needle to indicate movement. Nylon readily absorbs a small amount of water. As humidity increases, the nylon filament absorbs the moisture and stretches, permitting movement of the needle which indicates an increase in humidity.
If the humidity falls, the water evaporates and the nylon shrinks, pulling against the spring and moving the needle in the opposite direction indicating a reduction in humidity.
Since air movement will increase evaporation of moisture on your skin making you feel cooler, I think it isn't unreasonable to think the circulating air may evaporate moisture from the hygrometer.
To prove that, try setting the hygrometer in an area where it is shielded from the air movement and check to see if there is a change in the indicated humidity.

Answer 3

If a fan is working for some time,it becomes slightly hot due to friction in the ball-bearings.This you can cinfirm by touching the portion where the motor is located.It will be warmer.So, in a closed area, the continuos working of the fan will definitely add atleast some heat which may slightly increase the temperature of the room.Even though high temperature can hold more moisture, as it is a closed area, no addition of moisture is possible. Hence, the value of relative humidity will come down.

Answer 4

The fan will heat the room slightly (because it uses power) and as temperature goes up, the water bearing capacity of air goes up, so if the amount of water remains constant, the % relative humidity has to go down.
The fan will also eliminate pockets of higher relative humidity close to walls (where the presence of relatively cooler structure may cause a slight increase in relative humidity; the opposite of the effect explained above). Stir the air, and you have a more uniform distribution in the room.

But you have just as much moisture, and are actually a bit warmer...


And who let a parrot in?

Answer 5

The fan will heat the room slightly (because it uses power) and as temperature goes up, the water bearing capacity of air goes up, so if the amount of water remains constant, the % relative humidity has to go down.
The fan will also eliminate pockets of higher relative humidity close to walls (where the presence of relatively cooler structure may cause a slight increase in relative humidity; the opposite of the effect explained above). Stir the air, and you have a more uniform distribution in the room.

But you have just as much moisture, and are actually a bit warmer...


And who let a parrot in? The guy above me keeps stealing my answer??

Answer 6

Turning on a fan circulates the air, which drops the temperature of the room. Since the amount of water the air can hold decreases as air gets colder, the humidity would probably lower as the temperature lowered.

This is a guess though... So if there's a better answer posted, go with that one.