How do fans work and do they make our rooms any cooler? No, fans simply make us feel cooler since they are moving the same air over our skin. In fact, if the room is closed the fan may actually raise the room temperature but only very slightly. What they do is move relatively dry air across our skin which in turn picks up the skin moisture, such as sweat and takes it away.

On hot days our skin temperature reaches roughly the same temperature as the rest of our bodies making the process of cooling through sweat useless. However, if there’s a breeze then that moisture can be easily carried off, making room for more heat to make its way to the skin surface. In this way fans help lower our body temperature while not actually cooling us directly. Another way of looking at this is by thinking of the process as a speeded up version of evaporation.

The other process that fans tend to speed up is that of what’s called convection, this means that even if we aren’t sweating significantly fans can still lower our body temperature. Thermal energy tends to move from hotter places to cooler ones just like steam escaping from a boil-ing kettle. Similarly, the air immediately around us tends to be hotter due to this effect. Now, on hot days this process also stops being effective pretty quickly which is where the fan comes in. Fans take this hot air and move it away from us thus bringing in relatively cooler air to repeat the process.

The point to take away from this is that fans, through evaporation and convection, can lower our body tempera-tures but cannot actually cool a room. So, unless your fan is pointing toward a person or whisking in cool air from an open window switch it off if you’re not going to stay in the room and save some money on the electricity bill.

http://www.iflscience.com/