– If air temperature is consistent in a room, why does air from a room fan feel cool on our skin? It’s the same air with the same temp… just faster
In: Biology
Please search “How does a fan cool you” is asked every day in the summer.
Your body senses heat flow. If your body warms the air near your skin, it says “the air is cooling me”. If the skin can’t transfer heat to the air, or even worse heat is transferred from the air to your body, the nerves say “very hot here”.
When the air is still, you warm it and it hangs close to your skin, making you feel warm. This is why sweaters are nice in winter. But if a fan blows the warm air away and replaces it with “average” air from the room, your body can warm that new air up and you’ll feel cool.
I would say it’s partly mental but also some science to it.
Mental, because your brain automatically connects air flow to “cool breeze” so it feels better.
Scientifically I would say that your body is constantly radiating heat. Meaning there is a bubble of heat around your body that eventually dissipates/cools. As air blows over your skin, that heat is being pulled away from your body, rather than just idly radiating the heat away, which cools you down more/faster.
A facilities manager (maintenance guy) for a business I used to work at always got complaints about how hot it is in the offices. The temp was always at 70 during the day, and a lot of folks would dress appropriately if they were too cold, such as pants and sweaters. The manager would turn up fan speed a little bit, rather than drop the temperature, and the ones complaining were happier.
The temperature in a room is not quite consistent. There can be several degrees difference just across a room even when there is no particular heating or cooling. Around a heat source like a heater or a computer the air can be quite noticeably warmer as the air takes some time to disperse through the room. Of interest here however is the air around your skin. Your body generates heat, quite a bit of it actually. So your skin heats up the air around you. This hot air around your body slowly disperse through the rest of the room but this takes time so the air around your body is quite a bit warmer then the rest of the room. A fan helps blow this air away from your body replacing it with cooler room temperature air.
Moving air moves heat away from your body about 10x as efficiently as still air. Your body feels heat transfer not temperature, so moving air feels much colder.
This also applies to something like running though in that case you have extra effects of sweat evaporating which takes more heat away from the body. Compounding results as moving air will evaporate your sweat much better than comparable still air.
As long as your body is warmer than the room, your body heats the air around you.
Air from a fan transports the warm air away from you and replaced it with cooler air that hasn’t recently been heated by a body.
We cool through evaporative cooling – water, when it goes through a phase change from liquid to gas (evaporation) requires a bit of energy to make the leap to gas form. It pulls that energy from its surroundings- which is you if anything is evaporating from your skin’s surface. Evaporation is sped up when you blow more air against the evaporating material. If there is nothing to evaporate, the is no temperature change.
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