Why is wet bulb temperature important? How does it effect us?

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Edit: Thank you all for the detailed answers! You guys are awesome.

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Anonymous 0 Comments

For humidity you can imagine a glass of water and some sugar you want to add.

You start with just the water at 0% sugar. Then you start adding sugar and dissolving it to raise the sugar percentage.

Eventually you will reach a point where no matter how much you stir the water, the extra sugar just won’t dissolve anymore. That means your water is 100% saturated with sugar.

Basically the same thing with air and humidity where air->water and water->sugar.

Anonymous 0 Comments

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Anonymous 0 Comments

There are already plenty of good explanations here, so I won’t add to that.

I used to work in the lumber dry kiln industry. Wet bulb temperatures are very important! The comparison between wet bulb and dry bulb tells us the humidity inside the kiln. This is especially critical when drying certain hardwoods when they are green. The (computerized) kiln controller would at times actually inject steam into the kilns to raise the humidity (raise the wet bulb temp). It sounds counterproductive, but it is necessary.

Another point is that humidity makes a huge difference in how the temperature feels to a human. I was born and raised in the Midwest US, and later moved to the East Coast. The cold “bites” a lot more here in the East because of the humidity. 0F/-18C feels extremely cold here, but it’s not that bad in the Midwest.

Anonymous 0 Comments

It’s related to humidity. How it effects us is high wet bulb plus high temperature equals we can’t cool down which means we’ll die.

Anonymous 0 Comments

Incidentally, the answers here explain why the cold in the UK can feel colder than arctic canada, and if we have a hot summer, it starts killing people.

The UK perpetually lives between 70% – 100% humidity. The cold will soak you to the skin, and hypothermia follows very quickly behind, and if its hot, anywhere above 30 C can be equally as lethal.

Anonymous 0 Comments

Most people think that you have some really cold ice, and you add a lot of heat energy to it, and then it gets to melting temp of 0ºC, and you add a tiny bit more then it melts into 0ºC water, then you add a bunch more and it gets to 100ºC, then a tiny bit more to convert it to steam, and it flies off.

That’s a completely wrong picture. Here’s how it really works.

Say you have some really cold ice and you heat it until it becomes 100ºC water. What does the heat energy input look like?

Well, you add some amount of energy to get it to 0ºC. How much is the “tiny bit” of energy required to get this 0ºC ice to turn into 0ºC water? In other words, how much heat are we adding not to raise the temperature, but just to break apart the water molecules?

That “tiny bit” turns out to be the same amount of energy as it takes to get the water from 0ºC to 80ºC—four-fifths of the way to boiling!

Okay, so now we get it to 100ºC water. How much energy does it take to convert that to 100ªC steam, that is, just to break the water molecules apart into a gas without raising the temperature? It turns out this “tiny bit” of energy is enough to take that amount of 0ºC water to 100ºC *six times*, or six times the water from 0ºC to 100ºC, if you prefer to think of it that way.

Why am i telling you all of this? Because when you sweat, and water evaporates off of your skin, it is taking away that amount of heat energy from you … the same amount of energy it would take to heat six times that amount of water from 0ºC to 100ºC. That is how much it’s cooling you off.

Now, let’s say that you are in perfectly dry air, and every time you lose a bit of water, it flies off and is replaced with perfectly dry air. This is an ideal cooling environment, and however much you sweat is how much heat you’ll lose.

But now we start adding humidity to the air. We add enough such that the amount you sweat is replaced by water condensing out of the air onto you. This means the humidity is somewhere between 0% and 100%, but not at either extreme. In this environment, you cannot shed *any* heat from sweating. (That’s not quite true since the water could be evaporating and condensing at different temperatures, but it should be clear that that’s a second order effect in terms of how much that affects heat transfer.)

What if we keep adding humidity after that point? In this environment, we’re going past equilibrium. Now, more water is condensing on you than you’re losing. Not only can you not sweat, but the environment is adding heat energy to you.

Anonymous 0 Comments

Did you read that Indian heat wave post? First time iv read about wet bulb effect was less than 6h ago and I’m 34yo

Anonymous 0 Comments

When air flows over a wet surface, some of the water will evaporate into water vapor. This change from liquid water to water vapor absorbs energy (cools). This cooling from the evaporation of water is called evaporative cooling.

There is a limit to how much water vapor the air can hold. Hot air can hold more water vapor than cold air. This is why winter air is so dry – cold air can hold little or no water vapor.

The wet bulb temperature is the temperature which would be achieved if the maximum possible amount of evaporative cooling occurred. In other words the temperature after the cooling caused by evaporation if water evaporated until the air became saturated (I.e., 100% humidity).

This is important because humans use evaporative cooling to maintain body temperature. Humans sweat when hot, this sweat evaporates (it is especially effective if air is blowing over the sweaty body parts), and the evaporation of sweat cools the skins surface.

The wet bulb temperature represents a limit on human body cooling by sweating. As the wet bulb temperature approaches skin temp of a human body (97F/35C), we lose the ability to cool down by sweating. We lose the ability to regulate our body temperature. This makes the location unsurvivable without external cooling.

With global warming, we’re seeing locations approach this point where the wet bulb temperature approaches the human body temperature, making places unsuitable for human life.

Anonymous 0 Comments

[This guy covers it](https://youtu.be/2horH-IeurA)

He also goes over a fair amount of other stuff in that video but it is featured.

Anonymous 0 Comments

Wet bulb temperature is how temperature feels to a living being. As others have pointed out it has to do with humidity.

For example you are walking in downtown Seattle, it’s raining (100% humidity) and it’s 33 degrees F (just above freezing). You are miserable. People claim the cold “gets in your bones”. All that water is sucking the energy from your body in the form of heat.

Now you’re walking around in Saskatoon or any other bone dry Canadian prairie city and it’s 33 degrees F (AKA 0.5 degrees C). You’re wearing a sweater with a wind breaker and feeling pretty comfortable. It’s because you are well insulated against the cold air as there is very little water floating around stealing your energy. That’s why people say, “oh it’s fine, it’s a dry cold”

Same dry bulbs temps, very different wet bulb temps.

Wind can cause temps to feel different as well. Last January we had a day that was -27 but “felt like” -43. When I hear this I automatically know this means it’s way too cold to be wet out but so windy that it’s gonna hurt

When I lived in Seattle, in winter I pretty much just felt cold all the time regardless of temp