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[deleted] t1_j0kvqoh wrote

Reply to comment by TonyJPRoss in How does high humidity affect perceived temperature in hot and cold environments? by MindTheReddit

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Ninjaromeo t1_j0l4o14 wrote

Funny. I didn't think much about it for hot climates. When it is cold and you are wet, you definitely feel more cold.

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[deleted] t1_j0l6ffl wrote

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m31td0wn t1_j0l8gl9 wrote

That's just evaporative cooling, same as sweating. Although it is possible to cool the air by increasing relative humidity--that's how "swamp coolers" work. Basically humidifiers that spray a fine mist of water into the air, which in extremely arid environments evaporates quickly and lowers air temperature by raising relative humidity. It takes energy for water to phase shift from a liquid to a gas, and that energy comes directly out of the air it evaporates into.

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[deleted] t1_j0lhpn1 wrote

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m31td0wn t1_j0lo7hj wrote

Haha well temperature is just kinetic energy of molecules. Picture the atmosphere as a giant bag of marbles being shaken around. The faster it's being shaken, the more heat it contains. But if you add more marbles to the air, it becomes heavier, and harder to shake. So the shaking slows down. Keep adding more marbles, it's heavier and heavier, so it gets shaken slower and slower.

Not a perfect analogy but I think it gets the job done. The energy required to turn water into a gas is drawn out of the air, causing the air to lower in temperature.

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kilotesla t1_j0lvkj4 wrote

I think a better (but still sloppy and qualitative) analogy is that if the marbles bouncing around hit a layer of stationary marbles held together with pudding, and they knock loose some more marbles when they hit, that process will absorb use up some of their kinetic energy.

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Dani_924 t1_j0l8xoa wrote

It’s like being in a steam sauna but you’re outside and can’t escape it. High heat and humidity are brutal. Also see ‘wet bulb effect’. Sweating does absolutely nothing to cool you off. Swimming can help as long as the water is cooler than the air temperature.

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doghouse2001 t1_j0n1auw wrote

Swimming can help as long as water is cooler than your normal body temperature.

If it's 100 degress F and the water is 90 degrees F you'll still overheat and die.

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Dani_924 t1_j0nany9 wrote

Good point. I was thinking of a regular pool or natural body of water, which for the most part are usually cooler than a persons body temperature. I would definitely not recommend swimming in a hot tub during a heat event.

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s0rce t1_j0lgqxm wrote

Then the humidity would make you warmer by reducing evaporative cooling

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Dani_924 t1_j0mesr1 wrote

Yeah that’s exactly what happens. Where I live in Canada, in the summer there is the air temperature, and then there is the ‘humidex value’. So it can be 25 degrees Celsius but with the humidity it will “feel like” 30 degrees Celsius. It gets dangerous when the air temperature is already in the 30 degree range and the humidity makes it feel closer to 40 or higher. Then we get heat warnings for people to be careful because you can get heat stroke pretty easily.

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Ashmedai t1_j0lgqbb wrote

> Funny. I didn't think much about it for hot climates.

Not so fun fact. There is a rare environmental condition that can occur where the heat index around you can go up higher than the body's cooling ability can handle. If you are caught in such an environmental condition and cannot find shelter, you'll die. No amount of water will help, as sweating cannot cool you.

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kilotesla t1_j0lb1tj wrote

When you are wet is a little different from the air having high humidity. If you are wet, evaporative cooling has an impact, and if your clothes are wet, their insulation capability is degraded.

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[deleted] t1_j0lccuw wrote

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[deleted] t1_j0li6so wrote

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Dr_Vesuvius t1_j0lqxuw wrote

No, I don’t think so.

Firstly the UK’s humidity is one of the reasons why winters are relatively mild compared to Poland (for example).

The reason the UK struggles when snow falls is because we’re not so cold that snow is inevitable. People, business, and the government mostly aren’t prepared for snow and ice.

I’m in London which is one of the warmest parts of the country (southern + eastern + urban heat island) and we haven’t got anywhere close to -10. Our coldest nights might have got as low as -5 but every day has been above 0 except maybe Monday. I’d guess you’re probably in Scotland or Northern Ireland, maybe NW England or North Wales?

If we were like Canada, Northern Europe, or inland US, then local government, railway operators, and motorists would always be prepared for low temperatures and would react accordingly. The UK is not.

I will say that this week’s snow was met by the best response I can remember. There was a big snowstorm about ten years ago (maybe 2010?) that made normal life very difficult. By the time I left the house for work Monday morning, the main roads were clear, the pavements were gritted, trains were running as normal, and most Tube lines were partially open.

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[deleted] t1_j0lrrm0 wrote

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Dr_Vesuvius t1_j0ltj95 wrote

Ah, gotcha.

So I think there are three issues wrt. sensory sentiment.

  1. we’re sheltered by our humidity and the Gulf Stream, so we aren’t toughened against cold the way that Minnesotans (for example) are. We don’t wrap up as warm as those people do. I don’t own thermal underwear or insulated trousers, for example.

  2. our homes are generally poorly insulated. Right now it is 12 degrees in my house. The walls, loft, and floor are not insulated and the curtains have limited thermal properties.

  3. humid air takes longer to warm up. If you are drying laundry inside then you need to run the heater for longer to feel warm.

Suspect if you dropped a British person moaning about the cold somewhere dry and cold, they’d still moan about the cold. We like a very narrow temperature range!

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[deleted] t1_j0lv0kd wrote

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squirlol t1_j0n7ejk wrote

Mate, if you're bothered by the cold at the moment, get yourself some merino thermals/base layers (if you can afford them, smartwool, icebreaker, or similar brands are the best, but there are much cheaper options too). I'm from New Zealand where the weather is even milder than here in the UK (rarely goes below 0), but our houses are even more useless, often completely uninsulated and very draughty. So we're used to indoor temps of below 10 in the winter. When I was a student sometimes it was below 5 degrees, just the same temperature inside and out. Lived in thermals all winter as a matter of course. Now I've just brought that habit along with me to the UK and I'm finding it extremely comfortable here this winter.

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[deleted] t1_j0naeh5 wrote

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squirlol t1_j0nha8q wrote

Yeah, they don't overheat easily, if it's less than about 20 inside they're very comfortable for me, tolerable up to maybe 23. But they still make a huge difference outdoors or when it's cold inside. I wear mine to/at work, we have the office at 19 I believe.

They don't require a lot of washing, they still smell fine after 4-5 wears if you don't, like, exercise in them. Downside is they do need to be washed with wool detergent rather than normal laundry powder/liquid, but that's not a huge deal.

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CapOnFoam t1_j0lknvk wrote

Same! I always wondered why cold weather in dry climates felt "warmer" than the same temps in the Midwest. I've always associated humidity with "feels warmer". Very cool.

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iowamechanic30 t1_j0mq3qd wrote

This is actually how air conditioning and refrigeration work too. The difference is we force a refrigerant to evaporate using a pressure change witch draws heat out of the air; we then force it to condense using pressure and temperature changes to make into a continuous process.

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TWeaKoR t1_j0m5qza wrote

It's also why you should use air con when blowing hot air to demist your windows in your car. The air con cools the air, which lowers the humidity and condenses out some of the moisture, then heating it up leaves air with relatively lower humidity. This is because the air's capacity to hold water goes up with temperature, so if you have the same amount of water in cool air as hot, the hot will feel drier.

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iowamechanic30 t1_j0mqux2 wrote

This is done automatically in almost all cars on the road today and vintage cars aren't set up to work like that so don't turn the ac on to defrost your windows.

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TWeaKoR t1_j0n0iu3 wrote

It's done automatically in cars when you set it to the window clear settings, for the most part, and more and more cars have proper climate controls, but that isn't always the case.

Regardless, the reason it automatically turns AC on is because it clears the mist. If you have AC off and find you're getting misting on the windows, putting AC on will probably clear it, even when it isn't blowing on the front windshield it should lower the relative humidity in the cabin. Yes, it will use a tiny bit more electrical power from the engine, but it serves a purpose.

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iowamechanic30 t1_j0ojm98 wrote

I don't think we're on the same page. There are people that will read this post and turn their heat off and turn the ac on to defrost their windshield. I am trying to prevent that, when you turn the defroster on the car automatically engages the ac to dry the air out but also blows hot air. Just let the car do its thing.

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