100 % humidity

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This topic has 11 replies, 8 voices, and was last updated 15 years ago by molgrips.

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100 % humidity
slimtubing
Free Member

I still don’t understand this humidity malarky but here in Auckland we are “enjoying” our full complement and its most uncomfortable at night. last night it was 23 degrees all night and I don’t think anyone in the city slept at all. Would give my left one for a couple of hours of the UK’s weather.
Sweatytubing.

Posted 15 years ago

GrahamS
Full Member

100% humidity? Isn’t that water?

Posted 15 years ago

snaps
Free Member

I think it means that the airs ability to absorb water vapour is at 100%
Don’t you have aircon?

Posted 15 years ago

Fresh Goods Friday 700 - The censored edition

kevonakona
Free Member

IT’s also a non-sense indicator. Dew pint would be much more sensible.

Posted 15 years ago

gonefishin
Free Member

Dew point = 100% humidity by definition.

Snaps is essentially correct. It is a measure of how much water the air can hold, relative to the maximum, at that particular pressure and temperature.

Posted 15 years ago

sockpuppet
Full Member

measure of how much water the air is holding, relative to the maximum it can hold, at that temp and pressure

affects ease of evaporation – at 100% you don’t get any

Posted 15 years ago

molgrips
Free Member

It means 100% relative humidity, which means that the air is holding as much water vapour as it can. Sweat is meant to cool you down by evaporating from your skin and taking up some latent heat of evaporation as it does so. However this doesn’t work too well (at all?) in 100% relative humidity since the air’s already saturated. I guess sweat would only work if you were moving about – then sweat would be removed from your skin by the action of air flow.

Why don’t we overheat and die in 100% humidity if we stay still?

Posted 15 years ago

GrahamS
Full Member

Ah got you. So it is like a saturation point?

Posted 15 years ago

gonefishin
Free Member

“So it is like a saturation point?”

Sort of. It would certainly be true to say that the air is saturated with water but “saturated” in this context can actually mean other things as well.

Posted 15 years ago

thisisnotaspoon
Free Member

yep, theres two measures of humidity, absolute and relative

relative is a % compared to the maximum the air can hold, supercooled air can go above 100% (by supercooled i mean air that contains moisture that by all rights should have condensed by now, but has nothing to condense onto)

absolute is measured in grams H2O per m3 (or similar), but means nothing in reality as if its hot then relative humitidy drops and it feels very dry, whereas in the cold relative humidity rises (for the same absolute humidity) and it will feel clammy.

Posted 15 years ago

thomthumb
Free Member

HTH

Posted 15 years ago

molgrips
Free Member

Exactly, that’s the reason we get dew or frost in the evenings. The relative humidity might be say 80% in the day but as the temperature drops, the amount the air can hold goes down. So for the same amount of actual water vapour in the air, the relative humidity goes up. Eventually the air can’t hold all its water and it condenses onto the grass and stuff. Which is why at Mountain Mayhem even when it’s been sunny in the day it’ll feel really damp on those night laps. Then when it warms up again in the day, the moisture carrying capacity of the air increases and it feels much drier.

Interestingly, in Finland in the wintertime the humidity was often almost 100%. This is of course relative humidity – in absolute terms (as TINAS shows) there wasn’t much water vapour in the air but because it was so cold, the air couldn’t hold much. Because it was so far north the temperature hardly varies in the daytime, so there wasn’t any hoar frost and the air never warmed up.

Posted 15 years ago