Relative Humidity and Absolute Humidity!

Relative Humidity and Absolute Humidity!

Author
Discussion

paul.deitch

Original Poster:

2,155 posts

264 months

Saturday 28th October 2017
quotequote all
So I understand (more or less) RH and Dew Point etc.
But I want to understand how RH changes when you have a fixed amount of water vapour at a fixed atmospheric pressure and you change the temperature. I can't seem to find anything on it, but it may be because I am not using the correct search terms.
For example, a volume of air has 50% RH at 25C then what would the RH be at say 20C apart from "higher".

Anyone got a formula I can use please?

200Plus Club

11,193 posts

285 months

Saturday 28th October 2017
quotequote all
Just Google psychometric charts. Plenty of info on wiki how to read them etc. No need for calculating it yourself!
https://en.m.wikipedia.org/wiki/Psychrometrics

Edited by 200Plus Club on Saturday 28th October 23:26

Huff

3,226 posts

198 months

Sunday 29th October 2017
quotequote all
+1, look at a psychometric chart - example in SI units: http://eon.sdsu.edu/testhome/Test/solve/basics/tab...
Pick a line of constant temperature, water content ('mixing ratio' - teh nearly-vertical grey lines overlaid) or enthalpy to see how the values change relative to the constant(s) you've picked.

It's not a thing described by a single equation!

Another good word to understand: 'adiabatic'...

Edited by Huff on Sunday 29th October 00:34

paul.deitch

Original Poster:

2,155 posts

264 months

Sunday 29th October 2017
quotequote all
Thanks! My interest was to understand how much of the reduction of relative humidity in my cellar is due to the humidifier removing water and how much to the increased air temperature (about 1C) that the humidifier causes in the cellar. Not a lot is the answer.
I am now ejakated!

motco

16,229 posts

253 months

Sunday 29th October 2017
quotequote all
Psychrometrics will give you a better result than psychometrics.

200Plus Club

11,193 posts

285 months

Sunday 29th October 2017
quotequote all
What's an "r" between friends lol.
:-)
Could have been worse could have typed stoichometric lol

motco

16,229 posts

253 months

Sunday 29th October 2017
quotequote all
200Plus Club said:
What's an "r" between friends lol.
:-)
Could have been worse could have typed stoichometric lol
Only if you roll your Rs... biggrin

Simpo Two

87,088 posts

272 months

Sunday 29th October 2017
quotequote all
motco said:
Psychrometrics will give you a better result than psychometrics.
I did wonder what some silly HR test had to do with it!

hantsxlg

875 posts

239 months

Sunday 12th November 2017
quotequote all
Huff said:
Another good word to understand: 'adiabatic'...
Is that saturated or unsaturated ?