Humidity

[John Baird, RPT]

Dear Bud,

I think you've gathered good facts and definitions, but drew the wrong
conclusions.  (I read your post on the PianoTech list).

Relative Humidity *is* what counts.  40% RH at 80 F. and 40% RH at 40 F.
are two situations where there is in fact different amounts of absolute
moisture in the air, but in both cases the *same* amount of moisture is
*available* to go into the wood.  If RH stays the same, the amount of
moisture in the wood stays the same, no matter what the temperature.  If
RH drops, moisture comes out of the wood.

What happens if you have a sealed volumn of air that measures 40% RH at
80 F. and you drop the temperature?  The RH goes up.  The cooler air has
less capacity to hold moisture, so the same absolute amount of moisture in
that volumn represents a higher percentage of its capacity to hold
moisture--a relatively higher humidity.

>What I'm saying is that  Mr. Feeser's instrument at
)45deg/32%RH was in a very dry environment equivalent  to 68deg, 15%RH.

I believe you will find this statement to be incorrect. However, if you
were to seal off the room at 45 deg and 32% RH and raise the temp to 68
degrees, then you would get 15% RH.

Relative Humidity is what we need to be concerned with.

To close in a more humble fashion, I too am willing to be corrected if I
have got this all wrong.

Regards,

John Baird, RPT