Humidistat Accuracy

[Isaac OLEG]

Ron, your are certainly right too !

But is not the real weight of the water in the air the final factor we
should consider ? (as being able to affect piano parts)?

In this case, R.H is only an indication, that was the idea of my
(exaggerated) post.

Anyway, as I understand it, the warmer the air, the most water he is
able to accept before saturation, so for example when people open the
windows in winter believing they will add some moisture inside, in
fact they do not because the cold air outside is may be showing more
H.R, because nearer of saturation, when it goes in the warm room, the
quantity of water it contents is in fact less in proportion to the
saturation point (R.H.).

The same apply to the humidistat, so I say that H.R. values is not
sufficient, or we may say that we accept a range of H.R. and a range
of temperature together.
If my room is a bit warm and I read 50% RH it is fairly possible that
when colder there will not be as much R.H showed by my hygrometer, as
I understand it anyway, it is useless to maintain the same H.R all
along the year, or the temperature should be maintained too.

I have no idea of the amount of changes of the air pressure when at
ground level, but they play a role in the numbers that the hygrometers
give us too (and the way humidistat react.

It is not to say that the DC humidistat are precision devices, but I
guess that they are playing they role generally well (I hope so
anyway)
What I should be more concerned is of their use in the high humidity
ranges, as the rods may not be able to warm enough air to absorb
enough the moisture.
Then we obtain warm moist air, and that can be prejudicial to the
instrument.

In France the piano trade tend to consider high R.H as being good for
the pianos (i.e.) 50%-60%.

As these agree parameters easily encountered in homes this is a good
argument for selling pianos (and a bad one to sell Damp Chaser
systems) It may be an old habit from the iron strings, and wooden
frames.

Probably clear as mud, any clearing will be appreciated.


regards.

Isaac OLEG




> -----Message d'origine-----
> De : Ron Nossaman [mailto:RNossaman@cox.net]
> Envoyé : lundi 2 décembre 2002 23:56
> À : oleg-i@wanadoo.fr; Pianotech
> Objet : RE: Humidistat Accuracy
>
>
>
> >It may be in the high end of the switching zone.
> >
> >55% with a high temperature in the room is the same as 42% with a
> >colder one.
> >So the only data about RH is not enough for me, as you look (I
> >presume) for the stability of the wood.
> >
> >Regards.
> >
> >Isaac OLEG
>
> You're absolutely right. A 37°F room at 42%RH has an MC of
> about 8.23%. So
> does a room of 145°F at 55%RH. It's probably working fine
> and Terry just
> has his thermostat set 75°F too high. Could happen to anyone.
>
> Ron N
>
>