[pianotech] Clarification Question: i'll take a pass

[Dean May]

>> Wrong

Again! Dag nab it. And I so want to be right, too.  :-)


Dean

Dean May             cell 812.239.3359 

PianoRebuilders.com   812.235.5272 

Terre Haute IN  47802

 


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Friday, August 28, 2009 10:43 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Clarification Question: i'll take a pass

Dean May wrote:
> Actually, no, I am referring to freon type regular a/c units. What I am
> saying seems counter intuitive which is why I posted the warning. 
> 
> How does moisture condense out of the air? It is the dew point principle.
> You may have heard the evening weather man talk about the dew point
> temperature. For example, the current outdoor temperature may be 90
degrees
> F with a RH of 60%, the dew point temperature would be 74 degrees. What
that
> means is, assuming barometric pressure remains constant, if the
temperature
> would cool to 74 degrees the RH would approach 100% and water would begin
to
> condense out of the air. This is exactly how dew forms on the grass
> overnight. http://en.wikipedia.org/wiki/Dew_point_temperature

Right.


> This is also how the a/c units pull moisture out of the air. As the air
goes
> over the evaporator coils the temperature drops below the dew point (which
> means RH goes to 100%). For every degree below the dew point the air is
> cooled, water must condense out. So for our example of dew point at 74
> degrees, the air coming off the coils may be around 40 degrees F. Air at
40
> degrees and 100% RH won't hold as much water as air at 74 degrees and 100%
> RH. The difference is the amount of water that is condensed out.

Right again.


> What is important to realize, though, is the RH of the air coming off the
> coils is still at or near 100%. This is the air that comes out of the
vents,
> and if it is blowing on the piano, you are blowing really moist air on it
> (cold, but moist) and the piano will pick up moisture accordingly. 

Wrong. How can air that has had moisture removed from it by 
the process you outlined above have more moisture than the 
ambient room air from which it came? Again, RH% isn't MC.
Ron N