Where did the RH Go

[Sarah Fox]

Hi Bill,

My guess is that the humidity escaped via two routes.  Most immediately, it
probably dissipated to the rest of the house, where the RH was undoubtedly
lower.  This process would be very rapid with forced air ventillation and
slower with baseboard heat and open doorways.  Second, humidity is lost not
so much through solid materials (e.g. gypsum board, bricks, etc.), but
through air gaps in those materials.  An old house is bound to be very
leaky, so the inside air would exchange rather rapidly with the outside air
(requiring lots of work from the furnace, BTW).  As the humid inside air
escapes, the dry outside air enters.  When the dry air is heated, it falls
from, say, 70% RH to, say, 22% RH.  This very dry air from throughout *most*
of the house would freely exchange with the 34% RH air in the music room,
quickly dragging the room RH down to the household average -- 22% RH.

FAIW, I run two humidifiers in my home (in Ohio) to maintain the RH around
38%.  (Any higher, and I start to get condensation.)  One humidifier is in
the same room, at some distance.  The other is in an opposite room.  When my
humidifiers cycle off, the RH doesn't plummet and is relatively stable for a
fairly long period of time.  Sometimes the humidifiers will run out of water
a few hours before I can get to them, but the lower range of the RH beneath
my soundboard (stored in memory on my hygrometer) doesn't drop more than,
say, 1-2% when that happens.  The differences are that my house is tight and
that I humidify larger areas of my home.

A DC humidifier beneath my soundboard is quite unneccessary.  Besides that,
I question whether a teensy weensy column of steam can evenly distribute
over the underside of a grand piano.  (I have no question that it works well
in an upright.)  In contrast, whole-room/house humidification is fairly
stable and consistent if done well.

Peace,
Sarah


----- Original Message ----- 
From: "Bill Ballard" <yardbird@vermontel.net>
To: <pianotech@ptg.org>
Sent: Sunday, January 11, 2004 9:33 PM
Subject: Where did the RH Go


> I arrived to do a regular tuning on a Steinway M (1914 and all
> original) and which wanders quite a bit with the weather. The lady of
> the house had parked a room humidifier by the piano, and it was on
> duty for the first twenty minutes while I was there. My hygrometer,
> set on the corner of the piano farthest from the humidifier, read
> 34%. When the unit went "off-duty" (where it remained during the rest
> of my time there) the RH promptly descended, finally stabilizing at
> 22%. The temperature held steady during the whole time I was there.
>
> It was a shock to me, because although I was ready to assume that it
> was the air in the room which contained the 34% RH, I didn't expect
> to see the RH dissipate so fast. This was an old New England house,
> nicely remodeled but not recently enough to include
> from-the-inside-out insulation in the walls (ie., no vapor barrier).
> The only part of that side of the room which showed evidence of
> moisture content migrating outside was the glass on the nearest
> window, where there was a small corner of condensation.
>
> So where did the air's moisture content go? Apparently not through
> the walls, and the dissipation was far too fast for it to have been
> soaked up the the piano case and other wood surfaces in the room.
>
> For me, this was a pretty good demonstration that moisture content
> needs as direct a path into the piano as possible, as only a Climate
> Control system installed directly under the board can do. Clearly,
> any moisture poured into the air surrounding the piano vanished as
> soon as the supply cut off.
>
> Bill Ballard RPT
> NH Chapter, P.T.G.
>
> ".......true more in general than specifically"
>      ...........Lenny Bruce, spoofing a radio discussion of the Hebrew
> roots of Calypso music
> +++++++++++++++++++++
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