Rel. Humidity (was Re: Voicing question

[Greg Newell]

On Mon, 09 Mar 1998 18:43:21 -0800, Tim Keenan & Rebecca Counts
wrote:

>dpitsch wrote:
>> 
>> Yes, Damper Chasers[sic] affect the RH in the room, and in fact the home. <snip>
>
>earlier post:
>> > >  Hogwash.  Water in the air is a vaper.  All vapers disperse to
>> > >all parts of the room and home.  To think that the bellyrail would keep the extra humidity
>> > >from affecting the hammers and action is just not consistent with
>> > >how vapers react in an enviroment.
>> > >Davd Pitsch
>
>To which Greg Newell responded:
>
>> > Dave ,
>> >         Does this mean that Damp Chasers do not in fact control only
>> > the piano but in fact the entire room as well?????
>> >                                 Greg Newell
>> >True, to a point. However, as Dave points out, a Dampp-Chaser can not 
>come close to a room- or furnace-dehumidifier in adding absolute volume 
>of water to the air.  It doesn't try to, nor is that really relevant.
>
>RELATIVE humidity (RH)n is what we are talking about. The amount of water 
>which air can hold without condensing is a function of its temperature. 
>RH is an expression of the amount of water in a given volume of air at a 
>given temperature compared to the amount of water that the same volume of 
>air could hold at saturation point at the same temperature. Yes, water 
>diffuses through air quite quickly, but it moves from areas of high 
>concentration to areas of low concentration.  That is the definition of 
>diffusion.
>
>In a perfect world (or a museum) it is possible to maintain an 
>environment at a relatively constant RH.  In most houses, particularly in 
>climates where there is a 50 C (90 F) difference between summer and 
>winter temperatures, this is an impossibility.  In houses built in Canada 
>before the last 15 years or so, if you tried to maintain an interior 
>humidity of 45% at 21 C (72 F) when the outside temperature is -25 C (-10 
>F) there would be water running down all your windows and condensing in 
>your insulation, because in the boundary layer at the walls and windows, 
>the temperature is a lot lower than 21C and the RH is therefore >100%.
>
>To lower RH, in summer, you must either raise the temperature of the air, 
>or remove water from it. If the R.H. outside, at say 35 C (90 F) is 85%, 
>when you bring that air inside and cool it to 21 C (72 F), you are at or 
>near the dew point. In a house, where humidity is usually a problem in 
>summer, if at all, you don't want to raise the temperature, so you must 
>remove moisture by using refrigeration to create a "sink" -- a cold zone 
>where local RH is 100% so that water will condense and can be disposed 
>of.  Unfortunately, unless you have air locks on all your doors, this is 
>a losing proposition too, and it becomes practically impossible, or at 
>least very expensive, to keep R.H. down to 45% in summer.
>
>Wood doesn't care about what the relative humidity is on the other side 
>of the room. Moisture in the wood is in equilibrium with moisture in the 
>boundary layer of air around the wood. If you raise the RH, by adding 
>water to the air in the immediate vicinity of the soundboard, the wood 
>will reach equilibrium with that humidified air.  As long as you are 
>adding moisture to the immediate environment as fast as it can diffuse 
>away, you are accomplishing your aim.  Picture a cigarette burning in an 
>ashtray.  The smoke will diffuse to all areas of the house, and pretty 
>quickly, too--but it will always be orders of magnitude more concentrated 
>at the ashtray than on the other side of the room, as long as the 
>cigarette continues to burn.
>
>Another "thought experiment" (as Einstein called them).  Imagine having a 
>nice hot shower in winter with the bathroom door open and the exhaust fan 
>off.  Put a hygrometer on your vanity top and another on the other side 
>of the house, with all intervening doors open.  The R.H. in your bathroom 
>will be 100% within minutes, and will stay there until the hot water runs 
>out.  The R.H. on the other side of the house will never approach 100%, 
>no matter how long you run the shower.  The wallpaper in your bathroom 
>will peel, that in your bedroom won't.  That cellulose is the same as the 
>cellulose your soundboard is made of.  Likely even made of spruce.
>
>It is possible in some parts of North America to control room humidity 
>within the limits which we are told pianos "like", but in many areas it 
>is quite impractical, if not impossible.  I think the Dampp-Chaser system 
>is the next best thing.
> 
>Tim Keenan
>Noteworthy Piano Service
>Terrace, B.C.
>


Tim,
	This is all well and good. I agree that the D-C systems can
and do provide some level of stability in verticals.  I'll even
stipulate that they cna help a grand as well, but, you did not
address the disparity between the action cavity and the sounboard
area.  Are we creating imbalances? If so can this be a good thing for
the pianos structure as a whole?  What are the possible ramifications
of "wet" hammers and a "dry" soundoard and bridges  and pinblock? 
Any furthur thoughts?
						Greg
Greg and Mary Ellen Newell
Greg's Piano Forte`
Lakewood, Ohio 44107
gnewell@en.com