Dampp Chaser or not, that is that question!

[Farrell]

I would like to hear from others about DC dehumidifier system designs &
installations.

I live in Florida where most homes are air-conditioned, and relative
humidities (RH) range from a low of approximately 35% to perhaps 80%. I have
a 5' 10" Boston with the DC unit installed. I have monitored it for months
and it turns on when the RH reaches approximately 68% and turns off when it
reaches about 46%. I just checked it now and the unit is off and the RH is
59% @ the soundboard bottom. Clearly, this is not functioning as the
manufacturer advertises. I have 200W under my piano and when the room is 75%
RH, it is on approximately half the time to maintain the soundboard
environment in the 46% to 68% RH range.

I believe in the philosophy of putting a substantial amount of wattage under
the soundboard to enable lowering the RH to the 40% range under humid
conditions. I have observed that one needs to raise the temperature
approximately two degrees F for every three percent reduction in RH. Thus,
to reduce the RH in the area of a soundboard in a room that is 80 degrees F
and 70% RH, the soundboard area needs to be heated to a temperature of 100
degrees F to reduce the RH to 40%.

>From a previous post (below in its entirety):
>"....today the temp was 33 Celsius and 90% humidity. Now if I
was to install a D-C with 50 watts of heat it would bring the RH in the
piano down to 40% (rule of thumb 'for every watt of heat you remove 1% of
humidity') but that would mean that the heat would remain on constantly and
that in turn may cause considerable damage to the piano...."<

How on earth is a 50W rod going to pull RH down to 40%? Where does such a
rule of thumb come from? The grand installations that I see are usually only
50W. You should be able to put a ridiculous level of wattage under a piano
with no damage because the humidistat will turn it off.

I formerly had a 46" vertical piano that I put a 50W rod in. The rod would
raise the temp about 12 degrees F max for a drop in RH of approximately 18%.
So, if the room was 75% RH, my piano interior was about 58% RH. Better that
room RH, but my clients are not getting what they are paying for and think
they are getting.

I would like to know where the data used in the graphs in the DC brochure
comes from. That graph has room air going up to 95% RH and the piano
interior staying below 45% RH. That means that the piano interior would have
to be heated to a temperature about 33 degrees F above the room temp. How
many watts is required to KEEP the piano at say about 115 degrees F for the
summer?

What are others' thoughts on this. I would really like to hear from others
how many watts they put under a mid-sized grand, and if anyone else has
monitored the system's effectiveness, i.e. what are the turn-on RH and the
turn-off RH, and what percent of the time is the system energized.

Thanks, I feel better now.

Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com

----- Original Message -----
From: "Tony Caught" <caute@accessnt.com.au>
To: <pianotech@ptg.org>
Sent: Tuesday, February 01, 2000 8:20 AM
Subject: Re: Dampp Chaser or not, that is that question!


> John
>
> If you were in the tropics, yes I would go for the 55% humidity bar, but
you
> are not.
> What you have to remember is that their are two factors that control the
> moisture content of the timber in the soundboard (piano), humidity and
> temperature.
>
> I have a copy of the moisture content of various timbers as registered
with
> the CSIRO that cover most of Australia.
>
> You will find that in Newcastle the moisture content for Radiata Pine is
> very stable, varying 1 degree only from 15% to 16% with the average of
16%.
> Sydney, for the same timber in the same thickness (1/4") varies between
13%
> and 16% with the average of 14%.
> Melbourne goes from 12% to 17% with an average of 14%.
>
> Parramatta being further inland (not much but further) than Sydney, a
little
> less humid, thus you could expect the moisture content to be lower.
>
> Pianos in general are made with a moisture content in the soundboard of
8%.
> This 8% is expected to increase to say 12 or 13% to increase crown etc.
but
> that is another story. My point is that with your lower average
> temperatures, you require a lower humidity level in the soundboard.  Go
for
> the standard 42% humidity Dampp-chaser system, it will give you a better
> sound.
>
> Here in Darwin, today the temp was 33 Celsius and 90% humidity.  Now if I
> was to install a D-C with 50 watts of heat it would bring the RH in the
> piano down to 40% (rule of thumb 'for every watt of heat you remove 1% of
> humidity') but that would mean that the heat would remain on constantly
and
> that in turn may cause considerable damage to the piano.
> However the moisture content of the same timber in the tropics for Cape
York
> are 17% to 21% with a mean of 19%, thus a tropical or wet humidistat of
55%
> H was developed to ensure that the heater was not on all the time and that
> the piano moisture content was not reduced too much more than the lowest
> level of moisture content.
>
> Stick with the standard 42% is ideal around that area.
>
> Tony Caught IC PTG Australia
> caute@accessnt.com.au
>
> ----- Original Message -----
> From: Woodrow, John (Parramatta) <John.Woodrow@pil.com.au>
> To: 'Pianotech List' <pianotech@ptg.org>
> Sent: Tuesday, 1 February 2000 10:10
> Subject: Dampp Chaser or not, that is that question!
>
>
> > List,
> > Piano is a Kawai GS-30 grand that I am guessing is about 14 years old.
> The
> > piano is an ex-institution piano currently being restored.  It has lived
> all
> > its life in a mild coastal environment (60-90 F) where one can be pretty
> > certain the relative humidity of its environment was greater than 50%.
> The
> > soundboard has a few noticeable pressure ridges but nothing extreme.
Board
> > has minimal crown (although much the same as every other GS-30/40
> measured),
> > pins are TIGHT!  The to be restrung strings are rusty.
> >
> > The piano is now located in a room that the humidity swings from 60% to
> 80%.
> > On occasions it dips briefly to 50% on very 'dry' days.
> >
> > So my question to the list is do I:
> > (a) install a DC de-humidifier (tropical version which is set at 55% or
so
> I
> > believe), or
> > (b) because the piano has lived in a high humidity environment all its
> life
> > and settled into that groove just leave it alone.
> >
> > I am concerned that the pressure ridges may open up if the DC is
> constantly
> > trying to pull the humidity down from the 70% to 55%.
> >
> > Appreciate the wisdom of the list on this one.
> >
> > Regards,
> > John Woodrow
> > Sydney, Australia ICPTG.
>
>