Climate Control; DC thoughts and concerns

[Sarah Fox]

Hi Robert,

> ...Heat would escape the soundingboard from the topside, and so the
> effective temperature of the board would be roughly the numerical average
of
> the air temperature above and below the board.  Thus, the board would not
> really be kept at its target MC...
> <<<<
>
> I raised this very question with Bob Maier, who told me that their direct
> measurements of MC in the soundboard show closer control of wood MC than
> the "numerical average" analysis would lead you to believe.  I can imagine
> several explanations for such a fact.  For one, the air currents below the
> soundboard are being driven by a fairly large temperature gradient.  Above
> the soundboard, there is not so big a temperature gradient, so the air is
> more calm, which means the top the soundboard is not being washed by
> ambient air as much as the bottom is being washed by DC discharge
> air.  This would tend to bias the MC of the board closer to what is being
> forced by the DC discharge.

OK, this makes some sense.  I wonder if the system could be improved yet
again with a bottom cover and a couple or three tiny CPU cooling fans (i.e.
the 12VDC variety that goes on the CPU chip's heat sink -- hardly audible)
to circulate the air under the cover.  Has anyone tried anything weird like
this?

  Another factor is the location of the
> humidistat.  If the humidistat is located directly between the DC and the
> board, then the DC's immediate discharge is what is being controlled.  But
> if the humidistat is located a little off center so that it sees air that
> has already been partially diluted by ambient air, then THAT is what is
> being controlled, which means the immediate DC discharge will be beyond
the
> target humidity by some amount.  This may be just the amount necessary to
> compensate for the fact that the board is seeing DC air from the bottom
and
> ambient air from the top.

That makes sense.  Of course the mixing-fan idea (above) would make the
environment more homogenous and would partially nullify this beneficial
monitoring error.  Still, I would think it would be better to have the
atmosphere under the piano as homogenous as possible.

> You also mentioned DC cycling.  That is not a real concern.  The frequency
> of this cycling is bound to be quite high, compared to the MC response of
> the board.  The humidistat is a fast-acting plastic strip, while the board
> needs much longer exposure before it significantly changes its MC.

How fast to these DC units typically cycle?

Thanks for the very informative post!

Peace,
Sarah