I'm well out of my depth here as both a HVAC engineer and organ expert.
I'm wondering if this is a crazy idea.

Fairground organs often seem to have problems with intonation on hot
days.  In relatively constant climates like England this is an occasional
irritation on days with exceptional weather, but here in New England
variable weather is the name of the game, with fluctuation of 25 to 30
degrees Fahrenheit within a day being common and week-to-week variation
of 50 deg. F. not uncommon.

So, would it make sense to temper (and while you're at it, humidity
control) the air feeding the organ bellows or blower to a much narrower
range of variation?  I'm thinking mainly summer conditions and wanting
to lower (at an extreme) air at 95 deg. F. and 90% relative humidity (RH)
to 75 deg. F. and 50% RH.

With a little web sleuthing I've determined that the change in
enthalpy between those two conditions is 32.4 Btu/lb (I apologize for
the units -- air conditioning guys don't seem to have adopted metric
or SI units).  If a big organ takes 1000 cubic feet per minute, that is
about 451 pounds of air per hour, or 14,600 Btu/hr.  With efficiency
losses and building in a factor for heating of the air on compression
in the blower, that is still in the range of a big room air conditioner.
(I'm imagining a split unit with an oversize heat exchanger in the
organ supply plenum to achieve the transfer in a single pass and not
impede the air flow)

Given that it might be practical (I stand ready to be corrected), would
it cause more problems than it solves?  In a worst case I could imagine
condensation forming on pipework on a really hot, humid day.  Would
there be other unintended consequences of blowing cold air into a warm
pipe?  Would it actually solve the intonation problem?  (Is intonation,
in fact, the major issue on hot days?)  Would one be better off tuning
the organ for the hot condition and then supplying warmed, humidified
air on cooler days?

Thanks for your toleration of my musings!

Roger Wiegand
Wayland, Massachusetts, USA