Re. HVAC systems (Jim Ellis)

[Isaac OLEG]

I don't know if it can apply easily to large buildings, but I maintain
a little air pressure in my shop (pressure given by a dry airflow that
come from an electric dehumidifier - warm the external air to dry it
on silicate elements , the output is 20 - 25% HR and slightly warm).

The solution seem to work fine, as I where not able to have enough
protection with the outside, at last the pressure that comes from the
inside does not allow the humid air to come in (too much).

This method is certainly used in modern HVAC systems, together with
the drying of the renewed air.

Nowadays in PARIS actually the air is becoming more and more dusty,
and even in humid days, the R.H. stay lower than we could expect.

Interesting subject, the amount of money may be very large to provide
real solutions at those matters ?

Best Regards


Isaac OLEG

Entretien et reparation de pianos.

PianoTech
17 rue de Choisy
94400 VITRY sur SEINE
FRANCE
tel : 033 01 47 18 06 98
fax : 033 01 47 18 06 90
cell: 06 60 42 58 77

> -----Message d'origine-----
> De : caut-bounces@ptg.org [mailto:caut-bounces@ptg.org]De la part de
> James Ellis
> Envoye : vendredi 25 avril 2003 03:57
> A : CAUT@ptg.org
> Objet : Re. HVAC systems (Jim Ellis)
>
>
> Wim, Don, Chris:
>
> Wim, It's good that your university is having its HVAC
> system overhauled.
> However, I think asking that temperature be held to 72 F
> +/- 1 degree, and
> 50% RH +/- 2.5% is asking too much.  You said the engineer
> said he could
> not guarantee that.  I'll bet he can't, at least, not for what the
> university will be willing to pay for the job.  Are you
> talking about
> holding those specs throughout the whole building, or just
> for any given
> location in the building?
>
> The problem I have is with your 50% RH +/- 2.5%.  You just
> "ain't" going to
> get that where you are in Tuscaloosa, Alabama without going
> to all sorts of
> extreme measures.  That part of Alabama is a little hotter
> and more humid
> in summer than here in east Tennessee, but the variations
> aren't all that
> different.
>
> What I have found in this area is that too often,
> especially in large HVAC
> systems, the system may be more than capable of holding the
> temperature
> down, but it won't hold the humidity down because the
> chilled water is not
> cold enough in the heat exchanger to get the temperature
> down sufficiently
> to dehumidify the air.  That sounds like what you are
> describing there.
> There is a large church here in Oak Ridge where the HVAC system will
> quickly yank the temperature down into the 60ies in summer, but the
> humidity might still be up to 70%.  In the winter, it will
> be down to 30%.
> During the summer, where you are, when the outside humidity
> might be close
> to 100%, in order to get the inside humidity down, you
> might have to really
> chill the air to dehumidify it, and them warm it back up
> again to the
> temperature you want.  That engineer will know all about
> this, but it's
> going to cost plenty.
>
> Don Rose is right.  Except, where he lives, it would take
> those buffer
> zones he describes to hold the humidity IN during winter.
> Where you are,
> it would take the same to keep it OUT in summer.
>
> When I was a student at Carson-Newman (east Tennessee) back
> in 1950, and
> maintaining all pianos there, the music building had no
> HVAC at all.  Heat
> in winter was steam from a central plant on campus.  Summer
> cooling for the
> practice rooms on the top floor was by opening windows.
> Specs for the new
> music building that was completed in 1980 were that the
> system should hold
> RH between 40% and 60%.  I don't know what the temperature
> spec was, but
> the variation was not much.  That is reasonable, and the
> system will do it.
>  Tuning stability is worlds better in the new building than
> it was in the
> old one.
>
> Now, it's possible to achieve the specs you asked for, but
> when you do, the
> initial cost will go out the roof, and so will the utility
> bill.  When that
> happens, the budget people will raise the dickens, and shut
> the system back
> to keep the utility cost in line.
>
> Ask for something reasonable, and you might get it.  Ask
> for something
> unreasonable, and you will likely get nothing.  That's my
> view of it, for
> what it's worth.
>
> Jim Ellis
>
>
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