Re. HVAC systems (Jim Ellis)

[James 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