[CAUT] large and rapid humidity changes!

[Fred Sturm]

On 11/29/06 7:44 AM, "rwest1 at unl.edu" <rwest1 at unl.edu> wrote:

> 
> On Nov 28, 2006, at 4:25 PM, Fred Sturm wrote:
> 
>> Richard and Paul,
>>     Just to clarify, I am gathering that the problems you have been
>> describing are a result of a malfunctioning humidity control
>> system, within
>> the overall HVAC system. Is this correct? Not the result of an HVAC
>> system
>> pulling in wildly varying outdoor weather systems?
> 
> It may be a little of both.

    From various anecdotal sources, including this list, I have been coming
to the conclusion that some of the very worst situations for RH, with wildly
zigzagging levels, are in building with malfunctioning humidity control. I'm
starting to feel happy to be without <G>, although there are certainly other
places with well-functioning humidity control systems that leave me feeling
green with envy. 

> One element of the system wasn't used as far as I know.  In order to
> take moisture out of the building in the summer, there was a feature
> that supercooled the air to condense out the moisture and then the
> air would have to be heated to get a comfortable building
> temperature.  This was just too inefficient and expensive, even
> though I was told the building was equipped to heat air in the summer.

    Yes, this is in line with other anecdotal sources as well, that the
"super-cooling" and then re-heating of air to reduce RH in the summer tends
to be prohibitively expensive to run. My tendency is to think we should
advocate for at least a base level in winter - maybe lower than 40% in areas
with very cold winters, because of the various problems associated with
that, but at least 25-30% - and that the level might be adjusted seasonally.
IOW, allow it to rise and fall seasonally, but maintain reasonably tight
tolerances on a day to day and week to week basis. A seasonal variance,
carefully controlled, of 30-60% would be a dream come true for probably most
of us, and would cost a lot less to run than a 35-45% year round system.
    Bottom line, though, is we need to be talking to our HVAC and facilities
design people so that we can come to some kind of understanding. The
academics aren't real good at this sort of thing, for the most part. But
maybe over a few years we can come up with some basic guidelines and
alternatives, that we can make available. I think most of us are groping in
the dark on this subject.
Regards,
Fred Sturm
University of New Mexico