Recording hygrothermographs and dataloggers

Tom Dixon <tom.dixon [at] ngv__vic__gov__au> writes

>I would be grateful to hear from the list regarding positive and
>negative experiences of replacing recording hygrothermographs used
>for simultaneous monitoring of several large gallery spaces on a
>long term and continuous basis with newer technology.

There's an old saw that goes: "A man who has only a hammer is likely
to treat every problem like a nail." The converse of this funny old
saying is the fact that some problems really are like nails, and it
is equally unwise to use anything but your trusty old hammer to
drive them home. I believe this applies to the use of data loggers
vs. hygrothermographs.

For administrative purposes (satisfying loan requirements or
applying for grant money to upgrade HVAC systems for example), the
electronic information provided by data loggers is more portable,
flexible, and easier to store, copy and retrieve than
hygrothermograph charts. I once did a quick calculation for a client
and determined that their 6 hygrothermographs set to a 7-day cycle
would in one year generate a stack of charts 3-inches thick weighing
over 10 lbs (85mm/5 kilos)! Additionally, most data loggers provide
a means of calculating dew-point or absolute humidity directly from
the logger application, and this can be highly useful for technical
diagnostic purposes.

For practical day-to-day monitoring, I feel that hygrothermographs
have the edge over data loggers in that they are (as you've
mentioned) real-time, interactive monitors as well as recorders.
With a simple glance, anyone can tell what the conditions are
currently, as well as what they were yesterday or last weekend. The
more people who observe the data throughout the week, the more
likely it is that problems will be identified quickly and resolved
before damage results.

There are some data loggers on the market that include an LCD
read-out of temperature and humidity, some even have alarms that
will activate when defined limits have been exceeded. These are more
useful than the "black box" data loggers of the past. Still, as any
monitor becomes more discreet, fewer people will be paying regular
attention to what it says. This increases the likelihood that
dangerous trends will go unnoticed.

It's been my experience that a charts from a well-calibrated
hygrothermograph tend to carry a little more weight with building
HVAC engineers than the same information would from a logger placed
in the same location. The distinction is psychological: Some
engineers see data loggers as cheap devices employed by smarty-pants
conservators to spy on their more sophisticated building sensors,
where hygrothermographs are a little more innocuous and are accepted
as a functional indication of the conditions within the collection.
You mentioned that you encountered some turbulence in commissioning
your HVAC system. If you had presented the problems to your engineer
using logger data rather than hygrothermograph charts, you might have
endured a protracted "our sensors are better than your sensors"
battle as well.

In my opinion, you can hang onto the hygrothermograph units that you
have. As long as you can still get charts and pens for them, they
will remain useful for you long into the future. My feeling is that
hygrothermographs are essential to a proactive, performance-driven
monitoring practice, which is the best way to serve the collection.
If your units are starting to wear out, cannot be calibrated or if
you have trouble getting parts and supplies for them, then you
should consider replacing the number that you have, plus the
appropriate number that you need for your new building. Most of the
hygrothermographs sold these days have battery-driven quartz clocks
(no winding, no ticking) and can be set to a longer chart-cycle
(31-days or more) which can reduce both the amount of paper they
generate as well as the time you spend maintaining them.

You recognize the advantages your hygrothermographs offer and I
agree that they are indeed important. They're the hammers in the
environmental monitoring tool-box. Data loggers (though more useful
in some ways) share few of these advantages, and it does take some
time to download each logger and to observe and organize the
collected data, so for the purpose of regular monitoring, the
time-saving that they offer is marginal. They're still quite
effective, but none are a suitable replacement for a
hygrothermograph.

Craig Oleszewski
Hygrospec
Rhinebeck, NY


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                  Conservation DistList Instance 14:46
               Distributed: Wednesday, February 21, 2001
                       Message Id: cdl-14-46-006
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