Air exchange rate in exhibition cases

Chao-Chun Lu <lucc [at] npm__gov__tw> writes

>When purchasing exhibition case, should air exchange rate always be
>take into account or only considered special uses, such as
>nitrogen-filled cases. What level of the air exchange rate would be
>best?

When purchasing exhibition case, should air exchange rate always be
take into account or only considered special uses, such as
nitrogen-filled cases. What level of the air exchange rate would be
best?

The primary purpose of a display case is to isolate the artefact
placed in the showcase from the environment outside the showcase.
The showcase's performance in a number of aspects must be
predictable (for example security, accessibility, and off-gassing).
Clearly, the amount of influx of moisture, dust, and gaseous
pollutants is important, and to predict this influx you must be able
to measure the rate at which the case leaks.

A quick look through the distlist archives will reveal many
discussions and links on this topic. After some years of supplying
solutions for showcase environmental control, I have become a
fervent convert to the church of AER (Air Exchange Rate). The rate
of air exchange in a showcase is the prime indicator of the type of
solutions and approaches needed to stabilize and maintain an optimal
microclimate environment. (These could include sealing leaks,
providing passive buffering or active control, environmental
monitoring, modifying gallery conditions, and more.)

Note that air exchange rates can vary dramatically between nearly
identical showcases. In my view, an indication (or better, a
guarantee) of the Air Exchange Rate should be part of any
transaction where a showcase is ordered, built, or modified. The
extremely low case leakage levels needed for oxygen-free display
cases are not realistic for most applications, and need not be
considered here.

A number of links to articles on this topic can be found on my new
website at <URL:http://www.keepsafe.ca> by clicking on Microclimate
Solutions and following the appropriate links.

Jerry Shiner
Keepsafe Microclimate Systems
416-703 4696
800-683 4696


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                  Conservation DistList Instance 23:24
                 Distributed: Monday, January 11, 2010
                       Message Id: cdl-23-24-002
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