Relative humidity control in microenvironments

With regard to the query from Carol Gilderson-Duwe:

We use silica gel not only to keep display cases dry, but also to
maintain them at a specific humidity.  The gel is first conditioned
to the required RH (or usually a little higher, to allow for
losses.)  The effectiveness of this as a way of controlling case
humidity depends to a large extent on the airtightness of the case -
if the leakage rate is too high, then the silica gel will be unable
to compensate.  The gel maintains the humidity level for a variable
period of time, depending on both the leakage rate and the external
conditions.  It is then replaced with another conditioned batch.

An alternative method is the use of Micro Climate Generators, which
are essentially small air conditioning machines.  They take in air
from the display case, condition it to the required level, and pump
it back into the case.  Their operation is similarly circumscribed
by the airtightness of the case.  At present the cost of these
machines is around $5000 Canadian, so they are not a cheap option.  There
are also two larger machines available, one of which will control
several display cases at the same humidity level, while the other
has dual controls which allow two sets of case to be controlled at
two different RH levels.

The machines are manufactured by

    Micro Climate Technology Inc.
    4271 Longmoor Drive
    Burlington, Ontario L7L 5A4
    Canada
    905-637-8191
    Fax: 905-637-7888

I would be glad to discuss our environmental control experiences in
more detail.  Feel free to call me.

Helen Coxon
Conservator
Royal Ontario Museum
100 Queen's Park
Toronto Ontario  M5S 2C6
Canada
416-586-5897
Fax: 416-586-5863

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                  Conservation DistList Instance 10:7
                 Distributed: Wednesday, July 10, 1996
                        Message Id: cdl-10-7-001
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