Temperature control

We were asked for a advice concerning climatization in a planned new
art gallery in south western Germany. The top floor (intended for
old master pieces as well as contemporary art) is glazed with a sort
of translucent lantern heavily exposed to the sun.

According to the engineers, the HVAC-System is designed to work at a
constant temperature of 20 deg. C and constant relative humidity of
55%. The system will work fine at this setpoint up to an outdoor
temperature of 26 deg. C. But on very hot days the outdoor
temperature will be well above 26 deg. C and the museum is urged to
run its galleries theoretically at higher indoor temperature up to a
maximum of 26 deg. C (outdoor 32 deg. C, which according to German
building standards is supposed to be the maximum temperature for
this region). The question is how quick the temperature should be
allowed to rise within short periods (hours/day). Assuming that the
climate control won't break down ;-) : what is the difference in
risk between keeping the temperature down to 20 deg. C as long as
possible and then having a sharp increase vs. rising the temperature
over a longer time period following the outdoor temperature. We
think that keeping the temperature low allows for less increase in
chemical damage rate, whereas a steep increase might cause physical
problems within an art object (expansion). Is that correct? If so:
which risk are we to take more serious?

As the rising temperature at constant RH means that the amount of
absolute humidity is rising considerably, will this cause
significant problems at the envisioned temperature of 26 deg. C?
(moisture content, water activity, mold?)

We would welcome any input. Due to the tight time frame of this
project we welcome quick offline answers which we will summarize and
post to the list after christmas.

Joachim Huber and Karin von Lerber
Prevart GmbH
Oberseenerstrasse 93
CH-8405 Winterthur
+41 52 233 12 54
Fax: +41 52 233 12 57


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                  Conservation DistList Instance 19:29
                 Distributed: Tuesday, December 6, 2005
                       Message Id: cdl-19-29-025
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