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Subject: Temperature control

Temperature control

From: Steve King <stevek>
Date: Sunday, December 18, 2005
Joachim Huber <joachim.huber [at] prevart__ch> writes

>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. ...

I'm disappointed to hear that a HCVAC performance would have been
specified in the manner described. It suggests that the original
contractors/engineers were anxious to present a solution that
appeared responsible in terms of energy conservation and capital
cost of equipment, and the client didn't realise what would be the
real consequences of that approach.

A probably more effective energy efficiency measure, and one that is
still helpful to your present situation, is to review the setpoints
for an acceptable 'seasonal drift'.  In other words, let the
temperatures indoors go up modestly all the time in summer, and down
a little in winter. That rate of change will do less potential
damage than the rate of change associated with daily cycling of much
greater magnitude, which you would be presently experiencing,
probably quite a few times during a typical summer.  I don't suggest
a particular summer setpoint temperature here, because it needs a
proper review of your collection to determine that target.

Seasonal storage is a good idea in principle, because you are
probably finding that your storage areas are generally more stable,
even when the AC system fails for any reason.  In practice, you
should seriously consider that option in a proper risk management
framework--even with excellently trained staff, risks associated
with moving and packing the works may be greater than the accruing
risk from some periods of less than perfect environmental

Steve King
Centre for Sustainable Built Environments
University of NSW, Sydney, Australia

                  Conservation DistList Instance 19:32
                 Distributed: Tuesday, January 10, 2006
                       Message Id: cdl-19-32-002
Received on Sunday, 18 December, 2005

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