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Subject: Temperature control

Temperature control

From: Ryan Kershaw <rkershaw>
Date: Friday, December 16, 2005
Michael McHugh <mmchugh [at] vernerjohnson__com> writes:

>Dramatic/frequent temperature swings are more of a problem than
>elevated temperature or humidity for short periods (a heat wave).
>Can collection storage areas be kept at a constant temperature and
>humidity while gallery temperatures are allowed to fluctuate?
>Sensitive items could be stored seasonally.

If the rate of change in an environment is a critical factor in
conserving any works of art, you may want to have a look at your
HVAC system, and more specifically, the type of control it uses to
moderate the environment.  An older system may incorporate a simple
on/off control system, where the heating or cooling system is
activated only by the PV (Process Value, which in your case is
temperature), going outside a setpoint.  While I am new to the
lovely world of conservation, a prominent algorithm that has been
used in industrial control for quite some time has been the PID
(Proportional Band, Integral, Derivative), which among other things
allows the change in compensation to be slowed.  This would reduce
the dramatic/frequent temperature swings.  While an optimal PID
system would require a modulating control system (0% - 100%, rather
than on/off), the PID control can be used with an on/off control
system.  A good website that I found that quickly outlines this is:

Integrating a PID system can be as easy as replacing the controllers
for the HVAC system, and as complicated as replacing the HVAC system

>Dataloggers could be used to identify microclimates within the
>Museum (temperatures may fluctuate more on upper levels and near

It should also be noted that some EMS (Environmental Monitoring
Systems) can have alarms set based on a rate of change, as well as
the usual setpoint alarms.

Ryan Kershaw
Technical Sales
Bestobell AquaTronix
Canadian Hanwell Distributor
Toronto, Ontario
Fax: 416-231-9121

                  Conservation DistList Instance 19:32
                 Distributed: Tuesday, January 10, 2006
                       Message Id: cdl-19-32-003
Received on Friday, 16 December, 2005

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