Active and passive storage

Nora Lockshin <misslockshin [at] yahoo__com> writes

>Can anyone clarify as to whether there is a consensus on the
>definitions "passive" storage vs. "active"? The terms originate in
>climate and microclimate control, but I see the term passive used
>much more often, but also in combination with using "active"
>materials such as Microchamber board, Silvercloth, zeolites, etc.

FWIW, "Active" climate control generally means that there is some
sort of device or machine which needs to be plugged in and running
in order to regulate the climate over time. These systems are
sometimes called "micro-climate generators" and they rely on the
action of a fan blowing air across some kind of wet media to add
moisture, or across a cooling coil to remove moisture. Because
evaporation and condensation cause drastic changes in temperature,
the machines that produce them are usually located outside the
showcase or storage enclosure. The machines rely on the function of
a humidistat to turn themselves on and off automatically. Hence the
term "active".

Passive systems put moisture into the air without relying on the
function of any device or machine. Pre-conditioned silica gel is the
most common form of passive climate control (Arten or Art-Sorb).
Some others that are less common include using raw cotton,
pre-conditioned zeolite, open dishes of water and saturated salt
solutions within the showcase. I worked with a furniture collection
that had a temporary storage area which enjoyed excellent year-round
humidity thanks to the moisture-buffering capacity of all the wooden
crates that were in the room.

All passive systems use some kind of moisture-laden material that
has sufficient surface-area and vapor-pressure to bring the air in
the showcase into equilibrium with the desired relative humidity
(RH). These systems require a good seal on all cracks and openings
in order to function properly, but nothing needs to be plugged in or
running in order for them to work over time. Hence, they are
"passive" because you just put them in, seal them up and they work.
I hope this helps,

Craig Oleszewski
Hygrospec, New York City


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                  Conservation DistList Instance 16:30
                Distributed: Wednesday, October 30, 2002
                       Message Id: cdl-16-30-004
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