Climate control in southern Africa

Lara Wilson <l_a_wilson [at] hotmail__com> writes

>I am a paintings conservator temporarily (until October) working at
>the National Museum of Art in Maputo, Mozambique and have been asked
>to give advice about the introduction of air conditioning. I would
>really appreciate help from anyone with experience of preventive
>conservation in tropical/sub-tropical museums.

My experience of tropical Australia may be relevant.  You are
correct to be concerned about unreliable electricity supplies and
therefore also about the use of electrical equipment, and to
recommend the use of ventilation. However, you also need to be sure
about the actual climate conditions.  In tropical Australia (and in
almost all warm, humid climates) humidity levels vary considerably
during the day, even during the wet season.  You suggest this is
also the case in Maputo by saying there are frequent fluctuations.
However, the average level and the pattern remains constant for long
periods during the year and this is where tropical climates gain
their reputation for constant high humidity.  Your first step should
be to measure the conditions throughout the day both inside and
outside.  If constant high humidity is the problem then
dehumidification may be the only option in the short term.  If
variable humidity is more of a 'problem' then working creatively
with the climate may be a more realistic and sustainable option.

What was done before the introduction of electrical climate control
was to make use of the building, shade and favourable climatic
conditions wherever possible.  Buildings were oriented to make use
of breezes, walls and roofs were shaded with verandahs and trees to
reduce heating of the structure, and windows were sometimes opened
in the afternoon to introduce air at a time when it is driest
relatively.  The SOLARCH group at the University of New South Wales
in Sydney were looking at passive controls in buildings in tropical
regions so it might be useful contacting them.

Another important point is to estimate the actual danger from
humidity fluctuations.  If the paintings and other objects have been
in the building and climate since the 19th century what damage has
been caused in that time? If they are in reasonable condition now
then the risks from the climate may be relatively low (in comparison
with insect problems for example). Fluctuations in humidity to below
65% limit mould growth (see my articles in the IIC Preventive
Conservation preprints from Ottawa, 1994 and ICOM CC meeting in
Edinburgh in 1996).  Ventilation limits mould growth but also
introduces fluctuations.

There are dangers in trying to stabilise a climate in a building in
a humid climate   it may stabilise at too high a level.  Variations
in the climate may be preventing damage from occurring now so more
study is needed.  The best approach (in my opinion) is too look at
the condition of the objects and the building now and determine what
effect the 'natural' climate has had.  That analysis will point to
the real dangers in the future and choosing what, if any, controls
may be appropriate in those circumstances.

Graeme Scott
Head of Collections Management
Rijksmuseum voor Volkenkunde
(National Museum of Ethnology)
Postbus 212
NL 2300 BS Leiden
Netherlands
+31 71 516 8786
Fax: +31 71 512 8437


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                  Conservation DistList Instance 17:63
                  Distributed: Tuesday, March 30, 2004
                       Message Id: cdl-17-63-001
                                  ***