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Sistine Chapel
Background:
Preserving Michelangelo's frescoes in the Sistine Chapel, for future
generations to enjoy, became an important goal of the Vatican in
the early 1980's. The restoration of the wall and ceiling frescoes
and their continued preservation required technical intervention
to control the interior environmental conditions.
The
Challenge:
The Carrier Corporation (Farmington, CT), the world's largest air
conditioning equipment manufacturer, was given the challenge to
design and install an humidity control system of the Chapel. Carrier
selected three criteria for the humidity device to be used in their
control system.
The
humidity measurement needed to be accurate.
The
humidity instrument needed to be reliable. Access to the instrumentation
would be limited. The device had to have to highest degree of reliability.
The specific equipment requirements included: Few moving parts,
maximum time between maintenance, easy to maintain, and ability
to compensate for the effect of contamination.
The
equipment needed to be non-intrusive, minimizing any visual impact
on the frescoes.
The
Solution:
After an extensive evaluation, Carrier selected the EdgeTech Model
200 DewTrak™ humidity transmitter as the best technology to
provide a solution. Carrier reviewed the various technologies from
thin film (capacitance) to optical chilled mirror. They selected
optical chilled mirror for the direct measurement of absolute (vs.
relative) humidity. Chilled mirror is a primary measurement rather
than a calculated or inferred measurement. The Carrier-selected
DewTrak; Model 200 sensor incorporates a polished metallic surface
(the mirror) that is cycled between heating and cooling, allowing
condensation to form a dew layer. The presence of dew is detected
electro-optically by reflecting a highly collimated light source
(LED) at an angle off the mirror surface, and then measuring the
reflectivity with a photodetector. A full transmission is detected
when the mirror is heated to dry conditions. Less than full transmission
is detected when the mirror is cooled to the condensation dew point.
A platinum resistance thermometer is embedded beneath the surface
of the mirror which measures the mirror temperature. Any change
in dew point is automatically tracked by as feedback control circuit
which maintains the equilibrium dew layer.
The
Model 200 DewTrak™ humidity transmitters are located high
on the Chapel wall and ceiling. As such, special permission is required
to perform routine maintenance. Dust generated from the frescoes,
foot traffic, and the outside environment may collect on the mirror
over time. The humidity transmitters employ an optical scheme to
compensate for contaminates, reducing the need for maintenance.
The Model 200 humidity transmitters use a relay to feedback a signal
that the sensor requires service, if necessary.
The
third requirement of Carrier was that the units remain inconspicuous
in the Chapel. The Vatican insisted that the view of the newly renovated
Chapel not be impaired. The size of the DewTrak™ humidity
transmitter package is sufficiently small, enabling the units to
fit on a ledge thirty feet off the ground. Others are installed
in the ceiling itself.
The
success of this application demanded a clear analysis of the problem,
solid technical solutions and a good partnership between the user
and suppliers. For the companies involved, controlling environmental
conditions within the Sistine Chapel represented a technical challenge
with deep historical implications. Not unlike the frescoes, the
project had little room for error.
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