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Sistine Chapel Case Study

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.