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The Vatican called on Carrier to design and install an air conditioning system...

Sistine Chapel

Their popularity was killing them. Michelangelo's frescoes on the walls and ceiling of the Sistine Chapel attracted millions of awed observers each year – and with each group of visitors came a new load of dirt, heat and humidity.

The problem was made even worse following the Vatican's recent meticulous restoration of the masterworks to their original brightness and stunning colors. Removing centuries of candles soot, animal glue and ordinary dirt made the frescoes even more vulnerable to attack by moisture and temperature extremes created mainly by the daily influx of visitors.

The Vatican called on Carrier to design and install an air conditioning system that would let the frescoes rest in stable comfort while still allowing pilgrims from around the world to gaze at Michelangelo's works overhead.

Combining off-the-shelf cooling and heating products with computer-based electronic sensors and controls, Carrier created a system that bathed the ceilings and walls with temperate air and humidity. The air is cleaned with powerful filters that remove chemicals and even bacteria-sized particles. Visitors, meanwhile, are showered with a higher velocity air flow that keeps dirt and humidity at floor level. The system also allows the Vatican's conservators to seal the chapel's windows, keeping Roman car exhaust and the pollutants found in the air of any large city outside.

And unless you know where to look, the system is all but invisible to visitors and worshippers – no easy task in a building whose 400-year-old walls are 10-feet thick in places.

Conservation of the Frescos: The Sistine Chapel

"I live and love in God's peculiar light." -Michelangelo

Imagine what the frescoes on the ceiling of the Sistine Chapel would have been like had their creator really wanted the job.
As a sculptor who preferred above all else bringing life into cold, translucent slabs of marble from the quarries of Carrara north of Rome, it is clear that Michelangelo did not welcome the commission from Pope Julius II to paint the ceiling of the Sistine Chapel.

But Julius II, the nephew of the chapel's builder, Pope Sixtus IV, prevailed.

The Vatican's careful documentation, along with contemporary accounts and the artist's own correspondence, paint a true portrait of the young Michelangelo Buonarroti's four-year effort to adorn the ceiling of the Sistine Chapel.

That he painted the ceiling flat on his back is myth. That he worked mostly alone appears to be true. There were lapses in his work, too. At least one work stoppage occurred in 1510 while Pope Julius II traveled to Bologna and remained there until the middle of the following year.

In general, however, Michelangelo's work during those four years can be described as steady and energetic. Using hog-bristle brushes, he covered nearly 1,300 square meters of ceiling and walls with frescoes. In October of 1512, the Sistine Chapel ceiling was unveiled to the public.

If ceiling viewers experienced chaos at first sight, that's understandable. There are, someone counted, 336 figures up there. They are seated, standing, reclining or soaring in all directions in apparent disorder

Out of Darkness: Restoring The Frescoes' Brilliant Past

No one knows who mandated the ceiling's theme. After Michelangelo reportedly told Julius II that a mere rendering of Christ's 12 apostles (as originally proposed) would be a poor use of the space, the artist wrote to a friend saying he had been given a free hand to design whatever he wanted.

In essence, the ceiling's Old Testament and classical vignettes point forward in time toward the salvation that was to be man's through Jesus Christ's birth, death and resurrection.

The ceiling's possibilities are endless.

As long as they exist, the frescoes' significance will be analyzed, dissected and debated by theologians and critics. But for millions of us with ordinary stiff necks, the frescoes of Michelangelo exist just as powerfully outside these realms of formal, esoteric knowledge.

If we are willing to admit our innocent, unsophisticated awe in their presence, we will find their glory in the fact that one of our species created them. One of us, given a giant's share of craft and vision, elicited from pigment and flat plaster a monument as round, as moving, as lasting as sculpted Carrara marble.

As an artist, Michelangelo depended on that God-given light to create. As observers, we depend on it for our vision of the artist's greatness. Resident as we are in the final years of the 20th century, we are the lucky ones, for millions of others within the last four and a half centuries have seen Michelangelo's Chapel frescoes through smoked lenses. The frescoes' colorful brilliance has been shrouded in layers of oily black soot, dulled animal glue, ordinary dirt and the more recent residue of Rome's automotive gnats that swarm just outside the Vatican's ramparts.

The accumulated grime of centuries dulled colors and erased detail. It flattened the frescoes and robbed them of their succulent roundness.

But thanks to a decade-long effort by the Vatican's restorers, the mask has been lifted. Michelangelo supplied the originals, but in many ways, much of the credit for today's frescoes belongs to restorers like Gianluigi Colalucci, who, together with Maurizio Rossi, Piergiorgio Bonetti and Bruno Baratti, have cleaned the chapel's walls and ceiling by hand.

The frescoes, despite their age and discoloration, were in very good condition, primarily because the artist played by the rules of the buon fresco technique.

As the day began, Michelangelo, or an assistant, mixed a batch of lime with water and a volcanic ash called pozzolana. Michelangelo then spread a day's worth of wet plaster onto the ceiling and began painting. When the lime combined with the water in the plaster and carbon dioxide in the air, it formed calcium carbonate – the basic formula for limestone. Trapped in that stony matrix were bits of pigment that released their colors to the robust surface.

Vatican records reveal that within 20 years after his death, Michelangelo's frescoes were being "restored" to erase the effects of the environment – a pre-electric environment characterized by votive candles and flaming braziers used for heat and light. The earliest restoration attempts involved lightly scrubbing the surface with stale bread. Later technicians dabbed Greek wine on the surface to remove soot. The most significant change began as 16th century restorers brushed animal glue on the frescoes to smooth a surface roughened by salt that refracted light, dulled colors and reduced contrast.

The early restorers' attempts were successful, but only in the short term since animal glue, like the glop we used as aspiring five-year-old artists, darkens with age.

For months before the modern-day restorers began their actual cleaning, a battery of art historians and scientists used non-destructive evaluation techniques to probe the ceiling's plaster, the clumsy applications of glue, and sooty encrustations to determine which was Michelangelo's work and which came later.

Working at less than half the speed of Michelangelo, the restorers slowly began stripping away those centuries of gloom using distilled water and a paste of relatively benign chemicals, including ordinary baking soda.

Environmental Controls: Ensuring A Brilliant Future

It appears that turning back time is possible, given an artful touch and the right technology. We see the proof above our heads as we gaze at the Sistine Chapel frescoes, which now appear much as they did in 1512 when Michelangelo laid down his trowel and brushes. But because they are clean for the first time in centuries, the ceiling's masterworks are prey to the 20th-century dangers Michelangelo couldn't even contemplate. Fortunately, those conserving the frescoes have.

When the skin of dull brown animal glue was rinsed away, revealing the frescoes' lively colors, Vatican officials realized the process of decline would be repeated unless the atmosphere within the chapel's vault could be controlled.

Oily soot was no longer a problem, but the frescoes now would be exposed to particulates from automotive exhaust and aggressive airborne chemical pollutants found in most urban environments. The greatest potential damage, however, could be caused by condensation of moisture on the frescoes' surface and rapid changes in temperature and humidity as throngs of pilgrims and tourists passed through the chapel. With two million people a year visiting the chapel, it is as if everyone in Vienna or Phoenix were passing through, bringing with them tons of moisture to be controlled.

Temperature and air flow studies in the chapel's vault show a geyser of warm moist air erupting toward the ceiling each time visitors enter the space in the morning. This warm air then spreads across the ceiling, cools and descends along the walls. In the process it deposits dirt and can leave behind its moisture if the ceiling's surface temperature is lower than that of the air. Moisture left behind on the frescoes' surface increases the chances for harmful chemical reactions, the formation of molds or the deposition of salts as the plaster absorbs and then gives off moisture.

This is the paradox at work within the Sistine Chapel: Michelangelo's frescoes, especially after their cleansing, are creations to be shared with the world, yet the thousands gazing upward are the greatest threat to the Renaissance works. The goal, therefore, of the Carrier climate control system now operating in the chapel is to allow visitors by negating the effects of the moisture, heat and dirt they introduce into the atmosphere.

To surround the frescoes with atmospheric stability, the relative humidity of the air bathing the chapel's upper walls and ceiling will be kept at 55% (+/-5%) year-round. Relative humidity is the most important single variable because large swings would permit the porous ceiling plaster to "inhale" and "exhale" water vapor. This flow of water vapor into and out of the plaster could cause deterioration.

The air temperature also must be stabilized, but will be allowed to drift gradually as the seasons change from 25 degrees C in the winter to 20 degrees C in the summer. This will minimize the overall temperature differences across the walls and ceiling, reducing thermal stress and keeping any dirt from being attracted to the frescoes' surface.

The choices of these "setpoints" also will insure that the dewpoint (the temperature at which moisture condenses out of the air) will always be several degrees below the surface temperature of the frescoes to prevent moisture accumulation.

The system supplying the environmental stability craved by the frescoes is a collection of individual elements – water chillers, air handlers, pumps, valves, cooling towers – that are tied together by an electronic, computer-based control network that allows separate pieces of equipment to communicate with each other and respond to temperature and humidity information being gathered by sensors within the chapel. An organic comparison is often made: The sensors are the system's eyes and ears; the individual elements are its vital organs; the control system its brain and nervous system.

Since there are better things to look at within the chapel, the 92 sensors (40 of them for redundancy's sake) that continually monitor air temperature, dewpoint, and wall and ceiling surface temperatures are virtually invisible. The 26 kilometers of control wiring connecting the sensors to the system's computer-based controls also are hard to detect.

Two computer terminals, one sitting on a table in the Vatican's power station a five-minute walk away and the other residing with the Vatican's restoration scientists, merely allow humans to "talk" to the system and get information from it. The actual orchestration of the air conditioning system's separate elements, based on information being received from the sensors, is handled by microprocessor-based electronic controls distributed throughout the system.

If sensors in the chapel indicate the humidity is rising during a tourist-filled Roman summer day, the electronic control for the air handling unit determines that moisture must be removed from the air by cooling it, since cooler air carries less moisture.

That control signals its counterpart near a Carrier water chiller, located two floors below the chapel, to begin producing cold water. Other controls on the circuit open valves and start pumps that send the water through pipes on the outside of the chapel's south wall to the air-handling unit manufactured by Carrier S.A. in France. Outdoor air pulled into the air handler passes over pipes containing the cold water and is dehumidified. The temperature of the dehumidified air is then readjusted to the proper setting by an independent control circuit.

During the winter months, when there are fewer visitors, moisture must be added to the air being pulled in from outside the chapel. The process is reversed as the electronic controls signal the chiller to stop operation and instead open valves that bring hot water from the Vatican's boilers to heating coils in the air handler. The heated air, which now can hold more moisture, passes through an air washer whose high-pressure water nozzles add the needed humidity.

Besides being heated and cooled or humidified and dehumidified, the outdoor air pulled into the air handler is pre-filtered to remove dust and other "larger" particulates. It then passes through a chemical filter to remove gaseous pollutants the air washer missed; and then through a final filter that removes particles like bacteria, pollen or fly ash that are as small as .1 micron or 1/10,000,000th of a meter. All are particles that will no longer get the chance to darken Michelangelo's work.

The air is then ducted up the chapel's outside wall and distributed to individual diffusers concealed carefully beneath the chapel's six south windows.

The diffusers were designed only after the chapel's interior air flow patterns were painstakingly modeled on computers in Carrier's Corporate Engineering laboratories in Syracuse, N.Y. The diffusers create two separate air flows within the chapel – a very low velocity flow over the surface of the frescoes, and a gentle "shower" of conditioned air over the occupants at floor level, effectively isolating the chapel's upper realms from earthly contamination.

Design and installation of the system were, in many ways, team efforts between Carrier and the Vatican's Office of Technical Services, whose employees know the building's intricacies better than anyone. Computer modeling of the Chapel's thermal behavior would have been impossible without the detailed drawings supplied by Vatican Technical Services. Technical Services' general management was the driving force in gaining approval for thousands of details that had to be resolved before the equipment could be installed without damaging the chapel's structural and cultural integrity. They also analyzed the system's capacity independently to make sure it would meet strict requirements.

The Carrier system required engineering expertise from Italy, France and the United Sates, but installing leading-edge technology in a 15th-century structure also required finesse. With solid masonry walls anywhere from 1.5 to three meters thick, installing sensors, ductwork and wiring without disturbing the aesthetic integrity of the chapel required the wisdom of Solomon and the patience of Job, one of whom was watching from a lunette.

The Sistine Chapel is much more than a gallery for the frescoes of Michelangelo, Botticelli, Ghirlandaio and others – it is a functioning chapel used for Vatican religious services. In today's Rome, it may be hard to imagine the quiet of a 16th-century mass in the chapel, with little else but footfalls and perhaps Palestrina's Stabat Mater resonating off the walls. But turning back time has required eliminating as many 20th-century sounds as possible.

Sound-absorbing material in the double-walled air handler muffles much of the sound of moving air and machinery before it reaches the chapel. Sound-deadening material in the diffusers' moveable vanes absorbs most of what remains. The chillers and air handler also are mounted on vibration dampers. And with air conditioning, the windows that once provided ventilation can remain closed to the city's noise and burden of dirt and fumes.

Even if the restorer's art and modern technology can turn time backwards, they can't stop it. So Michelangelo's frescoes must be watched carefully. Perhaps that is the Carrier system's final benefit: history. The electronic control system constantly gathers information that will allow scientists to closely track the chapel's micro-climate. When combined with memory banks full of physical data about the frescoes gathered before and during the restoration, scientists will be able to anticipate any problems that could once again threaten to dim the brilliance of Michelangelo.

Vatican Calls Carrier to design an air conditioning system

Michelangelo's frescoes


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