Humidity Control Experts Save the Sistine Chapel


The marriage of AHI Carrier’s expert global team of AdvanTE3C engineers with United Technologies Corp and the Vatican’s historical museums team resulted in an on-going partnership of mutual trust and understanding regarding the new level of humidity control needed to save the Sistine Chapel’s matchless art frescoes.

No Sweat Just Don’t Breathe

For the 1.5 million visitors a year, the Sistine Chapel’s air-conditioning system was adequate … 20 years ago that is. Now, the prized art frescoes were at immediate risk due to the dust, the heat, sweat and breath of its six million annual visitors.

Humidity and heat control are the two of most vital factors affecting the Sistine’s works of art. The logistics though are formidable as a new system installation would be required to regulate and maintain stable conditions come what may – day and night with no one in sight and with 8 – 9 000 bodies milling around on any given day. It was either limit access to the chapel or find experts who could innovate. AHI Carriers were profiled to fit the bill.

Seven Critical Criterion for the AHI Carrier Experts

To meet the mission-critical specs, a dynamic computer simulation had to be created. Measuring outdoor weather variables, including solar radiation and heat flow coming through the windows, the heat conductions through the ancient walls and ceiling, radiant heat exchanges between the walls, floor and ceiling, the air in the massive space within the chapel and plus heat generated by visitors, which was calculated on 700 persons at any given time.

  1. Humidity control- Carriers experts achieve the delicate balance required with two 580-kilowatt capacity Carrier AquaForce 30XWV water-cooled chillers. To optimise protection for the art, the system is linked with video application.
  1. Still air for fresco surfaces – This was achieved by having the system inject air into the space from outlets under the windows. Window sills were the only option as no further openings could be cut for new ducts and outlets. Through grills located in the floor, exhaust fans – under slight pressure to prevent any return infiltration, silently lose the humidity as it builds. That’s humidity control par excellence.
  1. Controlled fresco temperatures – to be above the air dew-point sensors, several chilled mirror type units are positioned inconspicuously throughout the chapel. This ensures maximum humidity control.
  1. Invisible to visitors – Installed using existing ducting, which was originally installed by Carrier to be ‘quiet as a mouse’, the new HVAC system is not noticed by visitors. 2,000 visitors all at once can’t compromise the humidity control.
  1. Minimal pollutants- Overhead air ‘showers’ and floor level dust exhausts combine to minimize dust.
  1. Minimal noise level – Given that the chapel contains no sound-absorbing carpeting or wall hangings, this was a technical challenge. Using a large sound attenuation unit at the outlet, a minimum number of turns, low air velocity and acoustic insulations, a noise level of RC25 was achieved – computer programs for acoustic systems were effectively developed for this purpose by ASHRAE.
  1. Exceptional reliability – component failure is factored in by supplying duplicates, which are often automatically replaced. Requiring no human intervention, alarm sensors send notice to three separate sites ensuring prompt action. ICE, every computer-controlled component can be manually switched on.

After a three-year long collaboration, Carrier’s highly controlled micro-humidity climate system is a resounding success, ad Carrier provided their system to the Vatican free of charge. Discover the story of this extraordinary project on


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