Case Studies – Temporary Climate Solutions

Preserving priceless art with climate control

With 120 of the world’s most valuable art objects at stake, the government of Portugal was not willing to take any chances with humidity control when it lent the exhibit to the prestigious San Diego Museum of Art. Priceless pieces included several paintings of 18th-century Lisbon, fine silver, elaborate furniture, porcelain, unusual scientific instruments, and spectacular selections from the Portuguese crown jewels. Rare religious items included silk vestments from the Lisbon Cathedral, precious altar furnishings in both gold and silver and a spectacular gilded wood altarpiece that measured over 22 feet high.

Prior to its arrival in San Diego, the exhibit was on display at only one other American location, the National Gallery of Art in Washington, D.C. There, permanently installed, state-of-the-art technology enabled the Gallery to tightly control the environment. Curators in San Diego won the exhibit only after they agreed to maintain the same temperature and humidity conditions.


Many of the items in the exhibit were vulnerable to moisture. The gilded altar, the smaller wooden artifacts (that were trimmed with genuine gold leaf), and the tapestries were all extremely hygroscopic. Due to the risk, the Portuguese government required a guarantee that the temperature would not vary more than two degrees from 72 degrees Fahrenheit (°F) and that the humidity would not vary more than 5% from 55% relative humidity (RH). Not only did the Museum have to prove it could meet the standards, but every two weeks charts detailing conditions were shipped to Portugal as continuing proof.

Complicating the problem, the gallery area, nearly 400,000 cubic feet of space, would be visited by up to 2,000 people each day. This, plus the constant infiltration of outside air from opening doors and the natural leakage of the building, created the need for a fail-safe system.


The exhibit would run in San Diego for five months. So, the only practical solution for the Museum was a temporary humidity control system. Learning that Polygon specialized in temporary humidity control and that they had solved a similar problem in Texas, preserving Russia’s ‘Catherine the Great’ exhibit, Museum officials turned to Polygon.

It was immediately clear that the old HVAC system could not meet the conditions required. This was confirmed by chart recorders used to measure the temperature and humidity throughout the Museum. The chiller system that the Museum had in place was built in 1966. It had not been engineered to provide ‘tight’ control of humidity levels.

The Polygon team was under pressure to finish the system by the deadline. Just two weeks after we received the project, the exhibit was scheduled to open. To solve the problem, we installed two HoneyCombe® 4500-GA gas-fired desiccant dehumidifiers and a 44-ton chiller with two 20-ton coils. The need for a crane to lift the equipment onto the roof, where it would be integrated with the current HVAC system and kept out of sight, complicated the installation.

On the day US military transport aircraft airlifted the valuable artifacts to San Diego, the temporary system was finished and running to spec. Throughout the entire exhibit, the system maintained the conditions perfectly.


Customized Systems

In the case of the exhibit, particular parameters had to be reached and regularly tracked.  Polygon’s service allowed them to blend both temperature and humidity control into an integrated system. Should your requirements increase or decrease, you can add or subtract equipment without problems.

Absolute Protection

There was no room for disturbances because the San Diego exhibit would only be available for only a limited amount of time. Temporary humidity control by Polygon means you can achieve your objectives without disruption.



The San Diego Museum of Art attracts around 250,000 visitors annually. Its collections and temporary exhibits provide a rich and diverse cultural experience.