Fragments from the Temple Scroll, one of the most historically important of the Dead Sea Scrolls, required 50% to 53% rh and temperatures of 69° to 71° around the clock when it was displayed at the Maltz Museum of Jewish Heritage.


Museums often house priceless artifacts that must be maintained at proper interior space temperatures and strict humidification standards. However, moisture levels in museums can vary greatly. For some museums, 35% to 40% rh is adequate, while others may require a range of 48% to 52%.

What is being exhibited usually determines the appropriate moisture level. Artifacts that come from the ground may need a higher rh level, while certain paintings may benefit from a lower rh level. Regardless of the humidity level required, proper control is mandatory, since rapid changes in rh can cause serious damage to artifacts, including warping and splitting.

While museum curators often fret over proper environmental conditions for their regular exhibits, they must pay even closer attention to temperature and humidity levels when they host a traveling exhibit. For example, museums wanting to host the King Tut exhibit were contractually obligated to maintain humidity levels of 50% to 55% rh and indoor temperatures of 68°F to 72°.

There’s no doubt that designing a humidification system for a museum can be tricky, especially when realizing the items being displayed are often priceless and can never be replaced.

Humidification Needed Immediately

Cleveland’s Maltz Museum of Jewish Heritage, which opened in October 2005, had an immediate need for humidification last year. The museum, which illuminates the achievements, history, and traditions of the Jewish community, would be hosting the “Cradle of Christianity: Treasures from the Holy Land” exhibit. Part of that traveling exhibit included the Temple Scroll, which is considered to be one of the most important artifacts of the Dead Sea Scrolls.

The 2,000-year-old scrolls have been housed at Jerusalem’s Israel Museum since they were discovered in desert caves in the late 1940s, and March 2006 was the first time one of the Scrolls traveled outside the country. The Temple Scroll was housed in its own environmentally controlled glass case, but the remaining 15 tons of ancient treasures, which completed the exhibit, would be displayed in the open for visitors to see.

Before it would even release the artifacts for the exhibit, the museum in Jerusalem demanded that certain environmental conditions be in place at the Maltz Museum. The design criteria were based upon the need to maintain 50% to 53% rh and temperatures of 69° to 71° in the space 24 hours a day, seven days a week. The humidity readings had to be communicated into the Alerton BAS, which monitored and logged all the readings at specific time intervals. These values could then be sent to an insurance carrier as part of the requirements of space conditions for rare documents and artifacts.

The problem was that the recently constructed Maltz Museum had no humidification equipment, and the artifacts were due to arrive in only four weeks. Steve P’Simer, service operations manager, sales, service, and preventive maintenance for Jacco & Associates (Hudson, OH) had originally supplied the HVAC equipment for the museum, so the museum contacted him to see what could be done about humidifying the space.

“The museum approached me not too long after it opened, and I was told they were going to have the Dead Sea Scroll exhibit from Israel,” said P’Simer. “The 4,000-sq-ft space at the Maltz where the exhibit would be displayed didn’t have any kind of humidification or controls, so the dilemma was how were we going to condition the space to meet the requirements of the museum in Israel.”

P’Simer ended up retrofitting the existing system with one SCR-controlled Vapac LE132 electrode humidifier with two circuits feeding Vapasorb short absorption manifolds in the ductwork. The heart of this electrode-type humidifier is the plastic cylinder that contains one, two, or three sets of electrodes dipping in the water. Using the mineral conductivity of the water, the electrical current flows through the water between the positive and negative electrodes and vaporizes the water to create steam. When the electrodes are completely covered with scale from the water, the canisters can be easily replaced.

The purpose of a short absorption manifold is to distribute the steam generated by the humidifier (steam generator) evenly in the duct so the steam is absorbed by the airflow in a shorter distance (approx. 6 to 36 in.). The short absorption manifold is made of many tubes attached to the main header into which the steam is fed. The tubes have numerous holes from which the steam flows out and is dispersed in the airflow.

Retrofitting The System

The Maltz Museum’s original HVAC systems, which Jacco & Associates supplied, include two 60-ton AAON rooftop units that were placed on the ground. The units supply 56° air to every zone box in the VAV system, while a hot water boiler provides reheat to maintain the space temperatures.

The AAON units virtually split the museum into two VAV zones, which the Alerton BAS controls. One of the rooftop units conditions the air in the traveling exhibit space, as well as that of the administration, theater, and gift shop areas, while the other unit serves the rest of the museum.

Two zone boxes serve the traveling exhibit area, and P’Simer originally thought about installing two humidifiers in the space - one in each zone. However, that would mean running water, power, and drain lines into the space, and there was a concern about water being directed over the top of priceless artifacts.

Instead, the electric steam humidifier was placed in the boiler room, and the short absorption manifold was installed in the main supply duct for the whole unit. “The humidifier was designed around Ohio temperatures and the already existing control systems, the VAV boxes, and the Alerton system,” said P’Simer. “For our conditions of 4,000 cfm of outdoor air, 1° at 57% rh, a 56° supply air temperature at 69% makeup air conditions in the winter, they determined we needed an 18,000-cfm unit that could produce 120 lb of steam per hour at those maximum temperatures.”

Once it was decided what size was needed and where it would be installed, the challenge became how to get the humidifier built, delivered, and installed before the exhibit arrived. The lead time for a humidifier to be built is typically four to six weeks, but that would take too long. Instead, the humidifier had to be quick-built and quick-shipped to arrive in time. In the end, the unit was built on a Wednesday, driven down from Canada on a Saturday, and installation started on Monday.

Just in case the humidifier didn’t arrive on time or something went wrong during installation, a portable humidifier was mounted on the wall in the space to meet the necessary humidity requirements of the traveling exhibit.

Alka Seltzer To The Rescue

Once the unit arrived, P’Simer and his crew cut into the ductwork above the administration offices to install the already assembled stainless steel manifold, drain lines, and steam lines. It took two days to start up the humidifiers, thanks to some Alka Seltzer.

“Normally with our water conditions it takes at least three days for a humidifier to start producing the maximum amount of steam,” said P’Simer. “We didn’t have that kind of time, so we put Alka Seltzer in the cylinders to speed things along. That got the humidity to the required level in the space, so we could change the control settings, VFD settings, and outside air settings.”

Additional controls were installed for the Alerton system, so it would be possible to remotely monitor the conditions at the museum. The sensors allow the BAS to control the humidifier and provide the necessary readings for insurance purposes. The system is monitored 24 hours a day to ensure proper temperature and humidity levels.

The space in which the Dead Sea Scrolls exhibit was housed has no windows, so P’Simer didn’t have to worry about too much humidity causing condensate problems on the glass. In addition, the area is not a separate closed room, as it opens to the rest of the museum. Due to the open flow arrangement, humidity moves from the traveling exhibit area into other parts of the museum, so humidity build-up typically is not an issue.

One of the concerns with the artifacts on display in the open was that these items had been buried in the ground for 2,000 years, so they absorb many of the minerals found in the soil. When artifacts are brought out of the ground, these crystals remain on the items and can start growing if proper temperature and humidity levels are not maintained. Nobody at the Maltz Museum wanted that to happen, which is why extraordinary care was taken with this exhibit.

That’s not to say that museum officials weren’t concerned about how much it would cost to install and operate humidification equipment. Humidifiers can be expensive to operate, but the unit from Vapac was ultimately chosen because it only uses the amount of electricity required to make the steam.

“This humidifier doesn’t come on at 200 amps and just stay there,” explained P’Simer. “The LE will pulse the voltage to maintain an accurate steam output for energy conservation. It’s not on/off, where you’re turning on full heat until you have enough steam to turn off the full heat. It uses whatever amount of electricity it takes to make that steam and no more, then it starts dropping off.”

Jacco has a service agreement with the museum, so P’Simer regularly checks the temperature and humidity readings of the space and also provides the necessary maintenance. The system is working well, and there were no environmental concerns during the entire four months the Dead Sea Scrolls exhibit was on display.

“We’re still maintaining that same humidity in that space, because they had some paintings in there that required humidity,” said P’Simer. “Another exhibit is coming soon, and it has similar requirements to the Dead Sea Scrolls exhibit. We’re ready for it. I don’t anticipate any issues.” ES

Sidebar: Canadian Museum Is Highly Humidified

The Canadian Museum of Civilization in Ottawa has reached a new milestone: It just recently had 124 Nortec “NHDI” resistive humidifiers installed, making it the largest humidification project in the world to use resistive element humidifiers.

The museum, which opened at its current location in 1989, is celebrating 150 years of success. Built on the bank of the Ottawa River below Canada’s House of Parliament, the museum site covers an area of 24 acres and spans 3.5 city blocks. The footprint of the museum is over 1,000,000 sq ft. Under a 56-ft dome ceiling, the buildings and environment that make up Canada’s history are reconstructed and furnished with artifacts and in some cases, animated by actors.

The museum owns over 3.5 million artifacts and receives over 1.3 million visitors annually, and the building also houses the Canadian Postal Museum, the Canadian Children’s Museum, and an IMAX theater. With so many venues and varying artifacts, it was not possible to design a single central humidification system for the complex. The best fit for the museum is individual units to meet the specific requirements of each area and each type of artifact being conserved.

When the building was originally opened in 1989, it was designed with electrode steam electric humidifiers. As with most projects of this size, the complex was built in phases, with several manufacturers supplying varying versions of electrode steam humidifiers as each phase was completed. This did not make for easy going for the maintenance staff. After 17 years of continuous use, the museum decided to upgrade the humidification system. This time they were interested in resistive element humidifiers and specified that the project needed to be supplied by one manufacturer with the same product throughout the complex.

After the contract was awarded by the museum, Axair Nortec worked closely with the local consulting engineer to select the appropriate model to meet the specification. The resistive element humidifiers offer a packaged product for easy installation and maintenance, the tight humidity control required by museums, and the ability to communicate with standard building management systems.

The first 56 units were delivered in December 2005, and another 68 units were delivered in October 2006. Once all the units were installed, the museum staff was provided extensive O&M training for the humidifiers. The humidifiers are all reported to be operating exactly as specified with minimal maintenance required.