View Full Version : Some passive and active humidification solutions.

Jamie Hascall
12-13-2012, 10:45 AM
This posting is from a thread on the PACCIN listserv. The earlier parts of the discussion can be found there.

For background, a group of items were loaned to the museum with specific RH requirements of 40% plus or minus 5% in the loan agreement. In the time between the loan agreement and the time of installation, the boiler that served that area was replaced. Sadly, the State of NM purchasing specifications neglected to include a provision for humidification and thus we ended up with only the low ambient humidity of this high desert environment. This new reality was only realized about four weeks prior to opening and my department was then tasked with finding a solution that would keep these important objects safe for the run of the show.

The query that I posted earlier regarding passive case conditioning involved two different display cases with only one loaned object in each. Trying to fully condition the atmosphere in each of these cases for the sake of a single object proved to likely be very expensive and an immense amount of effort. The simple solution that we chose was to make a small vitrine and base to contain each object within the larger case, and only condition that volume of air. This proved both practical and effective, and even gives a certain degree of additional importance to the object by the special treatment. Pictures of these objects and ones that pertain to the rest of this article can be found at http://www.flickr.com/photos/24204269@N06/sets/72157632227203929/with/8267225036/ .

The more difficult problem was the display of a grouping of 17th C. furniture that needed the same RH levels. The platform that these were to be displayed on had already been designed with a Plexiglas front for security purposes. The addition of Mylar covered frames across the top of the platform enclosure made an contained space that we could then humidify. An adjacent wall segment that was hollow and the size of a small closet(approx. 3’x5’), provided a convenient site for humidification equipment.

Ideally, we needed a dependable humidifier that could be fed into a ducting system to distribute moist air throughout the platform, and would have a remote humidistat to turn the equipment on and off in response to the humidity needs within the platform space. McMaster-Carr proved to be the supplier with almost all needed parts. I selected a Herrmidifier brand centrifugal humidifier and fed its output into a 3” PVC pipe through a sanitary T fitting. This pipe travelled up to the upper facade of the case front where it joined to a piece of 4” PVC with another T fitting. This 4” pipe ran across the inside of the display facade with three more T fittings to release the moist air into the platform area. A small computer cooling fan was mounted into the end of the 4” pipe to blow across the 3” T fitting entrance and draw up the moist air from below and blow it out into the platform. A remote humidistat reads the RH level and calls for more humidity when needed. The small fan runs all the time and keeps the platform air mixed for even distribution of the humidity. All pipes and air outlets slope toward the source so any stray water drains off safely.

The final and key piece of the system is the water supply. Anytime there is water in an exhibit situation, I feel it must be contained and limited so there is no possibility of catastrophic release. The humidifier is meant to be plumbed with a supply line that is controlled by a float valve and serves a small reservoir in the base of the humidifier. There was not a plumbed supply available and I did not want an unlimited supply that could spring a leak. I opted to use five gallon jugs of reverse osmosis filtered water supplied by a local company. This I coupled with a FloJet BW 1000A bottled water pump that has an uptake wand that lowers into the jug and an output that senses the drop in back pressure of the float valve releasing and then pumps water to fill the reservoir. There is a small amount of excess water that drains from the system which is captured by drain trays and directed into a second jug for re-use. Both jugs sit in a Rubbermaid tub large enough to contain all available water in the system. Reverse Osmosis water was used for supply as the notoriously hard water in this region would either destroy the humidifier with mineralization, or leave a very fine layer of white mineral powder across the exhibit.

So far, the system is maintaining an observed RH between 36 and 42% and seems to be using about a 5 gallon jug per week. I predict water usage will continue to decrease as all the materials of the display come to an equilibrium moisture content. So far the system is operating as designed and I’ll be monitoring on an ongoing basis. Total cost was less than $1000 with a continuing cost of about $5 per week for the bottled water.

Thanks to all the list members that provided information and links regarding the passive conditioning of display cases. Additional thanks go to our Chief Conservator Mark MacKenzie for being a great help in the design of the active humidification system. I’m happy to answer questions that anyone might have.

Jamie Hascall
Chief Preparator
Museums of New Mexico Exhibits
Santa Fe