Hi Christine,

I served as Director of a museum in central Wisconsin with an extensive and mixed collection, ironically much of which was stored in the lower level of the library just like yours. Humidification was an issue as was de-humidification in summer (resolved through air conditioning). As far as raising the RH to an acceptable level there are different approaches you could take depending on your gas heating system. Is the system a forced hot air air system with ductwork from a central location; a forced hot air system that originates from one or more single fan units (no ductwork); or, a radiant system that uses circulating hot water? From your description it sounds like you have forced hot air, but one can't be sure.

With forced hot air systems there are relatively simple solutions that do require regular maintenance and won't break the bank. The most appropriate of these systems use electronic aspirators to inject a very fine vapor of filtered (A system that uses a pre-filter for sediment and then a charcoal filter works well) water into the duct system's supply side, after the air is heated. Some contractors will hook these directly to your public water supply although that is not recommended because minerals and impurities in the water will clog the system. The aspirators are controlled by humidistats in each heating zone of the space you occupy. When the humidistat calls for moisture, it opens a valve and water flows to the mister heads and is entrained in the heated air. These systems work very well with gas furnaces and they are particularly suited to archival environments. The annual maintenance is easy and could be done by you or museum staff.

Your contractor or maintenance people may try to steer you to either a drum system or flow through system as these are cheaper, easier to maintain, usually don't require filtered water, and are a little easier to install. DON'T LET THEM SELL YOU THESE SYSTEMS. Both of these types of systems are prone to mold and bacteria growth and involve either standing water or pads that are constantly being soaked with water.

I hope this is a help to you. Please feel free to call on me if you need any additional information or a referral to an engineer that specializes in environmental systems, I know of a good firm that does this type of engineering work for museums.

Cheers,

Larry Fisher
6 Belvedere Drive
Bristol, RI 02809
p: (401) 253-5335
e: [log in to unmask]

On 12/16/2010 10:59 AM, Cross, Christine wrote:

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Good Morning Listers,

We have a bit of a challenge at the museum and any advice would be appreciated. Our current average RH is 20%. The museum is a general topic museum with collections of taxidermy specimens, archives, Native American and local history artifacts, in other words a broad range of collection material. The museum is located in Wisconsin and is housed in the lower level of the library, it is approx. 2200 square feet of space. The building is older and uses natural gas furnaces for heating. When the furnaces were installed a humidification system was also put in place, but apparently this has never worked properly. Being owned by the city, the building maintenance department would like to take care of this issue in-house, but need some direction in terms of how to get the humidity levels up to an "acceptable" level, around 40% would be nice. So I am asking the list for any information/advice they wish to share.

Thank you in advance for the assistance!

Christine Cross

Director

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