If you are responsible for archival storage you may find yourself faced with a mountain of questions and a shortage of answers. Historical items that we deem most valuable are often the most fragile and susceptible to deterioration over time. Items such as books, video, film, paintings, furniture, and metals are all sensitive to the environment in which they are stored. It can be difficult to find a solution for preserving any one of these items long-term. Throw in the fact that each type of material prefers a different environment, and it can feel like living with a family that constantly fights over control of the thermostat. The only difference here is, temperature and humidity variation can actually be life-threatening for unstable materials.
There are so many environmental factors that contribute to the deterioration of materials. If left in a humid environment, books can become the unfortunate host to mold colonies in a matter of months. Paintings will develop cracks from shrinking if left in too dry of an environment. Chemically unstable objects such as old video film will deteriorate more quickly unless stored in a cold room. Improper air filtration can introduce ozone and particulates to the environment that can harm collections as well. Windows or lights will also harm sensitive materials over time. The type of environment required will greatly affect the cost to build it. You can save a lot of money if you can skip the refrigerated cleanroom and store your items in a typical office environment instead. Let’s look at books for one example: depending on the required lifespan of your particular collection, a typical office environment (75°F, 50% relative humidity (RH) in the summer) may be sufficient. A typical chilled-water or direct expansion (DX) cooling system would be adequate to cool and dehumidify this environment in the summer. In the winter, a humidifier may or may not be required depending on the local climate. To ensure that books last greater than 50 years with no noticeable degradation, a lower humidity environment is required, and it becomes increasingly complicated and expensive to create this environment with DX or chilled water cooling. If a storage room needs to be kept below approximately 45% RH, it may make more economical sense to use a desiccant dehumidification system.
Desiccant dehumidification allows the air to be dehumidified directly, rather than cooling the air down more than needed just to ‘wring-out’ the moisture, and then reheat the air to avoid overcooling the space. This approach will cost more upfront, but will greatly reduce the utility costs of maintaining the space temperature and humidity compared to using traditional cooling methods.
If you are faced with the challenge of storing valuable or historic materials and would like assistance, please contact Dane Heimerman, PE at firstname.lastname@example.org or (814) 237-2180. We will help you find the best solution.