Climate Notes is a free e-newsletter published by the Image Permanence Institute and designed for collection care staff in cultural institutions. Climate Notes covers a wide range of topics related to managing the environment for preservation.
Question: A hardcover book is stacked between other books on a shelf in a library. The relative humidity of the library has been steady at 30% for the last few months. Suddenly, the relative humidity jumps to 50% and remains there. Approximately how long does it take for the book to fully adjust (equilibrate) to the new relative humidity of the environment?
- One hour
- One day
- One week
- One month
- One Year
Answer: To find the answer, read on...
The importance of climate conditions in the preservation of museum and library collections is well recognized. Researchers at IPI have stated that, “for a large variety of museum objects and archival records, heat and humidity are the primary factors that govern the occurrence and rate of biological decay, chemical instability and mechanical damage.” To this effect, recommendations for environmental management often appear as low and high limits, specifying appropriate average levels of temperature and RH as well as the acceptable range of fluctuations.
These recommendations generally give preference to “flat lines” of temperature and relative humidity in the name of avoiding damage from fluctuating environments. However, even with the best environmental controls...
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DEFINITION:
Thermal Equilibration is the process of an object to adjust to the ambient temperature of the environment. An object reaches thermal equilibrium with its environment when the whole object -from its periphery to its core- neither gains nor loses heat (or thermal energy) from its constant, dynamic exchange of energy with the environment. |
Thermal Equilibration is most often discussed for managing access to materials kept in cold storage; in this context, the rate of thermal equilibration determines how long an object will need to stay in a staging room when coming out of cold storage. Allowing sufficient time for an object to warm above the dew point temperature of the air prevents condensation from forming on the surface of the object. (For more on Dew Point, see the previous volume of Climate Notes.) This article, however, will explore a few facts about the rate of thermal equilibration to understand the impact of environmental changes and various housing situations.
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In many ways, it is more difficult to evaluate the impact of fluctuations in the environment's relative humidity than the environment's temperature because Moisture Equilibration is influenced by more variables than thermal equilibration. For example, enclosures or housing situations may act as moisture barriers and thus influence the how quickly (or how slowly) the objects are exposed to the new humidity conditions. The temperature will also influence the rate of moisture equilibration. Furthermore, there is more variation in the capacity of the individual objects or materials to control moisture equilibration than thermal equilibration.
In order to explore a few basic concepts about moisture equilibration, this article will answer several basic questions: the Who, Why, When and How of moisture equilibration.
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