Heat serves as a catalyst in all chemical reactions. Controlling temperature is an important factor in slowing object deterioration rates. Chemically unstable objects are extremely sensative to thermal conditions and require low temperature storage. A general rule of thumb: every increase of 18 degrees Fahrenheit doubles the speed of a chemical reaction.
Temperature change encourages expansion and contraction of certain materials. Large fluctuations of temperature will affect the dimensional stability of an object. Multimedia objects are susceptible to thermally induced cracking since different materials expand and contract at different rates. Temperature also directly impacts relative humidity in a collection which plays a crucial role in the stability of organic materials. Rates of biological attack can be reduced by lowering temperature.
Surveying the literature on preservation in the last fifteen years indicates that optimum temperatures for mixed collections can only be addressed using a range of temperatures. Several factors make the determination of an absolute number impossible.
Items that are in long term storage and get low use will benefit most from colder storage, 62-65 degrees Fahrenheit. Generally speaking, optimum temperature ranges for most collections fall between 66-72 degrees Fahrenheit. Logical decisions should be made for collection items that frequently move in and out of storage. "Human comfort is often the factor controlling minimum storage tempertatures for collections. This is one of a number of reasons that, to the extent that long-term preservation is a goal, staff and user functions should be separated as much as possible from the stacks in which the research collections are housed."xxxxix Collections should be stored away from outer walls to reduce the effects of outdoor climate change. Consulting several resources for current temperature recommendations can be helpful in establishing an acceptable range for each collection. Stabilizing the environment within the acceptable range in most cases will provide maximum benefit to a greater percentage of the collection.
Controlling ambient temperature can be done several ways. "Regulating the environment of the entire building is ideal. However, in many instances it may be best to control the micro-environment rather than trying to control the whole building, especially if the latter is not feasible."L Determining the parameters for building controls will require information on the regional climate concerning humidity levels, average temperature ranges, prevailing wind direction and pollution levels. Most HVAC engineers utilize the American Society of Heating, Refrigeration and Air Conditioning (ASHRAE) standards that focus on human comfort and are less familiar with preservation needs. The capabilities of the heating, ventilation, and air conditioning systems should be carefully outlined. HVAC systems are costly to install, must run continuously in order to be effective, and will require continual maintenance and repair.
Direct refrigeration air conditioning units called DX or direct expansion units can be substituted for large HVAC systems when cost is an inhibitive factor. They are easy to install and maintain but will have a reduced life span in contrast with a properly maintained, HVAC system. A refrigerated air conditioning unit that maintains temperature stability within storage and user areas will increase control over relative humidity levels as well.
Creating circulating air paths using fans, open doors and windows is a minimum cost alternaative when little or no resources are available. One draw back is the introduction of ozone and caustic particles from pollution into the environment. Adding an attic fan and installation to walls and ceiling can lower temperature within a facility and aid in collection stability. Planting trees and using trellised vines set away from the building reduce the temperature inside the building. Reduction in window surface area or blocking current windows with awnings and curtains will reduce temperature and ultraviolet exposure.
Interior temperatures should be monitored daily for the first year and compared with exterior temperatures to graph the seasonal changes and determine possible problems and solutions.
temperature changes between 10 and 20 degrees Fahrenheit causes damage.
the percentage of water vapor in the air, compared to the total amount of water vapor in the air at 100% saturation at any given temperature.
small environments within larger ones. Example: exhibit case within museum building.