Certain specialized collections will benefit from storage at lower temperatures than can be provided by a standard HVAC system. However, cold or frozen storage is only appropriate for materials that are not used frequently, since the more often the materials are brought out of cold/frozen storage and acclimated to room temperature, the less long-term benefit cold/frozen storage provides.
Large collections will require specially designed insulated rooms/vaults or prefabricated chambers (which usually use a dessicant dehumidification system), but smaller collections can be stored in household-type refrigerators or freezers, provided the proper protocols are followed.
The Image Permanence Institute (IPI) has defined several levels for media storage. Room temperature storage is defined as close to 68°F. Cool storage is defined as close to 54°F. Cold storage is defined as close to 40°F, while frozen storage is defined as 32°F or below. All types of storage should have a stable relative humidity between 30 and 50%.
The lifespan of vulnerable media can be lengthened by freezing or storing at extremely low temperatures. These include motion picture film, photographic film and prints. Be aware, however, that some media may benefit from cold storage, but should not be frozen. These include glass plate negatives, magnetic tape, and CDs/DVDs.
The National Fire Protection Association has guidelines for construction of cabinets and vaults to house nitrate film; these guidelines are complex and are required by some localities. For most small institutions, it is best to store nitrate films in off-site cold storage (service copies might be made onto videotape) or transfer them to an institution that is better equipped to care for them. Acetate base and color films also greatly benefit from storage at cold temperatures, but again, this is generally not practical for small institutions with only a few films.
If cold or frozen storage is to be successful, you must be able to maintain stable low temperatures with controlled humidity. Humidity control can be managed through the careful use of packaging. Materials must be stored in a moderate relative humidity for several weeks before being packaged into moisture-proof freezer bags (this conditioning is necessary to avoid excessive moisture within the bag). Care must be taken when removing collections from storage so that condensation does not occur; the materials should be acclimatized at least overnight, or longer for a large amount of material, before being removed from the bag.