The HVAC system designed for the intended purpose of controlling the environment (temperature, humidity and pollutants) within a museum, a library or any type of archival facility is much more complex than the system designed simply for maintaining only human occupancy comfort. This system is designed to control the environment for the preservation of the artifacts, books, collections, artwork, etc. These HVAC systems must be operational 24/7, and often require redundancy.
Extremely tight control over all environmental parameters can ensure an object's survival, but at a price few cultural institutions can justify or are willing to pay. Therefore managing the risks, not avoiding it all together, is the objective.
Because of the variety of materials to be maintained, and the costs versus environmental risks deemed acceptable by each facility administrator, there are very few documented design parameters that are accepted by all such institutions. Therefore it is necessary for the project design team to include input from the facility's administrators, collection managers, curators and conservators to determine the acceptable temperature and humidity parameters for each site.
Authorities often disagree on the ideal temperature and relative humidity for library and archival materials. However, a frequent recommendation is a stable temperature no higher than 70°F and a stable relative humidity between a minimum of 30% and a maximum of 50% (i.e., approximately 33-55 gr/#, or 37-71°Fdp). Research indicates that relative humidity conditions at the lower end of this range are preferable since deterioration then progresses at a slower rate.