Practical Guide: Understanding What Humidity Does and Why PDF

One of a series of seven articles forming a practical guide to HVAC for museums and historical renovation. Examines the difference between relative humidity, specific humidity, and vapour pressure. Goes on to explore how those measures influence phenomena loosely attributed to 'humidity'. Considers how moisture affects materials and processes. Deals with condensation, moisture in the building structure, and mould and fungus growth. Explains the use of desiccants to control humidity. Discusses the phenomena of static electricity and rust. Notes dimensional changes in materials caused by moisture. Concludes that allowing materials to absorb and desorb moisture slowly in response to seasonal climate changes may be a successful way of maintaining long term stability in the materials and buildings that house them.

Article appeared in the Practical Guide to HVAC for Museums and Historic Renovation, which was included with the vol. 41, no. 4, April 1999 issue.