Development of an air drying index for lumber

Abstract

Lumber is often air dried in an air drying yard prior to being placed in a dry kiln for final moisture content removal. The rate of the air drying process is dependent on local weather conditions and wood moisture content. Introduced more than 30 years ago, the Drying Index is a method to estimate the relative drying time using the difference in vapor pressures between the dry bulb and wet bulb temperatures. This paper extends its application and describes the development and use of an Air Drying Index to estimate the relative potential of a geographic location to air dry lumber based on the average monthly climate conditions for that location. The monthly Air Drying Index for 252 US locations is presented, and the annual mean for each location was used to develop an air drying map.