Introduction to Psychrometry

The Times They Are A Changin'

If you have visited this site before March 2011 and have now returned you may be surprised at some of the content that has been changed.  Previously you would have found that it presented the basic concepts of structural drying which, for a number of years, have been held as the best practices in the field of Restoration.  It has come to our attention that some new insights are being gleaned in the Restoration field that challenge some of the accepted thinking of the past and provide a better understanding of the dynamics which occur in a drying environment.

The use of psychrometry is a critical tool at the restorer's disposal to help him or her get a handle on the complex forces in nature that are at the heart of every drying process. In the past, in an effort to understand and simplify the theories about structural drying, those who were pioneers in the field of restoration used scientific terms in ways which made the ideas easier to grasp and gave the restorer some solid information upon which to base the drying needs.  Unfortunately, in the process of simplifying what was going on scientifically, certain inaccurate conclusions have been drawn which, when used as a basis for a drying strategy, may fail to enhance the drying process in some circumstances.

In an effort to provide the best restoration services we can, we feel it is our responsibility to keep abreast of new research and to incorporate these findings into our strategies of drying.  We are excited by the new insights being shared with us and appreciate the dedication and integrity of those who have given so much time and effort to glean the key kernels of truth which are at the heart of our industry.  We hope that as you work through this material that you will be awakened as we were to a new vista of understanding and we encourage you to thoughtfully consider the data presented.

 What Is Psychrometry?

" What exactly is psychrometry?  'Psychrometrics deals with thermodynamic properties of moist air and uses these properties to analyze conditions and processes involving moist air'.  (1997 ASHRAE Handbook, 6.1 p1)

"Psychrometry is derived from the Greek word psychro which means 'cold' and metry whose root is 'metric'.  It is not a 'science' as some would suggest.  It is a measure, or a metric of the elements that influence changes in environmental air and water mixtures." (Leadership In Restorative Drying, page 78)

 The Key Elements In Psychrometry

The elements of psychrometry examined in a restorative drying context include:

• Dry Bulb Temperature
• Wet Bulb Temperature
• Vapor Pressure
• Relative Humidity
• Dew Point Temperature
• Humidity Ratio
• The cubic Feet of a Pound of Air
• Enthalpy
  • Sensible Heat
  • Latent Heat

(Leadership In Restorative Drying, page 78)