This is where I discuss the concept of VAPOR PRESSURE in detail.   Vapor Pressure is without any doubt the most important psychrometric property that needs to be understood for the HVAC engineer trying to learn psychrometrics.  It is bizarre that many students are going through “Psychrometric Chart”  training without even talking about Vapor Pressure.  The fact that ASHRAE chose not to show this property on their standard chart may have something to do with this trend.  You can “draw process lines” on the charts without any mention of Vapor Pressure but the penalty you pay is a loss of key underlying psychrometric concepts.

As usual conversion from PowerPoint to PDF and no narration leaves out a lot.  But I think the following will still be very helpful to new engineers.

Please send in your comments and corrections to me.  Thank you.

Psychrometry Part1-B