I actually ran into this on a test fixture designed for vacuum cleaners. Moisture content of the air was part of the power calculation.
Here is a paper on the equations needed to do what you want:
http://maxwellsci.com/print/rjaset/v6-2984-2987.pdf
Look through the equations and you see exponents are involved in getting the saturation vapor pressure. This math is beyond what a Jazz is designed to do. Floating points are needed.
Unless you're really a glutton for punishment. Google "Taylor Series Expansion of Exponential Functions", which can probably be done in a Jazz. Many, many moons ago I did this in a Siemens PLC to calculate cosine.
However, if you ask me to provide an example of how to do a Taylor Series in a Jazz I will reach through the Internet and choke you.
Joe T.