I'm a chemical engineering student at georgia tech, and this is basically a simple energy balance. I have an excel sheet that you can use to calculate the economics.
spreadsheet (for calculations)
http://sites.google.com/site/showerh...attredirects=0
Diagram
http://sites.google.com/site/showerh...attredirects=0
Description (open in openoffice)
http://sites.google.com/site/showerh...attredirects=0