You could use any standard simulation package or if you are looking for the water dew point a saturated steam table for water might do the trick (calculate water partial pressure and find the corresponding temperature in the table. If you have a lower temperature water will stat to condense). This methode should be considered inaccurate. I did a quick check win Design II: The table said 30 deg C but the simulation said 20 deg C - and most tables wont go below 0 deg C.
