Hello, I am fairly new to using psychrometrics, so I am hoping that this is a fairly simple solution. I was going back through some old problems and wanted to spot check a few calculations. In the process I converted the units on one of the problems and the enthalpies were not matching up. I am trying to calculate the enthalpy of a moist air mixture. The air conditions are: Tdb = Dry Bulb Temp = 20 C = 68 F X = Humidity Ratio = 7.26 grams/kg = 50.82 grains/lb = 0.00726 lb/lb P = Baro Pressure = sea level = 760 mmHg = 29.921 inHg I used both an Imperial and an SI psychrometric chart to do a quick spot check to see if the enthalpies match and got: h = 24.4 Btu/lb dry air h = 38.5 kJ/kg dry air I then converted the units and hit a wall, they are not even close to equivalent: h = 24.4 * 2.326 = 56.75 kJ/kg h = 38.5 * 0.429953 = 16.55 Btu/lb As another check I did a quick online calculator at http://www.uigi.com/WebPsycH.html, which yielded the same results. As yet ANOTHER check I used Eq 32 from Ch. 1.13, 2009 ASHRAE Handbook: h = 0.240*Tdb + W(lb/lb)*(1061+0.444*Tdb) = 24.24 Btu/lb Am I missing some super secret conversion factor here? Can you not convert enthalpies directly? I would think that a thermodynamic property would not change depending on your starting units.