NIST vs. Psychrometric Chart

1. NIST:

If you follow this link…

http://webbook.nist.gov/cgi/fluid.cgi?ID=C7732185&TUnit=F&PUnit=psia&DUnit=lbm%2Fft3&HUnit=Btu%2Flbm&WUnit=ft%2Fs&VisUnit=lbm%2Fft*s&STUnit=lb%2Fft&Type=IsoTherm&RefState=DEF&Action=Page

and enter the values…

T=100°F, .5 psia

The resulting value of enthalpy computed is…

h=1105.9 BTU/lbm.

1. Psychrometric Chart:

If you look up the enthalpy on a Psychrometric Chart (.5psia = 1.01801inHg) the resulting value for enthalpy is…

h=48.325 BTU/lb

1. The NIST value is almost 23 times the value reported on the Psychrometric Chart – WHY???