I am looking for a formula (not a chart) that uses Wetbulb to get Enthalpy values.

I am trying to make an excel mobile spreadsheet for my PDA that will calculate BTUH using Wetbulb and CFM as the variables. Currently, I have to pull out a chart to convert the WetBulb into Enthalpy first, for the following equation: BTUH = 4.5*CFM*Delta H

I would like to be able to leave the chart in the van and just type the Wetbulb into the PDA and have it calculate the enthalpy and have that input directly into the BTUH equation.