Prior to the advent of the programmable calculator, the psychrometric chart was the most convenient method of solving psychrometric problems. Psychrometric charts are designed for a given atmospheric pressure. If a chart is not available for the particular atmospheric pressure desired, correction factors have to be applied to any solutions obtained from the available charts. Inaccuracies in plotting psychrometric processes and reading the values from the usually small charts, coupled with approximate pressure correction factors, tend to reduce accuracy of the calculations to unacceptable levels. A more convenient method, however, is now available. The programs included herein are based on the psychrometric formula of ASHRAE.

The output of the program in the normal temperature range of air-conditioning system design compares favorably with data shown in Table A-20, page 169 of ASHRAE Energy Calculations 1.

Units: Dual