This paper presents a tutorial on the computation of psychrometric properties on the personal computer using a state-of-the-art, commercially available, nonlinear equation solver. Specifically, the ideal gas approximations are used to illustrate the ease with which the practicing HVAC engineer can computerize psychrometric calculations. This approach requires only that the user input the relevant psychrometric equations in algebraic form and input three independent thermodynamic properties from among the dry-bulb temperature, pressure, wet-bulb temperature, dew-point temperature, humidity ratio, relative humidity, degree of saturation, specific humidity, mole fractions, mass fractions, and/or specific volume. The program computes all remaining properties including the enthalpy, internal energy, entropy, available energy, as well as all other dependent properties. The results generated by this approach are compared to those based on the Hyland-Wexler (1980a, 1980b, 1983a, 1983b) formulation, and a graphical display of the accuracy for the enthalpy and entropy is shown on the ASHRAE psychrometric chart. The utility of PC-based process analysis is illustrated by application to several simple HVAC examples.

Units: Dual