SF-86-10-1 -- A Comparison of Three Moist Air Property Formulations for Computer Applications PDF

For computer applications in which moist air properties must be computed, compromises usually have to be made among the speed of computation, the accuracy of the psychrometric formulations, and the ease of programming. Three moist air property formulations are compared: perfect gas, perfect gas with enhancement factor, and Hyland-Wexler. The three methods are outlined briefly, and then properties calculated by the perfect gas formulations with and without the enhancement factor are compared to those calculated by the Hyland-Wexler formulation for accuracy at various points on the psychrometric chart. The computer times necessary to calculate psychrometric properties by each of the three methods are compared. Each of the three formulations is used to calculate state points, loads, and irreversibilities for two systems: an air handler with mixed air and cooling coil, and a cooling tower. This should provide engineers with quantitative information that will help to pick the best psychrometric formulation for a particular application.

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