Construction of a Generalized Psychrometric Chart for Different Pressures

Abstract

In textbooks of thermodynamics or air conditioning engineering we can find the psychrometric chart at atmospheric pressure. However, standard psychrometric charts cannot be used directly in those areas where urban elevations and barometric pressures are considerably different from those given on the charts. Based on the formulas suggested by ASHRAE, a generalized psychrometric chart for different pressures is constructed, using composite thermodynamic properties φ/ p, pw/p, and vp. A nomograph is given to relate these composite thermodynamic properties to the psychrometric variables φ, pw, and v with p. Other commonly used psychrometric variables can be read directly from the generalized psychrometric chart. Three numerical examples illustrate the use of the generalized psychrometric chart. It will be of material help in both the design of air conditioning systems for different barometric pressures and the teaching of psychrometrics.