Thermodynamic Properties of Real Moist Air, Dry Air, Steam, Water, and Ice (RP-1485)

Abstract

This research updates the modeling of moist air as a real gas mixture using the virial equation of state. It includes the Hyland and Wexler model (1983a, 1983b) and considers the Nelson-Sauer model (2002). All new National Institute of Standards and Technology reference equations and the latest International Association for the Properties of Water and Steam (IAPWS) standards, as well as the current values for the molar masses and gas constants, have been incorporated. The deviations of the proposed model to the Hyland-Wexler and Nelson-Sauer models are very low at ambient pressures but increase with increasing pressures and temperatures. The range of validity of the new model is in pressure from 0.01 kPa up to 10 MPa, in temperature from −143.15°C up to 350°C, and in humidity ratio from 0 kg_w/kg_a up to 10 kg_w/kg_a. This model was used to produce moist air and H₂O saturation property tables for the psychrometric chapter in the 2009 ASHRAE Handbook—Fundamentals (ASHRAE 2009). The paper summarizes ASHRAE Research Project 1485 (RP-1485).