RP-1485 -- Thermodynamic Properties of Real Moist Air, Dry Air, Steam, Water, and Ice ✓ Most Recent

This research revised the ASHRAE psychrometric model of moist air as a "real gas" mixture using the virial equation of state. It uses the latest universal gas constant, molar masses of dry air and water, the latest research from IAPWS, CODATA, IUPAC, NIST, NOAA and NASA and builds on the basic ASHRAE algorithm of Goff and Gratch (1945); updated by Hyland and Wexler (1983) and Nelson and Sauer (2001). The new model has a broadened range of validity with pressure from 0.01 kPa to 10 MPa, temperature from -143.15 to 350°C , and humidity ratio from 0 to 10 kgw/kga.

The model was used to produce moist air and H₂O saturation property tables for the psychrometric chapter in the 2009 ASHRAE Handbook of Fundamentals. The new moist air table is close to the 1985 table because moist air at ambient pressure behaves essentially as an ideal gas; also the underlying data used by Hyland and Wexler was quite accurate. Greater deviations to the former models occur at higher pressures and temperatures encountered in the compression stage of gas turbines and in compressed air energy storage applications.

The results of psychrometric research serves

1. ASHRAE and the air-conditioning industry,
2. the World Meteorological Organization and others involved in atmospheric research and meteorology,
3. the Association of Agricultural Engineers who rely on psychrometrics in their modeling and tracking of soil moisture and evaporation and plant transpiration, and
4. the engineering community that deals with (a) air conditioning from deep mines to space capsules, (b) deep vacuum processes, (c) high pressure processes, and (d) the gas and light oil turbine processes that power our airplanes and gas turbine-powered generators.

Units: Dual