5. Iterate the following formula to find t* by making use of PSYCHR. h+ (Ws(t*) -W) hw(t) = hs(t*) 7. Comments on the New Kelvin Temperature Scale The values for saturation pressure of water calculated by the algorithms presented herein are identical with those tabulated in table 2 of Chapter 21 of 1967 ASHRAE Book of Fundamentals. These values were, however, obtained by the Goff's calculation based upon the old Kelvin scale [t=T-273.16 (Centigrade vs. Kelvin)]. In October 1954, the Tenth General Conference on Weights and Measures adopted a new Kelvin scale T of absolute temperature on which the triplepoint of water is assigned the value 273.16. According to this new convention, the new temperature scale becomes t=T-273.15. Prof. J. A. Goff published new formulas corrected for this new temperature scale for saturation pressure in his most recent paper (Saturation Pressure of Water on the New Kelvin Temperature Scale, 1963 International Symposium on Humidity and Moisture, Washington, D.C.). According to that paper, the saturation pressure for the new temperature scale will be calculated by the following algorithms. According to this new formula, the corrections AP/P to the current ASHRAE table values of the saturation water vapor pressure are found to be extremely small, as shown in the following table. For the engineering calculation, the algorithms based upon Goff's 1949 paper for PSYCHR should, therefore, be sufficiently accurate. [1] Goff, J. A., and Gratch, S., Thermodynamic properties of moist air, ASHVE Transaction, 1945, pp. 125-164. [2] Goff, J. A., Standardization of thermodynamic properties of moist air, ASHVE Journal Section, HPAC, Nov. 1949. |