International Standards for Refrigerant Properties

M.O. McLinden, A. Laesecke, E.W. Lemmon, and R.A. Perkins >

Objective: To facilitate and promote international standards for the thermodynamic and transport properties of refrigerants.

Problem: The hydrofluorocarbons (HFCs) and other fluids are now seeing widespread commercial use in place of the ozone-depleting CFC and HCFC refrigerants. To evaluate the energy efficiency, capacity, etc., of any fluid in a thermodynamic cycle, knowledge of the thermophysical properties is required. Standards exist for determining and reporting the performance of air-conditioning systems at standard ratings conditions. But differences between multiple, "competing" property formulations lead to differing performance ratings. This is especially a problem in international trade.

Approach: We work with several international groups that develop and/or promulgate standards. Chief among these is Annex 18 of the International Energy Agency, a group that NIST organized in 1990. We are also active in the Transport Properties Subcommittee of IUPAC. Finally, the NIST REFPROP database has, itself, been adopted as a de facto standard within the refrigeration industry. We work within the IEA and IUPAC groups to promote REFPROP as the source of refrigerant property data. As new standards are adopted, we revise REFPROP, if needed, to conform to the new standards.

Results and Future Plans: The IEA Annex 18, Thermophysical Properties of the Environmentally Acceptable Refrigerants, concluded its third and final phase in 1999. The Annex carried out comprehensive evaluations of the available equations of state and sanctioned standards for R123, R134a, R32, R125, and R143a. Wide participation was invited in this process, and anyone could submit an equation of state for evaluation. Of the five fluids, the formulations for R123 and R143a developed at NIST were designated as international standards. A similar comparison of mixture models has facilitated the dissemination and adoption of a new mixture modeling approach. This model, based on Helmholtz energies for each of the mixture components and developed at the University of Idaho and NIST, is implemented in REFPROP and also forms the basis for an extensive tabulation of properties prepared by the Japan Society of Refrigerating and Air Conditioning Engineers. The final report for Annex 18 was presented at the quadrennial Congress of the International Institute of Refrigeration.

Under the auspices of the IUPAC Subcommittee on Transport Properties, NIST acts as one of three co-ordinators of a project on "Thermochemical, Thermodynamic and Transport Properties of Halogenated Organic Compounds and Mixtures." In the past NIST has organized, through IUPAC, an international round robin comparison of the viscosity and thermal conductivity of R134a. We are now working to develop formulations for propane, butane, and isobutane (so-called "natural refrigerants") that are of increasing interest.

The ISO has recently approved the establishment of a working group to establish standards for refrigerant properties. NIST will be active in this group, along with many of the Annex participants.

Publications:

McLinden, M.O. and Watanabe, K., "International Collaboration on the Thermophysical Properties of Alternative Refrigerants: Results of IEA Annex 18," Proc. 20th Int. Congress of Refrig., Sydney, Australia, September 19-24, 1999, Int. Inst. Refrig.