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Low-GWP Non-Flammable Alternative Refrigerant Blends for HFC-134a: Final Report



Piotr A. Domanski, Mark O. McLinden, Valeri I. Babushok, Ian Bell, Tara Fortin, Michael Hegetschweiler, Marcia L. Huber, Mark A. Kedzierski, Dennis Kim, Lingnan Lin, Gregory T. Linteris, Stephanie L. Outcalt, Vance (Wm.) Payne, Richard A. Perkins, Aaron Rowane, Harrison M. Skye


This project addresses the objectives of the Statement of Need number WPSON-17-20 "No/Low Global Warming Potential Alternatives to Ozone Depleting Refrigerants." Its goal was to identify low global-warming-potential (GWP), non-flammable refrigerants to replace HFC-134a (GWP=1300) in military environmental control units (ECUs) and to demonstrate their performance. This work is a follow-on to the limited-scope project WP-2740, which used thermodynamic cycle simulation models alone to screen over 100 000 refrigerant blends and identified over 20 candidate HFC-134a replacements. In the present study we narrowed the pool of blend candidates down to three 'best' blends, demonstrated their performance through 'drop-in' tests in a military ECU in environmental chambers over a wide range of operating conditions, and extrapolated the laboratory-measured performance to that of ECUs equipped with modified compressor for each blend to provide the same system capacity while maintaining the isentropic efficiency of the original HFC-134a compressor. The project involved preliminary experimental and analytical tasks in support of the final project task. These included measurements of thermodynamic and transport properties of the novel fluids considered and an update of simulation methods for these properties, fundamental tests exploring the flammability characteristics including calculation methods, fundamental measurements and modeling of forced-convection heat transfer performance, and measurements of cycle performance of candidate blends in a laboratory mini-breadboard heat pump apparatus as the final qualification step of the 'best' blends for full-scale testing in the ECU. The project's conclusion is that R-513A (GWP=573) and a blend we call Tern-1 [R-134a/1234yf/1234ze(E) (49.2/33.9/16.9*), GWP=640] are good replacement blends for HFC-134a offering a similar performance at GWP reduction of 66 % and 51 %, respectively. These fluids do not present any significant application difficulties. If greater reduction in GWP is desirable, R-515B (GWP=344) and CO2 (GWP=1) can be considered but they require further challenging research and developmental work. In the above blend selection, we adopted the ASTM E681 test method as stipulated by ASHRAE Standard 34 for qualifying 'non-flammability' of refrigerants. If military requirements for 'non-flammability' are more stringent than the E681 standard, a smaller reduction of GWP will be possible with qualifying blends.
NIST Interagency/Internal Report (NISTIR) - 8455
Report Number


Air conditioning, Coefficient of performance, Cycle simulation, Flammability, Refrigerants, Vapor compression, Volumetric capacity


Domanski, P. , McLinden, M. , Babushok, V. , Bell, I. , Fortin, T. , Hegetschweiler, M. , Huber, M. , Kedzierski, M. , Kim, D. , Lin, L. , Linteris, G. , Outcalt, S. , Payne, V. , Perkins, R. , Rowane, A. and Skye, H. (2023), Low-GWP Non-Flammable Alternative Refrigerant Blends for HFC-134a: Final Report, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed May 24, 2024)


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Created January 27, 2023