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Ngoc Dung (Rosine) Rohatgi, Ph.D., Spauschus Associates Inc. |
The presence of unsaturated fluorocarbon contaminants in the refrigerants used in HVAC&R systems may result in reaction products that could potentially cause problems in system performance or reliability. Since 2007, the 40 ppm limit for unsaturated halogenated contaminants in new and reclaimed refrigerants set by AHRI 700 has proven to be more restrictive to reclaimers, recyclers and HVAC&R system providers than previously thought. In addition, compounds such as hydro-fluoro-olefins (HFO) have been tested as low global warming potential (GWP) alternative refrigerants and shown to have acceptable stability in some applications. So, it may not be appropriate to classify all unsaturated compounds as unstable and blanket them under the same restrictive limit.
This research project aimed at determining the effects of halogenated unsaturated contaminants present in refrigerants on the stability of refrigerant/lubricant systems and recommending a concentration limit specific to the unsaturated contaminant below which the refrigerant/lubricant system is thermally stable. The following refrigerant/lubricant mixtures with their corresponding contaminants were selected for stability study in sealed tube tests: (1) R-134a/POE with with 1,1-dichloroethylene, 1,2-dichloroethylene, R-1131 and HFO-1234yf; (2) R-1234yf/POE with HFO-1225ye(Z), HCFC-1233xf and HFC-1243zf; (3) R-123/Mineral Oil with R-1122, R-1123 and R-1131.
Based on criteria such as visual changes, Total Acid Numbers (TAN), organic anion and dissolved metal concentrations after aging, it was concluded that the R-134a/POE system was as stable as the control (without contaminant) when the concentration of its contaminants was less than 1000 ppm. The R-1234yf/POE system was stable when its contaminants were less than 5000 ppm, while the R-123/Mineral Oil system was stable when its contaminants were less than three weight-%. These maximum concentration limits were however based on sealed tube stability tests and would need to be balanced against other safety concerns, such as toxicity, flammability, handling and recycling practices.
This research project aimed at determining the effects of halogenated unsaturated contaminants present in refrigerants on the stability of refrigerant/lubricant systems and recommending a concentration limit specific to the unsaturated contaminant below which the refrigerant/lubricant system is thermally stable. The following refrigerant/lubricant mixtures with their corresponding contaminants were selected for stability study in sealed tube tests: (1) R-134a/POE with with 1,1-dichloroethylene, 1,2-dichloroethylene, R-1131 and HFO-1234yf; (2) R-1234yf/POE with HFO-1225ye(Z), HCFC-1233xf and HFC-1243zf; (3) R-123/Mineral Oil with R-1122, R-1123 and R-1131.
Based on criteria such as visual changes, Total Acid Numbers (TAN), organic anion and dissolved metal concentrations after aging, it was concluded that the R-134a/POE system was as stable as the control (without contaminant) when the concentration of its contaminants was less than 1000 ppm. The R-1234yf/POE system was stable when its contaminants were less than 5000 ppm, while the R-123/Mineral Oil system was stable when its contaminants were less than three weight-%. These maximum concentration limits were however based on sealed tube stability tests and would need to be balanced against other safety concerns, such as toxicity, flammability, handling and recycling practices.
See more of: Challenges and Opportunities with Refrigerants