ASHRAE ST-16-008

Abstract

Scope: The presence of unsaturated fluorocarbon contaminants in the refrigerantsusedinHVAC&Rsystemsmayresult inreaction 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 the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) in AHRI Standard 700 (AHRI 2015) has proven to be more restrictive to reclaimers, recyclers, and HVAC&R system providers than previously thought. In addition, compounds such as hydrofluoroolefins(HFOs)have been tested as low global warming potential (GWP) alternative refrigerants and shown to have acceptable stability in some applications. So, itmaynot be appropriate to classify all unsaturated compounds as unstable and blanket them under the same restrictive limit. ASHRAE RP-1641 (Rohatgi and Clark 2015) aims at determining the effects of halogenated unsaturated contaminants present in refrigerants on the stability of refrigerant/ lubricant systems and recommends a concentration limit specific to the unsaturated contaminant below which the refrigerant/lubricant system is thermally stable. Based on a literature search and review, the following refrigerant/lubricant mixtures with their corresponding contaminants were selected for a stability study in sealed-tube tests: • R-134a (1,1,1,2-Tetrafluoroethane)/Polyolester (POE) with R-1130 (1,1-Dichloroethylene), R-1130(E) (Trans-1,2- Dichloroethylene), R-1131 (1-Chloro-2-fluoroethylene), and R-1234yf (2,3,3,3-Tetrafluoropropene • R-1234yf/POE with R-1225ye(Z) ((Z)-1,2,3,3,3-Pentafluoropropene), R-1233xf (2-Chloro-3,3,3-trifluoropropene), and R-1243zf (2,3,3-Trifluoropropene) • R-123 (2,2-Dichloro-1,1,1-trifluoroethane)/mineral oil with R-1122 (2-Chloro-1,1-difluoroethylene), R- 1123(1,1,2-Trifluoroethylene) and R-1131 Based on criteria such as visual changes, total acid numbers (TANs), organic anions, 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 30,000 ppm. These maximum concentration limits were based, however, on sealed-tube stability tests and would need to be balanced against other safety concerns, such as toxicity, flammability, and handling and recycling practices.