Performance and refrigerant mass distribution of a R290 split air conditioner with different lubricating oils

The charge mass of R290 in room air conditioners (RACs) is limited by relevant standards due to its flammability. Meanwhile, the selection of the lubricating oil for R290 RACs is not yet clear. Mineral oils (MOs) are used currently, but the system performance when using MO is constrained under the existing standards because of the high R290 solubility in compressor oil sump. Some polyalkylene glycol synthetic oils (PAGs) are less soluble with R290, but the use of PAG in R290 RACs is less studied. In this paper, the effects of different lubricating oils including a PAG and a MO on a 1.5 HP R290 split RAC were experimentally investigated under cooling and heating mode. The refrigerant mass distribution was measured at steady state by “Quick Closing Valve Technique”. The system performance and R290/oil mixture viscosity in oil sump were compared. Results showed that using the PAG could reduce the R290 mass in compressor by about 10–13 g and improve heating capacity by 1.8–2.3%, but the Coefficient of Performance (COP) was lower under heating mode due to the excessive R290/oil mixture viscosity in oil sump. Results also showed that the refrigerant mass in the liquid line accounted for about 15% of the total charge mass under heating mode, and only 4–8% under cooling mode. The results can provide guidance for the system design and selection of lubricating oil for R290 RACs.