Model validations for low-global warming potential refrigerants in mini-split air-conditioning units

To identify low global warming potential refrigerants to replace R-22 and R-410A, extensive experimental evaluations were conducted for multiple candidates of refrigerant at the standard test conditions and at high-ambient conditions with outdoor temperature varying from 27.8°C to 55.0°C. In the study, R-22 was compared to propane (R-290), DR-3, ARM-20B, N-20B, and R-444B in a mini split air-conditioning unit originally designed for R-22; R-410A was compared to R-32, DR-55, ARM-71A, L41-2 (R-447A) in a mini split-unit designed for R-410A. To reveal the physics behind the measured performance results, thermodynamic properties of the alternative refrigerants were analysed. In addition, the experimental data were used to calibrate a physics-based equipment model, for example, ORNL heat pump design model. The calibrated model translated the experimental results to key calculated parameters, i.e. compressor efficiencies and refrigerant side two-phase heat transfer coefficients, corresponding to each refrigerant. These calculated values provide scientific insights on the performance of the alternative refrigerants and are useful for other applications beyond mini split air-conditioning units.