Evaluation of alternative refrigerants for mini-split air conditioners

The phaseout of hydrochlorofiuorocarbon (HCFC) refrigerants in developing countries is currently underway according to the Montreal Protocol. R-22 is one of the most commonly used HCFCs in the developing nations. It is extremely well suited for air conditioning and refrigeration in high ambient temperature environments. Non-Article 5 countries have already gone through the phaseout ofHCFCs and settled on using R-410A as the refrigerant of choice for air-conditioning applications. Previous studies have shown that R-410A results in significant capacity and performance degradation at higher ambient temperature conditions. There is a growing concern about finding alternative refrigerants to R-22 that would have zero ozone depletion potential (ODP), lower global warming potential (GWP), and, at the same time, maintain acceptable performance at higher ambient temperatures. Furthermore, the developed world's transition through higher-GWP refrigerants such as hydrofluorocarbons (HFCs) and HFC blends resulted in significant direct CO₂ equivalent emissions. It is imperative to develop a bridge for developing nations to avoid the transition from HCFC to HFC and then from HFC to alternative lower-GWP refrigerants. This paper summarizes data from an experimental campaign on alternative refrigerant evaluation for R-22 and R-4I0A substitutes for mini-split air conditioners designedfor high ambient temperature environments. The experimental evaluation was performed according to ANSI/ASHRAE Standard 37 (2009), and the performance was rated at test conditions specified by ANSI/ AHR1210-240 (2008) and ISO 5151 (2010). Additional tests were conducted at outdoor ambient temperatures of 52°Cand 55°C (125.6°F and 131°F) to evaluate the refrigerants' performance at high ambient conditions. Alternative refrigerants, some ofwhich are proprietary, included R-444B, DR-3, N-20b, ARM-20b, R-290, andDR-93 as alternatives to R-22. R-32, DR-55, L41-2, ARM-71A, andHPR-2A were evaluated as alternatives to R-410A. The units' performances were first verified using the baseline refrigerant, and then a drop-in refrigerant evaluation followed, including soft optimization to ensure refrigerant performance was adequately represented. The soft optimization included (1) charge optimization, (2) lubricant change, and (3) flow control. This paper presents the relative performances (efficiency and capacity) of the alternative refrigerants compared with the baseline refrigerants at the different operating conditions. This paper concludes with remarks about the suitability of alternative refrigerants for R-22 and R-410A applications in high ambient temperature regions.