Refrigerants used in vapor-compression air conditioners and heat pumps have been the subject of environmental regulations, requiring the need to develop alternative solutions with lower GWP. In general, there is a trade-off when choosing alternative refrigerants between safety, performance, and GWP.

The California Air Resources Board (CARB) has approved a new regulation requiring refrigerants used in all new stationary residential air conditioning systems to have a 100-year GWP value of 750 or less. For reference, the most common refrigerant currently used in unitary air conditioning equipment is R-410A, which has a 100-year GWP of 2,088.

A number of refrigerant solutions have been developed to meet the CARB GWP requirement, but the majority of these refrigerants have a low level of flammability (A2L). While there are strategies for mitigating the risk of using flammable refrigerants, finding a non-flammable solution presents the easiest path to market and would not require additional safety controls and updates to codes and standards.

In a new case study, the Western Cooling Efficiency Center (WCEC) at the University of California, Davis Energy and Efficiency Institute evaluated one refrigerant solution, R-466A, that meets the CARB GWP limit and is also non-flammable (A1).The 100-year GWP is 733 which is 65% lower than R-410A and is design compatible with R-410A equipment. A previous study by the UC Davis WCEC showed that the efficiency and capacity are similar to R-410A and would not impact the product design.

This project provided a direct comparison between a Trane package rooftop unit (RTU) operating with R-466A and with R-410A. R-466A is a blend of R-32, R-125 and R-13I1 (CF3I), and the use of R-13I1 refrigerant in the blend presents some material compatibility challenges with certain existing materials used in air conditioning equipment. These concerns include the reaction of R-13I1 with zinc, which causes the molecule to break down. The standard Trane RTU used in the project was determined to have acceptable materials of construction in the compressor and heat exchangers. As a result, Trane Technologies developed a materials compatibility additive package to improve the compatibility of R-13I1 with system materials.

The system used in the case study was a production packaged Trane Technologies (Foundation Series) R-410A RTU, where R-410A was reclaimed and replaced with R-466A. The additive package was added to the oil, and the unit was shipped from the factory to the field site. (Note: this was an engineered retrofit and it would not be appropriate for all R-410A unit designs.)

According to the results of the test, the capacity between R-410A and R-466A were within the margin of error of the measurements. R-466A appeared to deliver slightly higher capacity than R-410A as outdoor temperatures increased. Total power draw showed a similar profile as capacity, with an increase in power consumption with increasing outdoor air temperatures. The COP for R-466A and R-410A showed very similar performance between the two refrigerants across all outdoor air temperature conditions.

The report concluded that as a replacement for R-410A, R-466A was very successful in showing similar capacity and COP across a wide range of outdoor air conditions. From an installation and maintenance perspective, the system was no different from a typical R-410A rooftop package unit, with the exception of an additive package to the oil and simple exchange of refrigerant. Assuming the compatibility issues with certain metals can be mitigated through the use of alternative materials and appropriate additives, the report stated that R-466A represents a viable alternative to R-410A that achieves comparable performance with significantly lower GWP.