ASHRAE-Standard-34-2013USA: ASHRAE is proposing to list a new low GWP R404A refrigerant replacement blend comprising an HFC, an HFO and CO2.

The refrigerant, R455A, is currently being considered as a possible addition to ANSI/ASHRAE Standard 34-2013, Designation and Safety Classification of Refrigerants, as an A2L “mildly flammable” gas.

Developed by Honeywell, the new refrigerant, with its GWP of just 145, has been developed as a replacement for R404A in condensing units. It consists of 75.5% of the HFO R1234yf with 21.5% of R32 and 3% CO2.

While further details are scarce at this time, the Cooling Post is aware of claims that R455A matches the capacity of R404A, while offering better efficiency.

DuPont’s best known low GWP R404A replacement blend is DR7, which like R455A , contains R32 and yf but without the CO2. It also has a higher GWP at around 250.

Honeywell has also been working with L40 – a blend of R32, R152a, R1234yf and R1234ze(E), with a GWP of 285.

Refrigerant manufacturers are known to have previously carried out tests with CO2 and HFOs in blends but only one other CO2 refrigerant blend is currently ASHRAE-listed. That refrigerant is R445A, better known as Mexichem’s AC6. This gas, still being touted as a possible alternative to yf in car air conditioning systems, adds 6% of CO2 and 9% R134a to the HFO R1234ze(E).

A search of Honeywell’s patents suggest past work with both HFO1234yf and ze in combinations with CO2 as potential replacement for a number of current refrigerants. Mexichem is also known to have researched other three-component blends involving CO2.

While CO2 has suppressant qualities, the small amounts of CO2 employed in these new gases suggests it is being used to boost system capacity rather than as a flammability suppressant.

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