Alternative mixtures for R134a

A NIST study identifies 23 non-flammable or slightly flammable mixtures as R134a alternatives in air conditioning.

In an article published in August in the International Journal of Refrigeration (IJR)1, the National Institute of Standards and Technologies (NIST) identifies 22 refrigerants that could theoretically work as low-GWP alternatives to R134a, in air conditioning applications.

Most of the identified mixtures combine R134a with one or two other pure refrigerants.

In 2017, NIST published a first study indicating that no low-GWP alternative single-component refrigerant was simultaneously non-flammable and well-performing in an air-conditioning system.

With this new research, NIST suggests that blends could offer better solutions, particularly when it comes to flammability.

Indeed, the study was conducted at the request of the US military, which wants to turn resolutely to non-flammable refrigerants. Domestic applications are moving towards mixtures that are at least slightly flammable, according to Ian Bell, engineer at the NIST.

The researchers who participated in the August 2019 IJR study selected 13 fluids capable of producing a mixture with the desired characteristics in terms of flammability, GWP, COP and volumetric capacity. Among these fluids were 8 HFOs, 4 low-GWP HFCs and CO2. The screening was based on a simplified cycle model, but with the inclusion of pressure drops in the evaporator and condenser.

But no mixture of these 13 fluids met all the selected criteria.

The researchers identified 16 non-flammable mixtures with a GWP that was more than 50% lower than that of R134a. 7 “marginally” flammable mixtures have been identified, with a reduction of GWP of up to 99%.

The performance of these mixtures was evaluated. The most promising non-flammable mixtures are slightly less effective than R134a and have a minimum GWP of 640. Indeed, their R134a proportion is quite important.

The study notes that slightly flammable mixtures are more efficient.

1 I. BELL, P. A. DOMANSKI; M. O. MCLINDEN, G. T. LINTERIS, The hunt for nonflammable refrigerant blends to replace R134a [in] International Journal of Refrigeration, Volume 104, August 2019, pp. 484-495. Available in FRIDOC.