02 May 2016

Why HFOs have a role to play

A-Gas Managing Director John Ormerod with an overview of how mildly inflammable refrigerants are taking centre stage

In our industry an ideal refrigerant would be non-toxic, non-flammable, energy efficient, have low installation and maintenance costs and have the right environmental credentials. But gone are the days when one class of refrigerant ticks all of these boxes.

HFCs meet four out of five of these demands but, as I am sure you are aware, they are under scrutiny for their impact on the environment. With few alternatives, we will have to start making compromises when it comes to selecting a refrigerant of choice. 

Hydrocarbons such as propane (R290) and propylene (R1270) provide energy efficiency at a relatively low-cost. However, their high flammability makes the overall installation expensive and raises safety concerns. Another natural refrigerant, CO2 (R744), is a fantastic gas due to its environmental credentials. But again, the equipment needed is costly when compared to traditional equipment running on HFCs. The energy efficiency of CO2 is also debatable as it depends largely on where in the world it is being used and in warmer climates it is not such an attractive proposition.

Ammonia is an excellent energy efficient, natural refrigerant that ticks the cost effective box but on the downside it is highly toxic. Ammonia installations require external plant rooms and secondary systems are needed to make the refrigerant a practical alternative. That said, secondary Heat Transfer fluids, such as MEG and MPG, are readily available making this a viable option.

HFOs are definitely starting to make their mark.  They have a short atmospheric life and don’t contribute to global warming like HFCs. However, HFOs do take us into a grey area because they are mildly flammable.

With regard to working practices we will have to wait and see what comes out of the redrafting of the European Standard EN378 which I think will provide the certainty the industry is looking for on how to deal with mild flammability issues. Once that is completed engineers should fully understand the areas that HFOs can be used in.

The two main HFO refrigerants around at the moment are R1234yf and R1234ze. R1234yf will be used in air conditioning systems for all new cars from the beginning of 2017 and there are already a million vehicles on the roads of Europe with R1234yf running in their ac systems. In most cases the motor industry has done a pretty good job of understanding mildly flammable refrigerants and also how to mitigate any risk where appropriate. The acr industry as a whole can learn from this.

R1234ze won’t be suitable as a drop-in for systems because of the volumetric capacity but for new systems it is a good energy efficient option.

Issues relating to the boiling point can be a bugbear elsewhere. These gases simply don’t boil low enough to be used for freezing. This means they have to be mixed with something else. So if you are looking to replace R404A for freezing applications neither of these HFOs are going to do the job on their own and will need to be mixed with some other molecule which will lower the boiling point.

As a result HFOs blends are emerging which do offer a practical alternative to high GWP refrigerants. The Solstice L40X (R455A) refrigerant from Honeywell is an ultra low GWP R404A replacement scheduled to be commercially available later in the year. This hybrid mixture contains R32 and CO2 and is classified as a mildly flammable gas. R455A matches the capacity of R404a and has the same or better efficiency. Solstice L40X is a refrigerant to keep an eye on.

Some supermarkets are already testing HFOs to gain an understanding of the mixtures involved and how they perform. A number of chiller manufacturers have incorporated R1234ze as a standard refrigerant in some of their equipment and there have been good reviews on this application. This could be an another area where HFOs will make their mark in the industry.

It is fair to say that we still have a lot to learn about HFOs. But to put this in perspective you must remember that other natural alternatives can be difficult to use – negatives like high flammability, toxicity or poor energy efficiency often outweigh the positives – and so this leaves the way clear for HFOs to play a role in the future.