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Facing the low GWP challenge

08 June 2018

The choice of low Global Warming Potential (GWP) alternatives for large refrigeration systems needs to widen to help the food processing industry argues Graham McDermott

The need to make the switch to low GWP refrigerants to meet F-gas phasedown requirements has received a lot of media attention. It forms part of the latest revisions of the F-gas regulations which aim to reduce the use of fluorinated gases. With refrigeration playing such a key role in the food processing industry some producers and suppliers have already taken the message on board but others are still left left with some big decisions to make.

Unless you are a refrigeration expert, it is not easy to be sure you are making the right choice for your system. This year’s 37% cut in the quota for the production of virgin refrigerants is affecting supplies. Prices for the go-to refrigerant R404A have risen steeply as the amount of virgin refrigerant available on the market is reduced.

So far most of the research into alternatives with a low GWP has centred on gases more suited to smaller refrigeration systems, focusing on blended refrigerants which work well if you are maintaining or fitting systems in convenience stores, restaurants and installations of a similar scale.

However, if you are working with larger, low temperature systems found in food processing plants there are no easy answers. Flooded evaporators are more likely to be employed in larger systems where in the past single component gases like the now-banned R12 and R22 were used. They were relatively easy to install and maintain. R134A for high temperature applications, and R507 for medium and low temperature jobs, offered a way forward but their high GWP means that these HFC blends have a short shelf life.

In this respect the new blended low GWP refrigerants offer no real alternative for medium and low temperature applications because they can be difficult to manage. There is a risk of the refrigerant distilling and its components splitting into their original form.

Zeotropic refrigerants, with a mixture of different boiling points, may provide a solution in the long term but at present there are no low GWP HFC alternatives for low temperature applications in the industrial sector where flooded evaporators are in use.

Hydrocarbons like propane and propylene have in some circumstances provided cooling solutions, but they are more expensive to install – flameproof equipment is needed – and you have the added responsibilities of the ATEX regulations to consider.

The new class of low GWP HFO refrigerants like R1234ZE and R1234YF are still in the early stages of development and more work is required here if they are to be considered.

Ammonia offers a good choice for large systems operating on an industrial scale. It is a versatile, effective and efficient natural refrigerant which does not deplete the ozone layer and has excellent thermodynamic qualities, providing a wide temperature range.

It is a natural refrigerant with a good safety record and is already used in many applications in the meat, poultry and dairy industries. Ammonia – even in small quantities – has a recognisable odour which can be viewed as its greatest single safety asset. Further, improvements in technologies involving heat exchangers, compressor controls and low-pressure receivers have allowed the charge size to be reduced and this has lowered the risk of leaks. Because ammonia is one alternative that is already with us and it has a proven track record it is important to educate system designers, installers and end-users about the benefits of this green alternative. It could make everyone’s life a lot easier in the long run.

Graham McDermott is director of Process Systems and Marine at J & E Hall.

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