ALTERNATIVE REFRIGERANTS
Unfortunately, the known natural alternatives to HFCs which have zero or close to zero GWP are fl ammable (hydrocarbons), toxic (sulphur dioxide) or both (ammonia), or operate at high pressures (CO2
).
Nevertheless, despite these varying handycaps as far as their inherent properties are concerned, much innovative and impressive engineering work has been and continues to be done on the use of CO2
in particular at lower
temperatures in supermarket and other applications where it is a viable alternative to the current crop of refrigerants generally in use today.
Various non-Rankine technologies have been investigated. For many years the thermally powered absorption cycle, based on ammonia/water or water/ lithium bromide, has found limited applications where its specifi c advantages outweigh its poor energy effi ciency.
Stirling Cycle, thermoacoustic, magnetic refrigeration and others have not been commercialised for a variety of reasons, not least of which are cost amd energy effi ciency. At this point, there does not appear to be a viable low cost eff ective technology emanating from this range of technologies to replace the existing range of refrigerants. Some more sophisticated
fl uorinated molecules (HFOs) are being deployed as refrigerant alternatives, and have a GWP considerably lower than the current range of HFCs, but are also very much more expensive compared to HFCs.
In essence, the low toxicity HFOs are potential replacements for R134a, but they are classifi ed as fl ammable by the ASHRAE in category 2, although this has not stopped signifi cant parts of the automobile industry using HFO 1234yf in air conditioning systems – notwithstanding Daimler Benz’s opposition on fl ammability grounds).
However, HFOs are not suitable
for use in below medium (-30°C) to low temperature (-40°C) applications without blending with one or more of the six HFCs available, namely R125, R32, R134a, R227ea, R143a and R152a. There is an intellectual consistency in phasing down HFCs while retaining their use in combination with other albeit low GWP compounds.
HFO/HFC blends to replace the widely used R404A must have GWPs above 1,000 to be non-fl ammable with an ASHRAE classifi cation of 1, while blends with GWP below 1,000 are fl ammable with a safety classifi cation of 2. There is no potential non-fl ammable HFO/ HFC blend for R410A and any non- fl ammable mixture has questions around suitable properties, in particular suffi cient capacity to compare with R410A.
So what does the future hold? There are a limited number of molecules available to replace the current range of refrigerants so the options are limited.
A brief forecast of likely solutions in the main market sectors: ■ Supermarkets: CO2
and HFO 1234yf on the high side
■ L arge industrial plants: 250 kgs upwards and suited to ammonia. CO2
a possibility in certain cases such as heat recovery.
■ Small industrial plants: up to 50 kgs where CO2
is less cost
eff ective because of scale. Ammonia not appropriate. HFOs are a possibility but have to be combined with an HFC(s).
■ Commercial chillers: suited to HFOs 1234yf/ze ■ Split air conditioners: Ammonia, CO2
and HCs not suitable for
fl ammability, toxicity and effi ciency reasons. HFOs also not appropriate as a R410A replacement since these are R134a alternatives. R32 being marketed as an interim replacement – GWP 675 being too high for long term. Likely long term solution is with hydrocarbons in re-designed systems.
© 2016 The Chemours Company FC,LLC. Opteon™ and any associated logos are trademarks or copyrights of The Chemours Company FC,LLC. Chemours™ and the Chemours Logo are trademarks of The Chemours Company.
www.acr-news.com December 2016 35 XP40 Refrigerant (R-449A)
Problem solved with low GWP Opteon™ XP40
• Excellent effi ciency and performance • Quick and easy replacement for R-404A • ASHRAE A1, non-fl ammable • One third the GWP of R-404A
• Widely available and supported by component manufacturers
“Opteon™ XP40 – the best solution for my customers”
Chemours
David Wilkinson General Manager GEA Refrigeration UK Ltd
www.opteon.com
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