REFRIGERANTS


Cooling, comebacks, and the road ahead


Refrigerants have shaped the modern world far more than most people realise, quietly enabling everything from global cold chains to comfortable indoor climates. In this piece, John Poole, Managing Director of Refrigerant Solutions, traces their evolution from early, often hazardous compounds, to today’s lowGWP alternatives, and explores where development, regulation, and sustainability pressures are steering the next generation of cooling chemistry.


'Air is used in non-Rankine technology, such as air conditioning systems in aircraft, where compressed air from the jet engines can be


exploited. However, generally, ‘air cycle’ systems are signifi cantly less energy effi cient than Rankine Cycle systems.'


M


ost cooling equipment currently operates on the following principles. ■ The compression of low vapour pressure using a mechanical compressor.


■ Cooling the hot, high-pressure vapour to condense it to a liquid.


■ Expansion of the liquid through a constriction into the evaporator.


■ Evaporation of the liquid with the intake of heat to produce cooling at the low pressure resulting from the compressor suction.


This sequence is known as the Rankine Cycle and has been used from the earliest days of refrigeration in the mid-19th century. Although many other cycles have been investigated, e.g., the Stirling Cycle, and a few have found niche applications, none has ever threatened the commercial prominence of the Rankine Cycle. Its advantages include good energy effi ciency and being readily adaptable to many applications by selecting refrigerants with appropriate boiling points.


The long march from ammonia to HFCs From 1840 to 1930, the fl uids employed were ammonia, hydrocarbons, ethers, sulphur dioxide and methyl chloride, all of which were either toxic, fl ammable or both. Where safety was important, for example in marine refrigeration, carbon dioxide was preferred despite its very high operating pressures and thus expensive engineering. With refrigerant hazards restricting the growth of refrigeration and air conditioning in the 1930s, the low-toxicity, non-fl ammable CFCs/HCFCs were introduced, but these still used the well- proven Rankine technology. Perhaps not surprisingly, when the ozone depletion


problem forced the phase-out of CFCs, the cooling equipment manufacturers wanted alternatives that could replace them in Rankine technology with minimum redesign. Indeed,


20 February 2026 • www.acr-news.com


this was the principal reason for HFC-134a being selected as the replacement for CFC-12. However, the change presented considerable technical challenges, like the earlier move to CFCs at the time, it was viewed as an incremental development, allowing the use of much existing expertise without compromising safety. Now, authorities are under pressure from environmental activists to phase down and ultimately phase out R134a and other HFCs because of their high global warming potential relative to carbon dioxide (~1300 times higher). Will this be yet another incremental development of Rankine Cycle Technology? To answer this question, it must be accepted that all possible volatile chemicals that might seriously be considered as refrigerants are known and that non-fl ammability requires either an organic molecule that contains a signifi cant number of fl uorine atoms or a simple inorganic molecule such as carbon dioxide.


By far the major contribution of cooling equipment to global warming arises from the emission of carbon dioxide from the burning of fossil fuels to supply power, not from the release of HFC refrigerants. But the decision to phase them out is political, not scientifi c, so there is no point in promoting other fl uorinated refrigerants, such as the fl uorinated ethers, with somewhat lower GWPs. By abandoning fl uorinated compounds, we lose the main class of non-fl ammable, low- toxicity refrigerants.


Back to the future Green activists promote the so-called ‘natural refrigerants’, ammonia, hydrocarbons (e.g. propane and isobutane), carbon dioxide, water and air. This is a ‘back to the future’ approach. Ammonia has been an established refrigerant since the 1870s and has continued to be used for industrial purposes such as food processing, but its toxicity and fl ammability prevent its use in air conditioning.


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