RACA Journal February 2025 RACA_February2025 | Page 7

Associations

THE JOURNEY TO A BETTER WORLD :

A REFRIGERATION PERSPECTIVE ( PART 2 )

By Andy Pearson , Star Refrigeration

RACA Journal is presenting the entire presentation in four sections . This is Part 2 of a four-part series .

… continued from Part 1 .

Throughout this process of refinement and redevelopment a great deal of good engineering has been completed . At the same time , however , we have seen many false dawns and wrong turns so the path of progress has not been straightforward . For example , many of the early blends developed to replace CFCs used components that had high global warming potential because they provided other favourable characteristics , and climate change had not yet become a major issue . R-404A is a three-component mixture ; a blend of mainly R-125 and R143a , both of which have a GWP of about 4 000 with a small amount of R-134a .

The blend was an acceptable alternative in the early 1990s to the ozone depleting substance R-22 , which had a lower GWP of 1 810 , but it fell out of favour once the need for low GWP fluids was recognised .

The debate over these two environmental topics , ozone depletion and global warming , created many attempts to define acceptability in terms of a single number metric , but the topic is too complex for that and every refrigerant choice turned out to be a compromise of some sort between competing and sometimes mutually exclusive factors . A logarithmic scale to characterise GWP ( UNEP RTOC , 2022 ), shown in Table 1 , was helpful , emphasising that the transition process was a continuum rather than a one-shot deal .

Table 1 : Characterisation of Global Warming Potential Range of GWP100 values Over 10 000 Over 3 000 Over 1 000

Classification Ultra-high Very high High 300 – 1 000 Moderate Below 300 Below 100 Below 30

Low Very low Ultra-low

One of the nice things about this classification method is that everything above 1 000 is considered to be high GWP , with some of the fluids being very high GWP and a further subset being ultra-high GWP . Likewise , everything below 300 is considered low GWP and so on . This enables legislators and system specifiers to say “ we do not permit the use of ‘ very high GWP ’ working fluids ” or “ we only permit ‘ ultralow GWP ’ fluids ”.

In parallel with the rolling programme of fluorocarbon development , new ways of using the so-called ‘ natural ’ refrigerants were also being developed . One of the greatest successes in this respect was

Dr Andy Pearson . the acceptance of hydrocarbons as a safe solution for domestic refrigerators . Early substitutes for R-12 used a mixture of propane ( R-290 ) and isobutane ( R-600a ) but component development enabled compressors with a larger displacement for a given motor size to be developed and soon all domestic refrigerator manufacturers in Europe were offering products with R-600a as the refrigerant . This solution has now been widely adopted all over the world , with an excellent safety record .

Carbon dioxide was introduced for the commercial market with mixed success . Many systems have been installed and run satisfactorily , but these plants are typically more expensive to install than the HCFC and HFC solutions that they replaced . It is difficult to keep them operating efficiently , although efficiency was never a high priority for the previous generation of systems either . Any design that uses suction superheat to control an expansion valve , even with clever ‘ minimum stable superheat ’ controls , is only paying lip service to full life efficiency and it is all too easy for an operator or service technician to increase the superheat setting to avoid unreliability problems .

Ammonia was reintroduced to the industrial market for food factories and warehouses in new system designs , created to reduce the risk of major leakages and it even found some success in the 1990s and 2000s in water chillers for building services including city centre office buildings , conference centres , exhibition halls , data centres and airports . The industrial sector also found uses for carbon dioxide , particularly in freezing equipment where the highly unusual physical properties of CO2 provide unique benefits in reduced freezing times and improved efficiency . Air cycle systems , which date back to 1844 in the history of refrigeration , have found some niche applications in low temperature freezing but they have not been widely commercialised .

All these successful developments were driven by environmental concerns but at the same time energy was becoming increasingly

© RACA Journal www . refrigerationandaircon . co . za RACA Journal I February 2025 5