… continued from Part 1 .

be a compromise of some sort between

GWP ’ working fluids ” or “ we only permit

competing and sometimes mutually

‘ ultra-low GWP ’ fluids ”.

exclusive factors . A logarithmic scale to

characterise GWP ( UNEP RTOC , 2022 ),

shown in Table 1 , was helpful , emphasising

In parallel with the rolling programme of fluorocarbon development , new ways of using the so-called ‘ natural ’ refrigerants

completed . At the same time , however , we

that the transition process was a continuum

were also being developed . One of the

have seen many false dawns and wrong

rather than a one-shot deal .

greatest successes in this respect was

turns so the path of progress has not been

the acceptance of hydrocarbons as a safe

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

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

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 very 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

Dr Andy Pearson . 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

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