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Associations
slightly higher compressor swept volume requirements for a given duty .
At the other end of the scale , in industrial systems , the development of low charge ammonia plant has greatly improved safety and reliability without any detriment to efficiency . Carbon dioxide , the subject of the Dreosti memorial lecture 20 years ago , has been used to great advantage for industrial freezer systems and has been applied in some other sectors including industrial air conditioning and large-scale heat pumps . The conclusions of the Dreosti lecture in 2004 were that the development process for CO2 in the industrial market was nearly complete , that CO2 was here to stay in the markets that it had reached at that time and that it would be used in other markets too , with product development filling in any gaps in the application range .
For the most part these predictions were correct . There have been attempts to apply carbon dioxide to other industrial applications beyond freezers and heat pumps but with limited success so far . If ammonia is acceptable , as it ought to be in a well-engineered , safe system , then it will likely be cheaper and more efficient than an equivalent CO2 system for industrial installation . It will always be possible to do a CO2 system at low cost but these solutions are not really feasible in the industrial market as they are expensive to maintain and difficult to keep efficient . They are also likely to have a much shorter life than is expected of an industrial system .
Between the extremes of the domestic and industrial markets the progress in development of environmental solutions to address the climate emergency has been patchier . Good progress has been made in the commercial refrigeration market for supermarkets and smaller convenience stores . Several types of carbon dioxide system have been proved in operation , including CO2 as a volatile secondary refrigerant and transcritical CO2 ( both mentioned in the Dreosti 2004 lecture ) and other retailers have opted for propane as the refrigerant in integral display cases , typically with a low-charge water cooled condenser for heat rejection to a chilled water circuit . Smaller self-contained systems have also used hydrocarbons , for example in bottle coolers , vending machines and ice-cream cabinets .
The preferred refrigerants for large water chillers are R-134a , R-1234yf , R-1234ze ( E ) and R-1233zd ( E ). These are all suitable for use in centrifugal compressors and still dominate the global market in building services applications . A few projects have been executed with ammonia as refrigerant but these have tended to be special cases . Even fewer have used CO2 or hydrocarbon , generally only as proof-of-concept installations .
Several designs of chiller have been developed using water as the refrigerant but none of these have yet challenged the dominance of the HFC and HFO chillers in the mainstream market . Chillers using water as the refrigerant can achieve exceptionally high efficiency but they are typically very large and expensive due to the high volume flow rate required .
Mobile air-conditioning has seen its fair share of wrong turns and dead ends over the years . The initial step in replacing R-12 was to move to R-134a but after the Kyoto Protocol was published this was restricted due to concerns about high leakage rates . The European MAC directive (‘ relating to emissions from air-conditioning systems in motor vehicles ’) was published in 2006 and other jurisdictions followed suit . Initially R-152a was proposed but the motor industry rejected it on grounds of flammability so R-1234yf was developed as the preferred option , even though it is also , to an extent , flammable . For a time it seemed that CO2 would be a viable alternative when R-152a was rejected and propane was also proposed as a low GWP alternative , based on many years ’ experience of retrofits to old R-12 systems in the southern US .
The majority of car manufacturers opted for R-1234yf and , although implementation was slightly delayed beyond the initial date of 2013 in the MAC directive , this accounts for the majority of car air-conditioning systems in the global market at present . These wrong turns are unfortunate because for many years there has been a very substantial and extremely safe market in retrofit fluids for car air-conditioners in hot climates .
It was estimated back in the early 2000s , before the moves to identify the replacement for R-134a really got going , that over 250 000 motor vehicles in the southern states of the US had been switched by amateurs from R-12 to some variant of R-290 , often sold under a brand name such as R-12a which hid the fact that it was a flammable hydrocarbon . This was usually done to improve the performance of the system in pulling down to temperature from a hot start and despite the lack of training and lack of awareness there were no press reports of accidents , injuries or deaths caused by this switch . This doesn ’ t mean that the process was trouble-free , only that alongside the high number of road traffic fatalities the change was not noticeable and was therefore acceptable to the general public . RACA Continued in Part 3 …
“ There have been attempts to apply carbon dioxide to other industrial applications beyond freezers and heat pumps ”
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RACA Journal I February 2025 www . refrigerationandaircon . co . za