Page 43 - Low Temperature Energy Systems with Applications of Renewable Energy

Principles and operation of refrigeration and heat pump systems 31

Current generation (after 2010). Since 2010, ozone-depleting refrigerants R21,
R22, R123 and R1245b are not allowed. Until 2025 in Europe, the use of refrigerants
with GWP < 2500 is permitted; after 2030 it is planned to not use refrigerants with
GWP > 150. Refrigerants R134a, R125, R404a, R407c, R507a, R410a, and in the
future R32 will not be allowed. The time is coming for hydrofluoroolefins (HFOs),
e.g., R1336mzz, R123yf, R1234ze, and R1233zd e all having GWP < 10. Mixtures
of refrigerants based on HFO, namely, R448a, R449a, R450a, R513a, and others are
being manufactured.
In developed countries, chlorofluorobromohydrocarbons (CFBHC) are no longer
used in cooling and air conditioning systems. HFC mixtures, namely, R407c and
R410a are considered an acceptable replacement for the ozone-depleting refrigerant
R22. ASHRAE 34-2007 allows the use of ozone-safe refrigerants ranging from
R429a to R437a, and R510a. The following sources of information may be used for
the designation of refrigerants and their possible replacements as environmental re-
strictions reduce the available working fluids [21e25].
Projecting into the future, it seems clear that the use of synthetic refrigerants will
become more and more restricted. Table 1.4 shows the current situation based on
the Montreal Protocol and the EU F-Gas 2 Impact. Table 1.5 shows the bans and re-
strictions facing the refrigerants. All HCFCs are subject to phase-down in the future
owing to their medium-level ODP. From Table 1.4, it can be seen there are only seven
natural refrigerants and two HFOs that are completely free of restrictions at this time.
The very first synthetic refrigerants developed in the 1930s and deployed thereafter
were the best ever conceived from a strictly technical performance standpoint. They
were crafted to yield excellent efficiency with outstanding safety characteristics for
personnel who had to work with them. The story is told by Charles Kettering [27]
about how Thomas Midgley, the engineer who led the development team at Frigidaire,
introduced R12 to an audience by inhaling the vapor from a beaker, filling his lungs
with R12, and then gently releasing it over a burning candle. It extinguished the flame
and he was not harmed by the vapor, thereby demonstrating both non-toxicity and non-
flammability simultaneously. It was only decades later that the detrimental impact
CFCs on the environment came to light.
Each new refrigerant created in the laboratory has both benefits, mainly environ-
mental, and drawbacks, mainly technological. Certainly they are less effective from
an efficiency standpoint, requiring more energy input to operate the RMs for the
same cooling effect. Actual operation of RMs and HPs has identified the technical
problems related to synthetic working substances. Ozone-safe refrigerants of the
HFC and PFC classes are very expensive compared to, say, R22. Higher pressure
for the system processes requires an increase in the strength of the heat exchanger ma-
terials and metal consumption; the necessity to use expensive high-hygroscopic, poly-
ester, synthetic oils for lubrication; and in the case of refrigerant mixtures, the
requirement to completely replace the refrigerant in the RM when there is any leakage,
no matter how small, since the preferential leakage of the low-boiling component
significantly alters the thermal properties of the working fluid and hence the system
performance.