Refrigerants are substances that can be used in the refrigeration cycle of air conditioning and refrigeration equipment because of their thermodynamic properties.
Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are synthetic substances used as refrigerants. These halogenated refrigerants have to be chemically synthesized as they either do not occur in nature at all or only in trace concentrations. CFCs and HCFCs are being phased out under the Montreal Protocol, an international agreement to protect the ozone layer. They have been controlled by the Montreal Protocol since 1987 because of their ozone depleting potential and high global warming potentials.
(refrigerant/foam blowing agent)
|Saturated chlorofluorocarbons||CFC||0.6-1||4750-14,400||R11, R12|
|Saturated hydrochlorofluorocarbons||HCFC||0.02-0.11||77-2310||R22, R141b|
|Saturated hydrofluorocarbons||HFC||-||124-14,800||R32, R134a|
|Unsaturated hydrofluorocarbons||u-HFC||-||<1-12||R1234yf, R1234ze, R1234yz|
|Natural refrigerants||-||0-3||R744 (carbon dioxide)
Consumption of HFCs however is growing dramatically world-wide due to their function as replacement substances for CFCs and HCFCs. Nevertheless HFCs are greenhouse gases. Their use should be avoided in order to slow global warming.
Unsaturated HFCs (u-HFCs, also marketed as hydrofluoroolefins, or “HFOs”) are synthetically made HFCs with no ODP and low GWP that have been developed specifically to fulfil regulations that prohibit HFCs with higher GWP (e.g., above 150). Some are slightly flammable and combustion can form hydrogen fluoride. In the atmosphere their decomposition leads to the formation of trifluoroacetic acid (TFA), which is a strong acid with toxicity to some organisms. There is no known degradation mechanism for TFA.
Natural refrigerants are climate friendly. They have a very low or zero global warming potential and zero ozone depletion potential; they are part of the natural biogeochemical cycles and do not form persistent wastes in the atmosphere, water or biosphere. Natural refrigerants are the naturally occurring substances CO2, ammonia, water, air and hydrocarbons such as propane, isobutene and propene/propylene. Their production is not energy intensive as even the hydrocarbons can be obtained without chemical transformation by separation. Natural refrigerants are widely used in some RAC applications, for example isobutane in domestic refrigerators and ammonia in large cooling processes. Natural refrigerants are relatively cheap because they are mass produced for a wide range of uses and are readily available if distribution structures are present. Natural refrigerants can often be sourced as by-products from other processes. Recycling or disposal after use in cooling systems is easier than with CFCs, HCFCs and HFCs.
All natural refrigerants have characteristics that require additional safety measures, compared to conventional CFCs, HCFCs and HFCs. Hydrocarbons (HCs) are flammable and ammonia is flammable, corrosive and of higher toxicity. Simple measures such as the use of appropriate materials, the selection of safe components and technician training can offset these undesirable characteristics. The following table gives a summary of refrigerant safety groups.
|Lower toxicity||Higher toxicity|
|No flame propagation||A1, e.g.: CFC-11, R404a, HFC-134a, R410a||B1, e.g.: HCFC-123|
|Lower flammability||A2, e.g.: u-HFC-1234yf, HFC-152||B2, e.g.: Methyl formate, R717 (ammonia)|
|Higher flammability||A3, e.g.: hydrocarbons, R430a, R510a||B3|
The growing use of HFCs in the RAC sectors can be clearly linked to the phase-out of CFCs and HCFCs in these industries, a fact that was specifically noted by the Rio+20 declaration in 2012 and other high level political declarations, such as by the Climate and Clean Air Coalition (CCAC).
In the past the phase-out of one group of refrigerants that damaged the environment has always led to the increased use of refrigerants that were only less damaging. This happened in the switch from CFCs to HCFCs (though note that HCFCs were regularly used before the phase-out of CFCs as well) and on to HFCs in developed countries and is currently visible in developing countries where HFCs are replacing HCFCs, and to some extent in developed countries where u-HFCs are being introduced. Switching directly from ozone depleting and climate harming fluorinated substances to natural refrigerants in energy-efficient systems and applications is often referred to as “leapfrogging”.
Within the Montreal Protocol, states have always been encouraged to choose alternatives that not only save the ozone layer but that also do not harm the climate. UN Secretary-General Ban Ki-moon urged parties and industries “to seize the opportunity provided by the HCFC phase-out to leapfrog HFCs wherever possible” in his 2011 Ozone Day message. A phase-down of HFCs is also being discussed as an amendment to the Montreal Protocol. With growing concern about future regulations prohibiting the use of HFCs, countries as well as industries have to look for opportunities to leapfrog. This will prevent them from having to phase new sets of fluorinated gases in and out again.