Choosing the correct refrigerant for a plant and for the planet is an issue that most refrigeration designers, and purchasers or procurers, of refrigeration systems address regularly. The major issues are of course (i) ozone depletion, (ii) global warming impact, cost and availability: see below.
(i) Ozone depletion - ozone is an extremely rare gas in the atmosphere, 300 parts per billion. It is nevertheless considered essential for life as it protects us from harmful ultraviolet B and Ultraviolet C radiation. In winter, over the poles, low temperature clouds at -78 °C, comprising tiny particles of water vapour and nitrogen and nitrogen oxides, act as a reservoir for hydrogen chloride, hydrochloric acid and chlorine nitrate. In the spring, when these clouds warm, ultraviolet light catalyses reactions on the surface of these ice crystals turning the inactive compounds into highly reactive chlorine monoxide. This compound rapidly depletes ozone and opens up the 'holes' in the ozone layer. These reservoirs of chlorine compounds are believed to come from the release of CFCs and HCFCs into the atmosphere. For this reason the Montreal Protocol and the ensuing national and international legislation has led to a phasing out of more traditional refrigerants. Their replacements are assessed for their ozone depleting potential.
(ii) Global warming impact - the global warming impact of a refrigerant system can be divided into two categories, direct and indirect. The total is generally calculated as the Total Equivalent Warming Impact.
Direct emissions - are made up of refrigerant leakage and refrigerant recovery losses. The Global Warming Potential (GWP) of a refrigerant is an indicator of its potency to warm the planet by action as a greenhouse gas. Preventive actions in the design of refrigeration systems are focused on:
Indirect emissions - due to the energy consumption of the system, are the major contribution of a refrigeration system to global warming. Carbon dioxide production in a power station burning fossil fuels can be as high as 0.8 kg/kW. A small improvement in efficiency is likely therefore to yield the largest reduction in the global warming impact of a refrigeration system.
Factors which affect the efficiency of a refrigeration system are:
You can find refrigerants thermal property data in databases listed on the Finding data page of this website.
Information on refrigerant selection can be obtained by downloading the extensive but low-price Refrigerant Selection Guide from the Australian Institute of Refrigeration, Air Conditioning and Heating.