Natural refrigerants

First stage compressor rack for transcritical CO2 plant, Exquisine, Thornbury, Victoria.

Alternatives to synthetic fluorocarbon refrigerants exist that can help to mitigate some of the environmental risks. Referred to as ‘natural’ refrigerants because the substances also occur in nature, these alternatives include ammonia, carbon dioxide and hydrocarbons.

These substances have been used as refrigerants for many years, however, they are now finding their way into applications where previously fluorocarbons were the preferred option.

Ammonia

Ammonia is a naturally-occuring substance that can be used as an alternative to fluorocarbon refrigerants in refrigeration systems. From an operational perspective, ammonia is generally accepted as the most efficient and cost effective industrial refrigerant available.

Beyond its economic advantages, ammonia is a natural refrigerant that is environmentally benign in the atmosphere. The advantages of ammonia in refrigeration are well known. Ammonia does not destroy atmospheric ozone and does not contribute to the greenhouse effect linked to global warming.

Ammonia has been in consistent use as a refrigerant since the 1800s. It can be a very efficient alternative to fluorocarbon refrigerants in a number of applications, and has been the refrigerant of choice in areas such as industrial refrigeration for many years. Because of ammonia’s proven applicability as a safe and efficient refrigerant for over 150 years, it is immediately available for wider usage and new applications.

Carbon Dioxide

Carbon dioxide (CO2) is a substance that has been used in the refrigeration industry since the 1860s. It declined between the 1890s and 1930s because of changes in technology and the introduction of fluorocarbon refrigerants, which were billed as ‘safety refrigerants’ at the time. Interest in the use of carbon dioxide resurfaced in the 1990s, with discussion of the phase out of ozone depleting refrigerants.

Carbon dioxide has an ozone depletion potential (OPD) of zero and a global warming potential (GWP) of 1. It is generally regarded as a cheap and easily available refrigerant, and many experts also regard it as having a ‘unique’ set of properties which make it an ideal refrigerant.

In addition to its basic environmental properties, carbon dioxide is non-toxic. It carries an A1 safety classification (the same as most fluorocarbon refrigerants), indicating that it has low toxicity and is non-flammable.

Hydrocarbons

Hydrocarbons were commonly used as refrigerants before the invention of fluorocarbon refrigerants in the 1930s. Interest in hydrocarbon refrigerants has been revived in recent years due to the phase out of ozone depleting refrigerants, although they have long been used widely in the oil, gas and petrochemical industries, particularly in very large refrigeration systems.

Hydrocarbon refrigerants have a number of favourable properties, and in the event of a leak they pose a much lower direct threat to the environment than fluorocarbon refrigerants.

The term ‘hydrocarbon’ encompasses a range of substances. The hydrocarbons most commonly used as refrigerants are ethane (known as R170), propane (R290), butane (R600), isobutane (R600a) and propylene (R1270).

While each of these substances has a different chemical composition, they all share the same basic environmental properties – an ozone depletion potential (ODP) of zero and a global warming potential (GWP) of 3.