Natural refrigerants are generally defined as naturally occurring substances being used as refrigerants in vapour compression systems. Naturally occurring substances are also widely used as working fluids in absorption refrigeration systems.
It is broadly accepted there are five natural refrigerants groups:
- Carbon Dioxide
Of these, the last three are becoming very popular globally, with the phasing out of the largely non-flammable synthetic refrigerants (CFC’s/HCFC’s/HFC’s) due to their environmental damage to the ozone layer and/or their high Global Warming Potential.
The multinational chemical companies have, in recent years, been introducing new families of synthetic refrigerants and blends, which includes HFO’s. Most of these new refrigerants and blends are flammable.
Background on the three most popular natural refrigerants:
Carbon Dioxide is classified under the ADG code as class 2.2, non-flammable, non-toxic gas. It’s predominant feature is an odourless asphyxiant and it can also interrupt the breathing reflex. CO2 started to be used as a refrigerant in the early part of the 20th century and was popular in the cold climates of the northern hemisphere as well as on board ships. CO2 has a narrow operating band due to its high triple point (-56.5C) and its low critical point (+30.98C), which restricts it’s application. By the mid 20th century, CO2 had been largely phased out as a refrigerant and was over taken by synthetic CFC’s. In the last couple of decades, CO2 has made an enormous comeback, and is now widely used in the commercial and industrial refrigeration sectors in the first stage of cascade refrigeration systems. It has also found traction in trans critical systems for refrigeration, heat pumps and automotive air conditioning.
Ammonia is classified under the ADG code as class 2.3, toxic gas. It’s predominant feature is it’s very pungent odour which repels mammals at concentrations far below that which can be toxic. Ammonia first became popular as a refrigerant in the 1860’s when it replaced hydrocarbons and by 1900 it was globally predominant. Ammonia maintained it popularity at the industrial end of refrigeration for the 20th century and in recent decades has grown in popularity as a replacement for the synthetic refrigerants being phased out.
Hydrocarbons are classified under the ADG code as class 2.1, flammable gases. The most popular hydrocarbons used as refrigerants are propane (R290) and Isobutane (R600a) and their predominant feature is flammability. They are also odourless. Hydrocarbon refrigerants have dramatically gained in popularity in Europe and Asia over the last 3 decades, particularly in domestic refrigerators, commercial unitary refrigeration equipment and fluid chillers/heat pumps for air conditioning.
Regulations and Codes
The Australian Refrigeration Standard, AS/NZS 1677 received an upgrade in 1998 which provided for the wider use of hydrocarbons and other flammable refrigerants. The dominant feature of this upgrade was to reduce the risk of flammable or toxic refrigerants leaking into indoor, occupied spaces creating concentrations which are dangerous.
AS/NZS 1677 is envisaged to be replaced by ISO5149 which is essentially based on EN378, the European standard. This standard deals extensively with the safe application of CO2, Ammonia and Hydrocarbons and all refrigeration equipment coming out of Europe or Asia will need to comply with these standards.
In Australia there are also State based codes of practice, regulatory and alert documents dealing with flammable and toxic refrigerants.
Gordon Brothers have always been at the forefront of compliance with standards and codes in the refrigeration industry and will continue to do so.