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Technical
THE POTENTIAL OF PROPANE AS A REFRIGERANT
Contributed by BITZER
With F-gas restrictions on fluorinated refrigerants tightening , the focus is falling on alternatives that could play a mainstream role in the future . Propane is a proven refrigerant with low GWP and excellent efficiency . Kevin Glass , Managing Director of BITZER UK , highlights its potential .
Propane is back in the spotlight as a major potential alternative refrigerant for the future . Harnessing it safely depends on correct application and handling and mitigating the known risks through effective system design and operation .
Designated R290 propane is a colourless , odourless gas that belongs to the hydrocarbon family . It is a highly efficient refrigerant and has gained popularity in recent years due to its excellent thermodynamic properties and low environmental impact .
Its low global warming potential ( GWP ) of three and zero ozone depletion potential ( ODP ) make it a viable alternative to conventional refrigerants with high GWP values . It can be used in several refrigeration and air-conditioning applications , including commercial , residential and industrial settings .
It is commonly used in small-scale systems , such as refrigerators , freezers and packaged air-conditioning units . However , it can also be used in larger commercial and industrial refrigeration applications , such as food storage and processing , the chemical industry and cold storage .
FLAMMABLE REFRIGERANTS Under ISO 817 , refrigerants are classified into categories A and B : category A includes non-toxic substances , and category B includes toxic refrigerants . Flammability is classified under four groups , where 1 is non-flammable , 2L is flammable with slow flame spread , 2 is flammable and 3 is highly flammable .
Within the A3 classification , the most important substances used as refrigerants are hydrocarbons such as propane , propene ( R1270 ), isobutane ( R600a ), butane ( R600 ) and ethane ( R170 ). All have a long history in refrigeration and air conditioning and provided a model for the development of many of the new synthetic refrigerants .
By definition , group A3 refrigerants are highly flammable . They can be ignited at concentrations as low as 2 % and as high as 10 % in air . Within this range , ignition can be achieved by the spark of a light switch , a steel tool falling on a concrete floor or statically charged work clothes , resulting in deflagration or explosion . Combustion products are mainly carbon dioxide and water , and in themselves harmless .
Effectively mitigating and managing the flammability risk is the key to the safe application of propane , and other hydrocarbon refrigerants .
APPLICATION Use of flammable refrigerants has a long history in household appliances and commercial refrigeration . Towards the end of the 19th century , the use of non-toxic , highly flammable hydrocarbons became widespread due to their good thermodynamic properties , along with ammonia , sulphur dioxide and carbon dioxide .
Propane is well suited to use in commercial refrigeration , air conditioning and heat pump applications . Boiling at -42 ° C , it can cover evaporating temperatures of -40 ° C and higher . When propane is compressed , it is possible to achieve usefully large temperature ranges .
R290 has a high cooling capacity , which means it can remove a large amount of heat in a short amount of time . It also has a high coefficient of performance ( COP ), reducing the amount of energy used to create a given cooling effect and cutting running costs . With rising energy prices , this is obviously highly attractive .
Pressure levels and refrigerating capacity with propane are similar to R22 , and its temperature behaviour is as favourable as R134a , combining these excellent properties of the two refrigerants without their environmental downsides .
There are no particular problems with materials compatibility . In contrast to ammonia , copper materials can be used , allowing propane to be used in semi-hermetic and hermetic compressors . Common mineral oils can be used as a lubricant over a wide application range , while polyol ester ( POE ) and polyalpha olefin ( PAO ) lubricants offer even more favourable properties .
SAFETY Propane-based refrigeration systems must be designed and installed with safety features that minimise the risk of fire and explosion . Such features may include ( but are not limited to ) pressure relief valves , flame arrestors and leak detection systems .
System design must comply with all relevant regulations and standards relating to maximum permitted charge size for the specific application , and mandatory risk mitigation measures .
Detailed guidance on using propane and other flammable refrigerants is provided by REFCOM in its Guidance Note : https :// www . refcom . org . uk / media / 1157 / bra-guide-to-flammable-refrigerants-issue-1-oct-12 . pdf
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RACA Journal I February 2024 www . refrigerationandaircon . co . za