The following types of hydrocarbons are commonly used as refrigerants:
- R290 Propane
- R600a Isobutane
- R1270 Propylene
A number of other hydrocarbons, such as blends containing ethane, propane or butane, are also used as refrigerants.
Propane has been discussed since the late 1980s as a replacement for CFCs and especially R22 (HCFC). Except its high flammability R290 has very similar properties as R22. It has a long history in refrigeration and is thus an interesting candidate. However, its flammability has limited its use. While isobutane (R600a) was introduced in household appliances in some parts of the world from the start of CFC phase out, R290 was introduced later and replaced R134a, R22 or R404A in a wide spectre of appliances.
Hydrocarbons have excellent thermodynamic properties, and in this respect they are as good as or better than HCF or HCFC refrigerants in most applications.
Hydrocarbons are highly flammable and must be handled with care. If they are used responsibly, hydrocarbons can be employed in a variety of refrigeration and air conditioning applications. In order to ensure safety, hydrocarbon applications are governed by various international, regional and national standards and regulation. Hydrocarbons can only pose an explosion risk if the concentration is between the lower and upper flammability limits. Safety standards are developing rapidly in these years and is this is necessary to exploit the full potential of these refrigerants. Main standards are the IEC 60335-2-40, IEC 60335-2-89, ISO 5149 and EN378.
When following the safety standards the concentration of leaked refrigerant will not get above LFL where ignition sources can ignite it, even in extreme situations. The necessary safety precautions and system design depend on the refrigerant charge. In general ignition sources inside the application must be avoided. Most hydrocarbons are non-toxic, with the main safety risk coming from their flammability, although gaseous hydrocarbons are heavier than air and will displace air in lungs.
|Lower flammability limit(LFL)||1 .8%||approx. 38 g/m3||2 .1%||approx. 38 g/m3|
|Upper flammability limit (UFL)||8 .5%||approx. 203 g/m3||9 .5%||approx. 171 g/m3|
|Auto-ignition temperature||494 °C|
|Lower and upper flammability limits|
Only authorized persons certified for the installation and maintenance of refrigeration systems containing flammable refrigerants should engage in installation and maintenance.
Hydrocarbons belong to the group of natural refrigerants and have zero ODP and negligible GWP. As a rule, hydrocarbons are by-products from the petrochemical industry.
The refrigeration properties of hydrocarbons, such as pressures, pressure ratios and discharge temperatures, are quite similar to those of HCFCs or HFCs in many respects.
The most commonly used hydrocarbons (propane and isobutane) are compatible with standard oils and materials used with HFCs. One exception is propene (propylene), which is not compatible with neoprene. Consequently, special O-rings must be used with this refrigerant.
The relative cost of a system using hydrocarbons largely depends on the application. In domestic and light commercial applications, the cost of the system is similar to that of systems with HFCs. In commercial and industrial refrigeration applications, systems with HCs tend to be relatively expensive due to the need for explosion-proof enclosures for electrical equipment, though for chillers placed outdoors the added cost for safety is more modest.
Typical applications for hydrocarbons are:
- Domestic refrigerators and freezers
- Bottle coolers
- Ice cream freezers and commercial freezers
- Commercial refrigerators
- Beer coolers
- Beverage dispensers
- Heat pumps
- Supermarket refrigeration (in combination with secondary cooling or as a high temperature stage in a cascade CO2 system)
- Small air conditioners