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Hydrocarbon refrigerants. Technology

Physical and chemical properties

Due to their thermal properties, some lower saturated and unsaturated hydrocarbons, and their blends can be used as refrigerants. Below are shown properties of the most commonly used hydrocarbon refrigerants.

  R290 (propane) R600a (isobutane) R1270 (propylene) R436A (56% R290 / 44% R600a) R436B (52% R290 / 48% R600a)
Chemical formula С3Н8 СН(СН3)3 С3Н6 - -
Relative molecular mass / average molecular mass of blend 44 58,1 42,1 49,33 49,87
Gas constant, J/kg·K 188,6 143,2 197,7 - -
Boiling point at 101.3 kPa -42,1°C -10,2°C -48°C -34,26°C -34,3°C
Melting point -188°C -145°C -185°C - -
Critical temperature 96,8°C 133,7°C 91,5°C 115,8°C 117,4°C
Critical pressure (abs.) 42,6 bar 37 bar 46 bar 42,7 bar 42,5 bar

Impact on human beings and environment

Hydrocarbon refrigerants are A3 safety group: low-toxic, flammable. R-numbers of some of these substances are shown above.

The major safety concern for hydrocarbons is their flammability. Hydrocarbons can explode when a source of ignition (open flame, electric spark, static discharge) is present and a certain concentration in the air (2.1–10.1% for propane, 1.8–8.4% for isobutane, 2–11.1% for propylene) is reached.

Hydrocarbons are hazardous if aspirated. Most hydrocarbon used as refrigerants are heavier than air, colorless and odorless, so proper ventilation must be ensured at the workplace especially below the ground level.

Hydrocarbon refrigerants do not deplete the ozone layer (ODP 0). Traditionally, their GWP was taken as equal to the number of carbons in a molecule: 3 for propane and propylene, and 4 for isobutane. As this value is obviously overestimated, GWP for hydrocarbon refrigerants was taken as <3. According to the 2018 report of the Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee, GWP of propane, isobutane and propylene is below 1. The Ozone Secretariat recommends using GWP-ODP Calculator that gives the same conservative estimate of CO2-equivalent of hydrocarbon refrigerants, GWP 1.

According to the TEAP Working Group 1 contribution to the IPCC’s Sixth Assessment Report, Climate change 2021: the Physical Science Basis, presented in August 2021, 100-year time-horizon GWP of propane is taken as equal to 0.02.

Production of hydrocarbon refrigerants

For industrial use, saturated hydrocarbons—alkanes including propane and isobutane—are separated from natural gas, oil associated gas, gaseous hydrogenation products of lignite and coal tar by fractionating, cracking, and other methods. Alkanes can also be synthesized from hydrogen and carbon monoxide.

In addition to straight-run isobutane, in industry isobutane can be generated by isomerization of normal butane (n-butane).

The common industrial processes generate 95–98 percent pure alkanes, so additional purification is needed to use those as refrigerants.

Propylene was earlier generated as a by-product of steam or catalytic cracking of hydrocarbons, but since the 1990s propylene from dehydrated propane has gained acceptance.

Use of hydrocarbon refrigerants

Propane (R-290)

With thermodynamic properties similar to those of HCFC R-22 and ten times smaller density, propane (R-290) can be used as a drop-in refrigerant in systems designed for R-22 but in a smaller amount.

Indian and Chinese manufacturers commercialize R-290 domestic split systems and automobile air conditioners.

Propane is also used in commercial refrigeration. As the charge of a flammable refrigerant is limited due to safety concerns, this refrigerant is used mostly in small ice-makers, self-contained cooling boxes and chest freezers, primary circles of central refrigeration systems.

Lately, small charge systems—consisting of several self-contained refrigerators with secondary refrigerant circles that remove heat from condensers—have gained acceptance. You can read more in a separate section.

Isobutane (R-600a)

Isobutane is mostly used in new refrigerators, small commercial freezers and vending machines.

In the early 1990s in Germany, GreenFreeze, an approach to use isobutane in domestic refrigerants, was developed. By 2021, 75–80% of all domestic refrigerants use isobutane, according to Greenpeace.

Propylene (R-1270)

Although propylene (R-1270) properties are similar to those of propane (R-290), higher specific refrigerating capacity and lower boiling point make it a refrigerant of choice in medium- and low-temperature systems, like chillers used in supermarkets.

Restricted use of hydrocarbon refrigerants

A number of interstate standards include safety requirements to the use of refrigerants, including hydrocarbon ones.

The use of hydrocarbon refrigerants is influenced much by, particularly, a maximum allowable charge. According to safety standards, the concentration of refrigerant in the air must not exceed the lower flammability limit even if the whole charge is leaked.

The intergovernmental standard GOST EN 378-1-2014 “Refrigeration systems and heat pumps. Safety and environmental requirements. Part 1. Definitions, classification and selection criteria” stipulates: “A factory sealed refrigerating system with less than 0.15 kg of A2 or A3 refrigerant can be located in an occupied space which is not a special machinery room without restriction.”

GOST IEC 60325-2-24-2016 “Household and similar electrical appliances. Safety. Part 2-24. Particular requirements for refrigerating appliances, ice-cream appliances and ice-makers” and GOST IEC 60335-2-89 “Safety of household and similar electrical appliances. Part 2-89. Particular requirements for commercial refrigerating appliances with an incorporated or remote refrigerant unit or compressor” de facto limit the charge of a flammable refrigerant in domestic and commercial refrigerators.
In 2019, the International Electrotechnical Commission (IEC) reviewed IEC 60335-2-89 to increase the charge limit of self-contained commercial refrigerators from 150 to 500 g of A3 refrigerants and to 1.2 kg of A2 and A2L refrigerants but the relevant GOST is not approved yet, so these requirements are not obligatory.

GOST IEC 60335-2-40-20220 “Household and similar electrical appliances. Safety. Part 2-40. Particular requirements for electrical heat pumps, air-conditioners and dehumidifiers” does not restrict the application of direct expansion systems containing up to four lower flammability limits. For common hydrocarbon refrigerants, four lower flammability limits are equal to 0.15–0.16 kg.

The code of practice СП 60.13330.2020 “Heating, ventilation, and air-conditioning” prohibits the use of A3 refrigerants in air-conditioners at public buildings up to 50 m, residential buildings up to 75 m, single-function and multifunctional buildings.

Additional materials

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