Support: Vacuum pumping: how long should it take?

Support: Categories of refrigerant

By Grant Laidlaw

What is the purpose of vacuum pumping in an air-conditioning system?

Jan asks: Grant, R1234yf — into what category does this fall? Thanks. 

Hi Jan. According to ASHRAE, R1234yf falls into category A2.

Let us look into this, as the topic of refrigerants is trending at the moment.

Designation and safety classification of refrigerants

This classification makes it possible to designate all refrigerants used in a clear and internationally recognised manner by classifying them according to their chemical composition.

Numbering of refrigerants

An identifying number shall be assigned to each refrigerant. It consists of a prefix, made up of letters, and a suffix, made up of digits.

Prefixes

The prefix is composed of the letter R (for refrigerant).

Examples: R22, R134a, R600a, R717.
Sometimes, the letter C is used in the prefix to denote carbon, preceded by B, C, or F (or a combination of these letters in the same order) to indicate the presence of bromine, chlorine, or fluorine. Compounds containing hydrogen must be preceded by the letter H.

Examples: HCFC22, HFC134a.
These prefixes must only be used in non-technical publications.

Note: The name of the brand or the manufacturer is also sometimes used — these names must not be used in official documents (identification labels and the like).

Suffixes

Hydrocarbons and derivatives:

  • The first digit on the right (units) is the number of fluorine (F) atoms.
  • The second digit on the right (tens) is one more than the number of hydrogen (H) atoms.
  • The third digit on the right (hundreds) is one less than the number of carbon (C) atoms (when the digit is zero, it is omitted from the number).
  • The third digit on the right (thousands) is equal to the number of unsaturated carbon-carbon bonds (when the digit is zero, it is omitted from the number).

For refrigerants that contain bromine (Br), the letter B is added after the identification number, followed by the number of atoms present. These refrigerants are no longer manufactured in developed countries since the application of the Montreal Protocol on substances that deplete the ozone layer.

The number of chlorine (Cl) atoms is found by subtracting the sum of fluorine, bromide, and hydrogen atoms from the total number of atoms that can be connected to the carbon atoms: 4 for methane derivatives (CH4), 6 for ethane derivatives (C2H6), and so on.

Example: R22 (chlorodifluoromethane – CHClF2)
R022
0: Number of carbon atoms – 1
2: Number of hydrogen atoms + 1
2: Number of fluorine atoms
Number of chlorine atoms: 1
(that is, 4 minus 1 hydrogen atom and minus 2 fluorine atoms)

For cyclic derivatives, the letter C is used before the refrigerant’s identification number. Example: RC318 (octafluorocyclobutane – C4F8)

In the case of isomers in the ethane series, each has the same number, with the most symmetrical one indicated by the number alone. As the isomers become more and more unsymmetrical, successive lower-case letters (that is,

 a, b or c) are appended.

Examples: R134 and R134a

Azeotropic and zeotropic mixtures

Mixtures are designated by their respective refrigerant numbers and mass proportions. Refrigerants shall be named in order of increasing normal boiling points of the components.

Mixtures with flammability and/or toxicity characteristics that may change as the composition changes during fractionation, shall be assigned a safety group classification based on the worst case of fractionation.

Zeotropic mixtures shall be assigned an identifying number in the 400 series. This number designates which components are in the mixture but not the amount of each. To differentiate among zeotropes having the same components with different amounts (percent by mass), an upper-case letter shall be added as a suffix.

The numbers are in chronological order of the refrigerants’ approval by ASHRAE.
Example: R407A [R32/R125/R134a (20/40/40)], R407B [R32/R125/R134a (10/70/20)], R407C [R32/R125/R134a (23/25/52)], R407D [R32/R125/R134a (15/15/70)], R407E [R32/R125/R134a (25/15/60)].

Zeotropic mixtures shall be assigned an identifying number in the 500 series.
Example: R507 [R125/R143a (50/50)].

Miscellaneous organic compounds

Miscellaneous organic compounds shall be assigned a number in the 600 series; numbers are given in numerical order.

Example: R600a, Isobutane

Inorganic compounds

Inorganic compounds shall be assigned a number in the 700 series, identification numbers are formed by adding the relative molecular mass of components to 700.

Example: R717 corresponds to ammonia, which has a molecular mass of 17.

Safety group classifications

This classification consists of two alphanumeric characters (for example A2); the capital letter corresponds to toxicity and the digit to flammability.

Toxicity classification

Refrigerants are divided into two groups according to toxicity:

  • Class A signifies refrigerants for which toxicity has not been identified at concentrations less than or equal to 400ppm;
  • Class B signifies refrigerants for which there is evidence of toxicity at concentrations below 400ppm.

Flammability classification

Refrigerants are divided into three groups according to flammability:

  • Class 1: Indicates refrigerants that do not show flame propagation when tested in air at 21°C and 101kPa.
  • Class 2: Indicates refrigerants having a lower flammability limit of more than 0.10kg/m3 at 21°C and 101kPa, and a heat of combustion of less than 19kJ/kg.
  • Class 3: indicates refrigerants that are highly flammable as defined by a lower flammability limit of less than or equal to 0.10kg/m3 at 21°C and 101kPa, or a heat of combustion greater than or equal to 19kJ/kg.

Classification of refrigerant groupsClassification of refrigerant groups.

Mixtures

Mixtures, whether zeotropic or azeotropic, with flammability and/or toxicity characteristics that may change as the composition changes during fractionation, shall be assigned a safety group classification based on the worst case of fractionation, for example R404A is classified as A1.

Jan, that should clear things up, thanks for the question.

Thank you for all your questions. Send your problems (and sometimes your creative solutions) to acra@netactive.co.za with “Solutions Page” in the subject line. You may include pictures.

  • This text is based on the American standard ANSI/ASHRAE 34.

Click here to read the September 2018 issue of RACA Journal



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