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Standard symbol representation for refrigerants: This standard specifies a simple numerical coding system for various common refrigerants, as an alternative to using their chemical names, molecular formulas, or trade names. The use of the refrigerant numbering method specified in this standard does not preclude the use of chemical names and molecular formulas. This standard adopts the international standard ISO 817-197 \"Mechanical refrigerants — Numerical symbols\". 1 Classification of refrigerants Refrigerants are classified into halohydrocarbons, cyclic organic compounds, azeotropes and non-azeotrope mixtures, various other organic and inorganic compounds, as well as unsaturated organic compounds. 2. Identification numbers for refrigerants: The identification numbers specified for each type of refrigerant are shown in the table below. The rules are as follows: 2.1 For halogenated hydrocarbons and hydrocarbons belonging to the methane, ethane, propane, and cyclobutane families, the identification numbers assigned must allow the structure of the compound to be deduced from the refrigerant’s number, without leading to any ambiguous interpretations. 2.1.1 The first digit from right to left is the number of fluorine (F) atoms in the compound. 2.1.2 The second digit from the right is the number equal to the number of hydrogen (H) atoms in the compound plus 1. 2.1.3 The third digit from right to left is the number equal to the number of carbon (C) atoms in the compound minus 1. When this number is zero, it is omitted. 2.1.4 The number of chlorine (CL) atoms in a compound is obtained by subtracting the sum of the numbers of fluorine (F) and hydrogen (H) atoms from the total number of atoms that can bond with carbon (C) atoms. For saturated compounds with only 1 carbon atom, the total number of atoms connected is 4. When there are 2 carbon atoms, the total number of bonded atoms is 6; if the compound is not saturated, the total number of bonded atoms is 4. For a saturated refrigerant, the total number of connected atoms is as follows: when C=1, it is 4 ； When C=2, it equals 6 ； ...... When C=n, it equals 2n+2. For single-unsaturated and cyclic refrigerants, the total number of connected atoms is as follows: when C=2, it equals 4 ； When C=3, it equals 6 ； ...... When C=n, the value is 2n. 2.1.5 For cyclic derivatives, the letter C is used before the identification number of the refrigerant. 2.1.6 When bromine replaces all or part of the chlorine, the same rules apply; however, the letter B is added after the identification number of the original chlorofluorocarbon to indicate the presence of bromine (Br), with the digits following B representing the number of bromine atoms. 2.1.7 Isomers of ethane have the same identification numbers, but the most symmetrical one is indicated by having no letters after its number. As the isomers become more and more asymmetric, letters such as a, b, c, etc., are added. Symmetry is determined by adding up the atomic weights of the atom groups attached to each carbon atom, and using the difference between these two total atomic weights; the smaller this difference, the more symmetric the product is. 2.1.8 The same rules apply to ethylene-based isomers, but for olefins, the digit 1 is used as the fourth digit from right to left. 2.2 Azeotrope-free mixtures and azeotropes are represented by the refrigerant code and the mass ratio of their components. Refrigerants should be labeled in order of increasing standard boiling point of their components. For example, when refrigerants R22 and R12 are combined in a mixture with a mass percentage of 90/10, it can be expressed as R22/R12 (90/12) or R22/R12 (90/10). 2.2.1 Commercially available azeotropes are assigned their identification numbers in sequence within number 500, according to the order of their application. 2.2.2 Commercially available azeotrope-free mixtures are assigned their identification numbers in sequence within number 400, according to the order of their application. 2.3 Various other organic compounds are assigned numbers starting from 600, while inorganic compounds are assigned numbers starting from 700. 2.3.1 In the 600-series numbering of organic compounds, the numbering is optional. 2.3.2 In the 700-series numbering for inorganic compounds, the molecular weight of the compound plus 700 gives the identification number of the refrigerant. 2.3.3 When two or more non-mechanical refrigerants have the same molecular weight, they are distinguished using letters such as A, B, C, etc. 3 Methods for indicating refrigerant numbers 3.1 Format 3.1.1 Place the letter “R” before the identification number. For example: R12, R22. 3.1.2 The manufacturer’s trademark or product name may also be placed before the refrigerant code. For example: (trademark) R12 or (product name) R12. 3.2 Application in written documentation and nameplates 3.2.1 When indicating the refrigerant in technical specifications or nameplates, it should be written as R12 or R22. 3.2.2 In the writing of books or manuals, the following notation can be used: “Refrigerators can use R12 and R22.” Standard symbols for refrigerants: Code, Chemical name, Molecular formula, Remarks. Halogenated hydrocarbons: R10 – Carbon tetrachloride, CCl4; R11 – Chlorofluoromethane, CFCL3; R12 – Dichlorodifluoromethane, CF2CL2; R13 – Chlorofluorocarbon-13, CF3CL; R13B1 – Trifluorobromomethane, CF3BR; R14 – Carbon tetrafluoride, CF4; R20 – Chloroform, CHCL3; R21 – Chlorodifluoromethane, CHFCL2