Chapter 14C Refrigerants

6/2/22 Chapter 14C: REFRIGERANTS • • • • • • • • • Background Classification Designation systems Desirable thermodynamic properties Desirable physical and, chemical properties Health safety Ozone depletion potential Global warming potential International protocols for refrigerant phaseout 1 Background Choice of suitable refrigerants is influenced by: - their thermodynamic properties which impact the energy efficient operation of the vapor compression system - their physical and chemical properties which impact safety, toxicity, stability, reliability, material compatibility - their environmental impact: - ozone depleting potential (ODP), - global warming potential (GWP), - life cycle climate performance (LCCP). This has resulted in international efforts to phase out certain wellestablished refrigerants, and to develop more benign ones. 2 1 6/2/22 Classification There is no single set of optimum characteristics for refrigerants (especially for thermodynamic properties), and so tradeoffs are to be made among desirable characteristics. Thus, a variety of refrigerants having a range of properties have been developed to meet the requirements of various applications. Azeotropes are mixtures of different substances whose composition and saturation temperature do not vary when boiled and have properties different from each constituent. They behave like simple pure substances Zeotropic blends, which change composition when boiled at constant pressure, and so can be separated into their components by distillation. These are used extensively in absorption systems, and also in VC systems 3 Table. Classification of Common Refrigerants Refrigerant class Inorganic (naturally Numerical Designation 717 744 Chemical Name Ammonia Carbon dioxide Chemical Formula NH3 CO2 Safety+ ODP+ B2 A1 0 0 GWP+ (100 yr) <1 1 occurring) 718 Halocarbon 11 (contain Water Trichloromonofluoromethane H2O CCl3F A1 A1 0 1 <1 4600 chlorine, fluorine or 12 Dichlorodifluoromethane CCl2F2 A1 0.82 10600 bromine)largest 22 Monochlorodifluoromethane CHClF2 A1 0.034 1700 market share 134a 502* Hydro50 carbon 170 Tetrafluoroethane Methane Ethane CH2FCF3 CClF2CF3 CH4 C2H6 A1 A1 A3 A3 0 0.221 0 0 ~ 1400 4500 23 ~20 (not used) Organic (naturally Propane Butane Methylamine C3H8 C4H10 CH3NH2 A3 A3 - 0 0 0 ~20 ~20 - 290 600 630 occurring) HCB 3- Chap 14D: Refrigerants 4 2 6/2/22 Designation System 5 Inorganic compounds are numbered by adding 700 to their molecular weight, a rather arbitrary methodology. Therefore, ammonia (molecular weight = 17) is numbered R717. Azeotropic mixtures use a serial numbering system beginning with 500 are not related to the chemical composition. As an example, a mixture of R-22 and R-115 on a mass basis of 48.8% and 51.2% respectively is designated by R-502. Zeotropic blends are also arbitrarily designated by the 400 series followed by the weight proportion of the components. For example, a mixture of 92% R-502 (azeotrope of R-22 and R-115) with 8% propane (R-290) will be designated by R290/22/115(8/45/47). 6 3 6/2/22 Common Refrigerants • R-12 Car A/C, household refrigerators • R-11 large centrifugal chillers • R-22 Window A/C Substitute HFC-134a R123 R407c R410a 7 Thermodynamic Properties Desirable characteristics are: • High latent enthalpy of vaporization i.e., a large refrigeration effect per unit mass, • High critical pressure which results in reduced compressor power, • Positive evaporating pressures will prevent atmospheric air leaking into refrigerant piping during operation, • Low but positive condensing pressures will allow lightweight equipment and piping to be used, and • Low temperature of vapor leaving compressor. 8 4