Chapter 14C: REFRIGERANTS Agami Reddy (rev- May 2017) Contents 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 HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants 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 well-established refrigerants, and to develop more benign ones. HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants 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 HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants Table 14.15 Classification of Common Refrigerants Refrigerant class Numerical Designation Chemical Name Chemical Formula Safety+ ODP+ GWP+ (100 yr) Inorganic (naturally occurring) 717 744 718 Ammonia Carbon dioxide Water NH3 CO2 H2O B2 A1 <1 1 Halocarbon (contain chlorine, fluorine or bromine)- largest market share 11 12 22 134a 502* Trichloromonofluoro- methane Dichlorodifluoro- Monochlorodifluoro- Tetrafluoroethane - CCl3F CCl2F2 CHClF2 CH2FCF3 CClF2CF3 0.82 0.034 0.221 4600 10600 1700 ~ 1400 4500 Hydro- carbon (not used) 50 170 290 Methane Ethane Propane CH4 C2H6 C3H8 A3 23 ~20 Organic (naturally occurring) 600 630 Butane Methylamine C4H10 CH3NH2 HCB 3- Chap 14D: Refrigerants ODP is the ozone depletion potential and GWP is a global warming potential indictor relative to carbon dioxide.

HCB 3- Chap 14D: Refrigerants Designation System HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants Inorganic compounds are numbered by adding 700 to their molecular weight, a rather arbitrary methodology. Therefore, ammonia (molecular weight = 17) is numbered R-717. 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 R-290/22/115(8/45/47). HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants Common Refrigerants Substitute R-12 Car A/C, household refrigerators HFC-134a R-11 large centrifugal chillers R123 R-22 Window A/C R407c R410a HCB 3- Chap 14D: Refrigerants

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. HCB 3- Chap 14D: Refrigerants

Operational Comparison Table 14.16 Comparison of different refrigerants in terms of performance between the operating temperatures of Tevap= -15o C and Tcond = 30o C Refrigerant Evaporation pressure (MPa) Condens. pressure Comp. ratio (-) Compressor exit temp. (o C) Refrigerating effect (kJ/kg) Refrigerant flow rate (kg/s.kW) COPstd Refrigerating efficiency R-12 0.183 0.745 4.07 38 116.58 0.00358 4.69 0.818 R-22 0.296 1.192 4.03 53 162.46 0.00616 4.75 0.829 R-114 0.047 0.252 5.41 30 99.19 0.01008 4.44 0.774 R-134a 0.160 0.770 4.81 43 150.71 0.00664 4.42 0.771 R-502 0.349 1.319 3.78 37 104.39 0.00958 4.43 0.773 R-717 0.236 1.164 4.94 98 1102.23 0.00091 4.84 0.844 HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14A: Refrigeration Cycles and Systems Fig. 14.29 HCB 3- Chap 14A: Refrigeration Cycles and Systems

HCB 3- Chap 14A: Refrigeration Cycles and Systems Another important practical consideration HCB 3- Chap 14A: Refrigeration Cycles and Systems

Desirable Physical and Chemical Characteristics Good thermodynamic properties such as density and specific heat, Good transport characteristics, i.e., properties conducive to high heat transfer such as thermal conductivity and viscosity, Noncorrosive in the presence of water and inert in terms of material used in the piping and components, High dielectric strength of vapor (a factor in hermetically sealed compressors where vapor comes in contact with motor windings), Low oil solubility (to maintain lubrication and prevent oil logging in the evaporator), Low water solubility (so as to avoid freezing the expansion device), Inert (non-reacting with piping materials), and Stable over time. HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants Health Safety HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants Ozone Depletion CFCs are very stable and persist in the atmosphere for many years Once in the upper atmosphere, CFC molecules break down and Cl is released which destroys the ozone layer In the lower atmosphere, the molecules absorb infrared radiation which contributes to global warming Ozone Depletion Potential (ODP) is a normalized index of the ozone destruction potential with 1.0 assigned to R-11. See Table 14.5 HCB 3- Chap 14D: Refrigerants

International Protocols Original 1987 Montreal protocol - limited the 1998 production of certain CFCs to 50% of their 1986 levels - Starting in 1991, the production of certain CFCs was frozen at their 1986 levels Copenhagen Amendment, 1994 - production of all CFC-based refrigerants stopped by 1995 (R-11, R-12, R-502) - existing stock can be used HCB 3- Chap 14D: Refrigerants

Global Warming Potential (GWP) The major environmental concern currently is not ozone, but rather the impact of refrigerants on climate change. Released refrigerants in the lower atmosphere trap the infrared radiation from the earth thereby contributing to the greenhouse effect. GWP is used to characterize this effect with that of carbon dioxide over a time duration of 100 years taken as the reference value of unity. Notice the very large GWP values for the halocarbon family of compounds (Table 14.15). HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants Fig. 14.30 Map of refrigerant evolution showing routes being taken in the phase-out of CFCs and HCFCs. Refrigerants in the future are likely to be the natural refrigerants, HFCs, unsaturated HFCs (also known as HFOs), and possibly blends of these refrigerants (©ASHRAE, www.ashrae.org. (2012) HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants The refrigerants of primary concerns for ozone depletion are the CFCs which include R-11, R-12 and R-502; these were the most destructive to the ozone layer and are first to be phased out. Regulations are in place to phase out HCFCs as well: - R-123 is now being used to temporarily replace R-11 but is causing efficiency reduction and certain operational problems, and is likely to be phased out in 10 years. - R-134a appears to be a satisfactory substitute for R-12. The HFC compounds are the least harmful to the ozone layer since they do not contain any chlorine, but their use is also being restricted due to global warming potential. Some of these “drop-in” replacements, in turn, are likely to be replaced by more benign compounds in the future such as natural refrigerants (Fig. 14.30) HCB 3- Chap 14D: Refrigerants

HCB 3- Chap 14D: Refrigerants Outcomes Understanding of the different types of considerations involved in selecting refrigerants Understanding of how refrigerants are classified Understanding of the designation system of refrigerants Knowledge of the desirable thermodynamic properties of various refrigerants and use of relevant tables Knowledge of the desirable physical and chemical properties of various refrigerants and use of relevant tables Understanding of the health safety categories Knowledge of the ozone depletion potential of refrigerants Knowledge of the global warming potential of refrigerants Understanding of the various international refrigerant phase-out efforts to mitigate environmental concerns HCB 3- Chap 14D: Refrigerants