Secondary refrigerants

Classification

1. SECONDARY AND ECO-FRIENDLY REFRIGERANTS By Dr.A.Lovelin Jerald Associate Professor Department of Food Processing and Preservation Technology

2. REFRIGERANT A refrigerant is a substance used in refrigeration systems to absorb heat in the evaporator, by changing state from a liquid to a vapour and rejects this heat in the condenser as it changes back to a liquid. In principle, any fluid can be used as a refrigerant. Air used in an air cycle refrigeration system can also be considered as a refrigerant

3. Refrigerant selection criteria: Selection of refrigerant for a particular application is based on the following requirements: Thermodynamic and thermo-physical properties Environmental and safety properties, and Economics

4. CLASSIFICATION

5. ODP & GWP Ozone Depletion Potential (ODP): Relative value that indicates the potential of a substance to destroy ozone gas as compared with the potential of chlorofluorocarbon-11 (CFC-11) which is assigned a reference value of 1. Thus, a substance with ODP of 2 is twice as harmful as CFC-11. According to the Montreal protocol, the ODP of refrigerants should be zero, i.e., they should be non-ozone depleting substances Global Warming Potential (GWP): GWP of a refrigerant is an indicator of its potency to warm the planet by action as a greenhouse gas Refrigerants should have as low a GWP value as possible to minimize the problem of global warming. Refrigerants with zero ODP but a high value of GWP (e.g. R134a) are likely to be regulated in future.

6. SECONDARY REFRIGERANT Secondary refrigerants allow the amounts of environmentally harmful primary refrigerants to be minimized and contained in a restricted area. Examples of secondary refrigerants include water, air, hydrocarbons, ammonia and carbon dioxide, which are more environmentally safe than traditional refrigerants such as HCFCs. They are safer (some are even incombustible and non-toxic) and generally suitable for refrigeration systems.

7. Secondary refrigerants absorb heat and change temperature in order to transfer heat from the substance or product to be cooled. They usually do not change state in the cooling cycle but change temperature by absorbing sensible heat. Secondary refrigerants should have a low freezing point, a low viscosity, a high specific heat, and a high thermal conductivity. Brines are often chosen as secondary refrigerants for large refrigeration systems, such as those supplying supermarkets, the most common brines being water-glycol solutions, water-ethanol solutions and acetate solutions.

8. Solutions of salts in water, called refrigeration brines, are used as secondary refrigerants. Sodium chloride brine is employed for temperatures down to – 15°C; Magnesium chloride brine, down to – 27°C; Calcium chloride brine, down to – 45°C. Antifreezes and Freons are used in low-temperature refrigerating systems. Aqueous solutions of propylene glycol are employed for temperatures down to – 47°C; Aqueous solutions of ethylene glycol, down to – 60°C; Freon-30, down to – 90°C and Freon-11, down to – 100°C.

9. CFC ALTERNATIVES: CFCs (Chlorofluorocarbons):  R11, R12, R113, R114, R115 HCFCs ( Hydrochlorofluorocarbons ):  R22, R123 HFCs ( Hydrofluorocarbons ):  R134a, R404a, R407C, R410a

10. ECO-FRIENDLY REFRIGERANTS In the aftermath of the Montreal protocol HFC’s have predominantly replaced CFC’s and HCFC’s. Due to their high GWP, HFC’s are not a good replacement solution. The solution are the natural refrigerants : Ammonia, Hydrocarbons and Carbon dioxide ozone depleting substance developed countries developing countries CFCs phased out end of 1995 total phase out by 2010 halons phased out end of 1993 total phase out by 2010 HCFCs total phase out by 2020 total phase out by 2040

11. HYDRO CARBONS Very promising non-halogenated organic compounds with no ODP and very small GWP values Their efficiency is slightly better than other leading alternative refrigerants Dominant in domestic market like household refrigerators and freezers Growing use in very small commercial systems like car air-conditioning system and window air conditioners of low charge Examples: R170, Ethane, C 2 H 6 R290 , Propane C 3 H 3 R600 , Butane, C 4 H 10 R600a, Isobutane, C 4 H 10

12. AMMONIA(NH 3 ) ODP = 0 GWP = 0 Excellent thermodynamic characteristics: small molecular mass, large latent heat, large vapour density and excellent heat transfer characteristics High critical temperature (132C) : highly efficient cycles at high condensing temperatures Its smell causes leaks to be detected and fixed before reaching dangerous concentration Relatively Low price

13. Some draw backs are, Toxic Flammable ( 16 – 28% concentration ) Not compatible with copper Temperature on discharge side of compressor is higher compared to other refrigerants

14. CARBON DIOXIDE (CO2) ODP-0 GWP-1 Excellent thermophysical properties, leading to high heat transfer; Efficient compression and compact system design due to high volumetric capacity; Non-flammable and low toxicity; Widely available at low cost. Its high operating pressure provides potential for system size and weight reducing potential. Drawbacks: Operating pressure (high side) : 80 bars Low efficiency

15. Type ASHRAE No. Chemical Name Molecular Formula ODP GWP CFC R-12 Dichlorodifluoro-methane CCl 2 F 2 1.0 2,400 HCFC R-22 Chlorofdiluoro-methane CHClF 2 0.05 1,700 HFC R-32 Difluoromethane CH 2 F 2 650 R-134a Tetrafluoroethane C 2 H 2 F 4 1,300 Refrigerant Azeotropic MCixtures R-407C R32+R125+R134a (23%+25%+52%) 23% CH 2 F 2  25% C 2 HF 5   52% C 2 H 2 F 4 1,610 R-410A R32 + R125 (50% + 50%) 50% CH 2 F 2 1,725 Natural Refrigerant R-717 Ammonia NH 3 R-744 Carbon Dioxide CO 2 1