Vapour compression refrigeration is used in almost 80 % of the refrigeration industries in the world for refrigeration, heating, ventilating and air conditioning. The application of vapour compression system cycles, using R-12 and R-22 and other halocarbon compounds, had gone deep in the field of refrigeration and air-conditioning before the advent of ozone depletion. The common use of CFC is being phased out due to its impact on the environment, especially to Ozone layer. So, the concerned industry has developed two alternative Refrigerants: one based on Hydro chloro Fluorocarbon (HCFC) and another based on Hydro Fluorocarbon (HFC). The high-grade energy consumption of these devices is very high and the working substance creates environmental problems due to environmental unfriendly refrigerants such as chlorofluorocarbons, hydro chlorofluorocarbons and hydro fluorocarbons.
The HCFCs have a 2 to 10% ozone depleting potential as compared to CFCs and also, they have an atmospheric life time between 2 to 25 years as compared to 100 or more for CFCs.
The HCFCs have a 2 to 10% ozone depleting potential as compared to CFCs and also, they have an atmospheric life time between 2 to 25 years as compared to 100 or more for CFCs.
The first generation of refrigerants was based on the availability. These refrigerants were often highly toxic, flammable and some very highly reactive.
The second generation of refrigerants focused on reducing toxicity and flammability.
Example: NH3, CFCs, HCFCs, HFCs, H2O etc.
The third generation of refrigerants focused on protecting the ozone layer.
Example - NH3, H2O, HCFCs, HFCs, HCs, , CO2 etc.
The fourth generation (from 2010 onwards) focused on refrigerants that do not contribute to global warming, ozone layer depletion, efficient, non flammable and non toxic with good stability.
Heating, ventilating, air conditioning and refrigeration industries are searching for ways to increase performance, durability of equipments and energy efficiency in a sustainable way while reducing the cost of manufacturing. With the present refrigerants, environmental problems such as ozone layer depletion, global warming potential, green house gases and carbon emission are increasing day by day. In response, the refrigeration industry has developed two alternative refrigerants; one based on Hydro chloro Fluorocarbon (HCFC), and another based on Hydro Fluorocarbon (HFC). The HCFCs have a 2 to 10% ozone depleting potential as compared to CFCs and also, they have an atmospheric lifetime between 2 to 25 years as compared to 100 or more years for CFCs (Brandt, 1992). However, even HCFCs are mandated to be phased out by 2005, and only the chlorine free (zero ozone depletion) HFCs would be acceptable.
Some of the alternative refrigerants’coefficients of performance values are found to be higher than their base traditional pure refrigerants. The effects of the main parameters of performance analysis such as refrigerant type, degree of sub cooling, and superheating on the performance coefficient, refrigerant charge rate and volumetric refrigeration capacity are investigated for various operating conditions as case studies. A theoretical performance study on a traditional vapour-compression refrigeration system with refrigerant mixtures based on HFC (134a, 32, 152a, 290) was done for various ratios and their results are compared with CFC (12, 22) and HFC134a as possible alternative replacements. The use of HFCs and HCFCs results in slightly lower efficiencies as compared to CFCs, but this may change with increasing efforts being made to replace CFCs.
Although, R-134a is presently been used as one of the best alternatives to R-12, there are still some notable problems. Problems are R134a will decrease both the capacity and efficiency by 5 to 10%. The effects of the main parameters of performance analysis such as refrigerant type, degree of sub cooling, and superheating on the refrigerating effect, coefficient of performance and volumetric refrigeration capacity are also investigated for various evaporating temperatures.
The use of CFCs is now beginning to be phased out due to their damaging impact on the protective troposphere ozone layer around the earth. The Montreal Protocol of 1987 and the subsequent Copenhagen agreement of 1992 mandate a reduction in the production of ozone depleting Chlorinated Fluorocarbon (CFC) refrigerants in a phased manner, with an eventual stop to all production by the year 1996.