Brief Information About LPG as Refrigerant
In India, more than 80 % of the domestic refrigerators utilize HFC134a as refrigerant, due to its excellent thermodynamic and thermo physical properties. But, HFC134a has a high global warming potential (GWP) of 1300. There is a need to assess various refrigerant options considering the existing refrigerators in the field and for the future market.
CFC’s are principally destroyed by ultraviolet radiations in the stratosphere; the chlorine released in the high stratosphere catalyzes the decomposition of ozone to oxygen; and ultraviolet radiation penetrates to lower altitudes. Credible calculations of the magnitude of this effect (Hoffman 1987) and his team predicted 3% global ozone depletion for constant CFC emissions of 700 thousand tonnes/year after a hundred years. The ozone impact of car air conditioners also cannot be ignored. Hydrofluorocarbons (HFC’s) can be thought of as a replacement, but unfortunately the radiation properties of HFC’s like R-134a make them powerful global warming agents. HFC134a and the HC blend have been reported to be substitutes for CFC12, but they have their own drawbacks in energy efficiency, flammability and serviceability aspects of the system. HFC134a is not miscible with mineral oil, and hence, polyol ester oil is recommended, which is highly hygroscopic in nature. This hygroscopicity demands stringent service practices, which otherwise results in moisture entry into the system.
Thus, hydrocarbon refrigerants; particularly LPG serves as the best contender to replace CFC’s from domestic refrigerators as well as car air conditioners.
LPG consists mainly of propane (R-290) and butane (R-600), and LPG is available as a side product in local refineries. In Cuba for already several decades LPG is used as a drop-in refrigerant. LPG mixtures have composition of a commercial LPG mixture suitable as ‘drop-in’ replacement for R-12 was calculated crudely as 64% propane and 36% butane by mass. Liquefied petroleum gas ( LPG) of 60% propane and 40% commercial butane has been tested as a drop-in substitute for R134a in a single evaporator domestic refrigerator with a total volume of 10 ft3.
LPG can offer following advantages when used as a refrigerant:
1) The cooling capacity of LPG is 10% higher than R-12 and the vapour pressure is appropriate.
2) LPG is naturally occurring and non-toxic.
3) Use of LPG as a refrigerant also improves the overall efficiency by 10 to 20%.
4) The ozone depletion potential (ODP) of LPG is 0 and global warming potential (GWP) is 8 which is significantly negligible as compared to other refrigerants.
5) Apart from environment friendly, use of LPG also gives us lot of cost advantages.
6) LPG does not form acids and thereby eliminates the problem with blocked capillaries.
7) There is 60% reduction in weight of the system due to higher density of LPG.
The only disadvantage of using LPG as a refrigerant is its flammability. It is highly flammable. This paper elaborates various precautions that need to be taken to safely use LPG as a refrigerant. The amount of LPG used for each appliance should be too small in order to avoid any risk for technicians and customers. Thus by minimizing the possibility of leak and following some international standards, the use of LPG as a refrigerant can be safely implemented.
