Refrigerant charge in refrigerating systems and strategies of charge reduction

For some years, European regulation concerning refrigerating systems has become more and more severe. Because of their design and technology, refrigeration units cannot avoid refrigerant leaks, and can thus have a harmful impact on the environment. Many studies aimed at minimizing the charge in a refrigerating machine were thus developed. On a global level, reduction of refrigerant charges must not affect energy aspects while respecting environmental constraints [Montreal 1987, Kyoto 1997]. The architecture and refrigerant charge distribution in the systems are of particular importance; their analyses permit the determination of the target elements and thus define those in which the refrigerant charge could be reduced (heat exchangers, liquid pipes, receivers, …). This paper presents a review of the refrigerant charge studies in a refrigerating plant (methodologies of charge measurement, void fraction correlations and characteristic values for various technologies). It also evaluates the influence of the refrigerant charge on the coefficient of performance (COP) and on the cooling capacity. Finally, it inventories the different means that allow the charge in a refrigerating system to be minimized.