Refrigeration apparatus and operating method thereof

A refrigeration apparatus having a closed circuit (C) in which a flow rate (P) of coolant circulates, said closed circuit comprising a main branch (M) provided with a main compressor, a cooling device to cool said coolant, expansion means to expand the coolant and an evaporator, said closed circuit further comprising a secondary economizer branch for a fraction of flow rate (X1) of said coolant, wherein an inlet section of said secondary economizer branch is arranged in a length of said closed circuit (C) between said cooling device and said expansion means and an outlet section of said secondary economizer branch is arranged in proximity of the suction of said main compressor, wherein said main branch (M) further comprises a reciprocating compressor arranged between said evaporator and said main compressor and provided with a cylinder, a rod and a piston, the piston being integrally constrained to said rod and translatable inside said cylinder, and wherein said secondary economizer branch comprises a control device for controlling actuation of said rod and adapted to divert at least one portion (X2) of said fraction (X1) of coolant coming from said secondary economizer branch to drive the displacement of said piston and compress the coolant coming from said evaporator and contained in said cylinder, and to reintroduce said portion (X2) of said fraction of coolant into said secondary economizer branch during the displacement of said piston in the step of suctioning the coolant coming from said evaporator, for the outflow of said portion (X2) of said fraction of coolant through said outlet section of said secondary economizer branch, wherein said outlet section of said secondary economizer branch is arranged downstream of said reciprocating compressor.