A unit for conversion of thermal energy including: - a first heat-exchange unit defining a first flow path for a first thermovector fluid; and - a second heat-exchange unit defining a second flow path for a second thermovector fluid, wherein: - said first heat-exchange unit includes a first inlet port for said first thermovector fluid, and a first outlet port for said first thermovector fluid, said first inlet port and first outlet port being located on a same side of said first heat-exchange unit and having a baffle set therebetween so as to give a substantially "U"-shaped geometry to said first flow path; - said second heat-exchange unit includes a second inlet port and a second outlet port for said second thermovector fluid, and further includes a plurality of cartridge elements, said second flow path developing from said second inlet port, through said cartridge elements, to said second outlet port, said cartridge elements being at least partially immersed in the first flow path; characterized in that said plurality of cartridge elements are in fluid communication with a first manifold element and a second manifold element, which bear said second inlet port and said second outlet port, respectively; - each cartridge element includes an inlet orifice and an outlet orifice for said second thermovector fluid, a heat-exchange area for exchange of thermal energy between said second thermovector fluid and said first thermovector fluid, and a first electrode (32E, 32FC) and a second electrode (32E, 32FC) connected to at least one element made of thermoelectric material of the cartridge element; and wherein moreover said first manifold element and said second manifold element each include a connection interface to said plurality of cartridge elements, which is configured for providing a hydraulic connection, respectively, with the inlet orifices and the outlet orifices of the cartridge elements, and an electrical connection, respectively, to the first electrodes (32E, 32FC) and second electrodes (32E, 32FC) of the cartridge elements. - a first heat-exchange unit defining a first flow path for a first thermovector fluid; and - a second heat-exchange unit defining a second flow path for a second thermovector fluid, wherein: - said first heat-exchange unit includes a first inlet port for said first thermovector fluid, and a first outlet port for said first thermovector fluid, said first inlet port and first outlet port being located on a same side of said first heat-exchange unit and having a baffle set therebetween so as to give a substantially "U"-shaped geometry to said first flow path; - said second heat-exchange unit includes a second inlet port and a second outlet port for said second thermovector fluid, and further includes a plurality of cartridge elements, said second flow path developing from said second inlet port, through said cartridge elements, to said second outlet port, said cartridge elements being at least partially immersed in the first flow path; characterized in that said plurality of cartridge elements are in fluid communication with a first manifold element and a second manifold element, which bear said second inlet port and said second outlet port, respectively; - each cartridge element includes an inlet orifice and an outlet orifice for said second thermovector fluid, a heat-exchange area for exchange of thermal energy between said second thermovector fluid and said first thermovector fluid, and a first electrode (32E, 32FC) and a second electrode (32E, 32FC) connected to at least one element made of thermoelectric material of the cartridge element; and