A compressor unit for a refrigerating machine for domestic or commercial use which comprises a rotary compressor having: - a compression element, - a motor with permanent brushless magnets, having a stator and a rotor which is inside said stator and connected to said compression element to actuate it, - a control device connected to said motor, for driving it at a variable speed; - a casing which encloses said motor and said compression element and which comprises a side wall inside of which said stator is fixed; characterized in that said compressor unit also comprises: - an operative shell covering said casing and in thermal contact with said side wall; said operative shell being configured in such a way as to dissipate heat transmitted to it by said casing to prevent overheating of the compressor wherein in its operation and in such a way as to contrast the transmission through it of sound waves having a frequency of between 4 kHz and 16 kHz, - a base, for resting on a supporting surface, said base being fixed to a lower wall of said casing, wherein said operative shell is configured in such a way as to cover an upper wall of said casing and said side wall, wherein said operative shell comprises an operative layer made of sound absorbent foam-type material having a first face in thermal contact with said side wall and with said upper wall of said casing, which operative layer is configured to maximise the surface of reciprocal contact between it and said side wall and upper wall to maximize the thermal conduction through the operative layer, wherein said operative shell also comprises a structural wall made of metallic material, which covers a second face of said operating layer, wherein said structural wall comprises: - a tubular jacket, configured for retaining said operating layer in thermal contact with the side wall of said casing and having an upper edge; - a cap configured for being superposed on the upper wall of said casing and having a collar shaped to match the upper edge of said jacket for being joined to the latter by means of a shape coupling. - a compression element, - a motor with permanent brushless magnets, having a stator and a rotor which is inside said stator and connected to said compression element to actuate it, - a control device connected to said motor, for driving it at a variable speed; - a casing which encloses said motor and said compression element and which comprises a side wall inside of which said stator is fixed; - an operative shell covering said casing and in thermal contact with said side wall; said operative shell being configured in such a way as to dissipate heat transmitted to it by said casing to prevent overheating of the compressor wherein in its operation and in such a way as to contrast the transmission through it of sound waves having a frequency of between 4 kHz and 16 kHz, - a base, for resting on a supporting surface, said base being fixed to a lower wall of said casing, wherein said operative shell is configured in such a way as to cover an upper wall of said casing and said side wall, wherein said operative shell comprises an operative layer made of sound absorbent foam-type material having a first face in thermal contact with said side wall and with said upper wall of said casing, which operative layer is configured to maximise the surface of reciprocal contact between it and said side wall and upper wall to maximize the thermal conduction through the operative layer, wherein said operative shell also comprises a structural wall made of metallic material, which covers a second face of said operating layer, wherein said structural wall comprises: - a tubular jacket, configured for retaining said operating layer in thermal contact with the side wall of said casing and having an upper edge; - a cap configured for being superposed on the upper wall of said casing and having a collar shaped to match the upper edge of said jacket for being joined to the latter by means of a shape coupling. - a tubular jacket, configured for retaining said operating layer in thermal contact with the side wall of said casing and having an upper edge; - a cap configured for being superposed on the upper wall of said casing and having a collar shaped to match the upper edge of said jacket for being joined to the latter by means of a shape coupling.