In a hermetic refrigeration compressor, the electric motor and compressor part are enclosed in a hermetically welded envelope.
The main advantage to a hermetic refrigeration compressor is its sealing system which is ensured by the enclosed envelope and does not depend on the state of one or several joints (i.e. the rotating shaft seal for example).
But this system does not only have advantages: the cooling of the motor is ensured by the refrigerant fluid bathing the inside of the casing which heats the fluid and is detrimental to the refrigeration cycle. In principle, the cooling capacity cannot be adjusted, except by varying the frequency of the supply current.
Another disadvantage is that it is impossible to open the enclosed envelope to make any repairs and as such if something stops working the whole refrigeration compressor must be replaced. Luckily, this system is fairly affordable.
Hermetic refrigeration compressors are reserved for low and medium power requirements.