There are two main categories of refrigerator. The 3 way absorption unit. The low voltage compressor unit.
The absorption design has no moving parts and relies on a heating device. This can be provided by burning gas, or with a 240v or 12v heating element. It is totally silent and generally low cost in comparison.
The compressor unit design uses a low voltage electric pump. This is controlled to provide an even temperature. Most units are 12 or 24 volts. A low buzz is emitted from the unit during operation. No flue required.
Sizes available are approximately 40 to 140 Ltr. Fridge freezers of single or two door design are available up to approximately 200 Ltr.
Good ventilation is essential for efficient operation of any fridge unit and kits are available to achieve this.