can have either a self-contained refrigeration system where the compressor is built into the unit, or a remote refrigeration system where the refrigeration components are located elsewhere, often the roof of the business. Compressor Most compressors are either positive displacement compressors or radial compressors. Positive displacement compressors are currently the most efficient type of compressor, and have the largest refrigerating effect per single unit (). They have a large range of possible power supplies, and can be , , or even higher. The principle behind positive displacement compressors utilizes a turbine to compress refrigerant into high-pressure vapor. Positive displacement compressors are of four main types: screw compressor, rolling piston compressor, reciprocating compressor, and rotary compressor. Screw compressors can yield the largest refrigerating effect among positive displacement compressors, with their refrigerating capacity normally ranging from to . Screw compressors also can be divided into single-screw type and dual-screw type. The Dual-screw type is more often seen in use because it is very efficient. Rolling piston compressors and reciprocating compressors have similar refrigerating effects, and the maximum refrigerating effect can reach . Reciprocating compressors are the most common type of compressor because the technology is mature and reliable. Their refrigerating effect ranges from to . They compress gas by utilizing a piston pushed by a crank shaft. Rotary compressors, mainly used in air conditioning equipment, have a very low refrigerating effect, normally not exceeding . They work by compressing gas using a piston pushed by a rotor, which spins in an isolated compartment. Condenser All condensers can be classified as one of three types: air cooling, water cooling, or evaporative cooling. An air cooling condenser uses air as the heat-conducting media by blowing air through the surface of condensers, which carries heat away from the high-pressure, high-temperature refrigerant vapor. A water cooling condenser uses water as the heat-conducting media to cooling refrigerant vapor to liquid. An evaporative condenser cools the refrigerant vapor by using heat exchange between the evaporator pipes and the evaporated water which is sprayed on the surface of the pipes. This type of condenser is capable of working in warm environments; they are also very efficient and reliable. Tube ice generator A tube ice generator is an ice generator in which the water is frozen in tubes that are extended vertically within a surrounding casing—the freezing chamber. At the bottom of the freezing chamber, there is a distributor plate