Centrifugal compressors belong to the velocity type, while piston and screw compressors belong to the volume type

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Centrifugal compressors rely on high-speed blades to transfer energy to the refrigerant gas flowing continuously within the pipeline, thereby imparting high speeds to the gas and increasing its pressure. They offer advantages such as high cooling capacity, low weight and compact size per unit of power, minimal space requirement, absence of vulnerable components like valves, pistons, or piston rings, the ability to achieve oil-free compression, stable and reliable operation, light equipment foundations, low pulsation in the air supply, and low maintenance costs. However, their disadvantages include lower efficiency, the need for larger individual units, limited adaptability to varying operating conditions, and higher noise levels compared to piston compressors. Screw compressors belong to the category of positive displacement rotary compressors; since there is no re-expansion process of the gas remaining in the clearance volume, there is a very small gap between the rotor and the casing, with no sliding friction between them, which results in high internal and mechanical efficiencies. As they lack suction and discharge valves, they have few vulnerable components, making maintenance straightforward, and they enjoy a long service life. For these reasons they are widely used and are likely to see further adoption. Their drawbacks, however, include higher noise levels and the fact that the individual unit capacity cannot be too small. Piston compressors are traditional positive displacement compressors and are currently the most widely used type. This type of compressor features mature manufacturing techniques, a wide range of operating pressures, strong adaptability to varying conditions, slightly lower thermal effects compared to screw compressors, generally lower rated speeds, pulsations in the air output, and some vibration during operation. Their structure is relatively complex, they have many vulnerable components, and maintenance intervals are short. Their noise level is lower than that of centrifugal and screw compressors, which is why they play a dominant role in small and medium-sized refrigeration systems. In general, centrifugal and screw compressors are suitable for large-scale refrigeration and air conditioning systems, while piston compressors are commonly used in small and medium-sized applications.