Chillers have been widely used in the central air-conditioning systems of factories, office buildings, shopping malls and other buildings. The models have also been diversified, and they are developing in the direction of energy efficiency. It relies on the centrifugal force generated by the high-speed rotating impeller in the centrifugal compressor to increase the pressure of the refrigerant vapor to obtain the compression process of the vapor, and then achieves refrigeration through processes such as condensation, throttling, pressure reduction, and evaporation. The main components are: Centrifugal compressors, evaporators, condensers, throttling mechanisms, extraction recovery devices, lubrication systems and electrical control condensers, throttling mechanisms, extraction recovery devices, lubrication systems and electrical control cabinets. It has the characteristics of large single-machine cooling capacity, but has the disadvantages of too high pressure, difficult to solve the sealing problem, high working speed and so on.

It belongs to a late-developed and more advanced technology. It has not been more than thirty years. The screw machine has developed rapidly in the past two decades. It uses the mutual engagement of two female and male rotors in a screw compressor to rotate inside the casing to complete the process of suction, compression and exhaust. Its main components are screw compressors, condensers, evaporators, thermal expansion valves and other control elements, which are less than centrifuges. It has the characteristics of compact structure, reliable and balanced operation, few wearing parts, and long service life, but its single unit cooling capacity is smaller than that of a centrifuge.

The cooling capacity of a single centrifugal compressor is large, which can be from 150-3000RT, so generally only one centrifugal compressor can be designed to meet the cooling capacity requirement. The refrigeration of a single screw compressor is smaller than that of a centrifuge, generally from 30RT to 400RT, so the screw refrigerators of large refrigeration now adopt a multi-head method, which is uniformly controlled and adjusted by a microcomputer, and each compressor Each has a separate refrigeration system. This difference in structural characteristics has a very important impact on the control, operation, and maintenance of the machine, which we will elaborate below.