Centrifugal Refrigeration System

Centrifugal Refrigeration System Points : centrifugal refrigeration system, centrifugal compressor refrigeration system, centrifugal compression refrigeration system This centrifugal refrigeration system employs the same general type of compression and refrigeration cycle. Large comfort installations use centrifugal type compressor these system use low pressure refrigerant and the evaporator operates at below atmospheric, pressure. Both condenser and evaporator are the shell and tube in evaporator the chilled water flows through the tubes in warmer then the refrigerant in the shell surrounding the tubes consequently the heat is transferred from chilled water to refrigerant this heat evaporates the refrigerant at a temperature corresponding to the pressure in thee evaporator as maintained y the compressor the evaporated refrigerant is drawn into the suction of the compressor the compressor is two stage centrifugal driven by hermetically sealed motor the suction gas which coming from the economizer through the hermetic motor is used for the motor cooling and this gas enters the second stage of the compressor the refrigerant discharged by the compressor, condenses on the ‘out side’ of the condenser tubes ‘(in the condenser shell) at the temperature corresponding to the condenser pressure this temperature is higher then that of the water in the tubes; so the heat is transferred into the condenser water the condensed refrigerant drained in to the condenser float chamber where a float valve maintains liquid “seal” to prevent gas from passing into the economizer this rising refrigerant level in this chamber.

Open the float valve and allows the liquefied refrigerant to pass into the economizer chamber. The pressure in the economizer chamber in the Iwo-stage compression is intermediate between the condenser and cooler pressure; consequently, enough of the refrigerant liquid evaporates to cool the remaining liquid to the lower temperature corresponding to the lower pressure in the economizer chamber. Thus evaporation takes place by rapid flushing into gas has it passes through the float valve and conduct leading into the economizer chamber. The evaporated portion passed through eliminators to the hermitic motor where it picks up a small amount of additional heat as it cools the motor. It then goes to the compressor and mixes with the gas which has been compressed by the first stage impeller. This mixture enters in the second stage impeller. The difference in the pressure between the condenser and the cooler is approximately the same for each stage.

Capacity is controlled by inlet vanes to the stage centrifugal compressor. The vanes may be both electronically or pneumatically controlled and hydraulically operated. During starting, vanes are closed to reduce the stating load. This compressor has a forced lubrication system. A separate motor drives the oil pump. This system has automatic purging device non-condensable gases. The evaporator, compressor suction line chilled liquid lines are always insulated.

This is accomplished by direct drive form a steam turbine or constant speed electric motor with variable speed drive unit. In the case of steam turbine drive the initial sensing device is generally a temperature controller in the chilled water leaving the evaporator. A decrease in load causes a drop in temperature and is transmitted to a valve regulating the flow of oil to the turbine and the speed drops, this arrangement will yield satisfactory capacity modulation of 100 percent load, for capacity control below this range. Variable speed is combined with one of the other means of capacity control usually inlet guide vanes.

Speed control the critically looks attractive but practically it has limitations that make it les desirable or inadequate as complete answer to part load performance. When speed control is combined with one of other means of capacity control, it can be quite helpful.