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The centrifugal compressor makes use of the centrifugal forces to pressurize the refrigerant. The blades of a rotating impeller induce the kinetic energy by increasing the flowrate of the refrigerant. This energy is converted into the potential energy in the diffuser to pressurize the refrigerant. The centrifugal compressor is more economic if used for capacities in excess 150 tph. The pressurizing capacity is not high. They are used where the condensing and evaporating pressure differences are not so big. This makes the centrifugal compressors used widely for the purpose of air conditioning. The capacity control is performed by the flowrate of the refrigerant at the suction port. Considerations in Selection of Water Cooling Sets with Centrifugal Compressor 1. Type R134a should be selected as the refrigerant. Almost all equipment manufacturers supply devices designed for the operation with R134a. 2. The compressor kits may have high COP values; therefore minimum COP value should be specified. COP values of the compressor kits should be selected around 6. 3. The friction losses in centrifugal compressors and evaporators are important and directly determine the prices. Therefore, maximum pressure loss should be specified. The pressure loss is directly proportional to the installed powers of the compressor and evaporator and therefore, the specified limits for the cooling sets should be adhered to. 4. The higher the difference between water regime temperatures, the lower is COP value. For example:
For 7/12; 29/34 regime (temperature difference is 5°C); COP = 5.682.
For 7/12; 30/36 regime (temperature difference is 6°C); COP = 5.208. 5. COP value of the device is proportional to the exit water temperature requested. For example:
For 29/34 and 6/12°C, COP = 5.31
For 29/34 and 7/13°C, COP = 5.556 6. The more the condenser entry water temperature, the higher is the condensation temperature and lowers the COP value. 7. With respect to the operation safety of the centrifugal compressor kits, single stage (single impeller) types should be preferred. 8. The price of the instrument decreases as COP value decreases. 9. For the centrifugal compressors, the operational performance records should also be obtained as the computer printouts in order to eliminate the surge problem. 10. The instruments are usually operated under partial loads and therefore, those featuring high efficiency under partial load should be preferred. To this end, APLV/IPLV values might be compared. 11. The ease of cleaning of the condenser in particular if "the marine water box” type connection is available in the engine room. 12. In large premises, the availability of pump-out system is preferred in order to facilitate the replacement of the refrigerant in the system.
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