Discharge

Fig. 37-8 Screw Compressor Compression Cycle Illustration.

their positive displacement characteristics, offer equal or superior performance under part-load conditions.

The typical operating speed for a screw compressor is about 3,600 rpm. They are, however, well suited for operation over a wide range of speeds. To avoid gearing requirements, they can sometimes be matched with the ideal operating speed of the driver. Screw compressor output capacity is reduced linearly with speed reduction. For example, operation at 1,800 rpm, which would be well suited for a reciprocating engine driver, would require a doubling of compressor size. Even though the added cost of the larger compressor is roughly equivalent to, or slightly greater than, the cost of the speed increaser, lower speed operation extends compressor life and reduces noise levels.

Legend

Legend

Low Pressure Vapor

M High Pressure ™ Liquid Refrigeranl jk Low Pressure V Liquid ftefrigeranl

Fig. 37-9 Illustration of Refrigeration Cycle for a Screw Compressor-Based Chiller System. Source: York International

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