Screw compressor

Abstract

A screw compressor is for use of a screw chiller, and comprises a pair of screw rotors and a casing housing the screw rotors, a capacity control valve for varying a ratio of volume, a motor for driving the screw rotors and an inverter for varying the rotational speed of the motor. The screw compressor is controlled using rotational speed control means by the inverter and mechanical capacity control means by the capacity control valve independently or combined together according to loads. The maximum efficient point in a capacity control performed solely by the inverter is set to a rotational speed side lower than the rated operation point. In a region where the rotational speed is higher than the maximum efficient point, the inverter solely takes control from a rated rotational speed to a high rotational speed side.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a screw compressor, and in particular, relates to a screw compressor suitable for a screw chiller.

[0002] As a screw compressor used for a conventional refrigerating apparatus, there is the one disclosed in JP-A-59-211790. A scroll wrap compressor of JP-A-59-211790 operates to vary a ratio of volume by performing an unload control with a capacity control valve (slide valve) in the capacity control range of 100% to 75% of a refrigerating capacity. Further, in the capacity control range of 75% to 37.5% of the refrigerating capacity, the scroll wrap compressor increases the rotational speed of the screw compressor by 1.5 times by an inverter, and by using the capacity control valve in the range of 50% to 25% of the refrigerating capacity, can operate to vary the ratio of volume. Such operation can provide efficiency better than when operated under a 100% load.

[0003] Further, as another conventional screw compressor, there ...

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