Screw compressor

Abstract

A screw compressor includes an internal-volume-ratio variable mechanism including a variable Vi valve configured to make a Vi value being an internal volume ratio variable. The screw compressor controls a position of the variable Vi valve in two stages. The position of the variable Vi valve when the Vi value is set to be large is set to attain a Vi value with which a compressor efficiency during operation under a predetermined high-load condition or a predetermined high-compression-ratio condition is equal to or higher than a set efficiency set in advance.

1 . A screw compressor comprising an internal-volume-ratio variable mechanism including a variable Vi valve configured to make a Vi value being an internal volume ratio variable,
 wherein the screw compressor controls a position of the variable Vi valve in two stages, and   wherein, in an operation range of the compressor, the position of the variable Vi valve when the Vi value is set to be large is set to attain a Vi value with which a compressor efficiency during operation under a predetermined high-load condition or a predetermined high-compression-ratio condition is equal to or higher than a set efficiency set in advance.   
     
     
         2 . (canceled) 
     
     
         3 . The screw compressor of  claim 1 ,
 wherein the position of the variable Vi valve when the Vi value is set to be small is set to attain a Vi value with which a value obtained by multiplying each of coefficients of performance at top one to top three operation loads having large weights in a primary annual performance factor calculated by applying weights for four operation loads, by the weight corresponding to the operation load is equal to or greater than a set value set in advance.   
     
     
         4 . The screw compressor of  claim 1 ,
 wherein the internal-volume-ratio variable mechanism includes   a piston coupled to the variable Vi valve; and   a cylinder configured to house the piston,   wherein inside of the cylinder is divided into two spatial chambers by the piston, and   wherein the two spatial chambers are disposed as a cylinder chamber into which a discharge pressure is normally introduced and a cylinder chamber into which a suction pressure or a discharge pressure is introduced via a valve unit, in order of closeness to the variable Vi valve.   
     
     
         5 . The screw compressor of  claim 1 ,
 wherein the internal-volume-ratio variable mechanism includes   a piston coupled to the variable Vi valve; and   a cylinder configured to house the piston,   wherein inside of the cylinder is divided into two spatial chambers by the piston, and   wherein the two spatial chambers are disposed as a cylinder chamber into which a suction pressure or a discharge pressure is introduced via a valve unit and a cylinder chamber into which a suction pressure is normally introduced, in order of closeness to the variable Vi valve.   
     
     
         6 . The screw compressor of  claim 1 , wherein capacity control is performed by inverter rotation speed control. 
     
     
         7 . The screw compressor of  claim 1 , wherein the high-load condition is a condition where the load is highest, and the high-compression-ratio condition is a condition where the compression ratio is largest. 
     
     
         8 . The screw compressor of  claim 1 , wherein the set efficiency is 95% when the maximum efficiency is 100%.