Number-of-compressors controlling system

Abstract

A number-of-compressors controlling system which has a simple configuration and can produce compressed air by immediately following the load used of the compressed air is provided. The number-of-compressors controlling system has a plurality of compressors ( 2 ), a receiver tank ( 3 ) in which compressed air is supplied from these compressors ( 2 ) and is fed to a compressed air utilization device, a pressure sensor ( 4 ) provided on the receiver tank ( 3 ), and a number-of-compressors controller ( 5 ) which changes the number of compressors being operated based on the detected pressure of the pressure sensor ( 4 ). A number-of-compressors decreasing pressure as a threshold value whether or not the number of compressors being operated is decreased by the number-of-compressors controller ( 5 ) is set to be lower as the number of compressors being operated is larger.

1 . A number-of-compressors controlling system comprising:
 a plurality of compressors;   a pressure sensor which is provided in a position where compressed air is supplied from these compressors and is fed to a compressed air utilization device and detects the pressure of the compressed air; and   a number-of-compressors controller which changes the number of compressors being operated based on the detected pressure of the pressure sensor,   wherein a number-of-compressors decreasing pressure as a threshold value whether or not the number of compressors being operated is decreased by the number-of-compressors controller is set to be lower as the number of compressors being operated is larger.   
     
     
         2 . The number-of-compressors controlling system according to  claim 1 ,
 wherein a plurality of compressors are all capacity-controlled even when operated at the same time,   wherein in the case that a load rate at stop is 0% and a load rate at full load is 100%, one compressor being operated is stopped when the load rate of each of the compressors being operated is equal to or less than a stop load rate calculated by the following equation:
   the stop load rate (%)=(the number of compressors being operated−1)/the number of compressors being operated×100.
 
   
     
     
         3 . The number-of-compressors controlling system according to  claim 1 ,
 wherein each of the compressors is capacity-controlled so that the pressure on the discharge side thereof is maintained between a lower limit pressure PL and an upper limit pressure PH,   wherein to stop one compressor being operated at the stop load rate according to the number of compressors being operated, the number-of-compressors decreasing pressure is set by the following equation based on the number of compressors being operated:
   the number-of-compressors decreasing pressure={(the upper limit pressure  PH −the lower limit pressure  PL )÷the number of compressors being operated}+the lower limit pressure  PL.  
 
   
     
     
         4 . The number-of-compressors controlling system according to  claim 3 ,
 wherein the number of compressors being operated is decreased after the detected pressure of the pressure sensor continues to be equal to or greater than the number-of-compressors decreasing pressure for a set time.   
     
     
         5 . The number-of-compressors controlling system according to  claim 3 ,
 wherein compressed air from each of the compressors is supplied to a shared receiver tank and is then fed to one or a plurality of compressed air utilization devices,   wherein the pressure sensor is provided on the receiver tank,   wherein a number-of-compressors increasing pressure as a threshold value whether or not the number of compressors being operated is increased by the number-of-compressors controller is set to be different based on a pressure change rate ΔP of a detected pressure P of the pressure sensor,   wherein in the case that the absolute value of the pressure change rate ΔP is less than a first set value ΔP1, one compressor is started when the detected pressure P of the pressure sensor is equal to or less than a second lower limit pressure PL2 as the number-of-compressors increasing pressure,   wherein in the case that the absolute value of the pressure change rate ΔP is equal to or greater than the first set value ΔP1 and is less than a second set value ΔP2, one compressor is started when the detected pressure P of the pressure sensor is equal to or less than a first lower limit pressure PL1 as the number-of-compressors increasing pressure, when the detected pressure P is still maintained to be equal to or less than the first lower limit pressure PL1, one compressor is started each time a predetermined continuous start prevention time elapses, and when the detected pressure P is equal to or less than the second lower limit pressure PL2 lower than the first lower limit pressure PL1, one more compressor is started without waiting for the elapse of the continuous start prevention time,   wherein in the case that the absolute value of the pressure change rate ΔP is equal to or greater than the second set value ΔP2, one compressor is started when the detected pressure P of the pressure sensor is equal to or less than the upper limit pressure PH as the number-of-compressors increasing pressure, when the detected pressure P is still maintained to be equal to or less than the upper limit pressure PH, one compressor is started each time the predetermined continuous start prevention time elapses, and when the detected pressure P is equal to or less than the first lower limit pressure PL1 lower than the upper limit pressure PH, one more compressor is started without waiting for the elapse of the continuous start prevention time.   
     
     
         6 . The number-of-compressors controlling system according to  claim 1 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         7 . The number-of-compressors controlling system according to  claim 6 ,
 wherein the number-of-compressors controller monitors the electric current used or the electricity used of each of the compressors,   wherein the compressor with less electric current used or electricity used is operated on a priority basis.   
     
     
         8 . The number-of-compressors controlling system according to  claim 2 ,
 wherein each of the compressors is capacity-controlled so that the pressure on the discharge side thereof is maintained between a lower limit pressure PL and an upper limit pressure PH,   wherein to stop one compressor being operated at the stop load rate according to the number of compressors being operated, the number-of-compressors decreasing pressure is set by the following equation based on the number of compressors being operated:
   the number-of-compressors decreasing pressure={(the upper limit pressure  PH −the lower limit pressure  PL )÷the number of compressors being operated}+the lower limit pressure  PL.  
 
   
     
     
         9 . The number-of-compressors controlling system according to  claim 4 ,
 wherein compressed air from each of the compressors is supplied to a shared receiver tank and is then fed to one or a plurality of compressed air utilization devices,   wherein the pressure sensor is provided on the receiver tank,   wherein a number-of-compressors increasing pressure as a threshold value whether or not the number of compressors being operated is increased by the number-of-compressors controller is set to be different based on a pressure change rate ΔP of a detected pressure P of the pressure sensor,   wherein in the case that the absolute value of the pressure change rate ΔP is less than a first set value ΔP1, one compressor is started when the detected pressure P of the pressure sensor is equal to or less than a second lower limit pressure PL2 as the number-of-compressors increasing pressure,   wherein in the case that the absolute value of the pressure change rate ΔP is equal to or greater than the first set value ΔP1 and is less than a second set value ΔP2, one compressor is started when the detected pressure P of the pressure sensor is equal to or less than a first lower limit pressure PL1 as the number-of-compressors increasing pressure, when the detected pressure P is still maintained to be equal to or less than the first lower limit pressure PL1, one compressor is started each time a predetermined continuous start prevention time elapses, and when the detected pressure P is equal to or less than the second lower limit pressure PL2 lower than the first lower limit pressure PL1, one more compressor is started without waiting for the elapse of the continuous start prevention time,   wherein in the case that the absolute value of the pressure change rate ΔP is equal to or greater than the second set value ΔP2, one compressor is started when the detected pressure P of the pressure sensor is equal to or less than the upper limit pressure PH as the number-of-compressors increasing pressure, when the detected pressure P is still maintained to be equal to or less than the upper limit pressure PH, one compressor is started each time the predetermined continuous start prevention time elapses, and when the detected pressure P is equal to or less than the first lower limit pressure PL1 lower than the upper limit pressure PH, one more compressor is started without waiting for the elapse of the continuous start prevention time.   
     
     
         10 . The number-of-compressors controlling system according to  claim 2 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         11 . The number-of-compressors controlling system according to  claim 3 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         12 . The number-of-compressors controlling system according to  claim 4 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         13 . The number-of-compressors controlling system according to  claim 5 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         14 . The number-of-compressors controlling system according to  claim 9 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         15 . The number-of-compressors controlling system according to  claim 10 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         16 . The number-of-compressors controlling system according to  claim 11 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         17 . The number-of-compressors controlling system according to  claim 12 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.   
     
     
         18 . The number-of-compressors controlling system according to  claim 13 ,
 wherein the number-of-compressors controller changes the number of compressors being operated based on the discharge flow rate of compressed air from each of the compressors, or the rotating speed, the electric current used, or the electricity used of each of the compressors, in addition to the detected pressure of the pressure sensor.