Control device of refrigerating cycle, heat source device, and control method therefor

Abstract

To provide a control device of a refrigerating cycle, a heat source device, and a control method therefor which are capable of realizing a stable low-load operation without using a hot gas bypass pipe. A centrifugal chiller includes a compressor compressing a refrigerant; a condenser condensing the refrigerant compressed by the compressor; an expansion valve expanding a liquid refrigerant delivered from the condenser; an evaporator evaporating the refrigerant expanded by the expansion valve; and a control device (10). The control device (10) includes a gas volume calculation unit (22) that calculates a current gas volume using a current actual cooling capacity; and a minimum gas volume calculation unit (23) that calculates a required minimum gas volume for the compressor using a parameter related to an operating condition of the compressor, in which if the current gas volume is less than the required minimum gas volume for the compressor, control is performed so as to increase an opening degree of the expansion valve.

1 . A control device of a refrigerating cycle including a compressor compressing a refrigerant, a condenser condensing the refrigerant compressed by the compressor, an expansion valve expanding a liquid refrigerant delivered from the condenser, and an evaporator evaporating the refrigerant expanded by the expansion valve, the control device comprising:
 a gas volume calculation unit that calculates a current gas volume using a current actual cooling capacity; and   a minimum gas volume calculation unit that calculates a required minimum gas volume for the compressor using a parameter related to an operating condition of the compressor,   wherein if the current gas volume is less than the required minimum gas volume for the compressor, the control device performs control so as to increase an opening degree of the expansion valve.   
     
     
         2 . The control device of a refrigerating cycle according to  claim 1 , further comprising:
 a reference command calculation unit that calculates a reference opening degree command value in response to a demanded cooling capacity;   a correction command calculation unit that calculates a correction opening degree command value in response to a difference between the current gas volume and the required minimum gas volume for the compressor; and   an opening degree command value calculation unit that calculates an opening degree command value of the expansion valve by adding the correction opening degree command value to the reference opening degree command value.   
     
     
         3 . The control device of a refrigerating cycle according to  claim 1 ,
 wherein the control device has opening degree command information in which an opening degree command value obtained by adding a correction opening degree command value for the required minimum gas volume for the compressor to a reference opening degree command value in response to a demanded cooling capacity is mapped to the demanded cooling capacity, and   wherein the control device determines an opening degree command value corresponding to a currently demanded cooling capacity, from the opening degree command information.   
     
     
         4 . The control device of a refrigerating cycle according to  claim 1 ,
 wherein the refrigerating cycle includes an economizer provided between the condenser and the evaporator, and the expansion valve includes a first expansion valve provided between the condenser and the economizer and a second expansion valve provided between the economizer and the evaporator, and   wherein if the current gas volume is less than the required minimum gas volume for the compressor, the control device performs control so as to increase an opening degree of the first expansion valve and an opening degree of the second expansion valve.   
     
     
         5 . A heat source device comprising:
 the control device of a refrigerating cycle according to  claim 1 .   
     
     
         6 . A control method of a refrigerating cycle including a compressor compressing a refrigerant, a condenser condensing the refrigerant compressed by the compressor, an expansion valve expanding a liquid refrigerant delivered from the condenser, and an evaporator evaporating the refrigerant expanded by the expansion valve, the method comprising:
 calculating a current gas volume using a current actual cooling capacity; and   calculating a required minimum gas volume for the compressor using a parameter related to an operating condition of the compressor,   wherein if the current gas volume is less than the required minimum gas volume for the compressor, control is performed so as to increase an opening degree of the expansion valve.