Expansion-valve control device, heat-source unit, and expansion-valve control method

Abstract

The degree-of-opening of an expansion valve is set to an appropriate degree-of-opening regardless of the load and external conditions for a heat-source unit. In a turbo refrigerator including a compressor that compresses a refrigerant; a condenser that condenses a compressed refrigerant by means of cooling water; an evaporator that evaporates a condensed refrigerant and also performs heat exchange between this refrigerant and cold water; and an expansion valve that causes a liquid-phase refrigerant retained in the condenser to expand, a expansion-valve control device ( 40 ) controls a degree-of-opening of the expansion valve ( 18 ). Also, the expansion-valve control device ( 40 ) calculates a degree-of-opening of the expansion valve ( 18 ) based on the difference between a target degree of a superheating for the refrigerant to be taken into the turbo compressor and a measured degree of superheating; calculates a degree-of-opening of the expansion valve ( 18 ) based on a planned CV value serving as an estimated value of a flow volume of the refrigerant that is allowed to pass through the expansion valve ( 18 ); and calculates an expansion-valve degree-of-opening command value from the above-described two types of the degree-of-opening calculated for the expansion valve ( 18 ).

1 . An expansion-valve control device that, in a heat-source unit including a compressor that compresses a refrigerant; a condenser that condenses a compressed refrigerant by means of a heat-source medium; an evaporator that evaporates a10 condensed refrigerant and also performs heat exchange between the refrigerant and a heating medium; and an expansion valve that causes a liquid-phase refrigerant retained in the condenser to expand, controls a degree-of-opening of the expansion valve, the expansion-valve control device comprising:
 a first calculating portion that calculates a degree-of-opening of the expansion valve based on the difference between a target value of a degree of superheating for the refrigerant to be taken into the compressor and a measured value of the degree of superheating;   a second calculating portion that calculates a degree-of-opening of the expansion valve based on an estimated value of a flow volume of the refrigerant that is allowed to pass through the expansion valve; and   a command-value calculating portion that calculates a command value for controlling the degree-of-opening of the expansion valve from the degree-of-opening of the expansion valve calculated by the first calculating portion and the degree-of-opening of the expansion valve calculated by the second calculating portion.   
     
     
         2 . An expansion-valve control device according to  claim 1 , wherein the target value of the degree of superheating is calculated based on the temperature of the heating medium that flows into the evaporator. 
     
     
         3 . An expansion-valve control device according to  claim 2 , wherein the target value of the degree of superheating is calculated so as to take a greater value with a decrease in the temperature of the heating medium that flows into the evaporator. 
     
     
         4 . An expansion-valve control device according to  claim 1 , wherein the flow volume is calculated based on at least one of the temperature of the heating medium that flows into the evaporator and the temperature of the heat-source medium that flows into the condenser. 
     
     
         5 . An expansion-valve control device according to  claim 4 , wherein the flow volume is calculated so as to take a smaller value with a decrease in the temperature of the heating medium that flows into the evaporator and so as to take a greater value with a decrease in the temperature of the heat-source medium that flows into the condenser. 
     
     
         6 . An expansion-valve control device according to  claim 1 ,
 wherein the heat-source unit is provided with a bypass pipe that forms a bypass path between a refrigerant intake port of the compressor and a refrigerant exhaust port of the compressor; and   wherein the measured value of the degree of superheating is calculated based on the temperature of the heating medium that has flowed out from the evaporator and the pressure of the refrigerant to be compressed at the compressor.   
     
     
         7 . A heat-source unit comprising:
 a compressor that compresses a refrigerant;   a condenser that condenses a compressed refrigerant by means of a heat-source medium;   an evaporator that evaporates a condensed refrigerant and also performs heat exchange between the refrigerant and a heating medium;   an expansion valve that causes a liquid-phase refrigerant retained in the condenser to expand; and   an expansion-valve control device according to  claim 1 .   
     
     
         8 . An expansion-valve control method of controlling, in a heat-source
 unit including a compressor that compresses a refrigerant; a condenser that condenses a compressed refrigerant by means of a heat-source medium; an evaporator that evaporates a condensed refrigerant and also performs heat exchange between this refrigerant and a heating medium; and an expansion valve that causes a liquid-phase refrigerant retained in the condenser to expand, a degree-of-opening of the expansion valve, the expansion-valve control method comprising:   a first step of calculating a degree-of-opening of the expansion valve based on the difference between a target value of a degree of superheating for the refrigerant to be taken into the compressor and a measured value of the degree of superheating;   a second step of calculating a degree-of-opening of the expansion valve based on an estimated value of a flow volume of the refrigerant that is allowed to pass through the expansion valve; and   a third step of calculating a command value for controlling the degree-of-opening of the expansion valve from the degree-of-opening of the expansion valve calculated in the first step and the degree-of-opening of the expansion valve calculated in the second step.