Refrigeration cycle apparatus

Abstract

A refrigeration cycle apparatus 100 includes a low-pressure compressor 113 , a high-pressure compressor 101 , a radiator 103 , a gas-liquid separator 107 , an expansion valve 109 , an expander 105 and an evaporator 111 . The low-pressure compressor 113 and the expander 105 are coupled by a shaft 116 , and the low-pressure compressor 113 is driven using power recovered by the expander 105 from a refrigerant. The low-pressure compressor 113 and the high-pressure compressor 101 are serially connected by an intermediate-pressure flow path 114 . The gas-liquid separator 107 and the intermediate-pressure flow path 114 are connected by the reciprocating flow path 115 . The reciprocating flow path 115 is configured to allow the refrigerant to circulate bidirectionally. It is possible to regulate the refrigerant flow rate in the reciprocating flow path 115 by controlling the opening degree of the expansion valve 109.

1 . A refrigeration cycle apparatus comprising:
 a positive displacement low-pressure compressor for pre-compressing a refrigerant;   a high-pressure compressor for further compressing the refrigerant that has been pre-compressed in the low-pressure compressor;   an intermediate-pressure flow path serially connecting the low-pressure compressor and the high-pressure compressor so as to allow the refrigerant that has been pre-compressed in the low-pressure compressor to be delivered to the high-pressure compressor;   a radiator for cooling the refrigerant that has been compressed in the high-pressure compressor;   a positive displacement expander for recovering power by allowing the refrigerant to expand, the expander being coaxially coupled to the low-pressure compressor for power transmission and configured to allow the entire amount of the refrigerant that has been cooled in the radiator to pass through itself;   a gas-liquid separator for separating the refrigerant that has been expanded in the expander into gas refrigerant and liquid refrigerant;   an evaporator for allowing the liquid refrigerant that has been separated in the gas-liquid separator to evaporate;   an expansion valve with variable opening degree, the expansion valve being provided on a flow path between a liquid refrigerant outlet of the gas-liquid separator and an inlet of the evaporator;   a reciprocating flow path connecting the intermediate-pressure flow path and the gas-liquid separator so as to allow switching between a first circulation state in which the refrigerant stored in the gas-liquid separator is introduced into an inlet of the high-pressure compressor without passing through the evaporator and the low-pressure compressor and a second circulation state in which a part of the refrigerant that has been pre-compressed in the low-pressure compressor flows back to the gas-liquid separator; and   a controller for regulating refrigerant flow rate in the reciprocating flow path in each state of the first circulation and the second circulation by controlling the opening degree of the expansion valve.   
     
     
         2 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the low-pressure compressor and the expander each have a constant cylinder volume, and   the cylinder volume of the low-pressure compressor is greater than the cylinder volume of the expander.   
     
     
         3 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the controller includes:
 a means for calculating a target intermediate pressure at which theoretical recovery power of the expander at an arbitrary optimal high pressure of a refrigeration cycle and theoretical compression work of the low-pressure compressor at the arbitrary optimal high pressure are equal; and 
 a means for controlling the opening degree of the expansion valve so that an actual pressure inside the gas-liquid separator approaches the calculated target intermediate pressure. 
   
     
     
         4 . The refrigeration cycle apparatus according to  claim 3 , further comprising:
 a first temperature sensor for detecting an inlet refrigerant temperature of the expander;   a second temperature sensor for detecting a refrigerant evaporation temperature of the evaporator; and   a third temperature sensor for detecting an inlet refrigerant temperature of the low-pressure compressor, wherein
 the controller calculates the arbitrary optimal high pressure and the target intermediate pressure based on the detection results of the first to the third temperature sensors. 
   
     
     
         5 . The refrigeration cycle apparatus according to  claim 4 , further comprising:
 a fourth temperature sensor for detecting a refrigerant temperature in the gas-liquid separator, wherein
 the means for controlling the opening degree of the expansion valve calculates the actual pressure inside the gas-liquid separator based on a detection result of the fourth temperature sensor. 
   
     
     
         6 . The refrigeration cycle apparatus according to  claim 1 , wherein
 assuming that a suction volume of the expander is V ex , a suction volume of the low-pressure compressor is V lc , a degree of dryness of a discharge refrigerant of the expander is Q exo , a suction refrigerant density of the expander is ρ exi  and a suction refrigerant density of the low-pressure compressor is ρ lci , a relationship expressed by the following formula 1 is satisfied:
   (1 −Q   exo )×(ρ exi /ρ lci )≦( V   lc   /V   ex )  (1).
 
   
     
     
         7 . The refrigeration cycle apparatus according to  claim 1 , wherein
 assuming that a suction volume of the expander is V ex , a suction volume of the low-pressure compressor is V lc , a suction refrigerant density of the expander is ρ exi  and a suction refrigerant density of the low-pressure compressor is ρ lci , a relationship expressed by the following formula 2 is satisfied:
   ( V   lc   /V   ex )≦(ρ exi /ρ lci )  (2).
 
   
     
     
         8 . The refrigeration cycle apparatus according to  claim 1 , wherein
 assuming that a suction volume of the expander is V ex , a suction volume of the low-pressure compressor is V lc , a degree of dryness of a discharge refrigerant of the expander is Q exo , a suction refrigerant density of the expander is ρ exi  and a suction refrigerant density of the low-pressure compressor is ρ lci ,   
       a relationship expressed by the following formula 3 is satisfied:
   (1 −Q   exo )×(ρ exi /ρ lci )≦( V   lc   /V   ex )≦(ρ exi /ρ lci )  (3).
 
 
     
     
         9 . The refrigeration cycle apparatus according to  claim 1 , further comprising:
 an expander injection path connecting a suction path of the expander and an expander injection port opening into an expansion chamber of the expander; and   an expander injection valve provided on the expander injection path, wherein
 the expander is capable of changing its suction volume by controlling the expander injection valve. 
   
     
     
         10 . The refrigeration cycle apparatus according to  claim 1 , wherein the low-pressure compressor and the expander are disposed in a common closed casing. 
     
     
         11 . A multi-functional heat pump system comprising:
 a heat pump water heater with a water-heating function for supplying heated water to a tap and/or a floor-heating function for heating indoor space by circulating heated water in a pipe running throughout a floor of a house; and   an air-conditioner configured to adjust an indoor temperature by heat exchange between indoor air and a refrigerant, wherein
 the refrigeration cycle apparatus according to  claim 1  is used as a common refrigeration cycle apparatus for the water heater and the air-conditioner.