Refrigeration cycle apparatus

Abstract

A refrigeration cycle apparatus ( 100 ) includes: a first compressor ( 101 ); a second compressor ( 102 ) connected in parallel with the first compressor ( 101 ) in a refrigerant circuit ( 200 ); a radiator ( 103 ) for cooling a refrigerant compressed by the first and second compressors; an expander ( 104 ) coupled to a rotation shaft of the first compressor ( 101 ); an evaporator ( 105 ) for evaporating the refrigerant expanded by the expander ( 104 ); and a controller ( 115 ). The controller ( 115 ) includes an efficiency enhancing means for performing a first process including a step of changing a rotation speed of the first compressor ( 101 ), as a process for increasing a coefficient of performance (COP) of the refrigeration cycle apparatus ( 100 ), when a temperature of a heat carrier flowing into the radiator ( 103 ) is in a predetermined temperature range, and for performing a second process including a step of changing a rotation speed of the second compressor ( 102 ), as a process for increasing the coefficient of performance, when the temperature of the heat carrier flowing into the radiator ( 103 ) is not in the predetermined temperature range.

1 . A refrigeration cycle apparatus comprising:
 a first compressor;   a second compressor connected in parallel with the first compressor in a refrigerant circuit;   a radiator for cooling a refrigerant compressed by the first and second compressors;   an expander coupled to a rotation shaft of the first compressor;   an evaporator for evaporating the refrigerant expanded by the expander; and   a controller including an efficiency enhancing means for performing a first process including a step of changing a rotation speed of the first compressor, as a process for increasing a coefficient of performance of the refrigeration cycle apparatus, when a temperature of a heat carrier to be heated in the radiator is in a predetermined temperature range, and for performing a second process including a step of changing a rotation speed of the second compressor, as a process for increasing the coefficient of performance, when the temperature of the heat carrier to be heated in the radiator is not in the predetermined temperature range.   
     
     
         2 . The refrigeration cycle apparatus according to  claim 1 , wherein the predetermined temperature range is a temperature range that is determined corresponding to an ambient temperature of the evaporator. 
     
     
         3 . The refrigeration cycle apparatus according to  claim 2 , wherein the predetermined temperature range further is a temperature range that is determined corresponding to the rotation speed of the second compressor in the first process and to the rotation speed of the first compressor in the second process. 
     
     
         4 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the step of changing the rotation speed of the first compressor is a step of changing the rotation speed of the first compressor so that a pressure Pd of the refrigerant on a high pressure side of a refrigeration cycle approaches an optimum high pressure Pm at which the coefficient of performance can be maximized, and   the step of changing the rotation speed of the second compressor is a step of changing the rotation speed of the second compressor so that a density ratio Q between a density ρe of the refrigerant at an inlet of the expander and a density ρc of the refrigerant at an inlet of the compressor approaches an optimum density ratio Qm at which the coefficient of performance can be maximized.   
     
     
         5 . The refrigeration cycle apparatus according to  claim 4 , wherein
 in the first process, the efficiency enhancing means compares the pressure Pd and the optimum high pressure Pm to judge whether or not the current pressure Pd needs to be changed, and increases the rotation speed of the first compressor when the pressure Pd is excessively low and decreases the rotation speed of the first compressor when the pressure Pd is excessively high, and   in the second process, the efficiency enhancing means compares the density ratio Q and the optimum density ratio Qm to judge whether or not the current density ratio Q needs to be changed, and increases the rotation speed of the second compressor when the density ratio Q is excessively small and decreases the rotation speed of the second compressor when the density ratio Q is excessively large.   
     
     
         6 . The refrigeration cycle apparatus according to  claim 5 , wherein the controller further includes an initializing means for setting initial rotation speeds of the first compressor and the second compressor so that the refrigeration cycle apparatus can provide a required capacity, on the condition that the controller receives a starting trigger to start up the refrigeration cycle apparatus. 
     
     
         7 . The refrigeration cycle apparatus according to  claim 1 , further comprising a radiator outlet temperature sensor for detecting a temperature of the refrigerant at an outlet of the radiator,
 wherein the temperature of the heat carrier to be heated in the radiator is detected indirectly based on the temperature detected by the radiator outlet temperature sensor.   
     
     
         8 . The refrigeration cycle apparatus according to  claim 1 , further comprising an injection circuit including a flow control valve, the injection circuit connecting an outlet of the radiator to an intermediate pressure portion of the expander through the flow control valve,
 wherein the second process further includes a step of changing an opening of the flow control valve.