Refrigeration cycle apparatus and method of controlling refrigeration cycle apparatus

Abstract

A predicted value of a condensing temperature of refrigerant and a predicted value of an evaporating temperature of the refrigerant after a compressor is started or after an operating capacity of the compressor is changed are calculated based on a condensor suction air temperature, an evaporator suction air temperature, and a compressor operating capacity. Then, an opening degree to be set for an expansion valve is determined based on the predicted value, the predicted value, and the compressor operating capacity.

1 . A refrigeration cycle apparatus for circulating refrigerant through a circuit in which a compressor having a changeable operating capacity, a condensor, an expansion valve having a changeable opening degree, and an evaporator are connected to each other by pipes, the refrigeration cycle apparatus comprising:
 a first temperature sensor for detecting a temperature of a heat medium to be subjected to heat exchange with the refrigerant in the condensor;   a second temperature sensor for detecting a temperature of a heat medium to be subjected to heat exchange with the refrigerant in the evaporator; and   a controller for controlling the operating capacity of the compressor and the opening degree of the expansion valve,   the controller being configured to, when starting the compressor or when changing the operating capacity of the compressor
 calculate a first temperature, which is a condensing temperature of the refrigerant, and a second temperature, which is an evaporating temperature of the refrigerant, being predicted after the compressor is started or after the operating capacity of the compressor is changed, based on a detection value of the first temperature sensor, a detection value of the second temperature sensor, and a setting value (VP) of the operating capacity to be set for the compressor and 
 set the opening degree of the expansion valve based on the first temperature, the second temperature, the setting value (VP) of the operating capacity to be set for the compressor, and a refrigerant density of the refrigerant being in a liquid state. 
   
     
     
         2 . The refrigeration cycle apparatus of  claim 1 , wherein the controller is configured to, when an actual measured value of the evaporating temperature in the evaporator is less than a predicted value (Te*) of the evaporating temperature,
 calculate a predicted value (ΔP*) of a pressure difference between a condensing pressure of the condensor and an evaporating pressure of the evaporator based on a predicted value (Tc*) of the condensing temperature and the predicted value (Te*) of the evaporating temperature and   correct the opening degree to be set for the expansion valve based on an actual measured value (ΔP) of the pressure difference between the condensing pressure of the condensor and the evaporating pressure of the evaporator and on the predicted value (ΔP*) of the pressure difference.   
     
     
         3 . The refrigeration cycle apparatus of  claim 1 , further comprising a third temperature sensor for detecting a discharge temperature of the refrigerant discharged from the compressor,
 wherein the controller is configured to
 calculate a target value (Tdm) for the discharge temperature of the refrigerant to be discharged from the compressor based on a predicted value (Tc*) of the condensing temperature, the predicted value (Te*) of the evaporating temperature, and the setting value (VP) of the operating capacity to be set for the compressor and 
 correct the opening degree to be set for the expansion valve based on a difference between a detection value of the third temperature sensor and the target value (Tdm) for the discharge temperature. 
   
     
     
         4 . The refrigeration cycle apparatus of  claim 1 , wherein the controller is configured to
 calculate a target value (Tdm) for a discharge temperature of the refrigerant to be discharged from the compressor based on a predicted value (Tc*) of the condensing temperature, the predicted value (Te*) of the evaporating temperature, and the setting value (VP) of the operating capacity to be set for the compressor and   correct, when the target value (Tdm) for the discharge temperature is more than a maximum value set in advance, the opening degree to be set for the expansion valve based on a difference between the maximum value and the target value (Tdm) for the discharge temperature.   
     
     
         5 . The refrigeration cycle apparatus of  claim 1 , wherein the refrigerant has a higher ratio of specific heat than R410A. 
     
     
         6 . A method of controlling a refrigeration cycle apparatus for circulating refrigerant through a circuit in which a compressor having a changeable operating capacity, a condensor, an expansion valve having a changeable opening degree, and an evaporator are connected to each other by pipes, the method comprising, when the compressor is started or when the operating capacity of the compressor is changed:
 a step of acquiring a setting value (VP) of the operating capacity to be set for the compressor;   a first temperature detection step of detecting a temperature of a heat medium to be subjected to heat exchange with the refrigerant in the condensor;   a second temperature detection step of detecting a temperature of a heat medium to be subjected to heat exchange with the refrigerant in the evaporator;   a step of calculating a first temperature, which is a condensing temperature of the refrigerant, and a second temperature, which is an evaporating temperature of the refrigerant, being predicted after the compressor is started or after the operating capacity of the compressor is changed, based on a detection value acquired in the first temperature detection step, a detection value acquired in the second temperature detection step, and the setting value (VP) of the operating capacity to be set for the compressor; and   a step of setting the opening degree of the expansion valve based on the first temperature, the second temperature, the setting value (VP) of the operating capacity to be set for the compressor, and a refrigerant density of the refrigerant being in a liquid state.   
     
     
         7 . A refrigeration cycle apparatus for circulating refrigerant through a circuit in which a compressor, a condensor, an expansion valve having a changeable opening degree, and an evaporator are connected to each other by pipes, the refrigeration cycle apparatus comprising:
 a controller for controlling the opening degree of the expansion valve,   the controller being configured to, when starting the compressor,
 make the opening degree of the expansion valve when the refrigerant at an inlet of the expansion valve is in a two-phase gas-liquid state larger than the opening degree of the expansion valve when the refrigerant at the inlet of the expansion valve is in a liquid state.