Heat pump

Abstract

A heat pump of the present invention has a compressor and an expander coupled with a common axis of rotation, a first throttling device disposed in a circulation passage of refrigerant, and a second throttling device disposed in a bypass passage diverted from the expander. A control device controls the openings of these throttling devices. The control device executes a first controlling in which the opening of the first throttling device is adjusted in order to bring a high pressure PH in a refrigeration cycle close to a predetermined value determined based on a value at which the coefficient of performance (COP) of the heat pump is optimized, and after the first controlling is completed, it executes a second controlling in which the opening of the second throttling device is adjusted in order to bring a degree of superheat SH close to a predetermined positive value. This ensures smooth and stable operations of the heat pump.

1 . A heat pump comprising: 
 a compressor; a radiator; an expander; and an evaporator;    a piping that forms a circulation passage in which refrigerant circulates through the compressor, the radiator, the expander, and the evaporator in that order, and a bypass passage in which the refrigerant flows from the radiator to the evaporator without flowing through the expander;    a first throttling device having a variable opening and disposed in the circulation passage between the radiator and the expander or between the expander and the evaporator;    a second throttling device having a variable opening and disposed in the bypass passage; and    a control device for adjusting the opening of the first throttling device and the opening of the second throttling device, wherein    the compressor and the expander are connected to a common rotation shaft; and    the control device executes a first controlling in which, when the difference between a high pressure PH of the refrigerant circulating in the circulation passage and a predetermined value PH T  determined based on a value at which a coefficient of performance of the heat pump is optimized is outside a predetermined range PH DR , the opening of the second throttling device is varied so that the absolute value of the difference between the pressure PHI and the predetermined value PH T  becomes smaller; and    after completing the first controlling, the control device executes a second controlling in which, when the difference between a degree of superheat SH of the refrigerant flowing into the compressor and a predetermined positive value SH T  is outside a predetermined range SH DR , the opening of the first throttling device is varied so that the absolute value of the difference between the degree of superheat SH and the predetermined value SH T  becomes smaller.    
   
   
       2 . The heat pump according to  claim 1 , wherein, in the first controlling, the control device varies the opening of the second throttling device so that the difference between the pressure PH and the predetermined value PH T  falls within the predetermined range PH DR .  
   
   
       3 . The heat pump according to  claim 1 , wherein, in the second controlling, the control device varies the opening of the first throttling device so that the difference between the degree of superheat SH and the predetermined value SH T  falls within the predetermined range SH DR .  
   
   
       4 . The heat pump according to  claim 1 , wherein, after completing the second controlling, the control device further executes the first controlling when the difference between the pressure PH and the predetermined value PH T  is outside the predetermined range PH DR .  
   
   
       5 . The heat pump according to  claim 1 , wherein, in the first controlling, 
 when the pressure PH is higher than the predetermined value PH T  and the difference between the pressure PH and the predetermined value PH T  is outside the predetermined range PH DR , the opening of the second throttling device is increased, and    when the pressure PH is lower than the predetermined value PH T  and the difference between the pressure PH and the predetermined value PH T  is outside the predetermined range PH DR , the opening of the second throttling device is decreased.    
   
   
       6 . The heat pump according to  claim 1 , wherein, in the second controlling, 
 when the degree of superheat SH is higher than the predetermined value SH T  and the difference between the degree of superheat SH and the predetermined value SH T  is outside the predetermined range SH DR , the opening of the first throttling device is increased, and    when the degree of superheat SH is lower than the predetermined value SH T  and the difference between the degree of superheat SH and the predetermined value SH T  is outside the predetermined range SH DR , the opening of the first throttling device is decreased.    
   
   
       7 . The heat pump according to  claim 1 , wherein the predetermined value SH T  is set at a numerical value that is within a range higher than 0° C. but lower than or equal to 20° C.  
   
   
       8 . The heat pump according to  claim 1 , further comprising, in order to specify the degree of superheat SH, a first sensor for detecting a temperature of the refrigerant flowing into the compressor, and a second sensor for detecting a temperature of the refrigerant in the evaporator.  
   
   
       9 . The heat pump according to  claim 1 , further comprising a pressure sensor for detecting a pressure of the refrigerant discharged from the compressor in order to specify the pressure PH.  
   
   
       10 . The heat pump according to  claim 1 , further comprising, in order to specify the pressure PH, a third sensor for detecting a temperature outside the heat pump system, and a fourth sensor for detecting a temperature of the refrigerant discharged from the compressor.  
   
   
       11 . The heat pump according to  claim 1 , wherein the control device determines whether or not the difference between the pressure PH and the predetermined value PH T  is within the predetermined range PH DR  by comparing a predetermined characteristic RP associated with the pressure PH and a predetermined value RP T  concerning the characteristic RP, the predetermined value RP T  being associated with the predetermined value PH T , without directly comparing the pressure PH and the predetermined value PH T .  
   
   
       12 . The heat pump according to  claim 1 , wherein, when the pressure PH exceeds a predetermined limit pressure or when the temperature of the refrigerant discharged from the compressor exceeds a predetermined limit temperature, the control device varies at least one opening selected from the opening of the first throttling device and the opening of the second throttling device beyond the variation ranges of the openings in the first controlling and the second controlling.  
   
   
       13 . The heat pump according to  claim 1 , wherein the compressor compresses the refrigerant so that the refrigerant discharged from the compressor is in a supercritical state.