Patent Publication Number: US-2023160616-A1

Title: REFRIGERATION CYCLE APPARATUS AND METHOD FOR CONTROLLING REFRIGERATION CYCLE APPARATUS [as amended]

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of International Patent Application No. PCT/JP2020/021779 filed on Jun. 2, 2020, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a refrigeration cycle apparatus and a method for controlling a refrigeration cycle apparatus. 
     BACKGROUND 
     For a refrigeration cycle apparatus, a coefficient of performance (COP) is used as an index representing the performance of the refrigeration cycle apparatus. The COP having a larger value means that a larger refrigeration capacity is achieved with smaller consumed compression power. As a method of improving the value of the COP for a refrigeration cycle apparatus, a method of increasing the degree of superheat (the degree of suction superheat) of the refrigerant suctioned into a compressor has been known. 
     There has conventionally been a refrigeration cycle apparatus using R32 as refrigerant. In the refrigeration cycle apparatus using R32, however, the value of the COP tends to decrease when the degree of suction superheat is increased. 
     In order to solve such a problem, a refrigeration cycle apparatus using R290 (propane) as refrigerant has been proposed. It is considered that R290 allows the degree of suction superheat to increase and also allows the value of the COP to be improved. For example, PTL 1 discloses a refrigeration cycle apparatus using R290 as refrigerant. 
     PATENT LITERATURE 
     PTL 1: WO2019/176053 
     In the refrigeration cycle apparatus using R290 (propane) as refrigerant, the value of the COP is increased by increasing the degree of suction superheat. 
     However, if the degree of suction superheat is increased too high, the value of the COP tends to become smaller, with the result that the performance of the refrigeration cycle apparatus degrades. 
     SUMMARY 
     The present disclosure has been made in order to solve the above-described problems, and an object of the present disclosure is to provide a refrigeration cycle apparatus that can be maximized in performance by adjusting the degree of suction superheat. 
     One refrigeration cycle apparatus according to the present disclosure is a refrigeration cycle apparatus using R290 as refrigerant, and includes a compressor, a condenser, an expansion valve, an evaporator, a refrigerant pipe, a heat absorber, a heat source, a branch pipe, and a flow rate regulating valve. The refrigerant pipe is connected to the compressor, the condenser, the expansion valve, the evaporator, and the compressor in sequential order, and the refrigerant flows through the refrigerant pipe. The heat absorber is provided in a portion of the refrigerant pipe, and the portion connects the evaporator and the compressor. The heat source is disposed in contact with the heat absorber and is higher in temperature than the refrigerant having flowed through the evaporator. The branch pipe is connected in parallel with the portion provided with the heat absorber in the refrigerant pipe. The flow rate regulating valve is provided in the branch pipe and configured to regulate a flow rate of the refrigerant. 
     Another refrigeration cycle apparatus according to the present disclosure is a refrigeration cycle apparatus including a compressor, a condenser, an expansion valve, and an evaporator, and includes a refrigerant pipe, a heat absorber, a heat source, and a branch pipe. The refrigerant pipe is connected to the compressor, the condenser, the expansion valve, the evaporator, and the compressor in sequential order, and refrigerant flows through the refrigerant pipe. The heat absorber is provided in a portion of the refrigerant pipe, and the portion connects the evaporator and the compressor. The heat source is disposed in contact with the heat absorber. The branch pipe is connected in parallel with the portion provided with the heat absorber in the refrigerant pipe. The refrigerant has a property that, as a degree of superheat of the refrigerant having flowed through the heat absorber increases, a coefficient of performance increases and subsequently decreases. The branch pipe is provided with a flow rate regulating valve configured to regulate a flow rate of the refrigerant. 
     According to one refrigeration cycle apparatus of the present disclosure, a heat absorber is provided in the portion between the evaporator and the compressor in the refrigerant pipe. The heat absorber is disposed in contact with the heat source. A branch pipe is connected in parallel with the portion provided with the heat absorber in the refrigerant pipe. The branch pipe is provided with a flow rate regulating valve configured to regulate a flow rate of the refrigerant. Thereby, the flow rate of the refrigerant flowing through the heat absorber can be regulated by the flow rate regulating valve, and thus, the degree of suction superheat of the refrigerant suctioned into the compressor can be adjusted. As a result, the value of the COP of the refrigeration cycle apparatus can be improved. 
     According to another refrigeration cycle apparatus of the present disclosure, a heat absorber is provided in a portion between the evaporator and the compressor in the refrigerant pipe. The heat absorber is disposed in contact with the heat source. A branch pipe is connected in parallel with the portion provided with the heat absorber in the refrigerant pipe. The branch pipe is provided with a flow rate regulating valve configured to regulate a flow rate of the refrigerant. The refrigerant has a property that, as the degree of superheat of the refrigerant having flowed through the heat absorber increases, the coefficient of performance increases and subsequently decreases. Thereby, the flow rate of the refrigerant flowing through the heat absorber can be regulated by the flow rate regulating valve, and thus, the degree of suction superheat of the refrigerant suctioned into the compressor can be adjusted. As a result, the value of the COP of the refrigeration cycle apparatus can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram showing an example of a refrigerant circuit of a refrigeration cycle apparatus according to an embodiment. 
         FIG.  2    is a Mollier diagram showing a relation between a refrigerant pressure and an enthalpy in the present embodiment. 
         FIG.  3    is a graph showing a relation between a COP and a degree of suction superheat in the present embodiment. 
         FIG.  4    is a diagram schematically showing an example of a heat source provided with a heat absorber in the present embodiment. 
         FIG.  5    is a diagram schematically showing another example of the heat source provided with the heat absorber in the present embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A refrigeration cycle apparatus according to an embodiment will be hereinafter described.  FIG.  1    shows an example of a refrigerant circuit of a refrigeration cycle apparatus  1 . As shown in  FIG.  1   , refrigeration cycle apparatus  1  includes a compressor  3 , a four-way valve  15 , a first heat exchanger  5 , an expansion valve  9 , and a second heat exchanger  11 . Refrigeration cycle apparatus  1  further includes a flow rate regulating valve  21 , a heat absorber  17 , and a heat source  19 . A first blower  7  is disposed in first heat exchanger  5 . A second blower  13  is disposed in second heat exchanger  11 . Further, as heat source  19 , an electric component  19   a  is disposed that accommodates a control circuit and the like for controlling the operation of refrigeration cycle apparatus  1 . 
     Compressor  3 , four-way valve  15 , first heat exchanger  5  (a condenser/an evaporator), expansion valve  9 , second heat exchanger  11  (an evaporator/a condenser), and compressor  3  are connected sequentially in this order by a refrigerant pipe  31  through which refrigerant flows. R290 (propane) is used as refrigerant flowing through refrigerant pipe  31  and the like. 
     Heat absorber  17  is provided in a portion of refrigerant pipe  31  between the evaporator (first heat exchanger  5  or second heat exchanger  11 ) and compressor  3 . Heat absorber  17  is disposed in contact with electric component  19   a  serving as a heat source. More specifically, heat absorber  17  is provided in a portion of refrigerant pipe  31  that connects four-way valve  15  and compressor  3 . A branch pipe  33  is connected in parallel with the portion provided with heat absorber  17  in refrigerant pipe  31 . Branch pipe  33  is provided with a flow rate regulating valve  21  configured to regulate the flow rate of the refrigerant. Refrigeration cycle apparatus  1  according to the present embodiment is configured as described above. 
     As an operation of refrigeration cycle apparatus  1  described above, a heating operation (see dotted arrows) will be first described. In this case, compressor  3 , four-way valve  15 , second heat exchanger  11 , expansion valve  9 , first heat exchanger  5 , four-way valve  15 , heat absorber  17 , and compressor  3  are connected sequentially in this order by refrigerant pipe  31 . By driving compressor  3 , high-temperature and high-pressure gas refrigerant is discharged from compressor  3 . The discharged high-temperature and high-pressure gas refrigerant (of a single phase) flows into second heat exchanger  11  through four-way valve  15 . In this case, second heat exchanger  11  functions as a condenser. 
     In second heat exchanger  11  functioning as a condenser, heat exchange is performed between the incoming gas refrigerant and the air supplied by second blower  13 . The high-temperature and high-pressure gas refrigerant is condensed into high-pressure liquid refrigerant (of a single phase). By this heat exchange, for example, a room is heated. The high-pressure liquid refrigerant delivered from second heat exchanger  11  is converted by expansion valve  9  into low-pressure gas-liquid two-phase refrigerant. The two-phase refrigerant flows into first heat exchanger  5 . In this case, first heat exchanger  5  functions as an evaporator. 
     In first heat exchanger  5  functioning as an evaporator, heat exchange is performed between the incoming two-phase refrigerant and the air supplied by first blower  7 . Then, liquid refrigerant is evaporated from the two-phase refrigerant, which results in low-pressure gas refrigerant (of a single phase). The low-pressure gas refrigerant delivered from first heat exchanger  5  passes through four-way valve  15  and flows into compressor  3  through heat absorber  17  or flow rate regulating valve  21 . The low-pressure gas refrigerant flowing into compressor  3  is compressed into high-temperature and high-pressure gas refrigerant, and then discharged from compressor  3  again. This cycle is thereafter repeated. The functions of flow rate regulating valve  21  and heat absorber  17  will be described later. 
     The following describes the case of a cooling operation (see solid arrows). In this case, compressor  3 , four-way valve  15 , first heat exchanger  5 , expansion valve  9 , second heat exchanger  11 , four-way valve  15 , heat absorber  17 , and compressor  3  are connected sequentially in this order by refrigerant pipe  31 . By driving compressor  3 , high-temperature and high-pressure gas refrigerant is discharged from compressor  3 . The discharged high-temperature and high-pressure gas refrigerant (of a single phase) flows into first heat exchanger  5  through four-way valve  15 . In this case, first heat exchanger  5  functions as a condenser. In first heat exchanger  5  functioning as a condenser, heat exchange is performed between the incoming refrigerant and the air supplied by first blower  7 . The high-temperature and high-pressure gas refrigerant is condensed into high-pressure liquid refrigerant (of a single phase). 
     The high-pressure liquid refrigerant delivered from first heat exchanger  5  is converted by expansion valve  9  into low-pressure gas-liquid two-phase refrigerant. The two-phase refrigerant flows into second heat exchanger  11 . In second heat exchanger  11 , heat exchange is performed between the incoming two-phase refrigerant and the air supplied by second blower  13 . Then, liquid refrigerant is evaporated from the two-phase refrigerant, which results in low-pressure gas refrigerant (of a single phase). By this heat exchange, for example, a room is cooled. 
     The low-pressure gas refrigerant delivered from second heat exchanger  11  passes through four-way valve  15  and flows into compressor  3  through heat absorber  17  or flow rate regulating valve  21 . The low-pressure gas refrigerant flowing into compressor  3  is compressed into high-temperature and high-pressure gas refrigerant, and then discharged from compressor  3  again. This cycle is thereafter repeated. 
     In the above-described refrigeration cycle apparatus  1  using R290 (propane) as refrigerant, the degree of suction superheat of the refrigerant suctioned into compressor  3  is adjusted, and thereby, the value of the COP can be improved, which will be hereinafter described. 
     First,  FIG.  2    shows the relation (a Mollier diagram) between the refrigerant pressure and the enthalpy (specific enthalpy) when refrigeration cycle apparatus  1  is operated to perform a cooling operation. The Mollier diagram also shows flow path points P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , and P 8  in refrigerant pipe  31  shown in  FIG.  1   . Note that each of the flow path points in parentheses indicates a flow path point set when refrigeration cycle apparatus  1  is operated to perform a heating operation. 
     During each of the heating operation and the cooling operation, in order to maintain the heat exchange performance of the evaporator (first heat exchanger  5 /second heat exchanger  11 ), the opening degree of expansion valve  9  provided upstream of the flow of the refrigerant with respect to the evaporator is adjusted such that the degree of dryness of the refrigerant having flowed out of the evaporator becomes approximately 1 (one). 
     The refrigerant having flowed out of the evaporator and having a degree of dryness of approximately 1 passes through four-way valve  15  and flows through branch pipe  33  into heat absorber  17 . Heat absorber  17  is in contact with electric component  19   a  as heat source  19 . In heat absorber  17 , heat exchange is performed between the incoming refrigerant and electric component  19   a  (heat). Thereby, the enthalpy rises while the refrigerant flows from flow path point P 6  to flow path point P 8 , and then, the degree of superheat of the refrigerant having flowed out of heat absorber  17  increases. 
     Thus, the refrigerant increased in degree of superheat with the degree of dryness of approximately 1 is suctioned into compressor  3 . 
       FIG.  3    shows the relation between the degree of suction superheat and the value of the COP. The horizontal axis represents the degree of suction superheat of the refrigerant suctioned into compressor  3 . The vertical axis represents the COP of refrigeration cycle apparatus  1 . A solid line graph A is a graph shown in the case of R290 (propane). A dotted line graph B is a graph shown in the case of R32 as a comparative example. The COP is represented by a ratio (%) with a score of 100 representing the peak value of the value of the COP in each refrigerant. 
     As shown by graph A, when the refrigerant is R290, the value of the COP gradually increases as the degree of suction superheat increases from 0 (K). On the other hand, as shown by graph B, when the refrigerant is R32, the value of the COP decreases as the degree of suction superheat increases from 0 (K). This shows that, in the case where the refrigerant is R290, the degree of suction superheat is increased and thereby the value of the COP can be improved. Examples of the refrigerant showing the same tendency as that of refrigerant R32 shown by graph B include HFC refrigerant. 
     In the case where the refrigerant is R290, however, the graph shows that the COP reaches a maximum value, for example, when the degree of suction superheat is about 7 (K), whereas the value of the COP becomes smaller as the degree of suction superheat increases beyond about 7 (K). In other words, in the case of R290, the performance of refrigeration cycle apparatus  1  can be improved by increasing the degree of suction superheat. However, when the degree of suction superheat becomes too high, the COP becomes smaller, with the result that the performance of refrigeration cycle apparatus  1  degrades. In actual refrigeration cycle apparatus  1 , the degree of suction superheat at which the COP reaches a maximum value depends on, for example, the efficiency or the like of compressor  3 . 
     Thus, in refrigeration cycle apparatus  1  as described above, the flow rate of the refrigerant flowing through heat absorber  17  is regulated by flow rate regulating valve  21  provided in branch pipe  33 , and thereby, the degree of suction superheat is adjusted. 
     When the degree of superheat of the refrigerant having flowed through heat absorber  17  is lower than the target degree of suction superheat at which the COP reaches the maximum value, flow rate regulating valve  21  is narrowed to increase the flow rate of the refrigerant that flows into heat absorber  17 . This increases the amount of heat exchange between electric component  19   a  (a heat source) and the refrigerant in heat absorber  17 , so that the degree of superheat of the refrigerant having flowed through heat absorber  17  can be increased to the target degree of suction superheat. 
     On the other hand, when the degree of superheat of the refrigerant having flowed through heat absorber  17  is higher than the target degree of suction superheat at which the COP reaches the maximum value, flow rate regulating valve  21  is opened to decrease the flow rate of the refrigerant that flows into heat absorber  17 . This decreases the amount of heat exchange between electric component  19   a  (a heat source) and the refrigerant in heat absorber  17 , so that the degree of superheat of the refrigerant having flowed through heat absorber  17  can be decreased to the target degree of suction superheat. 
     Thus, in refrigeration cycle apparatus  1  as described above, the degree of suction superheat of the refrigerant suctioned into compressor  3  is regulated by flow rate regulating valve  21 , and thereby, the performance of refrigeration cycle apparatus  1  can be maximized. 
     In refrigeration cycle apparatus  1  as described above, electric component  19   a  is cited as an example of heat source  19 . Heat source  19  is not limited to electric component  19   a  as long as it is higher in temperature than the refrigerant having flowed through the evaporator (first heat exchanger  5  or second heat exchanger  11 ). For example, as shown in  FIG.  4   , a compressor housing body  19   b  that accommodates compressor  3  may be applied as heat source  19 . Alternatively, as shown in  FIG.  5   , a housing  19 c that accommodates first heat exchanger  5 , second heat exchanger  11  or the like may be applied as heat source  19 . 
     Further, in the above description of refrigeration cycle apparatus  1 , R290 (propane) is cited as an example of refrigerant. The refrigerant is not limited to R290 and any type of refrigerant is applicable as long as the refrigerant has a property that, as the degree of superheat of the refrigerant having flowed through heat absorber  17  increases, the value of the COP of refrigeration cycle apparatus  1  increases and subsequently decreases. Also, the flow rate of the refrigerant flowing through heat absorber  17  is regulated by flow rate regulating valve  21 , and thereby, the performance of refrigeration cycle apparatus  1  can be maximized. 
     The embodiments disclosed herein are merely by way of example and not limited thereto. The present disclosure is defined by the scope of the claims, rather than the scope described above, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is effectively utilized for a refrigeration cycle apparatus using R290 or the like as refrigerant.