Patent Publication Number: US-2023135687-A1

Title: Heat pump

Description:
TECHNICAL FIELD 
     The present invention relates to a heat pump including an accumulator connected to a compressor. 
     BACKGROUND ART 
     Conventionally, it is known in a heat pump that if there is a liquid refrigerant around a compressor when the compressor gets started, it is concerned that the compressor is damaged by the liquid refrigerant. To suppress such a problem, a method of providing a heater on the compressor to warm up the compressor has been proposed (see, for example, Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Laid-Open Publication No. 2016-173201 
       
    
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     The heat pump disclosed in Patent Literature 1 is provided with a compressor and a heater for the compressor, and an alarm is notified when an energization duration period of the heater for the compressor elapses a predetermined time. In addition, an accumulator is provided in a suction path of the compressor. In the heat pump mentioned above, it is often the case where while a system is turned off, oil in the accumulator accumulates in a piping connecting the compressor and the accumulator via an orifice. In such an event, there is a problem that if turning on the heat pump, the oil accumulated in the piping flows into the compressor as an oil lump, so that it causes the compressor to be damaged. 
     The present invention is made to solve the problem mentioned above, and an object of the invention is to provide a heat pump capable of preventing a compressor from being damaged by delivering hot gas together with a refrigerant when turning on the system. 
     Means for Solving the Problems 
     A heat pump according to the present invention includes: a compressor; an oil separator provided in a discharge path of the compressor; and an accumulator connected to the compressor via a suction path, wherein a bypass circuit to deliver a gaseous refrigerant separated with the oil separator is provided, and the bypass circuit is connected to the suction path. 
     The heat pump according to the present invention may be configured such that a valve is provided in the bypass circuit, and the valve is controlled so that a degree of opening of the valve is decreased over time after the heat pump is started. 
     The heat pump according to the present invention may be configured such that a first piping to deliver oil separated with the oil separator to the compressor is provided, and the first piping is connected to the suction path above the accumulator in a vertical direction. 
     The heat pump according to the present invention may be configured such that the suction path has an upward extending part extending upward, a downward extending part extending downward, and a connection part to connect the upward extending part and the downward extending part, the upward extending part, the connection part, and the downward extending part are provided in the suction path in a stated order from an upstream side along a delivery direction of a refrigerant, and the first piping is connected to the upward extending part. 
     The heat pump according to the present invention may be configured such that the suction path has a plurality of paths and a branch part that connects to the plurality of paths, a second piping to return oil to the accumulator is connected to the branch part, and the second piping is connected to the suction path below the first piping in the vertical direction. 
     The heat pump according to the present invention may be configured such that a filter is housed in the branch part. 
     The heat pump according to the present invention may be configured such that an oil path through which oil delivered from the oil separator flows and an oil sensor to detect an amount of oil flowing through the oil path are provided, and the oil path is connected to the bypass circuit. 
     Effect of the Invention 
     According to the present invention, even if oil is stored in a piping of the accumulator when getting started, since the gaseous refrigerant flowing in from the bypass circuit is mixed with oil, this makes it possible to prevent oil from rushing into the compressor and damaging the same. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    shows a simplified circuit diagram of a refrigerant circuit of a heat pump according to an embodiment of the present invention. 
         FIG.  2    shows a schematically perspective view illustrating a structure in the vicinity of an accumulator and a suction path. 
         FIG.  3    shows a schematically side view illustrating a structure in the vicinity of the accumulator and the suction path. 
         FIG.  4    shows an explanatory diagram illustrating variations of a degree of opening of a bypass valve and a rotation speed of a compressor over time. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Now, a heat pump according to an embodiment of the present invention will be described below with reference to the drawings. 
       FIG.  1    is a simplified circuit diagram illustrating a refrigerant circuit of a heat pump according to an embodiment of the present invention. 
     The heat pump  1  has an outdoor unit to perform heat exchange with outdoor air and an indoor unit to perform heat exchange with indoor air. The outdoor unit includes compressors  2  (a first compressor  2   a , a second compressor  2   b , and a third compressor  2   c ), an oil separator  3 , a four-way valve  4 , an outdoor heat exchanger  5 , an accumulator  7 , and an outdoor expansion valve  11 . The indoor unit has an indoor heat exchanger  6  and an indoor expansion valve  12 . 
     The first compressor  2   a , the second compressor  2   b , and the third compressor  2   c  is driven with a driving source such as a gas engine, for example. The three compressors  2  are configured to be driven with a single gas engine via a belt or a flywheel, or each of them may be selectively driven by providing a clutch. The compressors  2  are not limited thereto, and they may be electric compressors which can be driven electrically. A discharge path of the first compressor  2   a  (first discharge path  41 ), a discharge path of the second compressor  2   b  (second discharge path  42 ), and a discharge path of the third compressor  2   c  (third discharge path  43 ) are integrated with a fluid merging part  44  into a single gas path  40 . 
     High temperature and high pressure gaseous refrigerant discharged from the compressors  2  are directed to the outdoor heat exchanger  5  or the indoor heat exchanger  6  with the four-way valve  4 . During a heating operation (solid line) the four-way valve  4  delivers the gaseous refrigerant to the indoor heat exchanger  6 , and during cooling operation (one-dot chain line) the four-way valve  4  delivers the gaseous refrigerant to the outdoor heat exchanger  5 . 
     During the heating operation, the indoor heat exchanger  6  transfers heat from the refrigerant to the indoor air and causes the gaseous refrigerant to change into a liquid state with low temperature and high pressure. Then, the refrigerant is delivered to the outdoor heat exchanger  5  via the indoor expansion valve  12  and the outdoor expansion valve  11 . A degree of opening of each of the indoor expansion valve  12  and the outdoor expansion valve  11  is controlled by a controller or the like where appropriate. 
     During the heating operation, the outdoor expansion valve  11  expands the liquid refrigerant and causes the liquid refrigerant to change into a liquid state (fog state) with low temperature and low pressure. Then, the outdoor heat exchanger  5  transfers heat from the outdoor air to the refrigerant and causes the refrigerant to change into a gaseous state with low temperature and low pressure. After passing through the outdoor heat exchanger  5 , the refrigerant passes through the four-way valve  4  and is delivered to a suction path  50  of the compressors  2 . 
     The accumulator  7  is provided in a path between the four-way valve  4  and the compressors  2 . The accumulator  7  temporarily stores the gaseous refrigerant. The gaseous refrigerant contains a small amount of a liquid refrigerant. These are separated in the accumulator  7 , and the liquid refrigerant is accumulated in the accumulator  7 . 
     The suction path  50  connecting the accumulator  7  and the compressors  2  has the branch part  51  connected to a plurality of paths and is branched into three paths (a first suction path  71 , a second suction path  72 , and a third suction path  73 ) via the branch part  51 . The first suction path  71 , the second suction path  72 , and the third suction path  73  are connected to the first compressor  2   a , the second compressor  2   b , and the third compressor  2   c , respectively. The structure in the vicinity of the suction path  50  will be described in detail with reference to  FIG.  2    later. 
     A filter  52  is housed in the branch part  51  to adsorb a foreign matter contained in the refrigerant. By providing the filter  52 , dirt from the refrigerant and oil can be removed as well as the refrigerant and the oil can be kept clean. In addition, a branch part  51  from which the path branches can handle multiple paths at a single location, this makes it possible to prevent extra filters  52  from being provided. 
     On the other hand, during a cooling operation, the high temperature and high pressure gaseous refrigerant discharged from the compressors  2  are delivered via the four-way valve  4  to the outdoor heat exchanger  5  which performs heat exchange with the outdoor air to bring the refrigerant into a low temperature and high pressure liquid state. The refrigerant having passed through the outdoor heat exchanger  5  is brought into a low temperature and low pressure liquid state (fog state) by passing through the indoor expansion valve  12 . Then, the refrigerant is delivered to the indoor heat exchanger  6  which performs heat exchange with the indoor air to bring the refrigerant into a low temperature and low pressure gaseous state. The refrigerant delivered from the indoor heat exchanger  6  is then delivered to the suction path  50  of the compressors  2  after passing through the four-way valve  4  and the accumulator  7 . 
     The oil separator  3  is provided between a discharge path of the compressors  2  and the four-way valve  4 . The oil separator  3  separates oil contained in the refrigerant. The oil separator  3  is connected to an oil return piping  20  (as an example of a first piping) for supplying the separated oil to the compressors  2 . The oil return piping  20  is branched into three pipings, a first oil return piping  21 , a second oil return piping  22 , and a third oil return piping  23 , which correspond to the first suction path  71 , the second suction path  72 , and the third suction path  73 , respectively. Specifically, the first oil return piping  21 , the second oil return piping  22 , and the third oil return piping  23  are connected to the first suction path  71 , the second suction path  72 , and the third suction path  73 , respectively. The first oil return piping  21 , the second oil return piping  22 , and the third oil return piping  23  may be each provided with a solenoid valve or the like to control a supply of oil separately. 
     The oil separator  3  is also connected to a bypass circuit  30  thorough which the separated gas refrigerant (hot gas) is delivered. The bypass circuit  30  is connected in the suction path  50  between the accumulator  7  and the branch part  51 . A bypass valve  13  (as an example of a valve), which controls the degree of valve opening and adjusts the flow rate of the gaseous refrigerant to be delivered, is provided in the bypass circuit  30 . 
     In addition, an oil path  60  independent of the oil return piping  20 , through which oil passes, is connected to the oil separator  3 . The oil path  60  is connected to the bypass circuit  30 , and by causing oil to pass through the oil path  60 , oil can be delivered to the filter  52  housed in the branch part  51 . By delivering an adequate amount of oil, performance of adsorbing debris of the filter  52  can be improved. An oil sensor  15  to detect the amount of oil passing through the oil path  60  and an oil valve  14  to control the delivery of oil are provided in the oil path  60 . By providing the oil path  60 , while the amount of oil can be detected by the oil sensor  15 , oil can be delivered to the filter through the bypass circuit  30 . 
     A second piping  53 , which returns oil to the accumulator  7 , is connected to the branch part  51 . Oil stored in the branch part  51  is delivered through the second piping  53  and accumulated in the accumulator  7 . 
     In the heat pump  1 , there is a case where oil is stored in the accumulator  7  while a system is turned off. According to this embodiment, the suction path  50  reaching the compressors  2  is connected to the bypass circuit  30 . Even if oil is stored in a piping of the accumulator  7  when getting started, since the gaseous refrigerant flowing in from the bypass circuit  30  is mixed with oil, this makes it possible to prevent oil from rushing into the compressors  2  and damaging the same. 
       FIG.  2    is a schematically perspective view illustrating a structure in the vicinity of the accumulator and the suction path, and  FIG.  3    is a schematically side view illustrating a structure in the vicinity of the accumulator and the suction path.  FIG.  3    shows the accumulator  7  in a transparent manner for the convenience of viewing. 
     The accumulator  7  encloses a U-shaped tube, and the refrigerant flowing into the accumulator  7  passes through the inside of the U-shaped tube. Oil delivered through the second piping  53  is once stored outside the U-shaped tube. An orifice (small hole) is provided on the lower side of the U-shaped tube, so that the refrigerant and oil stored outside the U-shaped tube are gradually drawn into the inside of the U-shaped tube through the orifice. A discharge port of the U-shaped tube is connected to the suction path  50  upside the accumulator  7 . 
     As mentioned above, the suction path  50  to deliver the refrigerant to the compressors  2  leads from the accumulator  7 . The suction path  50  has the branch part  51  located above the accumulator  7  in the vertical direction. The first suction path  71  leading from the branch part  51  has a first upward extending part  71   a  extending upward, a first downward extending part  71   c  extending downward, and a first connection part  71   b  connecting between the first upward extending part  71   a  and the first downward extending part  71   c . The first oil return piping  21  is connected to the first upward extending part  71   a . A shape of the first connection part  71   b  is not limited and may be variable to some extent in the vertical direction. 
     The first suction path  71  has the first upward extending part  71   a , the first connection part  71   b , and the first downward extending part  71   c  in the stated order along the refrigerant delivery direction between the upstream side where the branch part  51  is located and the downstream side where the first compressor  2   a  is located. Upon the system gets started, although the refrigerant (oil) flows along the delivery direction, but while the system is turned off, the refrigerant moves down by gravity. Namely, the refrigerant returns upstream at the first upward extending part  71   a , it does not move significantly at the first connection part  71   b , as well as it moves downstream at the first downward extending part  71   c . Therefore, while the compressors  2  are stopped, oil flowing into the first upward extending part  71   a  returns to the accumulator  7 , and thus it is possible to prevent oil from flowing into the compressors  2 . Furthermore, since oil flowing in through the first oil return piping  21  naturally flows downward, it is possible to prevent from producing an oil lump. 
     Furthermore, the second piping  53  is connected to the branch part  51  located below the oil return piping  20  (the first oil return piping  21 ) in the vertical direction. Accordingly, in a state where the compressors  2  are stopped, oil flowing in through the oil return piping  20  returns to the accumulator  7  through the branch part  51  and the second piping  53 . Namely, this makes it possible to be such a structure through which oil naturally returns without providing an additional power source. 
     Each of the second suction path  72  and the third suction path  73  has a shape substantially similar to the first suction path  71 , and the second suction path and the third suction path respectively have the second upward extending part  72   a  and the third upward extending part  73   a , which correspond to the first upward extending part  71   a , and the second connection part  72   b  and the third connection part  73   b , which correspond to the first connection part  71   b , as well as the second downward extending part  72   c  and the third downward extending part  73   c , which correspond to the first downward extending part  71   c . Since the flow of the refrigerant in the second suction path  72  and the third suction path  73  is the same as in the first suction path  71 , a detail explanation thereof is omitted except that they are configured so that oil can return to the accumulator  7  while the compressors  2  are stopped. 
     Next, the control of the degree of opening of the bypass valve  13  when the system gets started will be explained below with reference to  FIG.  4   . 
       FIG.  4    is an explanatory diagram illustrating variations of the degree of opening of the bypass valve and a rotation speed of a compressor over time. 
       FIG.  4    shows a degree of valve opening change characteristic line K 1 , which indicates a time-change in the degree of valve opening of the bypass valve  13 , and a rotation speed change characteristic line R 1 , which indicates a time-change in the rotation speed of the compressors  2 , and the horizontal axis represents a lapse of time. With respect to the degree of valve opening change characteristic line K 1 , the higher the vertical axis goes, the greater the degree of opening becomes, as well as with respect to the rotation speed change characteristic line R 1 , the higher the vertical axis goes, the greater the rotation speed becomes. Taking into account of variation to some extent, the rotation speed of the compressors  2  may be a rough value, and thus a slight error is allowed. 
     In  FIG.  4   , a time when the system gets started is shown as “0”. At time “0”, the bypass valve  13  is set to an upper limit degree of valve opening (upper limit degree of valve opening Km), and the rotation speed of the compressors is set to zero. The rotation speed of the compressors  2  increases over time, and it reaches a stable rotation speed (stable rotation speed Rr) at time “T 1 .” The stable rotation speed Rr is maintained thereafter. The bypass valve  13  is set to the upper limit degree of valve opening Km until the time “T 1 ”, and after the time “T 1 ”, the valve is gradually closed (the degree of valve opening is reduced). 
     Namely, the bypass valve  13  is controlled so that the degree of valve opening thereof is reduced over time after the heat pump  1  is started. While the bypass valve  13  is opened, as the gaseous refrigerant is delivered to the suction path  50  through the bypass circuit  30 , it is possible to prevent excessive oil from flowing into. After the lump of oil is diminished by flowing oil gradually, by decreasing the delivery amount of the gaseous refrigerant to control so that the proper amount of oil is delivered, a normal operating environment of the system can be returned. 
       FIG.  4    shows a part of an operation transition when the system gets started, and the rotation speed of the compressors  2  may be controlled to exceed the stable rotation speed Rr as appropriate thereafter. Furthermore, although the bypass valve  13 , in which the degree of valve opening is linearly decreased, is illustrated as an example, it is not limited thereto, and the degree of valve opening may be decreased in a step by step manner or the like if only the bypass valve  13  is closed finally. 
     It should be noted that embodiments disclosed above are exemplary in all respects, and the invention is not limitedly construed on a basis thereof. Therefore, the technical scope of the present invention should not be construed based on only above described embodiments but be defined based on the statement of the claims. Furthermore, any changes and modifications within the meaning and range equivalent to the claims fall within the scope of the invention. 
     This application claims the benefit of priority to Japanese Patent Application No. 2020-053960 filed as of Mar. 25, 2020. The entirety thereof is incorporated herein by reference. In addition, the entirety of the references cited is incorporated herein by reference. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               1  Heat pump 
               2  Compressor 
               3  Oil separator 
               4  Four-way valve 
               5  Outdoor heat exchanger 
               6  Indoor heat exchanger 
               7  Accumulator 
               11  Outdoor expansion valve 
               12  Indoor expansion valve 
               13  Bypass valve (an example of a valve) 
               14  Oil valve 
               15  Oil sensor 
               20  Oil return piping (an example of a first piping) 
               30  Bypass circuit 
               40  Gas path 
               44  Fluid merging part 
               50  Suction path 
               51  Branch part 
               52  Filter 
               53  Second piping 
               60  Oil path 
               71  First suction path 
               71   a  First upward extending part (an example of an upward extending part) 
               71   b  First connection part (an example of a connection part) 
               71   c  First downward extending part (an example of a downward extending part) 
               72  Second suction path 
               72   a  Second upward extending part (an example of an upward extending part) 
               72   b  Second connection part (an example of a connection part) 
               72   c  Second downward extending part (an example of a downward extending part) 
               73  Third suction path 
               73   a  Third upward extending part (an example of an upward extending part) 
               73   b  Third connection part (an example of a connection part) 
               73   c  Third downward extending part (an example of a downward extending part)