Patent Publication Number: US-2023137037-A1

Title: Heat pump

Description:
TECHNICAL FIELD 
     The present invention relates to a heat pump which circulates a refrigerant for cooling and heating. 
     BACKGROUND ART 
     Conventionally, a heat pump performs cooling and heating operations by exchanging heat of a refrigerant in a heat exchanger. Generally, in such a heat pump, during a heating operation the refrigerant is gasified by an indoor heat exchanger, liquefied by an outdoor heat exchanger, and returned to a compressor (see, Patent Literature 1, for example). 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Laid-Open Publication No. 2016-99067 
       
    
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     The heat pump disclosed in Patent Literature 1 includes a compressor and an oil separator, and an open/close valve is provided in an oil return path to return oil from the oil separator to the compressor. In the above mentioned heat pump, since the outdoor heat exchanger is intended to carry out heat exchange for all the refrigerant, there is a case where the amount of refrigerant beyond the capacity of the outdoor heat exchanger flows into the outdoor heat exchanger, so that it has caused such a problem that the refrigerant cannot be fully evaporated. 
     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 suppressing the refrigerant from excessively flowing into an outdoor heat exchanger. 
     Means for Solving the Problems 
     A heat pump of the present invention is provided with an indoor heat exchanger, an outdoor heat exchanger connected to the indoor heat exchanger, and an accumulator connected to the outdoor heat exchanger and circulates a refrigerant for cooling and heating, the heat pump includes: a first heat exchanger provided between the outdoor heat exchanger and the accumulator; and a bypass circuit to cause the refrigerant that flows out of the indoor heat exchanger to flow into the first heat exchanger. 
     The heat pump of the present invention may be configured such that the bypass circuit branches from a path connecting the indoor heat exchanger and the outdoor heat exchanger and is connected to an upstream of the first heat exchanger in a refrigerant delivery direction. 
     The heat pump of the present invention may be configured such that the bypass circuit is provided with a valve that controls a flow rate of the refrigerant flowing into the bypass circuit, and the valve is located above the first heat exchanger in a vertical direction. 
     The heat pump of the present invention may be configured such that a second heat exchanger is provided between the outdoor heat exchanger and the indoor heat exchanger, and the valve is located above the second heat exchanger in the vertical direction. 
     The heat pump of the present invention may be configured such that a degree of opening of the valve is controlled in its opening direction when an outside air temperature is within a range of a predetermined temperature. 
     Effect of the Invention 
     According to the present invention, when an amount of refrigerant beyond a capacity of an outdoor heat exchanger flows into an outdoor heat exchanger, by causing the refrigerant to flow into the bypass circuit, an excessive flow of the refrigerant into the outdoor heat exchanger can be suppressed, thereby it is possible to improve a heat exchange efficiency. 
    
    
     
       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 schematic side view of a structure around a heat exchanger for evaporation and a heat exchanger for cooling. 
         FIG.  3    shows a flow chart illustrating a flow of a commencement determination process to determine whether to commence a bypass control or not. 
         FIG.  4    shows a flow chart illustrating a process flow associated with an operation in the bypass control. 
     
    
    
     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 has a compressor  2 , an oil separator  3 , a four-way valve  4 , an outdoor heat exchanger  5 , an accumulator  7 , a heat exchanger for evaporation  8 , a heat exchanger for cooling  9 , and an outdoor expansion valve  11 . The indoor unit has an indoor heat exchanger  6  and an indoor expansion valve  12 . 
     The compressor  2  is driven with a driving source such as a gas engine, for example. A plurality of compressors  2  may be connected in parallel. Each of the plurality of compressors  2  may be driven with a single gas engine via a belt or a flywheel or selectively driven with it by providing a clutch. A discharge path  40  of the compressor  2  is connected to the four-way valve  4  via the oil separator  3 . 
     High temperature and high pressure gaseous refrigerant discharged from the compressor  2  is 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 compressor  2 . 
     An accumulator  7  is provided in a path between the four-way valve  4  and the compressor  2 . The accumulator  7  temporarily stores the gaseous refrigerant. The gaseous refrigerant contains a small amount of the liquid refrigerant. These are separated in the accumulator  7 , and the liquid refrigerant is accumulated in the accumulator  7 . 
     A filter housing part  51  to accommodate a filter  52  is provided in the suction path  50  connecting the accumulator  7  and the compressor  2 . The filter  52  adsorbs 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. When a plurality of compressors  2  are provided, the filter housing part  51  may branches the path to multiple paths. 
     Furthermore, a heat exchanger for evaporation  8  (as an example of the first heat exchanger) is provided between the four-way valve  4  and the accumulator  7 . The heat exchanger for evaporation  8  is defined as a heat exchanger which is heated with the gas engine of being the driving source for the compressor  2  and the like, for example. A cooling water for the gas engine can circulate through the heat exchanger for evaporation  8  so as to warm the refrigerant passing through the heat exchanger for evaporation  8 . 
     The heat pump  1  is provided with a bypass circuit  61  to deliver the refrigerant, which is flown out of the indoor heat exchanger  6  and flown into the outdoor heat exchanger  5 , to the heat exchanger for evaporation  8  during the heating operation. Specifically, the bypass circuit  61  branches from a path (connection path  60 ) connecting the indoor heat exchanger  6  (indoor expansion valve  12 ) and the outdoor heat exchanger  5  (outdoor expansion valve  11 ), and is connected to the upstream of the heat exchanger for evaporation  8  in the refrigerant flow direction (between the four-way valve  4  and the heat exchanger for evaporation  8 ). A bypass expansion valve  62  (as an example of a valve) is provided in the bypass circuit  61 , and the flow rate of the refrigerant passing through the bypass circuit  61  is controlled depending on the degree of opening of the bypass expansion valve  62 . 
     In the heat pump  1 , when the amount of refrigerant beyond the capacity of the outdoor heat exchanger  5  flows into the outdoor heat exchanger  5 , by causing the refrigerant to flow into the bypass circuit  61 , an excessive flow of the refrigerant into the outdoor heat exchanger  5  can be suppressed, thereby it is possible to improve a heat exchange efficiency. Also, by connecting the bypass circuit  61  to the upstream of the heat exchanger for evaporation  8 , the refrigerant can be surely delivered to the heat exchanger for evaporation  8 . The bypass control when causing the refrigerant to flow into the bypass circuit  61  will be described later in detail with reference to  FIGS.  3  and  4   . 
     On the other hand, during a cooling operation, the high temperature and high pressure gaseous refrigerant discharged from the compressor  2  is 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 of the compressor  2  after passing through the four-way valve  4  and the accumulator  7 . 
     The oil separator  3  is provided in a path between the four-way valve  4  and the compressor  2 . The oil separator  3  separates oil contained in the refrigerant. The oil separator  3  is connected to an oil return piping  20  to supply the separated oil to the compressor  2 . The oil return piping  20  is connected to the suction path  50 . A solenoid valve or the like may be provided in the oil return piping  20  and control supply of the oil. 
     The heat pump  1  is provided with the heat exchanger for cooling  9  (as an example of the second heat exchanger) to perform heat exchange between refrigerants passing through the path in order to improve a cooling efficiency. The heat exchanger for cooling  9  is provided in the connection path  60  between the outdoor expansion valve  11  and the indoor expansion valve  12 . Furthermore, the connection path  60  has a branch path  63  which branches from the upstream of the heat exchanger for cooling  9  in the refrigerant flowing direction. The branch path  63  is connected between the heat exchanger for evaporation  8  and the accumulator  7  through a branch expansion valve  64  and the heat exchanger for cooling  9 . 
     The cooling heat exchanger for cooling  9  performs heat exchange between the low temperature and low pressure liquid refrigerant delivered to the indoor expansion valve  12  through the connection path  60  and the refrigerant which is changed to the low temperature and low pressure liquid state (fog state) through the branch path  63  and the branch expansion valve  64 . Namely, the refrigerant to be delivered to the indoor expansion valve  12  through the connection path  60  is distributed into a refrigerant passing through the connection path  60  as it is and a refrigerant passing through the branch path  63  branching from the connection path. As a result, in the heat exchanger for cooling  9 , the liquid refrigerant passing through the connection path  60  is cooled by an atomized refrigerant passing through the branch path  63 . The atomized refrigerant is gasified by absorbing heat of the liquid refrigerant and then is delivered to the accumulator  7 . Thus, by providing the heat exchanger for cooling  9 , the temperature of the refrigerant can be properly controlled as well as the heat exchange efficiency can be further improved. 
     In the cooling of the heat exchanger for cooling  9 , a distribution ratio of the refrigerant between the connection path  60  and the branch path  63  may be regulated by controlling the degree of opening of the branch expansion valve  64 , for example. Also in the heat exchanger for cooling  9 , the connection path  60  and the branch path  63  only intersect, and the refrigerants passing therethrough never mix with each other. 
     The heat pump  1  may have various sensors or the like in the refrigerant circuit where appropriate and be configured to detect temperature, a flow rate, pressure, etc. of the refrigerant, the outside air, and the cooling water on the basis of outputs from the sensors or the like. A controller may also be provided to control various valves or the like based on information acquired by the sensors or the like. 
       FIG.  2    is a schematic side view of a structure around the heat exchanger for evaporation and the heat exchanger for cooling. 
       FIG.  2    shows components with a part being exposed, which are ordinarily enclosed inside the outdoor unit. Specifically,  FIG.  2    shows the accumulator  7 , the heat exchanger for evaporation  8 , the heat exchanger for cooling  9 , the bypass expansion valve  62 , and piping connected thereto. Components other than the components shown in  FIG.  2    may be enclosed inside the outdoor unit as appropriate. 
     As shown in  FIG.  2   , the bypass expansion valve  62  is located above the heat exchanger for evaporation  8  and the heat exchanger for cooling  9  in the vertical direction. Although water droplets produced due to condensation, etc. may stick to the heat exchangers, the bypass expansion valve  62  can be free from such water droplets since the heat exchangers are located below the bypass expansion valve  62 . 
     Other valves such as the outdoor expansion valve  11  and the branch expansion valve  64  may be placed in the vicinity of the bypass expansion valve  62 , preferably so as to keep from the water droplets. In addition, by collecting a plurality of valves in the same place, workability in installation and maintenance can be improved. 
     Next, the bypass control when causing the refrigerant to flow into the bypass circuit  61  will be described below with reference to  FIGS.  3  and  4   . 
       FIG.  3    is a flow chart illustrating a flow of a commencement determination process to determine whether to commence the bypass control or not. 
     In this embodiment, the bypass control is performed during the heating operation. Therefore, an initial state of a process flow shown in  FIG.  3    is set to the heating operation. 
     In step S 01 , it is determined whether outdoor unit condition is met or not. The outdoor unit condition is set with respect to an operation state of the outdoor unit. Specifically, when the degree of opening of the outdoor expansion valve  11  is not less than 80% and a degree of overheat of the refrigerant at the downstream of the heat exchanger for evaporation  8  is not less 25 degrees centigrade than a target temperature, it is determined that the outdoor unit condition is met. The degree of overheat of the refrigerant indicates a temperature difference between the saturation temperature of the refrigerant and the raised temperature of the refrigerant, and a target temperature for the degree of overheat of the refrigerant is set to a predetermined value. It may be determined that the outdoor unit condition is met when an outdoor-unit capability is also not less than 80%. The outdoor-unit capability is calculated based on a rating ratio of a theoretical refrigerant discharging amount of the compressor  2  (displacement volume of the compressor  2 × a compressor rotating speed). As for a refrigerant, pressure can be converted to temperature. After a determination that the outdoor unit condition mentioned above is met (step S 01 :Yes) is made, the operation proceeds to step S 02 . On the other hand, if the outdoor unit condition is not met (step S 01 :No), the operation is suspended until the conditions are met. 
     In step S 02 , it is determined whether the outdoor air temperature condition is met or not. Here, it is determined whether the outdoor air temperature falls within a predetermined temperature range or not. Specifically, it is determined that the outdoor air temperature condition is met when the outdoor air temperature is not less than 5 degrees centigrade, or the outdoor air temperature is no more than −5 degrees centigrade. After a determination that the outdoor air temperature condition is met (step S 02 :Yes) is made, the operation proceeds to step S 03 . After a determination that the outdoor air temperature condition is not met (step S 02 :No) is made instead, the operation returns to step S 01 . 
     In step S 03 , it is determined whether the cooling water condition is met or not. Here, it is determined that the cooling water condition is met when the temperature of the cooling water passing through the heat exchanger for evaporation  8  is not less than 59 degrees centigrade. After a determination that the cooling water condition is met (step S 03 :Yes) is made, the operation proceeds to step S 04 . After a determination that the cooling water condition is not met (step S 03 :No) is made instead, the operation returns to step S 01 . 
     In step S 04 , the bypass control commences. The operation of the bypass control will be described below in detail with reference to  FIG.  4   . 
     As mentioned above, in the commencement determination process, the bypass control can commence only when all of three conditions of steps S 01  through S 03  are met. If even one condition is not met, the commencement determination process is restarted. When restarting the commencement determination process, the operation may be suspended until a predetermined time elapses. Furthermore, the commencement determination process may be performed at the same timing as detection by a sensor or the like, and the sensor or the like may acquire information periodically at predetermined time intervals. 
       FIG.  4    is a flow chart illustrating a process flow associated with an operation in the bypass control. 
     An initial state in  FIG.  4    is just after the bypass control commences as a result of the commencement determination process shown in  FIG.  3   . 
     In step S 11 , the bypass expansion valve  62  is set to an initial degree of opening. Here, the initial degree of opening may be a predetermined value which is preset for each model of the heat pump  1 , for example. 
     In step S 12 , the bypass expansion valve  62  is gradually opened. Here, the degree of opening of the bypass expansion valve  62  is controlled in a valve opening direction. In this embodiment, the degree of opening of the bypass expansion valve  62  is controlled so as to open by a predetermined amount in a 60-second cycle. 
     In step S 13 , it is determined whether the bypass expansion valve  62  reaches an upper limit of the degree of opening or not. The upper limit of the degree of opening may be predetermined. As a result, when the bypass expansion valve  62  reaches the upper limit of the degree of opening (step S 13 :Yes), the process can proceed to step S 14 . On the other hand, when the bypass expansion valve  62  does not reach the upper limit of the degree of opening (step S 13 :No), the process returns to step S 12 . 
     In step S 14 , the bypass expansion valve  62  is caused to follow the outdoor expansion valve  11 . Specifically, the upper limit of the degree of opening of the bypass expansion valve  62  is set to the same value as the degree of opening of the outdoor expansion valve  11 , as well as the degree of opening of the bypass expansion valve  62  is set to the same as the degree of opening of the outdoor expansion valve  11 . 
     In the case where the bypass control is held, the operation in step S 14  may continue. Meanwhile, the commencement determination process may be performed during the bypass control, and the bypass control may stop if at least one of the outdoor unit condition, the outdoor temperature condition, and the coolant condition is not met. 
     Since the capability of the outdoor heat exchanger  5  is affected by the outdoor air temperature, by controlling the delivery of the refrigerant to the heat exchanger for evaporation  8  according to it, an optimal heat exchange can be achieved. In addition, by setting the outdoor unit condition, the bypass control can be performed as necessary. Furthermore, by setting the cooling water condition, the bypass control can be performed in the case where the heat exchange in the heat exchanger for evaporation  8  can be carried out sufficiently. 
     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. 2020-053961 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 
           8  Heat exchanger for evaporation (an example of the first heat exchanger) 
           9  Heat exchanger for cooling (an example of a second heat exchanger) 
           11  Outdoor expansion valve 
           12  Indoor expansion valve 
           20  Oil return piping 
           40  Discharge path 
           50  Suction path 
           51  Filter housing part 
           52  Filter 
           60  Connection path 
           61  Bypass circuit 
           62  Bypass expansion valve (an example of a valve) 
           63  Branch path 
           64  Branch expansion valve