Patent Publication Number: US-8984904-B2

Title: Refrigerating device

Description:
TECHNICAL FIELD 
     The present invention relates to a refrigerating device such as an air cooled heat pump chiller. 
     BACKGROUND ART 
     There is a conventional refrigerating device composed of a first refrigerating cycle unit including a first compressor, a second refrigerating cycle unit including a second compressor, and a control unit for controlling the volumes of the first and second compressors corresponding to a load required of the first and second refrigerating cycle units (see PTL 1: JP 7-111181 B2). 
     The control unit controls the volumes of both the first and second compressors to be 50% or less when the required load is 50% of a maximum load or below. 
     CITATION LIST 
     Patent Literature 
     
         
         
           
             PTL1: JP 7-111181 B2 
           
         
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, in the conventional refrigerating device, because the control unit controls the volumes of both the first and second compressors to be 50% or less when the required load is 50% of a maximum load or below, the first and second compressors are simultaneously operated at a low volume, which causes a problem of lowered COP (i.e., refrigerating capacity/power consumption). 
     Accordingly, an object of the present invention is to provide a refrigerating device which can improve COP when a required load is 50% of the maximum load or below. 
     Solution to Problem 
     As a solution, the present invention provides a refrigerating device comprising: 
     a first unit including a first compressor, a first heat source-side heat exchanger, a first expansion mechanism, and a common use heat exchanger, these components being connected in a loop in this order via a first refrigerant passage; 
     a second unit including a second compressor, a second heat source-side heat exchanger, a second expansion mechanism, and the common use heat exchanger, these components being connected in a loop in this order via a second refrigerant passage; and 
     a control unit configured to control a volume of the first compressor and a volume of the second compressor according to a load required of the common use heat exchanger, wherein 
     the control unit is configured to stop the second compressor and to control the volume of the first compressor when the required load is equal to or below a certain value that can be dealt with by the first unit only. 
     According to the refrigerating device in this invention, the control unit stops the second compressor and controls the volume of the first compressor only when the required load is equal to or below the certain value, so that COP (refrigerating capacity/power consumption) in the case where the required load is equal to or below the certain value can be improved as compared to the case of controlling both the first and the second compressors simultaneously to have low volumes. 
     In one embodiment, the first unit includes a first four-way selector valve arranged and configured to switch a circulating direction of a refrigerant inside the first refrigerant passage, and the second unit includes a second four-way selector valve arranged and configured to switch a circulating direction of a refrigerant inside the second refrigerant passage. 
     In the refrigerating device of this embodiment, because the first unit includes the first four-way selector valve and the second unit includes the second four-way selector valve, it is easy to switch between cooling and heating of a substance to be cooled which flows into the common use heat exchanger. 
     In one embodiment, the first heat source-side heat exchanger is a first condenser, the second heat source-side heat exchanger is a second condenser, and the common use heat exchanger is a common evaporator. 
     In the refrigerating device of this embodiment, because the first heat source-side heat exchanger is a first condenser, the second heat source-side heat exchanger is a second condenser, and the common use heat exchanger is a common evaporator, the substance to be cooled which flows into the common evaporator is cooled. 
     In one embodiment, the common evaporator is provided with a cooled substance passage which exchanges heat with the first and second refrigerant passages. The refrigerating device further comprises a temperature sensor arranged and configured to measure temperature of a substance to be cooled in the cooled substance passage outputted from the common evaporator, and when the required load is equal to or below the certain value, the control unit controls the volume of the first compressor in a phased manner while stopping the second compressor in a phased manner, based on a measured value of the temperature sensor. 
     In the refrigerating device of this embodiment, because the control unit controls the volume of the first compressor in a phased manner while stopping the second compressor in a phased manner based on a measured value of the temperature sensor when the required load is equal to or below the certain value, in the case of increasing the volume of the first compressor, it becomes possible to prevent the temperature of a substance to be cooled in the cooled substance passage from being excessively lowered due to excessive refrigerating capacity and to thereby prevent the cooled substance passage from being frozen up. 
     In one embodiment, when the required load is larger than the certain value, the control unit controls the volumes of the first and second compressors such that a ratio of the volume of the first compressor to a maximum volume thereof is equal to a ratio of the volume of the second compressor to a maximum volume thereof. 
     In the refrigerating device of this embodiment, when the required load is larger than the certain value, it is easy to control the volumes of the first and second compressors because these volumes are controlled such that the ratio of the volume of the first compressor to the maximum volume is equal to the ratio of the volume of the second compressor to the maximum volume. 
     Advantageous Effects of Invention 
     According to the invention, because the control unit is configured to stop the second compressor and to control the volume of the first compressor when the required load is equal to or below a certain value that can be dealt with by the first unit, COP in the case where the required load is equal to or below the certain value can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic structure view showing a refrigerating device in a first embodiment of the invention; 
         FIG. 2  is an explanatory view showing the comparison between the present invention and the prior art; 
         FIG. 3  is a flow chart explaining shift in volume of the first unit and the second unit; 
         FIG. 4A  is a schematic structure view showing a refrigerating device in a second embodiment of the invention in the state of cooling water; and 
         FIG. 4B  is a schematic structure view showing the refrigerating device in the second embodiment of the invention in the state of heating water. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinbelow, the invention will be described in detail in conjunction with the embodiments with reference to the drawings. 
     (First Embodiment) 
       FIG. 1  is a schematic structure view showing a refrigerating device in a first embodiment of the invention. The refrigerating device has a first unit  1 , a second unit  2 , and a control unit  3 . 
     The first unit  1  includes a first compressor  11 , a first condenser  12  (as a first heat source-side heat exchanger), a first expansion valve  13  (as an expansion mechanism), and a common evaporator  4  (as a common use heat exchanger). The first compressor  11 , the first condenser  12 , the first expansion valve  13 , and the common evaporator  4  are connected in a loop in order via a first refrigerant passage  10  (such as pipes). 
     The second unit  2  includes a second compressor  21 , a second condenser  22  (as a second heat source-side heat exchanger), a second expansion valve  23  (as an expansion mechanism), and a common evaporator  4  (as a common use heat exchanger). The second compressor  21 , the second condenser  22 , the second expansion valve  23 , and the common evaporator  4  are connected in a loop in order via a second refrigerant passage  20  (such as pipes). 
     The first compressor  11  has a volume controller  11   a  such as a slide valve. The second compressor  21  has a volume controller  21   a  such as a slide valve. 
     The first condenser  12  is equipped with a fan  12   a  so that heat is exchanged between air delivered by the fan  12   a  and a refrigerant which flows through the first refrigerant passage  10 . Similarly, the second condenser  22  is equipped with a fan  22   a  so that heat is exchanged between air delivered by the fan  22   a  and a refrigerant which flows through the second refrigerant passage  20 . 
     The common evaporator  4  is equipped with a cooled substance passage  40  (such as pipes) so that heat is exchanged between water (as a substance to be cooled) which flows through the cooled substance passage  40  and the refrigerants which flow through the first and second refrigerant passages  10 ,  20 . Provided at an outlet  40   a  from the common evaporator  4  of the cooled substance passage  40  is a temperature sensor  5  for measuring the temperature of the water in the cooled substance passage  40  outputted from the common evaporator  4 . 
     Description is now given of the flow of the refrigerant in the first unit  1 . As shown with arrows, the refrigerant compressed by the first compressor  11  passes the first condenser  12 , the first expansion valve  13 , and the common evaporator  4  in this order and returns to the first compressor  11 . In this case, air is warmed by the refrigerant in the first condenser  12 , while water is cooled by the refrigerant in the common evaporator  4 . 
     Description is now given of the flow of the refrigerant in the second unit  2  in the similar manner. As shown with arrows, the refrigerant compressed by the second compressor  21  passes the second condenser  22 , the second expansion valve  23 , and the common evaporator  4  in this order, and returns to the second compressor  21 . In this case, air is warmed by the refrigerant in the second condenser  22 , while water is cooled by the refrigerant in the common evaporator  4 . 
     The control unit  3  controls the volume of the first compressor  11  and the volume of the second compressor  21  according to a load required of the common evaporator  4 . The control unit  3  controls the volume controller  11   a  of the first compressor  11  and the volume controller  21   a  of the second compressor  21 . 
     When the required load is below a certain value that is able to be dealt with by the first unit  1  only (i.e., without operating the second unit), the control unit  3  stops the second compressor  21  and controls the volume of the first compressor  11 , whereas when the required load is larger than the certain value, the control unit  3  controls both the volume of the first compressor  11  and the volume of the second compressor  21 . 
     In this regard, the refrigerating capacity of the first unit  1  and that of the second unit  2  are identical and the maximum volume of the first compressor  11  and that of the second compressor  21  are identical, which means that the certain value is equal to 50% of the maximum load. 
     Concrete description is now given of volume control by the control unit  3  with reference to  FIG. 2 . The upper rows of the table in  FIG. 2  show conventional volume control, while the lower rows show volume control conducted in this invention. 
     As shown in the table in  FIG. 2 , when the required load is in a range of from 100% to 60%, the volumes of the first unit  1  (first compressor  11 ) and the second unit  2  (second compressor  21 ) are controlled in this invention as in the prior art. In short, when the required load is larger than 50% of the maximum load, a ratio of the volume of the first compressor  11  to the maximum volume thereof and a ratio of the volume of the second compressor  21  to the maximum volume thereof are equalized. 
     When the required load is in a range of 50% to 10%, both the volume of the first unit  1  (first compressor  11 ) and the volume of the second unit  2  (second compressor  21 ) are controlled in the prior art, whereas in this invention, the volume of the second unit  2  is set to zero (0) (i.e., operation is stopped), and only the volume of the first unit  1  is controlled. 
     Therefore, in this invention, as shown in the graph in  FIG. 2 , when the required load is 50% or below, COP (i.e., refrigerating capacity/power consumption) can be improved as compared to the prior art. In short, the performance is improved when the required load is 50% or less. 
     Description is now given of the shift in volume of the first unit  1  and the second unit  2  when the required load shifts from a value larger than 50% to a value equal to or below 50%. When the required load is equal to or below 50%, the control unit  3  controls the volume of the first compressor  11  in a phased manner while stopping the second compressor  21  in a phased manner based on a measured value of the temperature sensor  5 . 
     More specifically, when the required load shifts from 60% to 50%, the volume of the first unit  1  is shifted from 60% to 100%, and the volume of the second unit  2  is shifted from 60% to 0%. The shift in volume of the first unit  1  and the second unit  2  in this case will be explained next. As shown in  FIG. 3 , the volume of the first unit  1  is maintained at 60%, while the volume of the second unit  2  is shifted from 60% to 40%, and the control unit is put in standby mode for a time t 1  (Step S 1 ). 
     Then, the volume of the first unit  1  is shifted from 60% to 70%, while the volume of the second unit  2  is maintained at 40%, and the control unit is put in standby mode for the time t 1  (Step S 2 ). 
     Thereafter, the volume of the first unit  1  is maintained at 70%, while the volume of the second unit  2  is shifted from 40% to 20%, and the control unit is put in standby mode for the time t 1  (Step S 3 ). 
     Then, judgment about water temperature is performed by deciding whether or not an absolute value of a difference between a measured value of the temperature sensor  5  and a preset value is smaller than 0.5° C. (Step S 4 ), and if the absolute value is not smaller than 0.5° C., then the control unit is put in standby mode for a time t 2  (Step S 5 ) before the judgment about water temperature is performed again (Step S 4 ). 
     If the absolute value is smaller than 0.5° C., then the volume of the first unit  1  is shifted from 70% to 80%, while the volume of the second unit  2  is maintained at 20%, and then the control unit is put in standby mode for the time t 2  (Step S 6 ). 
     Then, judgment about water temperature is performed again by deciding whether or not an absolute value of a difference between a measured value of the temperature sensor  5  and the preset value is smaller than 0.5° C. (Step S 7 ), and if the absolute value is not smaller than 0.5° C., then the control unit is put in standby mode for the time t 2  (Step S 8 ) before the judgment about water temperature is performed again (Step S 7 ). 
     If the absolute value is smaller than 0.5° C., then the volume of the first unit  1  is shifted from 80% to 100%, while the volume of the second unit  2  is maintained at 20%, and the control unit is put in standby mode for the time t 2  (Step S 9 ). 
     Then, judgment about water temperature is performed by deciding whether or not an absolute value of a difference between a measured value of the temperature sensor  5  and the preset value is smaller than 0.5° C. (Step S 10 ), and if the absolute value is not smaller than 0.5° C., then the control unit is put in standby mode for the time t 2  (Step S 11 ) before the judgment about water temperature is performed again (Step S 10 ). 
     If the absolute value is smaller than 0.5° C., then the volume of the first unit  1  is maintained at 100%, while the volume of the second unit  2  is shifted from 20% to 0% (Step S 12 ). 
     As is explained above, when a measured value of the temperature sensor  5  is smaller than the preset value, the volumes of the first compressor  11  and the second compressor  21  are controlled in a phased manner such that the volume of at least one of the first compressor  11  and the second compressor  21  is changed to prevent temperature from becoming out of control. In short, when the capacity of each of the compressors  11 ,  21  has a large variation width, the temperature may become out of control on a major scale, and if the capacity becomes excessive for example, water temperature in the cooled substance passage  40  may fall and the cooled substance passage  40  may freeze. 
     According to the above-structured refrigerating device, the control unit  3  stops the second compressor  21  and controls the volume of the first compressor  11  when a required load is equal to or below 50% (certain value), so that COP (refrigerating capacity/power consumption) in the case where the required load is equal to or below 50% can be improved as compared to the case of controlling the first and the second compressors  11 ,  21  simultaneously to have a low volume. 
     Moreover, when the required load is equal to or below 50%, the control unit  3  controls the volume of the first compressor  11  in a phased manner while stopping the second compressor  21  in a phased manner based on a measured value of the temperature sensor  5 , so that in the case of increasing the volume of the first compressor, it becomes possible to prevent water temperature in the cooled substance passage  40  from being lowered due to excessive refrigerating capacity and to thereby prevent the cooled substance passage  40  from being frozen. 
     Moreover, when the required load is larger than 50%, a ratio of the volume of the first compressor  11  to the maximum volume thereof and a ratio of the volume of the second compressor  21  to the maximum volume thereof are equalized, so that it is easy to control the volumes of the first and second compressors  11 ,  21 . 
     (Second Embodiment) 
       FIGS. 4A and 4B  show a refrigerating device in a second embodiment of the invention. The second embodiment is different in structure from the first embodiment in that the circulating direction of a refrigerant which flows through the refrigerating device can be switched. It is to be noted that in the second embodiment, component members identical to those in the first embodiment are designated by identical reference signs to omit explanation. 
     As shown in  FIG. 4A , a first unit  1 A includes a first compressor  11 , a first heat source-side heat exchanger  12 A, a first expansion mechanism  13 , and a common use heat exchanger  4 A, which are connected in a loop in this order via a first refrigerant passage  10 . 
     A second unit  2 A includes a second compressor  21 , a second heat source-side heat exchanger  22 A, a second expansion mechanism  23 , and a common use heat exchanger  4 A, which are connected in a loop in this order via a second refrigerant passage  20 . 
     The first unit  1 A includes a first four-way selector valve  14  for switching a circulating direction of a refrigerant inside the first refrigerant passage  10 . The first four-way selector valve  14  is provided so as to cross a refrigerant passage between the first compressor  11  and the first heat source-side heat exchanger  12 A and a refrigerant passage between the first compressor  11  and the common use heat exchanger  4 A. 
     The second unit  2 A includes a second four-way selector valve  24  for switching a circulating direction of a refrigerant inside the second refrigerant passage  20 . The second four-way selector valve  24  is provided so as to cross a refrigerant passage between the second compressor  21  and the second heat source-side heat exchanger  22 A and a refrigerant passage between the second compressor  21  and the common use heat exchanger  4 A. 
     Description is now given of the flow of a refrigerant in the refrigerating device. 
     First, as shown in  FIG. 4A , the refrigerant of the first unit LA is made to flow through the first compressor  11 , the first heat source-side heat exchanger  12 A, the first expansion mechanism  13 , and the common use heat exchanger  4 A in this order as shown with arrows by switching of the first four-way selector valve  14 . In this case, the first heat source-side heat exchanger  12 A functions as a condenser to warm air with the refrigerant, while the common use heat exchanger  4 A functions as an evaporator to cool water with the refrigerant. 
     Similarly, the refrigerant of the second unit  2 A is made to flow through the second compressor  21 , the second heat source-side heat exchanger  22 A, the second expansion mechanism  23 , and the common use heat exchanger  4 A in this order as shown with arrows by the switching of the second four-way selector valve  24 . In this case, the second heat source-side heat exchanger  22 A functions as a condenser to warm air with the refrigerant, while the common use heat exchanger  4 A functions as an evaporator to cool water with the refrigerant. 
     Also, as shown in  FIG. 4B , the refrigerant of the first unit  1 A is made to flow through the first compressor  11 , the common use heat exchanger  4 A, the first expansion mechanism  13 , and the first heat source-side heat exchanger  12 A in this order as shown with arrows by switching of the first four-way selector valve  14 . In this case, the first heat source-side heat exchanger  12 A functions as an evaporator to cool air with the refrigerant, while the common use heat exchanger  4 A functions as a condenser to warm water with the refrigerant. 
     Similarly, the refrigerant of the second unit  2 A is made to flow through the second compressor  21 , the common use heat exchanger  4 A, the second expansion mechanism  23  and the second heat source-side heat exchanger  22 A in order as shown with arrows by the switching of the second four-way selector valve  24 . In this case, the second heat source-side heat exchanger  22 A functions as an evaporator to cool air with the refrigerant, while the common use heat exchanger  4 A functions as a condenser to warm water with the refrigerant. 
     The control unit  3  controls the volume of the first compressor  11  and the volume of the second compressor  21  according to a load required of the common use heat exchanger  4 A. When the required load is equal to or below a certain value (50% or less in this embodiment) that can be dealt with by the first unit  1 A only, the control unit  3  stops the second compressor  21  and controls the volume of the first compressor  11 . 
     When the required load is equal to or below the certain value, the control unit  3  controls the volume of the first compressor  11  in a phased manner while stopping the second compressor  21  in a phased manner based on a measured value of the temperature sensor  5  provided in the cooled substance passage  40  on the outlet side of the common use heat exchanger  4 A. 
     When the required load is larger than the certain value, the control unit  3  controls the volumes of the first and second compressors such that a ratio of the volume of the first compressor  11  to the maximum volume thereof is equal to a ratio of the volume of the second compressor  21  to the maximum volume thereof. 
     Since concrete volume control by the control unit  3  is similar to that in the first embodiment ( FIG. 2  and  FIG. 3 ), explanation thereof will be omitted. 
     According to the above-structured refrigerating device, the control unit  3  stops the second compressor  21  and controls the volume of the first compressor  11  when a required load is equal to or below the certain value, so that COP (refrigerating capacity/power consumption) in the case where the required load is equal to or below the certain value can be improved as compared to the case of controlling the first and the second compressors  11 ,  21  simultaneously to a low volume. 
     Moreover, the first unit  1 A includes the first four-way selector valve  14 , and the second unit  2 A includes the second four-way selector valve  24 , so that cooling or heating of an substance to be cooled, which flows into the common use heat exchanger  4 A, can be switched easily. 
     Moreover, when the required load is equal to or below the certain value, the control unit  3  controls the volume of the first compressor  11  in a phased manner while stopping the second compressor  21  in a phased manner based on a measured value of the temperature sensor  5 , so that in the case of increasing the volume of the first compressor  11 , it is possible to prevent water temperature in the cooled substance passage  40  from being lowered (or increased) too much due to excessive refrigerating capacity and to thereby prevent the cooled substance passage  40  from being frozen (or heated). 
     Moreover, when the required load is larger than the certain value, the control unit  3  equalizes a ratio of the volume of the first compressor  11  to the maximum volume thereof and a ratio of the volume of the second compressor  21  to the maximum volume thereof, so that it is easy to control the volumes of the first and second compressors  11 ,  21 . 
     The present invention shall not be limited to the embodiments disclosed. For example, the expansion valve as an expansion mechanism may be replaced by other components such as capillary tubes. Brine may be used as a substance to be cooled. The refrigerating capacities of the first unit  1  and the second unit  2  may not be identical, and the maximum volumes of the first compressor  11  and the second compressor  21  may not be identical either. 
     In the first embodiment, the first condenser  12  and the second condenser  22  may be replaced by evaporators, while the common evaporator  4  may be replaced by a common condenser, and the substance to be cooled may be warmed by the common condenser. 
     REFERENCE SIGNS 
     
         
         
           
               1 ,  1 A first unit 
               11  first compressor 
               11   a  volume controller 
               12  first condenser (first heat source-side heat exchanger) 
               12 A first heat source-side heat exchanger 
               12   a  fan 
               13  first expansion valve (first expansion mechanism) 
               14  first four-way selector valve 
               10  first refrigerant passage 
               2 ,  2 A second unit 
               21  second compressor 
               21   a  volume controller 
               22  second condenser (second heat source-side heat exchanger) 
               22 A second heat source-side heat exchanger 
               22   a  fan 
               23  second expansion valve (second expansion mechanism) 
               24  second four-way selector valve 
               20  second refrigerant passage 
               3  control unit 
               4  common evaporator (common use heat exchanger) 
               4 A common use heat exchanger 
               40  cooled substance passage 
               40   a  outlet 
               5  temperature sensor