The present invention relates to a refrigeration cycle apparatus used for water heaters, air conditioners, etc., having an expansion mechanism and compression mechanisms.
In recent years, for the purpose of further enhancing the efficiencies of refrigeration cycle apparatuses, there have been proposed power recovery type refrigeration cycle apparatuses using an expansion mechanism instead of an expansion valve, in which the expansion mechanism recovers the pressure energy as power during a process in which a refrigerant is expanded, and thus the electric power required for driving the compression mechanism is reduced by the amount of the power recovered. Such refrigeration cycle apparatuses use an expander-compressor unit, in which a motor, a compression mechanism, and an expansion mechanism are coupled by a shaft.
Since the compression mechanism is coupled to the expansion mechanism by the shaft in the expander-compressor unit, and there may be a case where the displacement of the compression mechanism is insufficient, or the displacement of the expansion mechanism is insufficient, depending on the operational conditions. In order to ensure adequate recovery power so that the COP (Coefficient of Performance) of the refrigeration cycle apparatus is kept high even under operational conditions where the displacement of the compression mechanism is insufficient, there also have been proposed refrigeration cycle apparatuses using a secondary compressor in addition to the expander-compressor unit (see Patent Literature 1, for example).
Furthermore, the refrigeration cycle apparatus of Patent Literature 1 has a bypass passage 160 bypassing the expansion mechanism 103, and an injection passage 150 for supplying additionally the refrigerant to the expansion mechanism 103 during the expansion process of the refrigerant. The bypass passage 160 and the injection passage 150 are provided with a bypass valve 161 and an injection valve 151 for controlling the flow rate, respectively. In the refrigeration cycle apparatus of Patent Literature 1, the bypass valve 161 is in a closed state and the injection valve 151 is in an opened state in winter. The opening of the injection valve 151 is determined according to the outside air temperature, etc. Thereby, it is possible to cope even with the case where the displacement of the expansion mechanism 103 is insufficient.
PTL 1: JP 2007-132622 A
In the refrigeration cycle apparatus with an injection passage, however, the refrigerant flowing through the injection passage is expanded to some extent at the injection valve unless the injection valve is in the fully opened state. This causes a problem in that a part of the expansion energy cannot be recovered.
As described above, the injection loss depends on the injection flow rate, that is, on the opening of the injection valve, and varies significantly according to it. Thus, it is preferable that the opening of the injection valve is determined so as to reduce the injection loss. However, Patent Literature 1 merely states that the method for determining the opening of the injection valve is defined according to the outside air temperature, etc.
The present invention has been accomplished in view of the foregoing. An object of the present invention is to suppress the injection loss in a refrigeration cycle apparatus having an expansion mechanism and compression mechanisms as well as an injection passage, by adjusting appropriately the opening of an injection valve.
With reference to
The present invention has been accomplished in view of the foregoing. The present invention provides a refrigeration cycle apparatus comprising:
a first compressor including a first compression mechanism for compressing a refrigerant, an expansion mechanism for recovering power from the refrigerant expanding, a first motor coupled to the first compression mechanism and the expansion mechanism by a shaft, and a first closed casing accommodating the first compression mechanism, the expansion mechanism and the first motor;
a second compressor including a second compression mechanism for compressing the refrigerant connected in parallel with the first compression mechanism in a refrigerant circuit, a second motor coupled to the second compression mechanism by a shaft, and a second closed casing accommodating the second compression mechanism and the second motor;
a radiator for radiating heat from the refrigerant discharged from the first compression mechanism and the second compression mechanism;
a first pipe connecting the first compression mechanism and the second compression mechanism to the radiator;
a second pipe connecting the radiator to the expansion mechanism;
an injection passage, branched from the second pipe, for supplying additionally the refrigerant to the expansion mechanism during an expansion process;
an opening-adjustable injection valve provided in the injection passage; and
a controller for performing an optimizing operation for the opening of the injection valve by controlling rotation speeds of the first motor and the second motor as well as the opening of the injection valve so as to bring the opening of the injection valve closer to a fully closed state or closer to a fully opened state while keeping a pressure or a temperature of the discharged refrigerant guided to the radiator through the first pipe approximately constant.
The refrigeration cycle apparatus of the present invention configured as mentioned above makes it possible to suppress the injection loss while keeping the high pressure of the refrigeration cycle at an optimal high pressure.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The first compressor 1 has a first closed casing 10 accommodating a first compression mechanism 11, a first motor 12, and an expansion mechanism 13 connected to each other by a first shaft 15. A second compressor 2 has a second closed casing 20 accommodating a second compression mechanism 21 and a second motor 22 connected to each other by a second shaft 25. The first compression mechanism 11 and the second compression mechanism 21 are connected to the radiator 4 via the first pipe 3a in which two branch pipes are merged into one main pipe. The radiator 4 is connected to the expansion mechanism 13 via the second pipe 3b. The expansion mechanism 13 is connected to the evaporator 5 via the third pipe 3c. The evaporator 5 is connected to the first compression mechanism 11 and the second compression mechanism 21 via the fourth pipe 3d in which one main pipe is branched into two branch pipes. More specifically, the first compression mechanism 11 and the second compression mechanism 21 are disposed in parallel with each other in the refrigerant circuit 30. In other words, the first compression mechanism 11 is connected in parallel with the second compression mechanism 21 in the refrigerant circuit 30.
The refrigerant compressed by the first compression mechanism 11 and that compressed by the second compression mechanism 21 are discharged into the first pipe 3a from the first compression mechanism 11 and the second compression mechanism 21, and then merged with each other while flowing through the first pipe 3a so as to be guided to the radiator 4. The refrigerants compressed by the compression mechanisms 11 and 21 may be discharged from the compression mechanisms 11 and 21 once into the closed casing 10 and 20, and then discharged from the closed casings 10 and 20 into the first pipe 3a. The refrigerant guided to the radiator 4 radiates heat there, and then is guided to the expansion mechanism 13 through the second pipe 3b. The refrigerant guided to the expansion mechanism 13 expands there. At this time, the expansion mechanism 13 recovers power from the expanding refrigerant. The expanded refrigerant is guided to the evaporator 5 through the third pipe 3c. The refrigerant guided to the evaporator 5 absorbs heat there, and then is divided while flowing through the fourth pipe 3d so as to be guided to the first compression mechanism 11 and the second compression mechanism 21.
The refrigeration cycle apparatus further includes an injection passage 6, branched from the second pipe 3b, for supplying additionally the refrigerant to the expansion mechanism 13 during the expansion process of the refrigerant. An opening adjustable injection valve 61 for controlling flow rate is provided in the injection passage 6.
The refrigeration cycle apparatus also includes a controller 7 that controls mainly the rotation speeds of the first motor 12 and the second motor 22, and the opening of the injection valve 61.
This refrigerant circuit 30 is filled with the refrigerant that reaches a supercritical state in a high-pressure portion (a portion from the first compression mechanism 11 and the second compression mechanism 21 to the expansion mechanism 13 through the radiator 4). In the present embodiment, the refrigerant circuit 30 is filled with carbon dioxide (CO2) serving as the refrigerant. It should be noted, however, that the type of the refrigerant is not particularly limited, and it may be a refrigerant (such as a fluorocarbon refrigerant) that does not reach the supercritical state during operation.
The refrigerant circuit included in the refrigeration cycle apparatus of the present invention is not limited to the refrigerant circuit 30 that allows the refrigerant to circulate only in one direction. It may be a refrigerant circuit in which the flowing direction of the refrigerant can be changed, for example, a refrigerant circuit having four-way valves, etc. so as to switch between a heating operation and a cooling operation.
Next, operation patterns of the refrigeration cycle apparatus of the present embodiment will be described using
In the case of
Contrary to
Although the apparent states of the refrigeration cycle apparatus are the same in all of the operation patterns shown in
Next, the control performed by the controller 7 will be described. The controller 7 performs a starting operation first, and then performs an optimizing operation for the opening of the injection valve (hereinafter simply referred to as “optimizing operation”) as mentioned above.
First, the starting operation will be described. The controller 7 brings the refrigeration cycle apparatus from a stopped state into a particular steady state. The particular steady state means a state in which the high pressure of the refrigeration cycle is approximately equal to an optimal high pressure (a pressure at which the COP is highest) corresponding to the outside air temperature at that time. In the present embodiment, as shown in
For example, the controller 7 increases, upon starting, the rotation speeds of the first motor 12 and the second motor 22 to the same rotation speed corresponding to the outside air temperature, and then adjusts opening X of the injection valve 61 so that the temperature Tc of the discharged refrigerant meets the target value. Thereby, the starting operation is performed. Performing the starting operation in this way broadens the range for rotation speed adjustment in the optimizing operation to be performed later because the rotation speeds of the first motor 12 and the second motor 22 become the same as each other. Therefore, application to wider operational ranges is possible.
Alternatively, the controller 7 increases, upon starting, the rotation speeds of the first motor 11 and the second motor 12 to different rotation speeds from each other corresponding to the outside air temperature, and then adjusts the opening X of the injection valve 61 so that the temperature Tc of the discharged refrigerant meets the target value. Thereby, the starting operation is performed. Performing the starting operation in this way makes it possible to suppress the amount of oil discharged from the first compressor 1 by allowing the rotation speed of the first compressor 1 having two rotating mechanisms, such as the first compression mechanism 11 and the expansion mechanism 13, to be lower than the rotation speed of the second compressor 2. More specifically, an oil for lubricating the rotating mechanisms is held in the first closed casing 10 and the second closed casing 20, and the oil is discharged out of the closed casings together with the refrigerant. Generally, a larger amount of oil is discharged out of the closed casing in the first compressor 1 having the plurality of rotating mechanisms than in the second compressor 2. Also, the total amount of the oils discharged from the first compressor 1 and the second compressor 2 decreases when the rotation speed of the first compressor 1 decreases. Thereby, a sufficient oil reservoir also is kept in the first compressor 1, enhancing the reliability of the apparatus.
In the refrigeration cycle apparatus of the present embodiment, the opening X of the injection valve 61 may be in the fully closed state at the time of starting. This makes it possible to generate promptly a difference between the low pressure and the high pressure in the refrigeration cycle upon starting, and shorten the transition time to the steady operation.
Next, the optimizing operation performed by the controller 7 will be described.
More specifically, as shown in
The controller 7 compares the current opening X with the reference opening PX (Step S3), and if the current opening X is lower than the reference opening PX (YES in Step S3), the controller 7 decides that the opening X should be brought closer to the fully closed state and proceeds to Step S11 shown in
Thereafter, the controller 7 repeats an adjustment process until the temperature Tc of the discharged refrigerant fails to reach a target value. In the adjustment process, the rotation speed f1 of the first motor 12 and the rotation speed f2 of the second motor 22 each are changed only by a specified amount and then the opening X of the injection valve 61 is changed so as to bring the temperature Tc of the discharged refrigerant closer to the target value. When the temperature Tc of the discharged refrigerant fails to reach the target value, the controller 7 returns the rotation speed f1 of the first motor 12 and the rotation speed f2 of the second motor as well as the opening X of the injection valve 61 to a condition one time earlier. Thereby, the optimizing operation is ended.
Specifically, if the controller 7 decides that the opening X should be brought closer to the fully closed state, it increases the rotation speed f1 of the first motor 12 by a Hz and decreases the rotation speed f2 of the second motor 22 by a Hz (Step S11). Subsequently, in order to reduce the injection flow rate by the amount of the increase in the rotation speed f1 of the first motor 11, the controller 7 decreases the opening X of the injection valve 61 and brings the temperature Tc of the discharged refrigerant closer to the target value (Step S12). This step is carried out by, for example, decreasing the opening X of the injection valve 61 step by step and checking whether the temperature Tc of the discharged refrigerant has reached the target value at each time. As a result, if the temperature Tc of the discharged refrigerant has reached the target value (YES in Step S13), there still is a possibility for the opening X to be decreased. Thus, the adjustment process (Steps S11 and S12) is performed once again. This adjustment process is repeated, and if the temperature Tc of the discharged refrigerant fails to reach the target value when or before the opening X of the injection valve 61 is brought into the fully closed state (0%) (NO in Step S13), the controller 7 decreases the rotation speed f1 of the first motor 12 by a Hz and increases the rotation speed f2 of the second motor 22 by a Hz (Step S14), readjusts the temperature Tc of the discharged refrigerant to the target value (Step S15), and ends the control.
In contrast, if the controller 7 decides that the opening X should be brought closer to the fully opened state, it executes a control opposite to the above-mentioned one. More specifically, the controller 7 decreases the rotation speed f1 of the first motor 12 by a Hz and increases the rotation speed f2 of the second motor 22 by a Hz (Step S21). Subsequently, in order to increase the injection flow rate by the amount of the decrease in the rotation speed f1 of the first motor 11, the controller 7 increases the opening X of the injection valve 61 and brings the temperature Tc of the discharged refrigerant closer to the target value (Step S22). This step is carried out by, for example, increasing the opening X of the injection valve 61 little by little and checking whether the temperature Tc of the discharged refrigerant has reached the target value at each time. As a result, if the temperature Tc of the discharged refrigerant has reached the target value (YES in Step S23), there still is a possibility for the opening X to be increased. Thus, the adjustment process (Steps S21 and S22) is performed once again. This adjustment process is repeated, and if the temperature Tc of the discharged refrigerant fails to reach the target value when or before the opening X of the injection valve 61 is brought into the fully opened state (100%) (NO in Step S23), the controller 7 increases the rotation speed f1 of the first motor 12 by a Hz and decreases the rotation speed f2 of the second motor 22 by a Hz (Step S24), readjusts the temperature Tc of the discharged refrigerant to the target value (Step S25), and ends the control.
Here, it is desirable that the increment/decrement of a Hz by which the rotation speeds of the first motor 12 and the second motor 22 are changed during one adjustment process in the optimizing operation be the minimum increment/decrement that the controller 7 can handle. It may be a larger increment/decrement than this (approximately 5 Hz, for example).
Such an optimizing operation makes it possible to suppress the injection loss while keeping the high pressure of the refrigeration cycle at the optimal high pressure. Thereby, highly effective power recovery can be realized.
Here, it can be considered to decrease the opening X of the injection valve 61 first, and then change the rotation speed f1 of the first motor 12 and the rotation speed f2 of the second motor so that the temperature Tc of the discharged refrigerant reaches the target value. In this case, however, there is a possibility that the temperature Tc of the discharged refrigerant cannot reach the target value because the minimum increment/decrement in adjusting the rotation speed usually is not so small. In contrast, in the case where the rotation speed f1 of the first motor 12 and the rotation speed f2 of the second motor are changed and thereafter the opening X of the injection valve 61 is adjusted as in the present embodiment, it is easier to adjust the temperature Tc of the discharged refrigerant to the target value because the minimum increment/decrement in adjusting the valve opening usually is extremely small.
When performing the optimizing operation after the starting operation, the controller 7 measures firstly power consumption w1 of the first motor 12 and power consumption w2 of the second motor 22 and calculates the total value Wa (=w1+w2) (Step S31). Subsequently, the controller 7 decreases the rotation speed f1 of the first motor 12 by a Hz and increases the rotation speed f2 of the second motor 12 by a Hz (Step S32). Thereafter, in order to increase the injection flow rate by the amount of the decrease in the rotation speed f1 of the first motor 12, the controller 7 increases the opening X of the injection valve 61 and brings the temperature Tc of the discharged refrigerant closer to the target value (Step S33). These Step S32 and Step S33 are performed in the same manner as Step S21 and Step S22 that are shown in
When the temperature Tc of the discharged refrigerant reaches the target value (YES in Step S34) as a result of Step S33, the controller 7 measures the power consumption w1 of the first motor 11 and the power consumption w2 of the second motor 12 once again and calculates total value Wb (=w1+w2) (Step S35). Thereafter, the controller 7 compares the total value Wb with the total value Wa calculated previously (Step S36), and judges whether the total value of the power consumption w1 of the first motor 11 and the power consumption w2 of the second motor 12 has been decreased or increased from that calculated before Step S32 and Step S33 were performed.
When Wb is smaller than Wa, that is, if the total value of the power consumptions has been decreased (YES in Step S36), the controller 7 decides that the opening X of the injection valve 61 should be brought closer to the fully opened state and proceeds to Step S21 shown in
With the above-mentioned configuration, the controller 7 can execute control while judging the total value of inputs to the first motor 12 and the second motor 22. Thus, the operation pattern can be shifted in such a manner that the COP of the refrigeration cycle apparatus certainly is enhanced. In addition, the temperature sensor 81 as described in Embodiment 1 is not necessary, and the configuration of the apparatus also can be simplified.
Although the power consumption w1 of the first motor 12 and the power consumption w2 of the second motor 22 are measured directly in the present embodiment, values of currents flowing through the motors 12 and 22 may be measured instead of the power consumptions. Generally, the power consumptions of the motors can be estimated from the values of the currents. Thus, the controller 7 can be configured simply at low cost by using the value of the current that is easier to measure.
Moreover, in the present embodiment, the control operates to increase the opening X of the injection valve 61 once in order to decide whether the opening X of the injection valve 61 should be brought closer to the fully closed state or closer to the fully opened state. However, the control may be opposite. More specifically, as shown in
In contrast, if YES in Step S34, the controller 7 proceeds to Step S35 as in the flow chart shown in
When performing the optimizing operation after the starting operation, the controller 7 detects firstly pressure Pe and temperature Te of the refrigerant flowing through the second pipe 3b by using a pressure sensor 82 and a temperature sensor 83 provided at the second pipe 3b, and detects valve downstream pressure Pi by using a pressure sensor 84 provided at the injection passage 6 (Step S41). Subsequently, the controller 7 calculates saturated injection pressure P using the pressure Pe and the temperature Te (Step S42). Here, the saturated injection pressure P is described using
Going back to
With the above-mentioned configuration, a highly accurate control can be executed according to the decision made by using the valve downstream pressure Pi.
Even when the pressure sensor 82 and the temperature sensor 83 are located on an upstream side of the injection valve 61 in the injection passage 6, it is possible to detect the pressure Pe and temperature Te of the refrigerant flowing through the second pipe 3b by using these sensors 82 and 83.
In the refrigeration cycle apparatus of each of the Embodiments, the temperature Tc of the discharged refrigerant is used when the controller 7 adjusts the opening X of the injection valve 61. However, the pressure of the discharged refrigerant may be used instead. This makes it possible to determine the opening X that maximizes the COP of the refrigeration cycle apparatus, based on the discharge pressures of the compression mechanisms 11 and 21.
Moreover, although the first compression mechanism 11 and the second compression mechanism 21 having the same displacement volume as each other are employed in the Embodiments, the first compression mechanism 11 and the second compression mechanism 21 may have different displacement volumes from each other. In this case, the first compression mechanism 11 and the second compression mechanism 21 may not use the same value of a Hz as the increment/decrement by which the rotation speeds of the first motor 11 and the second motor 21 are changed during one adjustment process in the optimizing operation as in each of the Embodiments, but may use different values from each other according to the ratio between the displacement volume of the first compression mechanism 11 and that of the second compression mechanism 21.
Moreover, in each of the Embodiments, the controller may end the optimizing operation when one of the rotation speeds of the first motor 12 and the second motor 22 is equal to a lower limit value or an upper limit value of an allowable driving range. With this configuration, it is possible to ensure the reliabilities of the first compressor 1 and the second compressor 2 and extend the lives of the devices.
Furthermore, in each of the Embodiments, the optimizing operation may be ended when the difference between the rotation speed of the first motor 12 and the rotation speed of the second motor 22 exceeds a certain threshold, or when the ratio of the rotation speed of the first motor 12 to the rotation speed of the second motor 22 exceeds a certain threshold. With this configuration, it is possible to prevent an extremely large difference from being generated between the rotation speeds, suppress the imbalance between the oil reservoirs held in bottom portions of the closed casings, ensure the reliabilities of the first compressor 1 and the second compressor 2, and extend the lives of the devices.
The refrigeration cycle apparatus of the present invention is useful as a means for recovering expansion energy of a refrigerant in a refrigeration cycle so as to recover power.
Number | Date | Country | Kind |
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2008-186735 | Jul 2008 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/002810 | 6/19/2009 | WO | 00 | 3/10/2010 |