REFRIGERATION CYCLE APPARATUS

Abstract

A refrigeration cycle apparatus includes a compressor, a radiator, an expander, an evaporator, a bypass circuit, and an injection circuit. The bypass circuit has a flow rate control valve and a gas-liquid separator. One end of the bypass circuit is connected to an intake conduit of the expander and the other end thereof is connected to a discharge conduit of the expander so that a portion of refrigerant passed through the radiator bypasses the expander and is guided to the flow rate control valve and that the liquid refrigerant separated by the gas-liquid separator returns to the discharge conduit of the expander. One end of the injection circuit is connected to a gas outlet portion of the gas-liquid separator and the other end thereof is connected to an intermediate pressure portion of the compressor.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a refrigeration cycle apparatus applied to hot water heaters, air-conditioners, and the like, and more particularly to a configuration and a control method therefor that achieve high efficiency by mixing a refrigerant that flows through a bypass circuit with a refrigerant that is in the process of compression.

2. Description of Related Art

A known refrigeration cycle apparatus uses a fluid machine in which both a positive displacement compressor and a positive displacement expander are coupled uniaxially so that the energy of expansion of the refrigerant recovered by the expander can be used as auxiliary driving power for the compressor. In this kind of refrigeration cycle apparatus, the compressor and the expander constantly rotate at the same frequency. Unless some special mechanism is provided, the intake capacity of the compressor and the intake capacity of the expander are also constant. Therefore, theoretically, the ratio between the density pc of the compressor's intake refrigerant and the density pe of the expander's intake refrigerant is constant at all times. When this constraint of constant density ratio exists, the refrigeration cycle apparatus is not permitted to operate outside that constraint. Thus, although such an apparatus originally is intended to achieve high cycle efficiency by the power recovery with the use of the expander, it does not necessarily achieve a high efficiency operation.

FIG. 12 illustrates a system that employs a bypass circuit for resolving such an issue. This system is provided with a control valve 12 for variably adjusting the passage area of the bypass circuit 11. By adjusting the opening of the control valve 12 to regulate the refrigerant flow rate passing through the expander 4 variably, the mass flow rate of the refrigerant that passes through the compressor 3 and the mass flow rate of the refrigerant that passes through the expander 4 may be made different from each other. In other words, the conventional constraint of constant density ratio on the cycle operation is eliminated (see, for example, JP 2001-116371A (FIG. 1)).

JP 2003-121018A discloses a refrigeration cycle apparatus including a compressor and an expander that are coupled directly by a single shaft. The refrigeration cycle apparatus has an expansion valve arranged in series with the expander, and a bypass valve for bypassing the expander. A gas-liquid separator is provided between the expander and the expansion valve so that the gas refrigerant separated from the liquid refrigerant by the gas-liquid separator is introduced to an intermediate pressure portion of the compressor.

SUMMARY OF THE INVENTION

However, a problem has been that the refrigerant flowing through the circuit that bypasses the expander does not contribute to improvements in system efficiency at all. This applies to both of the foregoing publications.

In view of this, it is an object of the present invention to provide a refrigeration cycle apparatus provided with a compressor, a radiator, an expander, and an evaporator, connected successively in series, that can increase the refrigerant flow rate through the radiator and at the same time avoid the constraint of constant density ratio.

Accordingly, the present invention provides refrigeration cycle apparatus including:

a compressor for compressing a refrigerant;

a radiator for cooling the refrigerant compressed by the compressor;

an expander for expanding the refrigerant cooled by the radiator and recovering mechanical power from the refrigerant under expansion;

an evaporator for heating the refrigerant expanded by the expander and supplying the refrigerant to the compressor;

a bypass circuit including a flow rate control valve and a gas-liquid separator that is provided downstream from the flow rate control valve and that is for separating the refrigerant passed through the flow rate control valve into a gas refrigerant and a liquid refrigerant, one end of the bypass circuit being connected to an intake conduit of the expander and the other end of the bypass circuit being connected to a discharge conduit of the expander so that a portion of the refrigerant passed through the radiator bypasses the expander and is guided to the flow rate control valve and that the liquid refrigerant separated by the gas-liquid separator returns to the discharge conduit of the expander; and

an injection circuit, one end of which being connected to a gas outlet portion of the gas-liquid separator and the other end of which being connected to an intermediate pressure portion of the compressor.

According to the present invention as described above, by allowing a portion of the refrigerant flowing out of the radiator to flow through the bypass circuit, the constraint of constant density ratio can be avoided. Moreover, since the liquid refrigerant and the gas refrigerant are separated by the gas-liquid separator provided in the bypass circuit and the gas refrigerant is injected into the intermediate pressure portion of the compressor, the refrigerant flow rate through the radiator can be increased. The specific enthalpy of the liquid refrigerant that flows out of the gas-liquid separator and returns to the discharge conduit of the expander is smaller than the specific enthalpy of the refrigerant (gas-liquid two-phase refrigerant) that has been expanded by the expander. Therefore, the specific enthalpy of the refrigerant at the inlet of the evaporator lowers and the enthalpy difference between the inlet and the outlet of the evaporator increases, leading to an improvement in the refrigerating capacity. Furthermore, the injection circuit enables the gas refrigerant flowing out of the gas-liquid separator to be mixed with the refrigerant that is in the compression process, preventing liquid compression from occurring in the compressor and thus ensuring a high degree of reliability of the compressor.

In another aspect, the present invention provides a refrigeration cycle apparatus including:

a compressor for compressing a refrigerant;

a radiator for cooling the refrigerant compressed by the compressor;

an expander for expanding the refrigerant cooled by the radiator and recovering mechanical power from the refrigerant under expansion;

an evaporator for heating the refrigerant expanded by the expander and supplying the refrigerant to the compressor;

a bypass circuit including a flow rate control valve, one end of the bypass circuit being connected to an intake conduit of the expander and the other end of the bypass circuit being connected to an intermediate pressure portion of the compressor so that a portion of the refrigerant passed through the radiator bypasses the expander and is guided to the flow rate control valve;

an intake temperature sensor for detecting the refrigerant after flowing out of the evaporator but before being taken into the compressor; and

a controller for controlling an opening of the flow rate control valve according to a detection result detected by the intake temperature sensor.

According to the present invention as described above, by allowing the refrigerant to flow through the bypass circuit, the refrigerant flow rate through the radiator can be increased while the constraint of constant density ratio is avoided. Therefore, the overall performance of the refrigeration cycle apparatus can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram illustrating a refrigeration cycle apparatus according to a first embodiment of the present invention;

FIG. 2 is a vertical cross-sectional view illustrating one example of a fluid machine including a compressor and an expander;

FIG. 3 is a view illustrating one example of injection ports provided in the compressor;

FIG. 4 is a Mollier diagram illustrating the refrigeration cycle according to the first embodiment of the present invention;

FIG. 5 is a control flow diagram of the refrigeration cycle apparatus according to the first embodiment of the present invention;

FIG. 6 is a configuration diagram illustrating a refrigeration cycle apparatus according to a second embodiment of the present invention;

FIG. 7 is a configuration diagram illustrating a refrigeration cycle apparatus according to a third embodiment of the present invention;

FIG. 8 is a configuration diagram illustrating a refrigeration cycle apparatus according to a fourth embodiment of the present invention;

FIG. 9 is a configuration diagram illustrating a refrigeration cycle apparatus according to a fifth embodiment of the present invention;

FIG. 10 is a Mollier diagram illustrating the refrigeration cycle according to the fifth embodiment of the present invention;

FIG. 11 is a control flow diagram of the refrigeration cycle apparatus according to the fifth embodiment of the present invention; and

FIG. 12 is a configuration diagram illustrating a conventional refrigeration cycle apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, embodiments of the refrigeration cycle apparatus according to the present invention will be described in detail with reference to the drawings.

FIRST EMBODIMENT

FIG. 1 is a configuration diagram illustrating a refrigeration cycle apparatus according to a first embodiment of the present invention. A refrigeration cycle apparatus 100A of the present embodiment is furnished with a compressor 101 for compressing a refrigerant such as hydrofluorocarbon or carbon dioxide, a radiator 102 for cooling the refrigerant compressed by the compressor 101, an expander 103 for decompressing and expanding the refrigerant cooled by the radiator 102 and recovering mechanical power from the refrigerant under expansion, an evaporator 104 for heating the refrigerant decompressed by the expander 103, and a plurality of main pipes 116 (main conduits) for connecting the compressor 101, the radiator 102, the expander 103, and the evaporator 104 in that order. The compressor 101, the radiator 102, the expander 103, the evaporator 104, and the main pipes 116 constitute a main circuit 117 through which the refrigerant circulates.

In the first embodiment, the compressor 101 and the expander 103 are coupled uniaxially to a motor 6 for driving the compressor 101. FIG. 2 is a vertical cross-sectional view illustrating one example of fluid machine including the compressor 101 and the expander 103 of this kind, and according to the present embodiment, the refrigeration cycle apparatus 100A includes such a fluid machine 200. As illustrated in FIG. 2, mechanical power obtained by the expander 103 is supplied to a shaft 7 and is utilized as auxiliary driving power for the compressor 101, which contributes to reducing the power consumption of the motor 6. Since the expander 103 and the compressor 101 revolve at the same frequency at all times, the refrigeration cycle apparatus including the fluid machine 200 is constrained by the constraint of constant density ratio.

As a means to avoid the constraint of constant density ratio, the refrigeration cycle apparatus 100A is, as illustrated in FIG. 1, further furnished with a bypass circuit 113, one end of which is connected to one of the main pipes 116 that is between the radiator 102 and the expander 103 and the other end of which is connected to another one of the main pipes 116 that is between the expander 103 and the evaporator 104, so that a portion of the refrigerant that has passed through the radiator 102 bypasses the expander 103. The former of the main pipes 116 is an intake conduit of the expander 103 and is also a discharge conduit of the radiator 102. The latter of the main pipes 116 is a discharge conduit of the expander 103 and is also an intake conduit of the evaporator 104.

The bypass circuit 113 includes a first flow rate control valve 105, a gas-liquid separator 110 provided downstream from the first flow rate control valve 105, and a plurality of bypass pipes 115. By allowing a portion of the refrigerant that has passed through the radiator 102 to flow through the bypass circuit 113, the ratio between the density of the refrigerant at the inlet of the compressor 101 and the density of the refrigerant at the inlet of the expander 103 can be varied.

The refrigerant that bypasses the expander 103 is introduced to the first flow rate control valve 105. The gas-liquid separator 110 has the function of separating the refrigerant that has passed through the first flow rate control valve 105 into a gas refrigerant and a liquid refrigerant, and it has a liquid outlet portion and a gas outlet portion. A bypass pipe 115 is connected to the liquid outlet portion so that the gas-liquid two-phase refrigerant that has changed from the liquid refrigerant into the gas-liquid two-phase refrigerant can be returned to one of the main pipes 116 that is between the expander 103 and the evaporator 104.

The refrigeration cycle apparatus 100A further includes an injection circuit 109, one end of which is connected to the gas outlet portion of the gas-liquid separator 110 and the other end of which is connected to an intermediate pressure portion of the compressor 101 (an intermediate pressure portion of the main circuit 117). The injection circuit 109 includes a second flow rate control valve 108 and a plurality of injection pipes 119. A portion or all of the gas refrigerant that has been separated from the liquid refrigerant by the gas-liquid separator 110 is injected into the intermediate pressure portion of the compressor 101 through the injection circuit 109.

As illustrated in FIG. 2, the intermediate pressure portion of the compressor 101 can be a portion of the interior of the compressor 101 that faces the refrigerant flow channel, that is, a portion thereof that faces a compression chamber 28. The compressor 101 is a scroll-type compressor in which the compression chamber 28 is formed between a stationary scroll 21 and an orbiting scroll 22, and an injection port 120 provided in the stationary scroll 21 serves as the intermediate pressure portion. One of the injection pipes 119 is connected to the injection port 120. The injection port 120 is located between an intake port 21a and an outlet port 21b in the refrigerant flow channel within the compressor 101. The gas refrigerant that has flowed out of the gas outlet portion of the gas-liquid separator 110 passes through the injection circuit 109, is injected into the compression chamber 28 through the injection port 120, and is mixed with the refrigerant that is being compressed.

An injection port 120 may be provided at one location in the stationary scroll 21, or, as illustrated in FIG. 3, a plurality of injection ports 120, 120 may be provided at a plurality of locations in the stationary scroll 21. The type of the compressor is not limited to the scroll type, and may be other types of positive displacement compressors such as a rotary type compressor. Likewise, the type of the expander is not limited either, although FIG. 2 shows a two-stage rotary compressor as the expander 103.

It should be noted that in the present specification the term “intermediate pressure” is intended to mean a pressure that is between a high pressure and a low pressure in the refrigeration cycle, in other words, a pressure between the pressure of the refrigerant flowing into the radiator 102 and the pressure of the refrigerant flowing out of the evaporator 104.

Referring back to FIG. 1, the description will proceed further. The bypass circuit 113 further may include a throttling device 114 provided downstream from the gas-liquid separator 110. The throttling device 114 may be a common expansion valve. Such a throttling device 114 is capable of changing the liquid refrigerant flowing out of the gas-liquid separator 110 into a gas-liquid two-phase refrigerant. This allows the gas-liquid two-phase refrigerant to be returned to the main pipe 116 that is between the expander 103 and the evaporator 104, which is advantageous in maintaining a desired operating condition. However, if the amount of the liquid refrigerant is small, it is possible to send the liquid refrigerant to the main pipe 116 without expanding it by the throttling device 114. It should be noted that the first flow rate control valve 105, the second flow rate control valve 108, and the throttling device 114 have a common function, so the same kind of expansion valves may be used for them.

In addition, it is recommended that two temperature sensors 111 and 112 be provided as a means for detecting the temperature of the refrigerant that circulates in the main circuit 117. One of the temperature sensors 111 is an intake temperature sensor that detects the temperature of the refrigerant after flowing out of the evaporator 104 but before being taken into the compressor 101, and it detects what is called a superheat temperature. The other one of the temperature sensors 112 is an outlet temperature sensor that detects the temperature of the refrigerant after being discharged from the compressor 101 but before flowing into the radiator 102. Furthermore, a controller 107 is provided, which controls the openings of the first flow rate control valve 105 and the throttling device 114 of the bypass circuit 113 as well as the opening of the second flow rate control valve 108 of the injection circuit 109. Signals that can identify the temperatures of the refrigerant are input from the two temperature sensors 111 and 112 to the controller 107. The controller 107 controls the openings of the first flow rate control valve 105, the throttling device 114, and the second flow rate control valve 108 according to the signals from the temperature sensors 111 and 112. This makes it possible to optimize the efficiency of the refrigeration cycle apparatus 100A.

The operations and effects of the refrigeration cycle apparatus 100A will be described with reference to the Mollier diagram of FIG. 4.

In the Mollier diagram of FIG. 4, the change of the refrigerant circulating in the main circuit 117 is represented as A→B→C→D→E→F→A. The refrigerant flowing through the bypass circuit 113 is branched at point E, which corresponds to the portion of the main circuit 117 that is between the radiator 102 and the expander 103, is then decompressed to point G by the first flow rate control valve 105, and is thereafter separated into a gas refrigerant and a liquid refrigerant by the gas-liquid separator 110. The liquid refrigerant, which is in the state of point H on the saturated liquid curve, is decompressed to point I by the throttling device 114, and is then merged with the refrigerant being at point F, which is discharged from the expander 103. Accordingly, the specific enthalpy of the refrigerant that has been discharged from the expander 103 and merged with the liquid refrigerant from the bypass circuit 113 is represented by point J. On the other hand, the gas refrigerant separated from the liquid refrigerant by the gas-liquid separator 110 flows into the compressor 101 and merges with the refrigerant at point B, which is the refrigerant under compression. The specific enthalpy of the refrigerant that has undergone the merge with the refrigerant being compressed by the compressor 101 and the gas refrigerant injected from the injection circuit 109 is represented by point C.

The refrigerant flow rate flowing through the radiator 102 is the sum of the refrigerant flow rate Ge flowing through the evaporator 104 and the refrigerant flow rate Gi flowing through the bypass circuit 106, and thus is represented as (Ge+Gi); therefore, the amount of heat exchanged by the radiator increases. In this way, it is possible to improve the performance of the refrigeration cycle apparatus 100A while avoiding the constraint of constant density ratio.

When the refrigerant flow rate flowing through the bypass circuit 113 is increased, the refrigeration cycle will be balanced so that the intake density of the compressor 101 increases. Accordingly, when the intake superheat of the compressor 101 needs to be reduced, the opening of the first flow rate control valve 105 provided in the bypass circuit 113 should be increased.

In addition, by increasing the opening of the second flow rate control valve 108 provided in the injection circuit 109 so as to increase the refrigerant flow rate flowing through the injection circuit 109, the specific enthalpy at point C becomes smaller, and thereby, the refrigerant discharge temperature (point D) of the compressor 101 can be controlled to be lower.

Thus, when the refrigerant flow rate flowing through the injection circuit 109 is increased, the refrigeration cycle will be balanced so that the refrigerant discharge temperature of the compressor 101 decreases. Conversely, when it is desired to elevate the refrigerant discharge temperature of the compressor 101, the opening of the second flow rate control valve 108 provided in the injection circuit 109 should be decreased.

The control procedure for the first flow rate control valve 105 and the second flow rate control valve 108 executed by the controller 107 will be described with reference to the flowchart of FIG. 5. Upon starting the operation, it is assessed at step 301 whether or not the difference between an actual superheat temperature T1 detected by the intake temperature sensor 111 and a target superheat TH1 falls within the tolerance range ±t₁ (dead zone). The tolerance t₁ may be set to be about 5% of the target superheat TH1.

If it is assessed that the difference (absolute value) between the actual superheat temperature T1 and the target superheat TH1 is greater than the tolerance t₁, the process proceeds to step 302, in which it is assessed whether or not the actual superheat temperature T1 is greater than the target superheat TH1. If the actual superheat temperature T1 is greater than the target superheat TH1, the process proceeds to step 303, in which a control process for increasing the opening of the first flow rate control valve 105 is executed. When the opening of the first flow rate control valve 105 is increased, the refrigerant flow rate flowing through the bypass circuit 113 increases; therefore, the refrigeration cycle will be balanced so that the superheat temperature T1 decreases.

On the other hand, if it is assessed at step 302 that the actual superheat temperature T1 is lower than the target superheat TH1, the process proceeds to step 304, in which a control process for decreasing the opening of the first flow rate control valve 105 is executed. Thereby, the refrigeration cycle will be balanced so that the superheat temperature T1 rises, and therefore, the superheat temperature can be controlled so as to approach the target value.

Next, it is assessed at step 305 whether or not the difference between an actual refrigerant discharge temperature T2 detected by the outlet temperature sensor 112 and a target refrigerant discharge temperature TH2 falls within the tolerance range ±t₂ (dead zone). The tolerance t₂ may be set to be about 5% of the target refrigerant discharge temperature, for example. If it is assessed that the difference between the actual refrigerant discharge temperature T2 and the target refrigerant discharge temperature TH2 falls within the tolerance range ±t₂, the control process is terminated.

On the other hand, if it is assessed at step 305 that the difference between the actual refrigerant discharge temperature T2 and the target refrigerant discharge temperature TH2 (absolute value) is greater than the tolerance t₂, the process proceeds to step 306, in which it is assessed whether or not the actual refrigerant discharge temperature T2 is greater than the target refrigerant discharge temperature TH2. If the actual refrigerant discharge temperature T2 is greater than the target refrigerant discharge temperature TH2, the process proceeds to step 307, in which a control process for increasing the opening of the second flow rate control valve 108 is executed. Increasing the opening of the second flow rate control valve 108 results in a greater refrigerant flow rate flowing through the injection circuit 109, and therefore, the refrigeration cycle will be balanced so that the refrigerant discharge temperature T2 decreases. Referring to the Mollier diagram of FIG. 4, the specific enthalpy at point C becomes smaller, and the refrigerant discharge temperature T2 of the compressor 101 (temperature at point D) decreases.

If it is assessed at step 306 that the actual refrigerant discharge temperature T2 is lower than the target refrigerant discharge temperature TH2, the process proceeds to step 308, in which a control process for decreasing the opening of the second flow rate control valve 108 is executed. Thereby, the refrigeration cycle will be balanced so that the refrigerant discharge temperature T2 rises, and therefore, the refrigerant discharge temperature can be controlled so as to approach the target value. According to the Mollier diagram of FIG. 4, the specific enthalpy at point C increases, and the refrigerant discharge temperature T2 of the compressor 101 (temperature at point D) rises. If the opening of the second flow rate control valve 108 is changed, the process returns to step 301. By executing the control process depicted in the flowchart of FIG. 5 repeatedly, in other words, by executing the control process periodically as needed, the superheat temperature and the refrigerant discharge temperature always can be kept at optimal values.

As has been described above, adjusting the openings of the first flow rate control valve 105 and the second flow rate control valve 108 to control the superheat temperature and the refrigerant discharge temperature enables the system performance to be kept optimally high while avoiding the constraint of constant density ratio.

The foregoing has described an embodiment in which the openings of the first and second flow rate control valves 105 and 108 are adjusted using the superheat temperature and the refrigerant discharge temperature of the compressor 101. The openings of the first and second flow rate control valves 105 and 108 may be controlled by one or a plurality of parameters selected from the group consisting of the superheat temperature, the refrigerant discharge temperature of the compressor 101, the high pressure of the refrigeration cycle, the evaporator temperature, and the frequency of the compressor 101, in addition to the combination of the superheat temperature and the refrigerant discharge temperature of the compressor 101.

SECOND EMBODIMENT

The first embodiment has described the case in which the injection circuit 109 is connected directly to the compressor 101. By contrast, the refrigeration cycle apparatus according to the second embodiment differs from the first embodiment in that it has a plurality of compressors. It should be noted, however, that the advantageous effects achieved by the bypass circuit and the injection circuit are common between the second embodiment and the first embodiment.

As illustrated in FIG. 6, a refrigeration cycle apparatus 100B of the second embodiment is furnished with a low-pressure-side compressor 101A, and a high-pressure-side compressor 101B connected in series with the low-pressure-side compressor 101A via one of the main pipes 116. Specifically, a multi-stage compressor including the low-pressure-side compressor 101A and the high-pressure-side compressor 101B is employed as the compressor for compressing a refrigerant. In this case, the intermediate pressure portion of the compressors 101A and 101B, to which the injection circuit 109 is connected, may be the main pipe 116 that is a joint portion for joining the low-pressure-side compressor 101A and the high-pressure-side compressor 101B. According to the present embodiment, the injection circuit 109 and the compressors 101A, 101B can be connected by connecting the injection pipe 119 and the main pipe 116, so the designing and assembling of the apparatus are made easy. Of course, a connecting component such as a joint may be provided between the injection pipe 119 and the main pipe 116.

The compressor that is coupled uniaxially to the expander 103 may be either the low-pressure-side compressor 101A or the high-pressure-side compressor 101B. The type of each of the compressors 101A and 101B is not particularly limited, and various types of positive displacement compressors such as a scroll type, a rotary type, or a reciprocating type compressor may be employed suitably. In addition, the type of the compressor that is not coupled uniaxially to the expander 103 may be a centrifugal compressor.

THIRD EMBODIMENT

FIG. 7 illustrates a configuration diagram of a refrigeration cycle apparatus according to a third embodiment. A refrigeration cycle apparatus 100C shown in FIG. 7 differs from that of the first embodiment in that an injection circuit 109′ further includes an injector 123 provided downstream from the second flow rate control valve 108. In other respects, the present embodiment is similar to the first embodiment, and in the drawings, the same reference numerals designate the same components.

The injector 123 in the injection circuit 109′ is capable of switching between an open state that permits passage of the refrigerant (gas refrigerant) and a closed state that inhibits passage of the refrigerant, and it may be, for example, a solenoid valve controlled by the controller 107. Thus, the present embodiment makes it possible to control even the timing of injecting the gas refrigerant into the intermediate pressure portion of the compressor 101. For example, by controlling the open/close operations of the injector 123 so as to synchronize the rotation of the compressor 101, the gas refrigerant can be injected into the compression chamber 28 inside the compressor 101 with more appropriate timing. It should be noted that the second flow rate control valve 108 may be omitted and only the injector 123 of this kind may be provided. The injector 123 may be disposed inside the shell of the compressor 101.

FOURTH EMBODIMENT

FIG. 8 illustrates a configuration diagram of a refrigeration cycle apparatus according to a fourth embodiment. A refrigeration cycle apparatus 100D shown in FIG. 8 additionally has a liquid refrigerant return circuit 125 for enabling the expander 103 to take in the liquid refrigerant that has been separated from the gas refrigerant by the gas-liquid separator 110, in addition to the elements of the refrigeration cycle apparatus of the first embodiment.

The liquid refrigerant return circuit 125 may be constituted by a similar pipe such as that used for the main pipes 116 and the bypass pipes 115. One end of the liquid refrigerant return circuit 125 is connected to a portion of the bypass circuit 113 that is between the liquid outlet portion of the gas-liquid separator 110 and the throttling device 114. The other end of the liquid refrigerant return circuit 125 is connected to the intake conduit of the expander 103 (corresponding to a portion of the main pipes 116) downstream from the branching location to the bypass circuit 113. One end of the liquid refrigerant return circuit 125 may be connected to the liquid outlet portion of the gas-liquid separator 110, and the other end thereof may be connected to the inlet (or a neighboring part of the inlet) of the expander 103.

By restricting the opening of the throttling device 114, a portion of the liquid refrigerant separated from the gas refrigerant by the gas-liquid separator 110 can be supplied to the liquid refrigerant return circuit 125. After circulating through the liquid refrigerant return circuit 125, the liquid refrigerant is taken into the expander 103. Thus, the refrigerant flow rate through the expander 103 can be increased, and therefore, the amount of power recovery can be increased and further improvement in the efficiency can be expected. Of course, the constraint of constant density ratio can be avoided because of the working of the injection circuit 109.

In addition, it is possible to supply the whole amount of the liquid refrigerant that has been separated from the gas refrigerant by the gas-liquid separator 110 to the liquid refrigerant return circuit 125 by fully closing the throttling device 114. Under certain circumstances, the throttling device 114 and the bypass pipe 115 downstream from the throttling device 114 may be omitted. Furthermore, the liquid refrigerant return circuit 125 may include a flow rate control valve (not shown).

FIFTH EMBODIMENT

FIG. 9 illustrates a configuration diagram of a refrigeration cycle apparatus according to a fifth embodiment. A refrigeration cycle apparatus 100E is furnished with a main circuit 117 and a bypass circuit 106. The configuration of the main circuit 117 is the same as that of the other embodiments, but the configuration of the bypass circuit 106 is different from that of the other embodiments.

As illustrated in FIG. 9, the bypass circuit 106 connects the intake conduit of the expander 103 and the intermediate pressure portion of the compressor 101 via the first flow rate control valve 105, and it is the circuit for introducing a portion of the refrigerant that has passed through the radiator 102 to the intermediate pressure portion of the compressor 101. As has been explained previously, the injection port(s) 120 (see FIG. 2) of the compressor 101 may be used as the intermediate pressure portion of the compressor 101.

As illustrated in the Mollier diagram of FIG. 10, the change of the refrigerant circulating in the main circuit 117 is represented as A→B→C→D→E→F→A. The refrigerant flowing through the bypass circuit 106 is branched at point E, which corresponds to the portion of the main circuit 117 that is between the radiator 102 and the expander 103, is then decompressed to point G by the first flow rate control valve 105, and thereafter is introduced into the intermediate pressure portion of the compressor 101, which is represented as point C. The refrigerant flow rate flowing through the radiator 102 is the sum of the refrigerant flow rate Ge flowing through the evaporator 104 and the refrigerant flow rate Gi flowing through the bypass circuit 106, and thus is represented as (Ge+Gi); therefore, the amount of heat exchanged by the radiator increases. In this way, it is possible to improve the performance of the refrigeration cycle apparatus 100E while avoiding the constraint of constant density ratio.

Here, the following equations (1) and (2) hold, wherein: the volume flow rate of the refrigerant that passes through the compressor 101 is represented as VC; the refrigerant density at the inlet of the compressor 101 is DC; the volume flow rate of the refrigerant that passes through the expander 103 is VE; the refrigerant density at the inlet of the expander 103 is DE; and the mass flow rate ratio of the refrigerant that flows through the bypass circuit 113 with respect to the total refrigerant is h, whereby the mass flow rate ratio of the refrigerant that flows through the expander 103 can be expressed as (1−h). It should be noted that the mass flow rate ratio of the compressor 101 is approximated as “1.”
VC×DC:VE×DE=1:(1−h)  (1)
VE×DE=(1−h)×VC×DC  (2)

According to these relationships, when the refrigerant flow rate flowing through the bypass circuit 106 is increased, the refrigeration cycle will be balanced so that the refrigerant density DC at the inlet of the compressor 101 increases. Accordingly, when the intake superheat of the compressor 101 is desired to be reduced, the opening of the first flow rate control valve 105 provided in the bypass circuit 106 should be increased.

The control procedure for the first flow rate control valve 105 executed by the controller 107 will be described with reference to the flowchart of FIG. 11. Upon starting the operation, it is assessed at step 201 whether or not the difference between an actual superheat temperature T1 detected by the intake temperature sensor 111 and a target superheat TH1 falls within the tolerance range ±t₁ (dead zone). The tolerance ti may be set to be about 5% of the target superheat TH1. If it is assessed that the difference between the actual superheat temperature T1 and the target superheat TH1 falls within the tolerance range ±t₁, the control process is terminated.

On the other hand, if it is assessed that the difference between the actual superheat temperature T1 and the target superheat TH1 (absolute value) is greater than the tolerance t₁, the process proceeds to step 202, in which it is assessed whether or not the actual superheat temperature T1 is greater than the target superheat TH1. If the actual superheat temperature T1 is greater than the target superheat TH1, the process proceeds to step 203, in which a control process for increasing the opening of the first flow rate control valve 105 is executed. Increasing the opening of the first flow rate control valve 105 results in a greater refrigerant flow rate flowing through the bypass circuit 106, and therefore, the refrigeration cycle will be balanced so that the superheat temperature T1 decreases. If it is assessed at step 202 that the actual superheat temperature T1 is lower than the target superheat TH1, the process proceeds to step 204, in which a control process for decreasing the opening of the first flow rate control valve 105 is executed. Thereby, the refrigeration cycle will be balanced so that the superheat temperature T1 increases, and therefore the superheat temperature can be controlled to be closer to the target value.

Thus, by adjusting the opening of the first flow rate control valve 105 so as to control the superheat temperature optimally, system performance can be kept high while avoiding the constraint of constant density ratio.

The foregoing has described an embodiment in which the first flow rate control valve 105 is controlled to optimize the superheat temperature. It is also possible to control the opening of the first flow rate control valve 105 in order to optimize the refrigerant discharge temperature of the compressor 101, using the outlet temperature sensor 112 of the compressor 101 (see FIG. 1). In addition, the bypass circuit 106 may include an injector 123 (see FIG. 7) as described in the third embodiment.

The foregoing several embodiments have described examples of refrigeration cycle apparatus furnished with a fluid machine in which a compressor and an expander are coupled, but it should be understood that the present invention is also applicable to separate-type systems in which the compressor and the expander are not coupled physically to each other. In the separate-type system, power consumption of the motor for driving the compressor can be reduced by converting the mechanical power that is recovered by the expander into electric power by a generator, and regenerating the electric power to a power supply line. In such a system, the frequencies of the compressor and the expander may be changed individually and freely, so the system is essentially free from the constraint of constant density ratio.

However, because the efficiencies of the motor and the generator change depending of their frequencies, the efficiency of the system may degrade significantly if the efficiencies of the motor and the generator are ignored. For this reason, for the separate-type system as well, it may be advantageous to provide and utilize the bypass circuit and the injection circuit as described in the present specification, and this makes it possible to avoid the constraint of constant density ratio while maintaining highly efficient workings of the motor and the generator, leading to further enhancement in the system efficiency.

The refrigeration cycle apparatus according to the present invention can be used for not only hot water heaters and air-conditioners but also for other various electric appliances such as dish dryers and garbage dryers.

Claims

1. A refrigeration cycle apparatus comprising:

a compressor for compressing a refrigerant;

a radiator for cooling the refrigerant compressed by said compressor;

an expander for expanding the refrigerant cooled by said radiator and recovering mechanical power from the refrigerant under expansion;

an evaporator for heating the refrigerant expanded by said expander and supplying the refrigerant to said compressor;

a bypass circuit including a flow rate control valve and a gas-liquid separator that is provided downstream from said flow rate control valve and that is for separating the refrigerant passed through said flow rate control valve into a gas refrigerant and a liquid refrigerant, one end of said bypass circuit being connected to an intake conduit of said expander and the other end of said bypass circuit being connected to a discharge conduit of said expander so that a portion of the refrigerant passed through said radiator bypasses said expander and is guided to said flow rate control valve and that the liquid refrigerant separated by said gas-liquid separator returns to said discharge conduit of said expander; and

an injection circuit, one end of which being connected to a gas outlet portion of said gas-liquid separator and the other end of which being connected to an intermediate pressure portion of said compressor.

2. The refrigeration cycle apparatus according to claim 1, wherein said compressor and said expander are coupled uniaxially to a motor for driving said compressor.

3. The refrigeration cycle apparatus according to claim 1, wherein:

said intermediate pressure portion of said compressor is a portion facing a compression chamber of said compressor; and

the gas refrigerant that flows out of said gas-side discharge portion of said gas-liquid separator passes through said injection circuit, is injected into said compression chamber, and is mixed with the refrigerant under compression.

4. The refrigeration cycle apparatus according to claim 1, wherein:

said compressor is a multi-stage compressor comprising a low-pressure-side compressor and a high-pressure-side compressor; and

said intermediate pressure portion of said compressor is a joint portion where said low-pressure-side compressor and said high-pressure-side compressor are connected.

5. The refrigeration cycle apparatus according to claim 1, wherein said injection circuit comprises a second flow rate control valve.

6. The refrigeration cycle apparatus according to claim 1, wherein said bypass circuit further comprises a throttling device provided downstream from said gas-liquid separator.

7. The refrigeration cycle apparatus according to claim 1, further comprising:

an intake temperature sensor for detecting a temperature of the refrigerant after flowing out of said evaporator but before being taken into said compressor; and

a controller for controlling an opening of said flow rate control valve according to a detection result detected by said intake temperature sensor.

8. The refrigeration cycle apparatus according to claim 5, further comprising:

an outlet temperature sensor for detecting a temperature of the refrigerant after being discharged from said compressor but before flowing into said radiator; and

a controller for controlling an opening of said second flow rate control valve according to a detection result detected by said outlet temperature sensor.

9. A refrigeration cycle apparatus comprising:

a compressor for compressing a refrigerant;

a radiator for cooling the refrigerant compressed by said compressor;

an expander for expanding the refrigerant cooled by said radiator and recovering mechanical power from the refrigerant under expansion;

an evaporator for heating the refrigerant expanded by said expander and supplying the refrigerant to said compressor;

a bypass circuit including a flow rate control valve, one end of said bypass circuit being connected to an intake conduit of said expander and the other end of said bypass circuit being connected to an intermediate pressure portion of said compressor so that a portion of the refrigerant passed through said radiator bypasses said expander and is guided to said flow rate control valve;

an intake temperature sensor for detecting the refrigerant after flowing out of said evaporator but before being taken into said compressor; and

a controller for controlling an opening of said flow rate control valve according to a detection result detected by said intake temperature sensor.