REFRIGERATION CYCLE APPARATUS

Abstract

A refrigeration cycle apparatus 100 is provided with a refrigerant circuit 106, an injection flow passage 111, and a high-pressure supply passage 130. The refrigerant circuit 106 includes a low-pressure stage compressor 105, a high-pressure stage compressor 101, a heat radiator 102, an expander 103, a gas-liquid separator 108, and an evaporator 104. The expander 103 and the low-pressure stage compressor 105 are coupled by a power-recovery shaft 107. The refrigeration cycle apparatus 100 is further provided with a flow passage-switching mechanism that selectively connects one of the evaporator 104 and the high-pressure supply passage 130 to the low-pressure stage compressor 105. The flow passage-switching mechanism, for example, is constituted by an on-off valve 131 and a check valve 132.

Description

TECHNICAL FIELD

The present invention relates to a refrigeration cycle apparatus.

BACKGROUND ART

A refrigeration cycle apparatus 700 shown in FIG. 15 is conventionally known as a refrigeration cycle apparatus provided with an expander that recovers power by expanding a refrigerant, and a second compressor that preliminarily increases the pressure of the refrigerant (for example, see JP 2003-307358 A). With reference to FIG. 15, the configuration of the conventional refrigeration cycle apparatus 700 is described.

As shown in FIG. 15, the refrigeration cycle apparatus 700 is provided with a refrigerant circuit 6 formed of a first compressor 1, a heat radiator 2, an expander 3, an evaporator 4, a second compressor 5, and flow passages 10a to 10e connecting these components in this order. The second compressor 5 is coupled to the expander 3 by a power-recovery shaft 7, and is driven by receiving, via the power-recovery shaft 7, mechanical energy recovered in the expander 3.

Further, a bypass passage 8 that bypasses the second compressor 5 and a bypass valve 9 that controls the flow of the refrigerant in the bypass passage 8 are provided therein. The upstream end of the bypass passage 8 is connected to the flow passage 10d that connects the outlet of the evaporator 4 and the suction port of the second compressor 5. The downstream end of the bypass passage 8 is connected to the flow passage 10e that connects the discharge port of the second compressor 5 and the suction port of the first compressor 1.

The refrigeration cycle apparatus 700 is activated according to the following procedures. First, the operation of the first compressor 1 is started, and the bypass valve 9 is opened. These allow the refrigerant in the evaporator 4 to be drawn into the first compressor 1 through the bypass passage 8 as shown by solid arrows in FIG. 15. The pressure of the refrigerant is increased in the first compressor 1 and the refrigerant is discharged therefrom, thereby causing an increase in the pressure at the suction port of the expander 3. As a result of this, a pressure difference is produced between before and after the expander 3, as shown in FIG. 16, so that the expander 3 and the second compressor 5 can be activated rapidly. After the expander 3 and the second compressor 5 are activated, the bypass valve 9 is closed. The refrigerant that has flowed out of the evaporator 4 is drawn into the second compressor 5 through the flow passage 10d as shown by dashed arrows in FIG. 15. In this way, smooth transfer to regular operation can be achieved by providing the bypass passage 8.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2003-307358 A

SUMMARY OF INVENTION

Technical Problem

In the refrigeration cycle apparatus 700, only the expander 3 is involved in the activation of the expander 3 and the second compressor 5, whereas the second compressor 5 does not contribute thereto. Rather, the second compressor 5 is a load during the activation of the expander 3. That is, friction, etc., between the power-recovery shaft 7 and the components of the second compressor 5 cause a driving resistance to the expander 3.

Meanwhile, in the regular operation of the refrigeration cycle apparatus 700, the second compressor 5 and the expander 3 form the refrigerant circuit 6 of a single channel, and their rotational speeds are identical because they are coupled to each other by the power-recovery shaft 7 that is commonly shared. Accordingly, the volume of the second compressor 5 and the volume of the expander 3 need to be set so that the mass of the refrigerant to be drawn by the second compressor 5 per unit time should be equal to the mass of the refrigerant to be drawn by the expander 3 per unit time.

FIG. 17 is an example of the Mollier diagram when carbon dioxide is used as the refrigerant in the conventional refrigeration cycle apparatus 700. As shown in FIG. 17, in the regular operation of the conventional refrigeration cycle apparatus 700, the refrigerant drawn by the second compressor 5 has a pressure of 40 kg/cm², and a temperature of about 10° C. (point A in FIG. 17), and the refrigerant has a density of 108.0 kg/m³. The refrigerant drawn by the expander 3 has a pressure of 100 kg/cm², and a temperature of 40° C. (point C in FIG. 17), and the refrigerant has a density of 628.61 kg/m³ at this time point.

Here, the suction volume (m³) of the second compressor 5 is referred to as Vc, the suction volume (m³) of the expander 3 is referred to as Ve, and the rotational speed (S⁻¹) of the power-recovery shaft 7 per second is referred to as N. The mass (kg/s) of the refrigerant that the second compressor 5 can draw per second and the mass (kg/s) of the refrigerant that the expander 3 can draw per second can be expressed respectively by Formula 1 and Formula 2.

(The mass of the refrigerant that the second compressor 5 can draw per second)=108.0×Vc×N   (Formula 1)

(The mass of the refrigerant that the expander 3 can draw per second)=628.61×Ve×N   (Formula 2)

When the mass of the refrigerant that the second compressor 5 can draw per second and the mass of the refrigerant that the expander 3 can draw per second are equal, the suction volume Vc of the second compressor 5 can be expressed by Formula 3 from the above-mentioned Formula 1 and Formula 2.

Vc=(628.61/108.0)×Ve≈5.8×Ve   (Formula 3)

That is, in the activation of the refrigeration cycle apparatus 700, the expander 3 is required to drive the second compressor 5 having a suction volume that is about 5.8 times that of the expander 3. Further, the larger the ratio between the density of the refrigerant to be drawn by the second compressor 5 and the density of the refrigerant to be drawn by the expander 3, the larger the ratio between the suction volume of the second compressor 5 and the suction volume of the expander 3 also should be. In other words, the suction volume of the expander 3 becomes smaller with respect to the suction volume of the second compressor 5, and the driving resistance to the expander 3 in the activation of the second compressor 5 becomes relatively larger. Accordingly, there is a possibility that the expander 3 cannot drive the second compressor 5 at the time of activation, depending on the operational conditions of the refrigeration cycle apparatus 700. Instead, it might be necessary to impose an excess pressure, as compared to that in the regular operation, on the suction port side of the expander 3 in order to obtain a driving force necessary to drive the second compressor 5. As a result, the input power to the first compressor 1 increases and the efficiency of the refrigeration cycle apparatus 700 is reduced.

The present invention aims to solve the above-mentioned problems, and it is an object of the present invention to provide a refrigeration cycle apparatus that can be activated surely and stably.

Solution to Problem

That is, the present invention provides a refrigeration cycle apparatus including: a main refrigerant circuit having a low-pressure stage compressor that compresses a refrigerant, a high-pressure stage compressor that further compresses the refrigerant that has been compressed in the low-pressure stage compressor, a heat radiator that cools the refrigerant that has been compressed in the high-pressure stage compressor, an expander that recovers power from the refrigerant that has been cooled in the heat radiator while expanding the refrigerant, the expander being coupled to the low-pressure stage compressor by a shaft so that the recovered power is transferred to the low-pressure stage compressor, a gas-liquid separator that separates the refrigerant that has been expanded in the expander into a gas refrigerant and a liquid refrigerant, and an evaporator that evaporates the liquid refrigerant that has been separated in the gas-liquid separator; an injection flow passage that introduces the gas refrigerant that has been separated in the gas-liquid separator into a portion of the main refrigerant circuit from the discharge port of the low-pressure stage compressor to the suction port of the high-pressure stage compressor; a high-pressure supply passage that communicates a portion of the main refrigerant circuit from the discharge port of the high-pressure stage compressor to the suction port of the expander and a portion of the main refrigerant circuit from the outlet of the evaporator to the suction port of the low-pressure stage compressor; and a flow passage-switching mechanism capable of selectively connecting one selected from the evaporator and the high-pressure supply passage to the low-pressure stage compressor.

From another aspect, the present invention provides a refrigeration cycle apparatus including: a main refrigerant circuit having a low-pressure stage compressor that compresses a refrigerant, a high-pressure stage compressor that further compresses the refrigerant that has been compressed in the low-pressure stage compressor, a heat radiator that cools the refrigerant that has been compressed in the high-pressure stage compressor, an expander that recovers power from the refrigerant that has been cooled in the heat radiator while expanding the refrigerant, the expander being coupled to the low-pressure stage compressor by a shaft so that the recovered power is transferred to the low-pressure stage compressor, a gas-liquid separator that separates the refrigerant that has been expanded in the expander into a gas refrigerant and a liquid refrigerant, an evaporator that evaporates the liquid refrigerant that has been separated in the gas-liquid separator, and an expansion valve provided on the flow passage between the gas-liquid separator and the evaporator; an injection flow passage that introduces the gas refrigerant that has been separated in the gas-liquid separator into a portion of the main refrigerant circuit from the discharge port of the low-pressure stage compressor to the suction port of the high-pressure stage compressor; a controller that fully closes the expansion valve in the activation of the refrigeration cycle apparatus so that the pressure at the suction port of the low-pressure stage compressor is prevented from being equal to the pressure at the discharge port of the low-pressure stage compressor via the injection flow passage.

Advantageous Effects of Invention

According to the refrigeration cycle apparatus of the present invention, the high-pressure stage compressor can draw the refrigerant in the evaporator and the gas-liquid separator through the injection flow passage. This allows the pressure on the high-pressure side of the main refrigerant circuit to increase rapidly.

Since a portion of the main refrigerant circuit from the discharge port of the low-pressure stage compressor to the suction port of the high-pressure stage compressor is connected to the gas-liquid separator by the injection flow passage, the pressure at the discharge port of the expander can be made equal to the pressure at the suction port of the high-pressure stage compressor. The pressure at the suction port of the expander is normally equal to the pressure on the high-pressure side of the main refrigerant circuit.

On the other hand, the pressure at the suction port of the low-pressure stage compressor can be made equal to the pressure on the high-pressure side of the main refrigerant circuit due to the functions of the flow passage-switching mechanism and the high-pressure supply passage. The pressure at the discharge port of the low-pressure stage compressor is normally equal to the pressure at the suction port of the high-pressure stage compressor.

In this way, according to the present invention, a pressure difference can be produced not only before and after the expander but also before and after the low-pressure stage compressor. Therefore, the refrigeration cycle apparatus of the present invention can be activated surely and stably, independent of operational conditions.

According to another aspect of the refrigeration cycle apparatus of the present invention, the high-pressure stage compressor can draw the refrigerant in the gas-liquid separator through the injection flow passage. This allows the pressure on the high-pressure side of the main refrigerant circuit to increase rapidly.

Since a portion of the main refrigerant circuit from the discharge port of the low-pressure stage compressor to the suction port of the high-pressure stage compressor is connected to the gas-liquid separator by the injection flow passage, the pressure at the discharge port of the expander can be made equal to the pressure at the suction port of the high-pressure stage compressor. The pressure at the suction port of the expander is normally equal to the pressure on the high-pressure side of the main refrigerant circuit.

On the other hand, the flow passages before and after the expansion valve can be separated from each other by fully closing the expansion valve. Accordingly, the pressure at the suction port of the low-pressure stage compressor can be prevented from being equal to the pressure at the discharge port of the low-pressure stage compressor via the injection flow passage. As a result, the pressure at the suction port of the low-pressure stage compressor can be maintained at the pressure of the main refrigerant circuit before the high-pressure stage compressor is driven (intermediate pressure). The pressure at the discharge port of the low-pressure stage compressor is normally equal to the pressure at the suction port of the high-pressure stage compressor.

In this way, according to the present invention, a pressure difference can be produced not only before and after the expander but also before and after the low-pressure stage compressor. Therefore, the refrigeration cycle apparatus of the present invention can be activated surely and stably, independent of operational conditions.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a refrigeration cycle apparatus in Embodiment 1 of the present invention.

FIG. 2 is a flow chart of the activation control of the refrigeration cycle apparatus in Embodiment 1 of the present invention.

FIG. 3 is a configuration diagram of a refrigeration cycle apparatus in Modification 1.

FIG. 4 is a flow chart of the activation control of the refrigeration cycle apparatus in Modification 1.

FIG. 5 is a configuration diagram of a refrigeration cycle apparatus in Modification 2.

FIG. 6 is a schematic view showing the state in the activation of the refrigeration cycle apparatus in Embodiment 1, Modification 1, and Modification 2.

FIG. 7 is a configuration diagram of a power recovery system.

FIG. 8 is a configuration diagram of a refrigeration cycle apparatus in Embodiment 2 of the present invention.

FIG. 9 is a flow chart of the activation control of the refrigeration cycle apparatus in Embodiment 2 of the present invention.

FIG. 10 is a configuration diagram of a refrigeration cycle apparatus in Modification 3.

FIG. 11 is a flow chart of the activation control of the refrigeration cycle apparatus in Modification 3.

FIG. 12 is a configuration diagram of a refrigeration cycle apparatus in Modification 4.

FIG. 13 is a flow chart of the activation control of the refrigeration cycle apparatus in Modification 4.

FIG. 14A is a schematic view showing the state in the activation of the refrigeration cycle apparatus in Embodiment 2 and Modification 3.

FIG. 14B is a schematic view showing the state in the activation of the refrigeration cycle apparatus in Modification 4.

FIG. 15 is a configuration diagram of a conventional refrigeration cycle apparatus.

FIG. 16 is a schematic view showing the state in the activation of the refrigeration cycle apparatus shown in FIG. 15.

FIG. 17 is a Mollier diagram when carbon dioxide is used as a refrigerant in the conventional refrigeration cycle apparatus.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention are described with reference to drawings. It should be noted that the present invention is not limited to the following embodiments.

Embodiment 1

<Configuration of Refrigeration Cycle Apparatus 100

FIG. 1 is a configuration diagram showing a refrigeration cycle apparatus 100 in Embodiment 1 of the present invention. As shown in FIG. 1, the refrigeration cycle apparatus 100 is provided with a refrigerant circuit 106 formed by sequentially connecting a high-pressure stage compressor 101, a heat radiator 102, an expander 103, a gas-liquid separator 108, an evaporator 104, and a low-pressure stage compressor 105, with flow passages 106a to 106f. The flow passages 106a to 106f each are constituted by a refrigerant pipe. An expansion valve 110 is provided on the flow passage 106d between the gas-liquid separator 108 and the evaporator 104. A check valve 132 is provided on the flow passage 106e between the evaporator 104 and the low-pressure stage compressor 105. Hereinafter, the flow passage 106f connecting the discharge port of the low-pressure stage compressor 105 and the suction port of the high-pressure stage compressor 101 may be referred to also as the “intermediate-pressure flow passage 106f”.

The high-pressure stage compressor 101 is constituted by a compression mechanism 101a and a motor 101b for driving the compression mechanism 101a. The high-pressure stage compressor 101 compresses the refrigerant to high temperature and high pressure. A positive displacement compressor such as a scroll compressor and a rotary compressor can be used as the high-pressure stage compressor 101. The discharge port of the high-pressure stage compressor 101 is connected to the inlet of the heat radiator 102 via the flow passage 106a.

The heat radiator 102 radiates heat (cools) of the refrigerant at high temperature and high pressure that has been compressed by the high-pressure stage compressor 101 through heat exchange with an external heat source. The outlet of the heat radiator 102 is connected to the suction port of the expander 103 via the flow passage 106b.

The expander 103 expands the refrigerant at intermediate temperature and high pressure that has flowed out of the heat radiator 102 and converts the expansion energy (power) of the refrigerant into mechanical energy to recover it. The discharge port of the expander 103 is connected to the inlet of the gas-liquid separator 108 via the flow passage 106c. A positive displacement expander such as a scroll expander and a rotary expander can be used as the expander 103. In addition, a fluid pressure motor expander can be also used as the expander 103. The fluid pressure motor expander is a positive displacement fluid machine that recovers power from a refrigerant by sequentially performing processes of drawing the refrigerant and discharging the drawn refrigerant without performing any substantial expansion process in a working chamber. The detailed structure and the operational principle of the fluid pressure motor expander are disclosed, for example, in WO 2008/050654 A.

The gas-liquid separator 108 serves to separate the refrigerant at low temperature and low pressure that has been expanded in the expander 103 into a gas refrigerant and a liquid refrigerant. The gas-liquid separator 108 can prevent the liquid refrigerant from being drawn into the high-pressure stage compressor 101 in a large amount in the activation of the refrigeration cycle apparatus 100. The gas refrigerant outlet of the gas-liquid separator 108 is connected to the flow passage 106f via an injection flow passage 111. The liquid-refrigerant outlet of the gas-liquid separator 108 is connected to the inlet of the evaporator 104 via the flow passage 106d provided with the expansion valve 110.

The expansion valve 110 serves to regulate the flow rate of the liquid refrigerant to flow into the evaporator 104 in the regular operation. Accordingly, a valve, which allows the degree of opening to be varied stepwise, capable of expanding a refrigerant, typically, an electric expansion valve is preferably used as the expansion valve 110. In the activation of the refrigeration cycle apparatus 100, the expansion valve 110 is fully opened or substantially fully opened. This allows the refrigerant in the evaporator 104 to be drawn by the high-pressure stage compressor 101 smoothly.

The evaporator 104 evaporates the liquid refrigerant at low temperature and low pressure that has been separated in the gas-liquid separator 108 through heat exchange with an external heat source. The outlet of the evaporator 104 is connected to the suction port of the low-pressure stage compressor 105 via the flow passage 106e provided with the check valve 132.

The low-pressure stage compressor 105 draws the refrigerant at intermediate temperature and low pressure that has flowed out of the evaporator 104, and discharges it into the intermediate-pressure flow passage 106f after preliminarily increasing the pressure thereof. The discharge port of the low-pressure stage compressor 105 is connected to the suction port of the high-pressure stage compressor 101 via the intermediate-pressure flow passage 106f. A positive displacement compressor such as a scroll compressor and a rotary compressor can be used as the low-pressure stage compressor 105. Further, a fluid pressure motor compressor can be used as the low-pressure stage compressor 105. The fluid pressure motor compressor is a positive displacement fluid machine that increases the pressure of a refrigerant by substantially sequentially performing processes of drawing the refrigerant from the evaporator 104 and discharging the refrigerant to the high-pressure stage compressor 101. In other words, the fluid pressure motor compressor is a fluid machine that allows substantially no change in the volume of the refrigerant in a working chamber. The fluid pressure motor compressor basically has the same structure as the fluid pressure motor expander, the detail of which is disclosed in the above-mentioned literature.

The expander 103 is coupled to the low-pressure stage compressor 105 by a power-recovery shaft 107. The mechanical energy (power) recovered in the expander 103 can be transferred to the low-pressure stage compressor 105 via the power-recovery shaft 107. That is, the expander 103, the low-pressure stage compressor 105, and the power-recovery shaft 107 function as a power recovery system 109 that recovers power from the refrigerant. As shown in FIG. 7, the expander 103 and the low-pressure stage compressor 105 are accommodated in a single closed casing 109a holding lubrication oil, together with the power-recovery shaft 107. Therefore, no particular sealing structure is needed.

In this embodiment, the low-pressure stage compressor 105 has a larger volume than the expander 103. In the case of using carbon dioxide as the refrigerant, the ratio (Vc/Ve) of the volume Vc of the low-pressure stage compressor 105 with respect to the volume Ve of the expander 103 is set, for example, to the range of 5 to 15. In the case of using R410A as the refrigerant, the ratio (Vc/Ve) is set, for example, to the range of 30 to 40. In the case of using a thin refrigerant like R410A as the refrigerant to be drawn into the compressor, the ratio (Vc/Ve) also tends to increase. Generally, the larger the ratio (Vc/Ve), the larger the driving force (torque) required for self-activation of the low-pressure stage compressor 105 and the expander 103 should be. In this regard, “the volume of the low-pressure stage compressor 105” means a confined volume, that is, the volume of the working chamber at the time of completion of the drawing process. This applies also to the expander 103.

The refrigeration cycle apparatus 100 is further provided with a high-pressure supply passage 130 and an on-off valve 131. The high-pressure supply passage 130 is connected to the main refrigerant circuit 106 so as to communicate the flow passage 106a and the flow passage 106e. The on-off valve 131 is provided on the high-pressure supply passage 130 and controls the flow of the refrigerant in the high-pressure supply passage 130.

The high-pressure supply passage 130 has an upstream end E₁ (one end) connected to the flow passage 106a and a downstream end E₂ (the other end) connected to the flow passage 106e. That is, the high-pressure supply passage 130 is a flow passage that can introduce the refrigerant in the flow passage 106a directly to the suction port of the low-pressure stage compressor 105 before the rotation of the power-recovery shaft 107. The high-pressure supply passage 130, typically, is constituted by a refrigerant pipe.

As long as the pressure at the suction port of the low-pressure stage compressor 105 can be increased in the activation of the refrigeration cycle apparatus 100, the position of the upstream end E₁ is not limited to the position shown in FIG. 1. That is, the position of the upstream end E₁ is not specifically limited, as long as a portion of the main refrigerant circuit 106 from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103 and a portion of the main refrigerant circuit 106 from the outlet of the evaporator 104 to the suction port of the low-pressure stage compressor 105 can be communicated. Specifically, the high-pressure supply passage 130 may be connected to the main refrigerant circuit 106 so as to communicate the flow passage 106b and the flow passage 106e. Depending on the circumstances, the high-pressure supply passage 130 may branch from the heat radiator 102. For example, in the case where the heat radiator 102 is constituted by an upstream part and a downstream part, the high-pressure supply passage 130 can easily branch from a portion between these two parts.

However, in the case where the upstream end E₁ is located on the flow passage 106a as shown in FIG. 1, the following effects are obtained. The density of the refrigerant in the flow passage 106a is lower than the density of the refrigerant in the flow passage 106b. Normally, the refrigerant in the flow passage 106a is in a gas phase. It is possible to prevent the liquid refrigerant from flowing into the high-pressure stage compressor 101 through the low-pressure stage compressor 105 by supplying the gas refrigerant to the suction port of the low-pressure stage compressor 105 through the high-pressure supply passage 130. This prevents liquid compression in the high-pressure stage compressor 101, leading to an enhancement in reliability of the refrigeration cycle apparatus 100.

The on-off valve 131 and the check valve 132 form a flow passage-switching mechanism capable of selectively connecting one selected from the evaporator 104 and the high-pressure supply passage 130 to the low-pressure stage compressor 105. When one selected from the evaporator 104 and the high-pressure supply passage 130 is selectively connected to the low-pressure stage compressor 105, the refrigerant is introduced from one selected from the evaporator 104 and the high-pressure supply passage 130 to the low-pressure stage compressor 105. The check valve 132 is provided in a portion of the main refrigerant circuit 106 from the outlet of the evaporator 104 to the downstream end E₂ of the high-pressure supply passage 130 (flow passage 106e).

The on-off valve 131 is closed in the regular operation, and is opened in the activation of the refrigeration cycle apparatus 100. By opening the on-off valve 131, it is possible to supply the refrigerant in the flow passage 106a directly to the suction port of the low-pressure stage compressor 105 through the high-pressure supply passage 130. At that time, the check valve 132 can block the flow of the refrigerant from the high-pressure supply passage 130 toward the evaporator 104. On the other hand, by closing the on-off valve 131, it is possible to supply the refrigerant from the evaporator 104 to the low-pressure stage compressor 105 while restricting the flow of the refrigerant from the high-pressure supply passage 130 to the low-pressure stage compressor 105. The check valve 132 has an advantage that there is no need for electrical control. Of course, it is also possible to replace the check valve 132 with a valve that can be arbitrarily opened and closed.

The refrigeration cycle apparatus 100 is further provided with the injection flow passage 111 and an injection flow-regulating valve 112. The injection flow passage 111 serves to introduce the gas refrigerant separated from the liquid refrigerant in the gas-liquid separator 108, to a portion of the main refrigerant circuit 106 from the discharge port of the low-pressure stage compressor 105 to the suction port of the high-pressure stage compressor 101 (intermediate-pressure flow passage 106f). Specifically, the injection flow passage 111 is connected to the main refrigerant circuit 106 so as to communicate the gas refrigerant outlet of the gas-liquid separator 108 and the intermediate-pressure flow passage 106f. The injection flow-regulating valve 112 is provided on the injection flow passage 111 and controls the flow of the refrigerant in the injection flow passage 111. The injection flow passage 111, typically, is constituted by a refrigerant pipe. As the injection flow-regulating valve 112, a valve, which allows the degree of opening to be varied stepwise, capable of expanding a refrigerant, typically, an electric expansion valve is preferably used.

The injection flow-regulating valve 112 serves to regulate the flow rate of the gas refrigerant to be injected into the intermediate-pressure flow passage 106f in the regular operation. On the other hand, the injection flow-regulating valve 112 is fully opened or substantially fully opened in the activation of the refrigeration cycle apparatus 100. When the injection flow-regulating valve 112 is opened in the activation, the high-pressure stage compressor 101 can draw the refrigerant present in the flow passage 106c, the gas-liquid separator 108, the flow passage 106d, and the evaporator 104. This enables the pressure on the high-pressure side of the main refrigerant circuit 106 to increase rapidly. Particularly, since the gas-liquid separator 108 is provided in this embodiment, it is possible to store a sufficient amount of refrigerant between the discharge port of the expander 103 and the check valve 132 during stoppage.

In order to improve the coefficient of performance of the refrigeration cycle apparatus 100, the gas refrigerant can be supplied from the gas-liquid separator 108 to the intermediate-pressure flow passage 106f through the injection flow passage 111 after the activation of the refrigeration cycle apparatus 100. By appropriately adjusting the degree of opening of each of the expansion valve 110 and the injection flow-regulating valve 112, it is possible to prevent the liquid refrigerant from flowing from the gas-liquid separator 108 into the intermediate-pressure flow passage 106f as well as preventing the backflow of the refrigerant from the intermediate-pressure flow passage 106f to the gas-liquid separator 108.

The refrigeration cycle apparatus 100 is further provided with a controller 117. The expansion valve 110, the injection flow-regulating valve 112, and the on-off valve 131 are controlled by the controller 117. The controller 117, typically, is constituted by a microcomputer. When a command to start the operation of the refrigeration cycle apparatus 100 is given to the controller 117 through an input device (not shown), a predetermined control program stored in an internal memory of the controller 117 is executed. Specifically, the controller 117 executes the predetermined activation control described below with reference to FIG. 2. Further, the controller 117 controls the action of the motor 101b that drives the high-pressure stage compressor 101.

The refrigeration cycle apparatus 100 is further provided with an activation detector 119 that detects the activation of the expander 103 or the low-pressure stage compressor 105. The controller 117 switches the control of the on-off valve 131 (flow passage-switching mechanism) from the control before the activation to the control after the activation, according to a detection result of the activation detector 119. Specifically, the on-off valve 131 is opened before the activation of the expander 103 and the low-pressure stage compressor 105 so that the refrigerant is introduced from the high-pressure supply passage 130 to the low-pressure stage compressor 105. After the activation of the expander 103 and the low-pressure stage compressor 105, the on-off valve 131 is closed so that the refrigerant is introduced from the evaporator 104 to the low-pressure stage compressor 105. For example, upon the reception of signals that indicate the activation of the low-pressure stage compressor 105 from the activation detector 119, the controller 117 closes the on-off valve 131. In this way, smooth transfer to the control in the regular operation can be achieved.

A temperature detector, a pressure detector, or the like can be used as the activation detector 119. The activation detector 119 as a temperature detector, for example, includes a temperature detecting element such as a thermocouple and a thermistor, and detects the difference ΔT between the temperature of the refrigerant at the suction port of the expander 103 and the temperature of the refrigerant at the discharge port of the expander 103. The activation detector 119 as a pressure detector, for example, includes a piezoelectric element, and detects the difference ΔP between the pressure of the refrigerant at the suction port of the expander 103 and the pressure of the refrigerant at the discharge port of the expander 103. Further, the activation detector 119 may include a timer that measures an elapsed time from the activation of the high-pressure stage compressor 101. Such a timer can be provided also as a function of the controller 117. In this case, the controller 117 itself can function as the activation detector 119. Furthermore, a contact or noncontact displacement sensor that detects the driving of the power-recovery shaft 107, such as an encoder, may be provided as the activation detector 119.

Depending on the type of the activation detector 119, the method for detecting the activation of the power recovery system 109 differs as follows. According to the following methods, it is possible to detect the activation of the power recovery system 109 easily.

In the case of using a pressure detector as the activation detector 119, a threshold P_th that has been determined experimentally or theoretically, for example, is preset in the controller 117. When the value obtained by subtracting the current pressure difference ΔP_n+1 detected by the pressure detector from the pressure difference ΔP_n (n: natural number) that has been detected by the pressure detector at a time going back for a unit time exceeds the specific threshold P_th, the activation of the expander 103 or the low-pressure stage compressor 105 is detected. In the controller 117, a single threshold P_th may be set, or a plurality of thresholds P_th associated with the outdoor temperature or the like may be set. In the latter case, the controller 117 selects an optimal threshold P_th on the basis of the outdoor temperature or the like. This applies also to other thresholds described below.

The difference ΔP between the pressure of the refrigerant at the suction port of the expander 103 and the pressure of the refrigerant at the discharge port of the expander 103 generally monotonically increases during the period after the activation of the high-pressure stage compressor 101 and before the activation of the expander 103. When the expander 103 starts to operate, the pressure difference ΔP turns to decrease temporarily, and becomes smaller than that immediately before the activation of the expander 103. It is possible to detect the activation of the expander 103 or the low-pressure stage compressor 105 by capturing this change in the pressure difference ΔP. Specifically, the pressure difference ΔP is detected at every unit time and stored in the memory of the controller 117. Then, the last pressure difference ΔP_n previously stored in the memory and the current pressure difference ΔP_n+1 are compared. When the current pressure difference ΔP₊1 significantly falls below the last past pressure difference ΔP_n, the expander 103 or the low-pressure stage compressor 105 can be determined to have been activated. In other words, when (ΔP_n−ΔP_n+1)>P_th is satisfied, the expander 103 or the low-pressure stage compressor 105 can be determined to have been activated. It should be noted that the “unit time” can be set arbitrarily to a sufficient time to capture a sudden decrease in the pressure difference ΔP, for example, in the range of 1 to 5 seconds.

Instead of the pressure difference ΔP, it is also possible to use the temperature difference ΔT. That is, when a value obtained by subtracting the current temperature difference ΔT_n+1 detected by the temperature detector from the temperature difference ΔT_n (n: natural number) that has been detected by the temperature detector at a time going back for a unit time exceeds a specific threshold T_th, the activation of the expander 103 or the low-pressure stage compressor 105 is detected.

Further, there is also a possibility that the activation of the power recovery system 109 can be detected on the basis of the discharge temperature from the expander 103 or the discharge pressure from the expander 103. When the power recovery system 109 is activated, the expander 103 is also rotated. The expander 103 draws the refrigerant, then expands the drawn refrigerant, and discharges it. Therefore, the temperature and pressure of the refrigerant after being discharged from the expander 103 are lower than those before being drawn. The power recovery system 109 can be determined to have been activated by capturing a sudden change in the temperature (or pressure) at the discharge port of the expander 103 while monitoring the temperature (or pressure) in chronological order.

Meanwhile, on the presumption that the power recovery system 109 is activated without fail, the activation of the expander 103 or the low-pressure stage compressor 105 may be detected by the method described below. The below-described method is rather a method of determining whether the power recovery system 109 is in a state that allows continuous operation, than a method of capturing the activation of the expander 103 or the low-pressure stage compressor 105. After the activation of the expander 103 or the low-pressure stage compressor 105 is detected by the below-described method, the control of the on-off valve 131 (flow passage-switching mechanism) can be switched from the control before the activation to the control after the activation according to the detected results. In this way, the power recovery system 109 continues to operate stably even after the on-off valve 131 is closed.

Specifically, in the case of using a temperature detector as the activation detector 119, a threshold T₁ that has been determined experimentally or theoretically, for example, is preset in the controller 117. When the temperature difference ΔT detected by the temperature detector exceeds the threshold T₁, the activation of the expander 103 or the low-pressure stage compressor 105 is detected.

In the case of using a pressure detector as the activation detector 119, a threshold P₁ that has been determined experimentally or theoretically, for example, is preset in the controller 117. When the pressure difference ΔP detected by the pressure detector exceeds the specific threshold P₁, the activation of the expander 103 or the low-pressure stage compressor 105 is detected.

The reason why the activation of the expander 103 or the low-pressure stage compressor 105 can be detected by comparison between the temperature difference ΔT and the threshold T₁, or comparison between the pressure difference ΔP and the threshold P₁ is as follows. When the high-pressure stage compressor 101 is activated, the refrigerant discharged from the high-pressure stage compressor 101 is supplied to the suction port of the low-pressure stage compressor 105 through the high-pressure supply passage 130. This activates the power recovery system 109. At this time, since the low-pressure stage compressor 105 serves as a driving source, the power recovery system 109 starts to rotate before the temperature difference between the suction temperature of the high-pressure stage compressor 101 and the discharge temperature of the high-pressure stage compressor 101 becomes significant. When the power recovery system 109 starts to rotate, the pressure difference in the cycle has not been sufficiently increased, and the power to rotate the power recovery system 109 is low. Therefore, the rotational speed of the power recovery system 109 is also low. When the rotational speed of the power recovery system 109 is low, the rotational speed of the expander 103 is also low. This state corresponds to a “narrowed state” that is a description for expansion valves. Accordingly, the discharge temperature and discharge pressure of the high-pressure stage compressor 101 gradually increase as well.

When the discharge temperature and discharge pressure of the high-pressure stage compressor 101 increase, the power to rotate the expander 103 and the low-pressure stage compressor 105 also increases, and the rotational speed of the power recovery system 109 increases. Then, when a high rotational speed is achieved, the power recovery system 109 stably rotates under the influence of the inertial force. The on-off valve 131 is desirably maintained open until such a stable rotation state is reached.

On the other hand, the suction temperature of the expander 103 gradually increases from the temperature during stoppage, which is substantially the same as the outdoor temperature. Depending on the suction temperature (or suction pressure) of the expander 103, the discharge temperature (or discharge pressure) of the expander 103 is determined. The suction temperature, the discharge temperature, the suction pressure, and the discharge pressure of the expander 103 each in the activation of the power recovery system 109 and in the regular operation of the power recovery system 109, for example, with the outdoor temperature being 10° C., are shown below as an example. It should be noted that the following values are calculated with the expansion ratio=2.0. The refrigerant is carbon dioxide.

<In Activation>

Suction temperature: 10° C.

Suction pressure: 5.0 MPa

Discharge temperature: −3.0° C.

Discharge pressure: 3.2 MPa

Difference between suction temperature and discharge temperature: 13° C.

Difference between suction pressure and discharge pressure: 1.8 MPa

<In Regular Operation>

Suction temperature: 40° C.

Suction pressure: 10.0 MPa

Discharge temperature: 13.4° C.

Discharge pressure: 4.9 MPa

Difference between suction temperature and discharge temperature: 26.6° C. Difference between suction pressure and discharge pressure: 5.1 MPa

When the power recovery system 109 is activated with the discharge temperature and discharge pressure of the high-pressure stage compressor 101 being low, the suction temperature of the expander 103 and the discharge temperature of the expander 103 each gradually increase as mentioned above. The difference between the suction temperature and the discharge temperature gradually increase as well. This applies also to the pressure. Therefore, the activation of the power recovery system 109 can be detected by setting appropriate values as the threshold T₁ and the threshold P₁, e.g., respective values that are slightly larger than the temperature difference and the pressure difference to be reached when the activation of the power recovery system 109 can be estimated.

In the case of using a timer as the activation detector 119, a threshold time t₁ that has been determined experimentally or theoretically, for example, is preset in the controller 117. When the time t measured by the timer exceeds the threshold time t₁, the activation of the expander 103 or the low-pressure stage compressor 105 is detected.

The “threshold time t₁” is written in the activation control program to be executed by the controller 117. For example, the time from the activation of the high-pressure stage compressor 101 to the activation of the low-pressure stage compressor 105 is actually measured under various operational conditions (such as outdoor temperatures). Then, a time at which the activation of the low-pressure stage compressor 105 can be surely determined under all the operational conditions can be set as the “threshold time t₁”. Theoretically, a model of the refrigeration cycle apparatus 100 is constructed, and a pressure difference that is necessary and sufficient to activate the power recovery system 109 is estimated by computer simulation. Thereafter, using parameters such as the volume of the high-pressure stage compressor 101 and the filling amount of the refrigerant in the main refrigerant circuit 106, the initial activation time necessary to produce the estimated pressure difference is calculated. The calculated initial activation time can be set as the “threshold time t₁”.

The method for detecting the activation of the expander 103 or the low-pressure stage compressor 105 is not limited to one, and a plurality of methods can be performed in combination. For example, the activation of the expander 103 or the low-pressure stage compressor 105 is accurately captured by a method of monitoring the pressure difference ΔP and/or the temperature difference ΔT between the suction port and the discharge port of the expander 103. Thereafter, whether the power recovery system 109 is in a state that allows continuous operation is determined by a method of comparing the temperature difference ΔT with the threshold T₁, a method of comparing the pressure difference ΔP with the threshold P₁, or a method of comparing the elapsed time t with the threshold time t₁. When these plurality of conditions are satisfied, the expander 103 or the low-pressure stage compressor 105 is determined to be activated, and the on-off valve 131 is closed.

<Operation of Refrigeration Cycle Apparatus 100>

FIG. 2 is a flow chart showing the activation control of the refrigeration cycle apparatus 100. The refrigeration cycle apparatus 100 starts the regular operation after performing the activation control shown in FIG. 2. In an operation standby state, the high-pressure stage compressor 101 is stopped, the expansion valve 110 is opened, and the pressure of the refrigerant in the main refrigerant circuit 106 is substantially uniform.

When an activation command is input in step S11, the controller 117 transmits control signals to the actuators of the expansion valve 110 and the injection flow-regulating valve 112 so that these valves 110 and 112 are fully opened (step S12). Further, it transmits control signals to the actuator of the on-off valve 131 so that the on-off valve 131 is opened (step S13). This allows the high-pressure supply passage 130 to be open.

Next, the controller 117 starts to supply power to the motor 101b in order to activate the high-pressure stage compressor 101 (step S14). This activates the high-pressure stage compressor 101 and causes the refrigerant present in the intermediate-pressure flow passage 106f, the injection flow passage 111, the flow passage 106c, the gas-liquid separator 108, the flow passage 106d, the evaporator 104, and a part of the flow passage 106e (portion between the evaporator 104 and the check valve 132) to be drawn into the high-pressure stage compressor 101.

Instead of opening the on-off valve 131 before the activation of the high-pressure stage compressor 101, it is also possible to open the on-off valve 131 upon the activation of the high-pressure stage compressor 101.

Upon the activation of the high-pressure stage compressor 101, a fan or pump that causes a fluid (air or water) for heat exchange with the refrigerant to flow into the heat radiator 102 is activated. This can prevent an excessive increase in the high pressure of the cycle. Likewise, a fan or pump of the evaporator 104 is activated upon the activation of the high-pressure stage compressor 101. This allows efficient production of the gas refrigerant to be drawn into the high-pressure stage compressor 101.

Once the drawing of the refrigerant into the high-pressure stage compressor 101 is started, the internal pressure of the intermediate-pressure flow passage 106f, etc., decreases. On the other hand, since the refrigerant compressed in the high-pressure stage compressor 101 is discharged, the pressure in flow passages from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103 (the flow passage 106a, the heat radiator 102, and the flow passage 106b), the high-pressure supply passage 130, and a part of the flow passage 106e (portion between the check valve 132 and the suction port of the low-pressure stage compressor 105) increases.

As a result, as shown in FIG. 6, the pressure at the suction port of each of the expander 103 and the low-pressure stage compressor 105 is rendered relatively high, and the pressure at the discharge port of each of the expander 103 and the low-pressure stage compressor 105 is rendered relatively low. That is, a pressure difference can be produced not only between the suction port and the discharge port of the expander 103, but also between the suction port and the discharge port of the low-pressure stage compressor 105. The pressure difference of the refrigerant acts on each of the expander 103 and the low-pressure stage compressor 105, and thus self-activation of the power recovery system 109 can be achieved easily. The high-pressure stage compressor 101 can draw a sufficient amount of the refrigerant to produce a large pressure difference because the injection flow passage 111 and the gas-liquid separator 108 are provided.

Upon detecting the activation of the low-pressure stage compressor 105 through the activation detector 119 (step S15), the controller 117 transmits control signals to the actuator of the on-off valve 131 so that the on-off valve 131 is closed (step S16). This allows the backpressure acting on the check valve 132 to be released, and the refrigerant is supplied from the evaporator 104 to the low-pressure stage compressor 105 through the flow passage 106e. Meanwhile, the gas-liquid two-phase refrigerant whose pressure has been reduced in the expander 103 is supplied to the gas-liquid separator 108. The opening degree of each of the expansion valve 110 and the injection flow-regulating valve 112 is adjusted so that excess supply of the liquid refrigerant to the high-pressure stage compressor 101 through the injection flow passage 111 and the flow passage 106f is prevented (step S17). After the completion of the activation control shown in FIG. 2, transfer to the regular operation where the refrigerant is circulated in the main refrigerant circuit 106 is performed in the refrigeration cycle apparatus 100.

When the operation of the refrigeration cycle apparatus 100 is intended to be stopped, the rotational speed of the high-pressure stage compressor 101, for example, is progressively reduced. After the high-pressure stage compressor 101 has been stopped, the refrigerant moves through the high-pressure stage compressor 101, the expander 103, and the low-pressure stage compressor 105, taking sufficient time. Therefore, the pressure difference in the main refrigerant circuit 106 is naturally released, and the pressure in the main refrigerant circuit 106 becomes substantially uniform to be stabilized. This causes the expander 103 and the low-pressure stage compressor 105 to be stopped naturally.

<Effects of Refrigeration Cycle Apparatus 100>

According to this embodiment, the high-pressure stage compressor 101 can draw and compress the refrigerant in the evaporator 104 and the gas-liquid separator 108 in the activation of the refrigeration cycle apparatus 100. Therefore, the pressure in flow passages from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103 can be rapidly increased. Since a large pressure difference is produced between the suction port and the discharge port of the expander 103, the power recovery system 109 is self-activated smoothly.

Further, the compressed refrigerant is introduced into a part of the flow passage 106e from the check valve 132 to the suction port of the low-pressure stage compressor 105 through the high-pressure supply passage 130. This produces a large pressure difference also between the suction port and the discharge port of the low-pressure stage compressor 105. This fact contributes to a smoother self-activation of the power recovery system 109. In this embodiment, the low-pressure stage compressor 105 and the expander 103 each have a certain suction volume. Particularly, when the suction volume of the low-pressure stage compressor 105 is larger than the suction volume of the expander 103, the power recovery system 109 is activated more smoothly by producing a pressure difference between the suction port and the discharge port of the low-pressure stage compressor 105.

In the case where a certain period of time has elapsed without detecting the activation of the expander 103 or the low-pressure stage compressor 105 after the activation of the high-pressure stage compressor 101, it can be determined that the activation of the power recovery system 109 has been failed. In the case where the activation of the power recovery system 109 has been failed, the controller 117 stops the high-pressure stage compressor 101 and performs the control to activate the power recovery system 109 again. In this way, it is possible to prevent an excessive increase in the pressure in flow passages from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103. It is also possible to prevent damages to the components of the expander 103 from occurring due to an excessive pressure difference between before and after the expander 103. Thus, the reliability of the refrigeration cycle apparatus 100 can be improved.

According to this embodiment, the heat radiator 102 is connected to the suction port of the expander 103, the evaporator 104 is connected to the suction port of the low-pressure stage compressor 105, and the gas-liquid separator 108 is connected to the discharge port of the expander 103. The gas-liquid separator 108 is connected also to the discharge port of the low-pressure stage compressor 105 via the injection flow passage 111. Since the volumes of the heat radiator 102, the evaporator 104, and the gas-liquid separator 108 are comparatively large, these components can function as a buffer space for the refrigerant in the activation of the refrigeration cycle apparatus 100. Thus, an effect of suppressing the pressure pulsation in the activation can be obtained.

The type of refrigerant (working fluid) that can be used in this embodiment is not specifically limited. For example, fluorine refrigerant such as R410A, natural refrigerant such as carbon dioxide, and low GWP (Global Warming Potential) refrigerant such as R1234yf can be used. Whichever the refrigerant is used, the above-mentioned effects can be obtained.

Modification 1

<Configuration of Refrigeration Cycle Apparatus 200>

FIG. 3 is a configuration diagram of a refrigeration cycle apparatus 200 in Modification 1. As shown in FIG. 3, the flow passage-switching mechanism is constituted by a three-way valve 133 in the refrigeration cycle apparatus 200. As the activation detector 119, a PTC (Positive Temperature Coefficient) heater 140 and a current detector 141 are used. Further, a bypass flow passage 201 and a bypass valve 202 are provided. Other configurations are the same as those in Embodiment 1. In this modification, the same components as those in Embodiment 1 are denoted by the same reference numerals, and the detailed descriptions thereof are omitted.

The three-way valve 133 as a flow passage-switching mechanism is provided at the downstream end E₂ of the high-pressure supply passage 130 so as to be capable of switching between a first state in which the refrigerant is introduced from the evaporator 104 into the low-pressure stage compressor 105 and a second state in which the refrigerant is introduced from the high-pressure supply passage 130 into the low-pressure stage compressor 105. In the first state, the flow of the refrigerant from the high-pressure supply passage 130 to the low-pressure stage compressor 105 is blocked. In the second state, the flow of the refrigerant from the evaporator 104 to the low-pressure stage compressor 105 is blocked. In this way, the on-off valve 131 and the check valve 132 in Embodiment 1 can be replaced with the three-way valve 133. The three-way valve 133 can suppress an increase in the number of components.

The bypass flow passage 201 is connected to the main refrigerant circuit 106 so as to bypass the expander 103. The upstream end E₃ of the bypass flow passage 201 is located on the flow passage 106b, and the downstream end E₄ thereof is located on the flow passage 106c. The bypass valve 202 is provided on the bypass flow passage 201. The bypass flow passage 201, typically, is constituted by a refrigerant pipe. As the bypass valve 202, a valve, which allows the degree of opening to be varied stepwise, capable of expanding a refrigerant, typically, an electric expansion valve is preferably used.

The current detector 141 detects the magnitude of the current flowing in the PTC heater 140. The PTC heater 140 is provided in a portion of the main refrigerant circuit 106 from the outlet of the heat radiator 102 to the suction port of the expander 103, that is, on the flow passage 106b. Specifically, the PTC heater 140 is located on the expander 103 side as seen from the upstream end E₃ of the bypass flow passage 201. When the PTC heater 140 is provided at such a position, the PTC heater 140 is less likely to be affected by the flow of the refrigerant toward the bypass flow passage 201. Therefore, it is possible to detect the flow of the refrigerant into the expander 103 accurately.

In the case of using the PTC heater 140 and the current detector 141 as the activation detector 119, a threshold ΔI₁ that has been determined experimentally or theoretically, for example, is preset in the controller 117. When the power recovery system 109 is activated, the refrigerant starts to flow also at the suction port of the expander 103. Then, the magnitude of the current also suddenly changes due to the temperature change (temperature reduction) of the PTC heater 140. In order to capture such a change, the amount of change per unit time in the current flowing in the PTC heater 140 can be preset as the threshold ΔI₁. The “unit time”, for example, can be set arbitrarily in the range of 1 to 5 seconds. The amount of change per unit time in the current flowing in the PTC heater 140 is calculated by the current detector 141, and when the calculated amount of change exceeds the threshold ΔI₁, the activation of the expander 103 or the low-pressure stage compressor 105 is detected. The PTC heater 140 and the current detector 141 can be used also in other embodiments and modifications.

<Operation of Refrigeration Cycle Apparatus 200>

FIG. 4 is a flow chart showing the activation control of the refrigeration cycle apparatus 200. When an activation command is input in step S21, the controller 117 transmits control signals to the actuators of the expansion valve 110, the injection flow-regulating valve 112, and the bypass valve 202 so that the expansion valve 110 and the injection flow-regulating valve 112 are fully opened as well as the bypass valve 202 is opened to a specific degree (step S22). Here, the phrase “the bypass valve 202 is opened to a specific degree” means to be set within a range of the degree of opening that allows the pressure difference between the suction port and the discharge port of the expander 103 to be maintained to the level that is required for the activation of the expander 103. This “specific degree of opening” can be determined experimentally or theoretically. In short, the bypass valve 202 is slightly opened so as to prevent excessive reduction in the pressure difference between before and after the expander 103.

Next, the low-pressure stage compressor 105 and the high-pressure supply passage 130 are connected by controlling the three-way valve 133 (step S23).

Next, the controller 117 starts to supply power to the motor 101b in order to activate the high-pressure stage compressor 101 (step S24). This activates the high-pressure stage compressor 101 and causes the refrigerant present in the intermediate-pressure flow passage 106f, the injection flow passage 111, the flow passage 106c, the gas-liquid separator 108, the flow passage 106d, the evaporator 104, and a part of the flow passage 106e (portion between the evaporator 104 and the three-way valve 133) to be drawn into the high-pressure stage compressor 101.

When the drawing of the refrigerant into the high-pressure stage compressor 101 is started, as has been described in Embodiment 1 with reference to FIG. 6, the pressure at the suction port of each of the expander 103 and the low-pressure stage compressor 105 is rendered relatively high, and the pressure at the discharge port of each of the expander 103 and the low-pressure stage compressor 105 is rendered relatively low. As a result, the power recovery system 109 is self-activated smoothly.

Upon detecting the activation of the low-pressure stage compressor 105 through the activation detector 119 (step S25), the controller 117 controls the three-way valve 133 so that the low-pressure stage compressor 105 and the evaporator 104 are connected (step S26). This allows the refrigerant to be supplied from the evaporator 104 to the low-pressure stage compressor 105 through the flow passage 106e. The opening degree of each of the expansion valve 110 and the injection flow-regulating valve 112 is adjusted because of the same reason as in Embodiment 1 (step S27). Further, the bypass valve 202 is closed. Thereafter, transfer to the regular operation is performed.

<Effects of the Refrigeration Cycle Apparatus 200>

According to this modification, the following effects can be obtained in addition to the effects described in Embodiment 1. According to this modification, the controller 117 opens the bypass valve 202, before the activation of the expander 103 and the low-pressure stage compressor 105, to a degree within the range that allows a pressure difference required for the activation of the expander 103 to be produced between the suction port and the discharge port of the expander 103. That is, the activation of the power recovery system 109 is attempted while the bypass valve 202 is slightly opened. The controller 117 closes the bypass valve 202 after the activation of the expander 103 and the low-pressure stage compressor 105. Thus, a sudden reduction in the pressure difference between before and after the expander 103 can be prevented from occurring immediately after the activation of the power recovery system 109. Accordingly, smooth transfer to the regular operation can be achieved while a driving force to continue the operation of the power recovery system 109 is sufficiently ensured.

Modification 2

FIG. 5 is a configuration diagram of a refrigeration cycle apparatus 300 in Modification 2. As shown in FIG. 5, the refrigeration cycle apparatus 300 differs from Embodiment 1 in that a temperature detector that detects the temperature of the refrigerant at the discharge port of the low-pressure stage compressor 105 is used as the activation detector 119. In this modification, the same components as those in Embodiment 1 are denoted by the same reference numerals, and the detailed descriptions thereof are omitted.

In the case of using a temperature detector as the activation detector 119, a threshold T₂ that has been determined experimentally or theoretically, for example, is preset in the controller 117. When a value obtained by subtracting a temperature that has been detected by the temperature detector at a time going back for a unit time from the current temperature detected by the temperature detector exceeds the specific threshold T₂, the activation of the expander 103 or the low-pressure stage compressor 105 is detected.

The temperature of the refrigerant at the discharge port of the low-pressure stage compressor 105 is low during the period after the activation of the high-pressure stage compressor 101 and before the activation of the expander 103. When the low-pressure stage compressor 105 starts to operate, the temperature of the refrigerant at the discharge port of the low-pressure stage compressor 105 suddenly increases. The change in the temperature of the refrigerant at the discharge port of the low-pressure stage compressor 105, for example, is about 10° C., though it depends also on the intended use, operational conditions, etc., of the refrigeration cycle apparatus 100. By capturing this temperature change, the activation of the expander 103 or the low-pressure stage compressor 105 can be detected. Specifically, the temperature T of the refrigerant at the discharge port of the low-pressure stage compressor 105 is detected per unit time and stored in the memory of the controller 117. Then, the last temperature T_n (n: natural number) previously stored in the memory and the current temperature T_n+1 are compared. When the current temperature T_n+1 significantly exceeds the last past temperature T_n, in other words, when (T_n+1−T_n)>T₂ is satisfied, the expander 103 or the low-pressure stage compressor 105 can be determined to have been activated. It should be noted that the “unit time” can be set to a sufficient time to capture the sudden reduction in the temperature T, for example, can be arbitrarily set in the range of 1 to 5 seconds.

Upon the activation of the low-pressure stage compressor 105, the refrigerant at high pressure and high temperature is drawn into the low-pressure stage compressor 105 from the high-pressure supply passage 130. Since the pressure in the flow passage 106f is low, the low-pressure stage compressor 105 temporarily functions as an expander. The refrigerant that has been expanded in the low-pressure stage compressor 105 is discharged into the flow passage 106f. The refrigerant that has been compressed in the high-pressure stage compressor 101 and that has been expanded again in the low-pressure stage compressor 105 obtains an enthalpy corresponding to the loss occurring in each of the high-pressure stage compressor 101 and the low-pressure stage compressor 105. That is, the refrigerant present in the flow passage 106f flows through the high-pressure stage compressor 101 and the low-pressure stage compressor 105, and when it returns to the flow passage 106f again, the temperature of the refrigerant increases by the increment in the enthalpy of the refrigerant. The temperature detector detects the activation of the low-pressure stage compressor 105 by comparing the temperature increase with the threshold T₂.

<Effects of Refrigeration Cycle Apparatus 300>

According to this modification, the following effects can be obtained in addition to the effects described in Embodiment 1. In this modification, the activation is detected on the basis of the temperature of the refrigerant at the discharge port of the low-pressure stage compressor 105. This can ensure the capture of the activation of the power recovery system 109, thereby enabling rapid transfer to the regular operation.

Embodiment 2

<Configuration of Refrigeration Cycle Apparatus 400>

FIG. 8 is a configuration diagram of a refrigeration cycle apparatus 400 in Embodiment 2. As shown in FIG. 8, the refrigeration cycle apparatus 400 differs from Embodiment 1 in that the high-pressure supply passage 130, the on-off valve 131, and the check valve 132 are omitted. In this embodiment, the same components as those in Embodiment 1 are denoted by the same reference numerals, and the detailed descriptions thereof are omitted.

In this embodiment, activation control that is different from that in Embodiment 1 is performed. That is, the expansion valve 110 is fully closed in the activation of the refrigeration cycle apparatus 400. This allows the pressure at the suction port of the low-pressure stage compressor 105 to be maintained at the pressure in a standby state (before the activation of the high-pressure stage compressor 101). Upon the activation of the high-pressure stage compressor 101, a pressure difference occurs between the suction port and the discharge port of the expander 103. Likewise, a pressure difference occurs between the suction port and the discharge port of the low-pressure stage compressor 105. As a result, the power recovery system 109 is activated.

In the activation of the refrigeration cycle apparatus 400, the injection flow-regulating valve 112 is fully opened or substantially fully opened. When the injection flow-regulating valve 112 is opened in the activation, the high-pressure stage compressor 101 can draw the refrigerant present in the flow passage 106c, the gas-liquid separator 108, and a part of the flow passage 106d. This enables the pressure on the high-pressure side of the main refrigerant circuit 106 to increase rapidly. Particularly, since the gas-liquid separator 108 is provided in this embodiment, it is possible to store a sufficient amount of refrigerant between the discharge port of the expander 103 and the expansion valve 110 during stoppage.

In this embodiment, the controller 117 controls the expansion valve 110 according to a detection result of the activation detector 119. Specifically, it fully closes the expansion valve 110 in the activation of the refrigeration cycle apparatus 400. This can prevent the pressure at the suction port of the low-pressure stage compressor 105 from being equal to the pressure at the discharge port of the low-pressure stage compressor 105 via the injection flow passage 111. On the other hand, the controller 117 opens the expansion valve 110 after the activation of the expander 103 and the low-pressure stage compressor 105. For example, upon the reception of signals that indicate the activation of the low-pressure stage compressor 105 from the activation detector 119, the controller 117 fully opens the expansion valve 110.

Also in this embodiment, the activation of the power recovery system 109 can be detected by the method described in Embodiment 1. The control of the expansion valve 110 can be switched from the control before the activation to the control after the activation, according to the detection result. In this way, after the expansion valve 110 is opened, the power recovery system 109 continues to operate stably.

In this embodiment, a temperature detector that detects the temperature of the refrigerant in a portion of the main refrigerant circuit 106 from the expansion valve 110 to the suction port of the low-pressure stage compressor 105 (a part of the flow passage 106d, the evaporator 104, and the flow passage 106e) can be further used as the activation detector 119. In this case, when the difference between a temperature in a standby state (before the activation of the high-pressure stage compressor 101) detected by the temperature detector and the current temperature detected by the temperature detector exceeds a specific threshold T₀, the activation of the expander 103 or the low-pressure stage compressor 105 is detected. Typically, a temperature detector that detects the evaporation temperature of the refrigerant in the evaporator 104 can be used as the activation detector 119.

Likewise, a pressure detector that detects the pressure of the refrigerant in a portion of the main refrigerant circuit 106 from the expansion valve 110 to the suction port of the low-pressure stage compressor 105 can be used as the activation detector 119. When the difference between a pressure in a standby state detected by the pressure detector and the current pressure detected by the pressure detector exceeds a specific threshold P₀, the activation of the expander 103 or the low-pressure stage compressor 105 is detected.

When the power recovery system 109 is activated, the low-pressure stage compressor 105 draws the refrigerant present in the evaporator 104. This causes a reduction in the temperature and the pressure in the evaporator 104. An optimal threshold T₀ or threshold P₀ determined by an experimental or theoretical technique is preset in the controller 117. The activation of the power recovery system 109 can be detected by comparing the temperature change in flow passages from the expansion valve 110 to the suction port of the low-pressure stage compressor 105 (flow passages on the low-pressure side) with the threshold T₀. Likewise, the activation of the power recovery system 109 can be detected by comparing the pressure change in flow passages on the low-pressure side with the threshold P₀.

Also in this embodiment, the method for detecting the activation of the expander 103 or the low-pressure stage compressor 105 is not limited to one, and a plurality of methods can be performed in combination. For example, the activation of the expander 103 or the low-pressure stage compressor 105 is accurately captured by a method of monitoring the temperature or pressure of the refrigerant in a portion of the main refrigerant circuit 106 from the expansion valve 110 to the suction port of the low-pressure stage compressor 105. Thereafter, whether the power recovery system 109 is in a state that allows continuous operation is determined by a method of comparing the temperature difference ΔT with the threshold T₁, a method of comparing the pressure difference ΔP with the threshold P₁, or a method of comparing the elapsed time t with the threshold time t₁. When these plurality of conditions are satisfied, the expander 103 or the low-pressure stage compressor 105 is determined to have been activated, and the expansion valve 110 is opened.

<Operation of Refrigeration Cycle Apparatus 400>

FIG. 9 is a flow chart showing the activation control of the refrigeration cycle apparatus 400. The refrigeration cycle apparatus 400 starts the regular operation after performing the activation control shown in FIG. 9. In an operation standby state, the high-pressure stage compressor 101 is stopped, the expansion valve 110 and the injection valve 112 are opened, and the pressure of the refrigerant in the main refrigerant circuit 106 is substantially uniform.

When an activation command is input in step ST11, the controller 117 transmits control signals to the actuator of the expansion valve 110 so that the expansion valve 110 is closed (fully closed) (step ST12).

Next, the controller 117 starts to supply power to the motor 101b in order to activate the high-pressure stage compressor 101 (step ST13). This activates the high-pressure stage compressor 101 and causes the refrigerant present in the intermediate-pressure flow passage 106f, the injection flow passage 111, the flow passage 106c, the gas-liquid separator 108, and a part of the flow passage 106d (portion between the gas-liquid separator 108 and the expansion valve 110) to be drawn into the high-pressure stage compressor 101. Instead of closing the expansion valve 110 before the activation of the high-pressure stage compressor 101, it is also possible to close the expansion valve 110 corresponding to the activation of the high-pressure stage compressor 101.

A fan or pump that causes a fluid (air or water) for heat exchange with the refrigerant to flow into the heat radiator 102 is activated, corresponding to the activation of the high-pressure stage compressor 101. This can prevent an excessive increase in the high pressure of the cycle. The fan or pump of the evaporator 104 may be activated corresponding to the activation of the high-pressure stage compressor 101, or may be activated after the expansion valve 110 is opened. In order to maintain the pressure at the suction port of the low-pressure stage compressor 105 to the pressure in a standby state, the latter operation is recommended.

Once the drawing of the refrigerant into the high-pressure stage compressor 101 is started, the internal pressure of the intermediate-pressure flow passage 106f, etc., decreases. On the other hand, since the refrigerant compressed in the high-pressure stage compressor 101 is discharged, the pressure in flow passages from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103 (the flow passage 106a, the heat radiator 102, and the flow passage 106b) increases. Meanwhile, the pressure of the refrigerant in flow passages from the expansion valve 110 to the suction port of the low-pressure stage compressor 105 (a part of the flow passage 106d, the evaporator 104, and the flow passage 106e) is maintained to the pressure in the refrigerant circuit 106 during stoppage of the refrigeration cycle apparatus 400.

As a result, as shown in FIG. 14A, a pressure difference can be produced not only between the suction port and the discharge port of the expander 103, but also between the suction port and the discharge port of the low-pressure stage compressor 105. The pressure difference of the refrigerant acts on each of the expander 103 and the low-pressure stage compressor 105, and thus self-activation of the power recovery system 109 can be achieved easily. The high-pressure stage compressor 101 can draw a sufficient amount of the refrigerant to produce a large pressure difference because the injection flow passage 111 and the gas-liquid separator 108 are provided.

Upon detecting the activation of the low-pressure stage compressor 105 through the activation detector 119 (step ST14), the controller 117 transmits control signals to the actuator of the expansion valve 110 so that the expansion valve 110 is fully opened (or substantially fully opened) (step ST15). This causes the gas-liquid two-phase refrigerant whose pressure has been reduced in the expander 103 to be supplied to the gas-liquid separator 108. After the completion of the activation control shown in FIG. 9, transfer to the regular operation where the refrigerant is circulated in the main refrigerant circuit 106 is performed in the refrigeration cycle apparatus 400. In the regular operation, the opening degree of each of the expansion valve 110 and the injection flow-regulating valve 112 is adjusted so that excess supply of the liquid refrigerant to the high-pressure stage compressor 101 through the injection flow passage 111 and the flow passage 106f is prevented.

Also in this embodiment, the operation of the refrigeration cycle apparatus 400 can be stopped according to the method described in Embodiment 1.

<Effects of Refrigeration Cycle Apparatus 400>

According to this embodiment, the high-pressure stage compressor 101 can draw and compress the refrigerant in the gas-liquid separator 108 in the activation of the refrigeration cycle apparatus 400. Therefore, the pressure in flow passages from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103 can be increased rapidly. Since a large pressure difference is produced between the suction port and the discharge port of the expander 103, the power recovery system 109 is self-activated smoothly.

Further, it is possible to maintain the pressure of the refrigerant in flow passages from the expansion valve 110 to the suction port of the low-pressure stage compressor 105 to the pressure in the refrigerant circuit 106 during stoppage of the refrigeration cycle apparatus 400 by closing the expansion valve 110. Therefore, a pressure difference occurs also between the suction port and the discharge port of the low-pressure stage compressor 105. This fact contributes to a smoother self-activation of the power recovery system 109. In this embodiment, the low-pressure stage compressor 105 and the expander 103 each have a certain suction volume. Particularly, when the suction volume of the low-pressure stage compressor 105 is larger than the suction volume of the expander 103, the power recovery system 109 is activated more smoothly by producing a pressure difference between the suction port and the discharge port of the low-pressure stage compressor 105.

In the case where a specific condition is satisfied without detecting the activation of the expander 103 or the low-pressure stage compressor 105 after the activation of the high-pressure stage compressor 101, it can be determined that the activation of the power recovery system 109 has been failed. When the activation of the power recovery system 109 has been failed, the controller 117 stops the high-pressure stage compressor 101 and performs the control to activate the power recovery system 109 again. That is, when a failure of the activation is detected, the expansion valve 110 is once fully opened. Thereafter, the activation control described with reference to FIG. 9 is performed. In this way, it is possible to prevent an excessive increase in the pressure in flow passages from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103. It is also possible to prevent damages to the components of the expander 103 from occurring due to an excessive pressure difference between before and after the expander 103. Thus, the reliability of the refrigeration cycle apparatus 400 can be improved.

The method for detecting a failure in the activation of the power recovery system 109 is not specifically limited. For example, after the activation of the high-pressure stage compressor 101, the current temperature (or pressure) of the refrigerant in flow passages from the expansion valve 110 to the suction port of the low-pressure stage compressor 105 (flow passages on the low-pressure side), e.g., in the evaporator 104 is detected. When the difference between the detected temperature (or pressure) and a reference temperature (or reference pressure) does not reach a specific threshold within a certain period of time, the power recovery system 109 can be determined to have failed to be activated. As the threshold, the aforementioned threshold T₀ or threshold P₀ can be used. As the reference temperature (or reference pressure), the temperature (or pressure) of the refrigerant in the evaporator 104 before the activation of the high-pressure stage compressor 101 can be used. In the case where a certain period of time has elapsed without detecting the activation of the power recovery system 109 after the activation of the high-pressure stage compressor 101, it can be determined that the activation of the power recovery system 109 has been failed. It is also possible to determine whether or not the activation of the power recovery system 109 has been failed by detecting the temperature or pressure in flow passages from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103 (flow passages on the high-pressure side), on the basis of the difference between the detected temperature or pressure and the temperature or pressure in the flow passages on the high-pressure side before the activation of the high-pressure stage compressor 101.

Modification 3

<Configuration of Refrigeration Cycle Apparatus 500>

FIG. 10 is a configuration diagram of a refrigeration cycle apparatus 500 in Modification 3. As shown in FIG. 10, the refrigeration cycle apparatus 500 is provided with the bypass flow passage 201 and the bypass valve 202. Other configurations are the same as those in Embodiment 2. In this modification, the same components as those in Embodiment 2 are denoted by the same reference numerals, and the detailed descriptions thereof are omitted.

The bypass flow passage 201 is connected to the main refrigerant circuit 106 so as to bypass the expander 103. The upstream end E₃ of the bypass flow passage 201 is located on the flow passage 106b, and the downstream end E₄ thereof is located on the flow passage 106c. The bypass valve 202 is provided on the bypass flow passage 201. The bypass flow passage 201, typically, is constituted by a refrigerant pipe. As the bypass valve 202, a valve, which allows the degree of opening to be varied stepwise, capable of expanding a refrigerant, typically, an electric expansion valve is preferably used.

The element portion of the activation detector 119 is provided on the flow passage 106b. The element portion of the activation detector 119 may be located on the heat radiator 102 side, or may be located on the expander 103 side, as seen from the upstream end E₃ of the bypass flow passage 201.

<Operation of Refrigeration Cycle Apparatus 500>

FIG. 11 is a flow chart showing the activation control of the refrigeration cycle apparatus 500. When an activation command is input in step ST21, the controller 117 transmits control signals to the actuators of the expansion valve 110 and the bypass valve 202 so that the expansion valve 110 is fully closed, and the bypass valve 202 is opened to a specific degree (step ST22). Here, the phrase “the bypass valve 202 is opened to a specific degree” means to be set within a range of the degree of opening that allows the pressure difference between the suction port and the discharge port of the expander 103 to be maintained to the level that is required for the activation of the expander 103. This “specific degree of opening” can be determined experimentally or theoretically. In short, the bypass valve 202 is slightly opened so as to prevent excessive reduction in the pressure difference between before and after the expander 103.

Next, the controller 117 starts to supply power to the motor 101b in order to activate the high-pressure stage compressor 101 (step ST23). This activates the high-pressure stage compressor 101 and causes the refrigerant present in the intermediate-pressure flow passage 106f, the injection flow passage 111, the flow passage 106c, the gas-liquid separator 108, and a part of the flow passage 106d to be drawn into the high-pressure stage compressor 101.

When the drawing of the refrigerant into the high-pressure stage compressor 101 is started, as has been described in Embodiment 2 with reference to FIG. 14A, a pressure difference can be produced not only between the suction port and the discharge port of the expander 103, but also between the suction port and the discharge port of the low-pressure stage compressor 105. The pressure difference of the refrigerant acts on each of the expander 103 and the low-pressure stage compressor 105, and thus self-activation of the power recovery system 109 can be achieved easily.

Upon detecting the activation of the low-pressure stage compressor 105 through the activation detector 119 (step ST24), the controller 117 transmits control signals to the actuator of the expansion valve 110 so that the expansion valve 110 is fully opened (or substantially fully opened) (step ST25). Further, it transmits control signals to the actuator of the bypass valve 202 so that the bypass valve 202 is fully closed.

<Effects of Refrigeration Cycle Apparatus 500>

According to this modification, the following effects can be obtained in addition to the effects described in Embodiment 2. According to this modification, the controller 117 opens the bypass valve 202, before the activation of the expander 103 and the low-pressure stage compressor 105, to a degree within the range that allows a pressure difference required for the activation of the expander 103 to be produced between the suction port and the discharge port of the expander 103. That is, the activation of the power recovery system 109 is attempted while the bypass valve 202 is slightly opened. The controller 117 closes the bypass valve 202 after the activation of the expander 103 and the low-pressure stage compressor 105. Thus, a sudden reduction in the pressure difference between before and after the expander 103 can be prevented from occurring immediately after the activation of the power recovery system 109. Accordingly, smooth transfer to the regular operation can be achieved while a driving force to continue the operation of the power recovery system 109 is sufficiently ensured.

Modification 4

<Configuration of Refrigeration Cycle Apparatus 600>

FIG. 12 is a configuration diagram of a refrigeration cycle apparatus 600 in Modification 4. As shown in FIG. 12, the refrigeration cycle apparatus 600 is further provided with a bypass flow passage 301 and a bypass valve 302. Other configurations are the same as in Embodiment 2. In this modification, the same components as those in Embodiment 2 are denoted by the same reference numerals, and the detailed descriptions thereof are omitted.

The bypass flow passage 301 is connected to the main refrigerant circuit 106 so as to communicate the flow passage 106b and the flow passage 106d. The bypass valve 302 is provided on the bypass flow passage 301 and controls the flow of the refrigerant in the bypass flow passage 301. The bypass flow passage 301, typically, is constituted by a refrigerant pipe. As the bypass valve 302, an on-off valve can be used.

Specifically, the bypass flow passage 301 has an upstream end E₅ located at a portion of the main refrigerant circuit 106 from the outlet of the heat radiator 102 to the suction port of the expander 103 (the flow passage 106b), and a downstream end E₆ located at a portion of the main refrigerant circuit 106 from the expansion valve 110 to the inlet of the evaporator 104 (a part of the flow passage 106d). The bypass flow passage 301 allows the refrigerant at high pressure in the flow passage 106b to be introduced directly to the suction port of the low-pressure stage compressor 105.

As long as the pressure at the suction port of the low-pressure stage compressor 105 can be increased, the positions of the upstream end E₅ and the downstream end E₆ are not limited to the positions shown in FIG. 12. That is, as long as the portion of the main refrigerant circuit 106 from the discharge port of the high-pressure stage compressor 101 to the suction port of the expander 103 and a portion of the main refrigerant circuit 106 from the expander 110 to the suction port of the low-pressure stage compressor 105 can be communicated, the position of the upstream end E₅ is not specifically limited. Specifically, the bypass flow passage 301 may be connected to the main refrigerant circuit 106 so as to communicate the flow passage 106a and the flow passage 106e. Depending on the circumstances, the bypass flow passage 301 may branch from the heat radiator 102. For example, in the case where the heat radiator 102 is constituted by an upstream part and a downstream part, the bypass flow passage 301 can easily branch from a portion between these two parts.

<Operation of Refrigeration Cycle Apparatus 600>

FIG. 13 is a flow chart showing the activation control of the refrigeration cycle apparatus 600. When an activation command is input in step ST31, the controller 117 transmits control signals to the actuators of the expansion valve 110 and the bypass valve 302 so that the expansion valve 110 is fully closed, and the bypass valve 302 is fully opened (step ST32).

Next, the controller 117 starts to supply power to the motor 101b in order to activate the high-pressure stage compressor 101 (step ST33). This activates the high-pressure stage compressor 101 and causes the refrigerant present in the intermediate-pressure flow passage 106f, the injection flow passage 111, the flow passage 106c, the gas-liquid separator 108, and a part of the flow passage 106d to be drawn into the high-pressure stage compressor 101.

When the drawing of the refrigerant into the high-pressure stage compressor 101 is started, as shown in FIG. 14B, a large pressure difference can be produced not only between the suction port and the discharge port of the expander 103, but also between the suction port and the discharge port of the low-pressure stage compressor 105. The pressure difference of the refrigerant acts on each of the expander 103 and the low-pressure stage compressor 105, and thus self-activation of the power recovery system 109 can be achieved easily. Particularly, according to this modification, the pressure at the suction port of the low-pressure stage compressor 105 can be increased due to the functions of the bypass flow passage 301 and the bypass valve 302.

Upon detecting the activation of the low-pressure stage compressor 105 through the activation detector 119 (step ST34), the controller 117 transmits control signals to the actuator of the expansion valve 110 so that the expansion valve 110 is fully opened (or substantially fully opened) (step ST35). Further, it transmits control signals to the actuator of the bypass valve 302 so that the bypass valve 302 is fully closed.

<Effects of Refrigeration Cycle Apparatus 600>

According to this modification, the following effects can be obtained in addition to the effects described in Embodiment 2. According to this modification, the pressure at the suction port of the low-pressure stage compressor 105 can be also increased through the bypass flow passage 301. Accordingly, the drive torque to be imparted to the low-pressure stage compressor 105 increases, and a smoother activation of the power recovery system 109 is enabled.

Various constituents described in the respective embodiments and modifications can be applied to other embodiments and modifications without restriction as long as no technical contradiction occurs. For example, the three-way valve 133 (see FIG. 3) described in Modification 2 can be applied to Embodiment 1 and Modification 2.

INDUSTRIAL APPLICABILITY

The refrigeration cycle apparatus of the present invention is useful for devices such as water heaters, air conditioners, and dryers.

Claims

1. A refrigeration cycle apparatus comprising:

a main refrigerant circuit having a low-pressure stage compressor that compresses a refrigerant, a high-pressure stage compressor that further compresses the refrigerant that has been compressed in the low-pressure stage compressor, a heat radiator that cools the refrigerant that has been compressed in the high-pressure stage compressor, an expander that recovers power from the refrigerant that has been cooled in the heat radiator while expanding the refrigerant, the expander being coupled to the low-pressure stage compressor by a shaft so that the recovered power is transferred to the low-pressure stage compressor, a gas-liquid separator that separates the refrigerant that has been expanded in the expander into a gas refrigerant and a liquid refrigerant, and an evaporator that evaporates the liquid refrigerant that has been separated in the gas-liquid separator;

an injection flow passage that introduces the gas refrigerant that has been separated in the gas-liquid separator into a portion of the main refrigerant circuit from a discharge port of the low-pressure stage compressor to a suction port of the high-pressure stage compressor;

a high-pressure supply passage that communicates a portion of the main refrigerant circuit from a discharge port of the high-pressure stage compressor to a suction port of the expander and a portion of the main refrigerant circuit from an outlet of the evaporator to a suction port of the low-pressure stage compressor;

a flow passage-switching mechanism capable of selectively connecting one selected from the evaporator and the high-pressure supply passage to the low-pressure stage compressor so that the refrigerant is introduced from the evaporator or the high-pressure supply passage to the low-pressure stage compressor; and

a controller that controls the flow passage-switching mechanism before activation of the expander and the low-pressure stage compressor so that the refrigerant is introduced from the high-pressure supply passage to the low-pressure stage compressor, while controlling the flow passage-switching mechanism after the activation of the expander and the low-pressure stage compressor so that the refrigerant is introduced from the evaporator to the low-pressure stage compressor, wherein

a discharge pressure of the high-pressure stage compressor is applied to the suction port of the low-pressure stage compressor and the suction port of the expander while a suction pressure of the high-pressure stage compressor is applied to the discharge port of the low-pressure stage compressor and a discharge port of the expander before activation of the expander and the low-pressure stage compressor.

2. The refrigeration cycle apparatus according to claim 1, wherein

the high-pressure supply passage has an upstream end connected to a portion of the main refrigerant circuit from the discharge port of the high-pressure stage compressor to an inlet of the heat radiator.

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

the high-pressure supply passage has a downstream end connected to a portion of the main refrigerant circuit from the outlet of the evaporator to the suction port of the low-pressure stage compressor, and

the flow passage-switching mechanism is constituted by an on-off valve provided on the high-pressure supply passage and a valve, provided in a portion of the main refrigerant circuit from the outlet of the evaporator to the downstream end of the high-pressure supply passage, capable of blocking flow of the refrigerant from the high-pressure supply passage toward the evaporator.

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

the high-pressure supply passage has a downstream end connected to a portion of the main refrigerant circuit from the outlet of the evaporator to the suction port of the low-pressure stage compressor, and

the flow passage-switching mechanism is constituted by a three-way valve provided at the downstream end of the high-pressure supply passage.

5. (canceled)

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

an activation detector that detects the activation of the expander or the low-pressure stage compressor, wherein

the controller switches control of the flow passage-switching mechanism from control before the activation to control after the activation, according to a detection result of the activation detector.

7. The refrigeration cycle apparatus according to claim 6, wherein

the activation detector includes a timer that measures an elapsed time from activation of the high-pressure stage compressor, and

when the time measured by the timer exceeds a specific threshold time, the activation of the expander or the low-pressure stage compressor is detected.

8. The refrigeration cycle apparatus according to claim 6, wherein

the activation detector includes a temperature detector that detects a difference between a temperature of the refrigerant at the suction port of the expander and a temperature of the refrigerant at the discharge port of the expander, and

when the temperature difference detected by the temperature detector exceeds a specific threshold, activation of the expander or the low-pressure stage compressor is detected.

9. The refrigeration cycle apparatus according to claim 6, wherein

the activation detector includes a pressure detector that detects a difference between a pressure of the refrigerant at the suction port of the expander and a pressure of the refrigerant at the discharge port of the expander, and

when the pressure difference detected by the pressure detector exceeds a specific threshold, activation of the expander or the low-pressure stage compressor is detected.

10. The refrigeration cycle apparatus according to claim 6, wherein

the activation detector includes a pressure detector that detects a difference between a pressure of the refrigerant at the suction port of the expander and a pressure of the refrigerant at the discharge port of the expander, and

when a value obtained by subtracting a current pressure difference detected by the pressure detector from a pressure difference that has been detected by the pressure detector at a time going back for a unit time exceeds a specific threshold, activation of the expander or the low-pressure stage compressor is detected.

11. The refrigeration cycle apparatus according to claim 6, wherein

the activation detector includes a temperature detector that detects a difference between a temperature of the refrigerant at the suction port of the expander and a temperature of the refrigerant at the discharge port of the expander, and

when a value obtained by subtracting a current temperature difference detected by the temperature detector from a temperature difference that has been detected by the temperature detector at a time going back for a unit time exceeds a specific threshold, activation of the expander or the low-pressure stage compressor is detected.

12. The refrigeration cycle apparatus according to claim 6, wherein

the activation detector includes a PTC heater provided in a portion from an outlet of the heat radiator to the suction port of the expander of the main refrigerant circuit, and

when the amount of change per unit time in an electric current flowing in the PTC heater exceeds a specific threshold, activation of the expander or the low-pressure stage compressor is detected.

13. The refrigeration cycle apparatus according to claim 6, wherein

the activation detector is a temperature detector that detects a temperature of the refrigerant at the discharge port of the low-pressure stage compressor, and

when a value obtained by subtracting a temperature that has been detected by the temperature detector at a time going back for a unit time from a current temperature detected by the temperature detector exceeds a specific threshold, activation of the expander or the low-pressure stage compressor is detected.

14. The refrigeration cycle apparatus according to claim 1, wherein

in the case where activation of the expander and the low-pressure stage compressor has been failed, the controller stops the high-pressure stage compressor and performs control to activate the expander and the low-pressure stage compressor again.

15. The refrigeration cycle apparatus according to claim 1, wherein

the expander and the low-pressure stage compressor are accommodated in a single closed casing.

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

a bypass flow passage that bypasses the expander; and

a bypass valve provided on the bypass flow passage, wherein

the controller opens the bypass valve to a specific degree before the activation of the expander and the low-pressure stage compressor and closes the bypass valve after the activation of the expander and the low-pressure stage compressor.

17. The refrigeration cycle apparatus according to claim 1, wherein

the expander and the low-pressure stage compressor each have a certain suction volume, and

the suction volume of the low-pressure stage compressor is larger than the suction volume of the expander.

18-30. (canceled)