JP5389184B2 - Refrigeration cycle equipment - Google Patents

Description

  The present invention relates to a refrigeration cycle apparatus that recovers power with an expander.

For example, in a conventional refrigeration cycle apparatus used for refrigeration or air conditioning, an expansion process is performed by a positive displacement expander, and the recovered expansion power is used for a compression process performed by a positive displacement compressor. is there.
However, since the compressor driven by the expander and the power collected by the expander is a rotary machine, “negative power” is generated inside due to frictional resistance, mechanism loss, and the like. For this reason, in order to start the expander and the compressor driven by the power recovered by the expander, power that can overcome this “negative power” is required. For this reason, a refrigeration cycle apparatus that reduces the “negative power” that tends to hinder the start-up (rotation) of the expander and the compressor driven by the power recovered by the expander, A refrigeration cycle apparatus has been proposed in which the power of the "power" (power to rotate the expander) is increased.

As such a refrigeration cycle apparatus, for example, “the structure is such that the drive shaft of another compressor and the output shaft of the expansion mechanism are linked. The gas suction port and the gas discharge port of the other compressor are connected and the other compressor shaft is connected. A bypass pipe that bypasses the compressor is provided, and a check valve that restricts refrigerant flow from the gas discharge port to the gas suction port is provided in the bypass pipe ”(for example, see Patent Document 1). Has been proposed.
In addition, as such a refrigeration cycle apparatus, an apparatus has been proposed in which the pressure difference between the inflow side and the outflow side of the expander is increased to increase the power that can be recovered by the expander (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 11-94379 (paragraphs [0009], [0013], FIG. 1) JP 2006-132818 A (paragraphs [0014] to [0021])

For example, in the refrigeration cycle apparatus described in Patent Document 1, the discharge side pressure and the suction side pressure of the compressor are equalized by a bypass pipe. This facilitates activation of the expander (expansion mechanism) and the compressor connected to the expander via a shaft.
However, since the compressor connected to the expander by the shaft is a positive displacement compressor, the pressure is increased inside the compressor.
FIG. 11 is an explanatory view showing a pressure change in a compression chamber of a compressor connected to an expander by a shaft in Patent Document 1. The pressure in the compression chamber of the compressor changes in the process indicated by the arrow in FIG. Since the compressor is a positive displacement compressor as described above, the pressure is increased inside the compressor. For this reason, in order to start this compressor, the compression power corresponding to the area C shown in FIG. 11 is required. That is, as shown in Patent Document 1, even if the suction side and the discharge side of the compressor are bypassed, “negative power” exists. For this reason, in some cases, the “negative power” is larger than the “positive power” obtained by the expander, and there is a problem that the expander may not be started.

  Further, when starting the expander or compressor, static friction acting on the thrust bearing or radial bearing of the expander or compressor is also affected. This static friction is larger than the dynamic friction that acts when the expander or compressor is driven. For this reason, in order to start up the expander or compressor, it is necessary to have "positive power" that overcomes the static friction that acts on the thrust bearings and radial bearings of the expander and compressor. Furthermore, it becomes unstable.

  For example, in a scroll-type compressor, in order to reduce the load applied to the thrust bearing (friction acting on the thrust bearing), it is common practice to introduce a refrigerant in the compression process on the back side of the orbiting scroll. . Similarly, in a scroll type expander, in order to reduce the load applied to the thrust bearing (friction acting on the thrust bearing), it is common practice to introduce a refrigerant in the expansion process on the back side of the orbiting scroll. Yes. However, these methods for reducing the load applied to the thrust bearing (friction acting on the thrust bearing) are based on the assumption that the orbiting scroll is rotating. That is, it is for reducing the dynamic friction which acts on a thrust bearing. For this reason, in the state where the orbiting scroll is stopped (the state where the pressure for reducing the thrust load is not acting on the back side of the orbiting scroll), it is not expected to reduce the static friction acting on the thrust bearing. If the pressure that reduces the thrust load is acting on the back side while the orbiting scroll is stopped, this pressure is due to the refrigerant leaking from the expansion chamber and the compression chamber. In such an expander or compressor, the performance improvement effect in a steady state where the swing scroll is swinging is significantly impaired, and the original purpose (expansion or compression of refrigerant) cannot be achieved.

  Furthermore, once the expander or the compressor fails to start and mechanical jamming (jamming) occurs, it is necessary to rotate a drive source such as a motor with a torque exceeding that. Alternatively, it is necessary to reverse the driving source slightly to eliminate the biting. In any case, it is not a reliable starting method.

Moreover, the refrigeration cycle apparatus described in Patent Document 2 makes it easy to start the expander by increasing the pressure difference between the inflow side and the outflow side of the expander. However, the expander is generally designed based on a steady state. That is, the expander is not designed on the assumption that the expander is started with a small pressure difference between the inflow side and the outflow side of the expander.
For this reason, when a high-density refrigerant (with a sparse isodensity curve) flows into the expander at the start-up, as shown in FIG. 12, the pressure change in the expansion chamber becomes large, resulting in overexpansion. That is, the power collected by the expander becomes power (negative power) corresponding to “Area F−Area G”, and the expander cannot continue to drive.
Although it is conceivable to design the expander with emphasis on startability, the expansion is insufficient during steady operation and a sufficient performance improvement effect cannot be obtained, and the original expander cannot be achieved.

  The present invention has been made to solve at least one of the above-described problems, and in a refrigeration cycle apparatus that recovers power with an expander, the expander is started more reliably than a conventional refrigeration cycle apparatus. An object of the present invention is to obtain a refrigeration cycle apparatus that can perform such a process.

The refrigeration cycle apparatus according to the present invention is a refrigerant in which a first heat exchanger serving as a first compressor, a radiator or a condenser, an expander, and a second heat exchanger serving as an evaporator are sequentially connected by piping. A circuit, a second compressor driven by power recovered by the expander, an inflow side of the second compressor and an inflow side of the expander, or an outflow side of the second compressor A bypass circuit that bypasses one of the outflow sides of the expander; and an on-off valve provided in the bypass circuit, wherein the second compressor is a positive displacement compressor, and the second compressor The compressor is connected in series with the first compressor, has one end of the bypass circuit at the connection location, and opens the on-off valve until the second compressor is started, The pressure on the discharge side of the second compressor is lower than the pressure on the suction side of the second compressor. It is intended to.

  The refrigeration cycle apparatus according to the present invention is a pressure adjusting device that makes the pressure on the discharge side of the second compressor lower than the pressure on the suction side of the second compressor at least until the second compressor is started. It has. For this reason, the compression power is reduced as compared with the conventional case, and the expander can be started more reliably than the conventional refrigeration cycle apparatus.

3 is a refrigerant circuit diagram of the refrigeration cycle apparatus according to Embodiment 1. FIG. 2 is a refrigerant circuit diagram illustrating a refrigerant flow in a steady state of the refrigeration cycle apparatus according to Embodiment 1. FIG. FIG. 3 is a refrigerant circuit diagram illustrating a refrigerant flow when the refrigeration cycle apparatus according to Embodiment 1 is started. It is explanatory drawing which shows the pressure change in the expansion chamber at the time of starting in the expander which concerns on Embodiment 1. FIG. It is explanatory drawing which shows the pressure change in the compression chamber at the time of starting in the 2nd compressor which concerns on Embodiment 1. FIG. It is a refrigerant circuit figure which shows another example of the refrigerating-cycle apparatus which concerns on Embodiment 1 of this invention. It is a refrigerant circuit figure which shows another example of the refrigerating-cycle apparatus which concerns on Embodiment 1 of this invention. 6 is a refrigerant circuit diagram of a refrigeration cycle apparatus according to Embodiment 2. FIG. 6 is a refrigerant circuit diagram illustrating a refrigerant flow in a steady state of the refrigeration cycle apparatus according to Embodiment 2. FIG. FIG. 6 is a refrigerant circuit diagram illustrating a refrigerant flow at the time of activation of the refrigeration cycle apparatus according to Embodiment 2. It is explanatory drawing which shows the pressure change in a compression chamber in the compressor connected with the expander shown in patent document 1 by a shaft. It is explanatory drawing which shows the pressure change in an expansion chamber when a high-density refrigerant | coolant flows in at the time of starting in the expander shown in patent document 2.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below.
FIG. 1 is a refrigerant circuit diagram of the refrigeration cycle apparatus according to Embodiment 1 of the present invention.
The refrigeration cycle apparatus 1 uses carbon dioxide as a refrigerant. The first compressor 2, the second compressor 3, the radiator 4, the expander 5, and the evaporator 6 are sequentially connected by refrigerant piping. It is configured. The drive shaft of the second compressor 3 and the starting shaft of the expander 5 are connected by a shaft 7. A plurality of radiators 4 and evaporators 6 may be provided.

  The first compressor 2 has a built-in motor that is powered and driven, for example, and can be driven independently of the expander 5. The second compressor 3 is a positive displacement compressor and is driven by power recovered by the expander 5. The expander 5 is a positive displacement expander, and supplies the power recovered when the refrigerant expands to the second compressor 3. Further, in the vicinity of the radiator 4, a fan 4 a that conveys air (heat medium) that exchanges heat with the refrigerant flowing through the radiator 4 to the radiator 4 is provided. In the vicinity of the evaporator 6, there is provided a fan 6 a that conveys air (heat medium) that exchanges heat with the refrigerant flowing through the evaporator 6 to the evaporator 6.

  Here, the radiator 4 corresponds to the first heat exchanger of the present invention. The evaporator 6 corresponds to the second heat exchanger of the present invention. The fan 4a corresponds to the heat medium transport device of the present invention.

The refrigeration cycle apparatus 1 is also provided with a check valve 10 and a bypass circuit 8. The check valve 10 is provided between the radiator 4 and the expander 5 and restricts the flow of refrigerant from the expander 5 to the radiator 4. The bypass circuit 8 has one end connected between the first compressor 2 and the second compressor 3 and the other end connected between the check valve 10 and the expander 5. Yes. The bypass circuit 8 is provided with an opening / closing valve 9 for opening and closing the bypass circuit 8.
Further, the refrigeration cycle apparatus 1 is provided with a temperature sensor 21 serving as a refrigerant temperature measuring device on the discharge side of the second compressor 3.
The controller 100 controls the rotational speed of the motor built in the first compressor 2, the rotational speed of the fan 4 a, the rotational speed of the fan 6 a, and the opening / closing of the on-off valve 9. The control device 100 also receives the detection value of the temperature sensor 21.

<Description of operation>
Operation | movement of the refrigerating-cycle apparatus 1 comprised in this way is demonstrated. First, the operation of the refrigeration cycle apparatus 1 during steady operation will be described. Then, operation | movement of the refrigerating cycle apparatus 1 at the time of starting is demonstrated.

(Operation during steady operation)
The operation of the refrigeration cycle apparatus 1 during steady operation will be described.
FIG. 2 is a refrigerant circuit diagram showing a refrigerant flow in a steady state of the refrigeration cycle apparatus according to Embodiment 1 of the present invention. In the steady state, the on-off valve 9 is closed. That is, the refrigerant does not flow into the bypass circuit 8 in a steady state. In FIG. 2, the pipe through which the refrigerant flows is indicated by a thick line.

  The refrigerant compressed to high temperature and intermediate pressure by the first compressor 2 is discharged from the first compressor 2. This high-temperature medium-pressure refrigerant is compressed to high temperature and high pressure (supercritical state) by the second compressor 3 and flows into the radiator 4. The refrigerant flowing into the radiator 4 dissipates heat to the air conveyed to the fan 4a, and becomes a low-temperature and high-pressure refrigerant. This low-temperature and high-pressure refrigerant passes through the first check valve 10 and flows into the expander 5. The refrigerant flowing into the expander 5 is decompressed and becomes a low-pressure low-dryness refrigerant. In this decompression process, the expander 5 recovers power. The recovered power is supplied to the second compressor 3 through the shaft 7. The low-pressure, low-dryness refrigerant that has flowed out of the expander 5 flows into the evaporator 6. The refrigerant flowing into the evaporator 6 absorbs heat from the air conveyed to the fan 6a, and becomes a low-pressure and high-dryness refrigerant or a low-pressure superheated gaseous refrigerant. The refrigerant that has flowed out of the evaporator 6 is sucked into the first compressor 2.

  Since the power recovered by the expander 5 is used as the compression power in the second compressor 3, the required power of the first compressor is reduced accordingly. For this reason, energy saving of the refrigeration cycle apparatus 1 can be achieved.

(Operation at startup)
Next, operation | movement of the refrigerating-cycle apparatus 1 at the time of starting is demonstrated.
FIG. 3 is a refrigerant circuit diagram showing a refrigerant flow at the time of starting the refrigeration cycle apparatus according to Embodiment 1 of the present invention. At startup, the on-off valve 9 is in an open state. In other words, the refrigerant flows through the bypass circuit 8 at the time of startup. In FIG. 3, the pipe through which the refrigerant flows is indicated by a thick line.

Since the second compressor 3 is still stopped at the time of startup, the refrigerant compressed to the high temperature and intermediate pressure by the first compressor 2 passes through the bypass circuit 8 and reaches the expander 5. At this time, the check valve 10 prevents the refrigerant flowing out of the bypass circuit 8 from flowing to the radiator 4 and the discharge side of the second compressor 3. That is, when the second compressor 3 is stopped, the pressure on the suction side of the second compressor 3 becomes the pressure of the refrigerant discharged from the first compressor 2, and the second compressor 3. It becomes larger than the pressure on the discharge side.
Even when the check valve 10 is not provided, when the second compressor 3 is stopped, the pressure on the suction side of the second compressor 3 is on the discharge side of the second compressor 3. Greater than pressure. The time from the start of the first compressor 2 to the start of the second compressor 3 is about several seconds (in the refrigeration cycle apparatus 1 according to the first embodiment, for example, about 2 to 3 seconds). . For this reason, the refrigerant flowing to the discharge side of the second compressor 3 is stored in the radiator 4 (the radiator 4 serves as a buffer), and the pressure increase on the discharge side of the second compressor 3 becomes insensitive. .
That is, the bypass circuit 8 and the on-off valve 9 are the pressure adjusting device of the present invention. In the first embodiment, a check valve 10 is provided in order to more reliably obtain a differential pressure between the suction side pressure and the discharge side pressure of the second compressor 3.

  Further, when the first compressor 2 is activated, the refrigerant on the outflow side of the expander 5 is sucked into the first compressor 2 via the evaporator 6. That is, when the expander 5 is stopped, the pressure on the outflow side of the expander 5 becomes smaller than the pressure on the inflow side of the expander 5. Moreover, since the refrigerant | coolant which flows into the inflow side of the expander 5 is a refrigerant | coolant which has not passed the heat radiator 4, it is a low density refrigerant | coolant. That is, the bypass circuit 8 and the on-off valve 9 serve as the expander activation promoting device of the present invention. Even when the check valve 10 is not provided, the refrigerant flowing to the inflow side of the expander 5 does not pass through the radiator 4 as long as the second compressor 3 is stopped. There is no low density refrigerant. For this reason, the check valve 10 may not be a configuration of the expander activation promoting device.

  When the difference between the pressure on the inflow side of the expander 5 and the pressure on the outflow side of the expander 5 (hereinafter also referred to as the differential pressure of the expander 5) becomes large, the expander 5 is started (driving starts). )

At this time, the pressure in the expansion chamber of the expander 5 is as shown in FIG.
FIG. 4 is an explanatory view showing a pressure change in the expansion chamber at the time of start-up in the expander according to Embodiment 1 of the present invention. The pressure in the expansion chamber of the expander 5 changes in the process indicated by the arrow in FIG. For reference, a change in pressure in the expansion chamber at the start-up of the expander according to Patent Document 2 is indicated by a broken line.
Since the differential pressure of the expander 5 at the time of startup is smaller than the differential pressure of the expander 5 in the steady state, it is slightly overexpanded, but the power (positive power) corresponding to “area D−area E” is can get. For this reason, the drive of the expander 5 can be continued.

On the other hand, in the second compressor 3 connected to the expander 5 via the shaft 7, the pressure in the compression chamber changes as shown in FIG.
FIG. 5 is an explanatory diagram showing a pressure change in the compression chamber at the time of start-up in the second compressor according to Embodiment 1 of the present invention. Note that the pressure in the compression chamber of the second compressor 3 changes in the process indicated by the arrow in FIG.
Since the pressure on the suction side of the second compressor 3 is larger than the pressure on the discharge side (reverse pressure), it is overcompressed. The compression power at this time is power corresponding to “Area A−Area B”, and is smaller than that of a conventional refrigeration cycle apparatus (for example, see Patent Document 1) that equalizes the discharge side pressure and the suction side pressure of the compressor. ing. For this reason, it is easier to start the second compressor 3 than the conventional refrigeration cycle apparatus. Depending on the degree of back pressure, recovery power corresponding to area B-area A can be obtained. This amount of power contributes to stable startup of the second compressor 3.

  When the expander 5 and the second compressor 3 are activated, it is possible to continue driving the expander 5 and the second compressor 3 even if the on-off valve 9 is closed. However, in the first embodiment, in order to continue the driving of the expander 5 and the second compressor 3 more reliably, the open / close valve 9 is opened until the refrigeration cycle apparatus 1 can be operated in a steady state. I have to.

More specifically, the control device 100 controls the on-off valve 9 as follows.
When the driving of the second compressor 3 is continued, the temperature of the refrigerant discharged from the second compressor 3 increases. Further, the pressure on the discharge side of the second compressor 3 becomes equal to or higher than the pressure on the suction side. That is, it is possible to operate the refrigeration cycle apparatus 1 in a steady state.
In the refrigeration cycle apparatus 1, the temperature sensor 21 detects the temperature of the refrigerant discharged from the second compressor 3. Then, the control device 100 determines that the refrigeration cycle apparatus 1 can be operated in a steady state when the temperature detected by the temperature sensor 21 exceeds a certain threshold value, and closes the on-off valve 9.

  Even when it is delayed to determine that the refrigeration cycle apparatus 1 can be operated in a steady state, the check valve 10 is provided, so that the discharge pressure of the second compressor 3 does not rapidly increase, and the refrigerant is supplied to the expander 5. Flows. For this reason, the refrigeration cycle apparatus 1 can be reliably started up without the high-pressure or high-temperature protection device working.

  As described above, in the refrigeration cycle apparatus 1 configured as described above, the pressure on the suction side of the second compressor 3 is the pressure on the discharge side of the second compressor 3 until at least the second compressor 3 is started. To be bigger than. Also, at least until the expander 5 is started, the pressure on the outflow side of the expander 5 is made smaller than the pressure on the inflow side of the expander 5 so that the refrigerant flowing to the inflow side of the expander 5 has a low density. I have to. For this reason, the 2nd compressor 3 and the expander 5 can be started more reliably than the conventional refrigeration cycle apparatus.

  It should be noted that the second compressor can be more reliably provided than the conventional refrigeration cycle apparatus by merely making the pressure on the suction side of the second compressor 3 larger than the pressure on the discharge side of the second compressor 3. 3 and the expander 5 can of course be activated. In addition, the conventional refrigeration cycle can be achieved simply by making the pressure on the outflow side of the expander 5 smaller than the pressure on the inflow side of the expander 5 so that the refrigerant flowing to the inflow side of the expander 5 has a low density. Of course, the second compressor 3 and the expander 5 can be started more reliably by the apparatus.

  Moreover, even if it provides a four-way valve in the refrigerating cycle apparatus 1 and a refrigerant | coolant flow can be switched, this invention can be implemented.

FIG. 6 is a refrigerant circuit diagram illustrating another example of the refrigeration cycle apparatus according to Embodiment 1 of the present invention. In the refrigeration cycle apparatus 51, the four-way valve 14 is provided on the discharge side of the second compressor 3. The four-way valve 14 switches the flow path of the refrigerant discharged from the second compressor 3 to a flow path that flows to the radiator 4 or a flow path that flows to the evaporator 6. Further, the flow path of the refrigerant flowing into the first compressor 2 is switched to the flow path flowing from the evaporator 6 or the flow path flowing from the radiator 4. When the refrigerant discharged from the second compressor 3 flows into the evaporator 6 (when the refrigerant flows into the first compressor 2 from the radiator 4), the radiator 4 becomes an evaporator, and the evaporator 6 becomes a radiator.
A four-way valve 15 is provided on the inflow side of the expander 5. With this four-way valve 15, the flow path of the refrigerant flowing into the expander 5 is switched to the flow path flowing from the radiator 4 or the flow path flowing from the evaporator 6.

When such a refrigeration cycle apparatus 51 is used for an air conditioner, an air conditioner capable of both a cooling operation and a heating operation can be obtained.
Since the expander 5 is a positive displacement type, the refrigerant can flow only in one direction. For this reason, a check valve 10 may be provided in the vicinity of the inlet of the expander 5, and a bypass circuit 8 may be connected between the check valve 10 and the expander 5.

In order to further save energy in the refrigeration cycle apparatus according to the first embodiment, an intermediate cooler 22 is provided between the first compressor 2 and the second compressor 3 as shown in FIG. May be. FIG. 7 shows an example in which the intercooler 22 is provided in the refrigeration cycle apparatus 1.
By cooling the high-temperature and medium-pressure refrigerant discharged from the first compressor 2, the refrigerant has an isentropic curve with a large slope on the Mollier diagram. That is, the power required when the second compressor 3 compresses the refrigerant can be reduced. Note that the connecting portion of the bypass circuit 8 between the first compressor 2 and the second compressor 3 may be upstream of the intermediate cooler 22 or downstream of the intermediate cooler 22. In the former case, it is possible to suppress a sudden increase in the discharge pressure of the first compressor 2 until the expander 5 is started. This effect can also be realized by replacing the opening / closing valve 9 with a flow rate adjusting valve and adjusting the opening degree.

  In the first embodiment, the heat medium that exchanges heat with the radiator 4 and the evaporator 6 is air. However, other heat medium may be used. For example, the heat medium that exchanges heat with the radiator 4 may be water, and the refrigeration cycle apparatus according to the first embodiment may be used for hot water supply. Alternatively, the heat medium that exchanges heat with the radiator 4 or the evaporator 6 may be water or brine, and the heat medium may be conveyed to the air-conditioned space to perform air-conditioning in the air-conditioned space.

  In the first embodiment, carbon dioxide having an ozone depletion coefficient of zero and a global warming coefficient that is much smaller than that of chlorofluorocarbons is used as the refrigerant. However, the type of refrigerant is arbitrary. However, the refrigeration cycle apparatus using carbon dioxide has a lower operating efficiency (COP) than the conventional refrigeration cycle apparatus using refrigerant. For this reason, it is very effective to implement the present invention in a refrigeration cycle apparatus using carbon dioxide. In addition, when using the refrigerant | coolant which is not compressed to a supercritical state, the heat radiator 4 functions as a condenser.

  In Embodiment 1, the expander 5 and the second compressor 3 are mechanically connected (by the shaft 7). However, the expander 5 and the second compressor 3 are electrically connected. May be. For example, the expander 5 and a generator may be connected, the power collected by the expander 5 may be converted into electric power, and this electric power may be supplied to the second compressor 3.

  Further, in the first embodiment, whether the refrigeration cycle apparatus 1 (refrigeration cycle apparatus 51) can be steadily operated is detected using the temperature sensor 21, but is the refrigeration cycle apparatus 1 (refrigeration cycle apparatus 51) steadily operable? A pressure sensor may be used to determine whether or not. More specifically, a pressure sensor is provided on each of the discharge side and the suction side of the second compressor 3. And when the difference of the detection value of these pressure sensors becomes a certain threshold value or more, you may judge that the refrigerating-cycle apparatus 1 (refrigeration cycle apparatus 51) can be operated steady.

Embodiment 2. FIG.
The present invention is not limited to the refrigeration cycle apparatus shown in the first embodiment, and can be implemented, for example, in a refrigeration cycle apparatus having the following configuration. In the second embodiment, items not particularly described are the same as those in the first embodiment.

  FIG. 8 is a refrigerant circuit diagram of the refrigeration cycle apparatus according to Embodiment 2 of the present invention. The refrigeration cycle apparatus 52 according to the second embodiment is different from the refrigeration cycle apparatus 1 according to the first embodiment in the following points. Other configurations of the refrigeration cycle apparatus 52 are the same as those of the refrigeration cycle apparatus 1.

First, the installation positions of the first compressor 2 and the second compressor 3 are reversed. Further, a check valve 13 is provided instead of the check valve 10. Further, instead of the bypass circuit 8 and the on-off valve 9, a bypass circuit 11 and an on-off valve 12 are provided.
The check valve 13 is provided between the expander 5 and the evaporator 6, and restricts the flow of refrigerant from the evaporator 6 to the expander 5.
The bypass circuit 11 has one end connected between the second compressor 3 and the first compressor 2, and the other end connected between the expander 5 and the check valve 13. Yes. The bypass circuit 11 is provided with an on-off valve 12 that opens and closes the bypass circuit 11.

<Description of operation>
The operation of the refrigeration cycle apparatus 52 configured as described above will be described. First, the operation of the refrigeration cycle apparatus 52 during steady operation will be described. Thereafter, the operation of the refrigeration cycle apparatus 52 at the time of startup will be described.

(Operation during steady operation)
The operation of the refrigeration cycle apparatus 52 during steady operation will be described.
FIG. 9 is a refrigerant circuit diagram showing a refrigerant flow in a steady state of the refrigeration cycle apparatus according to Embodiment 2 of the present invention. In the steady state, the on-off valve 12 is closed. That is, the refrigerant does not flow to the bypass circuit 11 in a steady state. In FIG. 9, the pipe through which the refrigerant flows is indicated by a thick line.

  The refrigerant compressed to high temperature and medium pressure by the second compressor 3 is discharged from the second compressor 3. This high-temperature medium-pressure refrigerant is compressed to a high temperature and high pressure (supercritical state) by the first compressor 2 and flows into the radiator 4. The refrigerant flowing into the radiator 4 dissipates heat to the air conveyed to the fan 4a, and becomes a low-temperature and high-pressure refrigerant. This low-temperature and high-pressure refrigerant flows into the expander 5. The refrigerant flowing into the expander 5 is decompressed and becomes a low-pressure low-dryness refrigerant. In this decompression process, the expander 5 recovers power. The recovered power is supplied to the second compressor 3 through the shaft 7. The low-pressure, low-dryness refrigerant that has flowed out of the expander 5 flows into the evaporator 6 through the check valve 13. The refrigerant flowing into the evaporator 6 absorbs heat from the air conveyed to the fan 6a, and becomes a low-pressure and high-dryness refrigerant or a low-pressure superheated gaseous refrigerant. The refrigerant that has flowed out of the evaporator 6 is sucked into the second compressor 3.

  Since the power recovered by the expander 5 is used as the compression power in the second compressor 3, the required power of the first compressor is reduced accordingly. For this reason, energy saving of the refrigeration cycle apparatus 52 can be achieved.

(Operation at startup)
Next, operation | movement of the refrigerating-cycle apparatus 1 at the time of starting is demonstrated.
FIG. 10 is a refrigerant circuit diagram showing a refrigerant flow at the time of activation of the refrigeration cycle apparatus according to Embodiment 2 of the present invention. At startup, the on-off valve 12 is in an open state. That is, the refrigerant flows through the bypass circuit 11 at the time of startup. Moreover, the fan 4a which conveys air to a heat radiator becomes the rotation speed (rotation speed) smaller than a stop or a steady state. In FIG. 10, the pipe through which the refrigerant flows is indicated by a thick line.

The refrigerant compressed by the first compressor 2 passes through the radiator 4 and reaches the expander 5. Further, when the first compressor 2 is activated, the refrigerant on the outflow side of the expander 5 is sucked into the first compressor 2 through the bypass circuit 11. At this time, the check valve 13 prevents the refrigerant on the suction side of the second compressor 3 from being sucked by the first compressor 2. That is, when the second compressor 3 is stopped, the pressure on the suction side of the second compressor 3 becomes larger than the pressure on the discharge side of the second compressor 3.
Even when the check valve 13 is not provided, when the second compressor 3 is stopped, the pressure on the suction side of the second compressor 3 is on the discharge side of the second compressor 3. Greater than pressure. The time from the start of the first compressor 2 to the start of the second compressor 3 is about several seconds (in the refrigeration cycle apparatus 52 according to the second embodiment, for example, about 2 to 3 seconds). . For this reason, most of the refrigerant sucked from the suction side of the second compressor 3 is the refrigerant stored in the evaporator 6 (the evaporator 6 serves as a buffer), and on the suction side of the second compressor 3. This is because the pressure drop is insensitive.
That is, the bypass circuit 11 and the on-off valve 12 are the pressure adjusting device of the present invention. In the second embodiment, a check valve 13 is provided in order to more reliably obtain a differential pressure between the suction side pressure and the discharge side pressure of the second compressor 3.

  In addition, when the expander 5 is stopped, the pressure on the outflow side of the expander 5 becomes smaller than the pressure on the inflow side of the expander 5. Moreover, since the refrigerant | coolant which flows into the inflow side of the expander 5 has little heat exchange amount in the heat radiator 4, it is a low density refrigerant | coolant. That is, the control device 100 that controls the rotation speed of the bypass circuit 11, the on-off valve 12, and the fan 4a is the expander activation promoting device of the present invention. Note that the check valve 13 may not be a configuration of the expander activation promoting device.

  When the differential pressure of the expander 5 increases, the expander 5 is activated (drive is started). At this time, the pressure in the expansion chamber of the expander 5 is as shown in FIG. 4 (the same as in the first embodiment). Since the differential pressure of the expander 5 at the time of startup is smaller than the differential pressure of the expander 5 in the steady state, it is slightly overexpanded, but the power (positive power) corresponding to “area D−area E” is can get. For this reason, the drive of the expander 5 can be continued.

  On the other hand, in the second compressor 3 connected to the expander 5 via the shaft 7, the pressure in the compression chamber changes as shown in FIG. 5 (the same as in the first embodiment). Since the pressure on the suction side of the second compressor 3 is larger than the pressure on the discharge side (reverse pressure), it is overcompressed. The compression power at this time is power corresponding to “Area A−Area B”, and is smaller than that of a conventional refrigeration cycle apparatus (for example, see Patent Document 1) that equalizes the discharge side pressure and the suction side pressure of the compressor. ing. For this reason, it is easier to start the second compressor 3 than the conventional refrigeration cycle apparatus. Depending on the degree of back pressure, recovery power corresponding to area B-area A can be obtained. This amount of power contributes to stable startup of the second compressor 3.

  When the expander 5 and the second compressor 3 are activated, it is possible to continue driving the expander 5 and the second compressor 3 even if the on-off valve 12 is closed. However, in the second embodiment, in order to continue the driving of the expander 5 and the second compressor 3 more reliably, the open / close valve 12 is opened until the refrigeration cycle apparatus 52 can be operated in a steady state. I have to.

More specifically, the control device 100 controls the on-off valve 12 as follows.
When the driving of the second compressor 3 is continued, the temperature of the refrigerant discharged from the second compressor 3 increases. Further, the pressure on the discharge side of the second compressor 3 becomes equal to or higher than the pressure on the suction side. That is, it is possible to operate the refrigeration cycle apparatus 52 in a steady state.
In the refrigeration cycle apparatus 52, the temperature sensor 21 detects the temperature of the refrigerant discharged from the second compressor 3. Then, the control device 100 determines that the refrigeration cycle apparatus 1 can be operated in a steady state when the temperature detected by the temperature sensor 21 exceeds a certain threshold value, and closes the on-off valve 12. Further, the rotational speed of the fan 4a is changed to a steady-state rotational speed. A pressure sensor may be used to determine whether or not the refrigeration cycle apparatus 52 is capable of steady operation.

  Even when it is delayed to determine that the refrigeration cycle apparatus 52 can be operated in a steady state, the check valve 13 is provided, so that the pressure on the suction side of the second compressor 3 does not rapidly decrease, and the expander The refrigerant flows to 5. For this reason, the refrigeration cycle apparatus 52 can be reliably started without the low-pressure or low-temperature protection device working.

  As described above, in the refrigeration cycle apparatus 52 configured as above, the pressure on the suction side of the second compressor 3 is the pressure on the discharge side of the second compressor 3 until at least the second compressor 3 is started. To be bigger than. Also, at least until the expander 5 is started, the pressure on the outflow side of the expander 5 is made smaller than the pressure on the inflow side of the expander 5 so that the refrigerant flowing to the inflow side of the expander 5 has a low density. I have to. For this reason, the 2nd compressor 3 and the expander 5 can be started more reliably than the conventional refrigeration cycle apparatus.

  It should be noted that the second compressor can be more reliably provided than the conventional refrigeration cycle apparatus by merely making the pressure on the suction side of the second compressor 3 larger than the pressure on the discharge side of the second compressor 3. 3 and the expander 5 can of course be activated. In addition, the conventional refrigeration cycle can be achieved simply by making the pressure on the outflow side of the expander 5 smaller than the pressure on the inflow side of the expander 5 so that the refrigerant flowing to the inflow side of the expander 5 has a low density. Of course, the second compressor 3 and the expander 5 can be started more reliably by the apparatus.

  DESCRIPTION OF SYMBOLS 1 Refrigeration cycle apparatus, 2 1st compressor, 3 2nd compressor, 4 Heat radiator, 4a fan, 5 Expander, 6 Evaporator, 6a fan, 7 axis | shaft, 8 Bypass circuit, 9 On-off valve, 10 reverse Stop valve, 11 Bypass circuit, 12 Open / close valve, 13 Check valve, 14 Four-way valve, 15 Four-way valve, 21 Temperature sensor, 22 Intermediate cooler, 51 Refrigeration cycle apparatus, 52 Refrigeration cycle apparatus, 100 Control apparatus.

Claims (7)

A refrigerant circuit in which a first heat exchanger to be a first compressor, a radiator or a condenser, an expander, and a second heat exchanger to be an evaporator are sequentially connected by piping;
A second compressor driven by the power recovered by the expander ;
A bypass circuit that bypasses either the inflow side of the second compressor and the inflow side of the expander, or the outflow side of the second compressor and the outflow side of the expander;
An on-off valve provided in the bypass circuit;
Have
The second compressor is a positive displacement compressor;
The second compressor is connected in series with the first compressor, and has one end of the bypass circuit at the connection location,
The open state of the on-off valve to the second compressor is activated, the second of the than the pressure on the suction side of the compressor the second low pressure discharge side of the compressor to Turkey and A refrigeration cycle apparatus characterized by. The refrigeration cycle apparatus according to claim 1, wherein the second compressor is provided between the first compressor and the first heat exchanger . In the path between the first heat exchanger and the expander, the refrigerant flow to the first heat exchanger is made closer to the first heat exchanger side than the place where the bypass circuit is connected. The refrigeration cycle apparatus according to claim 2, further comprising a check valve for regulating. The refrigeration cycle apparatus according to claim 1 , wherein the second compressor is provided between the second heat exchanger and the first compressor. A check valve that regulates the flow of refrigerant to the expander on the second heat exchanger side of the path between the second heat exchanger and the expander, rather than the location where the bypass circuit is connected. the refrigeration cycle apparatus according to claim 4, characterized in that with a. A heat transfer device that transfers a heat medium that exchanges heat with the refrigerant flowing through the first heat exchanger to the first heat exchanger;
At least until the second compressor is started
2. The refrigeration cycle apparatus according to claim 1 , wherein the number of rotations of the heat medium transport device is decreased from a target number of rotations or the heat medium transport device is stopped. The refrigeration cycle apparatus according to any one of claims 1 to 6 , wherein the refrigerant flowing through the refrigerant circuit is carbon dioxide.

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