JP4661561B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a refrigeration apparatus capable of switching between a two-stage compression refrigeration cycle and a single-stage compression refrigeration cycle.

  Conventionally, a refrigeration apparatus capable of switching between a two-stage compression refrigeration cycle and a single-stage compression refrigeration cycle is known. For example, Patent Literature 1 discloses an air conditioner configured by this type of refrigeration apparatus. The air conditioner of Patent Document 1 performs a two-stage compression refrigeration cycle when the outside air temperature is relatively low (for example, below 0 ° C.) during the heating operation, and when the outside air temperature is not so low. Perform a single-stage compression refrigeration cycle. Further, during the cooling operation, the air conditioner performs a single-stage compression refrigeration cycle.

The air conditioner of Patent Document 1 includes a gas-liquid separator for intermediate pressure refrigerant. When performing the two-stage compression refrigeration cycle, the so-called economizer effect is achieved by sucking the intermediate-pressure gas refrigerant separated by the gas-liquid separator into the high-stage compressor together with the refrigerant discharged from the low-stage compressor. Like to get. In other words, by mixing the saturated gas refrigerant from the gas-liquid separator, the degree of superheat of the refrigerant sucked into the high-stage compressor is reduced, thereby reducing the input to the high-stage compressor. Yes.
JP 2001-235245 A

  Here, in the refrigeration apparatus disclosed in Patent Document 1, when switching from the two-stage compression refrigeration cycle to the single-stage compression refrigeration cycle, the refrigerant circulated in the two-stage compression refrigeration cycle. The high-stage compressor and its suction side are blocked from the refrigerant circulation path, and the refrigerant is confined in these portions. If a large amount of refrigerant exists on the high-stage compressor or the suction side thereof, these refrigerants may enter the stopped high-stage compressor and be dissolved in the refrigeration oil in the high-stage compressor. When the high-stage compressor is started with a relatively large amount of refrigerant dissolved in the refrigeration oil, a phenomenon (so-called forming phenomenon) occurs in which the refrigerant dissolved in the refrigeration oil gasifies and the refrigeration oil bubbles. As a result, the high-stage compressor may suffer from poor lubrication and cause troubles such as seizure.

  The present invention has been made in view of the above points, and an object of the present invention is to prevent refrigerant from accumulating in a compressor that stops during a single-stage compression refrigeration cycle, and to start the compressor to perform two-stage compression. It is to prevent troubles when restarting the refrigeration cycle.

  1st invention is equipped with the refrigerant circuit (15) to which the 1st compressor (21), the 2nd compressor (31), and the gas-liquid separator (33) of the intermediate pressure refrigerant | coolant were connected, The said refrigerant circuit ( 15), the refrigerant discharged from the first compressor (21) and the intermediate-pressure gas refrigerant from the gas-liquid separator (33) are sucked into the second compressor (31) to perform two-stage compression and two-stage compression. A two-stage compression operation for performing an expansion refrigeration cycle, and a single-stage compression operation for performing a single-stage compression refrigeration cycle by stopping the second compressor (31) and compressing the refrigerant only by the first compressor (21). It is intended for refrigeration equipment that can be switched. A shut-off mechanism (50) that can be set to a shut-off state that shuts off a suction side of the second compressor (31) from a portion of the refrigerant circuit (15) in which the refrigerant circulates during the single-stage compression operation; At the time of switching from the two-stage compression operation to the single-stage compression operation, the second compressor (31) is operated by setting the shut-off mechanism (50) to the shut-off state and operating the second compressor (31). And a control means (90) for performing a refrigerant discharge operation for discharging the refrigerant from the suction side.

  In the first invention, the refrigeration apparatus (10) is configured to be switchable between a two-stage compression operation and a single-stage compression operation. In the refrigerant circuit (15) during the two-stage compression operation, the first compressor (21) and the second compressor (31) sequentially compress the refrigerant, and at the upstream and downstream of the gas-liquid separator (33), respectively. A two-stage compression and two-stage expansion refrigeration cycle is performed in which the refrigerant is expanded in two stages. On the other hand, in the refrigerant circuit (15) during the single-stage compression operation, the second compressor (31) is stopped and only the first compressor (21) is operated, and the refrigerant is compressed only by the first compressor (21). A single-stage compression refrigeration cycle is performed. During this single-stage compression operation, the shut-off mechanism (50) is set to a shut-off state, and the second compressor (31) is connected to the refrigerant circuit (15) from the portion where the refrigerant circulates during the single-stage compression operation. Shut off the suction side.

  In the present invention, when the two-stage compression operation is switched to the single-stage compression operation, the refrigerant discharge operation is performed by the control means (90). During the refrigerant discharge operation, the shut-off mechanism (50) is set in the shut-off state, and the second compressor (31) is sucked from the portion of the refrigerant circuit (15) where the refrigerant circulates during the single-stage compression operation. The side is blocked. During the refrigerant discharge operation, the second compressor (31) is operated in this state. The second compressor (31) sucks and compresses the refrigerant remaining on the suction side, and discharges the compressed refrigerant to the discharge side. Accordingly, during the refrigerant discharge operation, the refrigerant is discharged from the suction side of the second compressor (31).

  In a second aspect based on the first aspect, the gas-liquid separator (33) is such that the outflow side of the separated gas refrigerant is always in communication with the suction side of the second compressor (31), In the shut-off state, the shut-off mechanism (50) performs both the suction side of the second compressor (31) and the gas-liquid separator (33) during the single-stage compression operation in the refrigerant circuit (15). Further, the refrigerant is configured to be blocked from a portion where the refrigerant circulates.

  In the second invention, the shut-off mechanism (50) in the shut-off state is performing a single-stage compression operation in the refrigerant circuit (15) for both the suction side of the second compressor (31) and the gas-liquid separator (33). Shut off from the part where the refrigerant circulates. Even when the shut-off mechanism (50) is in the shut-off state, the gas-liquid separator (33) remains in communication with the suction side of the second compressor (31). During the refrigerant discharge operation, the second compressor (31) sucks the gas refrigerant not only from the suction side but also from the gas-liquid separator (33). Therefore, during the refrigerant discharge operation of the present invention, the remaining refrigerant is discharged from the gas-liquid separator (33) by the second compressor (31).

  According to a third aspect, in the first or second aspect, the control means (90) ends the refrigerant discharge operation when the suction pressure of the second compressor (31) during the refrigerant discharge operation becomes a predetermined value or less. It is comprised so that it may make it.

  In the third invention, the control means (90) determines the end of the refrigerant discharge operation based on the suction pressure of the second compressor (31). When the refrigerant remaining on the suction side of the second compressor (31) decreases during the refrigerant discharge operation, the pressure of the refrigerant sucked by the second compressor (31) (that is, the suction pressure) gradually increases. It will decline. Therefore, the control means (90) determines that the amount of refrigerant remaining on the suction side of the second compressor (31) has become sufficiently small when the suction pressure of the second compressor (31) is below the reference value. Then, the refrigerant discharge operation is terminated.

  In a fourth aspect based on the first or second aspect, the control means (90) ends the refrigerant discharge operation when the discharge temperature of the second compressor (31) during the refrigerant discharge operation becomes equal to or higher than a predetermined value. It is comprised so that it may make it.

  In the fourth invention, the control means (90) determines the end of the refrigerant discharge operation based on the discharge temperature of the second compressor (31). Here, when the refrigerant remaining on the suction side of the second compressor (31) decreases during the refrigerant discharge operation, the pressure of the refrigerant sucked by the second compressor (31) (that is, the suction pressure) gradually increases. Accordingly, the density of the refrigerant sucked by the second compressor (31) decreases accordingly, and the mass of the refrigerant passing through the second compressor (31) per unit time also decreases. And since the amount of heat applied to the refrigerant in the compression process of the second compressor (31) per unit time is substantially the same, when the mass flow rate of the refrigerant passing through the second compressor (31) decreases, along with that, The temperature rise of the refrigerant in the compression process of the second compressor (31) increases, and as a result, the temperature of the refrigerant discharged from the second compressor (31) (that is, the discharge temperature) increases. Therefore, the control means (90) determines that the amount of refrigerant remaining on the suction side of the second compressor (31) has become sufficiently small when the discharge temperature of the second compressor (31) becomes equal to or higher than the reference value. Then, the refrigerant discharge operation is terminated.

  In the present invention, the remaining refrigerant is discharged from the suction side of the second compressor (31) by performing the refrigerant discharge operation after the end of the two-stage compression operation. For this reason, a large amount of refrigerant is prevented from being dissolved in the refrigerating machine oil in the second compressor (31) even when the single compressor operation is performed and the second compressor (31) is stopped. it can. Therefore, according to the present invention, when the second compressor (31) is started and the two-stage compression operation is resumed, it is possible to prevent the forming phenomenon from occurring in the second compressor (31), and the poor lubrication due to the forming phenomenon. Troubles such as burn-in caused by the above can be prevented in advance.

  In the second aspect of the invention, the refrigerant that has accumulated in the gas-liquid separator (33) that is always in communication with the suction side of the second compressor (31) is also subjected to the refrigerant discharge operation to perform the gas-liquid separator. It can be discharged from (33). Accordingly, the refrigerant in the gas-liquid separator (33) can be prevented from entering the stopped second compressor (31), and a forming phenomenon occurs when the second compressor (31) is started thereafter. Can be surely prevented.

  According to the third and fourth aspects of the present invention, the refrigerant remaining on the suction side of the second compressor (31) is sufficiently monitored by monitoring the suction pressure and discharge temperature of the second compressor (31). It is possible to reliably determine that the amount has been reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The refrigeration apparatus of the present embodiment constitutes a heat pump type air conditioner (10) capable of cooling operation and heating operation.

  As shown in FIG. 1, this air conditioner (10) includes an outdoor unit (20) installed outside, an optional unit (30) constituting an expansion unit, and an indoor unit ( 40) and. The outdoor unit (20) is connected to the option unit (30) via the first connection pipe (11) and the second connection pipe (12). The indoor unit (40) is connected to the option unit (30) via the third connection pipe (13) and the fourth connection pipe (14). As a result, in this air conditioner (10), a refrigerant circuit (15) is configured in which a refrigerant circulates and a vapor compression refrigeration cycle is performed.

  The option unit (30) constitutes a power-up unit that can be applied to an existing separate type air conditioner. For example, even if an existing air conditioner performs a single-stage compression refrigeration cycle with a refrigerant circuit composed of an outdoor unit (20) and an indoor unit (40), these outdoor unit (20) and indoor unit (40) By connecting the optional unit (30) between the two, a two-stage compression and two-stage expansion refrigeration cycle is possible in the refrigerant circuit (15) of the air conditioner (10).

<Outdoor unit>
The outdoor unit (20) includes a low stage compressor (21) as a first compressor, an outdoor heat exchanger (22) as a heat source side heat exchanger, an outdoor expansion valve (25), A four-way switching valve (23) is provided.

  The low-stage compressor (21) is a hermetic scroll compressor. The outdoor heat exchanger (22) is a so-called cross fin type fin-and-tube heat exchanger. Although not shown, an outdoor fan is installed in the vicinity of the outdoor heat exchanger (22). The outdoor fan blows outdoor air to the outdoor heat exchanger (22). The outdoor expansion valve (25) is an electronic expansion valve having a variable opening.

  The four-way selector valve (23) is provided with four ports. In the four-way selector valve (23), the first port is connected to the discharge pipe (21a) of the low-stage compressor (21), and the second port is connected to the suction pipe (21b) of the low-stage compressor (21). Has been. In the four-way switching valve (23), the third port is connected to the second connection pipe (12) via the outdoor heat exchanger (22) and the outdoor expansion valve (25), and the fourth port is the first connection pipe. (11) is connected to each. The four-way switching valve (23) includes a first state (state indicated by a solid line in FIG. 1) in which the first port and the third port communicate with each other and the second port and the fourth port communicate with each other, It is possible to switch to a second state (state indicated by a broken line in FIG. 1) in which four ports communicate and the second port and third port communicate.

<Option unit>
The optional unit (30) includes a high-stage compressor (31) as a second compressor, a three-way valve (32), a gas-liquid separator (33), and an optional expansion valve (34). Is provided. The high-stage compressor (31) is a fully-enclosed scroll compressor.

  Furthermore, the optional unit (30) is provided with a main pipe (35). The main pipe (35) has one end connected to the second connecting pipe (12) and the other end connected to the fourth connecting pipe (14). The main pipe (35) is provided with a solenoid valve (SV).

  The gas-liquid separator (33) separates the gas-liquid two-phase refrigerant into a liquid refrigerant and a gas refrigerant. Specifically, the gas-liquid separator (33) is composed of a sealed container formed in a vertically long cylindrical shape. A liquid inflow pipe (33a) and a liquid outflow pipe (33b) are connected to the gas-liquid separator (33). Both the liquid inflow pipe (33a) and the liquid outflow pipe (33b) pass through the body of the gas-liquid separator (33). In the internal space of the gas-liquid separator (33), one end of the liquid inflow pipe (33a) is opened in the upper part, and one end of the liquid outflow pipe (33b) is opened in the lower part. In addition, a gas outflow pipe (33c) is connected to the gas-liquid separator (33). The gas outflow pipe (33c) passes through the top of the gas-liquid separator (33), and one end thereof opens near the upper end inside the gas-liquid separator (33).

  The other end of the liquid inflow pipe (33a) and the other end of the liquid outflow pipe (33b) are connected to the main pipe (35), respectively. In the main pipe (35), the liquid inflow pipe (33a) is located on the fourth communication pipe (14) side of the solenoid valve (SV), and the second communication pipe (12) side of the solenoid valve (SV). A liquid outflow pipe (33b) is connected to each. The other end of the gas outflow pipe (33c) is connected to the suction pipe (31b) of the high-stage compressor (31). That is, the gas outflow pipe (33c) for deriving the gas refrigerant from the gas-liquid separator (33) is always in communication with the suction side of the high stage compressor (31) via the suction pipe (31b). It has become.

  The option side expansion valve (34) is disposed in the liquid inflow pipe (33a). The option side expansion valve (34) is an electronic expansion valve with a variable opening. On the other hand, the liquid outflow pipe (33b) is provided with a first check valve (CV-1). This first check valve (CV-1) allows only the refrigerant flow in the direction from the gas-liquid separator (33) to the main pipe (35).

  The three-way valve (32) is provided with three ports. In the three-way valve (32), the first port is connected to the third connecting pipe (13), the second port is connected to the suction pipe (31b) of the high stage compressor (31), and the third port is connected to the first connecting pipe (11). ) Is connected to each. The three-way valve (32) has a first state (state indicated by a solid line in FIG. 1) in which the third port communicates with the first port and is blocked from the second port, and the third port communicates with the second port. Thus, it is possible to switch to a second state (state indicated by a broken line in FIG. 1) that is blocked from the first port.

  The discharge pipe (31a) of the high-stage compressor (31) is connected to a pipe connecting the first port of the three-way valve (32) and the third connection pipe (13). The discharge pipe (31a) is provided with a second check valve (CV-2). The second check valve (CV-2) allows only the refrigerant flow in the direction discharged from the high stage compressor (31).

  In the option unit (30) above, the three-way valve (32), solenoid valve (SV), option side expansion valve (34), and first check valve (CV-1) have two-stage compression operation and single-stage compression operation. The switching mechanism is configured to switch the refrigerant circulation path in the refrigerant circuit (15) so as to switch to each other. In addition, the three-way valve (32), the option side expansion valve (34), and the first check valve (CV-1) are located on the higher stage side from the part of the refrigerant circuit (15) where the refrigerant flows during the single stage compression operation. A shut-off mechanism (50) that shuts off the suction side of the compressor (31) and the gas-liquid separator (33) is configured. The two-stage compression operation and the single-stage compression operation will be described later.

<Indoor unit>
The indoor unit (40) is provided with an indoor heat exchanger (41) that is a use side heat exchanger and an indoor side expansion valve (42). The indoor heat exchanger (41) is a cross-fin type fin-and-tube heat exchanger. Although not shown, an indoor fan is installed in the vicinity of the indoor heat exchanger (41). The indoor fan blows indoor air to the indoor heat exchanger (41). The indoor expansion valve (42) is an electronic expansion valve having a variable opening.

<controller>
The air conditioner (10) of the present embodiment includes a controller (70). The controller (70) constitutes control means for performing a predetermined refrigerant discharge operation when switching from the two-stage compression operation to the single-stage compression operation.

  The controller (70) receives an actual value of the suction pressure of the high stage compressor (31). The controller (70) is configured to end the refrigerant discharge operation when the suction pressure of the high-stage compressor (31) falls below a predetermined reference value during the refrigerant discharge operation. Details of the operation performed by the controller (70) will be described later.

-Driving action-
The operation of the air conditioner (10) will be described.

<Cooling operation>
The operation during the cooling operation will be described with reference to FIG.

  A single-stage compression operation is performed during the cooling operation. In this cooling operation, the four-way switching valve (23) and the three-way valve (32) are set to the first state, and the electromagnetic valve (SV) is opened. In addition, the outdoor expansion valve (25) is set to the fully open state, and the option side expansion valve (34) is set to the fully closed state, while the opening of the indoor side expansion valve (42) is appropriately adjusted according to the operating conditions. The Furthermore, in this cooling operation, only the low-stage compressor (21) is operated, and the high-stage compressor (31) is stopped. And in a refrigerant circuit (15), the single stage compression refrigeration cycle which compresses a refrigerant only with a low stage side compressor (21) is performed.

  The refrigerant discharged from the low-stage compressor (21) is sent to the outdoor heat exchanger (22) where it dissipates heat to the outdoor air and condenses. The refrigerant condensed in the outdoor heat exchanger (22) is sent to the indoor unit (40) through the main pipe (35) of the option unit (30). The refrigerant flowing into the indoor unit (40) is decompressed to a low pressure when passing through the indoor expansion valve (42). The decompressed low-pressure refrigerant is sent to the indoor heat exchanger (41), and absorbs heat from the indoor air to evaporate. In the indoor heat exchanger (41), the room air is cooled, and the cooled room air is sent back into the room. The refrigerant evaporated in the indoor heat exchanger (41) passes through the three-way valve (32) of the optional unit (30), is sent to the outdoor unit (20), and is sucked into the low-stage compressor (21) for compression. Is done.

<First heating operation>
The operation during the first heating operation will be described with reference to FIG.

  During the first heating operation, a single-stage compression operation is performed. In the first heating operation, the four-way switching valve (23) is set to the second state, the three-way valve (32) is set to the first state, and the electromagnetic valve (SV) is opened. In addition, the indoor expansion valve (42) is set to the fully open state and the option side expansion valve (34) is set to the fully closed state, while the opening of the outdoor expansion valve (25) is appropriately adjusted according to the operating conditions. Is done. Further, in the first heating operation, only the low stage compressor (21) is operated, and the high stage compressor (31) is stopped. And in a refrigerant circuit (15), the single stage compression refrigeration cycle which compresses a refrigerant only with a low stage side compressor (21) is performed.

  The refrigerant discharged from the low-stage compressor (21) passes through the three-way valve (32) of the option unit (30) and is sent to the indoor unit (40). The refrigerant flowing into the indoor unit (40) dissipates heat to the indoor air and condenses in the indoor heat exchanger (41). In the indoor heat exchanger (41), the room air is heated, and the heated room air is sent back into the room. The refrigerant condensed in the indoor heat exchanger (41) is sent to the outdoor unit (20) through the main pipe (35) of the option unit (30). The refrigerant flowing into the outdoor unit (20) is depressurized when passing through the outdoor expansion valve (25), and then absorbs heat from the outdoor air and evaporates in the outdoor heat exchanger (22). The refrigerant evaporated in the outdoor heat exchanger (22) is sucked into the low stage compressor (21) and compressed.

<Second heating operation>
The operation during the second heating operation will be described with reference to FIG.

  During the second heating operation, a two-stage compression operation is performed. In the second heating operation, the four-way switching valve (23) and the three-way valve (32) are set to the second state, and the electromagnetic valve (SV) is closed. Further, the indoor side expansion valve (42) is set to a fully open state, and the opening degrees of the option side expansion valve (34) and the outdoor side expansion valve (25) are appropriately adjusted according to the operating conditions. Further, in the second heating operation, both the low stage compressor (21) and the high stage compressor (31) are operated. In the refrigerant circuit (15), the low-stage compressor (21) and the high-stage compressor (31) sequentially compress the refrigerant, and the option-side expansion valve (34) and the outdoor expansion valve (25). A two-stage compression and two-stage expansion refrigeration cycle for sequentially expanding the refrigerant is performed.

  The intermediate-pressure refrigerant discharged from the low-stage compressor (21) is sucked into the high-stage compressor (31) through the three-way valve (32) and the suction pipe (33b) of the option unit (30) in this order. . The intermediate-pressure gas refrigerant in the gas-liquid separator (33) is also drawn into the high-stage compressor (31) through the gas outlet pipe (33c) and the suction pipe (33b) in this order. The high-pressure refrigerant discharged from the high stage compressor (31) is sent to the indoor unit (40) through the discharge pipe (31a). The high-pressure refrigerant flowing into the indoor unit (40) dissipates heat to the indoor air and condenses in the indoor heat exchanger (41). In the indoor heat exchanger (41), the room air is heated, and the heated room air is sent back into the room.

  The refrigerant condensed in the indoor heat exchanger (41) flows into the liquid inflow pipe (33a) of the option unit (30) and is reduced in pressure by the option side expansion valve (34) to become an intermediate pressure. Flows into (33). In the gas-liquid separator (33), the gas-liquid two-phase intermediate pressure refrigerant is separated into a gas refrigerant and a liquid refrigerant. As described above, the saturated gas refrigerant separated by the gas-liquid separator (33) is sent to the suction side of the high stage compressor (31). On the other hand, the saturated liquid refrigerant separated by the gas-liquid separator (33) is sent to the outdoor unit (20) through the liquid outflow pipe (33b). The intermediate-pressure liquid refrigerant that has flowed into the outdoor unit (20) is depressurized to pass through the outdoor expansion valve (25), and then absorbs heat from the outdoor air and evaporates in the outdoor heat exchanger (22). The refrigerant evaporated in the outdoor heat exchanger (22) is sucked into the low stage compressor (21) and compressed.

<Refrigerant discharge operation>
As described above, when the two-stage compression operation is switched to the single-stage compression operation, the refrigerant discharge operation is performed by the controller (70). Specifically, the refrigerant discharge operation is performed when switching from the second heating operation to the cooling operation or the first heating operation. That is, when the second heating operation is switched to the cooling operation or the first heating operation, the second heating operation is temporarily ended and then the refrigerant discharge operation is performed, and then the cooling operation and the first heating operation are started. The

  During the refrigerant discharge operation, the controller (70) sets the three-way valve (32) to the first state, fully closes the option side expansion valve (34), and stops the low stage compressor (21) to increase the high pressure. Operate only the stage side compressor (31). During operation of the high-stage compressor (31), the first check valve (CV-1) close to the high-stage compressor (31) has a low pressure. For this reason, the first check valve (CV-1) is closed.

  During the refrigerant discharge operation, the suction side of the high-stage compressor (31) and the gas-liquid separator (33) include the three-way valve (32), the option side expansion valve (34), and the first check valve (CV-1 ) Is blocked from the portion of the refrigerant circuit (15) through which the refrigerant flows during the single-stage compression operation. When the high-stage compressor (31) is operated in this state, the high-stage compressor (31) removes the gas refrigerant remaining in the suction pipe (31b) and the gas refrigerant in the gas-liquid separator (33). Inhaled, the sucked gas refrigerant is compressed and discharged to the discharge pipe (31a). The refrigerant discharged from the high-stage compressor (31) to the discharge pipe (31a) passes through the second check valve (CV-2), and the refrigerant is discharged during the single-stage compression operation in the refrigerant circuit (15). It is sent out to the flowing part.

  When gas refrigerant is sucked out of the gas-liquid separator (33) by the high-stage compressor (31), the internal pressure of the gas-liquid separator (33) gradually decreases, and the liquid refrigerant in the gas-liquid separator (33) Evaporates. When the amount of the liquid refrigerant in the gas-liquid separator (33) decreases, the liquid refrigerant remaining in the liquid inflow pipe (33a) and the liquid outflow pipe (33b) further flows into the gas-liquid separator (33). Flows in. As described above, during the refrigerant discharge operation, the refrigerant remaining on the suction side of the high-stage compressor (31), the gas-liquid separator (33), and the like is transferred during the single-stage compression operation in the refrigerant circuit (15). It is discharged to the part where the refrigerant flows.

  During the refrigerant discharge operation, if the refrigerant remaining on the suction side of the high-stage compressor (31) or the gas-liquid separator (33) decreases, the refrigerant sucked by the high-stage compressor (31) The pressure (that is, the suction pressure) gradually decreases. Then, when the suction pressure of the high stage compressor (31) falls below a predetermined reference value (for example, 0.2 MPa), the controller (70) is configured such that the suction side and the gas-liquid separator of the high stage compressor (31). It is determined that the amount of refrigerant remaining in (33) or the like has sufficiently decreased, and the high-stage compressor (31) is stopped to end the refrigerant discharge operation.

-Effect of the embodiment-
In the present embodiment, the refrigerant discharge operation is performed after the end of the two-stage compression operation, whereby the remaining refrigerant is discharged from the suction side of the high-stage compressor (31). For this reason, it is possible to prevent a large amount of refrigerant from being dissolved in the refrigerating machine oil in the high-stage compressor (31) while the high-stage compressor (31) is stopped during the single-stage compression operation. . Therefore, according to this embodiment, when the high-stage compressor (31) is started and the two-stage compression operation is restarted, it is possible to prevent the forming phenomenon from occurring in the high-stage compressor (31), and the forming phenomenon It is possible to prevent troubles such as seizure due to poor lubrication.

  In addition, in the present embodiment, the refrigerant accumulated in the gas-liquid separator (33) that is always in communication with the suction side of the high-stage compressor (31) is also subjected to the refrigerant discharge operation, so that the gas-liquid separator ( 33) can be discharged. Therefore, the refrigerant in the gas-liquid separator (33) can be prevented from entering the stopped high stage compressor (31), and the forming phenomenon occurs when the high stage compressor (31) is started after that. It can be surely prevented from occurring.

  Further, according to the present embodiment, it is ensured that the refrigerant remaining on the suction side of the high stage compressor (31) has been sufficiently reduced by monitoring the suction pressure of the high stage compressor (31). The refrigerant discharge operation can be terminated at an appropriate timing.

-Modification 1 of embodiment-
In the present embodiment, the controller (70) may be configured to determine the end of the refrigerant discharge operation based on the temperature of the refrigerant discharged from the high stage compressor (31) (that is, the discharge temperature). .

  Specifically, the controller (70) of the present modification is configured to end the refrigerant discharge operation when the discharge temperature of the high-stage compressor (31) becomes a predetermined reference value (for example, 60 ° C.) or higher. May be.

  Here, when the amount of refrigerant remaining on the suction side of the high-stage compressor (31), the gas-liquid separator (33), or the like decreases, the high-stage compressor (31) during the refrigerant discharge operation is reduced. Since the pressure of the refrigerant sucked (that is, the suction pressure) gradually decreases and the density of the refrigerant sucked by the high stage compressor (31) decreases accordingly, the high stage compressor (per unit time) The mass of refrigerant passing through 31) will also decrease. And since the amount of heat applied to the refrigerant in the compression process of the high stage compressor (31) per unit time is almost the same, if the mass flow rate of the refrigerant passing through the high stage compressor (31) decreases, Accordingly, the temperature rise of the refrigerant in the compression process of the high-stage compressor (31) increases, and as a result, the temperature of the refrigerant discharged from the high-stage compressor (31) (that is, the discharge temperature) increases. go.

  Therefore, when the discharge temperature of the high-stage compressor (31) exceeds the reference value, the controller (70) remains on the suction side of the high-stage compressor (31), the gas-liquid separator (33), and the like. It is determined that the amount of the refrigerant has become sufficiently small, the high stage compressor (31) is stopped, and the refrigerant discharge operation is terminated.

-Modification 2 of embodiment-
In the said embodiment, although the air conditioning apparatus is comprised with the freezing apparatus which concerns on this invention, you may comprise the cold / hot water apparatus which cools and heats water with the freezing apparatus which concerns on this invention. In that case, in the refrigerant circuit (15), for example, a plate heat exchanger is provided as the use side heat exchanger. In this plate heat exchanger, water is heated and cooled by heat exchange with the refrigerant.

  In addition, the above embodiment is an essentially preferable illustration, Comprising: It does not intend restrict | limiting the range of this invention, its application thing, or its use.

  As described above, the present invention is useful for a refrigeration apparatus that can switch between a two-stage compression refrigeration cycle and a single-stage compression refrigeration cycle.

It is a piping system diagram of a refrigerant circuit showing the composition of an air harmony device. It is a piping system diagram of a refrigerant circuit showing the operation during cooling operation. It is a piping system diagram of a refrigerant circuit showing operation in the 1st heating operation. It is a piping system diagram of a refrigerant circuit showing operation during the 2nd heating operation. It is a piping system diagram of a refrigerant circuit showing refrigerant discharge operation.

Explanation of symbols

15 Refrigerant circuit
21 Low stage compressor (first compressor)
31 High stage compressor (second compressor)
33 Gas-liquid separator
50 Shut-off mechanism
90 Controller (control means)

Claims (4)

A refrigerant circuit (15) to which a first compressor (21), a second compressor (31), and a gas-liquid separator (33) for intermediate pressure refrigerant are connected;
In the refrigerant circuit (15), the refrigerant discharged from the first compressor (21) and the intermediate-pressure gas refrigerant from the gas-liquid separator (33) are sucked into the second compressor (31) to be A two-stage compression operation in which a two-stage compression refrigeration cycle is performed, and a single-stage compression refrigeration cycle in which the second compressor (31) is stopped and the refrigerant is compressed only by the first compressor (21). A refrigeration apparatus capable of switching between stage compression operation,
A shut-off mechanism (50) that can be set to a shut-off state that shuts off a suction side of the second compressor (31) from a portion where the refrigerant circulates during the single-stage compression operation in the refrigerant circuit (15);
At the time of switching from the two-stage compression operation to the single-stage compression operation, the second compressor (31) is operated by setting the shut-off mechanism (50) to the shut-off state and operating the second compressor (31). And a control means (90) for performing a refrigerant discharge operation for discharging the refrigerant from the suction side. In claim 1,
In the gas-liquid separator (33), the outflow side of the separated gas refrigerant is always in communication with the suction side of the second compressor (31),
In the shut-off state, the shut-off mechanism (50) performs both the suction side of the second compressor (31) and the gas-liquid separator (33) during the single-stage compression operation in the refrigerant circuit (15). The refrigeration apparatus is configured to be cut off from a portion where the refrigerant circulates. In claim 1 or 2,
The refrigeration apparatus characterized in that the control means (90) is configured to end the refrigerant discharge operation when the suction pressure of the second compressor (31) during the refrigerant discharge operation becomes a predetermined value or less. In claim 1 or 2,
The refrigeration apparatus characterized in that the control means (90) is configured to terminate the refrigerant discharge operation when the discharge temperature of the second compressor (31) during the refrigerant discharge operation reaches a predetermined value or more.

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