JP2013155972A - Refrigeration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a refrigeration device that can properly expand a refrigerant through an expansion valve disposed at an inlet of an intermediate heat exchanger.SOLUTION: A refrigeration device includes: a two-stage compressor 11; an intercooler 38 having an inlet connected to a lower stage side discharge port 24 of the two-stage compressor 11, and an outlet connected to an upper stage side suction port 26 of the two-stage compressor 11; a gas cooler 46 having an inlet connected to an upper stage side discharge port 28 of the two-stage compressor 11; and an intermediate heat exchanger 80 connected to an outlet of a gas cooler 46. The intermediate heat exchanger 80 is configured to exchange heat between a refrigerant flown in through the gas cooler 46 and a refrigerant decompressed by an expansion valve 83 after having passed the intermediate heat exchanger 80.

Description

  The present invention relates to a refrigeration apparatus including a two-stage compressor, a gas cooler, a throttle means, and an evaporator in a refrigerant circuit.

  A two-stage compressor, an intercooler that cools the refrigerant discharged from the first stage of the two-stage compressor, a gas cooler that cools the refrigerant discharged from the second stage of the two-stage compressor, and an intermediate connected to the outlet of the gas cooler Conventionally, a refrigeration apparatus having a heat exchanger and an evaporator into which a refrigerant cooled by an intermediate heat exchanger flows is known (see, for example, Patent Document 1).

  The intermediate heat exchanger has first and second flow paths for exchanging heat between the refrigerant flowing into each of the intermediate heat exchangers. The flow path of the refrigerant discharged from the gas cooler is divided into two, one flow path is connected to the first flow path, and the other flow path is connected to the second flow path. At this time, an expansion valve is disposed in the other channel, and the refrigerant expanded by the expansion valve is caused to flow into the second channel, so that the refrigerant discharged from the gas cooler and flowing into the first channel becomes the second channel. It is cooled by the refrigerant in the flow path. By using the refrigerant cooled by the intermediate heat exchanger, the cooling efficiency by the refrigeration apparatus has been improved.

JP 2011-137557 A

  In the refrigeration apparatus as described above, the refrigerant flowing through one of the flow paths branched from the gas cooler is decompressed by the expansion valve. The refrigerant flowing into the expansion valve is input while maintaining the state when discharged from the gas cooler. When the temperature difference between the refrigerant discharged from the gas cooler and the outside air is small, the state of the refrigerant is not stable, and when such unstable refrigerant is input to the expansion valve, the refrigerant is appropriately expanded. There is a risk of disappearing. That is, heat exchange between refrigerants in the intermediate heat exchanger may not be performed properly.

  This invention was made in order to solve said subject, and it aims at obtaining the freezing apparatus which can expand a refrigerant | coolant appropriately with the expansion valve provided in the inlet_port | entrance of an intermediate heat exchanger.

  To achieve the above object, the present invention provides a two-stage compressor, an inlet connected to a first-stage refrigerant discharge section of the two-stage compressor, and a second-stage refrigerant suction section of the two-stage compressor. An intercooler to which an outlet is connected; a gas cooler having an inlet connected to a second-stage refrigerant discharge portion of the two-stage compressor; and an intermediate heat exchanger connected to an outlet of the gas cooler; The exchanger is configured to exchange heat between the refrigerant flowing in through the gas cooler and the refrigerant reduced in pressure by the expansion valve after passing through the intermediate heat exchanger.

  Further, in the refrigeration apparatus according to the present invention, the intermediate heat exchanger has a first flow path having one end connected to the outlet of the gas cooler and the other end connected to the evaporator on the cooling target device side; A second flow path having one end connected to the refrigerant flow path between the first flow path and the device to be cooled and the other end connected to a second-stage refrigerant suction portion of the two-stage compressor; The expansion valve is connected to the inlet of the second flow path.

  Further, the present invention is characterized in that, in the refrigeration apparatus, the other end of the second flow path joins the refrigerant flow path that returns from the intercooler to the second-stage refrigerant suction section of the compressor.

  In the refrigeration apparatus according to the present invention, the refrigerant is carbon dioxide.

  According to the refrigeration apparatus of the present invention, since the refrigerant that has been sufficiently subcooled and stabilized flows into the expansion valve, the expansion valve can appropriately expand the refrigerant.

It is a refrigerant circuit figure of the refrigerating device concerning the embodiment of the present invention. It is a block diagram explaining the structure of a control apparatus.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a refrigerant circuit diagram of a refrigeration apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram illustrating a configuration of a control apparatus.
In FIG. 1, the refrigeration apparatus R in this embodiment includes a refrigeration unit 3, two showcase units 5A and 5B as devices to be cooled, and a control device C. The refrigeration unit 3 and each showcase unit. 5A and 5B are connected by the refrigerant pipes 7 and 9, and the predetermined refrigerant circuit 1 is comprised.
The refrigeration cycle performed by the refrigerant circuit 1 uses carbon dioxide whose refrigerant pressure (high pressure) on the high pressure side is equal to or higher than its critical pressure (supercritical) as a refrigerant. This carbon dioxide refrigerant is a natural refrigerant that is friendly to the global environment and takes into consideration flammability and toxicity.

  The refrigerator unit 3 includes two two-stage compressors 11 and 11 arranged in parallel. In the present embodiment, the two-stage compressor 11 is an internal intermediate pressure type multi-stage compression rotary compressor, and is a cylindrical hermetic container 12 made of a steel plate, and a driving machine arranged and housed in the inner space of the hermetic container 12. , A rotary compression mechanism section comprising a first rotary compression element (first stage compressor) 18 and a second rotary compression element (second stage compressor) 20 that are driven to rotate by the electric element. It is composed of. The first rotary compression element 18 is used on the lower pressure side than the second rotary compression element 20.

The first rotary compression element 18 compresses the low-pressure refrigerant sucked into the two-stage compressor 11 from the low-pressure side of the refrigerant circuit 1 through the refrigerant pipe 9, raises it to an intermediate pressure, and discharges it. The second rotary compression element 20 sucks an intermediate pressure refrigerant discharged from the first rotary compression element 18 and cooled by an intercooler 38, which will be described later, and compresses the compressed pressure to a high pressure. Discharge. The two-stage compressor 11 is a variable frequency compressor, and can control the rotation speed of the first rotary compression element 18 and the second rotary compression element 20 by changing the operating frequency of the electric element. It has become.
The hermetic container 12 includes a low-stage suction port 22 that serves as a refrigerant suction part of the first rotary compression element 18 (first stage in the two-stage compressor 11) and a low stage that serves as a refrigerant discharge part of the first rotary compression element 18. A side discharge port 24 is formed. Further, the sealed container 12 includes a high-stage suction port 26 serving as a refrigerant suction part of the second rotary compression element 20 (second stage in the two-stage compressor 11), and a refrigerant discharge part of the second rotary compression element 20. The higher-stage discharge port 28 is formed.
Refrigerant introduction pipes 30 are connected to the lower stage suction ports 22, 22 of the respective two-stage compressors 11, 11, and merge at the respective upstream sides and are connected to the refrigerant pipe 9.

In each of the two-stage compressors 11, 11, intermediate pressure discharge pipes 36, 36 are connected to the low-stage discharge ports 24, 24 from which the refrigerant gas compressed to the intermediate pressure is discharged, and the respective downstream sides thereof. And are connected to the inlet of the intercooler 38. The intercooler 38 cools the intermediate-pressure refrigerant discharged from the first rotary compression element 18 by air, and an intermediate-pressure suction pipe 40 is connected to the outlet of the intercooler 38. 40 is branched into two and then connected to the high-stage suction ports 26 and 26 of the respective two-stage compressors 11 and 11.
The medium-pressure (MP) refrigerant gas sucked into the second rotary compression element 20 from the high-stage suction port 26 is compressed in the second stage by the second rotary compression element 20 to generate a high temperature and high pressure (HP: normal). The refrigerant gas has a supercritical pressure of about 12 MPa in the operating state.

The high-pressure side pipes 42 and 42 are connected to the high-stage discharge ports 28 and 28 of the second rotary compression element 20 of the two-stage compressors 11 and 11, respectively. The side pipe 42 is connected to the inlet of the gas cooler 46 through the oil separator 44. Furthermore, the outlet of the gas cooler 46 and the intermediate heat exchanger 80 are connected via a high-pressure side pipe 43.
Here, the intermediate heat exchanger 80 has a first flow path 80A and a second flow path 80B, and constitutes a split cycle described later in detail. One end (inlet) of the first flow path 80 </ b> A is connected to the gas cooler 46 via the high-pressure side pipe 43. Further, the other end (exit) of the first flow path 80A is connected to the showcase units 5A and 5B via the refrigerant pipe 7. As will be described later, one end (inlet) of the second channel 80B is connected to the refrigerant channel between the first channel 80A and the showcase units 5A and 5B, and the other end (outlet) is The second stage compressor 11 is connected to a higher stage suction port 26 that is a second stage refrigerant suction section.

The gas cooler 46 cools the high-pressure refrigerant discharged from the two-stage compressor 11, and a gas cooler blower 47 for air-cooling the gas cooler 46 is disposed in the vicinity of the gas cooler 46. In this embodiment, the gas cooler 46 is juxtaposed with an intercooler 38 and an oil cooler 74 described later in detail, and these are arranged in the same air passage 45. The air passage 45 is provided with an outside air temperature sensor (outside air temperature detecting means) 56 that detects the outside air temperature at the location where the refrigerator unit 3 is disposed.
The high-stage discharge ports 28 and 28 have a high-pressure sensor (high-pressure detector) 48 that detects the pressure of the refrigerant discharged from the second rotary compression elements 20 and 20 and a discharge that detects the discharge refrigerant temperature. A temperature sensor (discharge temperature detecting means) 50 is provided. Further, a check valve 90 is provided in which the direction from the high-stage discharge port 28 toward the gas cooler 46 (oil separator 44) is the forward direction.

  On the other hand, the showcase units 5A and 5B are installed in a store, for example, and are connected in parallel to the refrigerant pipes 7 and 9. The showcase units 5 </ b> A and 5 </ b> B have the same configuration, and an evaporator 63 connected to the refrigerant pipe 7 through the case-side refrigerant pipe 60 and a throttle means provided in the refrigerant flow path by the case-side refrigerant pipe 60. A case-side expansion valve 62. The evaporator 63 is connected to the refrigerant pipe 9 via the case side refrigerant pipe 61. In addition, each showcase unit 5A, 5B is provided with a cool air circulation blower (not shown) that blows air to the evaporator 63. The refrigerant pipe 9 is connected to the low-stage suction port 22 serving as a refrigerant suction port to the first rotary compression element 18 of each of the two-stage compressors 11 and 11 via the refrigerant introduction pipe 30 as described above. ing. Thereby, in the refrigerant circuit 1, the refrigerant main flow path circulating through the evaporator 63, the first rotary compression element 18, the intercooler 38, the second rotary compression element 20, the gas cooler 46, and the intermediate heat exchanger 80 is provided. It is formed.

  Further, the control device (control means) C is constituted by a general-purpose microcomputer. As shown in FIG. 2, various sensors are connected to the control device C, and outputs from the various sensors are input. Further, various valve devices, two-stage compressors 11 and 11, a fan motor 47M of a gas cooler blower 47, and the like are connected to the control device C, and the control device C performs drive control of these devices. The details of the control device C will be described later according to each control.

(A) Split cycle Next, the split cycle of the refrigeration apparatus R in this embodiment will be described.
In the split cycle, heat exchange is performed between the refrigerant that is connected to the outlet of the gas cooler 46 and flows into the first flow path 80A, and the refrigerant that is expanded by the expansion valve 83 described later via the first flow path 80A. Cycle.
A flow divider 82 is provided in the refrigerant flow path of the refrigerant pipe 7 that connects the intermediate heat exchanger 80 and the showcase units 5A and 5B. A return refrigerant pipe 88 that constitutes a first return flow path from the refrigerant pipe 7 to the second flow path 80B of the intermediate heat exchanger 80 is connected to the flow divider 82. By the flow divider 82, the refrigerant flow from the first flow path 80A is divided into a flow toward the showcase units 5A and 5B and a flow toward the first return flow path. In addition, a strainer 87 and an expansion valve 83 are sequentially provided in the first return channel.

A junction 81 is provided at a predetermined portion of the intermediate pressure suction pipe 40 that connects the outlet of the intercooler 38 and the high-stage suction port 26 of the two-stage compressor 11, and the other end of the second flow path 80B. And the merger 81 are connected via a refrigerant pipe 89 constituting the second return flow path. An auxiliary refrigerant channel is formed by the first return channel, the second channel 80B, and the second return channel.
The refrigerant that has flowed from the refrigerant main flow path into the first return flow path is appropriately expanded by the expansion valve 83 under the control of the control device C, and then flows into the second flow path 80B. For this reason, the temperature of the refrigerant flowing in the second flow path 80B is lower than that of the refrigerant flowing in the first flow path 80A. In the intermediate heat exchanger 80, heat exchange is performed between the refrigerant flowing through the first flow path 80A and the refrigerant flowing through the second flow path 80B, and the refrigerant in the first flow path 80A is transferred to the second flow path 80B. It is cooled by the refrigerant.
Further, the other end of the second flow path 80B joins the refrigerant flow path that returns from the intercooler 38 to the high-stage side suction port 26 (second-stage refrigerant suction section of the two-stage compressor 11). For this reason, it is possible to smoothly join the refrigerant flow from the intermediate heat exchanger 80 to the intermediate pressure side of the refrigerant main flow path while preventing pressure loss in the intercooler 38.

  As shown in FIG. 2, the control device C includes a discharge temperature sensor (discharge temperature detection means) 50, a unit outlet side pressure sensor (unit outlet side pressure detection means) 58, an intermediate pressure sensor (intermediate pressure pressure detection means). ) 49, low pressure sensor (suction pressure detector) 32, gas cooler outlet temperature sensor (gas cooler outlet temperature detector) 52, unit outlet temperature sensor (unit outlet temperature detector) 54, unit inlet temperature sensor (inlet temperature detector) 34 is connected.

As described above, the discharge temperature sensor 50 is provided at the high-stage discharge port 28 of the two-stage compressor 11, 11 and detects the discharge temperature of the refrigerant discharged from the second rotary compression element 20. The unit outlet side pressure sensor 58 detects the pressure of the refrigerant flowing through the refrigerant pipe 7 toward the showcase units 5A and 5B. The unit outlet side pressure sensor 58 is provided so as to detect a refrigerant pressure that is the same as or downstream of a portion of the refrigerant pipe 7 to which a refrigerant amount adjusting tank 100 described later is connected.
The low-pressure sensor 32 is connected to the low-pressure side suction ports 22 and 22 of the two-stage compressors 11 and 11 on the low-pressure side of the refrigerant circuit 1, in this embodiment, on the downstream side of the evaporators 63 and 63. It is provided in the refrigerant pipe 9 and detects the pressure of the refrigerant toward the refrigerant introduction pipe 30. The intermediate pressure sensor 49 detects the refrigerant pressure after passing through the second flow path 80B of the intermediate heat exchanger 80 in the intermediate pressure region of the refrigerant circuit 1, in this embodiment, in the split cycle.

The gas cooler outlet temperature sensor 52 is provided on the outlet side of the gas cooler 46 and detects the temperature (GCT) of the refrigerant that has exited the gas cooler 46. The unit outlet temperature sensor 54 is provided on the outlet side of the intermediate heat exchanger 80 connected to the refrigerant pipe 7 and detects the unit outlet temperature (LT). The unit inlet temperature sensor 34 is provided in the refrigerant pipe 9 connected to the low-stage suction port 22 of the two-stage compressor 11 and detects the refrigerant suction temperature toward the refrigerant introduction pipe 30.
The control device C is connected to an expansion valve 83 that constitutes the split cycle. The opening of the expansion valve 83 is adjusted by a step motor under the control of the control device C.
Hereinafter, the opening degree control of the expansion valve 83 will be described in detail. The opening degree of the expansion valve 83 is controlled to be a predetermined initial valve opening degree when the operation of the two-stage compressor 11 is started. Thereafter, the control device C determines an operation amount for increasing the valve opening degree of the expansion valve 83 based on the following first control amount, second control amount, and third control amount.

(A-1) Valve Opening Increase Control of the Expansion Valve 83 The first control amount (DTcont) is obtained based on the discharged refrigerant temperature DT of the two-stage compressor 11. The control device C determines whether or not the temperature DT detected by the discharge temperature sensor 50 is higher than a predetermined value DT0. If the discharge refrigerant temperature DT is higher than the predetermined value DT0, the opening degree of the expansion valve 83 is determined. Is a control amount that acts in the direction of increasing. The predetermined value DT0 is set to a temperature (for example, + 95 ° C.) slightly lower than a limit temperature (for example, + 100 ° C.) that enables proper operation of the two-stage compressor 11, and when the temperature rises, By increasing the opening, the temperature rise of the two-stage compressor 11 is suppressed, and control is performed so that the two-stage compressor 11 does not reach the limit temperature.

The second control amount (MPcont) is a control amount for adjusting the amount of refrigerant flowing through the auxiliary refrigerant flow path in the split cycle to optimize the intermediate pressure (MP). In the present embodiment, the control device C calculates the appropriate value from the high pressure side pressure HP of the refrigerant circuit 1 detected by the unit outlet side pressure sensor 58 and the low pressure side pressure LP of the refrigerant circuit 1 detected by the low pressure sensor 32. First determine the intermediate pressure value. Further, the control device C determines whether or not the pressure MP in the intermediate pressure region of the refrigerant circuit 1 detected by the intermediate pressure sensor 49 is higher than the appropriate intermediate pressure value, and the pressure MP is higher than the appropriate intermediate pressure value. When it is low, control is performed in the direction of increasing the opening degree of the expansion valve 83.
The appropriate intermediate pressure value may be calculated from the geometric mean of the detected high-pressure side pressure HP and the low-pressure side pressure LP. In addition, an appropriate intermediate pressure value may be calculated from the high-pressure side pressure HP and the low-pressure side pressure LP in advance. The intermediate pressure value may be obtained experimentally and determined from a data table constructed based on this.

  In the present embodiment, the second control amount (MPcont) is determined by comparing the appropriate intermediate pressure value obtained from the high pressure side pressure HP and the low pressure side pressure LP with the pressure MP in the intermediate pressure region. However, the present invention is not limited to this. For example, the following may be adopted. That is, the overcompression determination value MPO is obtained from the pressure MP in the intermediate pressure region of the refrigerant circuit 1 detected by the intermediate pressure sensor 49 and the low pressure LP of the refrigerant circuit 1 detected by the low pressure sensor 32. Then, it is determined whether the overcompression determination value MPO is lower than the high pressure side pressure HP of the refrigerant circuit 1 detected by the unit outlet side pressure sensor 58, and the overcompression determination value MPO is lower than the high pressure side pressure HP. In this case, the direction of increasing the opening degree of the expansion valve 83 is controlled. By reflecting the second control amount in the opening degree control of the expansion valve 83, the pressure difference between the high pressure HP, the intermediate pressure region MP, and the low pressure LP can be properly maintained. Operation can be stabilized.

  The third control amount (SPcont) is a control amount for optimizing the refrigerant temperature LT output from the first flow path 80A of the intermediate heat exchanger 80. In the present embodiment, the control device C includes the refrigerant temperature GCT detected by the gas cooler outlet temperature sensor 52 and the first flow path 80A of the intermediate heat exchanger 80 detected by the unit outlet temperature sensor 54. It is determined whether or not the difference (GCT−LT) between the temperature of the passed refrigerant flow and the temperature LT is smaller than the predetermined value SP, and if it is smaller, the opening degree of the expansion valve 83 is increased.

Here, the predetermined value SP is different depending on whether the high-pressure side pressure HP is in the supercritical region or the saturation region of the refrigerant. In the present embodiment, whether the high-pressure side pressure HP is a supercritical region or a saturation region is based on the outside air temperature detected by the outside air temperature sensor 56, and when the outside air temperature is high, for example, at + 31 ° C. or higher, If it is determined that the temperature is in the supercritical region and the outside air temperature is low, for example, if it is less than + 31 ° C., it is determined that the region is a saturated region. If the supercritical region is determined, the predetermined value SP is set to be increased, and if the saturated region is determined, the predetermined value SP is set to be decreased. In the present embodiment, the predetermined value SP is 35 ° C. in the supercritical region and 20 ° C. in the saturation region.
The control device C adds the three control amounts obtained as described above, that is, the first control amount (DTcont), the second control amount (MPcont), and the third control amount (SPcont). Thus, the operation amount of the valve opening of the expansion valve 83 is determined, and the valve opening is increased based on this.

(A-2) Valve opening degree reduction control of the expansion valve 83 The control device C also discharges the temperature LT of the refrigerant flow that has passed through the first flow path 80A of the intermediate heat exchanger 80 or the two-stage compressor 11. An operation amount for reducing the valve opening degree of the expansion valve 83 is determined from the difference between the refrigerant temperature DT and the temperature GCT of the refrigerant passed through the gas cooler 46.
That is, the control device C determines whether or not the temperature LT of the refrigerant flow that has passed through the first flow path 80A of the intermediate heat exchanger 80 detected by the unit outlet temperature sensor 54 is lower than a predetermined value. The predetermined value is 0 ° C. as an example. As a result, when the unit outlet temperature is 0 ° C. or lower, the refrigerant flowing through the first flow path 80A is excessively cooled by operating in the direction of reducing the opening of the expansion valve 83. Can be resolved.
Further, the control device C determines whether the difference (DTGCT) between the temperature DT detected by the discharge temperature sensor 50 and the refrigerant temperature GCT detected by the gas cooler outlet temperature sensor 52 is lower than a predetermined value TDT. If it is low, the opening degree of the expansion valve 83 is controlled to be reduced.

Here, the predetermined value TDT differs depending on whether the high-pressure side pressure HP is in the supercritical region or the saturation region of the refrigerant. In the present embodiment, as in the case of obtaining the third control amount, whether the high-pressure side pressure HP is in the supercritical region or the saturated region is determined based on the outside air temperature. When it is determined that the region is a supercritical region, the predetermined value TDT is set to be lowered. When it is determined that the region is a saturated region, the predetermined value TDT is increased. In the present embodiment, the predetermined value TDT is 10 ° C. in the supercritical region and 35 ° C. in the saturation region.
When the temperature LT of the refrigerant flow passing through the first flow path 80A of the intermediate heat exchanger 80 is equal to or lower than a predetermined value (0 ° C.), the control device C, or the refrigerant temperature DT discharged from the two-stage compressor 11 and the gas cooler 46, when the difference from the refrigerant temperature GCT is lower than the predetermined value TDT, the operation amount of the expansion valve 83 is determined, and the valve opening is reduced based on this regardless of the valve opening increase control. Let

In the refrigeration apparatus R having the split cycle as described above, the refrigerant that has passed through the intermediate heat exchanger 80 is allowed to flow through the first return flow path that is branched from the refrigerant main flow path, and then expanded, and then the intermediate heat exchange is performed. Returning to the vessel 80, the returned refrigerant and the refrigerant from the gas cooler 46 are heat-exchanged.
Since the refrigerant that has been sufficiently cooled by the intermediate heat exchanger 80 is decompressed by the expansion valve 83 and then returned to the intermediate heat exchanger 80 to exchange heat with the refrigerant from the gas cooler 46, the gas cooler 46 The refrigerant from is efficiently cooled. At the inlet of each evaporator 63, 63, the specific enthalpy can be reduced, and the refrigeration effect is further increased.
Further, since the refrigerant flowing to the first return flow path side is supercooled and stabilized, the control device C can appropriately perform expansion control of the refrigerant in the expansion valve 83. In addition, the refrigerant flow that has flowed through the second flow path 80B is returned to the second rotary compression element 20 (intermediate pressure part) from the high-stage side suction port 26 of the two-stage compressor 11, so The amount of refrigerant sucked into the first rotary compression element 18 (low pressure portion) from the stage side suction port 22 decreases, and the compression work in the first rotary compression element 18 for compressing from the low pressure to the intermediate pressure decreases. As a result, the compression power in the two-stage compressor 11 is reduced and the coefficient of performance is improved.

  Here, the effect of the so-called split cycle depends on the amount of flow through the first flow path 80A and the second flow path 80B of the intermediate heat exchanger 80. That is, if the amount of refrigerant flowing through the second flow path 80B is too large, the amount of refrigerant from the first flow path 80A that finally evaporates in the evaporators 63 and 63 is insufficient. Conversely, if the amount of the refrigerant flowing through the second flow path 80B is too small, the effect of the split cycle is diminished. On the other hand, the pressure of the refrigerant decompressed by the expansion valve 83 is an intermediate pressure of the refrigerant circuit 1, and controlling the intermediate pressure controls the amount of the refrigerant in the second flow path 80B.

Here, in the present embodiment, as described above, when the temperature DT (discharge temperature sensor 50) of the refrigerant discharged from the two-stage compressor 11 is higher than the predetermined value DT0, the opening degree of the expansion valve 83 is increased. The expansion valve 83 when the pressure MP in the intermediate pressure region of the refrigerant circuit 1 is lower than the appropriate intermediate pressure value obtained from the first control amount and the high pressure side pressure HP and low pressure side pressure LP of the refrigerant circuit 1. The difference (GCT−LT) between the second control amount acting in the direction of increasing the opening degree and the temperature LT of the refrigerant passing through the gas cooler 46 and the temperature LT of the second refrigerant flow passing through the intermediate heat exchanger 80 is predetermined. When the third control amount acting in the direction of increasing the opening degree of the expansion valve 83 is calculated when the value is smaller than the value SP, the valve opening degree of the expansion valve 83 is calculated by adding these first to third control amounts. The amount of operation that increases is determined. Further, when the temperature LT is lower than a predetermined value, or when the temperature DT-GCT is lower than the predetermined value TDT, the operation amount is determined in the direction of reducing the valve opening degree of the expansion valve 83.
As a result, the temperature DT of the discharged refrigerant can be kept at a predetermined value DT0 or less by the first control amount, and the intermediate pressure MP of the refrigerant circuit 1 can be optimized by the second control amount. The pressure difference among LP, intermediate pressure MP, and high-pressure side pressure HP can be kept appropriate. In addition, the temperature LT of the refrigerant that has passed through the first flow path 80A of the intermediate heat exchanger 80 can be lowered by the third control amount, and the refrigeration effect can be maintained. As a result, it is possible to achieve high efficiency and stabilization of the refrigeration apparatus R as a whole.

Further, the control device C increases the predetermined value SP and decreases the predetermined value TDT when the high pressure side pressure HP is in the supercritical region, and decreases the predetermined value SP when the high pressure side pressure HP is in the saturation region. By increasing the value TDT, control is performed by changing the third control amount and the predetermined values SP and TDT of the first control amount separately for the case where the high pressure side pressure HP is in the supercritical region and the case where it is in the saturation region. It becomes possible to do.
Thereby, even when the high pressure side pressure HP is in the saturation region, the degree of superheat in the intermediate heat exchanger 80 can be reliably ensured, and the inconvenience of liquid back in the two-stage compressor 11 can be avoided. it can. Further, when the high-pressure side pressure HP is in the supercritical region, such a liquid back does not occur, and therefore, the efficiency can be set as a priority.

  The second control amount in the above embodiment is expanded when the overcompression determination value MPO obtained from the pressure MP and the low pressure LP in the intermediate pressure region of the refrigerant circuit 1 is lower than the high pressure HP in the refrigerant circuit. As the second control amount acting in the direction of increasing the opening degree of the valve 83, the operation amount of the opening degree of the expansion valve 83 is determined by adding the first to third control amounts. Similarly to the above, the intermediate pressure MP of the refrigerant circuit can be optimized, whereby the pressure difference among the low pressure side pressure LP, the intermediate pressure MP, and the high pressure side pressure HP can be kept appropriate.

(B) Refrigerant amount adjustment control Next, refrigerant amount adjustment control of the refrigerant circuit 1 of the refrigeration apparatus R in the present embodiment will be described. A refrigerant amount adjusting tank 100 is connected to the high pressure side, which is the supercritical pressure of the refrigerant circuit 1, via a first communication circuit 101. In the present embodiment, the refrigerant quantity adjustment tank 100 is connected to the refrigerant pipe 7 via the first communication circuit 101 on the downstream side from the location where the flow divider 82 is provided.
The refrigerant amount adjustment tank 100 has a predetermined volume. The first communication circuit 101 is connected to the upper part of the tank 100. The first communication circuit 101 is provided with an electric expansion valve 102 as a first opening / closing means having a throttling function. The opening / closing means having a throttle function is not limited to this. For example, the opening / closing means may be constituted by, for example, a capillary tube and an electromagnetic valve (open / close valve).

The refrigerant amount adjustment tank 100 is connected to a second communication circuit 103 that communicates the upper part of the tank 100 with the intermediate pressure region of the refrigerant circuit 1. An example of the intermediate pressure region is a portion of the intermediate pressure suction pipe 40 on the outlet side of the intercooler 38 of the refrigerant circuit 1, and the other end of the second communication circuit 103 is connected to this portion. The second communication circuit 103 is provided with an electromagnetic valve 104 as a second opening / closing means.
In addition, a third communication circuit 105 that connects the lower portion of the tank 100 and the intermediate pressure region of the refrigerant circuit 1 is connected to the refrigerant amount adjustment tank 100. An example of the intermediate pressure region is the same as the connection destination of the other end of the second communication circuit 103, and the other end of the third communication circuit 105 is an intermediate pressure suction pipe on the outlet side of the intercooler 38 of the refrigerant circuit 1. 40. The third communication circuit 105 is provided with an electromagnetic valve 106 as a third opening / closing means.

  As shown in FIG. 2, the control device C is connected to a unit outlet side pressure sensor (unit outlet side pressure detecting means) 58 and an outside air temperature sensor 56 on the input side. This unit outlet side pressure sensor 58 detects the pressure of the refrigerant toward the showcase units 5A and 5B on the downstream side of the refrigerant amount adjustment tank 100. The control device C includes an electric expansion valve (first opening / closing means) 102, an electromagnetic valve (second opening / closing means) 104, an electromagnetic valve (third opening / closing means) 106, and a fan of a gas cooler blower 47 for the gas cooler 46. A motor 47M is connected. The control device C controls the rotational speed of the fan motor 47M of the gas cooler blower 47 based on the detected temperature of the outside air temperature sensor 56 and the evaporation temperature of the refrigerant in the evaporators 63 and 63 as will be described in detail later.

(B-1) Refrigerant Recovery Operation Hereinafter, the refrigerant recovery operation of the refrigerant circuit 1 will be described. The control device C determines whether or not the detected pressure of the unit outlet side pressure sensor 58 exceeds a predetermined recovery threshold value, or a predetermined recovery protection value in which the detected pressure of the unit outlet side pressure sensor 58 is lower than the previous recovery threshold value. And the rotational speed of the gas cooler blower 47 is determined to be a maximum value.
In the present embodiment, since the intermediate pressure (MP) of the refrigerant circuit 1 has an appropriate value of about 8 MPa as an example, the value is set as a recovery protection value, and the recovery threshold is set to about 9 MPa, for example. Moreover, the maximum value of the rotation speed of the gas cooler blower 47 is set to 800 rpm as an example. Further, it may be a condition that a predetermined time elapses after the rotation number of the gas cooler blower 47 reaches the maximum value.
Thereby, the control device C exceeds the recovery protection value of 8 MPa when the detected pressure of the unit outlet side pressure sensor 58 exceeds the recovery threshold value of 9 MPa, or even if the detected pressure is equal to or lower than the recovery threshold value, and When the rotational speed of the gas cooler blower 47 reaches the maximum value of 800 rpm, it is determined that the excess pressure of the gas refrigerant circulates in the refrigerant circuit 1 and the high-pressure side pressure has abnormally increased. The refrigerant recovery operation is executed.

In this refrigerant recovery operation, the control device C opens the electric expansion valve 102 and the electromagnetic valve 104 with the electromagnetic valve 106 closed. Thus, the refrigerant that is cooled by the intermediate heat exchanger 80 and flows in the refrigerant pipe 7 toward the showcase units 5A and 5B is provided with an electric expansion valve 102 that is partially opened. The refrigerant flows into the refrigerant amount adjustment tank 100 through the one communication circuit 101.
At this time, since the electromagnetic valve 104 is opened, the pressure in the refrigerant quantity adjustment tank 100 can be released outside the tank via the second communication circuit 103. For this reason, even when the refrigerant in the refrigerant circuit 1 is in a gas cycle operation in which the refrigerant in the refrigerant circuit 1 is not liquefied, such as when the outside air temperature becomes high, the pressure in the refrigerant amount adjustment tank 100 decreases. The refrigerant flowing in is liquefied and accumulated in the tank 100. That is, when the pressure in the refrigerant quantity adjustment tank 100 drops below the supercritical pressure, the refrigerant changes from the gas region to the saturation region, and the liquid level can be secured.

As a result, the refrigerant in the refrigerant circuit 1 can be collected quickly and efficiently in the refrigerant amount adjustment tank 100. Accordingly, it is possible to eliminate the disadvantage that the high pressure side in the refrigerant circuit 1 becomes excessively high due to the excessive refrigerant, and it is possible to prevent the overload operation of the two-stage compressors 11 and 11 due to the high pressure abnormality.
In particular, unlike the case where the upper part of the refrigerant amount adjusting tank 100 and the intermediate pressure region of the refrigerant circuit 1 are communicated with each other via the second communication circuit 103, the low pressure side pressure is reduced. It is possible to avoid a decrease in cooling efficiency due to the increase.

  In the present embodiment, even if the pressure on the high pressure side detected by the unit outlet side pressure sensor 58 is equal to or lower than the recovery threshold value, the gas cooler blower that air-cools the gas cooler 46 that exceeds a predetermined recovery protection value. When the rotational speed of 47 is the highest value, the refrigerant recovery operation is performed, and therefore, the high pressure side of the refrigerant circuit 1 continues to be abnormally high in consideration of the operating state of the gas cooler blower 47. It is possible to prevent the efficiency from being reduced.

(B-2) Refrigerant holding operation On the other hand, the control device C determines whether or not the high-pressure side pressure detected by the unit outlet-side pressure sensor 58 has become a recovery protection value, which is 8 MPa or less in this embodiment, When it falls below the recovery protection value, the refrigerant recovery operation is terminated and the operation proceeds to the refrigerant holding operation. In this refrigerant holding operation, the controller C maintains the electromagnetic valve 106 closed, closes the electromagnetic valve 104, and maintains the opening of the electric expansion valve 102 at the opening in the refrigerant recovery operation.

The opening degree of the electric expansion valve 102 may be smaller than the opening degree in the refrigerant recovery operation. As a result, when the electromagnetic valve 104 is closed, the liquid level in the refrigerant amount adjustment tank 100 can be maintained by the pressure of the high pressure side region of the refrigerant circuit 1 via the opened electric expansion valve 102. . Therefore, liquid sealing in the refrigerant quantity adjustment tank 100 can be avoided, and safety can be ensured. Thereby, it becomes possible to maintain the amount of circulating refrigerant in the refrigerant circuit 1 appropriately.
Further, the control device C makes the opening degree of the electric expansion valve 102 in the refrigerant holding operation smaller than the opening degree in the refrigerant collecting operation, so that the refrigerant amount adjustment tank 100 in the refrigerant circuit 1 is contained in the refrigerant holding operation. The excessive recovery of the refrigerant makes it possible to effectively eliminate the disadvantage that the refrigerant shortage in the refrigerant circuit 1 occurs.

(B-3) Refrigerant Discharge Operation Then, the control device C has a predetermined discharge threshold (in this embodiment, about 7 MPa) in which the pressure detected by the unit outlet side pressure sensor 58 is lower than the recovery protection value (in this case, about 8 MPa). Or the detected pressure of the unit outlet side pressure sensor 58 is equal to or lower than the previous recovery protection value, and the rotational speed of the gas cooler blower 47 is equal to or lower than a predetermined specified value lower than the maximum value. Determine whether or not. In the present embodiment, the predetermined specified value is about 3/8 of the maximum value, that is, about 300 rpm when the maximum value is 800 rpm. Further, it may be a condition that a predetermined time elapses after the rotational speed of the gas cooler blower 47 becomes equal to or less than a predetermined specified value.
As a result, the control device C detects that the detected pressure of the unit outlet side pressure sensor 58 is below the discharge threshold value of 7 MPa, or the detected pressure is 8 MPa or less which is the recovery protection value, and the gas cooler blower 47 When the rotational speed is equal to or less than a predetermined specified value (here, 300 rpm), it is determined that the refrigerant in the refrigerant circuit 1 has become insufficient, and the refrigerant discharge operation is executed.

  In this refrigerant discharge operation, the control device C closes the electric expansion valve (first opening / closing means) 102 and the electromagnetic valve (second opening / closing means) 104 and opens the electromagnetic valve (third opening / closing means) 106. Thereby, the liquid refrigerant accumulated in the refrigerant quantity adjusting tank 100 is discharged to the refrigerant circuit 1 through the third communication circuit 105 in which the electromagnetic valve 106 connected to the lower part of the tank 100 is opened. Therefore, unlike the case where gas refrigerant is mixed from the upper part of the refrigerant amount adjustment tank 100 and discharged to the refrigerant circuit 1, the refrigerant in the refrigerant amount adjustment tank 100 can be quickly released to the refrigerant circuit 1. As a result, the refrigeration apparatus can be operated with high efficiency.

(B-4) Refrigerant holding operation Thereafter, the control device C determines whether or not the high-pressure side pressure detected by the unit outlet-side pressure sensor 58 has reached the recovery protection value, in this embodiment, 8 MPa or more. When the recovery protection value is exceeded, the refrigerant discharge operation is terminated and the operation proceeds to the refrigerant holding operation as described above. Thereafter, by repeatedly executing the refrigerant recovery operation-refrigerant holding operation-refrigerant releasing operation-refrigerant holding operation based on the high pressure side pressure of the refrigerant circuit 1, the refrigerant recovery / release can be controlled based on the high pressure side pressure, High pressure protection and overload operation can be prevented accurately. Thereby, the cooling capacity of the refrigeration apparatus can be ensured, and the COP can be optimized.

In particular, in the present embodiment, it is possible to control the refrigerant recovery / release operation in consideration of not only the high-pressure side pressure but also the rotational speed of the gas cooler blower 47 that air-cools the gas cooler 46, and the high-pressure side of the refrigerant circuit 1 is abnormal. It is possible to prevent a decrease in efficiency due to the continued high state.
In the present embodiment, the second communication circuit 103 and the third communication circuit 105 are both in communication with the outlet side of the intercooler 38 of the refrigerant circuit 1. Accordingly, it is possible to prevent pressure loss in the intercooler 38 and smoothly discharge the refrigerant from the refrigerant amount adjustment tank 100 to the refrigerant circuit 1.

Note that, when the two-stage compressors 11 and 11 stop operating, the control device C performs the refrigerant discharge operation. As a result, the disadvantage that the refrigerant amount in the refrigerant circuit 1 is insufficient when the two-stage compressors 11 and 11 are started up can be solved, and an appropriate high pressure can be obtained according to the high-pressure side pressure of the operated two-stage compressor 11. Side pressure can be realized.
In this case, the two-stage compressor 11 (compression means) employs a two-stage compression rotary compressor in which the first and second rotary compression elements 18 and 20 and the electric element are incorporated in the container 12. In addition to this, it may be of a type in which the refrigerant can be taken out and introduced from the intermediate pressure section with two single-stage rotary compressors or other types of compressors.

(D) Control of Blower 47 for Gas Cooler Next, control of the blower 47 for gas cooler that air-cools the gas cooler 46 as described above will be described. As shown in FIG. 2, the control device C is connected to high pressure sensors (high pressure detectors) 48, 48, a low pressure sensor 32, and an outside air temperature sensor 56. Here, since the pressure detected by the low pressure sensor 32 and the evaporation temperature TE in the evaporators 63 and 63 have a certain relationship, the control device C uses the pressure detected by the low pressure sensor 32. Then, the evaporation temperature TE of the refrigerant in the evaporators 63, 63 is converted and acquired. The control device C is connected to a gas cooler blower 47 that air-cools the gas cooler 46.
The control device C controls the rotation speed of the gas cooler blower 47 so that the high pressure side pressure HP detected by the high pressure sensor 48 becomes a predetermined target value (target high pressure: THP). Here, the target high pressure THP is determined from the outside air temperature TA and the evaporation temperature TE of the refrigerant in the evaporators 63 and 63.

In the refrigeration apparatus R in which the high pressure side of the refrigerant circuit 1 is equal to or higher than the supercritical pressure as in this embodiment, when the outside air temperature TA is a certain temperature, for example, + 30 ° C. or less, a saturation cycle is performed, and at a temperature higher than + 30 ° C. A gas cycle is performed. Since the refrigerant is not liquefied when the gas cycle is performed, the temperature and pressure are not uniquely determined by the amount of refrigerant in the refrigerant circuit 1 at that time. Therefore, the target high pressure THP differs depending on the outside air temperature TA.
In this embodiment, as an example, when the outside air temperature TA detected by the outside air temperature sensor 56 is equal to or lower than a lower limit temperature (for example, 0 ° C.), the target high pressure THP is constant at a predetermined lower limit value THPL. The target high pressure THP is constant at a predetermined upper limit value THPH when the outside air temperature TA is higher than a predetermined temperature (upper limit temperature) higher than 30 ° C. When the outside air temperature TA is higher than the lower limit temperature and lower than the upper limit temperature, the target high pressure THP is obtained as follows.

As the outside air temperature TA is lower than a predetermined reference temperature, for example, + 30 ° C., the target value THP for the high-pressure side pressure is determined to be lowered, and as the temperature is higher, the target value THP is determined to be higher. In addition, as described above, the higher the refrigerant evaporation temperature TE in the evaporators 63 and 63 obtained by conversion based on the pressure detected by the low pressure sensor 32, the higher the target value THP of the high pressure side pressure. Is determined in the direction of increasing the value, and the target value THP is determined in the direction of decreasing as the value decreases.
In the present embodiment, the control device C calculates the target high pressure THP from the outside air temperature TA and the evaporation temperature TE using an arithmetic expression. However, the present invention is not limited to this. The target high pressure THP may be acquired based on the data table acquired from the evaporation temperature TE.

  Then, the control device C uses the high pressure side pressure HP detected by the high pressure sensor 48 (high pressure detection means), the target high pressure THP, the deviation e between the HP and THP, and P (proportional deviation based on the deviation e). Proportional differential operation is performed from D (differentiation, control in the direction to reduce the change of the deviation e), and derived as an operation amount in proportion to the magnitude of e. The rotational speed of the gas cooler blower 47 to be used is determined. The rotational speed of the gas cooler blower 47 is increased as the target high pressure THP is higher, and the rotational speed of the gas cooler blower 47 is decreased as the target high pressure THP is lower.

  Thereby, the control apparatus C controls the rotation speed of the gas cooler blower 47 based on the outside air temperature TA and the evaporation temperature of refrigerant in the evaporator (converted from the low pressure detected by the low pressure sensor 32) TE. By doing so, even if the refrigeration apparatus R has a supercritical pressure on the high pressure side, the rotational speed of the gas cooler blower 47 can be controlled so as to have an appropriate high pressure. Thereby, high efficiency operation can be realized while reducing noise due to operation of the gas cooler blower 47.

  In the present embodiment, the control device C reduces the target value THP of the high-pressure side pressure of the refrigerant circuit 1 based on the outside air temperature TA and the evaporation temperature TE, for example, lowers the target value THP as the outside air temperature TA is lower. As the temperature TE is higher, the target value THP is determined in the direction of increasing the target value THP, and the gas cooler blower 47 is controlled so that the high-pressure side pressure becomes the target value THP. Considering the state of the refrigerant that changes in the gas cycle, and suitable high-pressure side pressure can be realized based on the evaporation temperature TE, thereby realizing highly efficient operation. The present invention is particularly effective in a supercritical refrigerant circuit (supercritical refrigeration cycle) using carbon dioxide as a refrigerant.

(E) Oil separator 44
The two-stage compressor 11 uses oil as lubricating oil. For example, existing oils such as mineral oil (mineral oil), alkylbenzene oil, ether oil, ester oil, PAG (polyalkyl glycol) and the like are used.
As described above, the oil separator 44 is interposed in the high-pressure side pipe 42 that connects the high-stage discharge port 28 of the two-stage compressor 11 and the gas cooler 46. The oil separator 44 is connected with an oil return circuit 73 that returns the captured oil to the two-stage compressor 11. In the oil return circuit 73, an oil cooler 74 for cooling the captured oil is provided.

The oil contained in the high-temperature and high-pressure refrigerant discharged from the high-stage discharge port 28 of each of the two-stage compressors 11 and 11 and flowing into the oil separator 44 is separated and captured. Since the inside of the sealed container 12 of the two-stage compressor 11 is maintained at an intermediate pressure, the trapped oil is caused to flow through the oil cooler 74 by the differential pressure between the high pressure in the oil separator 44 and the intermediate pressure in the sealed container 12. Through the oil return circuit 73 so as to return to the two-stage compressor 11. The oil return circuit 73 is branched into two systems on the downstream side of the oil cooler 74 and is connected to the hermetic container 12 of the two-stage compressor 11 via a flow rate adjusting valve (electric valve) 76, respectively. When the oil passes through the oil cooler 74 disposed in the same air passage 45 as the gas cooler 46, the oil is cooled by the operation of the gas cooler blower 47, and the temperature rise of the two-stage compressor 11 is suppressed. The hermetic container 12 of the two-stage compressor 11 is provided with an oil level sensor 77 that detects the level of oil retained in the hermetic container 12.
When carbon dioxide is used as a refrigerant as in the present embodiment, oil can be smoothly returned to the two-stage compressor 11 by performing the control as described above, and the refrigerating capacity can be effectively improved. It is possible to improve the performance.

(F) Improvement of startability of two-stage compressor (bypass circuit)
Next, startability improvement control of the two-stage compressor 11 will be described. As shown in FIG. 2, the intermediate pressure region of the refrigerant circuit 1 on the outlet side of the intercooler 38 of the refrigeration apparatus R, in this embodiment, the second communication circuit 103 or third connected to the outlet side of the intercooler 38. A bypass circuit 84 is provided that communicates the communication circuit 105 with the low-pressure side of the refrigerant circuit 1, in this embodiment, the refrigerant outlet side of the evaporators 63 and 63. An electromagnetic valve (valve device) 85 is interposed in the bypass circuit 84. The control device C is connected to the two-stage compressors 11 and 11 and the electromagnetic valve 85 as shown in FIG. The control device C can detect (acquire) the operating frequency of the two-stage compressor 11.

In a state where the two-stage compressor 11 is in operation, the low-pressure refrigerant gas sucked into the low-pressure portion of the first rotary compression element 18 from the low-stage suction port 22 is increased to the intermediate pressure by the first rotary compression element 18. And discharged into the sealed container 12. The intermediate-pressure refrigerant gas in the hermetic container 12 is discharged from the low-stage discharge port 24 of the two-stage compressor 11 to the intermediate-pressure discharge pipe 36 and cooled by the intercooler 38, and then flows through the intermediate-pressure suction pipe 40. Then, it is sucked into the high stage side suction port 26. The intermediate pressure region is a region that is discharged from the first rotary compression element 18 and is sucked into the second rotary compression element 20 through the high-stage suction port 26.
The medium-pressure refrigerant gas sucked into the intermediate pressure portion of the second rotary compression element 20 from the high-stage side suction port 26 is compressed at the second stage by the second rotary compression element 20 to become a high-temperature and high-pressure refrigerant gas. The high-pressure side discharge port 28 discharges the high-pressure side piping 42. On the high pressure side of the refrigerant, the oil separator 44, the gas cooler 46, the exhaust heat recovery heat exchanger 70, the intermediate heat exchanger 80, the refrigerant pipe 7, and the region up to the case side expansion valves 62, 62 of the showcase units 5A, 5B are high pressure. It is considered as a side.

And it is decompressed and expanded by the case side expansion valves 62 and 62. The low pressure side of the refrigerant circuit 1 is from the evaporators 63, 63 downstream of the case side expansion valves 62, 62 to the low stage side suction port 22 communicating with the first rotary compression element 18.
When restarting the two-stage compressor 11 after the operation of the two-stage compressor 11 is stopped, the control device C is in a period from when the two-stage compressor 11 is started up to a predetermined operating frequency. The electromagnetic valve 85 is opened and the flow path of the bypass circuit 84 is opened. The predetermined operating frequency is an operating frequency at which the two-stage compressor 11 can perform effective torque control. In the present embodiment, the predetermined operating frequency is set to 35 Hz as an example.
Thus, the electromagnetic valve 85 is opened until the two-stage compressor 11 is started from the stopped state and rises to the predetermined operating frequency, whereby the intermediate pressure discharge pipe 36 is discharged from the low-stage discharge port 24. Then, the refrigerant in the intermediate pressure region after passing through the intercooler 38 flows into the low pressure side region of the refrigerant circuit 1 via the bypass circuit 84. Thereby, the pressure in the intermediate pressure region and the low pressure side region of the refrigerant circuit 1 is equalized.

Therefore, at the time of starting from the start of the two-stage compressor 11 to the increase to the predetermined operating frequency, a predetermined torque cannot be ensured. During this time, the intermediate pressure region and the low pressure side region are equalized, so that the outside air Even in a situation where the intermediate pressure tends to increase due to the high temperature, the inconvenience that the intermediate pressure approaches a high pressure can be solved.
Therefore, it is possible to avoid a starting failure due to the pressure in the intermediate pressure region and the pressure in the high pressure region approaching while the torque shortage at the time of starting the two-stage compressor 11 occurs. In addition, highly efficient operation can be realized. In addition, after the operating frequency of the detected two-stage compressor 11 rises to a predetermined operating frequency, the control device C closes the electromagnetic valve 85 and closes the flow path of the bypass circuit 84, as described above. Perform a normal refrigeration cycle.

(G) Improvement of startability of two-stage compressor (check valve)
In addition, a check valve 90 is provided in the high-pressure side pipe 42 of each of the two-stage compressors 11 and 11 in the present embodiment. The check valve 90 has a forward direction from the two-stage compressor 11 toward the gas cooler 46.
Since the check valve 90 is composed of a reed valve, noise generation can be eliminated.
Even if the two-stage compressors 11 and 11 are stopped by the installation of the check valve 90, the high-pressure refrigerant on the gas cooler 46 side does not communicate with the two-stage compressor 11 side. Therefore, even if the operation of the two-stage compressor 11 is stopped and the high pressure side and the intermediate pressure are equalized in the sealed container 12, the case side provided in the vicinity of the evaporators 63 and 63 from the check valve 90 The pressure on the high pressure side of the refrigerant circuit 1 up to the expansion valves 62 and 62 can be maintained.

That is, when the check valve 90 is not provided, the high pressure side and the intermediate pressure side are equalized in the stopped two-stage compressor 11. On the other hand, it is difficult to equalize the low pressure side and the medium pressure side in the sealed container 12 easily because only the low pressure side is immersed in the oil. However, when starting the two-stage compressor 11, since the pressure difference in the refrigerant circuit 1 is large, a predetermined time is required until the pressure in the entire refrigerant circuit 1 is equalized, resulting in poor startability.
However, in the present embodiment, after the two-stage compressor 11 is stopped, the pressure on the high-pressure side of the refrigerant circuit 1 is maintained by the check valve 90, so that the startability of the two-stage compressor 11 is improved. be able to. Moreover, since the pressure inside the refrigerant circuit 1 is not equalized, the efficiency of the refrigeration cycle apparatus can be improved.

According to the refrigeration apparatus R of the present invention, the inlet is connected to the two-stage compressor 11 that compresses and discharges the sucked refrigerant, the low-stage discharge port 24 of the two-stage compressor 11, and the two-stage compressor 11 An intercooler 38 having an outlet connected to the high-stage suction port 26, a gas cooler 46 having an inlet connected to the high-stage discharge port 28 of the two-stage compressor 11, and intermediate heat connected to the outlet of the gas cooler 46. And an exchanger 80. The intermediate heat exchanger 80 is configured to exchange heat between the refrigerant that flows in through the gas cooler 46 and the refrigerant that has passed through the intermediate heat exchanger 80 and is decompressed by the expansion valve 83.
More specifically, the intermediate heat exchanger 80 has a first flow path 80A having one end connected to the outlet of the gas cooler 46 and the other end connected to the evaporator 63 on the showcase unit 5A, 5B side, One end is connected to the high-stage suction port 26 (second-stage refrigerant suction portion) of the two-stage compressor 11, and the other end is a refrigerant flow path between the first flow path and the showcase units 5A and 5B. The expansion valve 83 is connected to one end of the second flow path 80B.

  Therefore, after sufficient cooling is performed by the intermediate heat exchanger 80, the refrigerant decompressed by the expansion valve 83 is heat-exchanged with the refrigerant from the gas cooler 46, whereby the refrigerant from the gas cooler 46 is efficiently cooled. Therefore, the cooling efficiency of the refrigeration apparatus R is improved. Further, since the refrigerant that has been sufficiently subcooled and stabilized flows into the expansion valve 83, the expansion valve 83 can stably expand the refrigerant as desired. As in the embodiment of the present application, even when carbon dioxide having a low critical point and difficult to take a temperature difference from the outside air is used as the refrigerant, a sufficiently subcooled refrigerant that has passed through the intermediate heat exchanger 80 is used. By returning to the expansion valve 83 disposed at the inlet of the intermediate heat exchanger 80, the expansion control at the expansion valve 83 can be realized to stabilize the refrigerant. Furthermore, since the expansion valve 83 may expand the supercooled refrigerant, a small expansion valve 83 can be employed.

The other end of the second flow path 80B of the intermediate heat exchanger 80 joins the refrigerant flow path that returns from the intercooler 38 to the high-stage suction port 26 (second-stage refrigerant suction section of the two-stage compressor 11). To do.
For this reason, it is possible to smoothly join the refrigerant flow from the intermediate heat exchanger 80 to the intermediate pressure side of the refrigerant circuit 1 while preventing pressure loss in the intercooler 38.
Carbon dioxide is used as the refrigerant. Carbon dioxide is easy to manage refrigerant without toxicity or flammability.
In addition, although the case where the carbon dioxide was used was mentioned as an example as a refrigerant | coolant, the effect of this application can be acquired even if it uses another refrigerant | coolant.

5A, 5B showcase unit (cooling target equipment)
11 Two-stage compressor 24 Low-stage discharge port (first-stage refrigerant discharge section)
26 High-stage inlet (second-stage refrigerant inlet)
28 Higher stage outlet (second stage refrigerant outlet)
38 Intercooler 46 Gas cooler 63 Evaporator 80 Intermediate heat exchanger 80A First flow path 80B Second flow path 83 Expansion valve

Claims (4)

A two-stage compressor,
An intercooler having an inlet connected to a first-stage refrigerant discharge section of the two-stage compressor, and an outlet connected to a second-stage refrigerant suction section of the two-stage compressor;
A gas cooler having an inlet connected to a second-stage refrigerant discharge section of the two-stage compressor;
An intermediate heat exchanger connected to an outlet of the gas cooler,
The intermediate heat exchanger is configured to exchange heat between the refrigerant flowing through the gas cooler and the refrigerant reduced in pressure by an expansion valve after passing through the intermediate heat exchanger. Refrigeration equipment.   The intermediate heat exchanger has one end connected to the outlet of the gas cooler and the other end connected to the evaporator on the cooling target device side, and one end connected to the first flow path and the cooling target. A second flow path connected to the refrigerant flow path between the second stage and the second stage of the two-stage compressor. The refrigeration apparatus according to claim 1, wherein the expansion valve is connected.   The other end of the second flow path joins a refrigerant flow path that returns from the intercooler to a second-stage refrigerant suction portion of the two-stage compressor. Refrigeration equipment.   The refrigeration apparatus according to any one of claims 1 to 3, wherein the refrigerant is carbon dioxide.

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