JP6765086B2 - Refrigeration equipment - Google Patents

Description

The present invention relates to a refrigerating apparatus in which a refrigerant circuit is composed of a compression means, a gas cooler, a main drawing means, and an evaporator.

Conventionally, in this type of refrigerating apparatus, a refrigerating cycle is composed of a compression means, a gas cooler, a drawing means, etc., the refrigerant compressed by the compression means is dissipated by the gas cooler, depressurized by the drawing means, and then the evaporator It was supposed that the refrigerant was evaporated and the ambient air was cooled by the evaporation of the refrigerant at this time. In recent years, in order to prevent global warming, this type of refrigerating apparatus has been required to switch from a conventional fluorocarbon-based refrigerant to a refrigerant having a smaller global warming potential. For this reason, those using carbon dioxide, which is a natural refrigerant, as a substitute for the CFC-based refrigerant have been developed (see, for example, Patent Document 1).

On the other hand, in a refrigerating device that cools the inside of a refrigerator by utilizing the endothermic action in an evaporator installed in a showcase or the like, for example, the refrigerant temperature at the gas cooler outlet is high due to the high outside air temperature (heat source temperature on the gas cooler side). Under high conditions, the specific enthalpy at the inlet of the evaporator becomes large, so that there is a problem that the refrigerating capacity is significantly reduced. In such a case, if the discharge pressure (high pressure side pressure) of the compression means is increased in order to secure the refrigerating capacity, the compression power increases and the coefficient of performance decreases.

Therefore, the carbon dioxide refrigerant cooled by the gas cooler is divided into the first and second refrigerant streams, the first refrigerant stream is decompressed and expanded (temperature lowered) by the auxiliary throttle means, and then the split heat exchanger is used. It flows through one passage and returns to the intermediate pressure portion of the two-stage compressor having the low-pressure stage compression element and the high-pressure stage compression element, while the second refrigerant flow flows through the other flow path of the split heat exchanger and the first. A so-called split cycle refrigerating device has been proposed in which heat is exchanged with the refrigerant flow and then flows into the evaporator via the main drawing means. According to the refrigerating apparatus, the second refrigerant flow can be cooled by the first refrigerant flow, and the refrigerating capacity can be improved by reducing the specific enthalpy at the inlet of the evaporator (for example, patent). Reference 2).

Special Fair 7-18602 Japanese Unexamined Patent Publication No. 2011-133207

Conventionally, such a split cycle refrigerating device has been used in applications where the evaporation temperature is about −45 ° C. to −5 ° C. The reason why the upper limit of the evaporation temperature is about -5 ° C is as follows.

The mass flow rate of the refrigerant sucked by the high-pressure stage compression element must be equal to the sum of the mass flow rate of the refrigerant discharged by the low-pressure stage compression element and the mass flow rate of the first refrigerant flow in the split cycle. The intermediate pressure is the ratio of the exclusion volume of the high pressure stage compression element to the exclusion volume of the low pressure stage compression element (exclusion volume ratio), the ratio of the mass flow rate of the first refrigerant flow to the second refrigerant flow flowing through the split cycle, and , Evaporation pressure, etc. For example, the smaller the excluded volume ratio, the larger the mass flow rate ratio of the first refrigerant flow flowing through the split cycle, or the higher the evaporation pressure, the higher the intermediate pressure.

Further, in order to establish the split cycle, the tank located on the downstream side of the gas cooler and on the upstream side of the split heat exchanger is depressurized so that the temperature drops by about 5 ° C. in the auxiliary throttle means in a saturated state. After expansion, it is necessary to flow the refrigerant through the intermediate pressure portion of the compressor. That is, a certain amount of differential pressure is required between the inside of the tank and the intermediate pressure portion of the compressor.

However, there is a cost reason to lower the design pressure of the tank, the equipment on the downstream side of the tank, and the piping connecting them, and when the tank internal pressure reaches the critical point of carbon dioxide of 7.4 MPa or more, the refrigerant is gas-liquid separated. The internal pressure of the tank is usually about 6.0 MPa for the technical reason that it cannot be done.

That is, when the intermediate pressure increases as the evaporation temperature (evaporation pressure) rises, the differential pressure required to establish the split cycle is secured between the tank internal pressure, which is about 6.0 MPa, and the intermediate pressure. It may not be possible. Therefore, the upper limit of the evaporation temperature was set to about −5 ° C.

On the other hand, there is a demand for the evaporation temperature in a split cycle refrigerating apparatus to be 0 ° C. or higher, for example, when used for air conditioning in a showcase where the cold air temperature is slightly high or in a work room of a food processing plant.

Under such circumstances, it is an object of the present invention to enable the split cycle refrigerating apparatus to be used under the condition that the evaporation temperature is 0 ° C. or higher.

As a result of trial and error by the present inventors in order to solve the above problems, if the ratio of the excluded volumes (excluded volume ratio) of the two rotational compression elements constituting the two-stage compressor is within a predetermined range, the split cycle We have learned that the refrigeration system can be used at higher evaporation temperatures.

That is, in the refrigerating apparatus according to the present invention, a refrigerant circuit is composed of a compression means, a gas cooler, a main drawing means, and an evaporator, the high pressure side becomes a supercritical pressure, and the downstream side of the gas cooler is the main. A pressure adjusting squeezing means connected to the refrigerant circuit on the upstream side of the squeezing means, and a tank connected to the refrigerant circuit on the downstream side of the pressure adjusting squeezing means and upstream of the main squeezing means. , The split heat exchanger provided in the refrigerant circuit on the downstream side of the tank and on the upstream side of the main throttle means, and the refrigerant in the tank of the split heat exchanger via the auxiliary throttle means. After flowing into the first flow path, the auxiliary circuit sucked into the intermediate pressure portion of the compression means and the refrigerant flow out from the lower part of the tank and flow into the second flow path of the split heat exchanger, and the first. After exchanging heat with the refrigerant flowing through the flow path of the above, the main circuit flowing into the main throttle means and the pressure adjusting throttle means apply the high pressure side pressure of the refrigerant circuit on the upstream side of the pressure adjusting throttle means. The compression means includes a control means for adjusting, and the compression means has a low-stage rotary compression element that compresses the refrigerant from a low pressure to an intermediate pressure and a high-stage rotary compression element that compresses the refrigerant from an intermediate pressure to a high pressure. The exclusion volume of the high-stage rotational compression element is 85% or more of the exclusion volume of the low-stage rotational compression element.

According to the present invention, a refrigerating apparatus using a split cycle in which the refrigerant is carbon dioxide can be used under the condition that the evaporation temperature is 0 ° C. or higher.

It is a refrigerating circuit diagram of the refrigerating apparatus of one Example to which this invention was applied. It is a figure which shows the range of the exclusion volume ratio in which the refrigerating apparatus shown in FIG. 1 functions. It is a ph diagram when the refrigerating apparatus shown in FIG. 1 is operated at an evaporation temperature of 0 ° C.

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

(1) Configuration of Refrigerating Device R FIG. 1 is a refrigerant circuit diagram of the refrigerating device R according to an embodiment to which the present invention is applied. This refrigerant device R is a so-called split cycle refrigerating device including a split heat exchanger 29, as will be described in detail later. The refrigerating apparatus R includes a refrigerating machine unit 3 installed in a machine room or the like of a store such as a supermarket, and a showcase 4 of one or a plurality of units (only one is shown in the drawing) installed in the sales floor of the store. The refrigerator unit 3 and the showcase 4 are connected to each other by a refrigerant pipe (liquid pipe) 8 and a refrigerant pipe 9 via a unit outlet 6 and a unit inlet 7 to form a predetermined refrigerant circuit 1. ..

The refrigerant circuit 1 uses carbon dioxide (R744) as a refrigerant, which can have a refrigerant pressure on the high pressure side equal to or higher than the critical pressure (supercritical). This carbon dioxide refrigerant has a small global warming potential (GWP), is nonflammable, and is a non-toxic natural refrigerant. As the lubricating oil, existing oils such as mineral oil (mineral oil), alkylbenzene oil, ether oil, ester oil, and PAG (polyalkyl glycol) are used. Each arrow shown in FIG. 1 indicates the flow of the carbon dioxide refrigerant.

The refrigerator unit 3 includes a compressor 11 (an example of compression means). The compressor 11 is, for example, an internal intermediate pressure type two-stage compression type rotary compressor. The compressor 11 includes a closed container 12 and a rotary compression mechanism unit. The rotational compression mechanism unit includes an electric element 13 as a driving element housed in the upper part of the internal space of the closed container 12, and a first (lower stage side) rotational compression element (lower stage side) arranged below the electric element 13. It is composed of a first compression element) 14 and a second (higher side) rotary compression element (second compression element) 16. The compressor 11 is a two-stage compressor having a first rotary compression element 14 and a second rotary compression element 16 driven by the same rotary shaft (rotary shaft of the electric element 13). In such a two-stage compressor, the exclusion volume ratio between the low-stage side and the high-stage side is determined, and the intermediate pressure (MP) is determined according to the exclusion volume ratio.

The first rotary compression element 14 of the compressor 11 compresses the low-pressure refrigerant sucked into the compressor 11 from the low-pressure side of the refrigerant circuit 1 via the refrigerant pipe 9, boosts the pressure to an intermediate pressure, and discharges the refrigerant. The second rotational compression element 16 sucks in the intermediate pressure refrigerant discharged by the first rotational compression element 14, compresses it, boosts it to a high pressure, and discharges it to the high pressure side of the refrigerant circuit 1. The compressor 11 is a variable frequency compressor. The control device 57, which will be described later, controls the rotation speeds of the first rotational compression element 14 and the second rotational compression element 16 by changing the operating frequency of the electric element 13.

On the side surface of the closed container 12 of the compressor 11, a low-stage suction port 17 communicating with the first rotary compression element 14, a low-stage discharge port 18 communicating with the closed container 12, and a second rotary compression element 16 A high-stage side suction port 19 and a high-stage side discharge port 21 communicating with the high-stage side suction port 19 are formed. One end of the refrigerant introduction pipe 22 is connected to the low-stage suction port 17 of the compressor 11, and the other end is connected to the refrigerant pipe 9 at the unit inlet 7.

The low-pressure refrigerant gas sucked into the low-pressure portion of the first rotational compression element 14 from the low-stage suction port 17 is compressed in the first stage by the first rotational compression element 14 and boosted to an intermediate pressure. , Is discharged into the closed container 12. As a result, the inside of the closed container 12 becomes an intermediate pressure (MP).

One end of the intermediate pressure discharge pipe 23 is connected to the lower discharge port 18 of the compressor 11 from which the intermediate pressure refrigerant gas in the closed container 12 is discharged, and the other end is connected to the inlet of the intercooler 24. Has been done. The intercooler 24 air-cools the intermediate-pressure refrigerant discharged from the first rotational compression element 14. One end of the intermediate pressure suction pipe 26 is connected to the outlet of the intercooler 24. The other end of the intermediate pressure suction pipe 26 is connected to the high-stage suction port 19 of the compressor 11.

The intermediate pressure (MP) refrigerant gas sucked into the second rotary compression element 16 from the higher stage side suction port 19 of the compressor 11 is compressed in the second stage by the second rotary compression element 16. It becomes a high temperature and high pressure refrigerant gas.

Further, one end of the high-pressure discharge pipe 27 is connected to the high-stage side discharge port 21 provided on the high-pressure chamber side of the second rotary compression element 16 of the compressor 11, and the other end is a gas cooler (radiator) 28. It is connected to the entrance. Although not shown, an oil separator may be provided in the middle of the high pressure discharge pipe 27. The oil separated from the refrigerant by the oil separator is returned to the closed container 12 of the compressor 11.

The gas cooler 28 cools the high-pressure discharged refrigerant discharged from the compressor 11. A gas cooler blower 31 for air-cooling the gas cooler 28 is arranged in the vicinity of the gas cooler 28. In the present embodiment, the gas cooler 28 is arranged side by side with the above-mentioned intercooler 24, and these are arranged in the same air passage.

One end of the gas cooler outlet pipe 32 is connected to the outlet of the gas cooler 28, and the other end of the gas cooler outlet pipe 32 is connected to the inlet of the electric expansion valve 33 (an example of the pressure adjusting throttle means). The electric expansion valve 33 is for squeezing and expanding the refrigerant discharged from the gas cooler 28 and adjusting the high pressure side pressure of the refrigerant circuit 1 on the upstream side of the electric expansion valve 33. The outlet of the electric expansion valve 33 is connected to the upper part of the tank 36 via the tank inlet pipe 34.

The tank 36 is a volume body having a space of a predetermined volume inside the tank 36, and one end of the tank outlet pipe 37 is connected to the lower portion thereof, and the other end of the tank outlet pipe 37 is connected to the refrigerant pipe 8 at the unit outlet 6. It is connected. A second flow path 29B of the split heat exchanger 29 is provided in the middle of the tank outlet pipe 37. The tank outlet pipe 37 constitutes the main circuit 38 in this embodiment.

On the other hand, the showcase 4 installed in the store is connected to the refrigerant pipes 8 and 9. The showcase 4 is provided with an electric expansion valve 39 (an example of main throttle means) and an evaporator 41, and is sequentially connected between the refrigerant pipe 8 and the refrigerant pipe 9 (the electric expansion valve 39 is connected). Refrigerant pipe 8 side, evaporator 41 is refrigerant pipe 9 side). Next to the evaporator 41, a blower for circulating cold air (not shown) that blows air to the evaporator 41 is provided. Then, as described above, the refrigerant pipe 9 is connected to the low-stage side suction port 17 communicating with the first rotary compression element 14 of the compressor 11 via the refrigerant introduction pipe 22.

On the other hand, one end of the gas pipe 42 is connected to the upper part of the tank 36, and the other end of the gas pipe 42 is connected to the inlet of the electric expansion valve 43 (an example of the first auxiliary circuit throttle means). .. The gas pipe 42 causes the gas refrigerant to flow out from the upper part of the tank 36 and flows into the electric expansion valve 43.

One end of the intermediate pressure return pipe 44 is connected to the outlet of the electric expansion valve 43, and the other end of the intermediate pressure return pipe 44 is communicated with the middle of the intermediate pressure suction pipe 26 connected to the intermediate pressure portion of the compressor 11. ing. A first flow path 29A of the split heat exchanger 29 is provided in the middle of the intermediate pressure return pipe 44.

Further, one end of the liquid pipe 46 is connected to the tank outlet pipe 37 on the downstream side of the second flow path 29B of the split heat exchanger 29. The other end of the liquid pipe 46 is connected to the intermediate pressure return pipe 44 on the downstream side of the electric expansion valve 43. An electric expansion valve 47 (an example of a second auxiliary circuit throttle means) is provided in the middle of the liquid pipe 46.

The above-described electric expansion valve 43 (first auxiliary circuit throttle means) and electric expansion valve 47 (second auxiliary circuit throttle means) constitute the auxiliary throttle means in the present embodiment. Further, the intermediate pressure return pipe 44, the electric expansion valve 43, the electric expansion valve 47, the gas pipe 42, and the liquid pipe 46 form the auxiliary circuit 48 in the present embodiment.

As described above, the electric expansion valve 33 is located on the downstream side of the gas cooler 28 and on the upstream side of the electric expansion valve 39. Further, the tank 36 is located on the downstream side of the electric expansion valve 33 and on the upstream side of the electric expansion valve 39. Further, the split heat exchanger 29 is located on the downstream side of the tank 36 and on the upstream side of the electric expansion valve 39. As a result, the refrigerant circuit 1 of the refrigerating apparatus R in the present embodiment is configured.

Various sensors are attached to various parts of the refrigerant circuit 1.

For example, a high pressure sensor 49 is attached to the high pressure discharge pipe 27. The high-pressure sensor 49 detects the high-pressure side pressure HP of the refrigerant circuit 1 (the pressure between the high-stage side discharge port 21 of the compressor 11 and the inlet of the electric expansion valve 33).

Further, for example, a low pressure sensor 51 is attached to the refrigerant introduction pipe 22. The low-pressure sensor 51 detects the low-pressure side pressure LP (pressure between the outlet of the electric expansion valve 39 and the low-stage side suction port 17) of the refrigerant circuit 1.

Further, for example, the intermediate pressure sensor 52 is attached to the intermediate pressure return pipe 44. The intermediate pressure sensor 52 is the pressure in the intermediate pressure return pipe 44 downstream from the outlets of the electric expansion valves 43 and 47, which is the pressure in the intermediate pressure region of the refrigerant circuit 1, and is the lower stage of the compressor 11. A pressure equal to the pressure between the side discharge port 18 and the high-stage side suction port 19) is detected.

Further, for example, a unit outlet sensor 53 is attached to the tank outlet pipe 37 on the downstream side of the split heat exchanger 29. The unit outlet sensor 53 detects the pressure OP in the tank 36. The pressure in the tank 36 is the pressure of the refrigerant that exits from the refrigerator unit 3 and flows into the electric expansion valve 39 from the refrigerant pipe 8.

Each of the above-mentioned sensors is connected to an input of a control device 57 (an example of a control means) of the refrigerator unit 3 composed of a microcomputer. On the other hand, the electric element 13 of the compressor 11, the blower 31 for the gas cooler, the electric expansion valve 33, the electric expansion valve 43, the electric expansion valve 47, and the electric expansion valve 39 are connected to the output of the control device 57. The control device 57 controls each component on the output side based on the detection result from each sensor, the setting data, and the like.

In the following description, the electric expansion valve 39 on the showcase 4 side and the above-mentioned cold air circulation blower will also be described as being controlled by the control device 57, but these will be described as being controlled by the control device 57 via the main control device (not shown) of the store. It may be controlled by a control device (not shown) on the showcase 4 side that operates in cooperation with 57. Therefore, the control means in the present embodiment may be a concept including the control device 57, the control device on the showcase 4 side, the above-mentioned main control device, and the like.

(2) Operation of Refrigerating Device R Next, the operation of the refrigerating device R will be described. When the electric element 13 of the compressor 11 is driven by the control device 57, the first rotational compression element 14 and the second rotational compression element 16 rotate, and the first rotational compression element 14 is rotated from the lower suction port 17. Low-pressure refrigerant gas (carbon dioxide) is sucked into the low-pressure part of the. Then, it is boosted to an intermediate pressure by the first rotational compression element 14 and discharged into the closed container 12. As a result, the inside of the closed container 12 becomes an intermediate pressure (MP).

Then, the intermediate pressure gas refrigerant in the closed container 12 enters the intercooler 24 from the lower stage side discharge port 18 through the intermediate pressure discharge pipe 23, and is air-cooled in the intercooler 24.

The air-cooled gas refrigerant flows out from the intercooler 24 to the intermediate pressure suction pipe 26, and in the intermediate pressure suction pipe 26, the gas refrigerant flows into the intermediate pressure suction pipe 26 from the intermediate pressure return pipe 44 (details will be described later). Mix. The mixed gas refrigerant flows into the high-stage side suction port 19 (intermediate pressure portion) of the compressor 11.

The intermediate-pressure gas refrigerant flowing into the high-stage suction port 19 is sucked into the second rotational compression element 16, and the second rotational compression element 16 performs the second-stage compression to perform high-temperature and high-pressure gas refrigerant. It becomes. This gas refrigerant is discharged from the high-stage side discharge port 21 to the high-pressure discharge pipe 27.

(2-1) Control of Electric Expansion Valve 33 The gas refrigerant flowing into the gas cooler 28 from the high-pressure discharge pipe 27 is air-cooled by the gas cooler 28 and then reaches the electric expansion valve 33 via the gas cooler outlet pipe 32. The electric expansion valve 33 is provided to control the high pressure side pressure HP of the refrigerant circuit 1 on the upstream side of the electric expansion valve 33 to a predetermined target value THP, and is based on the output of the high pressure sensor 49. Controls the valve opening degree.

(2-1-1) Setting the opening degree of the electric expansion valve 33 at the start of operation First, at the start of operation, the control device 57 first sets the opening degree of the electric expansion valve 33 at the start of the refrigerating device R based on the outside air temperature (starting). Set the valve opening). Specifically, in the present embodiment, the control device 57 stores in advance a data table showing the relationship between the outside air temperature at the time of starting and the valve opening degree at the time of starting the electric expansion valve 33, and stores the outside air at the time of starting. From the temperature, the valve opening degree at the start of the electric expansion valve 33 is set with reference to the above data table.

The outside air temperature is detected by, for example, an outside air temperature sensor (not shown). The outside air temperature sensor is arranged inside or near the outdoor unit in which the intercooler 24, the gas cooler 28, the gas cooler blower 31 and the like are stored. Not limited to this, the control device 57 may detect the outside air temperature from the high pressure side pressure HP detected by the high pressure sensor 49 (hereinafter, the same applies). Since there is a correlation between the high pressure side pressure HP detected by the high pressure sensor 49 and the outside air temperature, the control device 57 can determine the outside air temperature from the high pressure side pressure HP. Specifically, the control device 57 stores in advance a data table showing the relationship between the high-pressure side pressure HP (outside air temperature) at the time of starting and the valve opening degree at the time of starting the electric expansion valve 33, and stores the data table at the time of starting. The outside air temperature is estimated, and the valve opening degree at the start of the electric expansion valve 33 is set with reference to the above data table.

(2-1-2) Setting the opening degree of the electric expansion valve 33 during operation During operation, the control device 57 is based on the detection pressure (high pressure side pressure HP) of the high pressure sensor 49, which is an index indicating the outside air temperature. The opening degree of the electric expansion valve 33 is set. In this case, the control device 57 sets the opening degree of the electric expansion valve 33 so that it becomes large when the high pressure side pressure HP (outside air temperature) is low. As a result, the pressure drop in the electric expansion valve 33 can be minimized, the pressure difference from the intermediate pressure (MP) of the intermediate pressure suction pipe 26 entering the compressor 11 is secured, and the refrigerating operation and the refrigerating operation can be performed. It can be done efficiently.

Here, the control device 57 stores in advance a data table showing the relationship between the high-pressure side pressure HP (outside air temperature) and the opening degree of the electric expansion valve 33, and opens the electric expansion valve 33 by referring to the data table. The degree may be set, or the opening degree may be calculated from the calculation formula.

(2-1-3) Control at the upper limit value MHP of the high-pressure side pressure HP When the control is performed as described above, the high-pressure side pressure on the upstream side of the electric expansion valve 33 due to the influence of the installation environment and the load. When the HP has risen to a predetermined upper limit value MHP, the control device 57 further increases the valve opening degree of the electric expansion valve 33. As the valve opening degree increases, the high pressure side pressure HP tends to decrease, so that the high pressure side pressure HP can always be maintained below the upper limit value MHP. As a result, it is possible to accurately suppress the abnormal rise in the high pressure side pressure HP on the upstream side of the electric expansion valve 33 and reliably protect the compressor 11, and forcibly stop (protect) the compressor 11 due to the abnormal high pressure. Operation) can be avoided in advance.

Here, when the refrigerant gas in the supercritical state flows out from the gas cooler 28, it is throttled by the electric expansion valve 33 to become a gas-liquid two-phase mixed state, and flows into the tank 36 from the upper part of the tank 36 via the tank inlet pipe 34. To do. The tank 36 has a role of temporarily storing the liquid / gas refrigerant discharged from the electric expansion valve 33 and separating gas and liquid, and the high pressure side pressure of the refrigerating device R (in this case, compression on the upstream side from the tank 36 to the tank 36). It plays a role of absorbing the pressure change and the fluctuation of the refrigerant circulation amount in the area up to the high-pressure discharge pipe 27 of the machine 11.

The liquid refrigerant accumulated in the lower part of the tank 36 flows out from the tank 36 to the tank outlet pipe 37 (main circuit 38). Hereinafter, the flow of the refrigerant in the main circuit 38 will be described.

The liquid refrigerant flowing out of the tank 36 flows into the second flow path 29B of the split heat exchanger 29, and is cooled (supercooled) by the refrigerant flowing through the first flow path 29A in the second flow path 29B.

After that, the liquid refrigerant splits at the outlet of the second flow path 29B. Of the diverted refrigerant, one exits from the refrigerator unit 3 and flows into the electric expansion valve 39 from the refrigerant pipe 8, and the other flows into the liquid pipe 46. The liquid refrigerant that has flowed into the liquid pipe 46 is throttled by the electric expansion valve 47, then flows into the intermediate pressure return pipe 44, merges with the gas refrigerant that has passed through the electric expansion valve 43, and flows into the first flow path 29A. .. The liquid refrigerant evaporates in the first flow path 29A. The endothermic action at this time increases the degree of supercooling of the liquid refrigerant flowing through the second flow path 29B.

In this way, in the split heat exchanger 29, heat exchange between the liquid refrigerant flowing out of the tank 36 and the refrigerant obtained by mixing the liquid refrigerant squeezed by the electric expansion valve 47 and the gas refrigerant squeezed by the electric expansion valve 43. Is done.

The refrigerant that has flowed into the electric expansion valve 39 is throttled and expanded by the electric expansion valve 39 to further reduce the pressure, and then flows into the evaporator 41 to evaporate. The cooling effect is exhibited by the endothermic action of this. The control device 57 controls the valve opening degree of the electric expansion valve 39 based on the output of a temperature sensor (not shown) that detects the temperature on the inlet side and the outlet side of the evaporator 41, and controls the degree of superheat of the refrigerant in the evaporator 41. To the proper value.

The low-temperature gas refrigerant discharged from the evaporator 41 returns from the refrigerant pipe 9 to the refrigerator unit 3, passes through the refrigerant introduction pipe 22, and communicates with the first rotary compression element 14 of the compressor 11. Is sucked into. The above is the flow of the refrigerant in the main circuit 38.

(2-2) The flow of the refrigerant in the control auxiliary circuit 48 of the electric expansion valve 43 will be described. The temperature of the gas refrigerant accumulated in the upper part of the tank 36 is substantially the saturation temperature at the refrigerant pressure in the tank 36. This gas refrigerant flows out from the tank 36 to the gas pipe 42. As described above, the electric expansion valve 43 is connected to the gas pipe 42. After being throttled by the electric expansion valve 43, the gas refrigerant merges with the liquid refrigerant that has passed through the electric expansion valve 47 and flows into the first flow path 29A of the split heat exchanger 29. Then, the gas refrigerant cools the refrigerant flowing through the second flow path 29B in the first flow path 29A, and then flows into the intermediate pressure suction pipe 26 via the intermediate pressure return pipe 44. Then, as described above, the gas refrigerant flowing from the intermediate pressure return pipe 44 into the intermediate pressure suction pipe 26 is mixed with the refrigerant discharged from the intercooler 24 and sucked into the high-stage suction port 19 of the compressor 11.

The electric expansion valve 43 plays a role of adjusting the pressure in the tank 36 (the pressure of the refrigerant flowing into the electric expansion valve 39) to a predetermined target value SP in addition to the function of squeezing the refrigerant flowing out from the upper part of the tank 36. .. Then, the control device 57 controls the valve opening degree of the electric expansion valve 43 based on the output of the unit outlet sensor 53. This is because if the valve opening degree of the electric expansion valve 43 increases, the amount of gas refrigerant flowing out from the tank 36 increases, and the pressure inside the tank 36 decreases.

In the present embodiment, the target value SP is set to a value lower than the high pressure side pressure HP and higher than the intermediate pressure MP. Then, the control device 57 adjusts the valve opening degree of the electric expansion valve 39 from the difference between the pressure OP (pressure of the refrigerant flowing into the electric expansion valve 39) in the tank 36 detected by the unit outlet sensor 53 and the target value SP. (Number of steps) is calculated and added to the valve opening at the time of starting, which will be described later, to control the pressure OP in the tank 36 to the target value SP. That is, when the pressure OP in the tank 36 rises above the target value SP, the valve opening degree of the electric expansion valve 43 is increased to allow the gas refrigerant to flow out from the tank 36 to the gas pipe 42, and conversely, the target value SP. When it descends further, the valve opening is reduced and controlled in the closing direction.

(2-2-1) Setting the opening degree of the electric expansion valve 43 at the start of operation The control device 57 sets the outside air temperature or the detection pressure (high pressure side pressure HP) of the high pressure sensor 49 which is an index indicating the outside air temperature. Based on this, the valve opening degree (valve opening degree at the time of starting) of the electric expansion valve 43 at the time of starting the refrigerating apparatus R is set. In the case of the present embodiment, the control device 57 stores in advance a data table showing the relationship between the outside air temperature at the time of starting or the relationship between the high pressure side pressure HP (outside air temperature) and the valve opening degree at the time of starting the electric expansion valve 43. There is.

Then, the control device 57 increases from the outside air temperature at the time of starting or the detected pressure (high pressure side pressure HP) as the high pressure side pressure HP (outside air temperature) increases based on the above data table, and conversely, the high pressure side pressure. The valve opening at the time of starting the electric expansion valve 43 is set so that the lower the HP, the lower the HP. As a result, it is possible to suppress an increase in the pressure inside the tank 36 at the time of starting in an environment where the outside air temperature is high, and to prevent an increase in the pressure of the refrigerant flowing into the electric expansion valve 39.

In the present embodiment, the target value SP of the pressure OP in the tank 36 is fixed and controlled, but as in the case of the electric expansion valve 33, the outside air temperature or the high pressure sensor 49 which is an index indicating the outside air temperature The target value SP may be set based on the detected pressure (high pressure side pressure HP). In this case, the control device 57 sets the target value SP higher as the outside air temperature or the high pressure side pressure HP increases. Therefore, in an environment where the outside air temperature is high, the target value SP during operation of the pressure of the refrigerant flowing into the electric expansion valve 39 becomes high.

That is, when the high pressure side pressure HP becomes high due to the influence of the high outside air temperature, the intermediate pressure MP can be increased by setting the target value SP of the pressure OP in the tank 36 high, so that the valve of the electric expansion valve 43 Even if the opening degree is increased, it becomes possible to prevent the inconvenience that the refrigerant becomes difficult to flow into the auxiliary circuit 48. On the contrary, when the high pressure side pressure HP becomes low due to the influence of the low outside air temperature, the amount of the refrigerant flowing into the auxiliary circuit 48 is reduced by reducing the valve opening degree of the electric expansion valve 43, and the unit outlet 6 is used. It becomes possible to prevent the inconvenience that the pressure of the refrigerant drops. As a result, regardless of the change in the outside air temperature due to the change of seasons, the valve opening degree of the electric expansion valve 43 can be appropriately controlled to suppress the change in the refrigerant pressure at the unit outlet 6, and the amount of the refrigerant can be accurately adjusted. Can be adjusted to.

(2-2-2) Control of tank pressure OP at specified value MOP When the control is performed as described above, the tank 36 pressure OP (electric expansion valve 39) is affected by the installation environment and load. When the pressure of the inflowing refrigerant) rises to a predetermined specified value MOP, the control device 57 increases the valve opening degree of the electric expansion valve 43 by a predetermined step. As the valve opening increases, the pressure OP inside the tank 36 tends to decrease, so that the pressure OP can always be maintained below the specified value MOP, suppressing the influence of pressure fluctuations on the high pressure side and electrically expanding. It is possible to surely achieve the effect of suppressing the pressure of the refrigerant conveyed to the valve 39.

(2-3) The flow of the refrigerant in the control auxiliary circuit 48 of the electric expansion valve 47 will be described. The liquid refrigerant accumulated in the lower part of the tank 36 flows from the tank 36 into the tank outlet pipe 37, passes through the second flow path 29B, and then splits. One of the separated liquid refrigerants flows into the liquid pipe 46 and is throttled by the electric expansion valve 47. After that, the liquid refrigerant flows into the intermediate pressure return pipe 44, merges with the gas refrigerant from the electric expansion valve 43, flows into the first flow path 29A of the split heat exchanger 29, and evaporates there. The endothermic action at this time increases the supercooling of the liquid refrigerant flowing through the second flow path 29B.

After that, the gas refrigerant discharged from the first flow path 29A flows into the intermediate pressure suction pipe 26, mixes with the refrigerant discharged from the intercooler 24, and is sucked into the high-stage suction port 19 of the compressor 11.

The control device 57 adjusts the amount of the liquid refrigerant flowing through the first flow path 29A of the split heat exchanger 29 by controlling the valve opening degree of the electric expansion valve 47. For example, the control device 57 controls the valve opening degree of the electric expansion valve 47 based on the temperature (discharge temperature) of the refrigerant discharged from the compressor 11 detected by the discharge temperature sensor 50 to the gas cooler 28. As a result, the amount of the liquid refrigerant flowing through the first flow path 29A of the split heat exchanger 29 is adjusted, and the discharge temperature of the refrigerant discharged from the compressor 11 to the gas cooler 28 is controlled to a predetermined target value TDT. That is, when the actual discharge temperature is higher than the target value TDT, the valve opening degree of the electric expansion valve 47 is increased, and when it is lower, the valve opening degree is decreased. As a result, the discharge temperature of the refrigerant of the compressor 11 is maintained at the target value TDT, and the compressor 11 is protected.

(3) Calculation of Exclusion Volume Ratio Conventionally, the refrigerating apparatus R has been used under the condition that the refrigerant temperature in the evaporator 41 is −5 ° C. or lower. It was examined by simulating whether such a refrigerating apparatus R could be used at an evaporation temperature higher than −5 ° C. That is, when the refrigerant evaporation temperature in the evaporator 41 is −10 ° C., −5 ° C., 0 ° C., 5 ° C., and 10 ° C., the condition for the refrigerating device R to function as the refrigerating device is set to the exclusion volume ratio ( The ratio of the excluded volume of the second rotational compression element 16 to the excluded volume of the first rotational compression element 14) was determined by simulation as a change parameter.

(3-1) Prerequisites The preconditions for performing the simulation are as follows.

(3-1-1) Lower limit of differential pressure of each rotational compression element 14 and 16 The rotational compression element can be used as a rotational compression element unless there is a certain amount of differential pressure between the suction pressure and the discharge pressure due to its structure. Cannot function effectively. For example, in the case of a rotary compressor, a differential pressure is used to press the sliding vane against the piston, and in the case of a scroll compressor, a differential pressure is used to press the swing scroll against the fixed scroll. The lower limit of the differential pressure of the rotational compression element is generally 0.5 MPa. Therefore, the lower limit of the differential pressure of the rotational compression elements 14 and 16 is set to 0.5 MPa. Since the intermediate pressure is the discharge pressure of the first rotational compression element 14, the lower limit of the differential pressure of the first rotational compression element 14 is 0.5 MPa, which means that 0.5 MPa is added to the evaporation pressure. Means that is the lower limit of the intermediate pressure. For example, when the evaporation temperature is 0 ° C., the evaporation pressure of carbon dioxide is 3.49 MPa, so the lower limit of the intermediate pressure is 3.99 MPa.

(3-1-2) Set value of internal pressure of tank 36 In a split cycle refrigeration system, there is a cost reason to reduce the design pressure of the tank, the equipment on the downstream side thereof, and the piping connecting them, and in the first place. The internal pressure of the tank is usually about 6.0 MPa for the technical reason that the refrigerant cannot be separated into gas and liquid when the internal pressure of the tank becomes 7.4 MPa or more, which is the critical point of carbon dioxide. Therefore, the set value of the internal pressure of the tank 36 was set to 6.0 MPa.

(3-1-3) Amount of Refrigerant Temperature Decrease in Electric Expansion Valve 43 In the split heat exchanger 29, in order to supercool the refrigerant flowing through the second flow path 29B with the refrigerant flowing through the first flow path 29A, The temperature difference of the refrigerant flowing through each flow path needs to be 5 ° C. or more. Therefore, the amount of temperature decrease of the gas refrigerant by the electric expansion valve 43 was set to 5 ° C. or higher. Since the set value of the internal pressure of the tank 36 is 6.0 MPa, the outlet pressure of the electric expansion valve 43 is 5.3 MPa or less. In order for the gas refrigerant to flow through the auxiliary circuit 48, the intermediate pressure must be lower than the outlet pressure of the electric expansion valve 43. Therefore, if the outlet pressure of the electric expansion valve 43 is 5.3 MPa or less, the intermediate pressure is 5.3 MPa. Must be less than.

(3-1-4) Flow rate ratio of auxiliary circuit 48 In the split cycle refrigeration system, the flow rate ratio of the refrigerant flowing through the auxiliary circuit is generally about 35%. Therefore, the flow rate ratio of the refrigerant flowing through the auxiliary circuit 48 was set to 35%.

(3-1-5) Volumetric efficiency and compression efficiency of the rotational compression elements 14 and 16 The volumetric efficiency and compression efficiency of the first rotational compression element 14 and the second rotational compression element 16 constituting the compressor 11 are different. The values were generally 95% and 70%.

(3-2) Calculation result The result of the simulation is shown in Table 1 and FIG. 2 which is a graph of this. As shown in Table 1 and FIG. 2, if the exclusion volume ratio is 84.6% or more and 135.7% or less, even when the evaporation temperature is 0 ° C., which is higher than the conventional use range, It has been found that the freezing device R can function as a freezing device. Fig. 3 (a) shows the hp diagram obtained by simulation when the evaporation temperature is 0 ° C. and the exclusion volume ratio is 84.6%, and p when the evaporation temperature is 0 ° C. and the exclusion volume ratio is 135.7%. The −h diagram is shown in FIG. 3 (b).

Further, it was found that when the evaporation temperature is set to a higher temperature of 5 ° C. and the exclusion volume ratio is 101.8% or more and 134.2% or less, the refrigerating apparatus R can function as a refrigerating apparatus. did. Further, it was found that when the evaporation temperature is further increased to 10 ° C. and the exclusion volume ratio is 121.7% or more and 132.1% or less, the refrigerating apparatus R can function as a refrigerating apparatus. did.

Further, from these simulation results, when the evaporation temperature is 2.5 ° C., the exclusion volume ratio is the median value between the case of 0 ° C. and the case of 5 ° C., that is, 93% (= (84.6 + 101.8) /. If it is 2) or more and 135% (= (135.7 + 134.2) / 2) or less, it can be reasonably estimated that the refrigerating apparatus R can function as a refrigerating apparatus. Similarly, when the evaporation temperature is 7.5 ° C, the exclusion volume ratio is the median value between the case of 5 ° C and the case of 10 ° C, that is, 112% (= (101.8 + 121.7) / 2) or more and 132%. If it is (= (134.2 + 132.1) / 2) or less, it can be reasonably estimated that the refrigerating apparatus R can function as a refrigerating apparatus.

It was found that when the evaporation temperature is -10 ° C, which is the conventional range of use, the refrigerating device R can function as a refrigerating device if the exclusion volume ratio is 59.5% or more and 131.8% or less. did. Further, it was found that when the evaporation temperature is −5 ° C., the refrigerating apparatus R can function as a refrigerating apparatus if the exclusion volume ratio is 70.8% or more and 134.1% or less. These simulation results are in good agreement with the fact that the refrigerating apparatus R has been conventionally used under the condition that the evaporation temperature is −5 ° C. or lower, and the exclusion volume ratio is set to about 70%.

Although the examples of the present invention have been described above, the present invention is not limited to the above examples, and various modifications can be made without departing from the spirit of the present invention.

The present invention is suitable for use in a refrigerating apparatus in which a refrigerant circuit is composed of a compression means, a gas cooler, a main drawing means, and an evaporator, and the high pressure side has a supercritical pressure.

R Refrigerant circuit 1 Refrigerant circuit 3 Refrigerant unit 4 Showcase 6 Unit outlet 7 Unit inlet 8, 9 Refrigerant piping 11 Compressor 12 Sealed container 13 Electric element 14 First rotary compression element 16 Second rotary compression element 17 Low stage Side suction port 18 Low-stage side discharge port 19 High-stage side suction port 21 High-stage side discharge port 22 Refrigerant introduction pipe 23 Intermediate pressure discharge pipe 24 Intercooler 26 Intermediate pressure suction pipe 27 High-pressure discharge pipe 28 Gas cooler 29 Split heat exchanger 29A 1st flow path 29B 2nd flow path 31 Gas cooler blower 32 Gas cooler outlet piping 33 Electric expansion valve (pressure adjusting throttle means)
34 Tank inlet piping 36 Tank 37 Tank outlet piping 38 Main circuit 39 Electric expansion valve (main throttle means)
41 Evaporator 42 Gas piping 43 Electric expansion valve (first auxiliary circuit throttle means)
44 Intermediate pressure return piping 46 Liquid piping 47 Electric expansion valve (squeezing means for the second auxiliary circuit)
48 Auxiliary circuit 49 High-voltage sensor 50 Discharge temperature sensor 51 Low-voltage sensor 52 Intermediate pressure sensor 53 Unit outlet sensor 57 Control device (control means)

Claims (2)

In a refrigerating apparatus in which a refrigerant circuit is composed of a compression means, a gas cooler, a main drawing means, and an evaporator, and the high pressure side has a supercritical pressure.
A pressure adjusting throttle means on the downstream side of the gas cooler and connected to the refrigerant circuit on the upstream side of the main throttle means.
A tank connected to the refrigerant circuit on the downstream side of the pressure adjusting throttle means and on the upstream side of the main throttle means.
A split heat exchanger provided in the refrigerant circuit on the downstream side of the tank and on the upstream side of the main throttle means.
An auxiliary circuit in which the gas refrigerant in the tank is allowed to flow into the first flow path of the split heat exchanger via the first auxiliary circuit throttle means and then sucked into the intermediate pressure portion of the compression means.
A main circuit in which a liquid refrigerant flows out from the lower part of the tank, flows into a second flow path of the split heat exchanger, exchanges heat with a gas refrigerant flowing through the first flow path, and then flows into the main throttle means. When,
The pressure adjusting throttle means includes a control means for adjusting the high pressure side pressure of the refrigerant circuit on the upstream side of the pressure adjusting throttle means.
The auxiliary circuit is on the downstream side of the second flow path of the split heat exchanger, is branched from the main circuit, and is on the downstream side of the throttle means for the first auxiliary circuit, and the split heat exchange. It is provided with a liquid pipe that joins the upstream side of the first flow path of the vessel and a second auxiliary circuit throttle means provided in the middle of the liquid pipe.
The compression means has a low-stage rotational compression element that compresses the refrigerant from a low pressure to an intermediate pressure, and a high-stage rotational compression element that compresses the refrigerant from an intermediate pressure to a high pressure.
A refrigerating apparatus in which the exclusion volume of the high-stage rotational compression element is 85% or more of the exclusion volume of the low-stage rotational compression element. The refrigerating apparatus according to claim 1, wherein the exclusion volume of the high-stage rotational compression element is 85% or more and 136% or less of the exclusion volume of the low-stage rotational compression element.

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