WO2014068967A1

WO2014068967A1 - Refrigeration device

Info

Publication number: WO2014068967A1
Application number: PCT/JP2013/006412
Authority: WO
Inventors: 裕輔倉田; 豊明木屋; 裕志八藤後; 三原　一彦; 光洋加藤
Original assignee: パナソニック株式会社
Priority date: 2012-10-31
Filing date: 2013-10-30
Publication date: 2014-05-08
Also published as: JPWO2014068967A1; JP6292480B2; CN104755858A

Abstract

Provided is a refrigeration device which can, independently of outside air temperature, ensure stable refrigeration performance when the high-pressure side has a supercritical pressure, and which can improve cost and the easiness of construction. A refrigeration device is provided with: a pressure regulating throttle means which is connected to a refrigerant circuit which is located downstream of a gas cooler and upstream of a main throttle means; a decompression tank which is connected to a refrigerant circuit which is located downstream of the pressure regulating throttle means and upstream of the main throttle means; a split heat exchanger which is provided in a refrigerant circuit which is located downstream of the decompression tank and upstream of the main throttle means; an auxiliary circuit which allows a refrigerant within the decompression tank to be sucked into the intermediate pressure section of a compressor after causing the refrigerant to flow to a first flow passage in the split heat exchanger through an auxiliary throttle means; and a main circuit which allows a refrigerant to flow out from the lower part of the decompression tank, causes the refrigerant to flow to a second flow passage in the split heat exchanger, subjects the refrigerant to heat exchange with a refrigerant flowing through the first flow passage, and then causes the refrigerant, having been subjected to heat exchange with the refrigerant flowing through the first flow passage, to flow into the main throttle means.

Description

Refrigeration equipment

The present invention relates to a refrigeration apparatus in which a refrigerant circuit is configured by a compression unit, a gas cooler, a main throttle unit, and an evaporator, and a high-pressure side becomes a supercritical pressure.

Conventionally, this type of refrigeration apparatus has a refrigeration cycle composed of a compression means, a gas cooler, a throttle means, etc., and the refrigerant compressed by the compression means dissipates heat in the gas cooler and is depressurized by the throttle means, and then in an evaporator. The refrigerant was evaporated, and ambient air was cooled by evaporation of the refrigerant at this time. In recent years, chlorofluorocarbon refrigerants cannot be used in this type of refrigeration system due to natural environmental problems. For this reason, the thing using the carbon dioxide which is a natural refrigerant | coolant is developed as a substitute of a fluorocarbon refrigerant | coolant. The carbon dioxide refrigerant is a refrigerant having a high and low pressure difference, and has a low critical pressure. It is known that the high pressure side of the refrigerant cycle is brought into a supercritical state by compression (see, for example, Patent Document 1).

Moreover, in the heat pump device constituting the water heater, a carbon dioxide refrigerant capable of obtaining an excellent heating action in the gas cooler has been used. In that case, the refrigerant discharged from the gas cooler is expanded in two stages, There has also been developed an apparatus in which a gas-liquid separator is interposed between expansion devices to enable gas injection into a compressor (see, for example, Patent Document 2).

On the other hand, for example, in an refrigeration system that uses an endothermic action in an evaporator installed in a showcase or the like to cool the interior, the refrigerant temperature at the outlet of the gas cooler is high due to factors such as high outside air temperature (heat source temperature on the gas cooler). Under higher conditions, the specific enthalpy at the inlet of the evaporator increases, which causes a problem that the refrigerating capacity is remarkably reduced. In such a case, if the discharge pressure (high-pressure side pressure) of the compression means is increased in order to ensure the refrigeration capacity, the compression power increases and the coefficient of performance decreases.

Therefore, the refrigerant cooled by the gas cooler is divided into two refrigerant streams, one of the divided refrigerant streams is squeezed by the auxiliary throttle means, and then flows into one passage of the split heat exchanger, and the other refrigerant stream is split. A so-called split-cycle refrigeration apparatus has been proposed in which heat is exchanged by flowing through the other flow path of the heat exchanger and then flows into the evaporator via the main throttle means. According to such a refrigeration apparatus, the second refrigerant flow can be cooled by the first refrigerant flow expanded under reduced pressure, and the refrigeration capacity can be improved by reducing the specific enthalpy at the inlet of the evaporator. (For example, refer to Patent Document 3).

Japanese Patent Publication No. 7-18602 JP 2007-178042 A JP 2011-133207 A

However, particularly in the case of refrigeration conditions such as a refrigeration showcase where the evaporation temperature of the refrigerant in the evaporator becomes high, the pressure of the refrigerant flowing into the main throttle means fluctuates greatly when the outside air temperature fluctuates, and the control of the main throttle means The refrigeration capacity becomes unstable. Also, in a store such as a supermarket, when supplying a refrigerant from a refrigerator equipped with a compression means or a gas cooler to a showcase in a store provided with a main throttle means or an evaporator, the main throttle means on the showcase side Since the high-pressure side pressure is high, it is necessary to use a long refrigerant pipe (liquid pipe) with a high pressure resistance, which is disadvantageous in terms of construction cost.

Further, when the operation is started in an environment where the outside air temperature is high, the first refrigerant flow is not liquefied in the refrigerant circuit under the refrigeration condition where the evaporation temperature is high. Even if the split cycle as described above is configured, the first refrigerant The cooling effect of the second refrigerant flow by the flow can hardly be expected. Therefore, the liquid refrigerant cannot be sent to the main throttle means. Further, when a refrigerant such as carbon dioxide is used, there is a problem that it is difficult to determine an appropriate refrigerant charging amount because the high-pressure side pressure varies greatly depending on the season.

The present invention was made to solve the conventional technical problems, and when the high pressure side becomes a supercritical pressure, it can ensure a stable refrigeration capacity without being influenced by the outside air temperature, It aims at providing the freezing apparatus which can also improve cost.

In the refrigeration apparatus of the present invention, a refrigerant circuit is constituted by a compression means, a gas cooler, a main throttle means, and an evaporator, and the high pressure side becomes a supercritical pressure. A pressure adjusting throttle connected to the upstream refrigerant circuit, a pressure reducing tank connected to the refrigerant circuit upstream of the main throttle and downstream of the pressure adjusting throttle, and downstream of the pressure reducing tank Then, after the split heat exchanger provided in the refrigerant circuit upstream of the main throttle means and the refrigerant in the decompression tank flow through the first flow path of the split heat exchanger via the auxiliary throttle means, After the auxiliary circuit to be sucked into the intermediate pressure part of the compression means, the refrigerant flows out from the lower part of the decompression tank, flows into the second flow path of the split heat exchanger, and after heat exchange with the refrigerant flowing through the first flow path, Main flow to flow into the main throttle means Characterized by comprising and.

According to a second aspect of the present invention, there is provided a refrigeration apparatus comprising control means for controlling the pressure adjusting throttle means in the above invention, and the control means flows into the main throttle means by controlling the opening degree of the pressure adjusting throttle means. The pressure of the refrigerant to be adjusted is adjusted to a predetermined specified value.

According to a third aspect of the present invention, there is provided the refrigeration apparatus according to the first aspect, wherein the control means opens the opening of the pressure adjusting throttle means when the high pressure side pressure of the refrigerant circuit upstream of the pressure adjusting throttle means rises to a predetermined upper limit value. Is increased.

In the refrigeration apparatus according to a fourth aspect of the present invention, in each of the above inventions, the auxiliary circuit upstream of the auxiliary throttle means causes the refrigerant to flow out from the upper part of the decompression tank and flows into the auxiliary throttle means, and the refrigerant from the lower part of the decompression tank. The liquid pipe is made to flow out and flow into the auxiliary throttle means through the valve device.

According to a fifth aspect of the present invention, in the refrigeration apparatus of the present invention, the control means controls the valve device based on an index representing the outside air temperature, and when the outside air temperature rises, the valve device is closed and the outside air temperature falls. Is characterized by opening.

The refrigeration apparatus of the invention of claim 6 is characterized in that, in the above invention, the control means closes the valve device at a lower outside air temperature as the evaporation temperature is higher, based on an index representing the evaporation temperature of the refrigerant in the evaporator. .

The refrigeration apparatus of the invention of claim 7 is characterized in that in each of the above inventions, an internal heat exchanger for exchanging heat between the refrigerant flowing into the main throttle means and the refrigerant discharged from the evaporator is provided.

In the refrigeration apparatus according to an eighth aspect of the present invention, in the above invention, the internal heat exchanger includes a first flow path of the internal heat exchanger through which the refrigerant flowing into the main throttle means flows, and an internal heat through which the refrigerant discharged from the evaporator flows. Two flow paths for the exchanger, heat exchange is performed between the refrigerant flowing through the first flow path of the internal heat exchanger and the refrigerant flowing through the second flow path of the internal heat exchanger, and the internal heat exchanger A bypass circuit connected in parallel to the first flow path or the second flow path of the internal heat exchanger, and a bypass valve device provided in the bypass circuit are provided.

According to a ninth aspect of the present invention, there is provided a refrigeration apparatus comprising a control means for controlling the bypass valve device according to the above-mentioned invention, wherein the control means is a refrigerant flowing into the first flow path of the internal heat exchanger and the first heat exchanger. When the temperature of the refrigerant exiting the second flow path of the internal heat exchanger is higher than the temperature of the refrigerant flowing into the first flow path of the internal heat exchanger based on the temperature of the refrigerant exiting the second flow path, The bypass valve device is opened.

The refrigeration apparatus of the invention of claim 10 is characterized in that carbon dioxide is used as a refrigerant in each of the above inventions.

According to the present invention, in the refrigerating apparatus in which the refrigerant circuit is configured by the compression unit, the gas cooler, the main throttle unit, and the evaporator, and the high pressure side is the supercritical pressure, the downstream side of the gas cooler and the main throttle unit A pressure adjusting throttle connected to the upstream refrigerant circuit, a pressure reducing tank connected to the refrigerant circuit upstream of the main throttle and downstream of the pressure adjusting throttle, and downstream of the pressure reducing tank Then, after the split heat exchanger provided in the refrigerant circuit upstream of the main throttle means and the refrigerant in the decompression tank flow through the first flow path of the split heat exchanger via the auxiliary throttle means, After the auxiliary circuit to be sucked into the intermediate pressure part of the compression means, the refrigerant flows out from the lower part of the decompression tank, flows into the second flow path of the split heat exchanger, and after heat exchange with the refrigerant flowing through the first flow path, Main flow to flow into the main throttle means Therefore, the refrigerant flowing in the first flow path of the split heat exchanger constituting the auxiliary circuit is expanded by the auxiliary throttle means, and flows into the second flow path of the split heat exchanger constituting the main circuit. The refrigerant can be cooled, and the specific enthalpy at the evaporator inlet can be reduced to effectively improve the refrigerating capacity.

Further, since the refrigerant flowing in the first flow path of the split heat exchanger is returned to the intermediate pressure portion of the compression means, the amount of refrigerant sucked into the low pressure portion of the compression means is reduced, and the refrigerant is compressed from low pressure to intermediate pressure. The amount of compression work in the compression means is reduced. As a result, the compression power in the compression means is reduced and the coefficient of performance is improved.

In particular, since the refrigerant discharged from the gas cooler is expanded by the pressure adjusting throttle means and flows into the decompression tank, the pressure of the refrigerant flowing into the main throttle means is lowered by the pressure adjusting throttle means. It is possible to use a pipe having a low pressure resistance as a pipe leading to the main throttle means. In addition, since the decompression tank has an effect of absorbing the fluctuation of the circulating refrigerant amount in the refrigerant circuit, the refrigerant filling amount error is also absorbed. These also make it possible to improve workability and construction cost.

Further, a part of the refrigerant liquefied by expansion by the pressure adjusting throttle means evaporates in the decompression tank to become a gas refrigerant having a lowered temperature, and the rest becomes liquid refrigerant and is temporarily stored in the lower part of the decompression tank. It becomes a shape. Then, since the liquid refrigerant in the lower part of the decompression tank flows into the main throttle means through the second flow path of the split heat exchanger constituting the main circuit, the refrigerant flows into the main throttle means in the full state. In particular, it is possible to improve the refrigerating capacity under refrigeration conditions where the evaporation temperature in the evaporator is high.

In particular, the control means controls the opening degree of the pressure adjusting throttle means and adjusts the pressure of the refrigerant flowing into the main throttle means to a predetermined specified value by the control means as in the second aspect of the invention. It is possible to prevent the refrigerant pressure flowing into the main throttle means from greatly fluctuating due to a change in the outside air temperature, and always maintain the same predetermined value. Thereby, especially in the refrigeration conditions where the evaporation temperature in the evaporator is high, the control of the main throttling means can be stabilized and the refrigerating capacity can be secured stably.

In this case, by providing the pressure adjusting throttle means, there is a risk that the high pressure side pressure of the upstream refrigerant circuit becomes high. However, as in the invention of claim 3, the control means is upstream of the pressure adjusting throttle means. When the high-pressure side pressure of the refrigerant circuit rises to a predetermined upper limit value, an abnormal increase in the high-pressure side pressure can be eliminated by increasing the opening of the pressure adjusting throttle means. Thereby, it is possible to avoid the stop (protection operation) of the compression means due to abnormally high pressure.

According to the invention of claim 4, in addition to each of the above-mentioned inventions, the auxiliary circuit upstream of the auxiliary throttle means includes a gas pipe for allowing the refrigerant to flow out from the upper part of the vacuum tank and into the auxiliary throttle means, and the lower part of the vacuum tank Since the refrigerant pipe is made to flow out into the auxiliary throttle means via the valve device, the refrigerant is liquefied by being expanded by the pressure adjusting throttle means and partially enters the decompression tank. The gas refrigerant and the remaining liquid refrigerant having evaporated and the temperature decreased can be selectively passed through the first flow path of the split heat exchanger by the gas pipe and the liquid pipe.

That is, for example, in a high outside air temperature environment where the outside air temperature is high, the pressure on the high pressure side of the refrigerant circuit also increases, so that the control means uses the pressure adjusting throttle to reduce the pressure of the refrigerant flowing into the main throttle means to, for example, the predetermined value described above. Control to reduce the opening of the means. In this situation, the liquid refrigerant stored in the decompression tank is reduced, and when it flows into the first flow path of the split heat exchanger, the liquid refrigerant going to the main throttle means is secured through the second flow path. It becomes difficult.

In addition, when the outside air temperature decreases and the inside / outside air temperature environment is reduced, and the high pressure side pressure is lowered, the control means opens the opening of the pressure adjusting throttle means and controls it slightly, but it is stored in the decompression tank. The amount of refrigerant to be increased also increases. Then, when the outside air temperature is further lowered to become a low outside air temperature environment and the high pressure side pressure is further lowered, a large amount of liquid refrigerant is stored in the decompression tank.

Therefore, as in the fifth aspect of the invention, the valve device is controlled by the control means based on the index representing the outside air temperature, and when the outside air temperature rises, the valve device is closed, and when the outside air temperature falls, the valve device is opened. For example, under the above-described high outside air temperature environment, the valve device of the liquid pipe is closed, and the gas refrigerant in the decompression tank can be flowed from the gas pipe to the first flow path of the split heat exchanger. As a result, the refrigerant flowing through the second flow path of the split heat exchanger is cooled by the gas refrigerant whose temperature has decreased in the decompression tank, and the liquid refrigerant in the decompression tank is cooled in the second flow path of the split heat exchanger. After cooling, it can be supplied to the main throttle means. In this state, the refrigerant circuit becomes a so-called two-stage expansion cycle.

On the other hand, in the above-mentioned medium / outside air temperature environment, the valve device of the liquid piping is opened, and the gas refrigerant and the liquid refrigerant in the decompression tank are allowed to flow from both the gas piping and the liquid piping to the first flow path of the split heat exchanger. Will be able to. As a result, the refrigerant flowing through the second flow path of the split heat exchanger is cooled by the gas refrigerant whose temperature has decreased in the decompression tank and the liquid refrigerant expanded by the auxiliary throttle means, and the liquid refrigerant in the decompression tank is split. After cooling more strongly in the second flow path of the heat exchanger, it can be supplied to the main throttle means. In this state, the refrigerant circuit is a combined cycle of the two-stage expansion cycle and a so-called split cycle.

Further, by opening the valve device of the liquid piping even under the low outside air temperature environment described above, the liquid refrigerant stored in the decompression tank can flow from the liquid piping to the first flow path of the split heat exchanger. become. Accordingly, the refrigerant flowing through the second flow path of the split heat exchanger is further strongly cooled by the liquid refrigerant expanded by the auxiliary throttle means, and the liquid refrigerant in the decompression tank is cooled to the second flow path of the split heat exchanger. After it has been cooled strongly, it can be supplied to the main throttle means. In this state, the refrigerant circuit is in the split cycle.

Thus, since the two-stage expansion cycle and the split cycle can be switched according to the outside temperature environment, the refrigeration apparatus can be operated more stably and with high efficiency.

In this case, as in the sixth aspect of the invention, the control means closes the valve device at a lower outside air temperature as the evaporation temperature is higher, based on an index representing the evaporation temperature of the refrigerant in the evaporator, so that the refrigeration condition When the outside air temperature becomes high during operation with a high evaporation temperature such as the above, it is possible to secure the liquid refrigerant toward the main throttle means by switching to the above-described two-stage expansion cycle at a faster stage. It becomes possible to maintain the refrigerating capacity under the conditions.

On the other hand, under the refrigeration conditions where the evaporation temperature is low, in the above-described two-stage expansion cycle, the refrigerant flowing into the main throttle means cannot be subcooled in the split heat exchanger. Thus, the refrigerant flowing into the main throttle means can be effectively supercooled. As a result, even when operating at different evaporation temperatures, the operating efficiency of the refrigeration apparatus can be optimized.

Further, as in the invention of claim 7, by providing an internal heat exchanger for exchanging heat between the refrigerant flowing into the main throttle means and the refrigerant discharged from the evaporator, the internal heat exchanger leaves the evaporator. Since the refrigerant flowing into the main throttle means can be cooled by the low-temperature refrigerant, the specific enthalpy at the evaporator inlet can be reduced to effectively improve the refrigerating capacity.

In particular, in a high outside air temperature environment where the outside air temperature is high, there is no difference in pressure between the pressure in the decompression tank adjusted to the specified value by the pressure adjusting throttle means and the intermediate pressure portion of the compression means. In such a case, since the auxiliary throttle means is substantially fully open, depending on the situation, the refrigerant in the main circuit flowing in the second flow path may be excessively passed by the refrigerant in the auxiliary circuit flowing in the first flow path in the split heat exchanger. Although it becomes almost impossible to cool the liquid-rich refrigerant to the main throttle means, the refrigerant flowing into the main throttle means by the low-temperature refrigerant discharged from the evaporator in the internal heat exchanger even under such circumstances Since the refrigerant can be supplied to the main throttle means in a full liquid state, it is possible to improve the refrigerating capacity.

Here, when pulling down, the temperature of the refrigerant coming out of the evaporator may be higher than the refrigerant flowing into the main throttle means, but it flows through the first flow path of the internal heat exchanger as in the invention of claim 8. The first flow path of the internal heat exchanger or the internal heat exchanger for exchanging heat between the refrigerant flowing into the main throttle means and the refrigerant flowing out of the evaporator and flowing through the second flow path of the internal heat exchanger A bypass circuit is connected in parallel to the second flow path, and a bypass valve device is provided in the bypass circuit, and flows into the first flow path of the internal heat exchanger by the control means as in the invention of claim 9. Based on the refrigerant and the temperature of the refrigerant that has exited the second flow path of the internal heat exchanger, the temperature of the refrigerant that has exited the second flow path of the internal heat exchanger flows into the first flow path of the internal heat exchanger. If the temperature of the refrigerant is higher than the temperature of the refrigerant, the main throttle means is opened with an internal heat exchanger by opening the bypass valve device. To flow refrigerant that is not the refrigerant exchanges heat from the calling device.

This makes it possible to eliminate the inconvenience that the refrigerant flowing out of the evaporator and the refrigerant flowing into the main throttle means is heated in reverse.

Particularly, when carbon dioxide is used as a refrigerant as in the invention of claim 10, the above inventions can effectively improve the refrigerating capacity and improve the performance.

It is a refrigerant circuit figure of the refrigerating device of one example to which the present invention is applied. FIG. 2 is a PH diagram of a two-stage expansion cycle executed by the control device of the refrigeration apparatus of FIG. FIG. 2 is a PH diagram of a combined cycle of a two-stage expansion cycle and a split cycle executed by the control device of the refrigeration apparatus of FIG. FIG. 2 is a PH diagram of a split cycle executed by the control device of the refrigeration apparatus of FIG. It is a figure explaining the switching operation | movement of the cycle of FIG. 2 thru | or FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a refrigerant circuit diagram of a refrigeration apparatus R according to an embodiment to which the present invention is applied. The refrigeration apparatus R in this embodiment is a show of a refrigerator unit 3 installed in a machine room or the like of a store such as a supermarket, and one or a plurality of units (only one is shown in the drawing) installed in the store sales area. The refrigerator unit 3 and the showcase 4 are connected by a refrigerant pipe (liquid pipe) 8 and a refrigerant pipe 9 via a unit outlet 6 and a unit inlet 7 so that a predetermined refrigerant circuit 1 is provided. It is composed.

This refrigerant circuit 1 uses, as a refrigerant, carbon dioxide whose refrigerant pressure (high pressure) on the high pressure side is equal to or higher than its critical pressure (supercritical). This carbon dioxide refrigerant is a natural refrigerant that is friendly to the global environment and takes into consideration flammability and toxicity. As the lubricating oil, existing oils such as mineral oil (mineral oil), alkylbenzene oil, ether oil, ester oil, and PAG (polyalkyl glycol) are used.

The refrigerator unit 3 includes a compressor 11 as compression means. In this embodiment, the compressor 11 is an internal intermediate pressure type two-stage compression rotary compressor, and includes an airtight container 12, an electric element 13 as a drive element disposed and housed in the upper part of the internal space of the airtight container 12, and the A first (low stage side) rotary compression element (first compression element) 14 and a second (high stage side) rotary compression element (first stage) disposed below the electric element 13 and driven by the rotating shaft thereof. 2 compression elements) 16 and a rotary compression mechanism.

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 through the refrigerant pipe 9 and raises it to an intermediate pressure for discharge. The rotary compression element 16 further sucks in the intermediate pressure refrigerant compressed and discharged by the first rotary compression element 14, compresses 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, and the rotational frequency of the first rotary compression element 14 and the second rotary compression element 16 can be controlled by changing the operating frequency of the electric element 13.

On the side surface of the sealed 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 inside of the sealed container 12, and a second rotational compression A high-stage suction port 19 and a high-stage discharge port 21 communicating with the element 16 are formed. One end of the refrigerant introduction pipe 22 is connected to the lower stage side suction port 17 of the compressor 11, and the other end is connected to the refrigerant pipe 9 at the unit inlet 7. A second flow path 15B of the internal heat exchanger 15 is interposed in the refrigerant introduction pipe 22.

The low-pressure refrigerant gas (LP: about 2.6 MPa in the normal operation state) sucked into the low-pressure portion of the first rotary compression element 14 from the low-stage suction port 17 is intermediate pressure by the first rotary compression element 14. The pressure is increased to (MP: about 5.5 MPa in a normal operation state) and discharged into the sealed container 12. Thereby, the inside of the airtight container 12 becomes an intermediate pressure (MP).

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

The intermediate pressure (MP) refrigerant gas sucked into the second rotary compression element 16 from the high-stage side suction port 19 is compressed in the second stage by the second rotary compression element 16 to generate a high temperature and high pressure (HP). : Supercritical pressure of about 9 MPa in a normal operation state).

One end of a high-pressure discharge pipe 27 is connected to the high-stage 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 (heat radiator) 28. Connected to the entrance. An oil separator 20 is provided in the high-pressure discharge pipe 27. The oil separator 20 separates the oil in the refrigerant discharged from the compressor 11 and returns it to the sealed container 12 of the compressor 11 via the oil passage 25A of the oil cooler 25 and the electric valve 25B. Reference numeral 55 denotes a float switch for detecting the oil level in the compressor 11.

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

One end of a 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 an inlet of a pressure adjusting throttle means (electric expansion valve) 33. The pressure adjusting throttle means 33 squeezes and expands the refrigerant discharged from the gas cooler 28, and its outlet is connected to the upper portion of the decompression tank 36 via a tank inlet pipe 34.

The decompression tank 36 is a volume body having a space of a predetermined volume inside, and one end of a tank outlet pipe 37 is connected to the lower part 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 interposed in the tank outlet pipe 37, and in the tank outlet pipe 37 downstream of the split heat exchanger 29, the internal heat exchanger 15 is connected. A first flow path 15A is interposed. This tank outlet pipe 37 constitutes a main circuit 38 in the present invention. Further, a bypass circuit 45 is connected in parallel to the first flow path 15A of the internal heat exchanger 15, and an electromagnetic valve 50 as a bypass valve device is interposed in the bypass circuit 45.

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 a main throttle means (electric expansion valve) 39 and an evaporator 41 as throttle means, which are sequentially connected between the refrigerant pipe 8 and the refrigerant pipe 9 (main throttle means 39). Is the refrigerant pipe 8 side, and the evaporator 41 is the refrigerant pipe 9 side). The evaporator 41 is provided with a cool air circulation blower (not shown) that blows air to the evaporator 41. The refrigerant pipe 9 is connected to the low-stage suction port 17 that communicates with the first rotary compression element 14 of the compressor 11 via the refrigerant introduction pipe 22 as described above.

On the other hand, one end of a gas pipe 42 is connected to the upper portion of the decompression tank 36, and the other end of the gas pipe 42 is connected to an inlet of auxiliary throttle means (electric expansion valve) 43. One end of the intermediate pressure return pipe 44 is connected to the outlet of the auxiliary throttle means 43, and the other end is connected to the middle pressure suction pipe 26 as an example of an intermediate pressure region connected to the intermediate pressure portion of the compressor 11. Yes. A first flow path 29A of the split heat exchanger 29 is interposed in the intermediate pressure return pipe 44, and an oil cooler 25 is provided in the intermediate pressure return pipe 44 on the downstream side of the split heat exchanger 29. A second flow path 25C is interposed.

Further, one end of a liquid pipe 46 is connected to the lower part of the decompression tank 36, and the other end of the liquid pipe 46 is communicated with the gas pipe 42. In addition, an electromagnetic valve 47 as a valve device is interposed in the liquid pipe 46. The intermediate pressure return pipe 44, the auxiliary throttle means 43, and the gas pipe 42 and the liquid pipe 46 on the upstream side of the auxiliary throttle means 43 constitute an auxiliary circuit 48 in the present invention.

With such a configuration, the pressure adjusting throttle means 33 is located downstream of the gas cooler 28 and upstream of the main throttle means 39. The decompression tank 36 is located downstream of the pressure adjusting throttle means 33 and upstream of the main throttle means 39. Furthermore, the split heat exchanger 29 is positioned downstream of the decompression tank 36 and upstream of the main throttle means 39, and the refrigerant circuit 1 of the refrigeration apparatus R in this embodiment is configured as described above.

Various sensors are attached to various parts of the refrigerant circuit 1. That is, a high pressure sensor 49 is attached to the high pressure discharge pipe 27 to detect the high pressure side pressure HP of the refrigerant circuit 1 (pressure between the high stage discharge port 21 of the compressor 11 and the inlet of the pressure adjusting throttle means 33). To do. A low pressure sensor 51 is attached to the refrigerant introduction pipe 22 to detect the low pressure LP of the refrigerant circuit 1 (the pressure between the outlet of the main throttle means 39 and the low stage suction port 17). Further, an intermediate pressure sensor 52 is attached to the intermediate pressure suction pipe 26, and an intermediate pressure MP (the pressure between the inside of the sealed container 12 and the high-stage side suction port 19 between the inside of the hermetic container 12 and the auxiliary throttle means). 43 outlet, pressure in the intermediate pressure return pipe 44).

Also, a unit outlet sensor 53 is attached to the tank outlet pipe 37 on the downstream side of the split heat exchanger 29, and this unit outlet sensor 53 detects the pressure TP in the decompression tank 36. The pressure in the decompression tank 36 is the pressure of the refrigerant that leaves the refrigerator unit 3 and flows into the main throttle means 39 from the refrigerant pipe 8. A unit outlet temperature sensor 54 is attached to the tank outlet pipe 37 on the upstream side of the internal heat exchanger 15 to detect the temperature IT of the refrigerant flowing into the first flow path 15A of the internal heat exchanger 15. Further, a unit inlet temperature sensor 56 is attached to the refrigerant introduction pipe 22 on the downstream side of the internal heat exchanger 15, and detects the temperature OT of the refrigerant that has exited the second flow path 15B of the internal heat exchanger 15.

These

sensors

49, 51, 52, 53, 54, 56 are connected to the input of the control device 57 that constitutes the control means of the refrigerator unit 3 constituted by a microcomputer, and the float switch 55 is also input to the control device 57. Connected to. The output of the control device 57 includes the electric element 13 of the compressor 11, the electric valve 25B, the gas cooler blower 31, the pressure adjusting throttle means 33, the auxiliary throttle means 43, the electromagnetic valve 47, the electromagnetic valve 50, and the main throttle means 39. Are connected, and the control device 57 controls them based on the output of each sensor, setting data, and the like.

In the following description, it is assumed that the main throttle means 39 on the showcase 4 side and the above-described cool air circulation blower are also controlled by the control device 57, but these are actually via a store main control device (not shown). Control is performed by a control device (not shown) on the showcase 4 side that operates in cooperation with the control device 57. Therefore, the control means in the present invention has a concept including the control device 57, the control device on the showcase 4 side, the main control device described above, and the like.

With the above configuration, the operation of the refrigeration apparatus R will be described next with reference to FIGS. When the electric element 13 of the compressor 11 is driven by the control device 57, the first rotary compression element 14 and the second rotary compression element 16 rotate and the first rotary compression element 14 is rotated from the low-stage suction port 17. The refrigerant gas having a low pressure (LP: about 2.6 MPa in a normal operation state) is sucked into the low pressure portion. Then, the pressure is increased to an intermediate pressure (MP described above: about 5.5 MPa in the normal operation state) by the first rotary compression element 14 and discharged into the sealed container 12. Thereby, the inside of the airtight container 12 becomes an intermediate pressure (MP).

Then, the intermediate-pressure refrigerant gas in the sealed container 12 enters the intercooler 24 from the low-stage discharge port 18 through the intermediate-pressure discharge pipe 23, and is then air-cooled there, and then through the intermediate-pressure suction pipe 26 to the high-stage suction. Return to mouth 19. The intermediate pressure (MP) refrigerant gas that has returned to the high-stage suction port 19 is sucked into the second rotary compression element 16, and the second stage compression is performed by the second rotary compression element 16, resulting in a high temperature. The refrigerant gas becomes high-pressure (HP: supercritical pressure of about 9 MPa in the above-described normal operation state) and is discharged from the high-stage discharge port 21 to the high-pressure discharge pipe 27.

The refrigerant gas discharged to the high-pressure discharge pipe 27 flows into the oil separator 20, and the oil contained in the refrigerant is separated. The separated oil is cooled in an oil passage 25A of the oil cooler 25 by an intermediate pressure refrigerant in an intermediate pressure return pipe 44 flowing in the second flow path 25C, as will be described later. 12 is returned. The control device 57 controls the motor-operated valve 25B based on the oil level in the sealed container 12 detected by the float switch 55, and adjusts the return amount of oil to maintain the oil level in the sealed container 12.

(1) Control of pressure adjusting throttling means and auxiliary throttling means On the other hand, the refrigerant gas from which the oil has been separated by the oil separator 20 then flows into the gas cooler 28 and is cooled by air, and then the pressure is adjusted via the gas cooler outlet pipe 32. The diaphragm means 33 is reached. The pressure adjusting throttle means 33 is provided to adjust the pressure in the pressure reducing tank 36 (pressure of the refrigerant flowing into the main throttle means 39) to a predetermined specified value (constant value) SP. The opening degree of the valve is controlled by the control device 57 based on the output of. The specified value SP is set to, for example, 6 MPa, which is lower than the normal high pressure HP and higher than the intermediate pressure MP. When the pressure in the decompression tank 36 (pressure of the refrigerant flowing into the main throttle means 39) detected by the unit outlet sensor 53 rises above the specified value SP, the control device 57 opens the valve of the pressure adjusting throttle means 33. The throttle is reduced by decreasing the degree, and conversely, when it falls below the specified value SP, the valve opening is increased and the opening is controlled.

The supercritical refrigerant gas exiting from the gas cooler 28 is liquefied by being squeezed and expanded by the pressure adjusting throttle means 33, and flows into the decompression tank 36 from above through the tank inlet pipe 34. Part evaporates. The decompression tank 36 temporarily stores and separates the liquid / gas refrigerant exiting the pressure adjusting throttling means 33 and absorbs the pressure change in the high-pressure side pressure and the refrigerant circulation amount. The liquid refrigerant accumulated in the lower part of the decompression tank 36 flows out of the tank outlet pipe 37 (main circuit 38), and the first flow path 29A as will be described later in the second flow path 29B of the split heat exchanger 29. After being cooled (supercooled) by the refrigerant flowing through the (auxiliary circuit 48), it is further cooled by the refrigerant flowing through the second flow path 15B in the first flow path 15A of the internal heat exchanger 15, and then the refrigerator It leaves the unit 3 and flows into the main throttle means 39 from the refrigerant pipe 8. The operation of the electromagnetic valve 50 will be described later.

The refrigerant that has flowed into the main throttling means 39 is squeezed there and expanded to further increase the liquid content and flow into the evaporator 41 and evaporate. The cooling effect is exhibited by the endothermic action. The control device 57 controls the valve opening degree of the main throttle means 39 based on the output of a temperature sensor (not shown) that detects the temperatures of the inlet side and the outlet side of the evaporator 41 and sets the superheat degree of the refrigerant in the evaporator 41 to an appropriate value. Adjust to. The low-temperature gas refrigerant discharged from the evaporator 41 returns to the refrigerator unit 3 from the refrigerant pipe 9, and after cooling the refrigerant flowing through the first flow path 15A with the second flow path 15B of the internal heat exchanger 15, the refrigerant The air is sucked into the low-stage suction port 17 communicating with the first rotary compression element 14 of the compressor 11 through the introduction pipe 22.

The above is the flow of the main circuit 38. Next, the flow of the auxiliary circuit 48 will be described. The temperature of the gas refrigerant accumulated in the upper part of the decompression tank 36 is lowered due to evaporation in the decompression tank 36. The gas refrigerant in the upper part of the decompression tank 36 flows out from the gas pipe 42 constituting the auxiliary circuit 48 connected to the upper part, is throttled through the auxiliary throttle means 43, and then the first flow of the split heat exchanger 29. It flows into the passage 29A. Therefore, after the refrigerant flowing through the second flow path 29B is cooled, it joins the intermediate pressure suction pipe 26 via the intermediate pressure return pipe 44 and is sucked into the intermediate pressure portion of the compressor 11.

The controller 57 detects a temperature of refrigerant discharged from the compressor 11, a temperature sensor (not shown), an intermediate pressure sensor 52, a low pressure sensor 51, a high pressure sensor 49, a temperature sensor (not shown) that detects the temperature of the refrigerant discharged from the gas cooler 28, and a unit outlet. Based on the temperature and pressure detected by the temperature sensor 54, the valve opening degree of the auxiliary throttle means 43 is controlled, and the amount of refrigerant flowing through the first flow path 29A of the split heat exchanger 29 is adjusted to an appropriate value. Since the valve opening of the auxiliary throttle means 43 also affects the pressure in the decompression tank 36, the control device 57 takes into account the valve opening of the auxiliary throttle means 43 and sets the valve opening of the pressure adjusting throttle means 33. The pressure in the decompression tank 36 (the pressure of the refrigerant flowing into the main throttle means 39) is adjusted to the predetermined value SP.

Further, based on the detected pressure (high pressure side pressure HP) of the high pressure sensor 49, which is an index indicating the outside air temperature, the control device 57, when the high pressure side pressure (outside air temperature) falls below the cycle switching value CP, The valve 47 is opened. When the electromagnetic valve 47 is opened, the liquid refrigerant accumulated in the lower part of the decompression tank 36 flows out from the liquid pipe 46, joins the gas pipe 42, and flows into the auxiliary throttle means 43 (note that the control device 57). Is closed when the high-pressure side pressure HP (outside air temperature) rises above the cycle switching value CP).

(1-1) Operation at High Outside Air Temperature The state of the refrigerant circuit 1 at this time will be described with reference to the PH diagrams of FIGS. For example, FIG. 2 shows a case where the outside air temperature is 30 ° C. or higher. Since the high-pressure side pressure HP is high at such a high outside air temperature and is equal to or higher than the cycle switching value CP described above, the control device 57 closes the electromagnetic valve 47. Accordingly, a gas refrigerant having a low temperature in the decompression tank 36 flows through the first flow path 29A of the split heat exchanger 29, and flows through the second flow path 29B using the cold heat (sensible heat) of the gas refrigerant. The liquid refrigerant will be cooled. Further, the valve opening degree of the pressure adjusting throttle means 33 is in the throttle state, and the auxiliary throttle means 43 is almost fully opened.

The line descending at X1 to X2 in FIG. 2 indicates the pressure reduction by the pressure adjusting throttling means 33. The liquid / gas is separated from the pressure reducing tank 36 at X2, and the line toward the right from there is the line of the auxiliary circuit 48. After the enthalpy of the gas refrigerant squeezed by the auxiliary throttle means 43 rises, it shows a state of returning to the intermediate pressure portion of the compressor 11, and the line toward the left is the excess of liquid refrigerant toward the main throttle means 39 of the main circuit 38. Indicates cooling. Then, the pressure is reduced by the main throttle means 39 at X3. In such a situation where the outside air temperature is high and the high pressure side pressure HP is high, the control device 57 closes the electromagnetic valve 47 and the refrigerant circuit 1 is in a so-called two-stage expansion cycle.

(1-2) Operation at Medium Outside Air Temperature Next, FIG. 3 shows a case where the outside air temperature is about 25 ° C., for example. Since the high-pressure side pressure HP is also lower than that in the case of FIG. 2 at such a medium / outside air temperature and is slightly lower than the cycle switching value CP described above, the control device 57 opens the electromagnetic valve 47. Therefore, both the gas refrigerant in the upper part of the decompression tank 36 and the liquid refrigerant in the lower part flow through the first flow path 29A of the split heat exchanger 29, and the cold heat of this gas refrigerant and the endothermic action due to the evaporation of the liquid refrigerant are performed. Utilizing this, the liquid refrigerant flowing through the second flow path 29B is cooled more strongly than in FIG. Further, the valve opening degree of the pressure adjusting throttle means 33 is open, and the auxiliary throttle means 43 is in the throttle state.

The line descending at X1 to X2 in FIG. 3 similarly indicates the pressure reduction by the pressure adjusting throttle means 33, and the liquid / gas is separated from the pressure reducing tank 36 at X2, and then falls to the right after that. A broken line indicates a state in which the enthalpy of the gas refrigerant squeezed by the auxiliary throttle means 43 of the auxiliary circuit 48 rises and then returns to the intermediate pressure portion of the compressor 11, and a broken line toward the right after descending from X2 indicates the auxiliary circuit 48. The change of the liquid refrigerant which flows into is shown. Similarly, the line from X2 to the left indicates the supercooling of the liquid refrigerant toward the main throttle means 39 of the main circuit 38. Similarly, the main throttle means 39 squeezes at X3 and the pressure drops. Thus, when the outside air temperature decreases and the high pressure side pressure HP decreases, the control device 57 opens the electromagnetic valve 47, so that the refrigerant circuit 1 becomes a combined cycle of a two-stage expansion cycle and a so-called split cycle.

(1-3) Operation at Low Outside Air Temperature Next, FIG. 4 shows a case where the outside air temperature is lowered to 20 ° C. or lower, for example. At such a low outside air temperature, the high pressure side pressure HP is also lower than that in the case of FIG. 3 and is much lower than the cycle switching value CP described above. Therefore, the controller 57 controls the electromagnetic valve 47 in the same manner as in FIG. Open. At such a low outside air temperature, the high pressure side pressure HP is low, and the valve opening degree of the pressure adjusting throttle means 33 is also increased. In addition, since the refrigerant that has exited the gas cooler 28 is liable to be liquefied due to the low outside air temperature, most of the refrigerant that has entered the decompression tank 36 through the pressure adjusting throttle means 33 has been liquefied, and is contained in the decompression tank 36. Becomes a state where a large amount of liquid refrigerant is stored.

Since the electromagnetic valve 47 is opened in such a state, the liquid refrigerant in the lower part of the decompression tank 36 flows into the first flow path 29A of the split heat exchanger 29, and the heat absorption action due to evaporation of this liquid refrigerant is utilized. Thus, the liquid refrigerant flowing through the second flow path 29B is further strongly cooled as shown in FIG. In addition, the auxiliary aperture means 43 is in the aperture state. Although X1 to X3 in FIG. 4 indicate the same points as described above, the refrigerant circuit 1 is in a split cycle at such a low outside air temperature.

In this way, the auxiliary circuit 48 in the portion located upstream of the auxiliary throttle means 43 causes the gas refrigerant to flow out from the upper part of the decompression tank 36 and flow into the auxiliary throttle means 43, and the liquid from the lower part of the decompression tank 36. Since the refrigerant pipe 46 is configured to cause the refrigerant to flow out and flow into the auxiliary throttle means 43 via the electromagnetic valve 47, the refrigerant is liquefied by being expanded by the pressure adjusting throttle means 33 and enters the decompression tank 36. Thus, the gas refrigerant whose temperature has been partially evaporated and the remaining liquid refrigerant and the remaining liquid refrigerant can be selectively passed through the first flow path 29A of the split heat exchanger 29 by the gas pipe 42 and the liquid pipe 46.

That is, for example, in a high outside air temperature environment where the outside air temperature is high, the high pressure side pressure HP of the refrigerant circuit 1 also increases, so that the pressure of the refrigerant flowing into the main throttle means 39 is lowered to the predetermined value SP. Control is performed so that the valve opening of the throttle means 33 is throttled. In this situation, the liquid refrigerant stored in the decompression tank 36 is reduced, and when it flows into the first flow path 29A of the split heat exchanger 29, it goes to the main throttle means 39 via the second flow path 29B. It becomes difficult to secure a liquid refrigerant.

In addition, when the outside air temperature decreases and becomes the inside / outside air temperature environment, and the high pressure side pressure HP also decreases, the control device 57 opens the valve opening degree of the pressure adjusting throttle means 33 and controls it slightly. The amount of refrigerant stored in the tank 36 also increases. Then, when the outside air temperature is further lowered to become a low outside air temperature environment and the high pressure side pressure HP is further lowered, a large amount of liquid refrigerant is stored in the decompression tank 36.

Based on this, the control device 57 controls the solenoid valve 47 based on the high-pressure side pressure HP that is an index representing the outside air temperature, and when the outside air temperature rises, the solenoid valve 47 is closed and the outside air temperature falls. Therefore, the solenoid valve 47 of the liquid pipe 46 is closed under a high outside air temperature environment so that the gas refrigerant in the decompression tank 36 can flow from the gas pipe 42 to the first flow path 29A of the split heat exchanger 29. become. Thereby, the refrigerant flowing through the second flow path 29B of the split heat exchanger 29 is cooled by the gas refrigerant whose temperature has decreased in the decompression tank 36, and the liquid refrigerant in the decompression tank 36 is cooled to the second of the split heat exchanger 29. After cooling in the flow path 29B, it can be supplied to the main throttle means 39 (two-stage expansion cycle in FIG. 2).

On the other hand, the electromagnetic valve 47 of the liquid pipe 46 is opened under the inside / outside air temperature environment, and the first flow path of the split heat exchanger 29 is supplied from both the gas pipe 42 and the liquid pipe 46 to the gas refrigerant and liquid refrigerant in the decompression tank 36. 29A will be able to flow. Thereby, in addition to the gas refrigerant (sensible heat) whose temperature has been reduced in the decompression tank 36, the split heat exchanger 29 has a latent heat of the liquid refrigerant that is expanded by the auxiliary throttle means 43 and evaporated in the first flow path 29A. The refrigerant in the main circuit 38 flowing through the second flow path 29B is cooled, and the liquid refrigerant in the decompression tank 36 is cooled more strongly in the second flow path 29B of the split heat exchanger 29, and then the main throttle means 39 (The combined cycle of the two-stage expansion cycle and the split cycle in FIG. 3).

And even under a low outside air temperature environment, the electromagnetic valve 47 of the liquid pipe 46 is opened, so that a large amount of liquid refrigerant stored in the decompression tank 36 flows from the liquid pipe 46 to the first flow path 29A of the split heat exchanger 29. Will be able to. As a result, the refrigerant flowing through the second flow path 29B of the split heat exchanger 29 is further strongly cooled by the latent heat of the liquid refrigerant that is expanded by the auxiliary throttle means 43 and evaporates in the first flow path 29A. After the liquid refrigerant in the inside is strongly cooled in the second flow path 29B of the split heat exchanger 29, it can be supplied to the main throttle means 39 (split cycle in FIG. 4).

Thus, since the two-stage expansion cycle and the split cycle can be switched according to the outside air temperature environment, the refrigeration apparatus R can be operated more stably and with high efficiency.

Here, FIG. 5 shows control for changing the cycle switching value CP described above according to the evaporation temperature of the refrigerant in the evaporator 41. Based on the pressure detected by the low pressure sensor 51 (low pressure side pressure LP), which is an index representing the refrigerant evaporation temperature in the evaporator 41, the control device 57 performs cycle switching as the evaporation temperature of the evaporator 41 increases as shown in FIG. Change the value CP to be lower. Thus, the higher the refrigerant evaporation temperature in the evaporator 41, the lower the high pressure side pressure HP (outside air temperature), the more the electromagnetic valve 47 is closed, and the refrigerant circuit 1 enters the two-stage expansion cycle. That is, when the showcase 4 is a refrigerated showcase, the solenoid valve 47 is opened from a higher high-pressure side pressure HP (outside air temperature) under conditions where the refrigerant evaporation temperature of the evaporator 41 is low, and the showcase 4 is a refrigerated showcase. Under the condition that the evaporation temperature of the evaporator 41 is high, the electromagnetic valve 47 is closed until the high-pressure side pressure HP (outside air temperature) becomes lower.

As described above, the controller 57 closes the electromagnetic valve 47 at a lower outside air temperature as the evaporation temperature is higher, based on the low pressure side pressure LP that is an index representing the evaporation temperature of the refrigerant in the evaporator 41. When the outside air temperature becomes high during operation with a high evaporation temperature under refrigeration conditions, such as in a refrigerated showcase, the liquid refrigerant toward the main throttle means 39 is secured by switching to the above-described two-stage expansion cycle at a faster stage. It becomes possible to maintain the refrigerating capacity under refrigerated conditions.

On the other hand, under refrigeration conditions such as a refrigeration showcase having a low evaporation temperature, the refrigerant that flows into the main throttle means 39 cannot be removed in the split heat exchanger 29 in the above-described two-stage expansion cycle, but the cycle switching value CP Since the operation is performed in the split cycle as much as possible, the refrigerant flowing into the main throttle means 39 can be effectively supercooled. As a result, the operating efficiency of the refrigeration apparatus R can be optimized even when operating at different evaporation temperatures.

In addition, since the flow path of the refrigerant circuit 1 is dammed by providing the pressure adjusting throttle means 33, there is a risk that the high-pressure side pressure of the refrigerant circuit 1 on the upstream side becomes higher. Therefore, the control device 57 determines that the high pressure side pressure HP is a predetermined upper limit value HHP (for example, 10.5 MPa) based on the output of the high pressure sensor 49 that detects the high pressure side pressure HP of the refrigerant circuit 1 upstream from the pressure adjusting throttle means 33. ), The valve opening degree of the pressure adjusting throttle means 33 is increased irrespective of the predetermined value SP of the pressure in the decompression tank 36.

The control device 57 is originally programmed to execute a protection operation for stopping the compressor 11 when the pressure detected by the high pressure sensor 49 rises to a protection stop value such as 11.5 MPa, for example. By increasing the valve opening degree of the pressure adjusting throttle means 33, the pressure in the pressure reducing tank 36 increases somewhat, but the high pressure side pressure HP upstream from the pressure adjusting throttle means 33 does not increase any more. Thereby, it is possible to avoid the stop (protection operation) of the compressor 11 due to the abnormally high pressure.

As described in detail above, the refrigerant circuit 1 is constituted by the compressor 11, the gas cooler 28, the main throttle means 39, and the evaporator 41, and in the refrigeration apparatus R in which the high pressure side becomes the supercritical pressure, on the downstream side of the gas cooler 28. The pressure adjusting throttle means 33 connected to the refrigerant circuit 1 upstream of the main throttle means 39, and connected to the refrigerant circuit 1 downstream of the pressure adjusting throttle means 33 and upstream of the main throttle means 39. The reduced pressure tank 36, the split heat exchanger 29 provided in the refrigerant circuit 1 downstream of the reduced pressure tank 36 and upstream of the main throttle means 39, and the refrigerant in the reduced pressure tank 36 After flowing through the first flow path 29A of the split heat exchanger 29 through the auxiliary circuit 48 for sucking into the intermediate pressure part of the compressor 11, the refrigerant is caused to flow out from the lower part of the decompression tank 36, and the split heat exchanger 2 The main circuit 38 that flows into the second flow path 29B, exchanges heat with the refrigerant flowing through the first flow path 29A, and then flows into the main throttle means 39, so that the split that constitutes the auxiliary circuit 48 is provided. The refrigerant flowing in the first flow path 29A of the heat exchanger 29 is expanded by the auxiliary throttle means 43, and the refrigerant flowing in the second flow path 29B of the split heat exchanger 29 constituting the main circuit 38 can be cooled. As a result, the specific enthalpy at the inlet of the evaporator 41 can be reduced to effectively improve the refrigerating capacity.

Further, since the refrigerant flowing through the first flow path 29A of the split heat exchanger 29 is returned to the intermediate pressure portion of the compressor 11, the amount of refrigerant sucked into the low pressure portion of the compressor 11 is reduced, and from low pressure to intermediate pressure. The amount of compression work in the compressor 11 for compression is reduced. As a result, the compression power in the compressor 11 is reduced and the coefficient of performance is improved.

In particular, since the refrigerant discharged from the gas cooler 28 is expanded by the pressure adjusting throttle means 33 and flows into the decompression tank 36, the refrigerant flowing into the main throttle means 39 by the pressure adjusting throttle means 33 is used. By reducing the pressure, it is possible to use a refrigerant pipe 8 having a low withstand pressure strength as the refrigerant pipe 8 reaching the main throttle means 39. Further, there is an effect that the decompression tank 36 absorbs the fluctuation of the circulating refrigerant amount in the refrigerant circuit 1. Therefore, even when the refrigerant charging amount is too large, an error from the appropriate amount is absorbed. As a result, it is possible to improve workability and construction cost when installing the refrigerator unit 3 and the showcase 4 of the refrigeration apparatus R in the store.

Furthermore, a part of the refrigerant liquefied by expansion by the pressure adjusting throttle means 33 evaporates in the decompression tank 36 to become a gas refrigerant having a lowered temperature, and the rest becomes a liquid refrigerant in the lower part of the decompression tank 36. Once it is stored. Then, the liquid refrigerant in the lower part of the decompression tank 36 flows into the main throttle means 39 via the second flow path 29B of the split heat exchanger 29 constituting the main circuit 38, so that the cycle switching described above is also performed. Successful, it is possible to allow the refrigerant to flow into the main throttling means 39 in a full liquid state, and in particular, to improve the refrigerating capacity in a refrigerated condition (such as a refrigerated showcase) where the evaporation temperature in the evaporator 41 is high. Become.

In particular, since the control device 57 controls the valve opening of the pressure adjusting throttle means 33 to adjust the pressure of the refrigerant flowing into the main throttle means 39 to a predetermined specified value SP, the change in the outside air temperature with the change of seasons. Thus, it is possible to prevent the refrigerant pressure flowing into the main throttle means 39 from fluctuating greatly and always maintain the same default value SP. As a result, the control of the main throttle means 39 can be stabilized and the refrigerating capacity can be ensured stably, particularly under refrigeration conditions (such as a refrigeration showcase) where the evaporation temperature in the evaporator 41 is high. In particular, it is possible to effectively improve the refrigerating capacity when carbon dioxide is used as a refrigerant as in the embodiment and to improve performance.

(2) Function of Internal Heat Exchanger 15 Next, control of the electromagnetic valve 50 by the control device 57 will be described. As described above, in the internal heat exchanger 15, the refrigerant flowing through the first flow path 15A and flowing into the main throttle means 39 is cooled by the low-temperature refrigerant discharged from the evaporator 41 flowing through the second flow path 15B. Therefore, the specific enthalpy at the inlet of the evaporator 41 can be further reduced to improve the refrigerating capacity more effectively.

In particular, in a high outside air temperature environment where the outside air temperature is high as shown in FIG. 2, the pressure in the decompression tank 36 (pressure X2 in FIG. 2) adjusted to the specified value SP by the pressure adjusting throttle means 33, and the compressor The pressure difference from the intermediate pressure (MP) of the intermediate pressure suction pipe 26 entering 11 disappears. In such a case, since the auxiliary throttle means 43 is almost fully opened as described above, depending on the situation, the second flow path is caused by the refrigerant in the auxiliary circuit 49 flowing in the first flow path 29A in the split heat exchanger 29. The refrigerant of the main circuit 38 flowing through 29B can hardly be supercooled.

In such a situation, the state of the refrigerant passing through the second flow path 29B of the split heat exchanger 29 and reaching the main throttle means 39 is substantially on the saturated liquid line indicated by X4 in FIG. It becomes. Therefore, the pressure of the refrigerant squeezed by the main squeezing means 39 starts to drop from X4 in FIG. 2 as indicated by a broken line in FIG. In this case, the enthalpy difference indicated by the lower side is reduced, and the refrigerating capacity is reduced.

However, in the embodiment, the refrigerant flowing into the main throttle means 39 is cooled by the low-temperature refrigerant discharged from the evaporator 41 in the internal heat exchanger 15, and as shown by X3 in FIG. Since it is possible to supercool to the cooling zone, the refrigerant can be supplied to the main throttle means 39 in a liquid-rich full state, and the refrigeration capacity can be improved even under such circumstances.

(2-1) Control of Electromagnetic Valve 50 On the other hand, when the refrigeration apparatus R is pulled down, the temperature of the refrigerant that exits the evaporator 41 may be higher than the refrigerant that flows into the main throttle means 39. Therefore, the control device 57 detects the temperature IT of the refrigerant flowing into the first flow path 15A of the internal heat exchanger 15 detected by the unit outlet temperature sensor 54 and the first temperature of the internal heat exchanger 15 detected by the unit inlet temperature sensor 56. Based on the temperature OT of the refrigerant exiting the second flow path 15B, when IT <OT, the electromagnetic valve 50 is opened (when IT ≧ OT, the electromagnetic valve 50 is closed).

Thus, the refrigerant bypasses the first flow path 15A of the internal heat exchanger 15 and flows between the bypasses 45 and flows into the main throttle means 39. Therefore, the refrigerant from the evaporator 41 is used as the main throttle means 39. It is possible to eliminate the inconvenience that the refrigerant flowing into the tank is heated in reverse.

In the embodiment, the bypass circuit 45 is connected in parallel to the first flow path 15A of the internal heat exchanger 15. However, the present invention is not limited thereto, and a bypass circuit and an electromagnetic valve may be provided in parallel to the second flow path 15B. Good.

R Refrigeration apparatus 1 Refrigerant circuit 3 Refrigerator unit 4 Showcase 8, 9 Refrigerant pipe 11 Compressor 15 Internal heat exchanger 15A First flow path 15B Second flow path 22 Refrigerant introduction pipe 26 Intermediate pressure suction pipe 28 Gas cooler 29 Split heat exchanger 29A First flow path 29B Second flow path 32 Gas cooler outlet piping 33 Pressure adjusting throttle means 36 Depressurization tank 37 Gas cooler outlet pipe 38 Main circuit 39 Main throttle means 41 Evaporator 42 Gas pipe 43 Auxiliary throttle means 44 Intermediate pressure return piping 45 Bypass circuit 46 Liquid piping 47 Solenoid valve (valve device)
48 Auxiliary circuit 50 Solenoid valve (Valve device for bypass)
57 Control device (control means)

Claims

In the refrigerating apparatus in which the refrigerant circuit is configured by the compression means, the gas cooler, the main throttle means, and the evaporator, and the high pressure side is the supercritical pressure
A pressure adjusting throttle means connected to the refrigerant circuit downstream of the gas cooler and upstream of the main throttle means;
A pressure reducing tank connected to the refrigerant circuit downstream of the pressure adjusting throttle means and upstream of the main throttle means;
A split heat exchanger provided in the refrigerant circuit downstream of the decompression tank and upstream of the main throttle means;
An auxiliary circuit that causes the refrigerant in the decompression tank to flow into the first flow path of the split heat exchanger via the auxiliary throttle means, and then sucks the refrigerant into the intermediate pressure portion of the compression means;
A main circuit that causes the refrigerant to flow out from the lower part of the decompression tank, flows into the second flow path of the split heat exchanger, exchanges heat with the refrigerant flowing through the first flow path, and then flows into the main throttle means; A refrigeration apparatus comprising:
Control means for controlling the pressure adjusting throttle means;
2. The refrigeration according to claim 1, wherein the control means adjusts the pressure of the refrigerant flowing into the main throttle means to a predetermined specified value by controlling an opening degree of the pressure adjusting throttle means. apparatus.
The control means increases the opening of the pressure adjusting throttle means when the high pressure side pressure of the refrigerant circuit upstream of the pressure adjusting throttle means rises to a predetermined upper limit value. Item 3. The refrigeration apparatus according to Item 2.
The auxiliary circuit upstream of the auxiliary throttle means allows the refrigerant to flow out from the upper part of the decompression tank and flows into the auxiliary throttle means, and causes the refrigerant to flow out from the lower part of the decompression tank, and through the valve device, The refrigeration apparatus according to any one of claims 1 to 3, wherein the refrigeration apparatus includes a liquid pipe that flows into the auxiliary throttle means.
The control means controls the valve device based on an index representing an outside air temperature, and closes the valve device when the outside air temperature rises and opens when the outside air temperature falls. Item 5. The refrigeration apparatus according to Item 4.
6. The refrigeration apparatus according to claim 5, wherein the control means closes the valve device at a lower outside air temperature as the evaporation temperature is higher based on an index representing the evaporation temperature of the refrigerant in the evaporator.
The refrigeration according to any one of claims 1 to 6, further comprising an internal heat exchanger for exchanging heat between the refrigerant flowing into the main throttle means and the refrigerant discharged from the evaporator. apparatus.
The internal heat exchanger includes a first flow path through which the refrigerant flowing into the main throttle means flows, and a second flow path through which the refrigerant discharged from the evaporator flows, and the first of the internal heat exchangers Heat exchange between the refrigerant flowing through the second flow path and the refrigerant flowing through the second flow path of the internal heat exchanger,
A bypass circuit connected in parallel to the first flow path of the internal heat exchanger or the second flow path of the internal heat exchanger; and a bypass valve device provided in the bypass circuit. The refrigeration apparatus according to claim 7.
Control means for controlling the bypass valve device;
The control means is based on the temperature of the refrigerant flowing into the first flow path of the internal heat exchanger and the temperature of the refrigerant exiting the second flow path of the internal heat exchanger. 9. The refrigeration apparatus according to claim 8, wherein the bypass valve device is opened when a temperature of the refrigerant exiting the flow path is higher than a temperature of the refrigerant flowing into the first flow path of the internal heat exchanger. .
10. The refrigeration apparatus according to any one of claims 1 to 9, wherein carbon dioxide is used as the refrigerant.