JP2018132224A - Binary refrigeration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binary refrigeration system enabling operation with excellent COP without generating capacity shortage, regardless of fluctuation of ambient temperature.SOLUTION: A binary refrigeration system (1) includes: a low-stage side refrigeration circuit (2) including a variable speed compressor (201); a high-stage side refrigeration circuit (3); a cascade heat exchanger (4) configured to perform heat exchange between low-stage side refrigerant in the low-stage side refrigeration circuit (2) and high-stage side refrigerant in the high-stage side refrigeration circuit (3); and control means (5) of operating the high-stage side refrigeration circuit (3) in a case where a frequency of the variable speed compressor (201) is not less than a threshold determined according to ambient temperature.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a low-stage refrigeration circuit, a high-stage refrigeration circuit, and a cascade for performing heat exchange between a low-stage refrigerant in the low-stage refrigeration circuit and a high-stage refrigerant in the high-stage refrigeration circuit. The present invention relates to a binary refrigeration system including a heat exchanger.

  In the refrigeration apparatus, a refrigeration cycle is composed of a compression means, a gas cooler, a throttle means, an evaporator, etc., and the refrigerant compressed by the compression means dissipates heat in the gas cooler, and then is decompressed by the throttle means and evaporates in the evaporator. . The ambient air is cooled by the evaporation of the refrigerant at this time.

  In recent years, in this type of refrigeration apparatus, it has become impossible to use chlorofluorocarbon refrigerants due to natural environmental problems and the like. Moreover, in order to prevent global warming, conversion to a refrigerant having a smaller global warming potential (GWP) is required. For this reason, a refrigeration apparatus using carbon dioxide, which is a natural refrigerant, has been developed as an alternative to a fluorocarbon refrigerant (see, for example, Patent Document 1).

  When carbon dioxide is used as the refrigerant, the operating pressure (particularly the condensation pressure) becomes extremely high, and the reliability of the devices constituting the refrigeration cycle becomes a problem. In order to solve this problem, Patent Document 2 discloses a cascade condenser including a high stage evaporator constituting a high stage refrigeration circuit using carbon dioxide as a refrigerant and a low stage side gas cooler constituting a low stage refrigeration circuit. A dual refrigeration apparatus is proposed.

Japanese Patent Publication No. 7-18602 Japanese Patent No. 3606043

  In general, the two-stage refrigeration system suffers from a shortage of capacity in the summer when the outside air temperature is high, and the COP deteriorates as a result of repeated starting and stopping of the high-stage refrigeration circuit in the winter and intermediate periods when the outside air temperature is low. There is a possibility.

  An object of the present invention is to provide a dual refrigeration system that does not fall short of capacity regardless of fluctuations in the outside air temperature and can operate with good COP.

  The binary refrigeration system according to the present invention includes a low-stage refrigeration circuit including a variable speed compressor, a high-stage refrigeration circuit, a low-stage refrigerant in the low-stage refrigeration circuit, and the high-stage refrigeration circuit. A cascade heat exchanger for exchanging heat with the higher-stage refrigerant, and the higher-stage refrigeration circuit when the frequency of the variable-speed compressor is equal to or higher than a threshold value corresponding to the outside air temperature. And control means for actuating.

  According to the binary refrigeration system according to the present invention, it is possible to operate with good COP without falling short of capacity regardless of fluctuations in outside air temperature.

1 is a refrigeration circuit diagram of a binary refrigeration system according to an embodiment to which the present invention is applied. It is an example of the information used for the switching of the operation state of a binary refrigeration system. It is a freezing circuit diagram of the binary refrigerating system of other examples to which the present invention is applied. FIG. 4 is a ph diagram of a low-stage refrigeration circuit of the binary refrigeration system shown in FIG. 3. It is explanatory drawing of the refrigerant | coolant amount adjustment timing in the low stage refrigeration circuit of the binary refrigeration system shown by FIG.

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

  FIG. 1 shows an example of a refrigeration circuit diagram of a binary refrigeration system 1 to which the present invention is applied. The binary refrigeration system 1 includes a main refrigerator A, a supercooling refrigerator B and a cascade unit C installed in a machine room of a store such as a supermarket, and a showcase D installed in a store sales area. Yes.

  1 is provided with only one showcase D, it is also possible to provide a plurality of these. In the binary refrigeration system 1 shown in FIG. 1, the main refrigerator A, the supercooled refrigerator B, the cascade unit C, and the showcase D are separate devices. For the cascade unit C, two or more of them can be a single device as required.

  Refrigerant outlet Aout of main refrigerator A and first refrigerant inlet Cin1 of cascade unit C, first refrigerant outlet Cout1 of cascade unit C and refrigerant inlet Din of showcase D, refrigerant outlet Dout of showcase D and main refrigerator A The refrigerant inlets Ain are respectively connected by refrigerant (low-stage refrigerant) piping. Further, the refrigerant outlet Bout of the supercooling refrigerator B and the second refrigerant inlet Cin2 of the cascade unit C, and the second refrigerant outlet Cout2 of the cascade unit C and the refrigerant inlet Bin of the supercooling refrigerator B are respectively refrigerant (high-stage refrigerant). ) Connected by piping.

  The main refrigerator A has a low stage compressor 201 and a low stage gas cooler 202. The cascade unit C has a cascade heat exchanger 4 having a first flow path 4A and a second flow path 4B. The showcase D includes a low-stage main throttle means 203 and a low-stage evaporator 204. The low-stage compressor 201, the low-stage gas cooler 202, the first flow path 4A, the low-stage main throttle means 203, and the low-stage evaporator 204 are connected by piping to form a refrigerant circulation path. A low-stage side refrigerant (for example, carbon dioxide) circulates in the refrigerant circuit, and the low-stage side refrigeration circuit 2 is configured.

  The supercooling refrigerator B includes a high stage compressor 301, a high stage side gas cooler 302, and a high stage side main throttle means 303. These and the 2nd flow path 4B of the cascade heat exchanger 4 are connected with piping, and the refrigerant circuit is comprised. A high stage side refrigerant (for example, carbon dioxide) circulates in the refrigerant circulation path, and the high stage side refrigeration circuit 3 is configured.

  Further, the binary refrigeration system 1 has a control device 5 composed of a microcomputer that controls the operation of each device constituting the low-stage refrigeration circuit 2 and the high-stage refrigeration circuit 3. The control device 5 constitutes a control means in the present invention. The control device 5 is connected to a frequency sensor S1 that detects the frequency of the low-stage compressor 201 and an outside air temperature sensor S2 that is attached to the main refrigerator A and detects outside air temperature, for example. The control device 5 may be a single control device that controls all of the main refrigerator A, the supercooling refrigerator B, the cascade unit C, and the showcase D, or individually controls these devices. It may be a combination of a plurality of control devices.

  The low-stage compressor 201 is a variable speed compressor that can control the frequency (number of rotations) by an inverter, and is, for example, a rotary compressor.

  The low stage side gas cooler 202 dissipates the heat of the low stage side refrigerant discharged from the low stage side compressor 201 into the outside air and cools it.

  The cascade heat exchanger 4 has a first flow path 4A disposed between the first refrigerant inlet Cin1 and the first refrigerant outlet Cout1, and a second flow path disposed between the second refrigerant inlet Cin2 and the second refrigerant outlet Cout2. 2 flow paths 4B. The low stage side refrigerant flows through the first flow path 4A and is further cooled by the high stage side refrigerant flowing through the second flow path 4B.

  The low stage side main throttle means 203 is composed of, for example, an electric expansion valve, and throttles and expands the low stage side refrigerant.

  The low-stage evaporator 204 is a heat exchanger for obtaining low-temperature air by exchanging heat between air supplied from a cool air circulation blower (not shown) and the low-stage refrigerant. The food displayed in the showcase D can be cooled by this low-temperature air.

  The high stage compressor 301 is a variable speed compressor capable of controlling the frequency (the number of rotations) by an inverter, and is, for example, a rotary compressor. The high-stage compressor 301 is not necessarily a variable speed compressor, and may be a constant speed compressor.

  The high stage side gas cooler 302 radiates the heat of the high stage side refrigerant discharged from the high stage side compressor 301 into the outside air and cools it.

  The high stage side main throttle means 303 is constituted by, for example, an electric expansion valve, and throttles and expands the low stage side refrigerant.

  The second flow path 4B of the cascade heat exchanger 4 functions as an evaporator. That is, the high-stage side refrigerant is heated by the low-stage side refrigerant flowing through the first flow path 4A when flowing through the second flow path 4B, and flows out of the cascade heat exchanger 4 as superheated steam.

  The binary refrigeration system 1 configured as described above operates as follows.

  Normally, the binary refrigeration system 1 operates only the low-stage refrigeration circuit 2, and does not operate the high-stage refrigeration circuit 3. That is, first, the low-stage refrigerant is compressed by the low-stage compressor 201 to be in a high temperature and high pressure state, and is cooled by the low-stage gas cooler 202. Next, the low-stage refrigerant passes through the first flow path 4A of the cascade heat exchanger 4 with almost no change in state, expands in the low-stage main throttle means 203, and is low-temperature and low-pressure wet steam. It becomes. Subsequently, the low-stage refrigerant evaporates in the low-stage evaporator 204 and exchanges heat with the surrounding air. In this way, the required temperature and amount of cold air is obtained.

  On the other hand, in the case where only the low-stage refrigeration circuit 2 does not provide the required temperature and quantity of low-temperature air, the control device 5 adds the low-stage refrigeration circuit 2 to the high-stage refrigeration. The circuit 3 is operated to supply the low-temperature high-stage refrigerant to the second flow path 4B of the cascade heat exchanger 4. Then, the low-stage refrigerant increases the degree of supercooling by exchanging heat with the high-stage refrigerant when passing through the first flow path 4A of the cascade heat exchanger 4. Accordingly, the amount of heat exchanged with the air in the showcase D in the low-stage evaporator 204 is increased, and the required temperature and amount of low-temperature air can be obtained.

  The control device 5 performs the operation of only the low-stage refrigeration circuit 2 and the operation of both the low-stage refrigeration circuit 2 and the high-stage refrigeration circuit 3, with the frequency of the low-stage compressor 201 corresponding to the outside air temperature. Then, it is switched by determining whether or not a predetermined threshold value or more is reached. The control device 5 stores information serving as a reference for switching on / off of the high-stage side refrigeration circuit 3, and can switch the operation state of the dual refrigeration system 1 according to this information.

  An example of such information is shown in FIG. The information shown in FIG. 2 is a graph in which the vertical axis represents the frequency of the low-stage compressor 201 and the horizontal axis represents the outside air temperature. In the region below the line shown in the graph, the low-stage refrigeration is performed. Only the circuit 2 is operated, and the high-stage side refrigeration circuit 3 is operated in addition to the low-stage side refrigeration circuit 2 in the region above and above the line.

  If the dual refrigeration system 1 is operated based on the information shown in FIG. 2, when the outside air temperature (the detected value of the outside air temperature sensor S2) is relatively high, for example, t1, the frequency of the low-stage compressor 201 (frequency) If the detection value of the sensor S1 is less than r1, which is relatively low, only the low-stage refrigeration circuit 2 operates, and if the detection value of the frequency sensor S1 becomes r1 or more, the high-stage refrigeration circuit 3 also operates. Therefore, even when the outside air temperature is relatively high and there is a fear that the refrigerating capacity required in the operation in which only the low-stage refrigeration circuit 2 is operated may not be obtained, the frequency of the low-stage compressor 201 is low. Since the operation of the high-stage refrigeration circuit 3 starts when the temperature rises to a relatively low r1, it is possible to prevent the binary refrigeration system 1 from becoming insufficient in refrigeration capacity.

  In addition, when the outside air temperature is relatively low t2, the high-stage refrigeration circuit 3 does not operate until the frequency of the low-stage compressor 201 becomes r2 or higher. Therefore, the high-stage refrigeration circuit 3 is not operated while the refrigeration capacity of the low-stage refrigeration circuit 2 is relatively large (the frequency of the low-stage compressor 201 is relatively low). It is possible to prevent the refrigeration capacity from becoming excessive.

  If the refrigeration capacity of the binary refrigeration system 1 becomes excessive, it is considered that the operation of the high-stage refrigeration circuit 3 may be stopped. However, the high-stage refrigeration circuit 3 was activated while the refrigeration capacity of the low-stage refrigeration circuit 2 was relatively large (the frequency of the low-stage compressor 201 was relatively low), and the refrigeration capacity became excessive. In such a case, if the operation of stopping the operation of the high stage side refrigeration circuit 3 is performed, the operation of the high stage side refrigeration circuit 3 is frequently started and stopped. In that case, since the operating conditions of the binary refrigeration system 1 are frequently changed, the COP of the entire binary refrigeration system 1 may be deteriorated. On the other hand, according to the information shown in FIG. 2, when the outside air temperature is relatively low, the high-stage refrigeration circuit 3 does not operate until the frequency of the low-stage compressor 201 is relatively high. It is possible to reliably prevent the deterioration of the COP of the entire binary refrigeration system 1 due to frequent start and stop of the operation of the stage side refrigeration circuit 3.

  Of course, the information used for switching control of the operating state of the binary refrigeration system 1 is not limited to the graph shown in FIG. For example, the graph may be such that the lower stage compressor frequency, which is the threshold value, decreases stepwise as the outside air temperature increases, or the dual refrigeration system 1 is used in an area where the fluctuation range of the outside air temperature is small throughout the year. In such a case, the low-stage compressor frequency that is a threshold value may be a graph that does not change depending on the outside air temperature.

<Other embodiments>
Next, with reference to FIG. 3, another embodiment according to the present invention will be described focusing on differences from the previous embodiment. In addition, in FIG. 3, the component apparatus of the supercooling refrigerator B is abbreviate | omitting illustration. In the present embodiment, the low-stage side refrigerant and the high-stage side refrigerant are described as carbon dioxide, but the low-stage side refrigerant and the high-stage refrigerant are not limited to carbon dioxide. .

  The low-stage refrigeration circuit 2 shown in FIG. 3 includes a low-stage compressor (hereinafter sometimes simply referred to as “compressor”) 201. The compressor 201 is, for example, an internal intermediate pressure type two-stage compression rotary compressor. The compressor 201 includes a sealed container and a rotary compression mechanism unit. The rotary compression mechanism section includes an electric element as a drive element housed in the upper part of the internal space of the hermetic container, a first rotary compression element 201a and a second rotary compression arranged below the electric element. It consists of element 201b. In such a compressor, the excluded volume ratio between the low stage side and the high stage side is determined, and the intermediate pressure (MP) is determined according to the excluded volume ratio.

  The first rotary compression element 201a of the compressor 201 compresses the low-stage refrigerant sucked into the compressor 201 from the low-pressure side of the low-stage refrigeration circuit 2, boosts the refrigerant to an intermediate pressure, and discharges it. The second rotary compression element 201b sucks in the intermediate pressure refrigerant discharged by the first rotary compression element 201a, compresses it to a high pressure, and discharges it to the high pressure side of the low-stage refrigeration circuit 2. The compressor 201 is a variable frequency compressor. The control device 5 controls the frequencies of the first rotary compression element 201a and the second rotary compression element 201b by changing the operating frequency of the electric element.

  On the side surface of the hermetic container of the compressor 201, a low-stage suction port that communicates with the first rotary compression element 201a, a low-stage discharge port that communicates within the hermetic container, and a second rotary compression element 201b. A high-stage suction port and a high-stage discharge port are formed. One end of the refrigerant introduction pipe L <b> 1 is connected to the lower stage side suction port of the compressor 201. The other end of the refrigerant introduction pipe L1 is connected to the discharge port of the low-stage evaporator 204.

  The low-pressure (LP) refrigerant gas sucked into the low-pressure portion of the first rotary compression element 201a from the low-stage suction port is boosted to an intermediate pressure (MP) by the first rotary compression element 201a and is stored in the sealed container. Discharged. Thereby, the inside of a sealed container becomes an intermediate pressure (MP).

  One end of the intermediate pressure discharge pipe L2 is connected to the lower stage discharge port of the compressor 201 from which the intermediate pressure refrigerant gas in the sealed container is discharged, and the other end is connected to the inlet of the intercooler 205. Yes. This intercooler 205 air-cools the intermediate pressure refrigerant discharged from the first rotary compression element 201a, and one end of an intermediate pressure suction pipe L3 is connected to the outlet of the intercooler 205. The other end of the pressure suction pipe L3 is connected to the high stage side suction port of the compressor 201.

  The intermediate-pressure (MP) refrigerant gas sucked into the second rotary compression element 201b from the high-stage side suction port is compressed in the second stage by the second rotary compression element 201b, so that the high-temperature and high-pressure (HP: (Supercritical pressure) refrigerant gas.

  One end of the high-pressure discharge pipe L4 is connected to the high-stage discharge port provided on the high-pressure chamber side of the second rotary compression element 201b of the compressor 201. The other end of the high-pressure discharge pipe L4 is connected to an inlet of a low-stage gas cooler (hereinafter sometimes simply referred to as “gas cooler”) 202.

  The gas cooler 202 cools the high-pressure refrigerant discharged from the compressor 201, and a gas cooler blower (not shown) that cools the gas cooler 202 in the air is disposed in the vicinity of the gas cooler 202. The gas cooler 202 and the intercooler 205 may be arranged side by side and arranged in the same air path.

  One end of a gas cooler outlet pipe L5 is connected to the outlet of the gas cooler 202, and the other end of the gas cooler outlet pipe L5 is connected to an inlet of an electric expansion valve 206 as a pressure adjusting throttle means. The electric expansion valve 206 squeezes and expands the refrigerant discharged from the gas cooler 202 and adjusts the high-pressure side pressure of the low-stage refrigeration circuit 2 upstream from the electric expansion valve 206, and its outlet is a tank. It is connected to the upper part of the intermediate tank 207 via the inlet pipe L6.

  The intermediate tank 207 is a volume body having a predetermined volume space inside, and one end of an intermediate tank outlet pipe L7 is connected to the lower part of the intermediate tank 207, and the other end of the intermediate tank outlet pipe L7 is connected to a low-stage side main throttle means (hereinafter referred to as the lower tank side throttle means) It may be simply referred to as “main throttle means.”) It is connected to the entrance of 203. A second flow path 208B of the split heat exchanger 208 is interposed in the intermediate tank outlet pipe L7, and a cascade heat exchanger is provided in the intermediate tank outlet pipe L7 on the downstream side of the split heat exchanger 208. Four first flow paths 4A are interposed. This intermediate tank outlet pipe L7 constitutes the main circuit in the present invention.

  On the downstream side of the first flow path 4A of the cascade heat exchanger 4, an electric expansion valve 203 as a main throttle means and a low-stage evaporator (hereinafter sometimes simply referred to as “evaporator”) in order. 204 is provided. The evaporator 204 is provided with a cool air circulation blower (not shown) that blows air to the evaporator 204. And the discharge port of the evaporator 204 is connected to the low stage side suction port connected to the 1st rotation compression element 201a of the compressor 201 via the refrigerant | coolant introduction piping L1, as mentioned above.

  On the other hand, one end of a gas pipe L8 is connected to the upper part of the intermediate tank 207, and the other end of the gas pipe L8 is connected to an inlet of an electric expansion valve 209 as a first auxiliary circuit throttle means. The gas pipe L8 causes the gas refrigerant to flow out from the upper part of the intermediate tank 207 and flow into the electric expansion valve 209. One end of the intermediate pressure return pipe L9 is connected to the outlet of the electric expansion valve 209, and the other end is communicated in the middle of the intermediate pressure suction pipe L3 as an example of an intermediate pressure region connected to the intermediate pressure portion of the compressor 201. Yes. A first flow path 208A of the split heat exchanger 208 is interposed in the intermediate pressure return pipe L9.

  Further, a liquid return pipe L10 is provided between the intermediate tank outlet pipe L7 on the downstream side of the split heat exchanger 208 and the intermediate pressure return pipe L9 on the downstream side of the electric expansion valve 209, and the liquid return pipe L10. An electric expansion valve 210 is provided as a second auxiliary circuit throttle means. The electric expansion valve 209 (first auxiliary circuit throttle means) and the electric expansion valve 210 (second auxiliary circuit throttle means) constitute auxiliary throttle means in the present application. The liquid return pipe L10 allows a part of the liquid refrigerant to flow into the intermediate pressure return pipe L9 from the intermediate tank outlet pipe L7. The intermediate pressure return pipe L9, the electric expansion valves 209 and 210, the gas pipe L8 on the upstream side of the electric expansion valve 209, and the liquid return pipe L10 constitute an auxiliary circuit in the present invention.

  Here, the electric expansion valve 206 is located downstream of the gas cooler 202 and upstream of the electric expansion valve 203. The intermediate tank 207 is located downstream of the electric expansion valve 206 and upstream of the electric expansion valve 203. The split heat exchanger 208 is located downstream of the intermediate tank 207 and upstream of the electric expansion valve 203. Furthermore, the first flow path 4 </ b> A of the cascade heat exchanger 4 is located downstream of the split heat exchanger 208 and upstream of the electric expansion valve 203. As described above, the low-stage refrigeration circuit 2 in the present embodiment is configured.

  Various sensors are attached to various parts of the low-stage refrigeration circuit 2. That is, a frequency sensor S <b> 1 that detects the frequency of the compressor 201 is attached to the electric element of the compressor 201. An outside air temperature sensor S2 for detecting the outside air temperature is attached to the casing of the gas cooler 202 or the like. A high-pressure sensor S3 that detects the high-pressure side pressure HP of the low-stage refrigeration circuit 2 (pressure between the high-stage discharge port of the compressor 201 and the inlet of the electric expansion valve 206) is attached to the high-pressure discharge pipe L4. Yes. The installation position of the high pressure sensor S3 may be the gas cooler outlet pipe L5. A low pressure sensor S4 that detects a low pressure LP of the low stage side refrigeration circuit 2 (pressure between the outlet of the electric expansion valve 203 and the low stage suction port) is attached to the refrigerant introduction pipe L1. An outlet pressure sensor S5 that detects an outlet pressure OP that is an outlet pressure of the main refrigerator A is attached to the gas pipe L8 on the upstream side of the electric expansion valve 209. The pressure in the intermediate tank 207 becomes the pressure of the refrigerant flowing into the electric expansion valve 203.

  Although not described in detail, the low-stage refrigeration circuit 2 includes a sensor that measures the refrigerant pressure and the refrigerant temperature in each part of the pipe in addition to the above.

  These sensors are connected to the input of the control device 5. The output of the control device 5 includes an electric element of the compressor 201, a gas cooler blower, an electric expansion valve (pressure adjusting throttle means) 206, electric expansion valves (auxiliary throttle means) 209 and 210, an electric expansion valve (main throttle). Means) 203, a high stage side compressor 301, and a high stage side main throttle means 303 are connected, and the control device 5 controls them based on the output of each sensor, setting data and the like.

  For example, when the frequency of the compressor 201 detected by the frequency sensor S1 is equal to or higher than a threshold value determined in accordance with the outside air temperature, the control device 5 causes the high-stage refrigeration circuit 3 (the high-stage compressor 301). ) And the operation of the high-stage refrigeration circuit 3 is stopped when the value falls below the threshold value.

  4 is a ph diagram of the low-stage refrigeration circuit 2 of the binary refrigeration system 1 shown in FIG. The state of the low-stage refrigerant is changed from X1 to X2 by being compressed in two stages by the compressor 201, and the state is changed from X2 to X3 by being cooled in the gas cooler 202. Subsequently, the low-stage refrigerant is decompressed by the electric expansion valve 206, and the state changes from X3 to X4.

  Thereafter, the low-stage refrigerant partially evaporates in the intermediate tank 207, and the state of the low-stage refrigerant turned into a gas changes from X4 to X5 and is reduced in pressure by the electric expansion valve 209, so that the state changes to X6. Change. The low-stage refrigerant further passes through the first flow path 208A of the split heat exchanger 208 and is compressed by the first rotary compression element 201a of the compressor 201 and then cooled by the intercooler 205. By mixing in the side refrigerant and the intermediate pressure suction pipe L3, the state changes to X7.

  On the other hand, the state of the low-stage liquid refrigerant in the intermediate tank 207 changes from X4 to X8 when passing through the second flow path 208B of the split heat exchanger 208. Here, when the high-stage refrigerant is not supplied to the cascade heat exchanger 4, that is, when the high-stage refrigeration circuit 3 is not operating, the low-stage refrigerant is electrically expanded with the state being X8. It flows into the valve 203 and is depressurized, and the state changes to X9. Thereafter, the evaporator 204 exchanges heat with the surrounding air, and the state changes to X1. A part of the refrigerant that passed through the second flow path 208B of the split heat exchanger 208 passed through the liquid return pipe L10 and the electric expansion valve 210 and changed to the state X12, and then was cooled by the intercooler 205. By mixing in the low stage side refrigerant and the intermediate pressure suction pipe L3, the state changes to X7.

  In contrast, when the high-stage refrigerant is supplied to the cascade heat exchanger 4, that is, when the high-stage refrigeration circuit 3 is operating, the low-stage refrigerant exchanges heat with the high-stage refrigerant. By doing so, the degree of supercooling is increased, and the state changes from X8 to X10. The low-stage refrigerant whose state becomes X10 is decompressed by the electric expansion valve 203, and the state changes to X11. Thereafter, the evaporator 204 exchanges heat with the surrounding air, and the state changes to X1.

  As is clear from FIG. 4, the refrigeration effect of the evaporator 204 is changed between the state X9 and the state X11 by causing the cascade heat exchanger 4 to exchange heat and changing the state of the low-stage refrigerant from X8 to X10. Increased by the specific enthalpy difference. That is, also in the present embodiment, the refrigeration capacity of the two-stage refrigeration system 1 can be increased or decreased by switching the operation of the high-stage refrigeration circuit 3 between on and off. Such on / off of the high-stage refrigeration circuit 3 is performed based on the frequency of the compressor 201 and the outside air temperature as in the previous embodiment.

<Refrigerant amount adjustment mechanism>
The low-stage refrigeration circuit 2 shown in FIG. 3 is operated so that the high-pressure side pressure HP detected by the high-pressure sensor S3 becomes a target pressure determined from the outside air temperature and the evaporation temperature. However, when the operation conditions change, such as when the operation of the high-stage refrigeration circuit 3 is started and stopped, the amount of refrigerant (refrigerant pressure) in the low-stage refrigeration circuit 2 changes, and the high-pressure side pressure HP becomes the target pressure. May be larger. In order to cope with such a state, the low-stage refrigeration circuit 2 shown in FIG. In the present embodiment, each device constituting the refrigerant quantity adjusting mechanism 250 is provided in the cascade unit C, but may be provided in the main refrigerator A or may be provided in an independent unit. .

  The refrigerant quantity adjustment mechanism 250 includes a refrigerant quantity adjustment tank 251, a high-pressure refrigerant path 252 connected to an inlet provided in the upper part of the refrigerant quantity adjustment tank 251, and a first flow provided in the lower part of the refrigerant quantity adjustment tank 251. A low pressure refrigerant path 253 connected to the outlet, an intermediate pressure refrigerant path 254 connected to a second outlet provided in the upper part of the refrigerant quantity adjustment tank 251, and a first valve 255 interposed in the high pressure refrigerant path 252. A second valve 256 interposed in the low-pressure refrigerant path 253, a third valve 257 interposed in the intermediate-pressure refrigerant path 254, a low-pressure refrigerant throttle means 258 interposed in the low-pressure refrigerant path 253, and an intermediate pressure A check valve 259 is provided in the refrigerant path 254.

  The high-pressure refrigerant path 252 is connected to the gas cooler outlet pipe L5 via the high-pressure service pipe L11. The low-pressure refrigerant path 253 is connected to the refrigerant introduction pipe L1 via the low-pressure service pipe L12. The intermediate pressure refrigerant path 254 is connected to the gas pipe L8 via the intermediate pressure service pipe L13.

  The first valve 255 is an electric valve that can adjust the opening, and the second valve 256 and the third valve 257 are electromagnetic valves that can be switched between open and closed states. These valves are controlled by the control device 5. The low-pressure refrigerant throttling means 258 is a capillary.

  When the refrigerant amount (refrigerant pressure) in the low-stage refrigeration circuit 2 changes, the control device 5 changes the states of the first valve 255, the second valve 256, and the third valve 257 as shown in FIG. The refrigerant amount adjusting mechanism 250 is controlled by switching.

  That is, when the high-pressure side pressure HP of the low-stage refrigeration circuit 2 measured by the high-pressure sensor S3 is equal to or lower than the target pressure HPT, the control device 5 determines that the state of the low-stage refrigeration circuit 2 is the pressure state 1. To do. In that case, the opening degree of the first valve 255 is 0 (closed), the second valve 256 is opened, and the third valve 257 is closed. At this time, the internal space of the refrigerant quantity adjustment tank 251 is connected to only the low pressure side of the low-stage refrigeration circuit 2 via the low pressure refrigerant throttle means 258. Therefore, the refrigerant in the refrigerant quantity adjustment tank 251 flows out of the refrigerant quantity adjustment tank 251 and its internal space gradually becomes a low pressure. Note that the low-pressure refrigerant passage 253 includes a low-pressure refrigerant constricting means 258, and the low-stage refrigerant expands here, so that no liquid refrigerant is supplied to the compressor 201.

  When the high pressure side pressure HP exceeds the target pressure HPT, the control device 5 determines that the state of the low stage side refrigeration circuit 2 is the pressure state 2. Also in this case, the opening degree of the first valve 255 is 0 (closed), the second valve 256 is opened, and the third valve 257 is closed.

  When the high-pressure side pressure HP further increases and exceeds the first set pressure HP1, the control device 5 determines that the state of the low-stage side refrigeration circuit 2 is the pressure state 3. In that case, the first valve 255 is set to a first predetermined opening, the second valve 256 is closed, and the third valve 257 is opened. At this time, the gas cooler outlet pipe L5 and the refrigerant quantity adjustment tank 251 communicate with each other through the high-pressure refrigerant path 252 and the gas pipe L8 and the refrigerant quantity adjustment tank 251 communicate with each other through the intermediate pressure refrigerant path 254. When the state of the low-stage refrigeration circuit 2 is the pressure state 1 and the pressure state 2, the inside of the refrigerant quantity adjustment tank 251 is connected only to the low-pressure side of the low-stage refrigeration circuit 2, It has become. Therefore, a part of the high-pressure refrigerant flows into the refrigerant amount adjustment tank 251. Thereby, the high-pressure side pressure HP can be reduced relatively quickly (the refrigerant amount in the low-stage side refrigeration circuit 2 can be reduced). Further, the low stage side refrigerant is gas-liquid separated in the refrigerant quantity adjustment tank 251.

  In addition, after the internal pressure of the refrigerant quantity adjustment tank 251 exceeds the outlet pressure, the high-pressure side refrigerant that has flowed into the refrigerant quantity adjustment tank 251 via the high-pressure refrigerant path 252 becomes a gas refrigerant and becomes an intermediate-pressure refrigerant path. It is supplied to the outlet pressure part (gas pipe L8) via 254. Even in this state, since the refrigerant recovery from the high pressure side is continued, the high pressure side pressure HP gradually decreases.

  When the high-pressure side pressure HP falls below the second set pressure HP2 that is lower than the first set pressure HP1, the control device 5 determines that the state of the low-stage side refrigeration circuit 2 is the pressure state 4. In that case, the first valve 255 has a second predetermined opening, the second valve 256 is opened after a predetermined time, and the third valve 257 is closed. As a result, during a predetermined time during which the second valve 256 is opened, a part of the refrigerant in the refrigerant amount adjustment tank 251 is returned to the low pressure side via the low pressure service pipe L12, and the high pressure side refrigerant A part of the refrigerant flows into the refrigerant quantity adjustment tank 251. Therefore, the high-pressure side refrigerant can flow into the refrigerant amount adjustment tank 251 at a slower pace than when the low-stage refrigeration circuit 2 is in the pressure state 3.

  In addition, after the second valve 256 is closed, the internal space of the refrigerant amount adjustment tank 251 is connected to only the high pressure side via the high pressure refrigerant path 252, so that the internal pressure gradually increases to the high pressure side. As the pressure approaches HP, the amount of high-pressure side refrigerant recovered gradually decreases.

  When the state of the low-stage side refrigeration circuit 2 becomes the pressure state 4 and the state of each valve is switched as described above, and the high-pressure side pressure HP decreases below the target pressure HPT, the control device 5 It is determined that the state of the circuit 2 is the pressure state 1. In that case, the opening degree of the first valve 255 is 0 (closed), the second valve 256 is opened, and the third valve 257 is closed.

  When the low-stage refrigeration circuit 2 is in the pressure state 4, the internal pressure of the refrigerant quantity adjustment tank 251 gradually approaches the high-pressure side HP as described above, and eventually the internal pressure also becomes the high-pressure side pressure HP. In such a state, the refrigerant quantity adjusting mechanism 250 does not perform any refrigerant quantity adjusting action, so the high pressure side pressure HP may rise again. Even after the state of the low-stage side refrigeration circuit 2 has changed from the pressure state 3 to the pressure state 4, if the high-pressure side pressure HP exceeds the first predetermined pressure HP1, the control device 5 It is determined that the state of the circuit 2 has become the pressure state 3. In that case, the first valve 255 is set to a first predetermined opening, the second valve 256 is closed, and the third valve 257 is opened. By switching the state of each valve in this way, the amount of refrigerant recovered from the high pressure side can be increased.

  The two-stage refrigeration system 1 shown in FIG. 3 includes the refrigerant amount adjusting mechanism 250 controlled as described above, so that the low-stage refrigeration circuit 2 is switched in accordance with the switching of the operation of the high-stage refrigeration circuit 3. Even if a situation occurs in which the high-pressure side pressure HP becomes higher than the target pressure HPT, it can be reduced below the target pressure HPT. That is, the low-stage refrigerant amount can be adjusted to be a predetermined amount or less.

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

  The present invention performs heat exchange between a low stage side refrigeration circuit, a high stage side refrigeration circuit, and a low stage side refrigerant in the low stage side refrigeration circuit and a high stage side refrigerant in the high stage side refrigeration circuit. It is suitable for use in a dual refrigeration system equipped with a cascade heat exchanger.

1 Binary refrigeration system A Main refrigerator B Supercooled refrigerator C Cascade unit D Showcase 2 Low stage refrigeration circuit 201 Low stage compressor (compressor)
201a 1st rotary compression element 201b 2nd rotary compression element 202 Low stage side gas cooler (gas cooler)
203 Lower stage main throttle means (main throttle means, electric expansion valve)
204 Low stage evaporator (evaporator)
205 Intercooler 206 Throttle means for pressure adjustment (electric expansion valve)
207 Intermediate tank 208 Split heat exchanger 209 First throttle circuit throttle means (electric expansion valve)
210 Second throttling means for auxiliary circuit (electric expansion valve)
250 Refrigerant amount adjusting mechanism 251 Refrigerant amount adjusting tank 252 High pressure refrigerant passage 253 Low pressure refrigerant passage 254 Intermediate pressure refrigerant passage 255 First valve 256 Second valve 257 Third valve 258 Low pressure refrigerant throttling means 259 Check valve 3 High stage Side refrigeration circuit 301 High stage compressor 302 High stage gas cooler 303 High stage main throttle means 304 High stage evaporator 4 Cascade heat exchanger 5 Control device (control means)
L1 Refrigerant introduction pipe L2 Intermediate pressure discharge pipe L3 Intermediate pressure suction pipe L4 High pressure discharge pipe L5 Gas cooler outlet pipe L6 Tank inlet pipe L7 Intermediate tank outlet pipe L8 Gas pipe L9 Intermediate pressure return pipe L10 Liquid return pipe L11 High pressure service pipe L12 Low pressure service Pipe L13 Intermediate pressure service pipe S1 Frequency sensor S2 Outside air temperature sensor S3 High pressure sensor S4 Low pressure sensor S5 Outlet pressure sensor

Claims (3)

A low-stage refrigeration circuit comprising a variable speed compressor;
A high-stage refrigeration circuit;
A cascade heat exchanger that performs heat exchange between the low-stage refrigerant in the low-stage refrigeration circuit and the high-stage refrigerant in the high-stage refrigeration circuit;
A two-way refrigeration system comprising: control means for operating the high-stage refrigeration circuit when the frequency of the variable speed compressor is equal to or higher than a threshold value determined in accordance with the outside air temperature. The low-stage refrigeration circuit is
A gas cooler disposed downstream of the variable speed compressor,
Main throttle means disposed downstream of the gas cooler;
An evaporator disposed downstream of the main throttle means and upstream of the variable speed compressor;
A pressure adjusting throttle means disposed downstream of the gas cooler and upstream of the main throttle means;
An intermediate tank disposed downstream of the pressure adjusting throttle means and upstream of the main throttle means;
A split heat exchanger disposed downstream of the intermediate tank and upstream of the main throttle means;
An auxiliary circuit for causing the low-stage refrigerant in the intermediate tank to flow into the first flow path of the split heat exchanger via auxiliary throttle means and then sucking into the intermediate pressure portion of the variable speed compressor;
After the low-stage refrigerant flows out from the lower part of the intermediate tank, flows into the second flow path of the split heat exchanger, and exchanges heat with the low-stage refrigerant flowing through the first flow path, the main throttle means Has a main circuit to flow into
The dual refrigeration system according to claim 1, wherein the cascade heat exchanger is disposed downstream of the second flow path of the split heat exchanger and upstream of the main throttle means. A refrigerant amount adjusting mechanism for adjusting a low-stage refrigerant amount in the low-stage refrigeration circuit;
The refrigerant quantity adjusting mechanism is
Refrigerant amount adjustment tank,
A high-pressure refrigerant path downstream of the gas cooler and flowing a low-stage refrigerant from the refrigerant flow path upstream of the pressure adjusting throttle means to the refrigerant quantity adjustment tank;
A low pressure refrigerant path downstream of the evaporator and flowing a low stage side refrigerant in the refrigerant quantity adjustment tank to a refrigerant flow path upstream of the variable speed compressor;
An intermediate pressure refrigerant path for flowing a low-stage refrigerant between a refrigerant flow path downstream of the intermediate tank and upstream of the first flow path of the split heat exchanger, and the refrigerant amount adjustment tank;
A first valve provided in the high-pressure refrigerant path;
A second valve provided in the low-pressure refrigerant path;
A third valve provided in the intermediate pressure refrigerant path, and a low pressure refrigerant throttle means interposed in the low pressure refrigerant path,
The control means is downstream of the variable speed compressor and upstream of the pressure adjusting throttle means, depending on the pressure of the low-stage refrigerant, the first valve, the second valve, and the second valve The two-way refrigeration system according to claim 2, wherein the opening degree of each of the three valves is adjusted.

Images