JP2007255864A - Two-stage compression type refrigerating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent excessive lowering of a high stage-side discharged gas temperature (or degree of superheat), contributing to restriction on operating conditions and conditions of used refrigerant in a two-stage compression type refrigerating device. <P>SOLUTION: This two-stage compression type refrigerating device comprising a two-stage compressor 1 and an intermediate cooler 4 in a refrigerant circuit, and cooling a high stage-side sucked gas of the two-stage compressor 1 by the refrigerant of intermediate pressure from the intermediate cooler 4, comprises a branch pipe 8 connecting a condenser 3 and the intermediate cooler 4, an electronic expansion valve 9 disposed on the branch pipe 8, and a controller 20 controlling the electronic expansion valve on the basis of the degree of superheat of a high stage-side discharged gas of the two-stage compressor 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a two-stage compression refrigeration apparatus having a plurality of stages of compression, and more particularly to control of the degree of superheat of the high-stage discharge gas.

  Two-stage compressor, condenser, receiver, intermediate cooler, evaporator, refrigerant pipe connecting them, capillary tube for controlling the flow rate of refrigerant flowing in each refrigerant pipe, liquid injection valve, expansion valve In the two-stage compression refrigeration system equipped with the above, after branching a part of the refrigerant liquefied by the condenser and reducing the branched refrigerant to an intermediate pressure, the main liquid refrigerant and intermediate cooling conveyed to the evaporator The economizer effect by supercooling is obtained by exchanging heat in the vessel.

  Furthermore, the two-stage compression type refrigeration which cools the branched liquid refrigerant heat-exchanged with the main refrigerant and the intercooler by combining with the high-stage intake gas and prevents an abnormal increase in the high-stage discharge gas temperature. An apparatus has been proposed (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-210480 (page 3, FIG. 1)

  In the above-mentioned Patent Document 1, a parallel circuit of a capillary tube and a liquid injection valve is provided in the branch pipe at the inlet of the intermediate cooler, and the liquid refrigerant flow rate required for the intermediate cooler and the low stage discharge gas are used as the high stage intake gas. When the minimum flow rate of the liquid refrigerant required to achieve an appropriate degree of superheat is secured by the capillary tube, and the temperature (or degree of superheat) of the high-stage discharge gas rises excessively due to fluctuations in the operating conditions of the refrigeration system Is to control the flow rate of the refrigerant so that the temperature or superheat degree of the high-stage side discharge gas is within an allowable value by operating the liquid injection valve and controlling its opening degree. In addition, an electromagnetic valve is provided upstream of the capillary tube and the liquid injection valve, and is always open during operation of the refrigeration apparatus.

  In the conventional refrigeration system, the purpose of cooling the high-stage intake gas is to prevent an abnormal increase in the high-stage discharge gas temperature, but the high-stage discharge gas temperature is low and the liquid injection valve is closed. Even in this case, the branched liquid refrigerant always cools the high-stage intake gas via the capillary tube.

  For example, when the condenser in the refrigeration apparatus is an air heat source type, the operation may be performed at a low high pressure under operating conditions where the outside air temperature is low, such as in winter. In this case, the high stage discharge gas temperature (or superheat degree) is in a relatively low operating state.

  In addition, when a refrigerant having a characteristic of lowering the discharge gas temperature, such as the refrigerant R404A, is used for the refrigeration apparatus, the cooling of the high-stage intake gas is unnecessary in the operation state where the high pressure is low. Alternatively, a trace amount may be sufficient. However, in the above refrigeration apparatus, the branched refrigerant always flows through the capillary tube due to the differential pressure between the high pressure and the intermediate pressure, so that the high-stage intake gas is excessively cooled and the high-stage discharge gas temperature (or superheat degree) is increased. May decrease excessively.

  In a refrigeration system equipped with an oil separator for separating and storing refrigeration oil contained in the high-stage discharge gas, if the high-stage discharge gas temperature (or superheat degree) drops more than necessary, Increased refrigerant solubility in machine oil may cause problems such as a decrease in the viscosity of oil supplied to the bearing and loss of refrigeration oil due to pressure fluctuations. This is a restriction on refrigerant conditions.

  An object of the present invention is to prevent an excessive decrease in high-stage-side discharge gas temperature (or superheat degree) that contributes to restrictions on operating conditions and refrigerant conditions to be used in a two-stage compression refrigeration system.

  In order to solve the above problems, a two-stage compression refrigeration apparatus according to the present invention includes a two-stage compressor and an intermediate cooler in a refrigerant circuit, and the high-stage side intake gas of the two-stage compressor is supplied from the intermediate cooler. In the two-stage compression refrigeration system cooled by the intermediate pressure refrigerant, a branch pipe connecting a condenser and the intermediate cooler, an electronic expansion valve provided in the branch pipe, and the two-stage compressor And a control means for controlling the electronic expansion valve based on the degree of superheat of the higher-stage discharge gas.

  In the two-stage compression refrigeration apparatus configured as described above, the electronic expansion valve provided on the inlet side of the intermediate cooler adjusts the subcooling of the main liquid refrigerant and the superheat degree of the high-stage discharge gas within an allowable range. Therefore, it is possible to control the flow rate of the branch liquid necessary for the purpose. The control target of this electronic expansion valve is the degree of superheat of the high-stage discharge gas, but the branch refrigerant merges with the high-stage intake gas via the intermediate cooler, so the main refrigerant is supercooled in the intermediate cooler. It is also possible to obtain an economizer effect. In addition, since the control target of this electronic expansion valve is the degree of superheat of the high-stage discharge gas, especially in a refrigeration system using a refrigerant having a characteristic that the discharge gas temperature is low, such as R404A, the high-stage discharge gas Under operating conditions where the gas temperature (superheat) is low and cooling of the high-stage intake gas is not required, the injection of branch liquid refrigerant into the high-stage intake gas is blocked by detecting the superheat of the high-stage discharge gas. In addition, an increase in the solubility of the refrigerant in the refrigerating machine oil can be suppressed.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of the two-stage compression refrigeration apparatus in the first embodiment, and FIG. 2 is a Mollier diagram for explaining the first embodiment. Moreover, the symbols a to g shown in FIG. 1 represent the state of the refrigerant at that location in the refrigerant circuit, and correspond to the symbols in the Mollier diagram shown in FIG. In FIG. 1, a dotted line represents a signal line.

  In FIG. 1, this two-stage compression refrigeration apparatus includes an oil separator 2, a condenser 3, an intercooler 4, and a two-stage compressor 1 including a high-stage compressor 1 a and a low-stage compressor 1 b. The refrigerant circuit which connected the expansion valve 5 and the evaporator 6 with the refrigerant | coolant piping 7 is provided. Further, a branch pipe 8 is provided in the refrigerant pipe 7 connecting the condenser 3 and the intermediate cooler 4 in this refrigerant circuit, and an electronic expansion valve 9 is provided in the branch pipe 8. A pressure sensor 21 and a temperature sensor 22 for detecting the pressure and temperature of the high-stage discharge gas of the two-stage compressor 1 are provided, and the pressure and temperature of the high-stage discharge gas detected by these sensors 21 and 22 are provided. Is provided with a controller (first control means) 20 for calculating the degree of superheat of the high stage discharge gas and controlling the opening degree of the electronic expansion valve 9 so that the degree of superheat falls within an allowable range. . The intermediate cooler 4 and the inlet of the high stage compressor 1a (the outlet of the low stage compressor 1b) are connected by an intermediate pressure refrigerant introduction pipe 10.

Next, the operation of the two-stage compression refrigeration apparatus configured as described above will be described with reference to FIGS.
The high-pressure and high-temperature refrigerant gas b discharged from the high-stage compressor 1a of the two-stage compressor 1 flows into the oil separator 2 and is separated into refrigerant gas and refrigerating machine oil. The separated refrigerating machine oil is stored in the oil separator 2 and supplied to the bearing oil supply or the like of the two-stage compressor 1 (note that the refrigerating machine oil supply path is not shown). The refrigerant gas b separated by the oil separator 2 then flows into the condenser 3, where it is cooled by exchanging heat with a condensing side heat source (not shown) to become a liquid refrigerant c, and then branched. The Of the branched liquid refrigerant, the main refrigerant flowing into the evaporator 6 exchanges heat with the other branch refrigerant, which is decompressed to the intermediate pressure f by the electronic expansion valve 9 provided in the branch pipe 8, with the intermediate cooler 4. Becomes the supercooled liquid d. The subcooled main refrigerant d is depressurized to a low pressure e by the expansion valve 5 and then vaporized by exchanging heat with an evaporation side heat source (not shown) in the evaporator 6 to become a gas refrigerant a. 1 is sucked into the low-stage compressor 1b.

  Here, the other branched refrigerant that has supercooled the main refrigerant in the intermediate cooler 4 passes through the intermediate pressure refrigerant introduction pipe 10 and merges with the high-stage intake gas (low-stage discharge gas) at g. Is used to prevent an abnormal rise in the high-stage discharge gas temperature.

  In the above, the pressure sensor 21 and the temperature sensor 22 detect the pressure and temperature of the high-stage side discharge gas, and the controller 20 determines the high-stage side discharge gas based on the pressure and temperature detected by these sensors 21 and 22. The degree of superheat 12 is calculated, and the opening degree of the electronic expansion valve 9 provided in the branch pipe 8 is controlled so that the degree of superheat 12 of the high stage side discharge gas is within the allowable range.

  That is, the electronic expansion valve 9 is controlled in a direction in which the flow rate of the liquid refrigerant f flowing through the branch pipe 8 is increased in an operation condition in which the superheat degree 12 of the high-stage side discharge gas is excessively increased. Similar to the liquid injection valve in Patent Document 1, it is possible to reduce the degree of superheat of the high-stage discharge gas.

  On the other hand, under the operating conditions in which the superheat degree 12 of the high-stage side discharge gas decreases, such as the operation at a high pressure of the high-stage side discharge gas at a low pressure, in Patent Document 1, the above-described Patent Document 1 Since the high-stage intake gas is always cooled during operation, the solubility of the refrigerant in the refrigerating machine oil stored in the oil separator 2 is increased. In the first embodiment, the branch pipe 8 is Since the electronic expansion valve 9 is provided, under operating conditions that do not require cooling of the high-stage intake gas, the injection of intermediate-pressure refrigerant (branch refrigerant) from the intermediate cooler 4 into the high-stage intake gas is blocked. be able to.

  As described above, according to the first embodiment, it is possible to suppress an excessive decrease in the superheat degree of the high stage discharge gas and an increase in the solubility of the refrigerant in the refrigeration oil. Operation at a lower pressure is possible. Therefore, this is particularly effective when a refrigerant having a characteristic of lowering the discharge gas temperature, such as the refrigerant R404A, is used in the refrigeration apparatus.

Embodiment 2
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a schematic configuration diagram of the two-stage compression refrigeration apparatus in the second embodiment, and FIG. 4 is a Mollier diagram for explaining the second embodiment. Also, the reference numerals a to g in FIG. 3 represent the state of the refrigerant at that point in the refrigerant circuit, and correspond to the reference numerals in the Mollier diagram of FIG.

  In the second embodiment, an electronic expansion valve 13 is provided instead of the expansion valve 5 in the first embodiment. Furthermore, a pressure sensor 24 and a temperature sensor 25 for detecting the pressure and temperature of the low-stage intake gas sucked into the low-stage compressor 1a of the two-stage compressor 1 are provided, and these sensors 24 and 25 detect the pressure and temperature. A controller that calculates the degree of superheat of the low-stage intake gas based on the pressure and temperature of the low-stage intake gas, and controls the opening degree of the electronic expansion valve 13 so that the superheat degree becomes an appropriate superheat degree (second Control means) 23 is provided. Since other configurations are the same as those of the first embodiment, the same reference numerals are used for the same components. The controller (second control means) 23 and the controller (first control means) 20 may be configured as one control means. Further, the second embodiment includes the configuration of the first embodiment, but may be a single configuration that does not include the configuration.

  In the two-stage compression refrigeration apparatus of the second embodiment, the same effect as that of the first embodiment is obtained, and the flow rate of the main liquid refrigerant (supercooled liquid refrigerant d) flowing into the evaporator 6 is evaporated. An electronic expansion valve 13 provided on the inlet side of the vessel 6 is normally controlled to an appropriate degree of superheat (generally about 5 ° C. to 15 ° C.) as a low-stage intake gas. When the superheat degree is excessively lowered, the controller 23 operates the electronic expansion valve 13 in the closing direction to forcibly set the superheat degree of the low-stage intake gas in the Mollier diagram of FIG. The temperature of the high stage side suction gas (low stage side discharge gas) is increased from g → g ′, and the temperature of the high stage side discharge gas is increased from b → b ′. Therefore, it is possible to suppress a decrease in the degree of superheat of the high-stage discharge gas.

  Also in the second embodiment, as in the first embodiment, an excessive decrease in the superheat degree of the high stage side discharge gas and an increase in the solubility of the refrigerant in the refrigeration oil can be suppressed. Operation at a lower pressure is possible. In particular, this is effective when a refrigerant having a characteristic of lowering the discharge gas temperature, such as the refrigerant R404A, is used in the refrigeration apparatus.

1 is a schematic configuration diagram of a two-stage compression refrigeration apparatus in Embodiment 1 of the present invention. It is a Mollier diagram in Embodiment 1 of the present invention. It is a schematic block diagram of the two-stage compression refrigerating apparatus in Embodiment 2 of this invention. It is a Mollier diagram in Embodiment 2 of the present invention.

Explanation of symbols

1 Two-stage compressor, 1a High-stage compressor, 1b Low-stage compressor, 2 Oil separator, 3 Condenser, 4 Intermediate cooler, 5 Expansion valve, 6 Evaporator, 7 Refrigerant pipe, 8 Branch pipe, 9 electronic expansion valve, 10 intermediate pressure refrigerant introduction pipe, 12 superheat degree of high-stage discharge gas, 13 electronic expansion valve, 20 controller (first control means), 21 high-stage discharge gas pressure sensor, 22 high stage Side discharge gas temperature sensor, 23 controller (second control means), 24 low stage suction gas pressure sensor, 25 low stage suction gas temperature sensor.

Claims (5)

In the two-stage compression refrigeration apparatus comprising a two-stage compressor and an intermediate cooler in the refrigerant circuit, and cooling the high-stage intake gas of the two-stage compressor with the intermediate pressure refrigerant from the intermediate cooler,
A branch pipe connecting the condenser and the intercooler;
An electronic expansion valve provided in the branch pipe;
Control means for controlling the electronic expansion valve based on the degree of superheat of the high-stage discharge gas of the two-stage compressor;
A two-stage compression refrigeration apparatus comprising:   The control means includes a pressure sensor and a temperature sensor for detecting the pressure and temperature of the high-stage discharge gas of the two-stage compressor, and is based on the pressure and temperature of the high-stage discharge gas detected by these sensors. The two-stage compression refrigeration apparatus according to claim 1, wherein the second stage compression refrigeration apparatus is configured to calculate a degree of superheat of the high-stage discharge gas. In the two-stage compression refrigeration apparatus comprising a two-stage compressor and an intermediate cooler in the refrigerant circuit, and cooling the high-stage intake gas of the two-stage compressor with the intermediate pressure refrigerant from the intermediate cooler,
An electronic expansion valve provided on the inlet side of the evaporator;
Second control means for controlling the electronic expansion valve based on the degree of superheat of the low-stage intake gas of the two-stage compressor;
A two-stage compression refrigeration apparatus comprising:   A branch pipe connecting the condenser and the intercooler, an electronic expansion valve provided in the branch pipe, and controlling the electronic expansion valve based on the degree of superheat of the high-stage discharge gas of the two-stage compressor The two-stage compression refrigeration apparatus according to claim 3, further comprising a first control means. The second control means includes a pressure sensor and a temperature sensor for detecting the pressure and temperature of the low-stage intake gas of the two-stage compressor, and the pressure and temperature of the low-stage intake gas detected by these sensors 5. The two-stage compression refrigeration apparatus according to claim 3, wherein a superheat degree of the low-stage intake gas is calculated based on a temperature.

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